This document presents and compares several control schemes for a Doubly Fed Induction Generator (DFIG) under unbalanced grid voltage conditions. It describes a previously proposed Direct Power Control (DPC) method that uses Notch filters to eliminate harmonic components during voltage unbalances. It also describes a previously proposed Stator Flux Oriented Control (SFOC) method that uses Notch filters and a newly proposed SFOC method that adds a Sequence Component Controller to eliminate negative sequences. Simulations show the enhanced stability of active power, reactive power and generator torque provided by these control schemes under unbalanced voltages.
Performance analysis of various parameters by comparison of conventional pitc...eSAT Journals
Abstract This paper deals with a variable speed wind turbine coupled with a permanent magnet synchronous generator connected through a two mass drive train. This drive train is connected to synchronous generator and after the conversion process finally connected to grid and the idea of transmission over a long distance makes the use of converter necessary and at the receiving end. The inverter is used to convert it back and the inverter is designed with a proper gate signal to get the best output three phase voltages. The fuzzy logic controller is used to track generator speed with varying wind speed to optimize turbine aerodynamic efficiency in the outer speed loop. Pitch angle control of wind turbine has been used widely to reduce torque and output power variation in high rated wind speed areas .The machine side converter is designed to extract maximum power from the wind. In this work a WECS connected with grid is designed in Matlab and a Fuzzy controller is designed to improve the output and we can see the major difference in DC link voltage and reactive power in transmission line. From the outputs we can also go through the reactive power issue which system is best for inductive load or capacitive load. The simple PI system is good for capacitive load and the fuzzy system is better option for the inductive load. The results of both the system of normal controller and fuzzy controller is compared and analyzed. Key Words: Fuzzy logic controller (FLC), permanent magnet synchronous generator (PMSG), insulated gate bipolar transistor (IGBT) , Pulse width modulation (PWM), Wind energy conversion system, DC link capacitor. FACTS Flexible A.C Transmission system, PI proportional integral
Performance analysis of various parameters by comparison of conventional pitc...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Load Frequency Control of DFIG-isolated and Grid Connected ModeIJAPEJOURNAL
Wind energy is one of the extraordinary promising sources of renewable energy due to its clean character, free availability and economic viability. A Doubly Fed Induction Generator (DFIG) feeds power from both the stator and the rotor windings at speeds above synchronous speed of the machine. This paper deals the load frequency control of doubly fed induction generator in isolated mode and grid connected mode. The wind turbine model is obtained using MATLAB/ SIMULINK which consists of DFIG, rotor side rectifier, grid side inverter and grid. This model is controlled by conventional controllerand proposed Load Frequency Control (LFC) method. The results are proven that frequency control gives better results in all the aspects
Impact of hybrid FACTS devices on the stability of the Kenyan power system IJECEIAES
Flexible alternating current transmission system (FACTS) devices are deployed for improving power system’s stability either singly or as a combination. This research investigates hybrid FACTS devices and studies their impact on voltage, small-signal and transient stability simultaneously under various system disturbances. The simulations were done using five FACTS devices-static var compensator (SVC), static synchronous compensator (STATCOM), static synchronous series compensators (SSSC), thyristor controlled series compensator (TCSC) and unified power flow controller (UPFC) in MATLAB’s power system analysis toolbox (PSAT). These five devices were grouped into ten pairs and tested on Kenya’s transmission network under specific contingencies: the loss of a major generating machine and/or transmission line. The UPFC-STATCOM pair performed the best in all the three aspects under study. The settling times were 3 seconds and 3.05 seconds respectively for voltage and rotor angle improvement on the loss of a major generator at normal operation. The same pair gave settling times of 2.11 seconds and 3.12 seconds for voltage and rotor angle stability improvement respectively on the loss of a major transmission line at 140% system loading. From the study, two novel techniques were developed: A performance-based ranking system and classification for FACTS devices.
Space Vector Modulation Based Direct Matrix Converter for Stand-Alone systemIJPEDS-IAES
In this paper Permanent Magnet Synchronous Generator (PMSG) is used for wind power generation in standalone system due to their feature of high efficiency and low maintenance cost, which was fed with smart direct matrix converter for direct AC-AC conversion, It provides sinusoidal output waveforms with minimal higher order harmonics and no sub harmonics and also it eliminate the usage of dc-link and other passive elements. Space vector modulation (SVM) controlled technique is used for matrix converter switching which can eliminate the switching loses by selected switching states. Proposed work is often seen as a future concept for variable speed drives technology. The proposed model for RL load was analysed and verified by varying the resistor and inductance value and analysed using MATLAB simulation.
Wind-Turbine Asynchronous Generator Synchronous Condenser with Excitation in ...IJMTST Journal
In this paper Standalone operation of a wind turbine generating system under fluctuating wind and variable load conditions is a difficult task. Moreover, high reactive power demand makes it more challenging due to the limitation of reactive capability of the wind generating system.The frequency is controlled by the Discrete Frequency Regulator block. This controller uses a standard three-phase Phase Locked Loop (PLL) system to measure the system frequency. The measured frequency is compared to the reference frequency to obtain the frequency error. This error is integrated to obtain the phase error. The phase error is then used by a Proportional-Differential (PD) controller to produce an output signal representing the required secondary load power. This signal is converted to an 8-bit digital signal controlling switching of the eight three-phase secondary loads. In order to minimize voltage disturbances, switching is performed at zero crossing of voltage.
Performance analysis of various parameters by comparison of conventional pitc...eSAT Journals
Abstract This paper deals with a variable speed wind turbine coupled with a permanent magnet synchronous generator connected through a two mass drive train. This drive train is connected to synchronous generator and after the conversion process finally connected to grid and the idea of transmission over a long distance makes the use of converter necessary and at the receiving end. The inverter is used to convert it back and the inverter is designed with a proper gate signal to get the best output three phase voltages. The fuzzy logic controller is used to track generator speed with varying wind speed to optimize turbine aerodynamic efficiency in the outer speed loop. Pitch angle control of wind turbine has been used widely to reduce torque and output power variation in high rated wind speed areas .The machine side converter is designed to extract maximum power from the wind. In this work a WECS connected with grid is designed in Matlab and a Fuzzy controller is designed to improve the output and we can see the major difference in DC link voltage and reactive power in transmission line. From the outputs we can also go through the reactive power issue which system is best for inductive load or capacitive load. The simple PI system is good for capacitive load and the fuzzy system is better option for the inductive load. The results of both the system of normal controller and fuzzy controller is compared and analyzed. Key Words: Fuzzy logic controller (FLC), permanent magnet synchronous generator (PMSG), insulated gate bipolar transistor (IGBT) , Pulse width modulation (PWM), Wind energy conversion system, DC link capacitor. FACTS Flexible A.C Transmission system, PI proportional integral
Performance analysis of various parameters by comparison of conventional pitc...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Load Frequency Control of DFIG-isolated and Grid Connected ModeIJAPEJOURNAL
Wind energy is one of the extraordinary promising sources of renewable energy due to its clean character, free availability and economic viability. A Doubly Fed Induction Generator (DFIG) feeds power from both the stator and the rotor windings at speeds above synchronous speed of the machine. This paper deals the load frequency control of doubly fed induction generator in isolated mode and grid connected mode. The wind turbine model is obtained using MATLAB/ SIMULINK which consists of DFIG, rotor side rectifier, grid side inverter and grid. This model is controlled by conventional controllerand proposed Load Frequency Control (LFC) method. The results are proven that frequency control gives better results in all the aspects
Impact of hybrid FACTS devices on the stability of the Kenyan power system IJECEIAES
Flexible alternating current transmission system (FACTS) devices are deployed for improving power system’s stability either singly or as a combination. This research investigates hybrid FACTS devices and studies their impact on voltage, small-signal and transient stability simultaneously under various system disturbances. The simulations were done using five FACTS devices-static var compensator (SVC), static synchronous compensator (STATCOM), static synchronous series compensators (SSSC), thyristor controlled series compensator (TCSC) and unified power flow controller (UPFC) in MATLAB’s power system analysis toolbox (PSAT). These five devices were grouped into ten pairs and tested on Kenya’s transmission network under specific contingencies: the loss of a major generating machine and/or transmission line. The UPFC-STATCOM pair performed the best in all the three aspects under study. The settling times were 3 seconds and 3.05 seconds respectively for voltage and rotor angle improvement on the loss of a major generator at normal operation. The same pair gave settling times of 2.11 seconds and 3.12 seconds for voltage and rotor angle stability improvement respectively on the loss of a major transmission line at 140% system loading. From the study, two novel techniques were developed: A performance-based ranking system and classification for FACTS devices.
Space Vector Modulation Based Direct Matrix Converter for Stand-Alone systemIJPEDS-IAES
In this paper Permanent Magnet Synchronous Generator (PMSG) is used for wind power generation in standalone system due to their feature of high efficiency and low maintenance cost, which was fed with smart direct matrix converter for direct AC-AC conversion, It provides sinusoidal output waveforms with minimal higher order harmonics and no sub harmonics and also it eliminate the usage of dc-link and other passive elements. Space vector modulation (SVM) controlled technique is used for matrix converter switching which can eliminate the switching loses by selected switching states. Proposed work is often seen as a future concept for variable speed drives technology. The proposed model for RL load was analysed and verified by varying the resistor and inductance value and analysed using MATLAB simulation.
Wind-Turbine Asynchronous Generator Synchronous Condenser with Excitation in ...IJMTST Journal
In this paper Standalone operation of a wind turbine generating system under fluctuating wind and variable load conditions is a difficult task. Moreover, high reactive power demand makes it more challenging due to the limitation of reactive capability of the wind generating system.The frequency is controlled by the Discrete Frequency Regulator block. This controller uses a standard three-phase Phase Locked Loop (PLL) system to measure the system frequency. The measured frequency is compared to the reference frequency to obtain the frequency error. This error is integrated to obtain the phase error. The phase error is then used by a Proportional-Differential (PD) controller to produce an output signal representing the required secondary load power. This signal is converted to an 8-bit digital signal controlling switching of the eight three-phase secondary loads. In order to minimize voltage disturbances, switching is performed at zero crossing of voltage.
Aircraft Electrical Power Generation & Distribution System Units Through an A...IJMTST Journal
This paper illustrates a generic Electrical Power Generation & Distribution System. The AC power frequency is variable and depends of the engine speed. The represents the generator mechanical drive and is modeled by a simple signal builder, which provides the mechanical speed of the engine shaft.The represents the power AC generator. It is composed of a modified version of the simplified synchronous machine. The mechanical input of the modified machine of 50 kW is the engine speed. The Generator Control Unit regulates the voltage of the generator to 200 volts line to line.The represents the Primary Distribution system. It is composed of three current and voltage sensors. There is also a 3-phase contactor controlled by the Generator Control Unit. Finally, a parasitic resistive load is required to avoid numerical oscillations. The section represents the secondary Power Distribution system. It is represented by 4 circuit breakers with adjustable current trip. The section represents the AC loads. There is a 4 kW Transformer and Rectifier Unit (which supplies 28 Vdc), a 12 kW induction machine (motor driving a pump), a 1 kW resistive load (lamps) and a 3 hp simplified (using an average value inverter) brushless DC drive (motor driving a ballscrew actuator)
Wind Energy Conversion System Using PMSG with T-Source Three Phase Matrix Con...IJTET Journal
This paper presents an analysis of a PMSG wind power system using T-Sourcethree phase matrix converter. PMSG using T-Source three phase matrix converterhas advantages that it can provide any desired AC output voltage regardless of DC input with regulation in shoot-through time. In this control system T-Source capacitor voltage can be kept stable with variations in the shoot-through time, maximum power from the wind turbine to be delivered. Inaddition, of a new future, the converter employs a safe-commutation strategy toconduct along a continuous current flow, which results in theelimination of voltage spikes on switches without the need for a snubber circuit. With the use of matrix converter the surely need forrectifier circuit and passive components to store energy arereduced. The MATLAB/Simulinkmodel of the overall system is carried out and theoretical wind energy conversion output load voltage calculations are madeand feasibility of the new topology has been verified and that theconverter can produce an output voltage and output current. This proposed method has greater efficiency and lower cost.
Power Quality Improvement Using Custom Power Devices in Squirrel Cage Inducti...IJPEDS-IAES
Wind farm is connected to the grid directly.The wind is not constant voltage fluctuations occur at point of common coupling (PCC) and WF terminal. To overcome this problem a new compensation strategy is used. By using Custom power devices (UPQC).It injects reactive power at PCC. The advantages of UPQC are it consists of both DVR and D-STATCOM. DVR is connected in series to the line and it injects in phase voltage into the line .D- STATCOM is connected shunt to the line .The internal control strategy is based on management of active and reactive power in series and shunt converters of UPQC. The power exchainge is done by using DC-link.
These slides presents at introductory level to Micro-grid Stability and Control Modes. Later classes the mathematical representations and simulation ideas will be presented.
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.
Performance analysis and simulation of solar pv wind hybrid energy system wit...THRIKOON G
Wind power is one of the most important kinds of renewable energies. Wind farm as a device which receives this energy needs some special conditions to work properly. The most common type of wind turbine is the variable-speed directly connected to the grid. Faults in the power system can originate the disconnection of wind farms. Dynamic voltage restorer (DVR) is a custom power device used for eliminating voltage sages and swells which is the result of the faults. This paper presents a simulation model of a 12-pulse DVR using photovoltaic (PV) as a mean of providing an alternative energy source for the DVR. Simulations were carried out using the Matlab Simulink. The simulation results proved the capability of PV-based DVR in eliminating voltage sag and swell distributed system. Improving the operation of wind farm as an energy generator and stabilizing its voltage is the main result of this work.
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.
Design and fabrication of rotor lateral shifting in the axial-flux permanent-...IJECEIAES
The development of axial-flux permanent-magnet (AFPM) machines has become a mature technology. The single-stator double-rotor (SSDR) AFPM structure has advantages on the compactness and the low up to medium power applications so the microscale size and low-cost applications are reachable to be designed. The research main objectives are designing and manufacturing the lateral shifting from the north poles of the first rotor face the north poles of the second rotor (NN) to the north poles of the first rotor face the south poles of the second rotor (NS) categories as well as finding the best performance of the proposed method and implementing in a low cost and micro-scale AFPMG. The novel lateral shifting on the one of the rotors shows performance at 19.2 0 has the highest efficiency at 88.39% during lateral shifting from N–N (0 0 ) to N–S (36 0 ) on rotor 2.
In this work, we are interested in improving the performance of a doubly-fed induction generator (DFIG)-based wind system, by applying a sliding mode control strategy. The objective is the regulation of the active and reactive power, also the voltage and the frequency of the signal injected into the distribution network. The model proposed for the control is based on the sliding mode technique with performance estimators. The proposed model was validated by a simulation on MATLAB/Simulink.
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.
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.
Improving Electrical Power Grid of Jordan and Control the Voltage of Wind Tur...IJAPEJOURNAL
In this paper, we improved the national grid of Jordan country by adding a renewable resources specifically a wind turbines generation unites distributed on different places in Jordan to compensate the losses of the power in Jordan and to dispense with using the generation of fuel and gas by representing the national grid of Jordan in ETAB simulator and we solved the voltage problems of wind turbines using a new mythology using smart grid techniques
These slides present the introduction to FACTS devices. Later we will discuss about its modelling and control aspect applications. This comes under the topic on power electronics application in smart and microgrid systems.
Voltage profile Improvement Using Static Synchronous Compensator STATCOMINFOGAIN PUBLICATION
Static synchronous compensator (STATCOM) is a regulating device used in AC transmission systems as a source or a sink of reactive power. The most widely utilization of the STATCOM is in enhancing the voltage stability of the transmission line. A voltage regulator is a FACTs device used to adjust the voltage disturbance by injecting a controllable voltage into the system. This paper implement Nruro-Fuzzy controller to control the STATCOM to improve the voltage profile of the power network. The controller has been simulated for some kinds of disturbances and the results show improvements in voltage profile of the system. The performance of STATCOM with its controller was very close within 98% of the nominal value of the busbar voltage.
A New Control Method for Grid-Connected PV System Based on Quasi-Z-Source Cas...IAES-IJPEDS
In this paper, a new control method for quasi-Z-source cascaded multilevel inverter based grid-connected photovoltaic (PV) system is proposed. The proposed method is capable of boosting the PV array voltage to a higher level and solves the imbalance problem of DC-link voltage in traditional cascaded H-bridge inverters. The proposed control system adjusts the grid injected current in phase with the grid voltage and achieves independent maximum power point tracking (MPPT) for the separate PV arrays. To achieve these goals, the proportional-integral (PI) controllers are employed for each module. For achieving the best performance, this paper presents an optimum approach to design the controller parameters using particle swarm optimization (PSO). The primary design goal is to obtain good response by minimizing the integral absolute error. Also, the transient response is guaranteed by minimizing the overshoot, settling time and rise time of the system response. The effectiveness of the new proposed control method has been verified through simulation studies based on a seven level quasi-Z- Source cascaded multilevel inverter.
Aircraft Electrical Power Generation & Distribution System Units Through an A...IJMTST Journal
This paper illustrates a generic Electrical Power Generation & Distribution System. The AC power frequency is variable and depends of the engine speed. The represents the generator mechanical drive and is modeled by a simple signal builder, which provides the mechanical speed of the engine shaft.The represents the power AC generator. It is composed of a modified version of the simplified synchronous machine. The mechanical input of the modified machine of 50 kW is the engine speed. The Generator Control Unit regulates the voltage of the generator to 200 volts line to line.The represents the Primary Distribution system. It is composed of three current and voltage sensors. There is also a 3-phase contactor controlled by the Generator Control Unit. Finally, a parasitic resistive load is required to avoid numerical oscillations. The section represents the secondary Power Distribution system. It is represented by 4 circuit breakers with adjustable current trip. The section represents the AC loads. There is a 4 kW Transformer and Rectifier Unit (which supplies 28 Vdc), a 12 kW induction machine (motor driving a pump), a 1 kW resistive load (lamps) and a 3 hp simplified (using an average value inverter) brushless DC drive (motor driving a ballscrew actuator)
Wind Energy Conversion System Using PMSG with T-Source Three Phase Matrix Con...IJTET Journal
This paper presents an analysis of a PMSG wind power system using T-Sourcethree phase matrix converter. PMSG using T-Source three phase matrix converterhas advantages that it can provide any desired AC output voltage regardless of DC input with regulation in shoot-through time. In this control system T-Source capacitor voltage can be kept stable with variations in the shoot-through time, maximum power from the wind turbine to be delivered. Inaddition, of a new future, the converter employs a safe-commutation strategy toconduct along a continuous current flow, which results in theelimination of voltage spikes on switches without the need for a snubber circuit. With the use of matrix converter the surely need forrectifier circuit and passive components to store energy arereduced. The MATLAB/Simulinkmodel of the overall system is carried out and theoretical wind energy conversion output load voltage calculations are madeand feasibility of the new topology has been verified and that theconverter can produce an output voltage and output current. This proposed method has greater efficiency and lower cost.
Power Quality Improvement Using Custom Power Devices in Squirrel Cage Inducti...IJPEDS-IAES
Wind farm is connected to the grid directly.The wind is not constant voltage fluctuations occur at point of common coupling (PCC) and WF terminal. To overcome this problem a new compensation strategy is used. By using Custom power devices (UPQC).It injects reactive power at PCC. The advantages of UPQC are it consists of both DVR and D-STATCOM. DVR is connected in series to the line and it injects in phase voltage into the line .D- STATCOM is connected shunt to the line .The internal control strategy is based on management of active and reactive power in series and shunt converters of UPQC. The power exchainge is done by using DC-link.
These slides presents at introductory level to Micro-grid Stability and Control Modes. Later classes the mathematical representations and simulation ideas will be presented.
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.
Performance analysis and simulation of solar pv wind hybrid energy system wit...THRIKOON G
Wind power is one of the most important kinds of renewable energies. Wind farm as a device which receives this energy needs some special conditions to work properly. The most common type of wind turbine is the variable-speed directly connected to the grid. Faults in the power system can originate the disconnection of wind farms. Dynamic voltage restorer (DVR) is a custom power device used for eliminating voltage sages and swells which is the result of the faults. This paper presents a simulation model of a 12-pulse DVR using photovoltaic (PV) as a mean of providing an alternative energy source for the DVR. Simulations were carried out using the Matlab Simulink. The simulation results proved the capability of PV-based DVR in eliminating voltage sag and swell distributed system. Improving the operation of wind farm as an energy generator and stabilizing its voltage is the main result of this work.
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.
Design and fabrication of rotor lateral shifting in the axial-flux permanent-...IJECEIAES
The development of axial-flux permanent-magnet (AFPM) machines has become a mature technology. The single-stator double-rotor (SSDR) AFPM structure has advantages on the compactness and the low up to medium power applications so the microscale size and low-cost applications are reachable to be designed. The research main objectives are designing and manufacturing the lateral shifting from the north poles of the first rotor face the north poles of the second rotor (NN) to the north poles of the first rotor face the south poles of the second rotor (NS) categories as well as finding the best performance of the proposed method and implementing in a low cost and micro-scale AFPMG. The novel lateral shifting on the one of the rotors shows performance at 19.2 0 has the highest efficiency at 88.39% during lateral shifting from N–N (0 0 ) to N–S (36 0 ) on rotor 2.
In this work, we are interested in improving the performance of a doubly-fed induction generator (DFIG)-based wind system, by applying a sliding mode control strategy. The objective is the regulation of the active and reactive power, also the voltage and the frequency of the signal injected into the distribution network. The model proposed for the control is based on the sliding mode technique with performance estimators. The proposed model was validated by a simulation on MATLAB/Simulink.
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.
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.
Improving Electrical Power Grid of Jordan and Control the Voltage of Wind Tur...IJAPEJOURNAL
In this paper, we improved the national grid of Jordan country by adding a renewable resources specifically a wind turbines generation unites distributed on different places in Jordan to compensate the losses of the power in Jordan and to dispense with using the generation of fuel and gas by representing the national grid of Jordan in ETAB simulator and we solved the voltage problems of wind turbines using a new mythology using smart grid techniques
These slides present the introduction to FACTS devices. Later we will discuss about its modelling and control aspect applications. This comes under the topic on power electronics application in smart and microgrid systems.
Voltage profile Improvement Using Static Synchronous Compensator STATCOMINFOGAIN PUBLICATION
Static synchronous compensator (STATCOM) is a regulating device used in AC transmission systems as a source or a sink of reactive power. The most widely utilization of the STATCOM is in enhancing the voltage stability of the transmission line. A voltage regulator is a FACTs device used to adjust the voltage disturbance by injecting a controllable voltage into the system. This paper implement Nruro-Fuzzy controller to control the STATCOM to improve the voltage profile of the power network. The controller has been simulated for some kinds of disturbances and the results show improvements in voltage profile of the system. The performance of STATCOM with its controller was very close within 98% of the nominal value of the busbar voltage.
A New Control Method for Grid-Connected PV System Based on Quasi-Z-Source Cas...IAES-IJPEDS
In this paper, a new control method for quasi-Z-source cascaded multilevel inverter based grid-connected photovoltaic (PV) system is proposed. The proposed method is capable of boosting the PV array voltage to a higher level and solves the imbalance problem of DC-link voltage in traditional cascaded H-bridge inverters. The proposed control system adjusts the grid injected current in phase with the grid voltage and achieves independent maximum power point tracking (MPPT) for the separate PV arrays. To achieve these goals, the proportional-integral (PI) controllers are employed for each module. For achieving the best performance, this paper presents an optimum approach to design the controller parameters using particle swarm optimization (PSO). The primary design goal is to obtain good response by minimizing the integral absolute error. Also, the transient response is guaranteed by minimizing the overshoot, settling time and rise time of the system response. The effectiveness of the new proposed control method has been verified through simulation studies based on a seven level quasi-Z- Source cascaded multilevel inverter.
STATCOM Based Wind Energy System by using Hybrid Fuzzy Logic ControllerIJMTST Journal
The influence of the hybrid system in the grid system concerning the power quality measurements are the active power, reactive power, voltage deviation, flicker, harmonics, and electrical behavior of switching operation and these are measured according to International Electro-Technical Commission (IEC). The STATCOM provides reactive power support to hybrid system and load. These voltage fluctuations can be eliminated with the help of advanced reactive power compensator device such as SVC and STATCOM. This work focus on design, modeling and analysis of FACTS device in wind farm interconnected with grid during fault. These devices can be controlled by Synchronous Reference Frame theory. The performance is analyzed with the help of PI controller and Fuzzy logic technique. by using Matlab/Simulink Model.
This paper presents the modeling and simulation of wind energy Conversion System using the Permanent Magnet Synchronous Generator (PMSG). The objectives are: to extract the maximum power of the wind speed by controlling the electromagnetic torque of the PMSG, to maintain constant the DC-link voltage despite the wind speed variations and to attain the unity power factor. In order to ensure a regulation with high performance and a good robustness against the internal and the external disturbances, a new control strategy called the Active Disturbance Rejection Control (ADRC) is used. Therefore, the Analysis and simulation of the ADRC and PI controllers are developed with MATLAB/Simulink software. The performance of these controllers is compared in term of references tracking, robustness and grid faults.
4.power quality improvement in dg system using shunt active filterEditorJST
Injection of power generated by the wind turbine system into an electric grid mainly effects the power quality. The performance of this wind turbine and its power quality is determined on the basis of its measurement of power ratings as per IEEE standards. The influence of the wind turbine in the grid system concerning the power quality measurements are the active power, reactive power, variation of voltage, flicker, harmonics, and electrical behavior of switching operation. To mitigate the power quality problems this paper proposes the shunt compensator techniques. Here, the proposed system is verified experimentally using both STATCOM and TSC compensators. This control schemes for grid connected wind energy system is simulated using Matlab/Simulink.
ENHANCED CONTROL OF DFIG IN WIND ENERGY CONVERSION SYSTEMIjorat1
The doubly-fed induction generator (DFIG) wind turbine is a variable speed wind turbine widely used
in the modern wind power industries. At present, commercial DFIG wind turbines primarily make use of the
technology that was developed a decade ago. But, it is found in the paper that there is limitations conventional
control method. This project presents a fuzzy-logic approach to control the DFIG. Based on which fuzzy-logic
approach is controlled for real power, reactive power flow and electromagnetic torque of the wind turbine. A
direct current vector control strategy is developed to control the rotor side voltage source converter. This scheme
of direct current vector control strategy allows the independent control of the generated active and reactive
power as well as the rotor speed. In this project, a fuzzy-logic approach is proposed to control the DFIG. The
active and reactive power is controlled by rotor voltage, which goes through back-to-back voltage source
converter and DC-link voltage is also maintained stable. The conventional control approach is compared with the
proposed control techniques for DFIG wind turbine control under both steady and gusty wind conditions. A
MATLAB based simulation system was build to validate the effectiveness of the proposed method. The proposed
method waveforms of real power, reactive power, DC link voltage and generator speed are compared with
conventional method. This paper shows that under the fuzzy-logic approach control techniques, a DFIG system
have a superior performance in various aspects.
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.
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.
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.
This paper focuses on the modeling and control of a wind energy conversion chain using a permanent magnet synchronous machine. This system behaves a turbine, a generator, DC/DC and DC/AC power converters. These are connected on both sides to the DC bus, where the inverter is followed by a filter which is connected to the grid. In this paper, we have been used two types of controllers. For the stator side converter, we consider the Takagi-Sugeno approach where the parameters of controller have been computed by the theory of linear matrix inequalities. The stability synthesis has been checked using the Lyapunov theory. According to the grid side converter, the proportional integral controller is exploited to keep a constant voltage on the DC bus and control both types of powers. The simulation results demonstrate the robustness of the approach used.
In power systems for smart grid, integration of renewable energy sources and super conducting devices brings more
positive effects. This paper suggests a Fuzzy controlled
Fault ride-through capability improvement of doubly fed induction generator (DFIG) for wind power generation. Since Fuzzy
controlled Active SFCL has higher controllability and flexibility,
derivation, cost evaluation and simulation are conducted and comparison is performed between with and without Active SFCL.
From the results active SFCL can limit the faulty currents flowing through t
compensate the terminal voltage
This paper proposes a feedback linearization control of doubly fed induction generator based wind energy systems for improving decoupled control of the active and reactive powers stator. In order to enhance dynamic performance of the controller studied, the adopted control is reinforced by a fuzzy logic controller. This approach is designed without any model of rotor flux estimation. The difficulty of measuring of rotor flux is overcome by using high gain observer. The stability of the nonlinear observer is proved by the Lyapunov theory. Numerical simulations using MATLAB-SIMULINK shown clearly the robustness of the proposed control, particularly to the disturbance rejection and parametric variations compared with the conventional method.
Indirect Control of a Doubly-Fed Induction Machine for Wind Energy ConversionIAES-IJPEDS
In this paper, a grid connected wind power generation scheme using a doubly fed induction generator (DFIG) is studied. The aims of this paper are: The modelling and simulation of the operating in two quadrants (torque-speed) of a DFIG, the analysis employs a stator flux vector control algorithm to control rotor current, the system enables optimal speed tracking for maximum energy capture from the wind and high performance active and reactive power regulation using the PI regulator. The simulation calculations were achieved ®®
using MATLAB -SIMULINK package. Lastly, the obtained results are presented, for different operating points, illustrating the good control performances of the system
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
Dynamic responses improvement of grid connected wpgs using flc in high wind s...ijscmcj
Environmental and sustainability concerns are developing the significance of distributed generation (DG) based on renewable energy sources. In this paper, dynamic responses investigation of grid connected wind turbine using permanent magnet synchronous generator (PMSG) under variable wind speeds and load circumstances is carried out. In order to control of turbine output power using Fuzzy Logic controller (FLC) in comparison with PI controller is proposed. Furthermore, the pitch angle based on FLC using wind speed and active power as inputs, can have faster responses, thereby leading to smoother power curves, enhancement of dynamic performance of wind turbine and prevention of mechanical damages to PMSG. Inverter adjusted the DC link voltage and active power is fed by d-axis and reactive power is fed by q-axis (using P-Q control mode). Simulation of wind power generation system (WPGS) is carried out in Matlab/Simulink, and the results verify the correctness and feasibility of control strategy.
DYNAMIC RESPONSES IMPROVEMENT OF GRID CONNECTED WPGS USING FLC IN HIGH WIND S...ijscmcjournal
Environmental and sustainability concerns are developing the significance of distributed generation (DG) based on renewable energy sources. In this paper, dynamic responses investigation of grid connected wind turbine using permanent magnet synchronous generator (PMSG) under variable wind speeds and load circumstances is carried out. In order to control of turbine output power using Fuzzy Logic controller (FLC) in comparison with PI controller is proposed. Furthermore, the pitch angle based on FLC using wind speed and active power as inputs, can have faster responses, thereby leading to smoother power curves, enhancement of dynamic performance of wind turbine and prevention of mechanical damages to PMSG. Inverter adjusted the DC link voltage and active power is fed by d-axis and reactive power is fed by q-axis (using P-Q control mode). Simulation of wind power generation system (WPGS) is carried out in Matlab/Simulink, and the results verify the correctness and feasibility of control strategy.
2. This paper will investigate the qualities of active
powers, reactive powers, and generator's torques under
the unbalanced grid voltage dip during transient and
steady states for the traditional and modified SFOC and
DPC methods of DFIG. In detail, one newly modified
control scheme is proposed in this study, and two other
control structures were previously suggested in [16] by
the authors. The modifications are single or combined
applications of PI controller, hybrid PI-Fuzzy controller,
Notch filter and SCC to eliminate the negative sequence
components. In which, the PI controllers with
anti-windup are always used to replace the classical PI
controllers even in the traditional SFOC or DPC. The
grid's voltage dip is modeled with a reduction of 25% of
the rated voltage in one phase. Meanwhile, the wind
speed is allowed to vary randomly during the process.
2. MATHEMATICAL MODELOFWIND
TURBINE
The model of wind turbine and its formulas of power
transferred to generator are presented in this session.
According to [11], the mechanical system of wind
turbine is shown in Fig. 1. Specifications of the wind
turbine are discussed in Section 4 of this paper.
Fig.1 The mechanical model of wind turbine [11].
The power extracted from the wind is
),(
2
1 3
pwturb
CAvP (1)
Where:
ρ (kg/m3
), is the air density. A = R2
(m2
), is the
cross-sectional area through which the wind passes.
R (m) is the length of turbine's blades. vw (m/s) is the
normal wind speed to the cross-session area A.
Cp( is the aerodynamic efficiency which depends
on the tip speed ratio λ, and the blade pitch angle β.
According to Betz's efficiency, the maximum theoretical
efficiency is 59.3% [12].
The tip speed ratio λ expressed in (2) is defined as the
speed at which the outer tip of the blade is moving
divided by the wind speed.
w
turb
v
R
(2)
Where: ωturb (rad/s)is the angular velocity of turbine.
The turbine efficiency Cp given by (3) is the function of
the tip-speed ratio , and the pitch angle β.
i
eC
i
p
5.12
54.0
116
22.0),(
(3)
3. DIRECT POWER CONTROLAND STATOR
FLUX ORIENTED CONTROLOF DFIG
3.1 Previously and newly proposed control schemes
The structure of our formerly modified control method
with DPC for DFIG is represented in Fig. 2. Besides, the
modified control scheme previously and newly proposed
one with SFOC are illustrated by Fig. 3 and Fig. 4,
respectively. In which, appropriate voltage vectors for
the RSC are selected to control the generated active and
reactive powers in DPC. Converters on the rotor side of
DFIG are controlled by SFOC to achieve the
independent control of active and reactive powers. In
Stator Flux Oriented Control, the equations for
controlling the active and reactive power are derived
from the machine model in a rotating reference frame
which is attached to the induction machine's stator flux
space vector. Therefore, the implementation of SFOC
requires continuously reference frame transformation.
According to [13], the control system, using hybrid
PI-Fuzzy controller, has provided better performances of
the generated powers. However, this is only verified with
the balanced grid voltage. To enhance the stability of the
powers during voltage unbalance situation, the inclusion
of Notch filter has been suggested by [14,15] and shown
in Fig. 2. In detail, Notch filters are used to eliminate
second-order harmonic components in positive and
negative sequences of the stator voltage. For the scheme
in Fig. 3, Notch filters are used with the positive
sequence of stator voltage and the negative sequence of
the rotor current [16].
Fig. 2 The typical configuration of the grid-connected
DFIG, using DPC with Notch Filter in [16].
On the other hand, as seen in Fig. 4, the control
SICE Annual Conference 2013
September 14-17, 2013, Nagoya, Japan
2582
3. scheme proposed in this study, applies SCC to eliminate
the negative sequences of the stator voltage which cause
distortions in power responses. Additionally, Notch filter
is also used to eliminate the second-order harmonic
component in the stator voltage. This suggested control
scheme reduces the number of current sensors and Notch
filter. The decreased amount of computational tasks is
achieved with PI controllers with anti-windup.
Fig. 5 shows the spatial relationships between the
stationary (α,β)s reference frame, the rotor (α,β)r
reference frame rotating at the speed of ωr, and the dq+
and dq−
reference frames rotating at the angular speed
of ωs and −ωs, respectively. In addition, as seen in this
figure, the d+
axis of the dq+
reference frame is fixed to
the positive sequence stator voltage ds
V
.
Fig. 3 The previous control scheme for RSC of DFIG
using PI-Fuzzy controllers and Notch filters in [16].
Fig. 4 The proposed control scheme for RSC of DFIG
using PI controllers, Notch filters and SCC in this study.
Referring in Fig. 5, the transformations between
(α,β)s, (α,β)r, dq+ and dq− reference frames are
expressed in (4).
( , ) ( , )
;S Sj t j t
dq s dq s
F F e F F e
(4)
According to (4) and [4,14,17], variables shown in
Figs. 3-4, , , , ,dq dq sdq dr qr
I I V I I
, are given by (5) to (9).
Fig. 5 Relationships between (α,β)s , (α,β)r , dq+ and
dq− reference frames [14].
2 2
;S Sj t j t
dq dq dq dq
I I e I I e
(5)
2 2
( , ) ( , )
;Sl Slj t j t
dq r dq r
I I e I I e
(6)
sdq
sdq s sdq s sdq
d
V R I j
dt
(7)
2 Sj t
dr dr dr dr dr
I I I I I e
(8)
2 Sj t
qr qr qr qr qr
I I I I I e
(9)
The active and reactive powers of stator, s
P
and s
Q
,
are expressed in (10) and (11), respectively.
1.5s ds ds qs qs
P V i V i
(10)
1.5s ds qs qs ds
Q V i V i
(11)
3.2 PI-Fuzzy controller for the scheme in Fig. 3
As presented in Fig. 6, PI-Fuzzy controllers are used
to control the errors between the set and actual values of
both the active and reactive powers delivered to the grid
by the generator. In which, the parameters of the PI
controller (Ti and KP) are tuned suitably by the fuzzy
logic controller (FLC) to obtain the finest output for
driving the errors to zero. The variable parameters of the
controllers, which are fixed in traditional PI controllers,
will help achieve the best performance of the system.
The outputs of these controllers are the commanded
values of d-q components of the rotor current in the dq+
reference frame. As illustrated by Fig. 3, these
commanded values of currents are used to regulate the
RSC for supplying the rotor phase voltage to DFIG.
3.3 Modifications in the newly proposed scheme
The proposed control scheme uses the PI controllers
with anti windup instead of a hybrid PI and Fuzzy
controllers as shown in the control scheme for SFOC in
[16]. The combination of Fuzzy logic in the PI controller
requires more computational time, especially in real-time
control for the scheme's practical application.
SICE Annual Conference 2013
September 14-17, 2013, Nagoya, Japan
2583
4. Fig. 6 PI-Fuzzy controller.
The newly proposed scheme also include a SCC
which help to eliminate the negative sequence
components of the fundamental frequency and all the
harmonics components of stator voltage. The Notch
filters are assigned to remove the negative sequence
components which cause oscillation in active power,
reactive power, and electromagnetic torque according to
equations (8) and (9) [4]. The oscillation in these
equations happens at twice the frequency of the positive
sequence component. However, the performance of
digitally designed Notch filters is not perfect. Therefore,
the inclusion of SCC helps to clear all the negative
sequence components.
SCC also functions as a current controller using PI
controllers to regulate the positive sequence components
of rotor current. Negative sequence components of rotor
current will increase the power rating of Rotor Side
Converter if being used to control generator's active and
reactive power [5].
4. SIMULATION RESULTS
Simulations of the modified control methods for the
2.3MW DFIG are carried out with the generator and
wind turbine's parameters as given by Table 1.
Operations in both sub-synchronous speed region
(70%-100% synchronous speed) and super-synchronous
speed region (up to 130% synchronous speed) are
simulated with the randomly variable wind speed shown
in Fig. 7. As illustrated by Fig. 8, the grid voltage
unbalance happens after the time t = 30 s. Meanwhile,
the commanded values of the active and reactive powers
change at the time t = 50 s. Any operation outside these
two speed regions will increase significantly the power
rating of converters connected between rotor and the
grid.
Comparisons of average values of active and reactive
powers (PS and QS) in the steady state with five different
controllers are presented in Table 2 and Table 3,
respectively. In detail, both actual values and the
percentage of references are also shown for evaluation.
In addition, the average electromagnetic torque of the
generator is described in Table 4.
Table 1. Parameters of the 2.3MW DFIG and wind
turbine in use.
Generator
Parameter Symbol Value
Stator inductance LS 159.2 (μH)
Rotor inductance Lr 159.2 (μH)
Magnetic inductance Lm 5.096 (mH)
Stator resistance RS 4 (mΩ)
Rotor resistance Rr 4 (mΩ)
Number of pole pairs P 2
Frequency of the
electric system
ωs 100π (rad/s)
Inertia of generator Igen 93.22 (kg.m2
)
Wind turbine
Power PS 2.3 (MW)
Radius R 40 (m)
Friction coefficient Kms 8.949×107
(Nm/rad)
Gear box 1: f 80
Inertia of turbine rotor IWTR
4.176×106
(kg.m2
)
Density of air ρ 1.225
(kg/m3
)
Damping coefficient Ignored
Fig. 7 Random variation of the wind speed.
29.95 29.96 29.97 29.98 29.99 30 30.01 30.02 30.03 30.04 30.05
-800
-600
-400
-200
0
200
400
600
800
Time [s]
Vabcs[V]
Fig. 8 Voltage unbalance after the time t = 30 s.
The mean, maximum, and minimum values of the
active power, reactive power and machine's torque
during the unbalanced voltage from the 39th
second to
the 49th
second, are represented in Tables 2 to 3. In
detail, the statistics of operations at the sub-synchronous
speed nr = 1400 rpm and the super-synchronous speed
nr = 1600 rpm, are also illustrated by these tables.
SICE Annual Conference 2013
September 14-17, 2013, Nagoya, Japan
2584
5. Table 2. Average values of active power (PS) in the
steady state for five controllers.
%
S Sref
Sref
P P
Deviation
P
During the unbalanced voltage, best performances of
active power are observed for DPC with Notch Filter,
then the traditional DPC without Filter.
In detail, the lowest value of PMax for DPC with
Notch filters is 5.0% of the commanded value when
nr =1400 rpm, and is 4.3% when nr = 1600 rpm.
The highest value of PMin for DPC with Notch Filter
is -4.2% of the commanded value when nr =1400 rpm,
and is -5.5% when nr = 1600.
Table 3. Average values of reactive power (QS) in the
steady state for five controllers.
%
S Sref
Sref
Q Q
Deviation
Q
During the unbalanced voltage, best performances of
reactive power are observed for the DPC with Notch
Filter, then the traditional DPC without Filter.
In detail, the lowest value of QMax for DPC with
Filter is 9.87% of the commanded value when nr =1400
rpm, and is 7.2% when nr = 1600 rpm.
The highest value of QMin for the DPC with Filter is
-11.8% of the set value when nr =1400 rpm, and is
-8.3% when nr = 1600 rpm.
Table 4. Average values of generator's torque in the
steady state for the five controllers.
According to Table 4, during the unbalanced voltage,
the best performances of machine's torque are observed
for the SFOC with PI and SCC, then the SFOC with PI.
In detail, the lowest value of TMax for SFOC with PI
and SCC is 15514 N.m when nr =1400 rpm, and is
14295 N.m when nr = 1600 rpm.
The highest value of TMin for SFOC with PI and SCC
is 9783 N.m when nr =1400 rpm, and is 7645 N.m when
nr = 1600 rpm.
The results of five control schemes are shown in Figs.
9 to 14 for the active and reactive powers.
20 30 40
1
1.5
2
2.5
3
3.5
TIME [S]
Ps[MW](nr=1400)
SFOC WITH PI
20 30 40
1
1.5
2
2.5
3
3.5
SFOC WITH PI & SCC
TIME [S]
20 30 40
1
1.5
2
2.5
3
3.5
SFOC WITH PI-F & FILTER
TIME [S]
20 30 40
0.5
1
1.5
2
2.5
3
SFOC WITH PI
TIME [S]
Ps[MW](nr=1600)
20 30 40
0.5
1
1.5
2
2.5
3
SFOC WITH PI & SCC
TIME [S]
20 30 40
1
1.5
2
2.5
3
3.5
SFOC WITH PI-F & FILTER
TIME [S]
20 30 40
1.9
1.95
2
2.05
2.1
2.15
Time [s]
Ps[MW](nr=1400)
DPC normally
20 30 40
1.9
1.95
2
2.05
2.1
2.15
DPC WITH FILTER
Time [s]
20 30 40
1.9
1.95
2
2.05
2.1
2.15
DPC normally
Time [s]
Ps[MW](nr=1600)
20 30 40
1.9
1.95
2
2.05
2.1
2.15
DPC WITH FILTER
Time [s]
Fig. 9 Active power of DFIG when the voltage
unbalance happens from the time t = 30 s.
20 40 60 80
0
0.5
1
1.5
2
2.5
3
3.5
TIME [S]
Ps[MW](nr=1400)
SFOC WITH PI
20 40 60 80
0
0.5
1
1.5
2
2.5
3
3.5
SFOC WITH PI & SCC
TIME [S]
20 40 60 80
0
0.5
1
1.5
2
2.5
3
3.5
SFOC WITH PI-F & FILTER
TIME [S]
20 40 60 80
-0.5
0
0.5
1
1.5
2
2.5
3
SFOC WITH PI
TIME [S]
Ps[MW](nr=1600)
20 40 60 80
-0.5
0
0.5
1
1.5
2
2.5
3
SFOC WITH PI & SCC
TIME [S]
20 40 60 80
-0.5
0
0.5
1
1.5
2
2.5
3
SFOC WITH PI-F & FILTER
TIME [S]
20 40 60 80
0.8
1
1.2
1.4
1.6
1.8
2
2.2
Time [s]
Ps[MW](nr=1400)
DPC normally
20 40 60 80
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC WITH FILTER
Time [s]
20 40 60 80
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC normally
Time [s]
Ps[MW](nr=1600)
20 40 60 80
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC WITH FILTER
Time [s]
Fig. 10 Active power of DFIG during transient state.
SICE Annual Conference 2013
September 14-17, 2013, Nagoya, Japan
2585
6. 49.5 50 50.5
0
0.5
1
1.5
2
2.5
3
TIME [S]
Ps[MW](nr=1400)
SFOC WITH PI
49.5 50 50.5
0
0.5
1
1.5
2
2.5
3
SFOC WITH PI & SCC
TIME [S]
49.5 50 50.5
0
0.5
1
1.5
2
2.5
3
SFOC WITH PI-F & FILTER
TIME [S]
49.5 50 50.5
0
0.5
1
1.5
2
2.5
SFOC WITH PI
TIME [S]
Ps[MW](nr=1600)
49.5 50 50.5
0
0.5
1
1.5
2
2.5
SFOC WITH PI & SCC
TIME [S]
49.5 50 50.5
0
0.5
1
1.5
2
2.5
SFOC WITH PI-F & NOTCH
TIME [S]
49.5 50 50.5
0.8
1
1.2
1.4
1.6
1.8
2
2.2
Time [s]
Ps[MW](nr=1400)
DPC normally
49.5 50 50.5
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC WITH FILTER
Time [s]
49.5 50 50.5
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC normally
Time [s]
Ps[MW](nr=1600)
49.5 50 50.5
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC WITH FILTER
Time [s]
Fig. 11 Dynamic responses of DFIG's active power
during transient state under the voltage unbalance.
20 30 40
0.5
1
1.5
2
2.5
TIME [S]
Qs[MVAR](nr=1400)
SFOC WITH PI
20 30 40
0.5
1
1.5
2
2.5
SFOC WITH PI & SCC
TIME [S]
20 30 40
0.5
1
1.5
2
2.5
SFOC WITH PI-F & FILTER
TIME [S]
20 30 40
0
0.5
1
1.5
2
SFOC WITH PI
TIME [S]
Qs[MVAR](nr=1600)
20 30 40
0
0.5
1
1.5
2
SFOC WITH PI & SCC
TIME [S]
20 30 40
0
0.5
1
1.5
2
SFOC WITH PI-F & FILTER
TIME [S]
20 30 40
0.85
0.9
0.95
1
1.05
1.1
1.15
Time [s]
Qs[MVAR](nr=1400)
DPC normally
20 30 40
0.85
0.9
0.95
1
1.05
1.1
1.15
DPC with FILTER
Time [s]
20 30 40
0.85
0.9
0.95
1
1.05
1.1
1.15
DPC normally
Time [s]
Qs[MVAR](nr=1600)
20 30 40
0.85
0.9
0.95
1
1.05
1.1
1.15
DPC with FILTER
Time [s]
Fig. 12 Reactive power of DFIG when the voltage
unbalance happens from the time t = 30 s.
20 40 60 80
0.5
1
1.5
2
2.5
TIME [S]
Qs[MVAR](nr=1400)
SFOC WITH PI
20 40 60 80
0.5
1
1.5
2
2.5
SFOC WITH PI & SCC
TIME [S]
20 40 60 80
0.5
1
1.5
2
2.5
SFOC WITH PI-F & FILTER
TIME [S]
20 40 60 80
0
0.5
1
1.5
2
2.5
SFOC WITH PI
TIME [S]
Qs[MVAR](nr=1600)
20 40 60 80
0
0.5
1
1.5
2
2.5
SFOC WITH PI & SCC
TIME [S]
20 40 60 80
0
0.5
1
1.5
2
2.5
SFOC WITH PI-F & FILTER
TIME [S]
20 40 60 80
0.8
1
1.2
1.4
1.6
1.8
2
2.2
Time [s]
Qs[MVAR](nr=1400)
DPC normally
20 40 60 80
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC with FILTER
Time [s]
20 40 60 80
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC normally
Time [s]
Qs[MVAR](nr=1600)
20 40 60 80
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC with FILTER
Time [s]
Fig. 13 Reactive power of DFIG during transient
states when the commanded values change.
49.5 50 50.5
0.5
1
1.5
2
2.5
TIME [S]
Qs[MVAR](nr=1400)
SFOC WITH PI
49.5 50 50.5
0.5
1
1.5
2
2.5
SFOC WITH PI & SCC
TIME [S]
49.5 50 50.5
0.5
1
1.5
2
2.5
SFOC WITH PI-F & FILTER
TIME [S]
49.5 50 50.5
0
0.5
1
1.5
2
2.5
SFOC WITH PI
TIME [S]
Qs[MVAR](nr=1600)
49.5 50 50.5
0
0.5
1
1.5
2
2.5
SFOC WITH PI & SCC
TIME [S]
49.5 50 50.5
0
0.5
1
1.5
2
2.5
SFOC WITH PI-F & FILTER
TIME [S]
49.5 50 50.5
0.8
1
1.2
1.4
1.6
1.8
2
2.2
Time [s]
Qs[MVAR](nr=1400)
DPC normally
49.5 50 50.5
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC with FILTER
Time [s]
49 49.5 50 50.5
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC normally
Time [s]
Qs[MVAR](nr=1600)
49.5 50 50.5
0.8
1
1.2
1.4
1.6
1.8
2
2.2
DPC with FILTER
Time [s]
Fig. 14 Dynamic responses of DFIG's reactive power
during transient state under the voltage unbalance.
SICE Annual Conference 2013
September 14-17, 2013, Nagoya, Japan
2586
7. The above figures demonstrate the power responses
when the voltage unbalance happens (from the time t =
30 s) and when the commanded values of powers
change (at the time t = 50 s) under the voltage unbalance.
Besides, Fig. 15 illustrates the torque response of the
generator.
The active power response of DFIG with SFOC is
improved when the either modification is included.
However, the improvements of SFOC's performance are
not as good as DPC's performance. Oscillation of active
power is strongly reduced with DPC for both speed
regions. Similarly, reactive power responses of DFIG
with SFOC are not as good as the responses of DPC as
shown in Figs 12 to 14.
20 40 60 80
2
4
6
8
10
12
14
16
18
TIME [S]
Te[kN.m](nr=1400)
SFOC WITH PI
20 40 60 80
2
4
6
8
10
12
14
16
18
SFOC WITH PI & SCC
TIME [S]
20 40 60 80
2
4
6
8
10
12
14
16
18
SFOC WITH PI+F & FILTER
TIME [S]
20 40 60 80
-0.2
1
4
7
10
13
16
SFOC WITH PI
TIME [S]
Te[KN.m](nr=1600)
20 40 60 80
-0.2
1
4
7
10
13
16
SFOC WITH PI & SCC
TIME [S]
20 40 60 80
-0.2
1
4
7
10
13
16
SFOC WITH PI-F & FILTER
TIME [S]
20 40 60 80
0
2
4
6
8
10
12
14
16
18
Time [s]
Te[kN.m](nr=1400)
DPC normally
20 40 60 80
0
2
4
6
8
10
12
14
16
18
DPC with FILTER
Time [s]
20 40 60 80
0
2
4
6
8
10
12
14
16
18
DPC normally
Time [s]
Te[kN.m](nr=1400)
20 40 60 80
0
2
4
6
8
10
12
14
16
18
DPC with FILTER
Time [s]
Fig. 15 The torque response of DFIG.
On the contrary with active and reactive powers, the
generator's torque responses in SFOC are much better
than the ones in DPC as shown in Fig. 15, especially
when SCC and PI with anti windup are used. Significant
reduction of torque's oscillation is observed for the
newly proposed control scheme when voltage unbalance
happens. All the performances of torque with SFOC are
better in the sub-synchronous speed region. The control
method proposed in this paper gives slightly better
result during the transient state under voltage unbalance
in super-synchronous speed region.
Significant oscillations are observed in the responses
of torque in DPC's performance during transient state
under voltage unbalance. Variation of torque is also
higher when voltage unbalance happens. The
observations are consistent for both speed regions.
5. DICUSSION
As shown in Table 2, two DPC-based methods have
shown good steady-state active power responses during
the voltage unbalance. In detail, the deviation of the
mean value of active power from the reference value is
almost zero percent with the inclusion of Notch filter;
and the deviation of the maximum and minimum values
from the mean value are within 5% at both the speed
regions above or below the synchronous speed.
Similarly, SFOC with PI-Fuzzy controller and Notch
filter is also giving the good performance with small
deviation of mean values from reference values (about
2.7% at the sub-synchronous speed and 7.6% at the
super-synchronous speed), and a minor fluctuation from
mean values of the maximum and minimum values in
both the speed regions. The oscillation of the active
power is observed to be smallest for DPC with Notch
filter during the voltage unbalance.
The traditional SFOC's active power response when
the voltage unbalance happens has higher ripples in
both speed regions, while the responses obtained with
the two DPC schemes and SFOC with PI-Fuzzy
controller and Notch filter are not significantly distorted
as shown in Figs 9 and 10. The fluctuation of active
power with the newly proposed method is less than the
one with traditional SFOC but higher than the one with
SFOC including PI-Fuzzy and Notch filter from the
table and figures.
Figure 11 shows that the dynamic response of active
power for SFOC with PI-Fuzzy controller and Notch
filter during the transient state under voltage unbalance
is slower than the one for the proposed control scheme.
As seen in Table 3, steady-state responses of the
reactive power are also very good when Notch filters
are included in DPC. In detail, the deviations are 0.05%
and 0.1% respectively for operations at below and
above the synchronous speed. Besides, the deviations of
reactive power's mean values for SFOC with PI-Fuzzy
controller and Notch filter are also reasonably small
during the voltage unbalance (0.05% and 1.2% for the
sub-synchronous and super-synchronous speed regions,
respectively). As illustrated by Fig. 12, the fluctuation is
observed to be smallest for DPC with Notch filter.
Additionally, higher ripples are observed in reactive
power responses of the traditional SFOC when the
voltage unbalance occurs as described in Fig. 12. The
observation is also consistent with statistics in Table 3.
As shown in the table and figures, the oscillation of
reactive power in the proposed method is improved
when compared with the one in traditional method.
Fig. 13 and Fig. 14 shows the dynamic responses of
reactive powers during transient states. In detail, the
slower dynamic response is also observed with SFOC
with PI-Fuzzy and Notch filter when compared with the
response in SFOC incorporating SCC and PI with
anti-windup.
Besides, as illustrated by Table 4, the proposed SFOC
with PI and SCC (shown in Fig. 4) gives the smallest
torque variation during voltage unbalance for both the
SICE Annual Conference 2013
September 14-17, 2013, Nagoya, Japan
2587
8. super- and sub-synchronous speed regions. And this
characteristic is highlighted with the red color in Fig. 15.
Furthermore, as represented in Fig. 11 and Fig. 14, the
dynamic responses of active and reactive powers of the
proposed control method are as fast as the responses of
DPC methods. Torque responses observed in Fig. 15 are
also consistent with statistics described in Table 4.
6. CONCLUSION
The proposed SFOC-based scheme for DFIG with the
inclusion of SCC has elevated the stability of the torque
response during the grid voltage unbalance when being
compared with other modifications of SFOC and DPC
for better stabilities during the unbalanced voltage dip.
This improvement helps reduce the electrical stress on
converters and the mechanical stress on the gear box.
Furthermore, the responses of active and reactive power
are ameliorated when being compared with a traditional
SFOC, although the oscillations are still quite high.
In this study, the observations are made during the
occurrence of the voltage dip in one phase, transient
states as well as steady states of the powers and torque
under the unbalanced condition. When being compared
with responses from DPC, the proposed scheme also
gives fast responses of active and reactive powers
during transient states under the voltage unbalance.
In all the observations, the independent controls of the
powers are still maintained for the suggested scheme.
Responses of the active power, reactive power, and
torque from all the control schemes are observed at the
sub-synchronous speed operation when the active power
is consumed on the rotor and delivered on the stator of
DFIG, and at the super-synchronous speed operation
when the active power is delivered on both the stator
and rotor of DFIG.
In the future, the experimental verification of the
proposed control scheme should be carried out to
validate the results obtained in simulations. Control
methods to reduce the oscillations in stator current and
to regulate the switching states of Grid Side Converter
should also be researched.
REFERENCES
[1] Ackermann, T. ; Wind power in power systems; John
Wiley and Sons, USA, 2003.
[2] Leonhard, W.; Control of electric drives;
Springer-Verlag, 3rd
edition, USA, 2001.
[3] Muljadi, E., Yildirim, D., Batan, T., and Butterfield,
C.P.; “Understand the unbalanced-voltage problem
in wind turbine generation”; Proceeding of IEEE
Industry Application Conference, Phoenix, USA,
pp.1359-1365, 1999.
[4] Baggu, M. M.; “Advanced control techniques for
doubly fed induction generator – based wind turbine
converters to improve low voltage ride- throught
during system imbalances”; PhD Thesis, Missouri
University of Science and Technology, 2009
[5] L. Xu, Y. Wang; “Dynamic modeling and control of
DFIG based wind turbines under unbalanced
network conditions”; IEEE Trans. Power Syst., Vol.
22, No. 1 , pp. 314–323, 2007.
[6] Santos-Martin, D., Rodriguez-Amenedo, J. L., and
Arnaltes, S.; “Providing a Ride-Through Capability
to a Doubly Fed Induction Generator Under
Unbalanced Voltage Dip”; IEEE Trans. of Power
Electronics, Vol. 24, No. 7, pp. 1747-1757, 2009.
[7] Zhang, S., Tseng, K. J., Choi, S. S., Nguyen, T. D.,
and Yao, D. L.; “Advanced Control of Series
Voltage Compensation to Enhance Wind Turbine
Ride Through”; IEEE Transactions of Power
Electronics, Vol. 27, No. 2, pp. 763-772, 2012.
[8] Seman, S., Niiranen, J., and Arkkio, A.;
“Ride-Through Analysis of Doubly Fed Induction
Wind-Power Generator Under Unsymmetrical
Network Disturbance”; IEEE Transactions of
Power Systems, Vol. 21, No.4, pp.1782-1789, 2006.
[9] Yikang, H., Jiabing, H., Rende, Z.; “Modeling and
Control of Wind-Turbine Used DFIG under
Network Fault Conditions”; Proceeding of ICEMS
2005, pp. 986-991, 2005.
[10] Zhao, J., Zhang, W., He, Y., and Hu, J.; “Modeling
and Control of a Wind-Turbine Driven DFIG
Incorporating Core Saturation During Grid Voltage
Dips”; Proceeding of ICEMS, pp. 2438-2442, 2008.
[11] Sorensen, P., Hansen, D.A.,Christensen, P., Mieritz,
M.; Bech, J., Bak-Jensen, B., Nielsen, H.;
“Simulation and Verification of Transient Events in
Large Wind Power Installation”; Project Report,
Risø National Laboratory, Roskilde, Norway, 2003.
[12]Masters, M. G.; Renewable and Efficient Electric
Power Systems; John Wiley and Sons, Inc.,
Publication, 2004.
[13]Pham-Dinh, T., Pham-Trung, H., Le-Thanh, H.,
“PI-Fuzzy Controller for Doubly Fed Induction
Generator Wind Turbine”; Proceedings of ASAC-
2011; pp. 79 – 81, 2011.
[14]Phan, V. T., Lee, H. H., Chun, T. W; “An Effective
rotor current controller for unbalanced stand – alone
DFIG systems in the rotor reference frame”; Journal
of Power Electronics, Vol.10, No.6, pp. 194-202,
2010.
[15]Jia-bing HU, Yi-kang HE, Lie X; “Dynamic
modeling and direct power control of wind turbine
driven DFIG under unbalanced network voltage
conditions”; Journal of Zhejiang University
SCIENCE, 2008.
[16]Pham-Dinh, T., Nguyen-Thanh H., Nguyen-Anh
N.; “Improving Stability For Independent Power
Control Of Wind-Turbine Doubly Fed Induction
Generator with SFOC and DPC During Grid
Unbalance”; Proceeding of 10th
IPEC, pp.155 – 160,
2012.
[17]Peterson, A., Harnefors, L., and Thiringer, T.;
“Comparison between stator-flux and grid flux
oriented rotor current control of doubly-fed
induction generators”; Proceeding of the 35th
Annual IEEE Power Electronics Specialist
Conference, Vol. 1, pp. 482–486, 2004.
SICE Annual Conference 2013
September 14-17, 2013, Nagoya, Japan
2588