A NEW METHOD OF PREDICTIVE DIRECT TORQUE CONTROL FOR DOUBLY FED INDUCTION GENERATOR UNDER UNBALANCED GRID VOLTAGE

In this paper, a new predictive direct torque control (PDTC) method is presented for doubly fed induction generator (DFIG) under unbalanced grid voltage. In PDTC, the future behavior of the system is first predicted using the system model, the appropriate voltage vector is then selected using an optimized cost function in each control period. This method is simple and has excellent steady-state and transient performance, because uses from both predicted and reference values. The main advantages of proposed method are that all of the voltage vectors examine in cost function and the voltage vector that minimizes cost function will be applied during the next sampling period. Also, two control targets presented for unbalanced condition. The first target eliminates electromagnetic torque oscillation and the second target eliminates active power pulsations. The simulation was conducted on a 1 MW DFIG and results shows the effectiveness and robustness of new DTC method. It can be seen that the torque and flux ripples are reduced and their transient response are within a few milliseconds.