Abstract
Power system stabilizers (PSS) have been widely used to enhance damping due to the electromechanical low frequency oscillations occurrence in power systems. In this paper, a new method is used for the online tuning of parameters of conventional power system stabilizers (CPSS) using fuzzy logic. Fuzzy logic enables mathematical modeling and computation of some nonlinear parameters of the system, which are usually, derived empirically by utilization of expert knowledge rules. Various literatures has shown that fuzzy logic controller is one of the most useful methods for expert knowledge utilization. This type of controller is adaptive in nature and can be used successfully as a power system stabilizer. The design of fuzzy logic controllers is mainly based on fuzzy rules and input/output membership functions. Simple and efficient clustering algorithms allow data classification in distinct groups using distance and/or similarity functions. In the present paper, the optimum generation of fuzzy rules base using Fuzzy C-means (FCM) clustering technique is used. In fact, data are classified and the number of fuzzy rules which depends on convergence radius is determined. Finally, the performance of proposed FCM controller is compared with that of conventional controller. The active power, reactive power and bus voltages used as inputs to the fuzzy logic network based power system stabilizer and the parameters of the optimum stabilizer , i.e. gain factor as well as time constants of the lead/lag compensator, are the outputs of the proposed system. The design method has been successfully implemented on a single machine power system connected to an infinite bus over various operating conditions.
Highlights
The performance of excitation systems and high gain Automatic Voltage Regulator (AVR) in terms of transient stability improvement and normal performance of the system is very desirable, but these excitation systems with high gain and fast action can cause system instability. This type of instability known as low frequency oscillation (LFO) in the range of 0.2-3 Hz reveals negative impact of excitation systems on utilization of a power system
The input can be a signal of frequency error, speed error, electric power, and/or a combination of these signals and the output signal of the stabilizer is applied to the generator excitation system
We use a simplified dynamic model of a power system, i.e. single machine system connected to an infinite bus (SMIB) as shown in Figure 1 [20]
Summary
We use a simplified dynamic model of a power system, i.e. single machine system connected to an infinite bus (SMIB) as shown in Figure 1 [20] This system includes a synchronous generator with a fast acting excitation system which its rated parameters are given in [20,21,22]. Considering the CPSS block involving a gain KSTAB and a two stages lead/lag block corresponding to T1 and T2 time constants, the linearized equations of the system can be written as the following state equations from Figure 2 (because of papers limitation, we ignore the computational details):.
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