An Optimal and Non-Linear Speed Control of OWC Wave Energy Plant with Wells Turbine and DFIG

Abstract

This paper presents controller scheme to maximize the turbine output power and thereby improve the efficiency in oscillating water column (OWC) wave power plant equipped with Wells turbine and doubly fed induction generator (DFIG). The scheme is based on flow coefficient estimation and controller design for tracking of rotational speed. Initially, a linear reference tracking (LRT) approach is applied to achieve the maximized output power by establishing a linear relationship between reference rotational speed and input pressure drop. This follows implementation of fuzzy theory based maximum power point tracking (FMPPT) approach to provide the optimal speed reference. Then, a backstepping (BS) controller is designed to track reference rotational speed of DFIG so as to improve the output power. The BS controller is derived using Lyapunov stability theorem which ensures the stability of the overall closed loop system. The advantages of the proposed control scheme over conventional PI control and the uncontrolled system is demonstrated for regular waves and irregular waves. Finally, the FMPPT-BS control approach has been validated with JONSWAP irregular wave model.