Global Power System Stabilizer Research Articles

Application of Improved Quasi-Affine Transformation Evolutionary Algorithm in Power System Stabilizer Optimization

This paper proposes a parameter coordination optimization design of a power system stabilizer (PSS) based on an improved quasi-affine transformation evolutionary (QUATRE) algorithm to suppress low-frequency oscillation and improve the dynamic stability of power systems. To begin, the simulated annealing (SA) algorithm randomly updates the globally optimal solution of each QUATRE iteration and matches the inferior solution with a certain probability to escape the local extreme point. This new algorithm is first applied to the power system. Since the damping ratio is one of the criteria with which to measure the dynamic stability of the power system, this paper sets the objective function according to the principle of maximization of the damping coefficient of the electromechanical mode, and uses SA-QUATRE to search a group of global optimal PSS parameter combinations to improve the safety factor of the system as much as possible. Finally, the method’s rationality and validity were validated by applying it to the simulation examples of the IEEE 4-machine 2-area system with different operation states. The comparison with the traditional optimization algorithm shows that the proposed method has more advantages for multi-machine PSS parameter coordination optimization, can restrain the low-frequency oscillation of the power system more effectively and can enhance the system’s stability.

Analyses of Hopf Bifurcation Characteristics in Longitudinal Power Systems by Using a Nonlinear Coupled Vibration Model

Power system is a large dynamic system, which includes a lot of nonlinear elements. According to the nonlinear analyses using Hopf bifurcation theory, it can be detected that a limit cycle exists around an operating point, which may affect the global stability of power system significantly. The authors have proposed a numerical method to analyze the nonlinear characteristics in power systems by observing the power swing after some perturbation where the coefficients of nonlinear terms are determined by the least squares method. In this paper the method is modified for the application to a longitudinally interconnected power system including an excitation system to consider the inuence of the modal interaction on the nonlinear phenomena. In this method the system is approximated by a nonlinear coupled vibration model. Then the bifurcation characteristics are evaluated numerically based on the approximate model. The method has been applied to the low-frequency oscillation in IEEJ WEST10-machine system.

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

This paper addresses the problem of the stabilization of composite mode electromechanical oscillations of generators. A Hybrid PSS of the two-level structure including of a local PSS and a global PSS is introduced. Time-scale decomposition is applied to the decoupling of the local and global stabilization problems, where determination of the global (inter area) control law is based on slow-coherency aggregation. Composite mode electromechanical rotor oscillations are observed, in practice, with weakly interconnected power systems. These oscillations are characterized by local and inter-area modes. In certain cases of operating conditions and/or network topology, the damping of these oscillatory modes may be negligible or even negative. The existing approaches to the stabilization of power system are basically in decentralized way, and the objective of the stability measures are largely concentrated on the damping improvement of local modes by means of a power system stabilizer (PSS), using only the local information. However, for those systems with poorly or negatively damped inter-area modes, applications of the locally tuned PSS cannot bring a total stabilization to the system, and the inter-area oscillations remain unaffected or possibly building-up to excessive margins. In this paper we have introduced the idea of the Hybrid PSS which is of a two-level control structure with local and global inputs, as in Fig. 1. The desired supplementary control signal for composite mode oscillations is obtained by a weighted combination of the local and global (inter-area) stabilization signals.