Abstract
In this paper, a feedback control strategy for a wave energy converter (WEC) with no prediction is proposed that provides performance rivaling a prediction-based controller, even when assuming perfect prediction. This innovative control scheme is derived first by abstracting the WEC in the same structure as an electrical circuit and by applying the Jacobi's maximum power transfer law to optimize WEC power absorption. By considering the implementation of complex conjugate control problem over a finite bandwidth, a causal controller can be realized. This causal controller can be defined such that its frequency response follows that of the complex conjugate controller as closely as possible using fitting techniques such as system identification. This suboptimal controller requires no prediction and only the device velocity needs to be measured to calculate control signals. Additionally, a model predictive controller (MPC) is designed to handle constraints with minimal (1-step) prediction. In implementing this MPC, prediction of wave elevation is not required either and the standard MPC block available in the MathWorks MPC toolbox can be employed, which is of great importance for practical applications. The MPC behaves as a predesigned causal controller and also acts as a supervisory controller to prevent the device from hitting end-stops. The performance of the proposed causal controllers and the MPC is compared with the complex conjugate controller in terms of the mean power absorption and it is shown that more than 90% of the theoretical maximum can be achieved.