Simple and Low-Model-Dependent Strategy for the Economic and Safe Control of Direct-Drive Wave Energy Converters

For engineering application and commercialization, a wave energy converter (WEC) should harness as much wave energy as possible to improve its economy and maintain each component works within their physical constraints for safe operation. Model predictive control (MPC) can maximize wave energy extraction under constraints for the direct-drive WEC. MPC requires accurate modelling parameters, wave prediction and complex computation, while these can hardly be guaranteed in real application. Besides, researchers generally take position and force constraints into consideration, while power constraint is neglected. In this work, we analyze the power extraction characteristics under constraints and propose a strategy to realize economic and safe control of WECs by decoupling it into different control modes of a permanent magnet synchronous generator (PMSG). In this way, the control is simple and low-model-dependent and power constraint can be also maintained. The strategy is put through comprehensive simulation tests with MPC as the benchmark, and it is proven to be effective under various wave conditions and constraint settings. Furthermore, experimental tests are carried out for a prototype device in a wave tank laboratory and these tests validate the applicability, effectiveness, and robustness of our strategy.