Model predictive control of wave energy converters with prediction error tolerance

Sea wave energy converter (WEC) control is a non-causal optimal control problem, and the control performance relies on the accuracy of the prediction of incoming wave profile and the fidelity of the control-oriented model. To maximize energy conversion in real scenario, three issues should be fully considered: (a) the existing wave prediction methods inevitably introduce prediction errors, which degrades the control performance; (b) the model mismatch between the linearized state-space model and the hydrodynamic model also affects the control performance; (c) safe operations with limited power take-off (PTO) should be ensured to rule out the possibility of device damages. To explicitly deal with these problems, this paper proposes a novel control scheme to maximize the energy output subject to inaccurate predictions, model mismatch and multiple constraints. This is achieved by applying a feedback model predictive control (MPC) to handle the constraints and a compensator to cope with the prediction error and model mismatch. Due to the extra compensation input, the state and input constraints of MPC subsystem are further tightened to ensure constraints on both the states and the control input to be satisfied. Theoretical proof and simulation results show that the proposed controller is robust to achieve the maximal energy output subject to inaccurate prediction and inaccurate control-oriented model.