On the power fluctuations of wind turbines fitted with a hydrostatic transmission

In this study, we analyzed a hydrostatic transmission that replaces the heavy, stiff current drive train. The energy converted is transmitted through the less stiff fluid system from a pump coupled to the rotor and delivered to a hydraulic motor at ground level that drives the electric generator. The low stiffness of the hydrostatic transmission is achieved by integrating a gas accumulator so that the amplitude of the load fluctuations can be reduced compared with a base configuration, diminishing the fatigue loads on the wind turbine. A kW scale hydraulic wind turbine placed alongside a standard counterpart setup was used to compare the power generation response under the same atmospheric conditions. They are assessed by changes in the turbine transfer function of the power spectrum (Tobin et al., 2015). The overall efficiency of the hydraulic transmission reached roughly 80% and the torque amplitude fluctuations lowered by about 40% with the hydraulic architecture also tested under controlled conditions using a cyber-physical system. Hydrostatic transmission for offshore applications has the potential to reduce LCOE by an order of 5 to 18%.