Investigations of a wave energy system by applying reactive control using stochastic analysis of the wave state

The power production of a point absorber wave energy converter is optimized in irregular waves by means of a stochastic analysis of the wave process. The dynamic response is assumed to be a stationary random process with zero mean value. Based on the assumption that the control moment constrains the velocity of the oscillator to be in phase with the incoming wave moment, the damping coefficient is expressed by the autocovariance function of the stationary excitation process. The paper examines four different control strategies by means of numerical simulations in the time domain. The effects on the structural loads are analyzed and compared for the different control cases. The load distribution show that the reactive system has larger moment amplitudes than the passive controlled system. However, for mild and relatively short waves the difference of the loading distribution seems to be small while for larger and longer waves the amount of reactive power which is fed into the system is significant. The structural loads i.e. the mechanical control moment and the inertia due to the angular acceleration are therefore increased.