Nonlinear Dynamic Modelling for the Novel Inverse-Pendulum Wave Energy Converter with a Constant-Pressure Hydraulic Power Take-off

Novel inverse-pendulum wave energy converter (NIPWEC) is an optional oscillating wave surge converter. It utilizes an adjustable internal mass to realize the wave–structure interaction system resonance and the efficient power generation. Several references have researched on its performance via wave flume tests or numerical simulations. However, the NIPWEC structure with a constant-pressure hydraulic power take-off (CPHPTO) has not been systematic investigated. This paper aims at the dynamic modelling and performance assessment of the NIPWEC with a CPHPTO. At first, a wave-to-wire nonlinear state space model (SSM) is constructed. Then, the SSM correctness is verified by comparing simulation results to the existing experimental/simulation data. Finally, the response curve analysis and performance assessment are implemented against different electric loads. Results show that the CPHPTO efficiency, output active power and wave-to-wire efficiency could all be weakened under the excessive resistance, vice versa. Besides, both the inductive and capacitive components possess the capability of reducing the values of the above three variables. According to the simulated efficiency values, NIPWEC can obtain the wave-to-wire efficiency of 0.4, when it is at a resonant state. In the future, we will further investigate the influence of different designed parameters on the NIPWEC operating performance based on the SSM.