Multi Stage Fuzzy Pid Load Frequency Controller in a Restructured Power System

In this paper, a multi stage fuzzy Proportional-Integral-Derivative (PID) type controller is proposed to solve the Load Frequency Control (LFC) problem in a restructured power system that operates under deregulation based on the bilateral policy scheme. In each control area, the effects of the possible contracts are treated as a set of new input signal in a modified traditional dynamical model. The multi stage controller uses the fuzzy switch to blend a Proportional-Derivative (PD) fuzzy logic controller with an integral fuzzy logic input. The proposed controller operates on fuzzy values passing the consequence of a prior stage on to the next stage as a fact. The salient advantage of this strategy is its high insensitivity to large load changes and disturbances in the presence of plant parameter variations and system nonlinearities. This newly developed strategy leads to a flexible controller with a simple structure that is easy to implement and therefore it can be useful for the real world power system. The proposed method is tested on a three-area power system with different contracted scenarios under various operating conditions. The results of the proposed controller are compared with the classical fuzzy PID type controller and mixed H2/H∞ controller through some performance indices to illustrate its robust performance.