On the Controllability of an Active Mechanical Motion Rectifier for Wave Energy Converters

In this paper, the controllability of an active mechanical motion rectifier (AMMR) based power take-off (PTO) designed for wave energy conversion systems is analysed. The AMMR significantly increases the complexity of the energy-maximising PTO control problem, with a discontinuous connection between the wave energy converter (WEC) body and the generator system, where the controlling torque is applied. Also, the choice of switching points, governing the connection/disconnection, can be seen as control freedom, which could potentially be exploited. Overall, the analysis of such a hybrid system is complex, requiring the development of analysis tools to assess, quantify, and understand the effect of the design parameters of the system. To this end, in this letter, we develop new controllability results for such a system, giving a solid analytic foundation for the control design process. To illustrate the utility of the analytical results, a numerical example for a flap-type WEC, utilising an AMMR-based PTO and a linear controller for the generator, is presented.