MPPT control of variable speed wind generators with squirrel cage induction machines

In order to realize maximum power point tracking (MPPT) control of wind energy generation system, it is necessary to regulate the wind turbine speed at an optimal tip-speed ratio (TSR). For obtaining the optimal tip-speed ratio, modern wind turbine controller usually uses wind speed information as a vital signal to implement the feedback of the controller. However, the rotor effective wind speed (EWS) cannot be measured by the anemometer installed at the front of the turbine. In this paper, we present two methods to estimate the rotor effective wind speed from the turbine torque and the turbine speed. Then, we utilize the estimated wind speed and the optimal tip-speed ratio to compute the generator reference speed. In the entire wind energy system, a back-to-back arrangement with two voltage source converters (VSC) has been considered: one on the machine side controlled by field oriented controller (FOC) and the other on the grid side controlled by voltage oriented controller (VOC). Finally, the comparisons of two estimation integrated with the wind energy system have been emulated to demonstrate good performance.