The Direct Power Contro; has many advantages like it avoids the usage of integration of PWM voltages which leads to stable operation even at zero rotor frequency, it is position sensor less and hence will not depend on machine parameters like stator or rotor resistance. In case of network unbalance, if the system is operated with constant active and reactive powers, it leads to oscillations in the electromagnetic torque and currents exchange with the grid will become non- sinusoidal, which is not good for the system as it increases the mechanical stress. In this paper, both the rotor connected converter and grid connected converter are fed with DPC strategy along with that a Torque Oscillations Cancellation scheme is applied to RSC and Proportional Integral control based power references generation strategy without calculating the sequence components and with elimination of DC bus voltage oscillations is applied to stator-side converter in order to achieve non-oscillating torque accompanied by quality improved current exchange with the grid. The simulation results of Doubly Fed Induction Generator with and without fault clearly shows that the performance of the proposed scheme is validated.
Low Voltage Ride-through for Doubly Fed Induction Generator Using Battery-Sto...IJPEDS-IAES
In this paper, enhanced field oriented control technique (EFOC) was adopted
in Rotor Side Control (RSC) of DFIG converter for improved response
during severe faults. The work is intended to damp pulsations in
electromagnetic torque, improve voltage mitigation and limit surge currents
and to enhance the operation of DFIG during voltage sags. The converter
topology uses a battery energy storage system with capacitor storage system
to further enhance operation of DFIG during faults. The battery and capacitor
system in coordination provide additional real and reactive power support
during faults and nearly constant voltage profile at stator and rotor terminals
and limit overcurrents. For EFOC technique, rotor flux reference changes its
value from synchronous speed to zero during fault for injecting current at the
rotor slip frequency. In this process DC-Offset component of flux is
controlled, decomposition during overvoltage faults. The offset
decomposition of flux will be oscillatory in a conventional FOC, whereas in
EFOC it will damp quickly. A comparison is made with proposed
methodology with battery energy storage system and a conventional system.
Later the system performance with under voltage of 50% the rated voltage
with fault at PCC during 0.8 to 1.2 seconds is analysed using simulation
studies.
Fault Ride-Through capability of DSTATCOM for Distributed Wind Generation SystemIJPEDS-IAES
In this paper, fault ride through analysis of a low voltage distribution system
augmented with distributed wind generation using squirrel cage induction
generator and distribution static compensator (DSTATCOM) is carried out
through modeling and simulation study in MATLAB. The impact of
unbalanced (single line to ground) fault in a low voltage distribution system
in normal and severe conditions is studied and analyzed in details. Analysis
on system instability is also shown in case of sever fault condition. A
distribution Static Compensator (DSTATCOM) is used to improve fault ride
through (FRT) capability of wind generation system by compensating
positive sequence voltage. A comparison of dynamic response of the system
with and without DSTATCOM and effects of DSTATCOM on voltage and
generator speed are presented. The simulation results shows that
DSTATCOM is capable of reducing the voltage dips and improving the
voltage profiles by providing reactive power support to distributed wind
generation system under unbalanced fault condition and enhances the fault
ride through capability of the wind generator.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
International Refereed Journal of Engineering and Science (IRJES)irjes
The core of the vision IRJES is to disseminate new knowledge and technology for the benefit of all, ranging from academic research and professional communities to industry professionals in a range of topics in computer science and engineering. It also provides a place for high-caliber researchers, practitioners and PhD students to present ongoing research and development in these areas.
Review of the DTC Controller and Estimation of Stator Resistance in IM DrivesIAES-IJPEDS
In recent years an advanced control method called direct torque control
(DTC) has gained importance due to its capability to produce fast torque
control of induction motor. Although in these systems such variables as
torque, flux modulus and flux sector are required, resulting DTC structure is
particularly simplistic. Conventional DTC does not require any mechanical
sensor or current regulator and coordinate transformation is not present, thus
reducing the complexity. Fast and good dynamic performances and
robustness has made DTC popular and is now used widely in all industrial
applications. Despite these advantages it has some disadvantages such as
high torque ripple and slow transient response to step changes during start
up. Torque ripple in DTC is because of hysteresis controller for stator flux
linkage and torque. The ripples can be reduced if the errors of the torque and
the flux linkage and the angular region of the flux linkage are subdivided into
several smaller subsections. Since the errors are divided into smaller sections
different voltage vector is selected for small difference in error, thus a more
accurate voltage vector is selected and hence the torque and flux linkage
errors are reduced. The stator resistance changes due to change in
temperature during the operation of machine. At high speeds, the stator
resistance drop is small and can be neglected. At low speeds, this drop
becomes dominant. Any change in stator resistance gives wrong estimation
of stator flux and consequently of the torque and flux. Therefore, it is
necessary to estimate the stator resistance correctly. This paper aims to
review some of the control techniques of DTC drives and stator resistance
estimation methods.
A Review of Matrix Converter and Novel Control Method of DC-AC Matrix Converteridescitation
For the past three decades, research work in matrix
converter has increased much. This paper presents a new
topology of DC-AC matrix converter, starting with a brief
historical review of different modulation and control strategies
which was developed recently. The purpose of the Paper is to
generate a multilevel output voltage equal to multilevel
inverter with reduced switches. An important part of the paper
is to design a dedicated DC-AC matrix converter and some
new arrays of bidirectional switches in a single module are
also presented. To find the performance of the module the
entire module is designed with MATLAB simulation and tested
with three phase induction motor.
Low Voltage Ride-through for Doubly Fed Induction Generator Using Battery-Sto...IJPEDS-IAES
In this paper, enhanced field oriented control technique (EFOC) was adopted
in Rotor Side Control (RSC) of DFIG converter for improved response
during severe faults. The work is intended to damp pulsations in
electromagnetic torque, improve voltage mitigation and limit surge currents
and to enhance the operation of DFIG during voltage sags. The converter
topology uses a battery energy storage system with capacitor storage system
to further enhance operation of DFIG during faults. The battery and capacitor
system in coordination provide additional real and reactive power support
during faults and nearly constant voltage profile at stator and rotor terminals
and limit overcurrents. For EFOC technique, rotor flux reference changes its
value from synchronous speed to zero during fault for injecting current at the
rotor slip frequency. In this process DC-Offset component of flux is
controlled, decomposition during overvoltage faults. The offset
decomposition of flux will be oscillatory in a conventional FOC, whereas in
EFOC it will damp quickly. A comparison is made with proposed
methodology with battery energy storage system and a conventional system.
Later the system performance with under voltage of 50% the rated voltage
with fault at PCC during 0.8 to 1.2 seconds is analysed using simulation
studies.
Fault Ride-Through capability of DSTATCOM for Distributed Wind Generation SystemIJPEDS-IAES
In this paper, fault ride through analysis of a low voltage distribution system
augmented with distributed wind generation using squirrel cage induction
generator and distribution static compensator (DSTATCOM) is carried out
through modeling and simulation study in MATLAB. The impact of
unbalanced (single line to ground) fault in a low voltage distribution system
in normal and severe conditions is studied and analyzed in details. Analysis
on system instability is also shown in case of sever fault condition. A
distribution Static Compensator (DSTATCOM) is used to improve fault ride
through (FRT) capability of wind generation system by compensating
positive sequence voltage. A comparison of dynamic response of the system
with and without DSTATCOM and effects of DSTATCOM on voltage and
generator speed are presented. The simulation results shows that
DSTATCOM is capable of reducing the voltage dips and improving the
voltage profiles by providing reactive power support to distributed wind
generation system under unbalanced fault condition and enhances the fault
ride through capability of the wind generator.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
International Refereed Journal of Engineering and Science (IRJES)irjes
The core of the vision IRJES is to disseminate new knowledge and technology for the benefit of all, ranging from academic research and professional communities to industry professionals in a range of topics in computer science and engineering. It also provides a place for high-caliber researchers, practitioners and PhD students to present ongoing research and development in these areas.
Review of the DTC Controller and Estimation of Stator Resistance in IM DrivesIAES-IJPEDS
In recent years an advanced control method called direct torque control
(DTC) has gained importance due to its capability to produce fast torque
control of induction motor. Although in these systems such variables as
torque, flux modulus and flux sector are required, resulting DTC structure is
particularly simplistic. Conventional DTC does not require any mechanical
sensor or current regulator and coordinate transformation is not present, thus
reducing the complexity. Fast and good dynamic performances and
robustness has made DTC popular and is now used widely in all industrial
applications. Despite these advantages it has some disadvantages such as
high torque ripple and slow transient response to step changes during start
up. Torque ripple in DTC is because of hysteresis controller for stator flux
linkage and torque. The ripples can be reduced if the errors of the torque and
the flux linkage and the angular region of the flux linkage are subdivided into
several smaller subsections. Since the errors are divided into smaller sections
different voltage vector is selected for small difference in error, thus a more
accurate voltage vector is selected and hence the torque and flux linkage
errors are reduced. The stator resistance changes due to change in
temperature during the operation of machine. At high speeds, the stator
resistance drop is small and can be neglected. At low speeds, this drop
becomes dominant. Any change in stator resistance gives wrong estimation
of stator flux and consequently of the torque and flux. Therefore, it is
necessary to estimate the stator resistance correctly. This paper aims to
review some of the control techniques of DTC drives and stator resistance
estimation methods.
A Review of Matrix Converter and Novel Control Method of DC-AC Matrix Converteridescitation
For the past three decades, research work in matrix
converter has increased much. This paper presents a new
topology of DC-AC matrix converter, starting with a brief
historical review of different modulation and control strategies
which was developed recently. The purpose of the Paper is to
generate a multilevel output voltage equal to multilevel
inverter with reduced switches. An important part of the paper
is to design a dedicated DC-AC matrix converter and some
new arrays of bidirectional switches in a single module are
also presented. To find the performance of the module the
entire module is designed with MATLAB simulation and tested
with three phase induction motor.
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
Current control scheme is commonly used in high voltage direct current (HVDC) to transmit power delivery. This scheme is done by adjusting trigger angle to regulate direct current (DC) in thyristor devices. The adaptive neuro-fuzzy inference system (ANFIS) control is widely applied for start and fault operation. But, solution for transient response of DC current in HVDC system is not clearly studied before. In this paper, supplementary control (SC) based on ANFIS is proposed to improve the transient response of the current. The SC control is designed by learning-processes and SC parameters are obtained by data-training automatically. For current reference at 1.05 pu and up-ramp at 20 pu/s, maximum overshoot is achieved at 5.12% and 7.72% for the SC and proportional integral controller (PIC), respectively. When the up-ramp is increased to 28 pu/s, the maximum overshoot is achieved at 10.01% for the SC. While, the peak overshoot for the PIC is 14.28%.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Simulation and Comparison of DVR and DSTATCOM Used for voltage sag mitigation...paperpublications3
Abstract: Power Quality problem in a system leads to various disturbances such as voltage fluctuations, transients and waveform distortions that results in a mis-operation or a failure of end user equipment. There are different types of custom power devices like Distribution Static Compensator (D-STATCOM) and Dynamic Voltage Restorer (DVR) which can effectively use for mitigation of different type of power quality problems. This paper describes the technique of correcting the supply voltage sag distributed system and also describes performance comparison are presented between DVR and DSTATCOM to know how both the devices successfully been applied to power system for regulating system voltage effectively. DSTATCOM and DVR both of them based on VSI principle. A DVR is a series compensation device which injects a voltage in series with system and a DSTATCOM is a shunt compensation device which injects a current into the system to correct the power quality problems. This paper presents a power system operation with PI controller with abc to dq0 convertor approach. Total Harmonics Distortion (THD) is also calculated for the system with and without compensation. Results are presented to assess the performance of devices as a potential custom power solution. Improve dynamic voltage control and thus increase system load ability. This paper presents modeling and simulation of DVR & DSTATCOM in MATLAB/Simulink.
Improving Stability of Utility-Tied Wind Generators using Dynamic Voltage Res...IJMTST Journal
The generation of electricity using wind power is significantly increasing and has received considerable attention in recent years. One important problem with the induction generator based wind farms is that they are vulnerable to voltage disturbances and short circuit faults. Any such disturbance may cause wind farm outages. Since wind power contribution is in considerable percentage, such outages may lead to power system stability issues and also violate the grid code requirements. Thus, improving the reliability of wind farms is essential to maintain the stability of the system. The proposed strategy is to use Dynamic Voltage Restorer (DVR), which is one of the promising devices to compensate the voltage disturbance and to improve the stability of the system. It provides the wind generator with the fault ride through capability and improves the reliability of the system. Fuzzy Logic controller is used as a controller in order to control the dc link voltages and to reduce the harmonics. Simulation results for a 2 MW wind turbine are presented, especially for asymmetrical grid faults. They show the effectiveness of the DVR in comparison to the low voltage ride-through of the DFIG using a crowbar that does not allow continuous reactive power production. Extensive simulation results are included to illustrate the operation of DVR and fault compensation.
SRF CONTROLLED DVR FOR COMPENSATION OF BALANCED AND UNBALANCED VOLTAGE DISTUR...IAEME Publication
The growth of power electronictechnology in the field of electric power sector has caused a greater awarenesson the power quality of distribution systems. With the re-structuring of powersystems and with shifting trend towards distributed and dispersed generation,the issue of power quality is going to take newer dimensions. The presentresearch is to identify the prominent concerns in this area and hence themeasures that can enhance the quality of power. This paper investigates theproblems of voltage sag, swell and its severe impact on nonlinear loads,sensitive loads.
Implementation of Fuzzy Controlled Photo Voltaic Fed Dynamic Voltage Restorer...ijfls
Power Quality(PQ) has become an area of concern in the electrical distribution system. Dynamic Voltage
Restorer(DVR) restores load voltage to a nominal balanced sinusoidal voltage, when the source voltage
has harmonic distortions, sag, swell and unbalances. In this paper a Photo Voltaic(PV) fed DVR is
proposed to mitigate PQ problems. The PV system can supply the maximum power to the load at a
particular operating point known as Maximum Power Point (MPP), at which the entire PV system operates
with maximum efficiency. A Fuzzy Controller based MPPT is implemented to generate the optimal voltage
from the photovoltaic system by modulating the duty cycle applied to the boost converter. The DVR is
implemented using a Fuzzy Logic Controller based voltage source inverter with Photovoltaic system. The
test system has been simulated and the efficacy of the proposed PV based Fuzzy controlled DVR is
compared with Proportional Integral (PI) controlled DVR.
The use of distributed generation (DG) within distribution systems has increased for the last two decades due to worldwide increase in demand for electricity and governmental policy change from “conventional” energy to “green” energy. High levels of penetration of DG have many significant benefits but also come with many drawbacks such as voltage drop and power losses. This study presents the impact of DG at different locations in a distribution feeder in terms of the feeder voltage profile. A radial distribution system is simulated using PSCAD/EMTDC simulation software while changing the size and location of DG in the system. The obtained results are used for better understanding on the impact of DG on voltage profile in radial distribution feeder.
PID Compensator Control Scheme of Synchronous Buck DC-DC Converter with ZVS L...IJRES Journal
This paper deals with PID compensator control of Synchronous Rectifier (SR) Buck Converter to improve its conversion efficiency under different load conditions with the help of a Zero Voltage Switching(ZVS)Logic Circuit. Since the freewheeling diode is replaced by a high frequency switch MOSFET in this buck configuration, the SR control technique itself will be sufficient under heavy load condition to attain better normal mode performance. However, this technique does not hold well in light load condition, due to increased switching losses. A newPID compensator control techniqueis introduced in the paper will enable synchronous buck converter to realize ZVS, while feeding light load. This is also cost effective and highly efficient simple control method without use of extra auxiliary switches and RLC components. This control technique also proved to be efficient under input voltage variations. Simulation is done for proving stabilization provided by the PID compensator with the help of ZVS logic circuit for synchronous rectifier (SR) buck converter in MATLAB Simulink.
Performance and High Robustness DPC for PWM Rectifier under Unstable VDC BusIJPEDS-IAES
This paper proposes a strategy de controlling a static AC / DC converter
based on direct power control (DPC). The instantaneous active and reactive
power is controlled in such a way to ensure the PWM rectifier with a
sinusoidal current absorption. This control has proven effective in terms of
reduction of total harmonic distortion (THD) of current absorbed. Offers a
good control of active and reactive power with an operation at unitary power
factor. The test of robustness carried out and the results have proven DPC
good performance with strong possibility of de integrate it into the field of
high voltage and high power as electric traction.
The voltage dip and doubly fed induction generator with considering uncertain...journalBEEI
The paper presents the transient behavior of the doubly fed induction generator (DFIG) in the wind turbine (WT) in the normal and voltage dip condition. When voltage dip occurs in to the grid, the rotor current increases and the DC-link voltage increases too and start to oscilate. In this paper, the proportional integral (PI) controllers are used to control the DFIG-basedwind farms for regulating the electronic devices including rotor side converter (RSC) and grid side converter (GSC) to control the active and reactive power of DFIG. The PI parameters are tuned by imperialist competitive algorithm (ICA). So, the transient behavour of the DFIG-based WF is explors when the voltage dip occurs. Hence, the induced electric motive force in to the rotor is measured. Also, an existed uncertainty for mutual inductance is considered caused by saturated curve during three-phase fault conditions and the bahavour of DFIG-based WT is examined and analyzed. All of simulation is done by Matlab/Simulink®.
Flux Based Sensorless Speed Sensing and Real and Reactive Power Flow Control ...ijeei-iaes
This aim of this paper is to design controller for Doubly Fed Induction Generator (DFIG) converters and MPPT for turbine and a sensor-less rotor speed estimation to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages. It is also aimed to meet desired reference real and reactive power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The turbine blade angle changes with variations in wind speed and direction of wind flow and improves the coefficient of power extracted from turbine using MPPT. Rotor side converter (RSC) helps to achieve optimal real and reactive power from generator, which keeps rotor to rotate at optimal speed and to vary current flow from rotor and stator terminals. Rotor speed is estimated using stator and rotor flux estimation algorithm. Parameters like tip speed ratio; coefficient of power, stator and rotor voltage, current, real, reactive power; rotor speed and electromagnetic torque are studied using MATLAB simulation. The performance of DFIG is compared when there is in wind speed change only; alter in reactive power and variation in grid voltage individually along with variation in wind speed.
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
Current control scheme is commonly used in high voltage direct current (HVDC) to transmit power delivery. This scheme is done by adjusting trigger angle to regulate direct current (DC) in thyristor devices. The adaptive neuro-fuzzy inference system (ANFIS) control is widely applied for start and fault operation. But, solution for transient response of DC current in HVDC system is not clearly studied before. In this paper, supplementary control (SC) based on ANFIS is proposed to improve the transient response of the current. The SC control is designed by learning-processes and SC parameters are obtained by data-training automatically. For current reference at 1.05 pu and up-ramp at 20 pu/s, maximum overshoot is achieved at 5.12% and 7.72% for the SC and proportional integral controller (PIC), respectively. When the up-ramp is increased to 28 pu/s, the maximum overshoot is achieved at 10.01% for the SC. While, the peak overshoot for the PIC is 14.28%.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Simulation and Comparison of DVR and DSTATCOM Used for voltage sag mitigation...paperpublications3
Abstract: Power Quality problem in a system leads to various disturbances such as voltage fluctuations, transients and waveform distortions that results in a mis-operation or a failure of end user equipment. There are different types of custom power devices like Distribution Static Compensator (D-STATCOM) and Dynamic Voltage Restorer (DVR) which can effectively use for mitigation of different type of power quality problems. This paper describes the technique of correcting the supply voltage sag distributed system and also describes performance comparison are presented between DVR and DSTATCOM to know how both the devices successfully been applied to power system for regulating system voltage effectively. DSTATCOM and DVR both of them based on VSI principle. A DVR is a series compensation device which injects a voltage in series with system and a DSTATCOM is a shunt compensation device which injects a current into the system to correct the power quality problems. This paper presents a power system operation with PI controller with abc to dq0 convertor approach. Total Harmonics Distortion (THD) is also calculated for the system with and without compensation. Results are presented to assess the performance of devices as a potential custom power solution. Improve dynamic voltage control and thus increase system load ability. This paper presents modeling and simulation of DVR & DSTATCOM in MATLAB/Simulink.
Improving Stability of Utility-Tied Wind Generators using Dynamic Voltage Res...IJMTST Journal
The generation of electricity using wind power is significantly increasing and has received considerable attention in recent years. One important problem with the induction generator based wind farms is that they are vulnerable to voltage disturbances and short circuit faults. Any such disturbance may cause wind farm outages. Since wind power contribution is in considerable percentage, such outages may lead to power system stability issues and also violate the grid code requirements. Thus, improving the reliability of wind farms is essential to maintain the stability of the system. The proposed strategy is to use Dynamic Voltage Restorer (DVR), which is one of the promising devices to compensate the voltage disturbance and to improve the stability of the system. It provides the wind generator with the fault ride through capability and improves the reliability of the system. Fuzzy Logic controller is used as a controller in order to control the dc link voltages and to reduce the harmonics. Simulation results for a 2 MW wind turbine are presented, especially for asymmetrical grid faults. They show the effectiveness of the DVR in comparison to the low voltage ride-through of the DFIG using a crowbar that does not allow continuous reactive power production. Extensive simulation results are included to illustrate the operation of DVR and fault compensation.
SRF CONTROLLED DVR FOR COMPENSATION OF BALANCED AND UNBALANCED VOLTAGE DISTUR...IAEME Publication
The growth of power electronictechnology in the field of electric power sector has caused a greater awarenesson the power quality of distribution systems. With the re-structuring of powersystems and with shifting trend towards distributed and dispersed generation,the issue of power quality is going to take newer dimensions. The presentresearch is to identify the prominent concerns in this area and hence themeasures that can enhance the quality of power. This paper investigates theproblems of voltage sag, swell and its severe impact on nonlinear loads,sensitive loads.
Implementation of Fuzzy Controlled Photo Voltaic Fed Dynamic Voltage Restorer...ijfls
Power Quality(PQ) has become an area of concern in the electrical distribution system. Dynamic Voltage
Restorer(DVR) restores load voltage to a nominal balanced sinusoidal voltage, when the source voltage
has harmonic distortions, sag, swell and unbalances. In this paper a Photo Voltaic(PV) fed DVR is
proposed to mitigate PQ problems. The PV system can supply the maximum power to the load at a
particular operating point known as Maximum Power Point (MPP), at which the entire PV system operates
with maximum efficiency. A Fuzzy Controller based MPPT is implemented to generate the optimal voltage
from the photovoltaic system by modulating the duty cycle applied to the boost converter. The DVR is
implemented using a Fuzzy Logic Controller based voltage source inverter with Photovoltaic system. The
test system has been simulated and the efficacy of the proposed PV based Fuzzy controlled DVR is
compared with Proportional Integral (PI) controlled DVR.
The use of distributed generation (DG) within distribution systems has increased for the last two decades due to worldwide increase in demand for electricity and governmental policy change from “conventional” energy to “green” energy. High levels of penetration of DG have many significant benefits but also come with many drawbacks such as voltage drop and power losses. This study presents the impact of DG at different locations in a distribution feeder in terms of the feeder voltage profile. A radial distribution system is simulated using PSCAD/EMTDC simulation software while changing the size and location of DG in the system. The obtained results are used for better understanding on the impact of DG on voltage profile in radial distribution feeder.
PID Compensator Control Scheme of Synchronous Buck DC-DC Converter with ZVS L...IJRES Journal
This paper deals with PID compensator control of Synchronous Rectifier (SR) Buck Converter to improve its conversion efficiency under different load conditions with the help of a Zero Voltage Switching(ZVS)Logic Circuit. Since the freewheeling diode is replaced by a high frequency switch MOSFET in this buck configuration, the SR control technique itself will be sufficient under heavy load condition to attain better normal mode performance. However, this technique does not hold well in light load condition, due to increased switching losses. A newPID compensator control techniqueis introduced in the paper will enable synchronous buck converter to realize ZVS, while feeding light load. This is also cost effective and highly efficient simple control method without use of extra auxiliary switches and RLC components. This control technique also proved to be efficient under input voltage variations. Simulation is done for proving stabilization provided by the PID compensator with the help of ZVS logic circuit for synchronous rectifier (SR) buck converter in MATLAB Simulink.
Performance and High Robustness DPC for PWM Rectifier under Unstable VDC BusIJPEDS-IAES
This paper proposes a strategy de controlling a static AC / DC converter
based on direct power control (DPC). The instantaneous active and reactive
power is controlled in such a way to ensure the PWM rectifier with a
sinusoidal current absorption. This control has proven effective in terms of
reduction of total harmonic distortion (THD) of current absorbed. Offers a
good control of active and reactive power with an operation at unitary power
factor. The test of robustness carried out and the results have proven DPC
good performance with strong possibility of de integrate it into the field of
high voltage and high power as electric traction.
The voltage dip and doubly fed induction generator with considering uncertain...journalBEEI
The paper presents the transient behavior of the doubly fed induction generator (DFIG) in the wind turbine (WT) in the normal and voltage dip condition. When voltage dip occurs in to the grid, the rotor current increases and the DC-link voltage increases too and start to oscilate. In this paper, the proportional integral (PI) controllers are used to control the DFIG-basedwind farms for regulating the electronic devices including rotor side converter (RSC) and grid side converter (GSC) to control the active and reactive power of DFIG. The PI parameters are tuned by imperialist competitive algorithm (ICA). So, the transient behavour of the DFIG-based WF is explors when the voltage dip occurs. Hence, the induced electric motive force in to the rotor is measured. Also, an existed uncertainty for mutual inductance is considered caused by saturated curve during three-phase fault conditions and the bahavour of DFIG-based WT is examined and analyzed. All of simulation is done by Matlab/Simulink®.
Flux Based Sensorless Speed Sensing and Real and Reactive Power Flow Control ...ijeei-iaes
This aim of this paper is to design controller for Doubly Fed Induction Generator (DFIG) converters and MPPT for turbine and a sensor-less rotor speed estimation to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages. It is also aimed to meet desired reference real and reactive power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The turbine blade angle changes with variations in wind speed and direction of wind flow and improves the coefficient of power extracted from turbine using MPPT. Rotor side converter (RSC) helps to achieve optimal real and reactive power from generator, which keeps rotor to rotate at optimal speed and to vary current flow from rotor and stator terminals. Rotor speed is estimated using stator and rotor flux estimation algorithm. Parameters like tip speed ratio; coefficient of power, stator and rotor voltage, current, real, reactive power; rotor speed and electromagnetic torque are studied using MATLAB simulation. The performance of DFIG is compared when there is in wind speed change only; alter in reactive power and variation in grid voltage individually along with variation in wind speed.
Enhanced dynamic performance of grid feeding distributed generation under va...IJECEIAES
Controlling weak grid-connected systems is very challenging. In transient, frequency and voltage oscillations may lead to voltage and/or frequency stability problems and finally lead to system collapse. During steady-state operation and at the point of common coupling (PCC), voltage degradation and grid voltage background harmonics restrict the inverter's functionality, reduce the power flow capability and cause poor power quality. With weak grid connection, grid impedance variance will contaminate the voltage waveform by harmonics and augment the resonance, destabilizing the inverter operation. In this paper, complete mathematical modeling is carried out and state feedback-plus-integral control is implemented to support the stabilization of the system. The proposed controller is adopted to provide a smooth transient under sudden load change by controlling the injected grid current under different grid inductance values. Furthermore, the proposed control is used to reduce the order and size of the inverter output filter while maintaining system stability. The proposed control has been compared with the conventional proportional integral (PI) controller under different scenarios to validate its effectiveness and to strengthen its implementation as a simple controller for distributed generator applications.
Most of generators utilized in wind turbines are the Doubly-Fed Induction Generator (DFIG). Indirect matrix converter (IMC) is a candidate for substituting the traditional back-to-back converter in the future due to advantages gained by elimination of electrolytic capacitor. Starting DFIG wind turbines and synchronizing to the grid is a challenge in practice because of large inrush currents that could damage switches. Synchronizing the DFIG wind turbine controlled by the IMC is presented in this paper. Also, maximum power point tracking algorithm performance of this configuration is examined. A laboratory scale prototype of the proposed configuration is built. Experimental results have confirmed effectiveness of this configuration.
This paper presents the optimization design and a detailed implementation in FPGA (Field-Programmable Gate Array) of a power control strategy. This strategy is based on the phase shift angle of the inverter output voltage with respect to the grid voltage and DSPWM (Digital Sinusoidal Pulse Width Modulation) patterns “Phase shift angle-DSPWM” for an inverter for photovoltaic system connected to the grid. The proposed control can synchronize a sinusoidal inverter output current with a grid voltage and control the power injected into the grid. Detailed development of a digital controller with lower hardware and computation requirement is proposed. Description on the digital implementation of the A/D converter, the PI compensator, the phase shift and the DPWM, is provided. This digital control exhibit simplicity, reduction of the memory requirements and power calculation for the control. The functional structure of this system with digital control has been validated with simulations and experimental results.
This article proposes a novel scheme to improve the doubly-fed induction generator (DFIG) behavior during grid fault. The DFIG’s are sensitives to voltage variations when abrupt variations of the wind velocity arrive. For enhancing DFIG behavior, protecting the converters, and smoothing the fluctuations power output of the DFIG under sag voltage; a novel hybrid energy storage system scheme and its controller are proposed. The main advantages of our approach are a faster response and suppressing overvoltage on DC bus and globally less stress in the storage system. The control structure decreases the tiredness on the battery and restores the DC bus voltage rapidly, globally the battery system operating time increases. The results obtained by simulations in MATLAB validate the benefits of the suggested control.
A Hybrid Control Scheme for Fault Ride-Through Capability using Line-Side Con...Suganthi Thangaraj
As the wind power installations are increasing in number, Wind Turbine Generators (WTG) are required to have Fault Ride-Through (FRT) capabilities. Lately developed grid operating codes demand the WTGs to stay connected during fault conditions, supporting the grid to recover faster back to its normal state. In this paper, the generator side converter incorporates the maximum power point tracking algorithm to extract maximum energy from wind turbine system. A hybrid control scheme for energy storage systems (ESS) and braking choppers for fault ride-through capability and a suppression of the output power fluctuation is proposed for permanent-magnet synchronous generator (PMSG) wind turbine systems. During grid faults, the dc-link voltage is controlled by the ESS instead of the line-side converter (LSC), whereas the LSC is exploited as a STATCOM to inject reactive current into the grid for assisting in the grid voltage recovery. A simple model of the proposed system is developed and simulated in MATLAB environment. The effectiveness of the system is validated through extensive simulation results
TRANSIENT STABILITY ENHANCEMENT BY USING DSSC AND PSSIAEME Publication
Synchronous operation of generators in power system is required to supply continuous electricity to customers. Proper transient stability must be maintained for stable operation of power system. To enhance the transient stability of power system FACTS or D-FACTS technology can be used. In this paper, Distributed Static Series Compensator (DSSC) which, belongs to D-FACTS technology is used to enhance the transient stability of two-machine system with Power System Stabilizer (PSS) as an auxiliary controller and it is found that DSSC along with PSS is able to maintain required transient stability during severe three-phase to ground fault.
Analysis of PMSG in Wind Integration using T Source Inverter with Simple Boos...IJTET Journal
The Analysis of PMSG in wind integration using a T-source Inverter with the Simple Boost Control technique for
improving voltage gain is proposed. The Permanent Magnet Synchronous Generator (PMSG) offers higher performance than other
generators because of its higher efficiency with less maintenance. Since they don’t have rotor current, can be used without a gearbox,
which also implies a reduction of the weight of the nacelle with a reduction of costs. T-Source Inverter has high frequency, low
leakage inductance transformer and one capacitance this is the main difference from the Z-source Inverter. It has low active
components in compare with conventional ZSI. The T source network has an ability to perform DC to AC power conversion. It
provides buck boost operation in a single stage, but the traditional Inverter cannot provide such feature. All the components of the
wind turbine and the grid-side converter are developed and implemented in MATLAB/Simulink.
Improved Control Strategy for Low Voltage Ride Through Capability of DFIG wit...ecij
This paper deals with a protection and control strategy to enhance the low voltage ride through capability of a wind turbine driven doubly fed induction generator (DFIG). As the wind power penetration continues to increase, wind turbines are required to provide Low Voltage Ride-Through (LVRT) capability. Crowbars are commonly used to protect the power converters during voltage dips and their main drawback is that the DFIG absorbs reactive power from the grid during grid faults. According to emergency grid code requirements, wind farms should have the ability to stay connected and continue generation under external voltage failure conditions, that is, wind turbines have to keep in connection with grid and own continue reactive power supply. This paper proposes a hysteresis current control strategy for the crowbar protection
and a reactive power control to satisfy the grid code requirements. Consequently, the dynamic model of double fed wind turbines is established to study the transient behavior of DFIG. Simulation results are presented to show the effectiveness of the proposed control scheme.
In our homes or offices, security has been a vital issue. Control of home security system remotely always offers huge advantages like the arming or disarming of the alarms, video monitoring, and energy management control apart from safeguarding the home free up intruders. Considering the oldest simple methods of security that is the mechanical lock system that has a key as the authentication element, then an upgrade to a universal type, and now unique codes for the lock. The recent advancement in the communication system has brought the tremendous application of communication gadgets into our various areas of life. This work is a real-time smart doorbell notification system for home Security as opposes of the traditional security methods, it is composed of the doorbell interfaced with GSM Module, a GSM module would be triggered to send an SMS to the house owner by pressing the doorbell, the owner will respond to the guest by pressing a button to open the door, otherwise, a message would be displayed to the guest for appropriate action. Then, the keypad is provided for an authorized person for the provision of password for door unlocking, if multiple wrong password attempts were made to unlock, a message of burglary attempt would be sent to the house owner for prompt action. The main benefit of this system is the uniqueness of the incorporation of the password and messaging systems which denies access to any unauthorized personality and owner's awareness method.
Augmented reality, the new age technology, has widespread applications in every field imaginable. This technology has proven to be an inflection point in numerous verticals, improving lives and improving performance. In this paper, we explore the various possible applications of Augmented Reality (AR) in the field of Medicine. The objective of using AR in medicine or generally in any field is the fact that, AR helps in motivating the user, making sessions interactive and assist in faster learning. In this paper, we discuss about the applicability of AR in the field of medical diagnosis. Augmented reality technology reinforces remote collaboration, allowing doctors to diagnose patients from a different locality. Additionally, we believe that a much more pronounced effect can be achieved by bringing together the cutting edge technology of AR and the lifesaving field of Medical sciences. AR is a mechanism that could be applied in the learning process too. Similarly, virtual reality could be used in the field where more of practical experience is needed such as driving, sports, neonatal care training.
Image fusion is a sub field of image processing in which more than one images are fused to create an image where all the objects are in focus. The process of image fusion is performed for multi-sensor and multi-focus images of the same scene. Multi-sensor images of the same scene are captured by different sensors whereas multi-focus images are captured by the same sensor. In multi-focus images, the objects in the scene which are closer to the camera are in focus and the farther objects get blurred. Contrary to it, when the farther objects are focused then closer objects get blurred in the image. To achieve an image where all the objects are in focus, the process of images fusion is performed either in spatial domain or in transformed domain. In recent times, the applications of image processing have grown immensely. Usually due to limited depth of field of optical lenses especially with greater focal length, it becomes impossible to obtain an image where all the objects are in focus. Thus, it plays an important role to perform other tasks of image processing such as image segmentation, edge detection, stereo matching and image enhancement. Hence, a novel feature-level multi-focus image fusion technique has been proposed which fuses multi-focus images. Thus, the results of extensive experimentation performed to highlight the efficiency and utility of the proposed technique is presented. The proposed work further explores comparison between fuzzy based image fusion and neuro fuzzy fusion technique along with quality evaluation indices.
Graphs have become the dominant life-form of many tasks as they advance a
structure to represent many tasks and the corresponding relations. A powerful
role of networks/graphs is to bridge local feats that exist in vertices as they
blossom into patterns that help explain how nodal relations and their edges
impacts a complex effect that ripple via a graph. User cluster are formed as a
result of interactions between entities. Many users can hardly categorize their
contact into groups today such as “family”, “friends”, “colleagues” etc. Thus,
the need to analyze such user social graph via implicit clusters, enables the
dynamism in contact management. Study seeks to implement this dynamism
via a comparative study of deep neural network and friend suggest algorithm.
We analyze a user’s implicit social graph and seek to automatically create
custom contact groups using metrics that classify such contacts based on a
user’s affinity to contacts. Experimental results demonstrate the importance
of both the implicit group relationships and the interaction-based affinity in
suggesting friends.
This paper projects Gryllidae Optimization Algorithm (GOA) has been applied to solve optimal reactive power problem. Proposed GOA approach is based on the chirping characteristics of Gryllidae. In common, male Gryllidae chirp, on the other hand some female Gryllidae also do as well. Male Gryllidae draw the females by this sound which they produce. Moreover, they caution the other Gryllidae against dangers with this sound. The hearing organs of the Gryllidae are housed in an expansion of their forelegs. Through this, they bias to the produced fluttering sounds. Proposed Gryllidae Optimization Algorithm (GOA) has been tested in standard IEEE 14, 30 bus test systems and simulation results show that the projected algorithms reduced the real power loss considerably.
In the wake of the sudden replacement of wood and kerosene by gas cookers for several purposes in Nigeria, gas leakage has caused several damages in our homes, Laboratories among others. installation of a gas leakage detection device was globally inspired to eliminate accidents related to gas leakage. We present an alternative approach to developing a device that can automatically detect and control gas leakages and also monitor temperature. The system detects the leakage of the LPG (Liquefied Petroleum Gas) using a gas sensor, then triggred the control system response which employs ventilator system, Mobile phone alert and alarm when the LPG concentration in the air exceeds a certain level. The performance of two gas sensors (MQ5 and MQ6) were tested for a guided decision. Also, when the temperature of the environment poses a danger, LED (indicator), buzzer and LCD (16x2) display was used to indicate temperature and gas leakage status in degree Celsius and PPM respectively. Attension was given to the response time of the control system, which was ascertained that this system significantly increases the chances and efficiency of eliminating gas leakage related accident.
Feature selection problem is one of the main important problems in the text and data mining domain. This paper presents a comparative study of feature selection methods for Arabic text classification. Five of the feature selection methods were selected: ICHI square, CHI square, Information Gain, Mutual Information and Wrapper. It was tested with five classification algorithms: Bayes Net, Naive Bayes, Random Forest, Decision Tree and Artificial Neural Networks. In addition, Data Collection was used in Arabic consisting of 9055 documents, which were compared by four criteria: Precision, Recall, F-measure and Time to build model. The results showed that the improved ICHI feature selection got almost all the best results in comparison with other methods.
In this paper Gentoo Penguin Algorithm (GPA) is proposed to solve optimal reactive power problem. Gentoo Penguins preliminary population possesses heat radiation and magnetizes each other by absorption coefficient. Gentoo Penguins will move towards further penguins which possesses low cost (elevated heat concentration) of absorption. Cost is defined by the heat concentration, distance. Gentoo Penguins penguin attraction value is calculated by the amount of heat prevailed between two Gentoo penguins. Gentoo Penguins heat radiation is measured as linear. Less heat is received in longer distance, in little distance, huge heat is received. Gentoo Penguin Algorithm has been tested in standard IEEE 57 bus test system and simulation results show the projected algorithm reduced the real power loss considerably.
08 20272 academic insight on applicationIAESIJEECS
This research has thrown up many questions in need of further investigation.There was an expressive quantitative-qualitative research, which a common investigation form was used in.The dialogue item was also applied to discover if the contributors asserted the media-based attitude supplements their learning of academic English writing classes or not.Data recounted academic” insights toward using Skype as a sustaining implement for lessons releasing based on chosen variables: their occupation, year of education, and knowledge with Skype discovered that there were no important statistical differences in the use of Skype units because of medical academics major knowledge. There are statistically important differences in using Skype units. The findings also, disclosed that there are statistically significant differences in using Skype units due to the practice with Skype variable, in favors of academics with no Skype use practice. Skype instrument as an instructive media is a positive medium to be employed to supply academic medical writing data and assist education. Academics who do not have enough time to contribute in classes believe comfortable using the Skype-based attitude in scientific writing. They who took part in the course claimed that their approval of this media is due to learning academic innovative medical writing.
Cloud computing has sweeping impact on the human productivity. Today it’s used for Computing, Storage, Predictions and Intelligent Decision Making, among others. Intelligent Decision-Making using Machine Learning has pushed for the Cloud Services to be even more fast, robust and accurate. Security remains one of the major concerns which affect the cloud computing growth however there exist various research challenges in cloud computing adoption such as lack of well managed service level agreement (SLA), frequent disconnections, resource scarcity, interoperability, privacy, and reliability. Tremendous amount of work still needs to be done to explore the security challenges arising due to widespread usage of cloud deployment using Containers. We also discuss Impact of Cloud Computing and Cloud Standards. Hence in this research paper, a detailed survey of cloud computing, concepts, architectural principles, key services, and implementation, design and deployment challenges of cloud computing are discussed in detail and important future research directions in the era of Machine Learning and Data Science have been identified.
Notary is an official authorized to make an authentic deed regarding all deeds, agreements and stipulations required by a general rule. Activities carried out at the notary office such as recording client data and file data still use traditional systems that tend to be manual. The problem that occurs is the inefficiency in data processing and providing information to clients. Clients have difficulty getting information related to the progress of documents that are being taken care of at the notary's office. The client must take the time to arrive to the notary's office repeatedly to check the progress of the work of the document file. The purpose of this study is to facilitate clients in obtaining information about the progress of the work in progress, and make it easier for employees to process incoming documents by implementing an administrative system. This system was developed with the waterfall system development method and uses the Multi-Channel Access Technology integrated in the website to simplify the process of delivering information and requesting information from clients and to clients with Telegram and SMS Gateway. Clients will come to the office only when there is a notification from the system via Telegram or SMS notifying that the client must come directly to the notary's office, thus leading to an efficient time and avoiding excessive transportation costs. The overall functional system can function properly based on the results of alpha testing. The results of beta testing conducted by distributing the system feasibility test questionnaire to end users, get a percentage of 96% of users agree the system is feasible to be implemented.
In this work Tundra wolf algorithm (TWA) is proposed to solve the optimal reactive power problem. In the projected Tundra wolf algorithm (TWA) in order to avoid the searching agents from trapping into the local optimal the converging towards global optimal is divided based on two different conditions. In the proposed Tundra wolf algorithm (TWA) omega tundra wolf has been taken as searching agent as an alternative of indebted to pursue the first three most excellent candidates. Escalating the searching agents’ numbers will perk up the exploration capability of the Tundra wolf wolves in an extensive range. Proposed Tundra wolf algorithm (TWA) has been tested in standard IEEE 14, 30 bus test systems and simulation results show the proposed algorithm reduced the real power loss effectively.
In this work Predestination of Particles Wavering Search (PPS) algorithm has been applied to solve optimal reactive power problem. PPS algorithm has been modeled based on the motion of the particles in the exploration space. Normally the movement of the particle is based on gradient and swarming motion. Particles are permitted to progress in steady velocity in gradient-based progress, but when the outcome is poor when compared to previous upshot, immediately particle rapidity will be upturned with semi of the magnitude and it will help to reach local optimal solution and it is expressed as wavering movement. In standard IEEE 14, 30, 57,118,300 bus systems Proposed Predestination of Particles Wavering Search (PPS) algorithm is evaluated and simulation results show the PPS reduced the power loss efficiently.
In this paper, Mine Blast Algorithm (MBA) has been intermingled with Harmony Search (HS) algorithm for solving optimal reactive power dispatch problem. MBA is based on explosion of landmines and HS is based on Creativeness progression of musicians-both are hybridized to solve the problem. In MBA Initial distance of shrapnel pieces are reduced gradually to allow the mine bombs search the probable global minimum location in order to amplify the global explore capability. Harmony search (HS) imitates the music creativity process where the musicians supervise their instruments’ pitch by searching for a best state of harmony. Hybridization of Mine Blast Algorithm with Harmony Search algorithm (MH) improves the search effectively in the solution space. Mine blast algorithm improves the exploration and harmony search algorithm augments the exploitation. At first the proposed algorithm starts with exploration & gradually it moves to the phase of exploitation. Proposed Hybridized Mine Blast Algorithm with Harmony Search algorithm (MH) has been tested on standard IEEE 14, 300 bus test systems. Real power loss has been reduced considerably by the proposed algorithm. Then Hybridized Mine Blast Algorithm with Harmony Search algorithm (MH) tested in IEEE 30, bus system (with considering voltage stability index)- real power loss minimization, voltage deviation minimization, and voltage stability index enhancement has been attained.
Artificial Neural Networks have proved their efficiency in a large number of research domains. In this paper, we have applied Artificial Neural Networks on Arabic text to prove correct language modeling, text generation, and missing text prediction. In one hand, we have adapted Recurrent Neural Networks architectures to model Arabic language in order to generate correct Arabic sequences. In the other hand, Convolutional Neural Networks have been parameterized, basing on some specific features of Arabic, to predict missing text in Arabic documents. We have demonstrated the power of our adapted models in generating and predicting correct Arabic text comparing to the standard model. The model had been trained and tested on known free Arabic datasets. Results have been promising with sufficient accuracy.
In the present-day communications speech signals get contaminated due to
various sorts of noises that degrade the speech quality and adversely impacts
speech recognition performance. To overcome these issues, a novel approach
for speech enhancement using Modified Wiener filtering is developed and
power spectrum computation is applied for degraded signal to obtain the
noise characteristics from a noisy spectrum. In next phase, MMSE technique
is applied where Gaussian distribution of each signal i.e. original and noisy
signal is analyzed. The Gaussian distribution provides spectrum estimation
and spectral coefficient parameters which can be used for probabilistic model
formulation. Moreover, a-priori-SNR computation is also incorporated for
coefficient updation and noise presence estimation which operates similar to
the conventional VAD. However, conventional VAD scheme is based on the
hard threshold which is not capable to derive satisfactory performance and a
soft-decision based threshold is developed for improving the performance of
speech enhancement. An extensive simulation study is carried out using
MATLAB simulation tool on NOIZEUS speech database and a comparative
study is presented where proposed approach is proved better in comparison
with existing technique.
Previous research work has highlighted that neuro-signals of Alzheimer’s disease patients are least complex and have low synchronization as compared to that of healthy and normal subjects. The changes in EEG signals of Alzheimer’s subjects start at early stage but are not clinically observed and detected. To detect these abnormalities, three synchrony measures and wavelet-based features have been computed and studied on experimental database. After computing these synchrony measures and wavelet features, it is observed that Phase Synchrony and Coherence based features are able to distinguish between Alzheimer’s disease patients and healthy subjects. Support Vector Machine classifier is used for classification giving 94% accuracy on experimental database used. Combining, these synchrony features and other such relevant features can yield a reliable system for diagnosing the Alzheimer’s disease.
Attenuation correction designed for PET/MR hybrid imaging frameworks along with portion making arrangements used for MR-based radiation treatment remain testing because of lacking high-energy photon weakening data. We present a new method so as to uses the learned nonlinear neighborhood descriptors also highlight coordinating toward foresee pseudo-CT pictures starting T1w along with T2w MRI information. The nonlinear neighborhood descriptors are acquired through anticipating the direct descriptors interested in the nonlinear high-dimensional space utilizing an unequivocal constituent guide also low-position guess through regulated complex regularization. The nearby neighbors of every near descriptor inside the data MR pictures are looked during an obliged spatial extent of the MR pictures among the training dataset. By that point, the pseudo-CT patches are evaluated through k-closest neighbor relapse. The planned procedure designed for pseudo-CT forecast is quantitatively broke downward on top of a dataset comprising of coordinated mind MRI along with CT pictures on or after 13 subjects.
The cognitive radio prototype performance is to alleviate the scarcity of spectral resources for wireless communication through intelligent sensing and quick resource allocation techniques. Secondary users (SU’s) actively obtain the spectrum access opportunity by supporting primary users (PU’s) in cognitive radio networks (CRNs). In present generation, spectrum access is endowed through cooperative communication-based link-level frame-based cooperative (LLC) principle. In this SUs independently act as conveyors for PUs to achieve spectrum access opportunities. Unfortunately, this LLC approach cannot fully exploit spectrum access opportunities to enhance the throughput of CRNs and fails to motivate PUs to join the spectrum sharing processes. Therefore, to overcome this con, network level cooperative (NLC) principle was used, where SUs are integrated mutually to collaborate with PUs session by session, instead of frame based cooperation for spectrum access opportunities. NLC approach has justified the challenges facing in LLC approach. In this paper we make a survey of some models that have been proposed to tackle the problem of LLC. We show the relevant aspects of each model, in order to characterize the parameters that we should take in account to achieve a spectrum access opportunity.
In this paper, the author provides insights and lessons that can be learned from colleagues at American universities about their online education experiences. The literature review and previous studies of online educations gains are explored and summarized in this research. Emerging trends in online education are discussed in detail, and strategies to implement these trends are explained. The author provides several tools and strategies that enable universities to ensure the quality of online education. At the end of this research paper, the researcher provides examples from Arab universities who have successfully implemented online education and expanded their impact on the society. This research provides a strategy and a model that can be used by universities in the Middle East as a roadmap to implement online education in their regions.
We have compiled the most important slides from each speaker's presentation. This year’s compilation, available for free, captures the key insights and contributions shared during the DfMAy 2024 conference.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
An Approach to Detecting Writing Styles Based on Clustering Techniquesambekarshweta25
An Approach to Detecting Writing Styles Based on Clustering Techniques
Authors:
-Devkinandan Jagtap
-Shweta Ambekar
-Harshit Singh
-Nakul Sharma (Assistant Professor)
Institution:
VIIT Pune, India
Abstract:
This paper proposes a system to differentiate between human-generated and AI-generated texts using stylometric analysis. The system analyzes text files and classifies writing styles by employing various clustering algorithms, such as k-means, k-means++, hierarchical, and DBSCAN. The effectiveness of these algorithms is measured using silhouette scores. The system successfully identifies distinct writing styles within documents, demonstrating its potential for plagiarism detection.
Introduction:
Stylometry, the study of linguistic and structural features in texts, is used for tasks like plagiarism detection, genre separation, and author verification. This paper leverages stylometric analysis to identify different writing styles and improve plagiarism detection methods.
Methodology:
The system includes data collection, preprocessing, feature extraction, dimensional reduction, machine learning models for clustering, and performance comparison using silhouette scores. Feature extraction focuses on lexical features, vocabulary richness, and readability scores. The study uses a small dataset of texts from various authors and employs algorithms like k-means, k-means++, hierarchical clustering, and DBSCAN for clustering.
Results:
Experiments show that the system effectively identifies writing styles, with silhouette scores indicating reasonable to strong clustering when k=2. As the number of clusters increases, the silhouette scores decrease, indicating a drop in accuracy. K-means and k-means++ perform similarly, while hierarchical clustering is less optimized.
Conclusion and Future Work:
The system works well for distinguishing writing styles with two clusters but becomes less accurate as the number of clusters increases. Future research could focus on adding more parameters and optimizing the methodology to improve accuracy with higher cluster values. This system can enhance existing plagiarism detection tools, especially in academic settings.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
HEAP SORT ILLUSTRATED WITH HEAPIFY, BUILD HEAP FOR DYNAMIC ARRAYS.
Heap sort is a comparison-based sorting technique based on Binary Heap data structure. It is similar to the selection sort where we first find the minimum element and place the minimum element at the beginning. Repeat the same process for the remaining elements.
Literature Review Basics and Understanding Reference Management.pptxDr Ramhari Poudyal
Three-day training on academic research focuses on analytical tools at United Technical College, supported by the University Grant Commission, Nepal. 24-26 May 2024
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
Understanding Inductive Bias in Machine LearningSUTEJAS
This presentation explores the concept of inductive bias in machine learning. It explains how algorithms come with built-in assumptions and preferences that guide the learning process. You'll learn about the different types of inductive bias and how they can impact the performance and generalizability of machine learning models.
The presentation also covers the positive and negative aspects of inductive bias, along with strategies for mitigating potential drawbacks. We'll explore examples of how bias manifests in algorithms like neural networks and decision trees.
By understanding inductive bias, you can gain valuable insights into how machine learning models work and make informed decisions when building and deploying them.
2. ISSN: 2502-4752
IJEECS Vol. 5, No. 2, February 2017 : 277 – 289
278
DFIG is described with and without crowbar protection for a sudden voltage dip. DFIM is
studied with control of RSC under abnormal condition [7], in which control of active and
reactive power can be independently achieved with results showing that speed, torque and
power factor can be matched with the reference signals by regulating individually but the
inverter has to be disconnected during the fault to avoid high oscillations in stator and rotor
currents. In [8], the variations in active and reactive power abd DC bus voltage is addressed
and both the GSC and RSC are dynamically controlled by active and reactive power of DFIG.
The objective of maintaining DC link voltage at constant level is achieved in [9] for variable
speed performance but it is not dealt with the unbalanced voltage case. The DC bus voltage
and electromagnetic torque oscillations due to fault in [10] is not addressed properly. A Stator
Voltage Oriented Direct Power Control (SVODPC) scheme and a new crowbar control
technique was proposed in [11], capable of suppressing the oscillations in currents and Tem
caused due to fault state along with recovering the grid voltage by injecting the reactive power
and limit the peak values of rotor currents by new crowbar protection technique. Mathematical
analysis of the stator and rotor fault currents is deduced for the DFIG during a grid fault in
presence of crowbar resistors which influence the electrical behavior. The fault currents and
Tem are analyzed for different values of crowbar resistances for different DFIG parameter sets
[12]. In [13], a novel crowbar protection technique along with a DPC scheme is proposed for
DFIG. During grid fault, a voltage dip is caused due to which large transient currents are
induced in rotor windings, which has to be avoided otherwise it will damage the RSC. DPC
strategy applied to RSC suppresses the fault currents transient oscillations and also Tem
oscillations. In [14], a DTC technique along with a reference rotor flux amplitude generation
strategy is applied to RSC of DFIM under voltage dip. With the implementation of the scheme,
controlled torque and considerable reduction of stator and rotor over currents is achieved but
the scheme does not avoid the crowbar protection completely, it is avoided during the low
depth voltage dips. The DTC technique is applied to the RSC to control the torque oscillations
but the DC bus oscillations and consideration of unbalanced load condition was unaddressed.
A new DTC scheme for a DFIG under unbalanced grid voltage condition is proposed in [15].
Independent control of electromagnetic torque and reactive power is achieved by controlling
the torque angle (δ) and rotor voltage magnitude because of that the reduction in pulsations of
Tem is achievable. In this proposed method, Proportional-Integral and Resonant (PI+R)
controller is used to achieve the reduction of pulsations in Tem. A proper value of crowbar
resistance is chosen, which is connected to RSC, in order to limit the rotor current which
generally increases almost 8 times its nominal rated value and even fluctuations in DC-link
voltage are limited by which DFIG performance is improved [16]. A real time adjustable
resistance crowbar structure is described in [17], for DFIG variable speed operation system
and the performance of the system is analyzed for a grid fault. During the fault the grid voltage
is assisted by providing reactive power by supply-side converter and also by machine side
converter and the scheme described is used to control rotor currents and DC-link voltage
values within the limits.
The various strategies mentioned above are used to minimize the effects of stator and
rotor over currents, fluctuations in DC-link voltage, oscillations in Tem, control of active and
reactive power on the power converters employed for control of DFIM when there is network
unbalance in the DFIG system but in most of the cases crowbar protection is employed and
non-sinusoidal currents are exchanged with the grid which is not good for a wind turbine. In
[18], the solution for the problem discussed above is explained with the active (P) and reactive
(Q) power references generation for the rotor connected converter and for the grid connected
converter, the power references are calculated by means of stator voltage and grid current
sequence components in order to eliminate the torque oscillations and achieve sinusoidal
currents, which are exchange with the grid. In this paper, a new DPC strategy is proposed for
both the rotor connected converter and grid connected converter along with the Torque
Oscillations Cancellation (TOC) strategy without any sequence calculations for RSC and a
new Proportional Integral (PI) control based power references generation strategy along with
elimination of DC bus voltage oscillations is employed for Grid Side Converter (GSC) without
calculating the stator voltage and grid current sequence components, which is actually taken
into consideration in [18]. The performance of the proposed scheme is verified by simulation
results for the conditions of with and without grid fault and the results clearly shows that the
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behavior of the Doubly Fed Induction Generator (DFIG) is improved with elimination of
oscillations in Tem and achieving exchange of sinusoidal currents with the grid.
2. Proposed System
As shown in Figure 1, the proposed scheme is analyzed by the condition of three
phase fault, which is applied near the grid. During the fault there is sudden dip in stator voltage
due to which over currents will be produced in stator and rotor currents and the currents
become non-sinusoidal and also this condition will lead to oscillations in the Tem. If no special
control efforts are used these conditions will prevail in DFIG system when operating with
constant P and Q reference generations [18]. For both the rotor connected converter and grid
connected converter the DPC technique is employed as shown in Figure 1. The stator active
power new reference (Ps_ref) generation value and the reference value of stator active power
(Ps_required) are compared and likewise the stator reactive power new reference (Qs_ref)
generation value and the reference reactive power of stator (Qs_required) are compared for the
generation of pulses for RSC. This DPC technique applied for RSC is used to deal with the
problems associated with the grid voltage unbalance. Similarly, the grid side active and
reactive power values are compared for the generation of pulses for GSC. This DPC
technique applied for grid side converter is used for controlling the active and reactive powers
directly. The specifications of the DFIG used are shown the Table 1.
Figure 1. Proposed scheme
Table 1. Ratings of DFIG
Rated Power (P) 2.6MW
RMS Voltage (Vrms) 690V
Frequency (f) 50Hz
Pairs of Poles (p) 2
Stator Resistance (Rs) 0.0108pu
Rotor Resistance (Rr’) 0.0121pu
Stator Leakage Inductance (Lls) 0.102pu
Rotor Leakage Inductance (Llr’) 0.1pu
Magnetizing Inductance (Lm) 3.362pu
Inertia Constant (H) 0.5s
Friction Coefficient (F) 0.05479pu
The stator and rotor voltage and flux equations of DFIG based on the stator reference frame
are given below:
̅ ̅
̅
(1)
̅ ̅
̅
̅ (2)
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̅ ̅ ̅ (3)
̅ ̅ ̅ (4)
The electromagnetic torque of DFIG is given by:
{̅ ̅ } ( ) {̅ ̅ } (5)
The instantaneous apparent power representation under unbalanced operating conditions is
given by:
⃗ ( ) ( ) ( ) *̅ ̅ + (6)
From the expression the active and reactive powers can be written as:
( ) *̅ ̅ + ( ) (7)
( ) *̅ ̅ + ( ) (8)
The (7) and (8) are used to calculate the estimated values of active and reactive powers of the
DFIG.
3. Control Strategy for Rotor Connected Converter
3.1. Stator Active Power Reference Generation
In this section, the Torque Oscillations Cancellation (TOC) scheme without the
necessity of sequence calculations method is presented. This strategy is very simple in
implementation and makes it possible to avoid Tem oscillations caused by grid fault.
Considering the general unbalance case, the stator and rotor flux space vector can be
represented mathematically as [18]:
̅ ̂ ( δ) ̂ ( δ) (9)
Similarly,
̅ ̂ ( ) ̂ ( ) (10)
Substituting the above expressions in the expression of the torque (5), we obtain:
*(̂ ̂ ̂ ̂ ) δ (̂ ̂ ̂ ̂ ) ( δ)+ (11)
That can represented as:
( ) (12)
Where
The above expression clearly shows that, during the unbalanced situation, the torque
has one constant term and other an oscillating term, that is, the overall behavior is oscillating
in nature. For normal operation of DFIM, the oscillating component of the torque should be
zero that means it has to be compensated or cancelled by any means. This can be obtained
with the following condition.
̂ ̂ ̂ ̂ (13)
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Which implies,
̂ ̂ ̂ ̂ (14)
From that, we can write:
̂
̂
̂
̂
(15)
That is ratio of rotor and stator flux amplitudes to be maintained constant to make the
torque constant with sinusoidal currents exchange with the grid. And this can be achieved by
either direct or indirect way of rotor flux reference generation. Generation of rotor flux
reference is explained as follows:
Similar to (5) and (11), the mechanical power and the stator active power can be
represented respectively as:
{̅ ̅ }
* + (16)
*(̂ ̂ ̂ ̂ ) δ (̂ ̂ ̂ ̂ ) ( δ)+ (17)
{̅ ̅ } (18)
* +
*(̂ ̂ ̂ ̂ ) δ (̂ ̂ ̂ ̂ ) ( δ)+ (19)
The above expressions (17) and (19) can be written as:
( ) (20)
Where .
( )
(21)
Where .
From the equations (20) and (21), it can be clearly seen that, during unbalance
situation, the mechanical power and stator active power are also oscillating, similar to the
torque.
The simple control strategy applied to obtain constant torque with sinusoidal grid
currents, without sequence calculations is subtracting the oscillating component obtained from
torque ( , from the above expression (11)) from the estimated stator active power ( s, we
can notice in the above expression (21), i.e., oscillating term) and then adding it to the
reference value ( s required) to obtain the new reference value ( s ref).
As shown in Figure 2, the s ref is generated by adding the s required to the difference
of oscillating term obtained from the electromagnetic torque and the estimated stator power. It
is also described by the equation:
s ref s required ( s
s
p em) (22)
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Figure 2. RSC active power reference generation
This new reference value obtained will be oscillating in nature, which indirectly creates
the oscillatory rotor flux space vector amplitude that closely follows the oscillatory stator flux.
Thus maintaining the torque, i.e., (5) constant, at any instant and even obtaining exchange of
sinusoidal currents with the grid, that means, the oscillating term will be become zero, making
the torque to be constant.
The advantage of this improved method is that there is no requirement of calculating
the sequence components in order to avoid the Tem oscillations. Different methods to avoid the
power and torque oscillations are presented in [18] including the Torque Oscillations
Cancellation Without Sequence Calculation (TOC-WSC), which is the best strategy compared
to the other strategies. The complex calculations required for estimating the sequence
components is avoided by employing this strategy.
In this paper, the average wind speed is assumed as 12ms
-1
, at this average speed of
the wind, the DFIG is assumed to be running at 1100rev/min. At this value of the wind speed
the reference value of stator active and reactive power is taken as 0.17pu and 0.34pu
respectively and reference grid-side reactive power is taken as -0.34pu. When the wind speed
changes, the DFIG rotor speed also changes that means active and reactive powers will also
change. The required pulses are generated and fed to the RSC and GSC from the three level
active hysteresis comparators and two level reactive hysteresis comparators respectively as
shown in Figure 1.
4. Control Strategy for Grid Connected Converter
4.1. Grid Connected Converter Analysis
As shown in Figure 1, the grid-side active and reactive power errors are fed to the
DPC strategy in order to achieve the objective of the GSC, which is generally used to control
the active (Pg) and reactive (Qg) powers, which are exchanged through the grid connected
converter to the grid and also to control the DC bus voltage (Vbus) oscillations. And not only
that the GSC has to even address the unbalance caused in voltage due to the grid fault and
but also the oscillations caused in the rotor active power supplied by the machine side
converter to the DC voltage bus. Due to the grid fault as mentioned there will be unbalance in
stator voltages, which produces active power oscillations in the DC bus. These DC-link voltage
oscillations which are at two times the frequency of the grid are caused because of the
oscillations produced in the currents flowing through the DC-link in between the GSC and
RSC, which are actually produced because of the oscillations in active and reactive powers at
both ac sides of the converter.
4.2. PI based Power References Generation Method
The grid-side active ( g ref) and reactive power ( g ref) new reference values are
obtained as shown in Figure 3. The grid-side active power compensating component ( g ) is
obtained from the PI controller, which is fed by the difference of magnitude of reference and
estimated three-phase stator voltage. g is added to the reference grid-side active power
( g required) to get the new reference component, g ref. g requiredis obtained from DC bus
voltage PI regulator, which is fed by the difference of the reference and estimated DC-link
voltage.
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Likewise, the grid-side reactive power compensating component ( g ) is obtained
from the PI controller, which is fed by the stationary two-axis reference frame -component of
current, Δi (not shown in Figure 3), obtained by applying Clarke’s transformation to the
difference of ig abc and ig abc. g is added to the reference grid-side reactive power ( g required)
to obtain the new reference g ref value. The gains of the PI controllers are obtained by using
the auto-tunable PI controllers in MATLAB/Simulink, which is made possible by obtaining
transfer function from the input and output data set. The data set for auto-tunable DC bus
voltage PI controller is obtained by input (error value of DC link voltage) and output (reference
grid-side active power).
Figure 3. GSC active and reactive power reference generation
The compensating components g and g are added to the g required and
g required, so that the estimated values of grid-side active and reactive powers, g and g are
within the range of the new reference values, g refand g ref, and there are no additional
oscillations in the g and g; thus, inferring that the oscillating active and reactive powers
exchanged through the rotor will address the unbalance voltage operating conditions and also
exchange sinusoidal currents with the grid. These will propagate through the rotor as a
function of slip speed i.e., indirectly depends on the mechanical speed of the DFIG.
slip s m
s
(23)
The expressions of g and g from the Figure 3 can be written as,
vs |v|s abc |v|s abc (24)
g p vs i ∫ vs dt (25)
Likewise,
ig ig abc ig abc (26)
From the Clarke’s ransformation,
i
√3
igb √3
igc (27)
i
3
iga 3
igb 3
igc iga (28)
g p i i ∫ i dt (29)
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That is,
g p (
√3
igb √3
igc) i ∫ (
√3
igb √3
igc) dt (30)
As mentioned the proposed GSC active and reactive power reference generation
strategy is shown in Figure 3. The values of g ref and g ref from the Figure 3 can be
obtained as:
g ref g required g (31)
g ref g required g (32)
During unbalance, there is requirement of increase in voltage at both the ac sides of
the converters, because of this the DC bus voltage increases. As the active and reactive
powers exchanged on both sides of the converters are oscillatory; hence, the DC bus voltage
is also oscillatory because the amplitude of the oscillations of DC bus voltage depends on the
active and reactive powers exchanged. In particularly the oscillations in DC bus voltage are
due to oscillations in active power of the rotor. This can be shown mathematically as follows:
As we know that,
r em
r
p
(33)
where, r s m
Substituting the expression of the Torque (11), we get:
r
3
r
m
s r
*(̂ s
̂ r
̂ s
̂ r
) sin δ (̂ s
̂ r
̂ s
̂ r
) sin( t δ)+ (34)
And also,
〈 g〉 〈 r〉 converter (35)
That is, mean value of the grid-side active power is equal to the sum of mean value of
the exchanged rotor active power and converters active power losses.
From the expressions (34) and (35), it clearly shows that during unbalance, the grid-
side active power is also oscillating in nature.
As shown in Figure 3, the DC bus voltage PI regulator must be tuned for smooth
dynamics (as the difference between the reference DC bus voltage and the unbalance
affected DC bus voltage may produce additional oscillations), so that, it produces only the
mean value of the grid-side active power as given by (35), that means, producing mean value
of the rotor active power. Further, indicating that there are no additional oscillations in both the
grid-side active power and rotor active power, which signifies that there is reduction in the
oscillations of DC bus voltage. If the mean value is not generated, then the new reference
value of grid-side active power produce oscillations which causes additional oscillations in the
estimated grid-side active power and thus, in the rotor active power.
Another approach is to increase the DC bus voltage value, as its amplitude depends
on the active and reactive powers exchanged on both sides of the converter. During
unbalance, there is requirement of increase in voltage at both ac sides of converters, due to
induced voltage oscillations. This fact increases the necessary DC bus voltage [18]. That
means, if value of DC bus voltage is increased beforehand, as said above, then there is no
requirement of much increase in voltage at both ac sides of converters. From this it can be
deduced that the amplitude of the oscillations of active and reactive powers exchanged on
both sides of the converter are reduced. Hence, the amplitude of the DC bus voltage
oscillations is reduced. But still taking the necessary actions as described above, the DC bus
voltage is not constant; there is slight variation, which is shown in results.
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The unbalance voltage due to the unbalanced condition will produce unbalance grid
voltage which is unfortunately almost equivalent to the unbalance created in the stator
currents, which is clearly indicated in the results and discussion section. The proposed control
strategy contributes to the elimination of mechanical torque oscillations as Tem oscillations are
eliminated by which it is possible to avoid the necessity to disconnect the wind turbine from the
grid supply whenever there is any unbalance in the system. The proposed method makes the
unbalance voltage produced in the system to be less severe without completely avoiding the
cause.
5. Results and Discussion
5.1. Simulation Results of Proposed Strategy
The performance of the proposed system is verified for the steady state operating
condition along with grid voltage unbalance, which refers to operation of DFIG with s required
and s required values set to 0.17p.u. and 0.34p.u. respectively, as mentioned and g required is
as shown in Figure 3, while the g required value is set to -0.34p.u. at constant speed of
1100rev/min. The magnitudes of the RSC and GSC with cancellation of oscillations produced
in electromagnetic scheme and grid-side power references generation are shown in Figure 4.
The control strategy of TOC and the PI based g ref and g ref generations are shown in Figure
2 and 3 respectively and these control strategies were discussed in previous section. The
power tracking behavior of stator-side active and reactive powers for cancellation of
oscillations in Tem and also the g and g for cancellation of oscillations produces in DC-link
voltage are shown in Figure 4(e)-(h) respectively.
A small unbalance can create large torque and active power oscillations. In this paper,
2.2% of line voltage unbalance factor (ratio of maximum stator voltage deviation from the
average line voltage of stator to the average line voltage of stator) is taken into consideration
as most of the wind farms are located remotely and therefore most of the times the wind farms
are succumbed to the unbalance voltage conditions. Therefore, there is large deviation in
stator and grid side active and reactive power estimated values with respect to reference
values as shown in Figure 4(e), (f), (g), (h).
DC bus voltage waveform in the case of 1198-1202rpm is shown in Figure 4(b).
Figure 4(a)-(c) clearly shows the outcomes of the proposed control strategy as it indicates that
there is reduction in oscillations in the DC-link voltage and no oscillations are present in Tem
respectively.
The unbalance load causes non-sinusoidal currents, which are actually reactive
currents drawn from grid, these currents cause distortions in the grid voltage, which can be
observed from the Fig. 4(d), the unbalanced load is applied at 0.05s.
Figure 4(i) and (j) shows the grid and rotor currents respectively, which are exchanged
with the grid and rotor of the DFIG. Eventually, the unbalance caused in the system makes the
grid and rotor currents to be unbalanced still they are sinusoidal in nature. Hence, clearly it
can be said that sinusoidal currents are exchanged through the grid. The response of the rotor
speed is shown in Figure 4(k) and the wind input taken for this simulation is shown in
Figure 4(l). In the simulation results, the nonlinearities and losses of the DFIG are not
considered.
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In the next context, the performance of the system is analyzed for a three-phase grid
fault with all the other parameters considered to be same as previous case. The results shown
in Figure 5(a) and (b) describe the outputs of DC-link voltage and the Tem respectively, which
are similar to the previous case. Figure 5(c) shows the output of the grid voltage, which clearly
shows the deterioration and the unbalance nature of the grid voltage in particularly when the
unbalance is created at 0.05s. The results clearly show that the oscillations are completely
avoided with the help of the proposed control strategy. The stator and grid-side active and
reactive power references and estimated values are shown in Figure 5(d) to (g). From the
results, it is clearly indicated that the active and reactive powers of both stator and grid-side
are deteriorated at the time of grid fault operation, which is applied for the duration of 0.006s
i.e., from 0.05s to 0.056s. Because of this unbalance condition, the estimated values will not
completely deviate, will be within the limits as shown in Figure 5(d) to (g) and still it will follow
the reference values as close as possible once the unbalance condition is removed. The
unbalance in the grid voltage will be reflected onto the stator and rotor currents and this can
be seen clearly in Figure 5(h) and (i). The results of stator and rotor currents are little more
unbalance in nature compared to the previous case and still the currents are sinusoidal.
Hence the behavior of the DFIG is improved even during the grid fault operating condition with
the help of the proposed system.
6. Conclusion
In this paper, addressing the problem of DFIG based wind turbines in case of network
unbalance due to grid fault has been addressed. Under fault operating condition by
implementing the DPC scheme to both rotor connected converter and grid connected
converter with Torque Oscillations Cancellation strategy applied to RSC and PI control based
generation of power references strategy along with elimination of DC bus voltage oscillations
without voltage and current sequence component calculation applied to GSC, it has been
shown that the electromagnetic torque oscillations are eliminated which leads to reduction in
mechanical stresses and achieving sinusoidal current exchange with the grid hence achieving
stable operation of the DFIG.
From the power and torque estimation calculation an oscillating stator active reference
is generated by which it is possible to achieve the non-oscillating torque and ensure exchange
of sinusoidal currents with grid, thus avoiding completely the sequence components
calculation. The simulation results demonstrates that the difficulties of DFIG operation at the
time of grid unbalance which can be easily avoided by implementation of proposed new DPC
strategy for both rotor connected converter and grid connected converter.
References
[1] Pena R, Clare J, Asher G. Doubly-fed induction generators using back-to-back PWM converters
and its applications to variable-speed wind energy generation. IEE Proceedings-Electric Power
Applications. 1996; 143: 231-241.
[2] Madhav GV, Obulesu YP. A Fuzzy Logic Control Strategy for Doubly Fed Induction Generator for
Improved Performance under Faulty Operating Conditions. International Journal of Power
Electronics and Drive Systems. 2014; 4(4): 419.
[3] Takahashi I, Ohmori Y. High-performance direct torque control of an induction motor. IEEE
Transactions on Industrial Applications. 1989; 25(2): 1090-1093.
[4] Depenbrock M. Direct self-control (DSC) of inverter-fed induction machine. IEEE Transactions on
Power Electronics. 1988; 3(4): 420-429.
[5] Onishi T. Three phase PWM converter/inverter by means of instantaneous active and reactive
power control. Proceedings of the Intl. Conference on Industrial Electronics Control and
Instrumentation (IECON). 1991; 1: 819-824.
[6] Seman S, Niiranen J, Kanerva S, Arkkio A. Analysis of a 1.7 MVA doubly fed wind-power induction
generator during power systems disturbances. Proceedings of the Nordic Workshop of Power and
Industrial Electronics. 2004.
[7] Chayawatto N, Ortojohann E. Dynamic Behaviour of a Doubly Fed Induction Machine with
Generator-side Converter under Abnormal Condition. National Science and Technology
Development Agency (NSTDA). Thailand. 2004.
[8] Nora Z, Hocine L. Active and Reactive Power Control of a Doubly Fed Induction Generator.
International Journal of Power Electronics and Drive Systems. 2014; 5(2): 244.
13. IJEECS ISSN: 2502-4752
A Control Strategy for DFIM to Minimize DC Bus Voltage Fluctuations… (G. Venu Madhav)
289
[9] Boulahia A, Adel M, Benalla H. Predictive Power Control of Grid and Rotor Side converters in
Doubly Fed Induction Generators Based Wind Turbine. Bulletin of Electrical Engineering and
Informatics. 2013; 2(4): 258-264.
[10] Ananth DV, Kumar VN. Flux Based Sensorless Speed Sensing and Real and Reactive Power Flow
Control with Look-up Table based Maximum Power Point Tracking Technique for Grid Connected
Doubly Fed Induction Generator. Indonesian Journal of Electrical Engineering and Informatics
(IJEEI). 2015; 3(4): 239-260.
[11] Peng Z, Yikang H. Control Strategy of an Active Crowbar for DFIG Based Wind Turbine under Grid
Voltage Dips. Proceedings of the Intl. Conference on Electrical Machines and Systems. Seoul.
2007: 259-264.
[12] Zhang W, Zhou P, He Y. Analysis of the By-Pass Resistance of an Active Crowbar for Doubly-Fed
Induction Generator Based Wind Turbines under Grid Faults. International Conference on Electrical
Machines and Systems (ICEMS). 2008: 2316-2321.
[13] Zhou P, He Y, Sun D, Zhu JG. Control and Protection of a DFIG-Based Wind Turbine under
Unbalanced Grid Voltage Dips. In Industry Applications Society Annual Meeting (IAS ’08). 2008: 1-
8.
[14] Madhav GV, Obulesu YP. Low Voltage Ride-Through of Doubly Fed Induction Machine using
Direct Torque Control Strategy. International Journal of Power Electronics and Drive Systems.
2013; 3(1): 95.
[15] Pimple BB, Vekhande VY, Fernandes BG. New direct torque control of DFIG under balanced and
unbalanced grid voltage. TENCON 2010. IEEE Region 10 Conference. 2010: 2154-2158.
[16] Kalantarian SR, Heydari H. A New Crowbar Protection Method for Improvement in Performance of
Doubly Fed Induction Generator under Fault Conditions. 10
th
Environment and Electrical
Engineering International Conference (EEEIC). 2011: 1-4.
[17] Ren Y, Zhang W. A Novel Control Strategy of an Active Crowbar for DFIG-Based Wind Turbine
during Gird Faults. International conference on Electric Machines & Drives Conference (IEMDC).
2011: 1137-1142.
[18] Abad G, Rodriguez MA, Iwanski G, Poza J. Direct power control of doubly-fed-induction-generator-
based wind turbines under unbalanced grid voltage. IEEE Transactions on Power Electronics.
2010; 25(2): 442-452.