Wave to wire power maximisation from a wave energy converter

In this paper a back-to-back voltage source converter controlled linear permanent magnet generator (LPMG) is utilised as the power take off (PTO) for a point absorber wave energy converter system (WEC). It is shown that reactive control which seems promising when an ideal PTO is assumed, is actually infeasible with a real PTO as the electrical losses of the LPMG are excessive when the wave frequency is lower than the natural frequency. A Zero Order Hold (ZOH) and First Order Hold (FOH) Model Predictive Control (MPC) which maximises the mechanical power is first utilised. The two MPC systems show that more electrical power is extracted for a lower horizon when the MPC is optimised for mechanical power. The electrical losses from the LPMG and voltage source converter (VSC) are then incorporated in the cost function of the MPC systems and demonstrates significant improvements in the electrical power extracted when compared to the electrical power extracted via mechanical power optimisation. PTO force and heave displacement constraints are then incorporated into the optimisation, to further demonstrate the limitations of performance when a realistic PTO is utilised. It is shown here that the electrical power can be maximised, whilst the PTO force and heave displacement are shown to be within limits. The power quality from the ZOH MPC is then compared to the power quality from the FOH MPC