Power System Stabilizers Design for Interconnected Power Systems

This paper proposes a method of designing fixed parameter decentralized power system stabilizers (PSS) for interconnected multi-machine power systems. Conventional design technique using a single machine infinite bus approximation involves the frequency response estimation called the GEP(s) between the AVR input and the resultant electrical torque. This requires the knowledge of equivalent external reactance and infinite bus voltage or their estimated values at each machine. Other design techniques using P-Vr characteristics or residues are based on complete system information. In the proposed method, information available at the high voltage bus of the step-up transformer is used to set up a modified Heffron-Phillip's model. With this model it is possible to decide the structure of the PSS compensator and tune its parameters at each machine in the multi-machine environment, using only those signals that are available at the generating station. The efficacy of the proposed design technique has been evaluated on three of the most widely used test systems. The simulation results have shown that the performance of the proposed stabilizer is comparable to that which could be obtained by conventional design but without the need for the estimation and computation of external system parameters.

I. Introduction

One of the major problems in power system operation is related to the small-signal oscillatory instability caused by insufficient natural damping in the system. The most cost-effective way of countering this instability is to use auxiliary controllers called power system stabilizers (PSS), to produce additional damping in the system [1], [2]. The concept of PSS and their tuning procedures are well explored in [1]–[4]. The fixed gain stabilizers perform reasonably well if they have been tuned properly [5]. Though these stabilizers have simple robust structures, tuning them either by computer simulation modeling [2], [4] or by actual field tests [3] is an involved process which requires considerable expertise and also a knowledge of system parameters external to the generating station. These parameters may not be readily available and may vary during normal operation of the power system. Even in the case of single machine infinite bus model, estimates of equivalent line impedance and the voltage at the external bus are required. The PSS design also requires information of the rotor angle measured with respect to an external bus. These parameters cannot be measured directly and need to be estimated based on reduced order models of the rest of the system connected to the generator. If the available information for the rest of the system is inaccurate, the conventionally designed PSS results in poor system performance.