Application of policy iteration technique based adaptive optimal control design for automatic voltage regulator of power system

Abstract

This paper presents an adaptive optimal control design approach for automatic voltage regulator (AVR) system using policy iteration technique based adaptive critic scheme. The infinite horizon optimal control design using linear quadratic regulator (LQR) by solution of algebraic Riccati equation (ARE) and Hamilton-Jacobi-Bellman (HJB) equation require the complete knowledge of the system dynamics, and giving solution offline. Policy iteration technique which is based on actor-critic structure consists of two-step iteration: policy evaluation and policy improvement. The online policy iteration technique based control scheme gives online the continuous-time adaptive optimal control solution without using the complete knowledge of the system's internal dynamics. The knowledge of systems internal dynamics (i.e. matrix A) is not needed for evaluation of cost or the update of control policy; only the knowledge of input matrix B is required for updating the control policy. Thus this control scheme becomes partially model-free. The proposed control scheme has been implemented for AVR system for its both models neglecting and including sensor dynamics. The simulation results and performance analysis are presented to justify the robustness & effectiveness of control scheme. The comparative performance analysis of adaptive critic control scheme and LQR is also presented. © 2014 Elsevier Ltd. All rights reserved.