Valve shifting time in a digital fluid power system: Energy efficiency versus fatigue loading

A discrete fluid power force system has been proposed as a possible technology for improvement of the energy production of wave energy converters. Discrete force changes may however increase the fatigue loading experienced in the wave energy converter. Various research projects have studied how force oscillations in discrete fluid power systems may be avoided however some system limits sets bounds for the effectiveness of the developed algorithms. In the current study the correlation between force shifting time and fatigue loading is investigated by simulating a discrete fluid power power take-off (PTO) system. The force applied by the PTO system is measured during 100 wave periods and transformed to an equivalent load force. This equivalent load force is compared for various valve shifting times and compared to the energy production. The study shows a request for a trade-off between energy production and the equivalent load.