The UPFC is installed for the purpose of multiple control functions, one of which will be the suppression of low-frequencyoscillations occurring in the system. In literature [3-6] the effectiveness of improving the oscillation damping by a FACTS supplementarydampingcontroller has been explored. Various feedback signals namely, deviation in generator rotor angle, deviations in real power flow through the transmission line, accelerating power, have been identified as capable of contributing direct electric damping torque to the electromechanical oscillation loop of the generator. The selection criteria chosen in these works consider the control cost, robustness of the feedback signal to variations of system operating conditions and local availability of signal. A judicious selection of the feed back signal can be done based on its capability in improving the damping of desired mode of oscillation. This work considers the deviation in rotor angle as input signal for the single machine infinite bus system aiming at improving the local mode of oscillation and the locally available power flow through the transmission line at which UPFC is connected, aiming at improving the poorly damped oscillation mode for the case of multi-machine. Thus these signals are capable of generating efficient database for the training of adaptive controller.
The eect of an Interline Power Flow Controller (IPFC) on dampinglowfrequencyoscillations has been implied in some papers, but has not been investigated in detail. This paper investigates the damping control function of an interline power ow controller installed in a power system. For this purpose, a single machine-innite bus model, integrated with IPFC, is used and the linearized model is established. Using this model, the Phillips-Heron model of the system for steady state digital simulations is derived. In this paper, the numerical results are presented using the MATLAB simulink toolbox, which shows the signicant eect of IPFC on damping inter-area oscillations.
The Benefits of Flexible AC Transmission Systems (FACTs) usages to improve powersystems stability are well known , . The growth of the demand for electrical energy leads to loading the transmission system near their limits. Thus, the occurrence of the LFO has increased. FACTs controllers has capability to control network conditions quickly and this feature of FACTs can be used to improve power system stability. The UPFC is a FACTS device that can be used to the LFO. The primarily use of UPFC is to control the power flow in powersystems. The UPFC consists of two voltage source converters (VSC) each of them has two control parameters namely me, δe, mb and δb . The UPFC used for power flow control, enhancement of transient stability, mitigation of system oscillations and voltage regulation . A comprehensive and systematic approach for mathematical modeling of UPFC for steady-state and small signal (linearized) dynamic studies has been proposed in [4-7]. The other modified linearized Heffron-Philips model of a power system installed with UPFC is presented in  and . For systems which are without power system stabilizer (PSS), excellent damping can be achieved via proper controller design for UPFC parameters. By designing a suitable UPFCcontroller, an effective damping can be achieved. It is usual that Heffron-Philips model is used in power system to study small signal stability. This model has been used for many years providing reliable results .
The Benefits of Flexible AC Transmission Systems (FACTs) usages to improve powersystems stability are well known . The growth of the demand for electrical energy leads to loading the transmission system near their limits. Thus, the occurrence of the LFO has increased. FACTs controllers has capability to control network conditions quickly and this feature of FACTs can be used to improve power system stability. The UPFC is a FACTS device that can be used to the LFO. The UPFC consists of two voltage source converters (VSC) each of them has two control parameters namely m e , δ e , m b and δ b . The UPFC used for power flow
on transmission lines . SVC controls reactive power by controlling the susceptance of passive devices. System voltage is controlled by controlling the reactive power and hence indirectly active power is controlled which results in damping of electromechanical oscillations [10-15]. Damping of electromechanical oscillations can be achieved through designing of appropriate external control for SVC. Proportional Integral (PI) and Proportional Integral Derivative (PID) controllers are the most frequently used conventional techniques available as an SVC external control. PI controller is the other commonly used scheme [16, 17]. Although the PI controllers present ease and simplicity of design, but their operating condition becomes less effective when the system conditions vary extensively or large disturbances take place . To circumvent these drawbacks, recently, Fuzzy Logic Controllers (FLCs) and Artificial Neural Network Controllers (ANNCs) have been used for oscillationsdamping control in the powersystems [19-23]. But majority of these artificial intelligence based control for SVC are designed for linearized power system and its control parameters are updated off-line. As power system is highly nonlinear and any vagueness in the system can drastically change its operating point. So these linear control designs may not give better performance under such circumstances.
Powersystems over the worldwide becoming complex day to day and continuous requirements are coming for stable, secured, controlled, economic and better quality power. These requirements become more essential when environment becoming more vital and important deregulation. Power system stability may be defined as that property of a power system that enables it to remain in a state of operating equilibrium under normal operating conditions and to regain acceptable state of equilibrium after being subjected to a disturbance . Dakka Obulesu et al worked on development of control strategies by combining fuzzy, pod and UPFCcontroller for three phase fault . In this paper, a modest attempt has been made to simulate a fuzzy logic control scheme with a UPFC for a FACTS power system to dampen the power system oscillations  . A. Majid Dejamkhooy et al worked on damping of lowfrequency oscillation for single machine system. In this paper a mathematical modelling of single machine system has been given . The introduction of Power oscillation dampingcontroller and its working with UPFC is well illustrated in paper given by Rusejla Sadikovic .
The dynamic characteristics of system can be influenced by location of eigenvalues, for a good system response in terms of overshoots/undershoot and settling time, a particular location for system eigenvalues is desired depending upon the operating conditions of the system. The dampingpower and the synchronizing power are related respectively, to real part and imaginary part of eigenvalue that correspond to incremental change in the deviation of the rotor speed and deviation of rotor angle, this Eigenvalue is known as electromechanical mode. Power oscillation damping can be improved if real part of eigenvalue associated with mode of oscillation can be shifted to left-side in complex s-plane as desired. This thesis present controller such that the closed loop designed system will have a desired degree of stability [13, and 14]. For the power system representation in state – space form, a closed loop gain matrix A-BK obtained by choosing the gain matrix K through state feedback control law U = −KX will have all its eigenvalue lies in left side of complex-plane. It is an easy task to design power oscillation dampingcontroller. Making use of proposed controller design approach, UPFCbasedpower oscillation dampingcontroller is designed to damping of lowfrequencypoweroscillations. This has been attempted on a sample system. The expectation from UPFCbased POD controller is to provide instantaneous solution to power oscillation damping, the settling time as obtained from response of system is expected to be as small as possible. For minimizing settling time real part of eigenvalue corresponding to mode of oscillation are required to be shifted more and more on LHS of complex plane, this will require control effort. There is a hardware limit of any designed controller, for the case of UPFC, in view of this, the control input parameters m e ,δ e and
A comprehensive and analytical approach for mathematical modeling of UPFC for steady state and linearised dynamic stability has been proposed. Several years the power system stabilizer act as a common control approach to damp the system oscillations. However, in some operating conditions, the PSS may fail to stabilize the power system, especially in lowfrequencyoscillations . It is proved that the FACTS devices are very much effective in power flow control as well as damping out the swing of the system during fault. Among all FACTS devices the UPFC is the most popular controller for effective damping.
In recent years, new artificial intelligence-based approaches have been proposed to design a FACTS- basedsupplementarydampingcontroller. These approaches include genetic algorithm , particle swarm optimization , differential evolution , and multi-objective evolutionary algorithm . Since 1989, artificial neural networks (ANN) methodology has captured the interest in a large number of applications in electrical power engineering . The applications include economical load dispatching, power system stabilizers (PSS), etc., The artificial neural network controllerbased on fuzzy control (ANFIScontroller) is applied for FACTS device. For the design purpose MATLAB/SIMULINK model of the power system with UPFCcontroller is developed. Simulation results are presented at different operating conditions and under various disturbances to show the effectiveness of the proposed controller. And the results prove that the proposed UPFC-basedANFIScontroller can improve transient stability and also can damp power oscillation more efficient than SSSC.
data concentrators that can be treated as integral parts of the WAM network. At the control center, the phasor data is first converted into the reference frame inde- pendent (RFI) output quantities (such as active power, reactive power, and voltage magnitude). In the case of output feedback control ,    , the RFI output quantities measured are directly processed through a gain matrix to generate the WAC signals. On the other hand, an intermediate level of state estimation is required in the case of state feedback control , . The state feedback controller generates WAC signals based upon the observable dynamic states of the system. The dynamic states of the system are determined by means of an extended Kalman filter (EKF)  or unscented Kalman filter (UKF) , . Typically, the dynamic state estimation is carried by using subsystem models; therefore, the EKF/UKF algorithm employed should also have the capacity to dynamically determine the inputs to each subsystem . After generating the WAC signals, those are transmitted to power system components (such as generators’ excitation systems  or FACTS devices ) via a WAC network. The implementation of the output feedback control is sim- pler than the implementation of the state feedback control since the former does not require any state estimator. However, the controller performance may be superior in the case of the state feedback control. This is because the system condition is more precisely addressed while designing and implementing the state feedback controller.
Abstract: In this paper, use of the additional supplementarydampingcontroller for unified power flow controller (UPFC) to damp out lowfrequencyoscillations in a heavily loaded power system is investigated. Normal damping controllers are inferior when the power system is subjected to large and fast changing loads. In order to handle the situation, an additional supplementarydampingcontroller for UPFC is designed using Fuzzy logic technique. The effectiveness of the proposed controller on dampinglowfrequencyoscillations is tested and demonstrated through simulation studies for single machine connected to infinite bus power system (SMIB). In addition power system response with UPFCdampingcontroller & Fuzzy logic basedsupplementarydampingcontroller (FLSDC) are compared at various loading conditions. It can be concluded that Fuzzy logic basedsupplementarydampingcontroller improves greatly the system stability under heavily loaded conditions.
suitable remote signals coming from the whole system, as supplementary in- puts, for a separate better damping of specific inter-area modes, has been de- veloped. Each local PSS controller is designed separately for each of the inter- area modes of interest. The PSS controller uses only those local and remote input signals in which the assigned single inter-area mode is most observable and is located at a generator which is most effective in controlling that mode. The local PSS controller, designed for a particular single inter-area mode, also works mainly in a frequency band given by the natural frequency of the as- signed mode. The locations of the local PSS controllers are obtained based on the amplitude gains of the frequency responses of the best-suited measure- ment to the inputs of all generators in the interconnected system. For the se- lection of suitable local and supplementary remote input signals, the features or measurements from the whole system are pre-selected first by engineering judgment and then using a clustering feature selection technique. Final selec- tion of local and remote input signals is based on the degree of observability of the considered single mode in them.
The power transfer in a coordinated power system is compelled by transient stability, voltage soundness and small signal stability. These limitations limit a full use of accessible transmission passageways. Flexible AC Transmission Systems (FACTS) are the innovation that gives the required adjustments of the transmission usefulness so as, to completely use the current transmission offices and thus, limiting the gap between as far as possible and thermal limit. Modern power system has been connected by means of weak tie lines. Lowfrequency electromechanical oscillations are experienced among the group of interconnected generators. These oscillations create severe hazard to the normal operation of the power system. The oscillations residing within a plant are called local mode of oscillations. The range of frequency is in between 0.7– 2.0 Hz. The oscillations available in the interconnected power system are called inter-area mode oscillations. The range of frequency is in between 0.1–0.8 Hz. Power system stabilizers are also used to damp out oscillations and they cause large voltage variations with leading power factor operation and loose stability under severe disturbances. Fast development in the field of power electronics has opened new opportunities for the exercise of the Flexible AC Transmission System (FACTS) devices. Modulation of bus voltage, phase shift between the buses and the transmission line reactance are used to improve power system operation controllability and power transfer limits and they can be achieved by FACTS devices.
In recent years, the fast progress in the field of power electronics has opened new opportunities for the power industry via utilization of the controllable Flexible AC Transmission System devices like Unified Power Flow Controller which offer an alternative means to mitigate power system oscillations . Oscillation Stability analysis and control has been an important subject in power system research and applications. The deregulation and competitive environment in the contemporary power networks [1, 2] will imply a new scenario in terms of load and power flow condition and so causing problems of line transmission capacity. But, nowadays, some problems exist like power system oscillation stability & refers to the damping of electromechanical oscillations occurring in powersystems with oscillation frequency in the range of 0.2 Hz. to 2 Hz. These low-frequencyoscillations are the consequence of the development of interconnection of large powersystems. A lowfrequency oscillation in a power system constrains the capability of power transmission, threatens system security and damages the efficient operation of the power system .
Abstract––Lowfrequency electromechanical oscillations are inevitable characteristics of powersystems and they greatly affect the transmission line transfer capability and power system stability. Traditionally, power system stabilizers (PSS) are being used to damp these oscillations. Unified Power Flow Controller (UPFC) is a well-known FACTS device that can control power flow in transmission lines. It can also replace PSS to damp lowfrequencyoscillations effectively through direct control of voltage and power. In this paper a liberalized Philips-Heffron model of a (Single Machine– Infinite Bus) power system with a unified power flow controller is considered. The designed fuzzy-basedUPFCcontroller adjusts four UPFC inputs by appropriately processing of the input error signal, and provides an efficient damping. The results of the simulation show that the UPFC with fuzzy-based controllers is effectively damping the LFO. Keywords—LowfrequencyOscillations (LFO), Unified Power Flow Controller (UPFC), Fuzzy logic, Dampingcontroller, Flexiable AC transmission System (FACTS)
The frequency-based stabilizer is dependent on terminal frequency which is derived from terminal current and voltage. Its main advantage is sudden phase shift in transient condition. The improvement of stability under high communication delays is discussed in . The authors of , discusses the eigen values of three different power system and the accuracy, convergence and consistency of eigen value calculations and alternative methods are discussed. H∞ loop shaping techniques are introduced to design robust PSS for SMIB designing. The selection of weighting functions is shown for the controller. Various operating parameters are compared with the conventional model in .
Abstract— This paper presents a systematic procedure for modeling and simulation of a power system equipped with FACTS type Gate Controlled Series Compensator (GCSC) based stabilizer controller. Single Machine Infinite Bus (SMIB) power system was investigated for evaluation of GCSC stabilizing controller for enhancing the overall dynamic system performance. PSO algorithm is employed to compute the optimal parameters of dampingcontroller. Eigenvalues of system under various operating condition and nonlinear time domain simulation is employed to verify the effectiveness and robustness of GCSC stabilizing controller in dampinglowfrequencyoscillations (LFO) modes.
FACTS (Flexible AC Transmission System) technology based on high speed power electronic devices is intro- duced for the improvement of controllability and opti- mal usage of the existing power system capacities. The latest generation of FACTS controllers uses the Solid State Synchronous Voltage Sources (SVS) concept that is introduced by L.Guygyi. The SVS acts like an best alternator means it generates 3-ø balanced voltages of variable phase angle and amplitude having funda- mental frequency. Voltage source converters (VSC) are used to implement SVS. In order to damp this in- ter area mode oscillations FACTS controllers  such as Unified power flow controllers(UPFC),Static series syn- chronous compensator (SSSC),Static synchronous compensator (STATCOM) etc. are used. The UPFC is one of the most flexible device, which is a grouping of SSSC and STATCOM, DC link capacitor acts as com- mon between both shunt and series converters. In this paper, a new control method using unified power flow controllers (UPFC) along with superconducting mag- netic energy storage system (SMES) [2,3,7,9] using fuzzy logic controller
To have sustainable growth and social progress, it is necessary to meet the energy need by utilizing the renewable energy resources like wind, biomass, hydro, co-generation, etc In sustainable energy system, energy conservation and the use of renewable source are the key paradigm. The need to integrate the renewable energy like wind energy into power system is to make it possible to minimize the environmental impact on conventional plant. The integration of wind energy into existing power system presents a technical challenges and that requires consideration of voltage regulation, stability, power quality problems. The power quality is an essential customer- focused measure and is greatly affected by the operation of a distribution and transmission network. The issue of power quality is of great importance to the wind turbine . There has been an extensive growth and quick development in the exploitation of wind energy in recent years. The individual units can be of large capacity up to 2 MW, feeding into distribution network, particularly with customers connected in close proximity . Today, more than 28 000 wind generating turbine are successfully operating all over the world. In the fixed-speed wind turbine operation, all the fluctuation in the wind speed are transmitted as fluctuations in the mechanical torque, electrical power on the grid and leads to large voltage fluctuations. During the normal operation, wind turbine produces a continuous variable output power. These power variations are mainly caused by the effect of turbulence, wind shear, and tower-shadow and of control system in the power system. Thus, the network needs to manage for such fluctuations.
generation control scheme in electric powersystems. Among the various types of load frequency controllers, the most widely employed is the conventional proportional integral (PI) controller. The PI, PID and Fuzzy-PID and ANFIS controllers are very simple for implementation and gives better dynamic response, but their performance deteriorate when the complexity in the system increases due to disturbance like load variation . Therefore, there is need of controllers which can overcome these problems. The artificial intelligent controllers like fuzzy and neural control approaches are more suitable in this respect. Literature survey shows that most of earlier work in the area of LFC pertains to interconnected reheat thermal power system. In this paper, the performance evaluation based on ANFIS, Fuzzy-PID and conventional PID for two area thermal interconnected system.