Authors: Reza Pourramezan, Sadegh Vaez-Zadeh, and Hamid Reza Nourzadeh
Published in 2007 IEEE Power Engineering Society General Meeting (PES)
DOI: 10.1109/PES.2007.385692
In this paper, a detail design and description of a predictive current control scheme are adopted for three-phase grid-connected two-level inverter and its application in wind energy conversion systems. Despite its advantages, the predictive current controller is very sensitive to parameter variations which could eventually affected on system stability. To solve this problem, an estimation technique proposed to identify the value of harmonic filter parameter based on Model reference adaptive system (MRAS). Lyapunov stability theory is selected to guarantee a robust adaptation and stable response over large system parameter variation. The simulation results shows the efficiency of the proposed techniques to improve the current tracking performance.
In grid connected system, unity power factor current injection into the grid is vital. This can be achieved by choosing the right inverter topology, passive filter components, current controllers, and PWM switching scheme. This paper compares the output current harmonics profile between when using the conventional proportional resonant (PR) current controller and when using the modified PR current controller. By applying the latter technique, via experimental validation using TMS320F2812, the THD of the injected grid current in a parallel connected inverters system is improved.
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.
Total Harmonic Distortion Analysis of a Four Switch 3-Phase Inverter Fed Spee...IJPEDS-IAES
This paper investigates the performance of a Model reference adaptive system (MRAS) based cost-effective drive system of an induction motor (IM) for low-cost applications - high performance industrial drive systems. In this paper, the MRAS is used as a speed estimator and the motor is fed from a four-switch three-phase (FSTP) inverter instead of a conventional six- switch three-phase (SSTP) inverter. This configuration reduces the cost of the inverter, the switching losses, and the complexity of the control algorithms and interface circuits, the proposed control approach reduces the computation for real-time implementation. The robustness of the proposed MRAS-based FSTP inverter fed IM drive is verified by Experimental results at different operating conditions using digital signal processor (DSP1103) for a 1.1 Kw motor. A performance comparison of the proposed FSTP inverter fed IM drive with a conventional SSTP inverter system is also made in terms of speed response and total harmonic distortion (THD) of the stator current. The proposed FSTP inverter fed IM drive is found quite acceptable considering its performance, cost reduction and other advantages features.
The aim of this paper is to prove that fuzzy logic algorithm is a suitable control technique for fast processes such as electrical machines. This theory has been experimented on different kinds of electrical machines such as stepping motors, dc motors and induction machines (with 6 phases) and the experimental results show that the proposed fuzzy logic algorithm is the most suitable control technique for electrical machines since this algorithm is not time consuming and it is also robust between plant parameters variations.
Optimized Aircraft Electric Control System Based on Adaptive Tabu Search Algo...ijeei-iaes
Three conventional control constant instantaneous power control, sinusoidal current control, and synchronous reference frame techniques for extracting reference currents for shunt active power filters have been optimized using Fuzzy Logic control and Adaptive Tabu search Algorithm and their performances have been compared. Critical analysis of Comparison of the compensation ability of different control strategies based on THD and speed will be done, and suggestions will be given for the selection of technique to be used. The simulated results using MATLAB model are presented, and they will clearly prove the value of the proposed control method of aircraft shunt APF. The waveforms observed after the application of filter will be having the harmonics within the limits and the power quality will be improved.
Tuning of PI and PID Controller with STATCOM, SSSC and UPFC for Minimizing Da...IOSRJEEE
This paper presents the comparative performance of directly and feedback connected PI and PID controller scheme with Flexible AC Transmission System (FACTS) devices, such as Static Synchronous Compensator (STATCOM), Static Synchronous Series Compensator (SSSC) and Unified Power Flow Controller (UPFC) in terms of improvements in transient stability, extenuation of system oscillations and furnishing voltage support in single machine infinite bus system (SMIB). Firstly, rotor angle deviation and speed deviation analyzed for directly connected PI and PID with UPFC, SSSC and STATCOM then for feedback connected. The comparisons of all the results are performed using Matlab simulink in term of maximum overshoot and settling time.
In this paper, a detail design and description of a predictive current control scheme are adopted for three-phase grid-connected two-level inverter and its application in wind energy conversion systems. Despite its advantages, the predictive current controller is very sensitive to parameter variations which could eventually affected on system stability. To solve this problem, an estimation technique proposed to identify the value of harmonic filter parameter based on Model reference adaptive system (MRAS). Lyapunov stability theory is selected to guarantee a robust adaptation and stable response over large system parameter variation. The simulation results shows the efficiency of the proposed techniques to improve the current tracking performance.
In grid connected system, unity power factor current injection into the grid is vital. This can be achieved by choosing the right inverter topology, passive filter components, current controllers, and PWM switching scheme. This paper compares the output current harmonics profile between when using the conventional proportional resonant (PR) current controller and when using the modified PR current controller. By applying the latter technique, via experimental validation using TMS320F2812, the THD of the injected grid current in a parallel connected inverters system is improved.
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.
Total Harmonic Distortion Analysis of a Four Switch 3-Phase Inverter Fed Spee...IJPEDS-IAES
This paper investigates the performance of a Model reference adaptive system (MRAS) based cost-effective drive system of an induction motor (IM) for low-cost applications - high performance industrial drive systems. In this paper, the MRAS is used as a speed estimator and the motor is fed from a four-switch three-phase (FSTP) inverter instead of a conventional six- switch three-phase (SSTP) inverter. This configuration reduces the cost of the inverter, the switching losses, and the complexity of the control algorithms and interface circuits, the proposed control approach reduces the computation for real-time implementation. The robustness of the proposed MRAS-based FSTP inverter fed IM drive is verified by Experimental results at different operating conditions using digital signal processor (DSP1103) for a 1.1 Kw motor. A performance comparison of the proposed FSTP inverter fed IM drive with a conventional SSTP inverter system is also made in terms of speed response and total harmonic distortion (THD) of the stator current. The proposed FSTP inverter fed IM drive is found quite acceptable considering its performance, cost reduction and other advantages features.
The aim of this paper is to prove that fuzzy logic algorithm is a suitable control technique for fast processes such as electrical machines. This theory has been experimented on different kinds of electrical machines such as stepping motors, dc motors and induction machines (with 6 phases) and the experimental results show that the proposed fuzzy logic algorithm is the most suitable control technique for electrical machines since this algorithm is not time consuming and it is also robust between plant parameters variations.
Optimized Aircraft Electric Control System Based on Adaptive Tabu Search Algo...ijeei-iaes
Three conventional control constant instantaneous power control, sinusoidal current control, and synchronous reference frame techniques for extracting reference currents for shunt active power filters have been optimized using Fuzzy Logic control and Adaptive Tabu search Algorithm and their performances have been compared. Critical analysis of Comparison of the compensation ability of different control strategies based on THD and speed will be done, and suggestions will be given for the selection of technique to be used. The simulated results using MATLAB model are presented, and they will clearly prove the value of the proposed control method of aircraft shunt APF. The waveforms observed after the application of filter will be having the harmonics within the limits and the power quality will be improved.
Tuning of PI and PID Controller with STATCOM, SSSC and UPFC for Minimizing Da...IOSRJEEE
This paper presents the comparative performance of directly and feedback connected PI and PID controller scheme with Flexible AC Transmission System (FACTS) devices, such as Static Synchronous Compensator (STATCOM), Static Synchronous Series Compensator (SSSC) and Unified Power Flow Controller (UPFC) in terms of improvements in transient stability, extenuation of system oscillations and furnishing voltage support in single machine infinite bus system (SMIB). Firstly, rotor angle deviation and speed deviation analyzed for directly connected PI and PID with UPFC, SSSC and STATCOM then for feedback connected. The comparisons of all the results are performed using Matlab simulink in term of maximum overshoot and settling time.
This paper introduces experimental comparison study between six and four switch inverter fed three phase induction motor drive system. The control strategy of the drive is based on speed sensoreless vector control using model reference adaptive system as a speed estimator. The adaptive mechanism of speed control loop depends on fuzzy logic control. Four switch inverter conFigureurations reduces the cost of the inverter, the switching losses, the complexity of the control algorithms, interface circuits, the computation of real-time implementation, volume-compactness and reliability of the drive system. The robustness of the proposed model reference adaptive system based on four switch three-phase inverter (FSTPI) fed induction motor drive is verified experimentally at different operating conditions. Experimental work is carried using digital signal processor (DSP1103) for a 1.1 kW motor. A performance comparison of the proposed FSTP inverter fed IM drive with a conventional six switch three-phase inverter (SSTP) inverter system is also made in terms of speed response. The results show that the proposed drive system provides a fast speed response and good disturbance rejection capability. The proposed FSTP inverter fed IM drive is found quite acceptable considering its performance, cost reduction and other advantages features.
PI and fuzzy logic controllers for shunt active power filterISA Interchange
This paper presents a shunt Active Power Filter (APF) for power quality improvements in terms of harmonics and reactive power compensation in the distribution network. The compensation process is based only on source current extraction that reduces the number of sensors as well as its complexity. A Proportional Integral (PI) or Fuzzy Logic Controller (FLC) is used to extract the required reference current from the distorted line-current, and this controls the DC-side capacitor voltage of the inverter. The shunt APF is implemented with PWM-current controlled Voltage Source Inverter (VSI) and the switching patterns are generated through a novel Adaptive-Fuzzy Hysteresis Current Controller (A-F-HCC). The proposed adaptive-fuzzy-HCC is compared with fixed-HCC and adaptive-HCC techniques and the superior features of this novel approach are established. The FLC based shunt APF system is validated through extensive simulation for diode-rectifier/R–L loads.
Line Losses in the 14-Bus Power System Network using UPFCIDES Editor
Controlling power flow in modern power systems
can be made more flexible by the use of recent developments
in power electronic and computing control technology. The
Unified Power Flow Controller (UPFC) is a Flexible AC
transmission system (FACTS) device that can control all the
three system variables namely line reactance, magnitude and
phase angle difference of voltage across the line. The UPFC
provides a promising means to control power flow in modern
power systems. Essentially the performance depends on proper
control setting achievable through a power flow analysis
program. This paper presents a reliable method to meet the
requirements by developing a Newton-Raphson based load
flow calculation through which control settings of UPFC can
be determined for the pre-specified power flow between the
lines. The proposed method keeps Newton-Raphson Load Flow
(NRLF) algorithm intact and needs (little modification in the
Jacobian matrix). A MATLAB program has been developed to
calculate the control settings of UPFC and the power flow
between the lines after the load flow is converged. Case studies
have been performed on IEEE 5-bus system and 14-bus system
to show that the proposed method is effective. These studies
indicate that the method maintains the basic NRLF properties
such as fast computational speed, high degree of accuracy and
good convergence rate.
Design and Performance Analysis of Genetic based PID-PSS with SVC in a Multi-...IDES Editor
Damping of power system oscillations with the help
of proposed optimal Proportional Integral Derivative Power
System Stabilizer (PID-PSS) and Static Var Compensator
(SVC)-based controllers are thoroughly investigated in this
paper. This study presents robust tuning of PID-PSS and
SVC-based controllers using Genetic Algorithms (GA) in
multi machine power systems by considering detailed model
of the generators (model 1.1). The effectiveness of FACTSbased
controllers in general and SVC-based controller in
particular depends upon their proper location. Modal
controllability and observability are used to locate SVC–based
controller. The performance of the proposed controllers is
compared with conventional lead-lag power system stabilizer
(CPSS) and demonstrated on 10 machines, 39 bus New England
test system. Simulation studies show that the proposed genetic
based PID-PSS with SVC based controller provides better
performance.
Enhancing Power Quality in Transmission System Using Fc-TcrIJMER
FACTS methodology is totally based on power electronics devices which are used to increase the transmission capability. To make the power system flexible, FACTS technology is used to attain entire control of power system i.e. transmission, distribution and generation. This paper is mainly concerned about the significance of Fixed Capacitor Thyristor Control Reactor (FC-TCR) acquiring automatic power and steady state voltage stability with the help of fuzzy logic controller. In transmission systems, the fuzzy rules are set to generate the required firing angle of FC-TCR to maintain a flat profile of steady state voltage and stability. The fundamental model is simulated in MATLAB along with the fuzzy logic control strategy. The results obtained are trust worthy and it can be used for controlling the voltage and reactive power in any electrical transmission system.
Comparing of switching frequency on vector controlled asynchronous motorijscai
Nowadays, asynchronous motors have wide range use in many industrial applications. Field oriented
control (FOC) and direct torque control (DTC) are commonly used methods in high performance vector
control for asynchronous motors. Therefore, it is very important to identify clearly advantages and
disadvantages of both systems in the selection of appropriate control methods for many industrial
applications. This paper aims to present a new and different perspective regarding the comparison of the
switching behaviours on the FOC and the DTC drivers. For this purpose, the experimental studies have
been carried out to compare the inverter switching frequencies and torque responses of the asynchronous
motor in the FOC and the DTC systems under different working conditions. The dSPACE 1103 controller
board was programmed with Matlab/Simulink software. As expected, the experimental studies showed that
the FOC controlled motors has a lessened torque ripple. On the other hand, the FOC controlled motor
switching frequency has about 65-75% more than the DTC controlled under both loaded and unloaded
working conditions
Optimal Placement of DG for Loss Reduction and Voltage Sag Mitigation in Radi...IDES Editor
This paper presents the need to operate the power
system economically and with optimum levels of voltages has
further led to an increase in interest in Distributed
Generation. In order to reduce the power losses and to improve
the voltage in the distribution system, distributed generators
(DGs) are connected to load bus. To reduce the total power
losses in the system, the most important process is to identify
the proper location for fixing and sizing of DGs. It presents a
new methodology using a new population based meta heuristic
approach namely Artificial Bee Colony algorithm(ABC) for
the placement of Distributed Generators(DG) in the radial
distribution systems to reduce the real power losses and to
improve the voltage profile, voltage sag mitigation. The power
loss reduction is important factor for utility companies because
it is directly proportional to the company benefits in a
competitive electricity market, while reaching the better power
quality standards is too important as it has vital effect on
customer orientation. In this paper an ABC algorithm is
developed to gain these goals all together. In order to evaluate
sag mitigation capability of the proposed algorithm, voltage
in voltage sensitive buses is investigated. An existing 20KV
network has been chosen as test network and results are
compared with the proposed method in the radial distribution
system.
An Adaptive Neuro-Fuzzy Inference Distributed Power Flow Controller (DPFC) in...IAES-IJPEDS
A well-prepared abstract enables the reader to identify the basic content of a document quickly and accurately, to determine its relevance to their interests, and thus to decide whether to read the document in its entirety. The Abstract should be informative and completely self-explanatory, provide a clear statement of the problem, the proposed approach or solution, and point out major findings and conclusions. The Abstract should be 100 to 200 words in length. The abstract should be written in the past tense. Standard nomenclature should be used and abbreviations should be avoided. No literature should be cited. The keyword list provides the opportunity to add keywords, used by the indexing and abstracting services, in addition to those already present in the title. Judicious use of keywords may increase the ease with which interested parties can locate our article.
FLC based on static var compensator for power system transient stability enha...TELKOMNIKA JOURNAL
Transient Stability is the capability of a system to be able to return to its normal state after experiencing large disturbances. The static var compensator (SVC) is a shunt device of the flexible AC transmission systems (FACTS) family using power electronics to improve transient stability in power system. For the SVC control, it is usually used a PI controller, although PI controller is simpler and cheaper but not suitable when power system is subjected to transient stability since power system become non-linear system. In order to overcome this problem, the PI controller combined with Fuzzy controller is designed. Two types of faults were considered for this study to examine the effect of the fuzzy-SVC controller on system transient stability, the proposed fault types are single line to ground fault and three lines to ground fault. The performance and behavior of the designed fuzzy controller compared with that of the conventional PI controller in term of terminal voltage, rotor angle, and transmission line active power.
This research implements a PI controller based on harmony search (HS) optimization algorithm for voltage source inverter to improve the output performance under step load change conditions. The HS algorithm aims to handle the trial and error procedure used in finding the PI parameters and then apply the proposed control algorithm via the eZdsp TMS320F28355 board to link the inverter prototype with the Matlab Simulink. The mean absolute error (MAE) is used as an optimization problem to minimize the output voltage error for the developed controller (PI-HS) as compared to the PI controller based particale swarm optimization algorithm (PI-PSO). Based on the experimental results obtained, it is noted that the proposed controller (PI-HS) provides a good dynamic performance, robustness, constant voltage amplitude, and fast response in terms of overshoot, transient, and steady-state.
Direct Torque Control (DTC) is widely applied for ac motor drives as it offers high performance torque control with a simple control strategy. However, conventional DTC poses some disadvantages especially in term of variable switching frequency and large torque ripple due to the utilization of torque hysteresis controller. Other than that, performance of conventional DTC fed by two-level inverter is also restricted by the limited numbers of voltage vectors which lead to inappropriate selection of voltage vectors for different speed operations. This research aims to propose a Constant Switching Frequency (CSF) torque controller for DTC of induction motor (IM) fed by three-level Neutral-Point Clamped (NPC) inverter. The proposed torque controller utilizes PI controller which apply different gain for different speed operation. Besides, the utilization of NPC inverter provides greater number of voltage vectors which allow appropriate selection of voltage vectors for different operating condition. Using the proposed method, the improvement of DTC drives in term of producing a constant switching operation and minimizing torque ripple are achieved and validated via experimental results.
Online Voltage Stability Analysis using Synchrophasor Technologyijsrd.com
Voltage instability has been a major problem in all the emerging power systems across the world. Several instances of blackouts in North America, including the 1996 Western Interconnection and the 2003 North East US /Canada blackout are primarily due to voltage collapse. So Monitoring and maintaining voltage stability in real-time is extremely important for operating a power system reliably. In this paper Synchrophasor technology is introduced. Synchrophasor technology has the capability to monitor voltage stability over a wide area in real time. In this paper different methods are introduced for finding the voltage collapse point in the system and also one new method given for identification of voltage collapse point.
Load Flow Based Voltage Stability Indices for Voltage Stability and Contingen...TELKOMNIKA JOURNAL
Electrical power system is growing rapidly with the current increasing demand. One of many
important issues being faced in power system is the voltage instability. With that being said, this work
investigates the voltage stability indices with contingency analysis used in order to determine the voltage
stability of the network system. These approaches are used to detect and avoid voltage instability in the
distribution network. The behavior of the distribution network is determined based on the contingency
analysis. STATCOM is injected into selected buses in the distribution network of the system to determine
the system’s stability during the contingency condition. Distributed generation (DG) is utilized to enhance
the network stability. Different scenarios have been assumed in order to test the proposed technique under
different conditions. The work has been implemented in Digsilent power factory environment. The
proposed technique has been tested on IEEE 30 bus system. Promising results have been obtained with
respect to previous published literature, in term of identifying the weak buses and enhancing the overall
stability of the network.
Basically, the direct torque control (DTC) drive system is operated at light load. At light load, supplying the drive system with rated flux will decrease the efficiency of the system. To maximize the efficiency of drive system, an optimal flux has been applied during steady-state but when a torque is suddenly needed, for example during acceleration, the dynamic of the torque response would be degraded. Therefore, a modification to the voltage vector as well as look-up table has been proposed for the torque response improvement. The proposed voltage vector is generated by adding two adjacent conventional voltage vectors and implemented by using duty ratio. The duty ratio is used to estimate the activation time of each conventional voltage vector in order to produce the proposed voltage vector.
DTC Scheme for a Four-Switch Inverter-Fed PMBLDC Motor Emulating the Six-Swit...IJRST Journal
The paper deals with the direct torque control (DTC) of brushless DC (BLDC) motor drives fed by four-switch three phase inverters (FSTPI) rather than six-switch inverters (SSTPI) in conventional drives. For any three phase inverter require six switches, but these switches are reduced to four. This reduction of power switches from six to four improves the reliability of the inverter, size of the inverter is reduced and cost of the inverter is also reduces. The FSTPI could be regarded as a reconfigured topology of the SSTPI in case of a switch/leg failure which represents a crucial reliability benefit for many applications especially in electric and hybrid propulsion systems. The DTC of FSTPI-fed BLDC motor drives is treated considering two strategies, such as: 1) DTC-1: a strategy inspired from the one intended to SSTPI-fed BLDC motor drives; 2) DTC-2: a strategy that considers a dedicated vector selection subtable in order to independently control the torques developed by the phases connected to the FSTPI legs during their simultaneous conduction. The operational principle of the four-switch BLDC motor drive and the developed control scheme are theoretically analyzed and the performance is demonstrated by simulation.
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International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
This paper introduces experimental comparison study between six and four switch inverter fed three phase induction motor drive system. The control strategy of the drive is based on speed sensoreless vector control using model reference adaptive system as a speed estimator. The adaptive mechanism of speed control loop depends on fuzzy logic control. Four switch inverter conFigureurations reduces the cost of the inverter, the switching losses, the complexity of the control algorithms, interface circuits, the computation of real-time implementation, volume-compactness and reliability of the drive system. The robustness of the proposed model reference adaptive system based on four switch three-phase inverter (FSTPI) fed induction motor drive is verified experimentally at different operating conditions. Experimental work is carried using digital signal processor (DSP1103) for a 1.1 kW motor. A performance comparison of the proposed FSTP inverter fed IM drive with a conventional six switch three-phase inverter (SSTP) inverter system is also made in terms of speed response. The results show that the proposed drive system provides a fast speed response and good disturbance rejection capability. The proposed FSTP inverter fed IM drive is found quite acceptable considering its performance, cost reduction and other advantages features.
PI and fuzzy logic controllers for shunt active power filterISA Interchange
This paper presents a shunt Active Power Filter (APF) for power quality improvements in terms of harmonics and reactive power compensation in the distribution network. The compensation process is based only on source current extraction that reduces the number of sensors as well as its complexity. A Proportional Integral (PI) or Fuzzy Logic Controller (FLC) is used to extract the required reference current from the distorted line-current, and this controls the DC-side capacitor voltage of the inverter. The shunt APF is implemented with PWM-current controlled Voltage Source Inverter (VSI) and the switching patterns are generated through a novel Adaptive-Fuzzy Hysteresis Current Controller (A-F-HCC). The proposed adaptive-fuzzy-HCC is compared with fixed-HCC and adaptive-HCC techniques and the superior features of this novel approach are established. The FLC based shunt APF system is validated through extensive simulation for diode-rectifier/R–L loads.
Line Losses in the 14-Bus Power System Network using UPFCIDES Editor
Controlling power flow in modern power systems
can be made more flexible by the use of recent developments
in power electronic and computing control technology. The
Unified Power Flow Controller (UPFC) is a Flexible AC
transmission system (FACTS) device that can control all the
three system variables namely line reactance, magnitude and
phase angle difference of voltage across the line. The UPFC
provides a promising means to control power flow in modern
power systems. Essentially the performance depends on proper
control setting achievable through a power flow analysis
program. This paper presents a reliable method to meet the
requirements by developing a Newton-Raphson based load
flow calculation through which control settings of UPFC can
be determined for the pre-specified power flow between the
lines. The proposed method keeps Newton-Raphson Load Flow
(NRLF) algorithm intact and needs (little modification in the
Jacobian matrix). A MATLAB program has been developed to
calculate the control settings of UPFC and the power flow
between the lines after the load flow is converged. Case studies
have been performed on IEEE 5-bus system and 14-bus system
to show that the proposed method is effective. These studies
indicate that the method maintains the basic NRLF properties
such as fast computational speed, high degree of accuracy and
good convergence rate.
Design and Performance Analysis of Genetic based PID-PSS with SVC in a Multi-...IDES Editor
Damping of power system oscillations with the help
of proposed optimal Proportional Integral Derivative Power
System Stabilizer (PID-PSS) and Static Var Compensator
(SVC)-based controllers are thoroughly investigated in this
paper. This study presents robust tuning of PID-PSS and
SVC-based controllers using Genetic Algorithms (GA) in
multi machine power systems by considering detailed model
of the generators (model 1.1). The effectiveness of FACTSbased
controllers in general and SVC-based controller in
particular depends upon their proper location. Modal
controllability and observability are used to locate SVC–based
controller. The performance of the proposed controllers is
compared with conventional lead-lag power system stabilizer
(CPSS) and demonstrated on 10 machines, 39 bus New England
test system. Simulation studies show that the proposed genetic
based PID-PSS with SVC based controller provides better
performance.
Enhancing Power Quality in Transmission System Using Fc-TcrIJMER
FACTS methodology is totally based on power electronics devices which are used to increase the transmission capability. To make the power system flexible, FACTS technology is used to attain entire control of power system i.e. transmission, distribution and generation. This paper is mainly concerned about the significance of Fixed Capacitor Thyristor Control Reactor (FC-TCR) acquiring automatic power and steady state voltage stability with the help of fuzzy logic controller. In transmission systems, the fuzzy rules are set to generate the required firing angle of FC-TCR to maintain a flat profile of steady state voltage and stability. The fundamental model is simulated in MATLAB along with the fuzzy logic control strategy. The results obtained are trust worthy and it can be used for controlling the voltage and reactive power in any electrical transmission system.
Comparing of switching frequency on vector controlled asynchronous motorijscai
Nowadays, asynchronous motors have wide range use in many industrial applications. Field oriented
control (FOC) and direct torque control (DTC) are commonly used methods in high performance vector
control for asynchronous motors. Therefore, it is very important to identify clearly advantages and
disadvantages of both systems in the selection of appropriate control methods for many industrial
applications. This paper aims to present a new and different perspective regarding the comparison of the
switching behaviours on the FOC and the DTC drivers. For this purpose, the experimental studies have
been carried out to compare the inverter switching frequencies and torque responses of the asynchronous
motor in the FOC and the DTC systems under different working conditions. The dSPACE 1103 controller
board was programmed with Matlab/Simulink software. As expected, the experimental studies showed that
the FOC controlled motors has a lessened torque ripple. On the other hand, the FOC controlled motor
switching frequency has about 65-75% more than the DTC controlled under both loaded and unloaded
working conditions
Optimal Placement of DG for Loss Reduction and Voltage Sag Mitigation in Radi...IDES Editor
This paper presents the need to operate the power
system economically and with optimum levels of voltages has
further led to an increase in interest in Distributed
Generation. In order to reduce the power losses and to improve
the voltage in the distribution system, distributed generators
(DGs) are connected to load bus. To reduce the total power
losses in the system, the most important process is to identify
the proper location for fixing and sizing of DGs. It presents a
new methodology using a new population based meta heuristic
approach namely Artificial Bee Colony algorithm(ABC) for
the placement of Distributed Generators(DG) in the radial
distribution systems to reduce the real power losses and to
improve the voltage profile, voltage sag mitigation. The power
loss reduction is important factor for utility companies because
it is directly proportional to the company benefits in a
competitive electricity market, while reaching the better power
quality standards is too important as it has vital effect on
customer orientation. In this paper an ABC algorithm is
developed to gain these goals all together. In order to evaluate
sag mitigation capability of the proposed algorithm, voltage
in voltage sensitive buses is investigated. An existing 20KV
network has been chosen as test network and results are
compared with the proposed method in the radial distribution
system.
An Adaptive Neuro-Fuzzy Inference Distributed Power Flow Controller (DPFC) in...IAES-IJPEDS
A well-prepared abstract enables the reader to identify the basic content of a document quickly and accurately, to determine its relevance to their interests, and thus to decide whether to read the document in its entirety. The Abstract should be informative and completely self-explanatory, provide a clear statement of the problem, the proposed approach or solution, and point out major findings and conclusions. The Abstract should be 100 to 200 words in length. The abstract should be written in the past tense. Standard nomenclature should be used and abbreviations should be avoided. No literature should be cited. The keyword list provides the opportunity to add keywords, used by the indexing and abstracting services, in addition to those already present in the title. Judicious use of keywords may increase the ease with which interested parties can locate our article.
FLC based on static var compensator for power system transient stability enha...TELKOMNIKA JOURNAL
Transient Stability is the capability of a system to be able to return to its normal state after experiencing large disturbances. The static var compensator (SVC) is a shunt device of the flexible AC transmission systems (FACTS) family using power electronics to improve transient stability in power system. For the SVC control, it is usually used a PI controller, although PI controller is simpler and cheaper but not suitable when power system is subjected to transient stability since power system become non-linear system. In order to overcome this problem, the PI controller combined with Fuzzy controller is designed. Two types of faults were considered for this study to examine the effect of the fuzzy-SVC controller on system transient stability, the proposed fault types are single line to ground fault and three lines to ground fault. The performance and behavior of the designed fuzzy controller compared with that of the conventional PI controller in term of terminal voltage, rotor angle, and transmission line active power.
This research implements a PI controller based on harmony search (HS) optimization algorithm for voltage source inverter to improve the output performance under step load change conditions. The HS algorithm aims to handle the trial and error procedure used in finding the PI parameters and then apply the proposed control algorithm via the eZdsp TMS320F28355 board to link the inverter prototype with the Matlab Simulink. The mean absolute error (MAE) is used as an optimization problem to minimize the output voltage error for the developed controller (PI-HS) as compared to the PI controller based particale swarm optimization algorithm (PI-PSO). Based on the experimental results obtained, it is noted that the proposed controller (PI-HS) provides a good dynamic performance, robustness, constant voltage amplitude, and fast response in terms of overshoot, transient, and steady-state.
Direct Torque Control (DTC) is widely applied for ac motor drives as it offers high performance torque control with a simple control strategy. However, conventional DTC poses some disadvantages especially in term of variable switching frequency and large torque ripple due to the utilization of torque hysteresis controller. Other than that, performance of conventional DTC fed by two-level inverter is also restricted by the limited numbers of voltage vectors which lead to inappropriate selection of voltage vectors for different speed operations. This research aims to propose a Constant Switching Frequency (CSF) torque controller for DTC of induction motor (IM) fed by three-level Neutral-Point Clamped (NPC) inverter. The proposed torque controller utilizes PI controller which apply different gain for different speed operation. Besides, the utilization of NPC inverter provides greater number of voltage vectors which allow appropriate selection of voltage vectors for different operating condition. Using the proposed method, the improvement of DTC drives in term of producing a constant switching operation and minimizing torque ripple are achieved and validated via experimental results.
Online Voltage Stability Analysis using Synchrophasor Technologyijsrd.com
Voltage instability has been a major problem in all the emerging power systems across the world. Several instances of blackouts in North America, including the 1996 Western Interconnection and the 2003 North East US /Canada blackout are primarily due to voltage collapse. So Monitoring and maintaining voltage stability in real-time is extremely important for operating a power system reliably. In this paper Synchrophasor technology is introduced. Synchrophasor technology has the capability to monitor voltage stability over a wide area in real time. In this paper different methods are introduced for finding the voltage collapse point in the system and also one new method given for identification of voltage collapse point.
Load Flow Based Voltage Stability Indices for Voltage Stability and Contingen...TELKOMNIKA JOURNAL
Electrical power system is growing rapidly with the current increasing demand. One of many
important issues being faced in power system is the voltage instability. With that being said, this work
investigates the voltage stability indices with contingency analysis used in order to determine the voltage
stability of the network system. These approaches are used to detect and avoid voltage instability in the
distribution network. The behavior of the distribution network is determined based on the contingency
analysis. STATCOM is injected into selected buses in the distribution network of the system to determine
the system’s stability during the contingency condition. Distributed generation (DG) is utilized to enhance
the network stability. Different scenarios have been assumed in order to test the proposed technique under
different conditions. The work has been implemented in Digsilent power factory environment. The
proposed technique has been tested on IEEE 30 bus system. Promising results have been obtained with
respect to previous published literature, in term of identifying the weak buses and enhancing the overall
stability of the network.
Basically, the direct torque control (DTC) drive system is operated at light load. At light load, supplying the drive system with rated flux will decrease the efficiency of the system. To maximize the efficiency of drive system, an optimal flux has been applied during steady-state but when a torque is suddenly needed, for example during acceleration, the dynamic of the torque response would be degraded. Therefore, a modification to the voltage vector as well as look-up table has been proposed for the torque response improvement. The proposed voltage vector is generated by adding two adjacent conventional voltage vectors and implemented by using duty ratio. The duty ratio is used to estimate the activation time of each conventional voltage vector in order to produce the proposed voltage vector.
DTC Scheme for a Four-Switch Inverter-Fed PMBLDC Motor Emulating the Six-Swit...IJRST Journal
The paper deals with the direct torque control (DTC) of brushless DC (BLDC) motor drives fed by four-switch three phase inverters (FSTPI) rather than six-switch inverters (SSTPI) in conventional drives. For any three phase inverter require six switches, but these switches are reduced to four. This reduction of power switches from six to four improves the reliability of the inverter, size of the inverter is reduced and cost of the inverter is also reduces. The FSTPI could be regarded as a reconfigured topology of the SSTPI in case of a switch/leg failure which represents a crucial reliability benefit for many applications especially in electric and hybrid propulsion systems. The DTC of FSTPI-fed BLDC motor drives is treated considering two strategies, such as: 1) DTC-1: a strategy inspired from the one intended to SSTPI-fed BLDC motor drives; 2) DTC-2: a strategy that considers a dedicated vector selection subtable in order to independently control the torques developed by the phases connected to the FSTPI legs during their simultaneous conduction. The operational principle of the four-switch BLDC motor drive and the developed control scheme are theoretically analyzed and the performance is demonstrated by simulation.
ER Publication,
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International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Enhancement of Power System Dynamics Using a Novel Series Compensation SchemeIJMER
Phase imbalanced capacitive compensation is a “hybrid” series compensation scheme, where the
series capacitive compensation in one phase is created using a single-phase TCSC in series with a fixed capacitor
(Cc), and the other two phases are compensated by fixed series capacitors (C). The TCSC control is initially set
such that its equivalent compensations at the power frequency combined with the fixed capacitor yield a
resultant compensation equal to the other two phases. Thus, the phase balance is maintained at the power
frequency while at any other frequency, a phase imbalance is created. The effectiveness of the scheme in damping
power system oscillations for various network conditions, namely different system faults and tie-line power flows is
evaluated using the MATLAB/SIMULINK Software
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.
A robust dlqg controller for damping of sub synchronous oscillations in a ser...eSAT Journals
Abstract This paper investigates the use of Discrete Linear Quadratic Gaussian (DLQG) Compensator to damp sub synchronous oscillations in a Thyrisor Controlled Series Capacitor (TCSC) compensated power system. The study is conducted on IEEE First Benchmark Model (FBM) in which, TCSC is modelled as a discrete linear time-invariant modular unit in the synchronously rotating DQ reference frame. This modular TCSC is then integrated with the Linear Time Invariant (LTI) model of the rest of the system. The design of DLQG includes the design of a Kalman filter for full state estimation and a full state feedback for control. Since the order of the controller is as large as the order of the system considered here(27 states), the practical implementation of the controller is difficult. Hence by using Hankels norm approximation technique, the order of the controller is reduced from 27 to 15 without losing the significant system dynamics. The eigen analysis of the system shows that the use of DLQG can damp torsional oscillations as well as the swing mode oscillations simultaneously, which is practically difficult for a conventional sub-synchronous damping controller. The performance of the system with DLQG is appreciable for all operating conditions and it shows the robustness of the controller. Index Terms: Sub-Synchronous Resonance (SSR), Torsional Oscillations, Thyristor Controlled Series Capacitor (TCSC), Discrete Linear Quadratic Gaussian(DLQG)Compensator, Model Order Reduction (MOR).
A robust dlqg controller for damping of sub synchronous oscillations in a se...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.
Power Factor Improvement in Distribution System using DSTATCOM Based on Unit ...RSIS International
Power factor plays important role in the function of
the power system network. Hence, the power factor
improvement will increase the performance of power system
equipments. This paper presents the design and implementation
of distribution static compensator (DSTATCOM) with the stardelta
transformer for improvement of the power factor in threephase
four wire distribution system in the presence of threephase
linear load in the events of single phase, two-phase and
three phase trippings. The unit vector template method based
control algorithm has been implemented for the control of the
proposed DSTATCOM. The proposed test model has been
simulated in SIMULINK/MATLAB environment. The
simulations results show the effectiveness of proposed algorithm
Transient Stability Assessment and Enhancement in Power SystemIJMER
Power system is subjected to sudden changes in load levels. Stability is an important concept
which determines the stable operation of power system. For the improvement of transient stability the
general methods adopted are fast acting exciters, circuit breakers and reduction in system transfer
reactance. The modern trend is to employ FACTS devices in the existing system for effective utilization
of existing transmission resources. The critical clearing time is a measure to assess transient instability.
Using PSAT, the critical clearing time (CCT) corresponding to various faults are calculated. The most
critical faults were identified using this calculation. The CCT for the critical faults were found to change
with change in operating point. The CCT values are predicted using Artificial Neural Network (ANN) to
study the training effects of ANN. TCSC is selected as the FACTS device for transient stability
enhancement. Particle Swarm Optimization method is used to find the optimal position of TCSC using
the objective function real power loss minimization. The result shows that the technique effectively
increases the transient stability of the system
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.
Performance evaluation of different configurations of system with DSTATCOM us...nooriasukmaningtyas
The proposed Icosϕ control technique has been applied for power quality improvement using different configurations of system with distribution static compensator (DSTATCOM). Modeling, design and control of DSTATCOM are analysed in detial. Three phase reference current are extracted with this technique. The proposed technique has been used for power factor enhancement, voltage regulation, harmonic suppression and load balancing under dynamic condition with non-linear load. The proposed control is very effective for three different configurations of system with DSTATCOM for power quality improvement. Results for each configuration of system with DSTATCOM are simulated using MATLAB/Simulink sim power tool box. For teaching the power quality course, these can also be helpful.
Neural Network-Based Stabilizer for the Improvement of Power System Dynamic P...TELKOMNIKA JOURNAL
This paper develops an adaptive control coordination scheme for power system stabilizers (PSSs)
to improve the oscillation damping and dynamic performance of interconnected multimachine power
system. The scheme was based on the use of a neural network which identifies online the optimal
controller parameters. The inputs to the neural network include the active- and reactive- power of the
synchronous generators which represent the power loading on the system, and elements of the reduced
nodal impedance matrix for representing the power system configuration. The outputs of the neural
network were the parameters of the PSSs which lead to optimal oscillation damping for the prevailing
system configuration and operating condition. For a representative power system, the neural network has
been trained and tested for a wide range of credible operating conditions and contingencies. Both
eigenvalue calculations and time-domain simulations were used in the testing and verification of the
performance of the neural network-based stabilizer.
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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.
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2. 2
The paper is organized as follows. The two-area test
power system, PSS and TCSC POD controller are briefly de-
scribed in section II. The identification process together with
the OE and ARX model structures are presented in section III.
Section IV describes The GA-based coordinated design of
controllers. The results of power system identifications, the
coordinated tuning of controllers using identified models and
the time domain evaluation of tuned controllers are presented
in section V. The conclusion is given in section VI.
II. POWER SYSTEM AND CONTROLLERS
A. Power System
Fig. 1 presents the single line diagram of the two-area
power system which is particularly designed for inter-area
oscillations studies [14]. It consists of two generators in each
area. All generators are equipped with similar simple exciters.
The two areas are connected via a 220-km weak tie line. With
400MW power flow from area 1 to area 2, a poorly damped
inter-area mode of frequency 0.61 Hz and two local modes of
1.18 and 1.14 Hz are the system most critical modes. The
most contingency for this system is the loss of a line between
the two areas. This contingency leads to system low-
frequency oscillations. Hence, the controllers should be tuned
to work properly in both system pre-fault (Fig. 1) and post-
fault configuration (while a line is opened).
Area 1 Area 2
1G
4G
3G
2G
A
B
9L 10L
1 5 6 9 11 10
2 4
8 7 3
Fig. 1. Two-area test power system single line diagram.
B. PSS and TCSC POD Controller
In this paper, a PSS is installed on generator 3 which the
participation factor analysis shows it is the most critical gen-
erator. As the principal function of TCSC is to compensate for
the inductive impedance of weak lines, a TCSC is installed on
tie A. Therefore, the installing location of the TCSC POD
controller must be on tie A. Local signals, such as line current
magnitude, line active power and bus voltages, can be used as
TCSC POD controller input [15]. In this paper, the line cur-
rent magnitude is used as the controller input. Fig. 2 presents
linear structures that are used for controllers [12], [15].
The structures consist of a gain, a washout filter, a two-
stage dynamic compensator and a first-order lag block. The
gain Kw determines the amount of damping added to the sys-
tem by a controller. The washout filter prevents the controller
response to dc changes of input signal. The dynamic compen-
sator consists of two (or more) lead-lag blocks to provide nec-
essary phase-lead characteristics. Finally, the control signals,
V*
PSS and Xm, pass through the lag blocks, which represent the
PSS and TCSC regulators natural responses.
TCSC TCSC
TCSC
W W
W
sK T
1 sT+
TCSC
TCSC
1
2
1 sT
1 sT
+
+
TCSC
TCSC
3
4
1 sT
1 sT
+
+ TCSCe
1
1 sT+
mXlineI TCSCX
refX
maxX
minX
PSS PSS
PSS
W W
W
sK T
1 sT+
PSS
PSS
1
2
1 sT
1 sT
+
+
PSS
PSS
3
4
1 sT
1 sT
+
+
genω PSSV ∗
PSSV
PSSe
1
1 sT+
maxPSSV
minPSSV
(a)
(b)
Fig. 2. Power system controller block diagrams: (a) PSS (b) TCSC controller.
The output of the PSS regulator is VPSS which modifies the
exciter reference voltage. The output of TCSC regulator,
XTCSC, is a capacitive reactance with a reference value Xref
ordered by the power flow control. If a perturbation occurs,
the POD controller will modulate Xm to change TCSC capaci-
tive reactance XTCSC to damp the oscillations.
III. MIMO LOW-ORDER IDENTIFICATION
Fig. 3 illustrates the Two Input- Two Output (TITO) power
system plant equipped with PSS and TCSC POD controller.
For coordinated design of controllers, the identified model
should be a MIMO transfer function Gjk(s), which includes
four SISO transfer functions from jth inputs to kth output.
According to the Fig. 3, the inputs are PSS regulator reference
voltage V*
PSS and TCSC regulator modulating reactance Xm,
and the outputs are generator rotor speed ωgen and line current
magnitude Iline.
lineI
genωPSSV ∗
mX
( )jkG s
PSS
TCSC
Controller
Fig. 3. Power system two input-two output block diagram.
To achieve a suitable model, the identification input data,
which is a probing signal applied to the system optional in-
puts, should excite all modes of interest. The PRBS is one of
the most common signals used for identification that can be
produced by using a shift-register with feedback. Two differ-
ent PRBS probing signals are used for simultaneous excitation
of the power system inputs (V*
PSS and Xm illustrated in Fig. 3).
The amplitude and duration of PRBSs are selected such that
the system remains in linear operational region. During the
simulations, the power system outputs (ωgen and Iline) are
measured by an appropriate sampling time.
Using input/output identification data sets, different model
structures can be used to describe the system dynamic behav-
ior. The OE and ARX structures are used as power system
3. 3
model structures. Two subsequent sections represent a brief
description of these models and the methods to optimize their
parameters [6], [7], [13].
A. Multivariable OE Structure
The Output Error method estimates the parameters of a
linear model described by:
1
( )
ˆ ( ) ( ) ( ) (1)
( )
jn
jk
k j
jkj
B z
y t u t v t
F z=
= +∑
where t is the sampled data number, uj and ˆky are the model
optional inputs and outputs respectively and v(t) is the noise.
Bjk(z) and Fjk(z) are the OE nominator and denominator poly-
nomials respectively, that are given by:
11
0 1
1
1
( )
( ) 1 (2)
− +−
−−
= + + +
= + + +
L
L
bjk
f jk
n
jk jk jk jkn
n
jk jk jkn
B z b b z b z
F z f z f z
Because of nonlinear parameterization, the multivariable
OE and its parameters have to be estimated with nonlinear
optimization techniques [7]. Assuming that the model orders
nbjk and nfjk are given, the output error method estimates the
parameters by using Prediction Error Method (PEM) iterative
search algorithm to minimize the loss function given by:
2
1
1
( ) ( ) (3)
s
N
OE OE
s t n
V t t
N n
ε
= +
=
− ∑
where N is the number of data samples, ns is the number of
parameters to be optimized. The prediction error criterion,
εOE(t), is defined by:
( )
1
( )
( ) ( ) ( ) 4
( )
jn
jk
OE j
jkj
B z
t y t u t
F z
ε
=
= − ∑
where y is the actual system output. The full description of
this method can be found in [13].
B. Multi-variable ARX Structure
If it is assumed that all denominators polynomials in (1)
are identical (Fjk = Ak), the ARX model structure will be de-
fined as:
1
ˆ( ) ( ) ( ) ( ) ( ) (5)
=
= +∑
jn
k k jk j
j
A z y t B z u t v t
where Bjk(z) is similar to that of in (1) and Ak(z) is defined by:
1
1( ) 1 (6)
−−
= + + +L j
j
n
k k knA z a z a z
A multi-variable ARX can be identified by linear regres-
sion techniques. Therefore, the ARX model parameters can be
estimated by a linear least square technique. The least squares
estimation problem is solved by using QR factorization to
optimize the ARX model parameters. The least squares loss
function is defined as:
2
1
( ) (7)
= +
= ∑s
N
LS ARX
t n
V tε
where the equation error criterion εARX(t), is described by:
1
( ) ( ) ( ) ( ) ( ) (8)
=
= − ∑
jn
ARX k k jk j
j
t A z y t B z u tε
the ARX structure and algorithm details are described in [7].
Obtaining the model orders and parameters, the identified
models can be evaluated by comparing their outputs with the
actual system outputs. To evaluate identified models, a fitness
criterion can be performed as:
( )2
2
ˆ1
100 (9)
− −
= ×
−
k k
k k
y y
Fitness
y y
where y is the mean of y and ˆy is the identified model output
resulting from the same PRBS applied to the actual system.
Moreover, mode comparisons and different time domain re-
sponses using alternative probing signals can be performed
for further evaluation.
IV. COORDINATED DESIGN OF CONTROLLERS
GA optimization methods are based on natural selection,
which is a process of biological evolution. GA can be applied
to solve the optimization problems that are not well suited for
classical optimization methods, particularly the problems in
which the objective function is discontinuous, highly non-
linear or non-differentiable.
GA repeatedly modifies a population of individuals, which
are possible solutions of an optimization problem. The algo-
rithm starts with an initial random population. GA selects the
best individuals of a population to be parents of next genera-
tion's children. During successful generations, the population
approaches an optimal solution. GA implemented in MATL-
AB find a solution to minimize a given objective function.
The full description of GA can be found in [16].
For coordinated design of controllers, the transfer function
from the kth input to the jth output, Gjk(s) illustrated in Fig. 3,
can be expressed in term of system eigenvalues and the corre-
sponding residues as:
( )
( )1
s = (10)
n
ijk
jk
i i
R
G
s λ= −
∑
where Rijk is the residue associated with ith eigenvalue λi, and
n is the number of system’s eigenvalues.
The system phase lag at poorly damped mode frequency
4. 4
(ωi), which must be compensated by lead-lag compensators, is
given by [17]:
( )180 arg (11)lag ijkRφ = −
As mentioned before, controllers should perform appropri-
ate phase lead characteristics in both pre-fault and post-fault
configurations of the system. Once the system pre-fault and
post-fault phase lags are obtained from identified models, an
objective function for every controller is minimized using GA.
Considering that the inter-area mode frequency is different in
pre-fault and post-fault configurations, the objective function
ofφ is defined as the Integral of Squared Errors (ISE) of the
system phase lag and the compensator phase lead at the same
frequency (inter-area mode frequency):
( ) ( )
2 2
, , , , (12)= − + −lag pre C pre lag post C postofφ φ φ φ φ
where φlag,pre and φlag,post are the system phase lag in pre-fault
and post-fault respectively. φC,pre and φC,post are the phase lead
produced by compensators in pre-fault and post-fault respec-
tively.
Once the compensator parameters T1, T2, T3 and T4 are ob-
tained separately for each controller, the coordinated design
of controllers is reduced to tuning the washout time constants
Tw and the gains Kw. The washout time constants are selected
Tw = 10 sec. and the lag block time constants are selected Te =
10 ms. for both PSS and TCSC POD controller [17], [18]. For
gain tuning (Kw,PSS and Kw,TCSC), the identified models perform
under both controllers, and a mixed objective function can be
optimized by GA to reach the desirable performance.
Let λi = αi ± jβi be the ith closed-loop system eigenvalue.
Its damping ratio ξi can be found as:
2 2
(13)i
i
i i
αξ
α β
=
+
It is clear that by increasing the controllers gain the inter-
area mode will be shifted to the left hand side of complex
plane. However, further increase of the PSS gain and the
TCSC controller gain, the local mode and a higher frequency
mode called controller mode approach the imaginary axis
respectively, and ultimately become instable. The objective
function is provided to maximize the damping ratio of inter-
area mode. If all closed-loop eigenvalues for both pre-fault
and post-fault configurations, are in a convex region in the left
hand side of complex plane with damping ratio greater than a
specific value, the objective function ofξ to be minimized by
GA, is defined as:
( )2 2
, ,- (14)I pre I postofξ ξ ξ= +
where ξI,pre and ξI,post are inter-area mode damping ratio in
pre-fault and post-fault configurations respectively.
If one of the closed-loop poles are instable or their damp-
ing ratio is lower than the specific value, the objective func-
tion will then be set to a high value (Infinity). Thus, the GA
minimizes the objective function and the controllers gain will
be obtained simultaneously to maximize the ISE of inter-area
mode damping ratio in both configurations.
V. RESULTS
A. Identification Results
To identify the MIMO models in pre-fault and post-fault
configurations, the methods described in section III are ap-
plied and controllers design are carried out followed by exten-
sive simulations. All time domain simulations and modal
analyses in this paper were performed by using Power System
Analysis Toolbox (PSAT), which is incorporated in MATLAB
[19]. MATLAB Genetic algorithm and Direct Search Tool-
box was used for objective function optimizations [20].
The magnitudes of simultaneously applied PRBSs are 0.5
and 1 percent of exciter and TCSC reference values respec-
tively. Therefore, during the simulations the system remains
in the linear region. To ensure that all system low-frequency
modes are excited, the PRBSs are produced such that to ex-
cite an approximate frequency range of 0.005 ≤ f ≤ 3.33 Hz.
The system is perturbed by two different PRBSs groups of 30
sec. duration. One of the two data sets is used for model esti-
mation and the second is used for model validation. The sam-
pling interval is 50ms.
Using estimation data, two input-one output models of sys-
tem (ωV,X and IV,X ), are identified by means of either OE or
ARX methods. To evaluate, the validation PRBS is applied to
identified models and the resulting outputs are compared with
the actual validation data sets. Fig. 4 depicts the error between
rotor speed of identified models and that of the actual system
in pre-fault configuration.
0 5 10 15 20 25 30
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
x 10
-6
Time [sec.]
RotorSpeedDeviations[p.u.]
Modeling Error, Pre-Fault
OE
ARX
Fig. 4. Modeling error of rotor speed model, Pre-fault configuration.
Fig. 5 illustrates the error between the line current of the
identified models and the actual system in pre-fault configura-
tion. Fig. 6 and Fig. 7 depict the rotor speed and the line cur-
rent modeling errors of the post-fault identified system, re-
spectively. It is clear from Fig. 4 to Fig. 7 that when a PRBS is
applied, the outputs of the identified models follow the out-
5. 5
puts of the actual system with negligible differences. Al-
though, in some cases the OE modeling error is lower than
that of the ARX (Fig. 5 and Fig. 7), and in some other cases
the ARX models are more accurate (Fig. 4 and Fig. 6). Table I
lists these differences by means of the fitness of the identified
models.
0 5 10 15 20 25 30
-1
-0.5
0
0.5
1
1.5
2
x 10
-3
Time [sec.]
LineCurrentMagnitude[p.u.]
Modeling Error, Pre-Fault
OE
ARX
Fig. 5. Modeling error of line current model, Pre-fault configuration.
0 5 10 15 20 25 30
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
x 10
-6
Time [sec.]
RotorSpeedDeviations[p.u.]
Modeling Error, Post-Fault
OE
ARX
Fig. 6. Modeling error of rotor speed model, Post-fault configuration.
0 5 10 15 20 25 30
-1
-0.5
0
0.5
1
1.5
2
x 10
-3
Time [sec.]
LineCurrentMagnitude[p.u.]
Modeling Error, Post-Fault
OE
ARX
Fig. 7. Modeling error of line current model, Post-fault configuration.
All 12-ordered identified models present the inter-area
mode and the local mode of area 2 of the 40-ordered actual
system. The comparison between the actual and the identified
modes is presented in Table II. It can be observed that using
both methods, the inter-area mode is identified more accurate
than the local mode.
TABLE I
FITNESS OF TWO INPUT-ONE OUTPUT IDENTIFIED MODELS.
TABLE II
MODE COMPARISON OF ACTUAL AND IDENTIFIED MODELS.
For further evaluation of the identified models, step re-
sponse comparisons are performed. A 1% step is applied to
the exciter reference voltage at t = 0.2 sec. and after 30ms a
5% step is applied to the TCSC reference reactance. Fig. 8
depicts the rotor speed step response of the actual system and
the identified models in pre-fault configuration. Fig. 9 pre-
sents the line current magnitude step response in pre-fault
configuration. Fig. 10 and Fig. 11 depict the same step re-
sponses of the system post-fault configuration.
0 5 10 15 20 25 30
-3
-2
-1
0
1
2
3
4
5
6
7
x 10
-5
Time [sec.]
RotorSpeedDeviations[p.u.]
Rotor Speed Step Response, Pre-fault
Actual
OE
ARX
Fig. 8. Rotor speed step response, pre-fault configuration.
It can be concluded from Fig. 8 to Fig. 11 that OE- identi-
fied models are more effective than ARX-identified models in
following the actual system step response, although the vali-
dation data with PRBS excited signals and mode comparisons
did not distinguish the difference. As the mode comparison
shows, the two methods approximately determine poles with
the same accuracy. Hence, the difference between the identi-
6. 6
fied models may arise from the identified zeros. So, one can
suggest that OE method identifies zeros more accurately than
ARX method.
0 5 10 15 20 25 30
2.12
2.125
2.13
2.135
2.14
Time [sec.]
LineCurrentMagnitude[p.u.]
Line Current Step Response, Pre-fault
Actual
OE
ARX
Fig. 9. Line current step response, pre-fault configuration.
0 5 10 15 20 25 30
-5
0
5
10
x 10
-5
Time [sec.]
RotorSpeedDeviations[p.u.]
Rotor Speed Step Response, Post-fault
Actual
OE
ARX
Fig. 10. Rotor speed step response, post-fault configuration.
0 5 10 15 20 25 30
4.2
4.21
4.22
4.23
4.24
4.25
4.26
4.27
4.28
4.29
4.3
Time [sec.]
LineCurrentMagnitude[p.u.]
Line Current Step Response, Post-fault
Actual
OE
ARX
Fig. 11. Line current step response, post-fault configuration.
B. Coordinated Design of Controllers
Table III lists the system pre-fault and post-fault phase lag
together with the corresponding frequencies that are obtained
from OE and ARX identified models. It is seen that the resi-
dues obtained from OE and ARX models are close but not the
same. Using the mentioned objective function ofφ and the GA-
based phase compensation design within a wide bound of
search, the compensator parameters listed in Table IV, are
obtained for OE and ARX models. Due to the similarity of
residues listed in Table III, the parameters of OE and ARX
designed controllers are also similar. The gains of controllers
are then simultaneously tuned using damping ratio objective
function ofξ optimized by GA. The obtained gains of PSS and
TCSC controllers for both OE and ARX models are also listed
in Table IV.
TABLE III
RESIDUES OF IDENTIFIED MODELS USED FOR CONTROLLER TUNING.
TABLE IV
CONTROLLER PARAMETERS OBTAINED USING GA APPLIED TO THE IDENTIFIED
MODELS.
Table V shows the critical modes of the actual and the OE
models under the OE-based designed controllers. It is clear
that the inter-area and local modes of the actual closed-loop
system are shifted to the left and their damping ratios have
increased compared to those of the open-loop system. The
controller mode associated with TCSC controller has been
kept away sufficiently from the imaginary axis. The same
results for ARX-based designed control are listed in Table VI.
TABLE V
MODE COMPARISON OF CLOSED-LOOP ACTUAL AND OE MODELS DESIGNED
BY USING OE MODELS.
It can be deduced from Table V and Table VI that the
identified models have generally an acceptable similarity with
the actual one. Nevertheless, the inter-area and local modes of
the closed-loop identified and actual models are not com-
pletely the same. It is clear that they present the damping ratio
of the inter-area mode, slightly greater than that of the actual
model. They also show the damping ratio of the local mode
lower than that of the actual one. However, damping ratio of
7. 7
the controller mode is identified exactly. It can be concluded
that, applying any design method, the controllers will improve
the overall system performance.
TABLE VI
MODE COMPARISON OF CLOSED-LOOP ACTUAL AND ARX MODELS DESIGNED
BY USING ARX MODELS.
Ultimately, time domain simulations are performed to
show the performance of the designed controllers. Two con-
tingencies are considered:
• Contingency 1: Loss of line B that is parallel with line A
where the TCSC is located, at t = 0.2 sec. (post-fault
configuration).
• Contingency 2: A 1% step change in generator 3 exciter
reference voltage at t = 0.2 sec. (pre-fault configura-
tion).
Both contingencies lead to system low-frequency oscilla-
tions which are poorly damped without complementary con-
trollers. Fig. 12 depicts the active power flow of line A for the
actual system without and with PSS and TCSC POD control-
ler, while contingency 1 occurs. It can be seen that with both
OE and ARX-based designed controls, the oscillations are
damped in a few seconds.
0 1 2 3 4 5 6 7 8 9 10
3.4
3.6
3.8
4
4.2
4.4
Time [sec.]
LineActivePowerDeviations[p.u.]
Time Domain Response
No Controller
OE Model Designed Controller
ARX Model Designed Controller
Fig. 12. Line active power deviations of actual model, Contingency 1.
Fig. 13 depicts the active power flow of line A for open-
loop and closed-loop actual systems in pre-fault configuration,
while contingency 2 occurs. Once again, it is seen that both
OE and ARX-based controls improve the system performance
significantly; although, the OE designed control damps the
oscillations slightly faster.
0 1 2 3 4 5 6 7 8 9 10
1.978
1.98
1.982
1.984
1.986
1.988
1.99
1.992
1.994
1.996
1.998
Time [sec.]
LineActivePowerDeviations[p.u.]
Time Domain Response
No Controller
OE Model Designed Controller
ARX Model Designed Controller
Fig. 13. Line active power deviations of actual model, Contingency 2.
VI. CONCLUSIONS
In this paper, the OE and the ARX identification methods
are separately used to develop power system MIMO low-
order transfer functions, suitable for coordinated design of
PSS and TCSC POD controller. The above mentioned con-
trollers are simultaneously tuned by applying appropriate GA-
based optimizations to identified transfer functions.
The two input-two output transfer functions of a two-area
power system have been identified and then evaluated in dif-
ferent ways including the comparison of time domain re-
sponses of the identified models with those of the actual sys-
tem, the comparison of the inter-area and local modes of the
identified models with those of the actual system and com-
parisons between the step responses of the identified and the
actual system. The results of all evaluations show that the
identified models are accurate and suitable for dynamic stud-
ies.
The GA-based coordinated controllers tuning method is
applied to the obtained models. First, the parameters of com-
pensators block are tuned such that to compensate for the
phase-lag characteristics of the system. The simultaneous gain
tuning of the controllers is then provided.
Eventually, the actual power system is equipped with the
tuned controllers. In each operating condition, a contingency
is simulated. The performances of model-based controllers
show the potential benefits of PSS and TCSC POD controller
to enhance power system stability, and also confirm the valid-
ity of the identification methods.
The authors are currently working on providing a decen-
tralized control design that satisfies both system H∞ norm
minimization and regional pole placement. The preliminary
results show that the identified models are also suitable for
use in such designs. It is suggested that the proposed identifi-
cation methods are applied to large-scale power plants for
further evaluation.
8. 8
VII. REFERENCES
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VIII. BIOGRAPHIES
Reza Pourramazan was born in Sari, Iran, on September
30, 1979. He received the B.S. degree from Shahid
Beheshti University, Tehran, Iran, in 2003, and the M.S.
degree from School of Electrical Engineering, University
of Tehran, Tehran, Iran, in 2006, all in Electrical
Engineering.
His main research fields are Power System analysis,
modeling and control. He is currently working on coordinated use of PSS and
FACTS device stabilizers.
Sadegh Vaez-Zadeh (S'95–A'03–SM’05) received the
B.Sc. degree from Iran University of Science and
Technology, Tehran, Iran in 1985 and the M.Sc. and
Ph.D. degrees from Queen’s University, Kingston, ON,
Canada, in 1993 and 1997 respectively, all in Electrical
Engineering.
He has been with several research and educational
institutions in different positions before joining the
University of Tehran as an assistant professor in 1997
where he became an associate professor in 2001 and a full professor in 2005. He
served the university as the Head of Power Division from 1998 to 2000 and
currently is the Director of Advanced Motion Systems Research Laboratory
which he founded in 1998 and the Director of Electrical Engineering Laboratory
since 1998.
His research interests include advanced rotary and linear electric machines and
drives, magnetic levitation, electric vehicles and power system analysis and
control. He has published over 130 research papers. Dr. Vaez-Zadeh is an Editor
of IEEE Transactions on Energy Conversion, a Co-Editor of Journal of Asian
Electric Vehicles and a founding member of the editorial board of Iranian Jour-
nal of Electrical and Computer Engineering. He has been very active in IEEE
sponsored conferences as a member of technical and steering committees as well
as session chair.
Prof. Vaez-Zadeh is a member of IEEE PES Motor Sub-Committee and Power
System Stability Control Sub-Committee. He has received a number of awards
domestically including a best paper award form Iran Ministry of Science, Re-
search and Technology in 2001 and a best research award form the University of
Tehran in 2004.
Hamid Reza Nourzadeh (SM’2006) was born in Te-
hran, Iran, on September 18, 1978. He received the B.S.
degree from Shahid Beheshti University, Tehran, Iran, in
2003, and the M.S. degree from School of Electrical
Engineering, K. N. Toosi University of technology,
Tehran, Iran, in 2006, all in Electrical Engineering.
His main fields of interest are system identification and
robust control. He is currently with Process laboratory,
K. N. Toosi University of technology, working on Adaptive Universal Control
System.