In recent years, the concept of flexible ac transmission systems (FACTS) brought radical changes in the powersystem operation and control. The FACTS devices linked to the improvements in semiconductor technology opened new opportunities for controlling power and enhancing the usable capacity of existing transmission lines. As supplementary functions, damping the inter-area modes and enhancing powersystem stability using FACTS controllers have been extensively studied and investigated. In these years, Voltage Source Converter (VSC)-based series connected FACTS controllers, known as the new FACTS generation, which can inject a voltage with controllable magnitude and phase angle at the fundamental frequency, are found to be more capable of handling power flow control, transient stability and oscillation damping enhancement. In a recent literature , a novel methodology for tuning static synchronous compensator (STATCOM) baseddamping controller in order to enhance the damping of system low frequency oscillations has been described. This paper investigates the damping capabilities of static synchronous series compensator (SSSC), which is one of the VSC-based series connected FACTS controllers. SSSC is a solid-state controllable voltage source inverter that is connected in series with power transmission lines. With the injected voltage in quadrature with the line current and the capability of dynamically changing its reactance characteristic from capacitive to inductive, SSSC becomes an effective tool for power flow control . In addition, an auxiliary stabilizing signal can be superimposed on its power flow control function to improve powersystem oscillation stability . An attempt has been made to apply hybrid neuro- fuzzy approach for the coordination between the conventional power oscillation damping (POD) controllers for multimachine power systems. With the help of MATLAB, a class of adaptive networks, that are functionally equivalent to fuzzy inference systems, is proposed. The proposed architecture is referred to as ANFIS (Adaptive Neuro-Fuzzy Inference System) -. In this paper, ANFISbasedSSSCcontrollers are developed where each controller uses the speed of a synchronous machine
In , a SSSC-based controller employing Bacteria Foraging Optimization Algorithm (BFOA) for damping low frequency oscillations in a Single Machine Inﬁnite Bus (SMIB) powersystem has been presented. The design of lead-lad controller is formulated as an optimization problem to minimize a time domain based objective function by employing BFO technique. Gravitational Search Algorithm (GSA) is employed in [15,16] to design a supplementary lead-lag structured damping controller for a SSSC for powersystem dynamic performance enhancement. The linear model of powersystem has been used for design and analysis pur- pose. A hybrid approach involving PSO and BFOA is pre- sented for the design of SSSCbaseddamping controller in  where the parameters of the lead-lag structured SSSC con- troller as well as the gains of AC and DC voltage regulator are optimized. Coordinated design of SSSC with PowerSystem Stabilizers by hybrid PSO and BFOA  and Improved Lozi map based Chaotic Optimization Algorithm (ILCOA) is proposed in . A multi-objective GA approach is pre- sented in  to design the SSSCbaseddamping controller to improve the transient performance of a powersystem sub- jected to a severe disturbance by minimizing the power angle, terminal voltage and power ﬂow time trajectory deviations with respect to a post-contingency equilibrium point for a powersystem. In , NSGA-II has been applied to design a Thyristor Controlled Series Compensator (TCSC) based con- troller where the design objective was to improve the stability of the powersystem with minimum control effort. An Adaptive Neuro-Fuzzy Inference System (ANFIS) method based on the ANN is presented in  to design a SSSCbased controller for the improvement of transient stability where the ANFIS structures were trained using the generated database by the fuzzy controller of the SSSC.
Fuzzy gain scheduling is a procedure normally used for making controllers for power systems dynamic output varies nonlinearly with the operating parameters of the system. It is generally applied when the variation between the system dynamics and operating parameters are given, and for which a linear time- variant model is not enough . Nowadays, gain scheduling is performed according to the step frequency deviation response of the model for various values of the integral gain. A larger value of integral gain reduces the maximum overshoot value of the system frequency but the system oscillation takes place for a longer duration, but higher values of integral gain yield higher maximum frequency but the system oscillation takes place for a longer duration, but higher values of integral gain yield higher maximum frequency deviation in the starting but then delivers effective damping after few cycles, this shows the importance of a variable integral gain, hence large values of integral gain are planned at the beginning and then varied gradually based on the system frequency variations. Here, this methodology to control the performance parameters of the Fuzzy-PID controller according to the change of the new areacontrol error (ACE) and the change in areacontrol error (dACE) .
With the development of interconnection of large electric power systems there have been spontaneous system oscillations at low frequencies in the order of several cycles per minute. These low frequency oscillations are predominantly due to the lack of damping of mechanical mode of the system. Since power oscillation is a sustained dynamic event, it is necessary to vary the applied compensation to counteract the accelerating and decelerating swings of the disturbed machine . The concept of Flexible AC transmission system (FACTS) envisages the use of solid state controllers to achieve flexibility of powersystem by fast and reliable control of powersystem parameters affecting power flow in transmission line, namely voltage, impedance and or phase angle . Unified Power Flow Controller (UPFC), a multifunctional Flexible AC Transmission system (FACTS) Controller  opens up new opportunities for controlling power and enhancing the usable capacity of present, as well as new and upgraded lines.
Nowadays, electricity generation is very important because of its increasing necessity. The dynamic behavior of the system depends on disturbances and on changes in the operating point. The quality of the generated electricity in power stations is depending on the system output, it has to be of constant frequency and should maintain the scheduled power . Therefore, Load Frequency Control (LFC) is very important for powersystem in order to supply reliable and quality electric power. The conventional controllers such as PI, PID can give control action for one particular operating condition, where as in real situation the parameters change from time to time. So it is difficult to arrange the required gains to achieve zero frequency deviation. Hence there is a necessity to provide automatic correction. However research is going on and several methods are developed to overcome this difficulty . A number of control techniques have been employed in the design of load frequency controllers in order to achieve better dynamic performance. Comparing the various types of load frequency controllers, the most common and widely employed is the conventional proportional (PI) controller. Conventional controller is simple for implementation but gives large frequency deviation. Most of state feedback controllersbased on linear optimal control theory have been proposed to achieve better performance. Fixed gain controllers are designed at nominal operating conditions and fail to provide best control performance over a wide range of operating conditions. So to keep the system performance near to its optimum it is desirable to track the operating conditions and use updated parameters to compute the control. Adaptive controllers with self adjusting gains settings have been proposed for LFC to achieve the function compared to PI Controller.
For change in load of the systems, a mismatch occurs between generation and the load. So frequency fluctuation is caused by deficiency or sufficiency of generation. The deterioration and fluctuations in frequency affects consumer’s equipments & powersystem as a whole in an adverse manner. Therefore, it is necessary to regulate the frequency at its nominal value within a short span of time. To ensure more reliable and stable powersystem operation, it may be beneficial to introduce energy storage devices to alleviate power fluctuations. When energy storage system (ESS) connected at the output side, it has been shown to reduce the uncertainty, which leads to better scheduling of its generation  and beneficial for stabilizing frequency oscillations of power generation during peak load periods. In another similar domain of devices, the benefits of utilizing FACTs devices in overall improvement of powersystem operation and control has already been established [2-6]. The co-ordination of ESS and FACT devices facilitates extra storage source, permits independent adjustment of certain system variables and therefore makes the system more controllable and secure. The work probes into the optimum utilization of ESS and FACTs devices to enhance controllability of system frequency, with load variation. Energy storage is generally used in various applications. Examples of some primary applications are in traction and transportation systems , FACTs devices , uninterruptible power supplies (UPS)  and many more. Further transient stability is improved , by utilizing an ESS integrated FACTs devices. The several types of ESS, such as BESS, SCESS, ―flywheel energy storage system‖ (FESS)  and SMES , used in powersystem applications. Among some more prevalent devices in the FACTs family, the use of supplementary control can be applied for devices connected in series with interconnected tie-line power systems to damp the inter-area oscillations and power flow control . Due to sudden dynamic output, series FACTs devices such as TCPS , SSSC and thyristor controlled series capacitor (TCSC)  are used in powersystem to reduce the frequency oscillations and tie-line power variations.
Dept. of Electrical and Computer Engineering, Queen’s University, Kingston, Canada Abstract– After a disturbance occurrence, fast damping of power oscillations is essential to reduce the risk of instability and thus increase the power transfer capacity of transmission systems. Recently, the Static Series Synchronous Compensator (SSSC) has justified its ability to improve power oscillation damping. Due to substantial interactions among the SSSCdampingcontrol loops and the powersystem variables, the use of conventional Single-Input Single-Output (SISO) control approaches results in a poor damping performance. In this paper, these interactions are taken into consideration, and a powersystem equipped with an SSSC is modeled as a multivariable system. The impact of the SSSC’s dc voltage dynamic is also considered in the modeling. The powersystem equipped with an SSSC is multivariable with effective interactions among its variables. Traditional SISO control design techniques do not take into consideration these interactions and therefore cannot provide adequate damping over a wide range of operating conditions. Based on this developed multivariable modeling, a multivariable controller is proposed to improve power oscillation damping while keeping the dc-link voltage regulated. Simulation results verify the validity of the proposed modeling and control and show that the proposed approach can successfully damp out powersystem oscillations. Further simulation results show that the proposed controller provides a superior performance and a better robustness when compared to conventional SISO controllers.
ABSTRACT: The main aim of this work is to damp out powersystem oscillations, which has been recognized as one of the major concerns in powersystem operation. In a Static Synchronous Series Compensator (SSSC), a controllable AC voltage is generated by a voltage-source converter. There are twocontrol channels for controlling the magnitude and phase of the voltage. This work describes the damping of power oscillations by static synchronous series compensator (SSSC) baseddampingcontrollers. The advantage of this approach is that it can handle the nonlinearities, at the same time it is faster than other conventional controllers and it improve the reactive power of the system. Simulation studies will be carried out in Matlab/Simulink environment to evaluate the effectiveness of the proposed Static synchronous series compensator (SSSC) of multi-areapowersystem. Results will show that the proposed SSSCbaseddampingcontrollers improve the damping performance in the event of a major disturbance.
As far as modern control theory is concerned, several approaches have been proposed to improve the PSS design problem; these include optimal control, adaptive control, variable structure control and intelligent control. The present paper introduces a power stabilizer based on Grey Prediction and ANFIS design controllers. The influence of the proposed GrANFIS-PSS design on the dynamic characteristics of the controlled system is investigated. Simulation results to illustrate the effectiveness of the proposed controller are presented. These results have been obtained from a simulation study on a four-machine power network. In this study, the system has been subjected to a severe type of disturbance, i.e. a sudden three-phase short circuit fault at the end of one of the system busbars. This test demonstrates the enhancement of the transient stability of the system. In this GrANFIS-PSS based design, a rule was extracted from a conventional controller to give an initial solution. A speed deviation and its derivative are used as an input to the GrANFIS-PSS. The ANFIS is used as a second design method. Training data are taken from the output of a conventional controller and are fed to ANFIS for training. The proposed design approaches are applied to a 4 machine two-areapowersystem. Different size of an input/output membership function and defuzzification methods are used to assess the effectiveness of the proposed controller in terms of damping out the electromechanical modes of oscillation.
The main aim of this paper is to damp out powersystem oscillations, which has been recognized as one of the major concerns in powersystem operation. This paper describes the damping of power oscillations by hybrid neuro-fuzzy coordinated control of Flexible AC Transmission System (FACTS) baseddampingcontrollers. The advantage of this approach is that it can handle the nonlinearities, at the same time it is faster than other conventional controllers. ANFIS (Adaptive Neuro-Fuzzy Inference System) is employed for the training of the proposed fuzzy logic controllers (FLC). Simulation studies are carried out in Matlab/Simulink environment to evaluate the effectiveness of the proposed neuro-fuzzy controller on multi-machine power systems installed with Static synchronous series compensator (SSSC). Results show that the proposed neuro-fuzzy intelligent controls improve the damping performance of the SSSCbaseddampingcontrollers in the event of a major disturbance. Keywords: ANFIS, Coordinated control, Damping performance, FACTS, Fuzzy logic, Matlab/Simulink, SSSC, Training of FLC.
Abstract: Static Synchronous Series Compensator (SSSC) is a series compensating Flexible AC Transmission System (FACTS) controller for maintaining to the power flow control on a transmission line by injecting a voltage in quadrature with the line current and in series mode with the transmission line. In this work, an Adaptive Network-based Fuzzy Inference System controller (ANFISC) has been proposed for controlling of the SSSC- baseddampingsystem and applied in a Single Machine Infinite Bus (SMIB) powersystem. For implementation of the learning process of this controller, we use from one approach of the learning ability that named as Forward Signal and Backward Error Back-Propagation (FSBEBP) method for improving of the system efficiency. This artificial intelligence-basedcontrol model leads to a controller with adaptive structure and improved correctness of the system, and finally cause to enhancing to the high damping ability and dynamic performance. System implementation is easy and requires 49 fuzzy rules for inference engine of the system. As compared with the other complex neuro-fuzzy systems, this controller has medium number of the fuzzy rules and low number of the layers, but it has high accuracy. In order to demonstrate of the proposed controller ability, it is simulated and its output compared with that of the classic Lead-Lag-based Controller (LLC) and PI controller.
WAMS are additionally useful for efficient operation of deregulated electricity markets because of the requirements for uninhibited exchange of power over long distances and quick changes in the operating conditions. Enhancement to the existing Supervisory Control and Data Acquisition (SCADA) and Emergency Management Systems (EMS) can be done using WAMS . The SCADA/EMS functions are tools that assist the powersystem/grid operator in his effort to optimise the powersystem operation, with respect to economy, operational security and robustness, as well as human and material safety. These enhancements are aimed at two key areas: information availability and information interpretation. The operator can have all vital information at his fingertips in an efficient way. For example, with a better analysis tool for voltage instability, the operator can accurately track the power margin across an interface and thus can confidently push the limit of power transfer across that interface .
The model proposed in fig.1 can be improved by introducing the load-frequency characteristic of the areas in the dynamic equation of the powersystem and representing in more detail the speed governor and the turbine-generator of the power plants. Then, assuming neglected line losses, the deviation of interchanged real power can be written as
Abstract— Development of electric power transmission facilities is constrained despite the fact that bulk power transfers and use of transmission systems by consumers are increasing rapidly. Due to this fact powersystem stability is becoming the major issue these days. Due to vast and complex powersystem variation in the load occurs with respect to time which results in rotor angle instability which causes the oscillations in the powersystemPowersystem oscillation is one of the major problems in powersystem operation. If not damped, these oscillations can grow and decrease transmission capacity of the lines which may cause interruption in energy supply. Traditionally, these oscillations have been damped by powersystem stabilizers (PSS). Recently, FACTS devices such as static synchronous compensator (SVC) equipped with a power oscillation damper (POD) have been also efficiently used for damping oscillation. The function of SVC is to regulate voltage at its terminal by changing the amount of reactive power exchanges with the powersystem and power oscillation damping is also provided by this device.
The wind turbine generator is controlled by pitch angle of blades due to frequency oscillations and output variation. We have to fix the set point for pitch angle and the pitch system is changing the pitch angle according to wind speed and direction. The mathematical model of wind turbine is the total power generated by wind speed is expressed as
The large-scale power systems are normally composed of control areas (i.e. multi-area) or regions representing coherent groups of generators. The various areas are interconnected through tie-lines. The tie-lines are utilized for contractual energy exchange between areas and provide inter-area support in case of abnormal conditions. Without loss of generality we shall consider a two-area case connected by a single line as illustrated in Fig. 4.4. The concepts and theory of two-areapowersystem is also applicable to other multi-areapower systems i.e. three- area, four-area, five-area etc.
1. One of the structures used in this thesis to modulate the SSSC injected voltage is the lead-lag structure as shown in fig.5.11. This structure consists of a gain block, washout block and two stage lead-lag block. The two stage lead-lag block provides the appropriate phase-lead characteristics to compensate for the phase lag between input and the output signals. The washout block acts as a high pass filter to allow signals associated with oscillations to pass as it is. The inputs to the POD controller are the bus voltage at Bus no.2 and the current flowing in Line 1.The Power Oscillation Damping Controller takes input as Vabc ,Iabc& it convert it as power.
The prime mover driving a generator unit may be a steam turbine or a hydro turbine. The models for the prime mover must take account of the steam supply and boiler controlsystem characteristics in the case of a steam turbine, or the penstock characteristics for a hydro turbine. Here only the simplest prime-mover model, the non reheat turbine, is considered. The model for a non reheat turbine shown in figure 1. Relates the position of the valve that controls emission of steam into the turbine to the power output of the turbine.
Abstract- Due to the continuous change in load, the frequency and tie-line power of control areas get disturbed from their scheduled value which is undesirable. Automatic Generation Control (AGC) is an essential mechanism in electric power systems which balance generated power and demand in each controlarea in order to maintain the system frequency at nominal value and tie-line power at its scheduled value. This necessitates an accurate and fast acting controller to maintain constant nominal frequency. The limitations of conventional controllers i.e. Integral (I), Proportional Integral (PI) are slow and lack of efficiency in handling system errors. This paper proposes Particle Swarm Optimization (PSO) technique for AGC of two-area interconnected powersystem. Firstly, the conventional controllers i.e. Integral (I), Proportional Integral (PI) are used for AGC of two-area interconnected powersystem. Then PSO basedcontrollers are used and various responses due to various controllers have been compared. The responses of the proposed methods are demonstrated by MATLAB simulations.
Power quality issues have become a major concern in recent years due to the widespread use of nonlinear loads such power electronic converters, variable speed motor drives and consumer electronics. Nonlinear loads introduce harmonics into the power network which cause a number of disturbances such as distortion of the current and voltage waveforms, electromagnetic interference, overheating of power distribution components inducing losses and reducing their lifetime. Active Power Filters (APFs) also called Active Power Line Conditioners (APLCs) are a relatively new technology which offers a more flexible alternative and provides superior filtering performance characteristics and faster transient response as compared to conventional passive filters consisting of custom designed LC filters which are tuned to provide fixed frequency compensation . AFPs basically consist of a power electronic inverter and a control circuit.