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.     

电力系统稳定器实现于调速系统之研究 第二部分：多机系统中特性分析

本文利用MIMO频域理论,通过引入附加阻尼比矩阵,论证了调速侧电力系统稳定器GPSS具有多机解耦特性,给出了多机电力系统中GPSS的设计方法和一个三机系统设计示例。理论分析和仿真结果均表明,基于相位补偿原理的单机系统GPSS设计方法可以推广于多机系统,从而,避免了多机PSS参数协调的难题,有效地抑制了系统中的增幅低频振荡和弱阻尼振荡。     

Damping enhancement of multimachine power system using adaptive generator control system with neural networks

The authors proposed a nonlinear adaptive generator control system with neutral networks for improving damping of power systems, and showed its effectiveness in a one-machine infinite bus test power system in a previous paper. The proposed neurocontrol system adaptively generates appropriate supplementary control signals to the conventional controllers such as the automatic voltage regulator and speed governor so as to enhance transient stability and damping of the power system. In this paper, the applicability of the proposed neurocontrol system to multimachine power systems is discussed. Digital time simulations are carried out for a 4-machine test power system, where one or several synchronous generators is equipped with the neurocontrol system. As a result, also in the multimachine power system, the proposed adaptive neurocontrol systems improve the system damping effectively and they work adaptively against the wide changes of the operating conditions and the network configuration.     

Stability assessment of multimachine power systems using multivariable frequency response methods

Two feedback representations of linearized models of power systems are presented. One features torque loops and the other exciter loops. The torque loops representation is used to study damping and synchronizing torque coefficients. In the power system community, stability of linear models is associated with positive damping torques. Design of controllers is based on maximizing damping torques. A previous result that used the Nyquist criterion showed that in a single-machine infinite-busbar system a positive damping torque is sufficient but not necessary for the system to be stable. This result is stated briefly and generalized to multimachine power systems using the generalized Nyquist stability theorem. A multimachine system is used to demonstrate the results. The excitation loops are also investigated and the role of system zeros explained.     

Optimization and coordination of damping controls for improvingsystem dynamic performance

This paper presents a global tuning procedure for FACTS device stabilizers (FDS) and power system stabilizers (PSS) in a multi-machine power system using a parameter-constrained nonlinear optimization algorithm implemented in a simulation program. This algorithm deals with such an optimization problem by solving a sequential quadratic programming using the dual algorithm. The main objective of this procedure is to simultaneously optimize pre-selected parameters of the FDSs and PSSs having fixed parameters in coping with the complex nonlinear nature of the power system. By minimizing a nonexplicit target function in which the oscillatory rotor modes of the generators involved and suing characteristics between areas are included, interactions among the FACTS controls under transient conditions in a multimachine power system are improved. A multimachine power system equipped with a TCSC and an SVC as well as three PSSs is applied to demonstrate the efficiency and robustness of the tuning procedure presented. The results obtained from simulations validate the improvement in damping of overall power oscillations in the system in an optimal and globally coordinated manner. The simulations also show that the stabilizers tuned are robust in providing adequate damping for a range of conditions in the system     

Transient stabilization of structure preserving power systems with excitation control via energy-shaping

In this paper, the transient stability of multimachine power systems based on structure preserving model (SPM) is considered. The interconnection and damping assignment passivity-based control (IDA-PBC) methodology is extended to solve the excitation regulation problem of SPM represented by a set of differential-algebraic equations. By shaping the total energy function via the introduction of a virtual coupling between the electrical and the mechanical dynamics of the power system, a decentralized excitation control law is proposed to ensure the asymptotic stability of the closed-loop system. The controller is proved to be effective in damping the oscillations and enhancing the system stability by the results of simulation research.     

Effects of large dynamic loads on power system stability

This paper investigates the critical parameters of power systems which affect the stability of the system. The analysis is conducted on both a single machine infinite bus (SMIB) system and a large multimachine system with dynamic loads. To further investigate the effects of dynamic loads on power system stability, the effectiveness of conventional as well as modern linear controllers is tested and compared with the variation of loads. The effectiveness is assessed based on the damping of the dominant mode and the analysis in this paper highlights the fact that the dynamic load has substantial effect on the damping of the system.     

Optimal placement and parameter setting of SVC and TCSC using PSO to mitigate small signal stability problem

This paper aims to select the optimal location and setting parameters of SVC (Static Var Compensator) and TCSC (Thyristor Controlled Series Compensator) controllers using PSO (Particle Swarm Optimization) to mitigate small signal oscillations in a multimachine power system. Though Power System Stabilizers (PSSs) associated with generators are mandatory requirements for damping of oscillations in the power system, its performance still gets affected by changes in network configurations, load variations, etc. Hence installations of FACTS devices have been suggested in this paper to achieve appreciable damping of system oscillations. However the performance of FACTS devices highly depends upon its parameters and suitable location in the power network. In this paper the PSO based technique is used to investigate this problem in order to improve the small signal stability. An attempt has also been made to compare the performance of the TCSC controller with SVC in mitigating the small signal stability problem. To show the validity of the proposed techniques, simulations are carried out in a multimachine system for two common contingencies, e.g., load increase and transmission line outage. The results of small signal stability analysis have been represented employing eigenvalue as well as time domain response. It has been observed that the TCSC controller is more effective than SVC even during higher loading in mitigating the small signal stability problem.     

Using Decoupled Characteristic in the Synthesis of Stabilizers in Multimachine Systems

A decoupled characteristic between the damping of a specific swing mode and the stabilizer gain of the corresponding machine in multimachine power systems is identified. Using this decoupled characteristic a power system stabilizer (PSS) synthesis approach which is based on the phase compensation concept is verified on a 9-machine system and the dynamic performance of this system is significantly improved. This method is proved to be effective, simple and it can provide useful guidances for the PSS field tuning.     

Pole placement by coordinated tuning of Power System Stabilizers and FACTS-POD stabilizers

This work presents the application of the Decentralized Modal Control method for pole placement in multimachine power systems utilizing FACTS (Flexible AC Transmission Systems), STATCOM (Static Synchronous Compensator) and UPFC (Unified Power Flow Controller) devices. For this, these devices are equipped with supplementary damping controllers, denominated POD (Power Oscillation Damping), achieving a coordinated project with local controllers (Power System Stabilizers - PSS). Comparative analysis on the function of damping of the FACTS, STATCOM and UPFC is performed using the New England System that has 10 generators, 39 buses and 46 transmission lines.     

Location and design of stabilizers in multimachine power systems

A new procedure for the design of decentralized power system stabilizers (PSS) in multimachine power systems (MMPS) is presented in this paper. In the proposed approach, the generators most effective for stabilizer applications are first identified using participation factors and mode controllability matrix. The method determines the parameters of stabilizers by assigning mechanical modes at desired locations. The algorithm uses transfer function matrix between inputs and outputs, to assign the mechanical modes.     

Load modelling in studies of power system damping

This paper considers the significance of load voltage dynamics in studies of power system damping. A generic model of dynamic loads is used to investigate the influence of active and reactive power dynamics on the damping of oscillations in a multimachine power system. The interaction between the load and the power system is explored in terms of load and system transfer functions. It is shown that the power system transfer function is composed of a static part and a dynamic part. The static part is derived from the power flow Jacobian. The investigations indicate that load voltage dynamics can significantly influence the damping of modal oscillations. Static load models can give quite misleading predictions of damping when loads actually exhibit dynamic behaviour     

Optimal Power System Stabilizers design via Cuckoo Search algorithm

Cuckoo Search (CS) algorithm is introduced in this paper for optimal Power System Stabilizers (PSSs) design in a multimachine power system. The PSSs parameter tuning problem is formulated as an optimization problem which is solved by CS Algorithm. An eigenvalues based objective function involving the damping ratio, and the damping factor of the lightly damped electromechanical modes is considered for the PSSs design problem. The performance of the proposed CS based PSSs (CSPSS) has been compared with Genetic Algorithm (GA) based PSSs (GAPSS) and the Conventional PSSs (CPSS) under different operating conditions and disturbances. The results of the developed CSPSS are verified through time domain analysis, eigenvalues and performance indices. Also, the effectiveness of the proposed algorithm in providing good damping characteristics is confirmed.     

Robust design of a damping controller for static VAr compensatorsin power systems

This paper presents a systematic procedure for the synthesis of a supplementary damping controller (SDC) for static VAr compensators (SVC) in multimachine power systems. The robust performance in terms of the structured singular value (SSV or μ) is used as the measure of control performance. A wide range of operating conditions are used for testing. Simulation results on standard test systems show that the resulting SDC effectively enhances the damping of the interarea oscillations, providing robust stability and good performance characteristics both in frequency domain and in time domain     

Stabilization control for multimachine system using decentralized H∞ excitation controller realizing terminal voltage control and damping control

In this paper, to achieve both damping of power system oscillation and terminal voltage control simultaneously on a multimachine power system, we propose a decentralized H_∞ excitation controller. In the proposed method, H_∞ control via the Normalized Coprime Factorization approach is used to achieve the proposed design idea. By the Normalized Coprime Factorization approach, the weighting function in H_∞ control design is simplified, and output feedback controllers that take into account the realities and constraints of the power systems are designed. The proposed controller is subjected to model reduction of H_∞ controllers, and is transformed to a discrete system to perform digital control by computer systems in consideration of application to a real system. We verify that the proposed excitation controller can achieve both damping of power system oscillation and terminal voltage control by computer simulations of a multimachine power system. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(1): 33–41, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10254     

Damping of system oscillatory modes by a phase compensated gas turbine governor

The proliferation of gas turbines in power systems increases the scope for taking advantage of mechanical torque control for improved network damping. This paper describes a phase compensated governor for a gas turbine and explores its potential contributions to system damping in a multimachine context. It is shown that the inclusion of phase compensation in the governor control loop is capable of achieving dynamic stability for the system without the need of a power system stabilizer (PSS) in the generator excitation control loop and without adversely influencing terminal voltage control. In addition, it is demonstrated that a phase compensated governor (PCG) is also capable of significantly improving transient stability and by complementing the effectiveness of a conventional PSS, enables a superior overall contribution to network damping.     

An Efficient Power System Stabilizer Design for Multimachine Systems

ABSTRACT

This paper presents a novel approach for the design of power system stabilizers (PSS) for both single-machine infinite-bus systems and multimachine systems. The method determines the parameters of the PSS such that all the eigenvalues corresponding to the mechanical modes of the machines are assigned exactly to pre-specified locations in the complex plane. In the case of single-machine infinite-bus systems, the extra design freedom available in the second-order PSS is utilized to shift the unassigned eigenvalues to stable locations. In multimachine systems, the extra design freedom available in each PSS is effectively made use of to achieve fast convergence. Numerical examples are worked out to illustrate the proposed technique.     

Analysis of a local transient control action by partial energyfunctions

A partial energy function is used to quantify the energy of a local transient control action. The function is used to analyze the energy transactions of a single generator in a multimachine power system. This is in contrast with a global energy analysis of the system. Special attention is drawn to an explanation of damping as being caused by tuned control policies. Negative damping is seen as the result of tuned controllers that increase power flows during the backswing more than during the foreswing     

A DECENTRALIZED MRAC-BASED PSS FOR MULTIMACHINE POWER SYSTEMS

ABSTRACT

A digital PSS design technique for multimachine power systems suitable for easy integration into the power system computer control hierarchy at the generating plant level is presented in this paper. The adaptive PSS design algorithm is based on a decentralized model reference adaptive control concept using a Lyapunov function technique. The effectiveness of the proposed technique is demonstrated on a multi-machine power system using computer simulation studies. Results obtained show an improvement in the overall system damping characteristics.     

AN EFFICIENT METHOD OF SYSTEM MATRIX FORMULATION FOR MULTIMACHINE POWER SYSTEMS WITH STATOR AND DAMPING WINDINGS TRANSIENTS INCLUDED

ABSTRACT

In this paper an efficient method of system matrix formulation for multimachine power systems with stator and damping windings transients included is presented. A singular perturbation analysis of the synchronous machine equations in the (d, q) reference frame reveals that reduced order linearized model of multi-machine power systems can be derived systematically from the fundamental machine equations. The application of the developed model in Small Signal (Dynamic) Stability Study of the power system of Serbia is given. The valuable discussion on the practical implementation of the models and dependence on the exciter type is given, too.