Optimum design of gearbox ratio for the electrical drive train of hinged-type wave energy converters

For hinged-type wave energy converters (WECs) that use electrical drive trains as their power take-offs (PTOs), the gearbox ratio is a key parameter to be designed for optimal energy conversion performance. Here we take the kW-scale multi-float M4 with electrical drive train as a case study. Firstly, an integrated hydrodynamic-electrical WEC-PTO model is built. Then, numerical simulations are carried out with realistic irregular wave inputs to investigate how different values of the gearbox ratio influence electrical power recovery, copper loss and constraint violations of the system. Although reliable, this design method requires simulations to be run repeatedly on a time domain WEC-PTO model, which is not computationally efficient. To reduce design and computational efforts, a new design method is also proposed. This method decouples the integrated dynamics between the WEC platform and the PTO. The effect of varying design parameters is extracted as consequential torque-speed constraints so that simulations can be run only with the WEC’s hydrodynamic model, dramatically accelerating the PTO design process. The effectiveness of the proposed method is validated against results obtained from WEC-PTO model based simulations, using the design of gearbox ratio as an example.