Improving Wave-to-Wire Efficiency of Direct-Drive Wave Energy Converters With Loss-Aware Model Predictive Control and Variable DC Voltage Control

Existing advanced controls for direct-drive wave energy converters (DDWECs) have primarily focused on the maximization of mechanical energy capture, rather than the net electricity generation. In this article, a detailed electrical loss analysis is carried out theoretically and experimentally, and the results indicate that the wave-to-wire (W2W) efficiency will be compromised if electrical losses are neglected in controller design. Accordingly, a novel control strategy is proposed, which consists of a) a loss-aware model predictive control (MPC) that balances between maximization of mechanical energy and efficient mechanic-to-electric conversion and b) a variable dc voltage control that mitigates the switching and pulse-width-modulation (PWM)-induced losses. A full DDWEC testing platform comprising a WEC prototype and a power-electronic converter with an embedded controller is established, and the improvement of power generation, by means of incorporating electrical losses of the entire W2W chain in control, is validated through wave tank testing for the first time. In particular, the electrical losses have a significant impact on the electricity output under irregular waves, while the proposed controller can achieve an electricity output increase of over 150%.