Variable speed and constant frequency control of hydraulic wind turbine with energy storage system

Abstract

To eliminate the adverse effect of the fluctuation and intermittence of wind power on the quality and stability of electrical power system, an energy storage system is introduced into the closed-loop hydraulic system of hydraulic wind turbine for the first time. The whole hydraulic system consists of a fixed displacement pump, a variable displacement motor, two proportional control valves and an energy storage system. The energy storage system absorbs or releases oil as the wind fluctuates. When the wind suddenly disappears, the generator can continue to produce electrical energy by means of the discharge of the hydraulic energy stored in the energy storage system. On the basis of modelling all hydraulic components, the simulation model of the hydraulic system is established. A new control method is presented within this article, which keeps the motor speed constant to generate constant frequency electrical power when the rotational speed of the wind wheel changes. Ultimately, simulations under the two conditions of step and sine wind wheel speeds are done. The simulation results demonstrate how the motor, the proportional valves and the energy storage system work together when the wind wheel speed varies and also prove validity of the control method we designed.