Overall power control strategy for small-scale WECS incorporating flux weakening operation

This study presents an overall power control strategy for control of fixed-pitch small-scale wind energy conversion system (WECS). The overall power control strategy is designed in such a way that the WECS efficiently operates for both underrated and overrated wind speeds. At underrated wind speeds, maximum power point tracking is achieved through a proportional–integral (PI) mechanical torque controller while no wind speed sensor is required. The PI mechanical torque controller together with a high-gain observer, estimating mechanical torque, generates the reference electrical torque. At overrated wind speed, the control strategy limits the generated power to rated power of generator via an anti-windup algorithm. In this case, the flux weakening strategy then is invoked. The optimal (reference) flux magnitude is provided by off-line numerically solving an optimisation problem. An space-vector modulation (SVM)-based direct-torque control (DTC) is used to track the electrical torque and flux references. In particular, the SVM-DTC is composed of a reference voltage vector calculator providing a desired voltage vector. The effectiveness of the proposed overall power control strategy is verified by applying the strategy to a commercial 10 kW wind turbine simulated in MATLAB/Simulink.