A Novel Direct Torque Control Strategy for Doubly-Fed Wound Rotor Induction Machines

In this paper, a novel direct torque control of doubly- fed wound rotor induction machines is studied. A rotor unity power factor based direct torque control strategy is proposed. By keeping the rotor power factor to be one, a switching-table- based hysteresis direct torque control system is built and the corresponding rotor voltage vector table is obtained. The feasibility of the proposed method is tested through Simulink simulations. Such a control strategy show several significant advantages. As only the feedback signals of the rotor side are required by the control, the system is simple. Due to the unity rotor power factor, the capacity of the inverter is reduced to the lowest level. The stator voltage and current waveforms are kept sinusoidal, which reduces the harmonic pollution to power grids.