Damping controller design for power system oscillations usingglobal signals

This paper describes a new power system stabilizer (PSS) design for damping power system oscillations focusing on interarea modes. The input to the PSS consists of two signals. The first signal is mainly to damp the local mode in the area where PSS is located using the generator rotor speed as an input signal. The second is an additional global signal for damping interarea modes. Two global signals are suggested; the tie-line active power and speed difference signals. The choice of PSS location, input signals and tuning is based on modal analysis and frequency response information. These two signals can also be used to enhance damping of interarea modes using SVC located in the middle of the transmission circuit connecting the two oscillating groups. The effectiveness and robustness of the new design are tested on a 19-generator system having characteristics and structure similar to the Western North American grid     

Coordinated design of PSS and TCSC to mitigate interarea oscillations

Thyristor controlled series compensator (TCSC) as a promising series flexible AC transmission system (FACTS) device is generally used for controlling the real power flow in transmission lines. It can increase the system stability as the complementary functionality by minimizing the power oscillations. The effectiveness of TCSC in its primary and supplementary applications depends on the selection of its optimal location and defining a proper input signal. In this paper, a new method based on the active power sensitivity approach is applied to find the optimal location of TCSC. In addition, Hankel singular values (HSVs) and right half plane-zeros (RHP-zeros) analyses have been proposed to find the most appropriate stabilizing input signal for the supplementary functionality of TCSC to damp out the interarea modes of oscillation. Finally, the optimal design of power oscillation damper (POD) and simultaneous coordinated design of power system stabilizer (PSS) and POD are implemented separately in a large-scale power system. The tuning problem of POD-TCSC parameters as well as the coordinated POD-TCSC & PSS are converted to a multi-objective optimization problem and solved using particle swarm optimization (PSO) algorithm. The performance of the proposed method has been validated through eigenvalue analysis and nonlinear time domain simulation in a 16-machine 68-bus test system. The simulation results show a satisfactory robust performance with an excellent capability in damping of local and interarea power oscillations.     

Optimization method of P+ ω PSS parameters for stability and robustness enhancement in a multimachine power system

Recent steady increase of electric power demand causes power sources to be large and far from cities. Wide area power interchanges lead to larger and more complex power systems. This makes the network susceptible to poor damping power swing oscillations of relatively low frequencies which influence the whole system. This paper describes a newly developed generator's double input signal PSS (P+ ω input PSS) design method. Several power system conditions (power flow and/or power patterns) are considered to satisfy a well‐stabilized power system for each system condition. Major features of this method are: (1) Weighting factor for eigenvalue sensitivity of the oscillation mode is considered when the parameters of the PSS are updated during the optimization process. (2) The new method provides good results for the generator's local and interarea oscillation modes under peak and off‐peak power flow conditions. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 19–31, 2000     

Power system stabilization control based on the wide area phasor measurement

This paper presents a method of tuning power system stabilizers (PSS) in order to damp low‐frequency oscillations in a multimachine power system based on wide area phasor measurements. The authors have developed a method for detecting interarea low‐frequency modes from measured small oscillations associated with load fluctuations by approximating the oscillations as a coupled vibration model. In this paper, the coupled vibration model is extended to include the effect of PSS. PSS are tuned directly by using the extended model, since the model includes parameters of PSS. The advantage of this method is that steady state phasor fluctuations are available for tuning PSS and assessing the effect of the tuning control. That is, a large disturbance like a line fault is not necessary since the stability of major modes can be investigated directly by using eigenvalues of the extended model. The identification process does not require information on the input to the system for perturbation. Some numerical analyses demonstrate the effectiveness of the method by using phasor dynamical data obtained by a power system simulation package. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(1): 16–24, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20640     

Generator Coherency Using the Hilbert–Huang Transform

Coherency between generators is tracked, by examining the instantaneous phase differences among interarea oscillations and swing curves in disturbed multiarea power systems. Huang's empirical mode decomposition is applied to extract dominant oscillatory modes from interarea oscillations/swing curves. Hilbert transform on these modes yields their instantaneous phase. The coherency is thus revealed by the temporal evolution of the phase difference among interarea oscillations/generator swing curves. The technique is illustrated using simulations on a test system, as well as actual wide-area measurements.      

Slow-coherency based composite mode oscillatory stabilization bymeans of a hybrid PSS

The authors address the problem of the stabilization of composite mode electromechanical oscillations of electric generators. A hybrid PSS (power system stabilizer) with a two-level structure composed of a local PSS and a global PSS is proposed. A weighted combination of local and global control signals is used as the supplementary signal for the improvement of the damping characteristics of both local and interarea modes. Time-scale decomposition is applied to the decoupling of the local and interarea modes. Determination of the global control law is based upon a slow-coherency aggregated model     

基于微粒群优化算法的最优电力系统稳定器设计

传统电力系统稳定器的性能受其参数影响很大,为提高电力系统机电暂态模型的阻尼,文中提出了一种优化电力系统稳定器参数的新方法。该方法以两个特征值基目标函数为基础,采用改进的微粒群优化技术对电力系统稳定器进行参数优化。特征值分析和非线性仿真结果表明,经过参数优化的电力系统稳定器能有效抑制本地和区域间振荡,提高系统的鲁棒性。     

Optimal multiobjective design of robust power system stabilizers using genetic algorithms

Optimal multiobjective design of robust multimachine power system stabilizers (PSSs) using genetic algorithms is presented in this paper. A conventional speed-based lead-lag PSS is used in this work. The multimachine power system operating at various loading conditions and system configurations is treated as a finite set of plants. The stabilizers are tuned to simultaneously shift the lightly damped and undamped electromechanical modes of all plants to a prescribed zone in the s-plane. A multiobjective problem is formulated to optimize a composite set of objective functions comprising the damping factor, and the damping ratio of the lightly damped electromechanical modes. The problem of robustly selecting the parameters of the power system stabilizers is converted to an optimization problem which is solved by a genetic algorithm with the eigenvalue-based multiobjective function. The effectiveness of the suggested technique in damping local and interarea modes of oscillations in multimachine power systems, over a wide range of loading conditions and system configurations, is confirmed through eigenvalue analysis and nonlinear simulation results.     

A Hybrid Power System Stabilizer Using Neuro-identifier and Predictive Controller

This paper presents the development of a hybrid power system stabilizer (PSS) model designed to enhance the damping characteristics of a practical power system network representing a part of the Electricity Generating Authority of Thailand (EGAT) system. The PSS consists of a predictive controller and a neuro-identifier which has been developed based on the functional link network (FLN) model. A recursive on-line training algorithm has been proposed to train the neural network. Simulation results have been obtained under various operating conditions and severe disturbance cases that show that the proposed PSS can provide a better damping to the local as well as interarea modes of oscillations, as compared with a conventional PSS.     

Estimation of interarea electromechanical modes during ambient operation of the power systems using the RDT–ITD method

An accurate awareness of the properties of the interarea electromechanical oscillation modes is essential for the secure operation of the power systems. Previously, the Ibrahim time domain (ITD) method has been applied to estimate the interarea oscillation modes using ring-down signals caused by major disturbances (such as three phase faults). In this paper, through the combination of the random decrement technique (RDT) and the ITD method, the RDT–ITD method is proposed to estimate the interarea modes during ambient operation of the power systems, using random responses caused by random changes of the loads. The estimated parameters include the frequencies, damping ratios and mode shapes. Considering the fact that both the ambient excitations and the measurement noise are stochastic in nature, Monte Carlo simulations were conducted to evaluate the performances of the RDT–ITD method in a statistical way. Simulation results in the 16 machine nonlinear power system model, as well as comparison results with the RDT-Prony method, the NExT-ERA method and the Subspace method realized by N4SID (Numerical algorithm for Subspace State Space System Identification) show that the RDT–ITD method is promising in estimating the interarea modes during ambient operation conditions. The RDT–ITD method was also validated using real PMU measurements from Sichuan power grid of China.     

Parameter optimization of multimachine power system stabilizers using genetic local search

A genetic local search (GLS) algorithm for optimal design of multimachine power system stabilizers (PSSs) is presented in this paper. The proposed approach hybridizes the genetic algorithm (GA) with a heuristic local search in order to combine their strengths and overcome their shortcomings. The potential of the proposed approach for optimal parameter settings of the widely used conventional lead–lag PSSs has been investigated. Unlike the conventional optimization techniques, the proposed approach is robust to the initial guess. The performance of the proposed GLS-based PSS (GLSPSS) under different disturbances, loading conditions, and system configurations is investigated for different multimachine power systems. Eigenvalue analysis and simulation results show the effectiveness and robustness of the proposed GLSPSS to damp out local as well as interarea modes of oscillations and work effectively over a wide range of loading conditions and system configurations.     

Analysis of the inter-area mode phenomenon in power systemsfollowing large disturbances

The authors analyze interarea mode phenomena in stressed power systems, following large disturbances. It is shown that the interarea mode phenomenon could occur as a result of a nonlinear interaction of the natural modes of oscillation in the system. A technique for determining the interaction is developed and the machines participating in the interaction are identified. A procedure for predicting the onset of the interarea mode is presented. The technique was tested on two realistic sample test systems: a 50 generator system and a 126 generator system. The results of this analysis indicate that the procedure can detect the onset of the interarea mode phenomenon and also detect the machines which participate in the interacting natural modes of oscillation     

Robust decentralized multi-machine power system stabilizer design using quantitative feedback theory

A new robust power system stabilizer (PSS) design using Quantitative Feedback Theory (QFT) for damping electromechanical modes of oscillations and enhancing power system stability is proposed in this paper. The design procedure is carried out on a multi-input–multi-output (MIMO), non-minimum phase and unstable plant. A multi-machine electric power system with system parametric uncertainties is considered as a case study. To show the effectiveness of the QFT technique, the proposed method is compared with a conventional PSS (CPSS) whose parameters are tuned using the classical lead-lag compensation and genetic algorithms. Several nonlinear time-domain simulation tests indicate that the suggested control scheme is robust to the changes in the system parameters and also to successfully reject the disturbances. The results also show that the performance of the QFT method given in this paper is more desirable than CPSS and genetic algorithm (GA).     

An adaptive fuzzy logic power system stabilizer

The paper presents an adaptive fuzzy logic power system stabilizer (PSS) design for damping oscillatory electromechanical modes of oscillations and enhancing the first-swing synchronous stability margins. The novel design utilizes a multivariable damping signal vector consisting of machine speed deviation, rate of speed deviation, and voltage deviation. The design is based on a multizonal PID structure and fuzzy logic variable-gain scheduling to optimize the damping action. The fuzzy logic PSS is proposed for use in parallel with the conventional analog type PSS with added simple switching criteria. The two PSS blocks can be allowed independent, sequential, and/or combined operation with different effective stabilizing weighting. The paper investigates an individual conventional PSS, a rule based fuzzy PSS, and hybrid operation. The parallel operation of a conventional PSS and a fuzzy logic one provides optimal sharing of the damping action under small- as well as large-scale generation-load mismatch or variations in external network topology due to fault or switching conditions.     

Wide-Area Measurements-Based Two-Level Control Design Considering Signal Transmission Delay

In this paper the design of power system stabilizers for small-signal stability using phasor measurements is considered. An approach based on optimal control with structural constraints is proposed to design a two-level control structure. Time delays are included in the design. The method is combined with order reduction to ensure faster convergence of the design algorithm and to facilitate the choice of the weighting matrices for damping interarea modes. The control scheme is discussed and modal analysis and time-domain simulations of two Brazilian equivalent systems are performed to assess the control performance. The robustness to loss of communication links, topological changes, and variations of time delay is evaluated.      

利用单神经元模型改善概率PSS的阻尼特性

在电力系统稳定器(PSS)设计中,用概率方法可以考虑更多的系统运行方式。为了进一步改善PSS的鲁棒性,将单神经元模型引入PSS设计中,形成附加控制单元,附加控制参数可以随运行方式而变化。为确定参数变化方程,在一8机系统上进行了大量的试算和分析,考虑了不同配置方案,包括附加控制单元的数量和地址,本地和远方控制信号等。与固定参数的概率PSS性能相比较,引入单神经元模型后,各方案的阻尼特性均有不同程度的改善,临界阻尼比最大改善量达40%。     

Stabilization of inter-area and/or oscillatory modes in large-scale power system by voltage impedance power system (VIPS) apparatus based on decentralized control scheme

New technologies such as power electronics have made it possible to change continuously the impedance of a power system not only to control power flow but also to enhance stability. A power system incorporating a variable impedance apparatus such as a variable series capacitor (VSrC) and high-speed phase shifter (HSPS) is called VIPS (Variable Impedance Power System) by the authors. This paper proposes a novel control method of VIPS apparatus such as VSrC and HSPS installed at an interconnecting point for stabilizing inter-area unstable and/or oscillatory modes. The proposed design method of the control system is a kind of hierarchical decentralized control method of a large-scale power system based on a Lyapunov function. Under the proposed control scheme, each subsystem can be stabilized independently by local controllers such as AVR, speed governor and PSS, and then the whole interconnected system can be stabilized by VIPS apparatus taking into account interactions between subsystems. The effectiveness and robustness of the VIPS apparatus control are shown by numerical examples with model systems including a large-scale power system.     

New approach to power system stabilizer design

A generalized method for the design of excitation control or a power system stabilizer (PSS) based on complex frequency is described. The method selects PSS parameters such that exact assignment of eigenvalues associated with the mechanical modes of oscillation to desired locations is achieved. Numerical examples are used to illustrate the concepts of the proposed new technique.     

Assessment and Enhancement of Small Signal Stability Considering Uncertainties

This paper proposes a probabilistic small signal stability assessment (PSSSA) methodology based on the application of Monte Carlo approach for iterative evaluation, via modal analysis of small signal stability (SSS). Operation states represented by random values of generation and demand are analyzed. A probabilistic instability risk index based on cumulative probability distribution function of damping ratios of oscillatory modes is calculated, as well as a power system stabilizer (PSS) devices location index based on eigenvectors and participation factors, which are considered random variables. Moreover, the impact of long-distance power flows on oscillatory modes (OM) and how the damping of OM depends on the orientation and magnitude of power flows is investigated. Further, an additional index concerns qualitatively the determination of transfer capability as affected by small signal stability. PSSSA is tested on a reduced order model of New England–New York's interconnected system considering uncertainties around three different system conditions separately: highly loaded, fairly loaded, and lowly loaded. The results highlight the main advantages of PSSSA over deterministic SSS studies such as instability risk assessment, small signal stability enhancement through adequate PSS location, and the proposal of possible restrictions for transfer capability in order to avoid poorly damped oscillations in the face of the diversity in power system operation.      

Power system stabilizer design using Strength Pareto multi-objective optimization approach

Power system stabilizers (PSSs) are the most well-known and effective tools to damp power system oscillation caused by disturbances. To gain a good transient response, the design methodology of the PSS is quite important. The present paper, discusses a new method for PSS design using the multi-objective optimization approach named Strength Pareto approach. Maximizations of the damping factor and the damping ratio of power system modes are taken as the goals or two objective functions, when designing the PSS parameters. The program generates a set of optimal parameters called Pareto set corresponding to each Pareto front, which is a set of optimal results for the objective functions. This provides an excellent negotiation opportunity for the system manager, manufacturer of the PSS and customers to pick out the desired PSS from a set of optimally designed PSSs. The proposed approach is implemented and examined in the system comprising a single machine connected to an infinite bus via a transmission line. This is also done for two familiar multi-machine systems named two-area four-machine system of Kundur and ten-machine 39-bus New England system. Parameters of the Conventional Power System Stabilizer (CPSS) are optimally designed by the proposed approach. Finally, a comparison with famous GAs is given.