Optimisation and control of a hydraulic power take-off unit for a wave energy converter in irregular waves

The optimisation of a wave energy converter hydraulic power take-off for sea states of varying wave amplitude, direction and frequency is a significant problem. Sub-optimal configuration can result in very inefficient energy conversion, so understanding the design trade-offs is key to the success of the technology. This work focuses on a generic point absorber type wave energy converter. Previous work by the authors has considered the optimisation of this device for regular waves to gain an understanding of the fundamental issues. This work extends the analysis to the more realistic case of irregular waves. Simulations are performed using an irregular wave input to predict how the power take-off will operate in real sea conditions. Work is also presented on a motor speed control strategy to maintain the maximum flow of electrical power to the grid, assuming the use of a doubly fed induction generator. Finally, the sizing of key components in the power take-off is considered in an attempt to maximise power take-off efficiency and generated power.