Direct torque control of induction motor for railway traction in whole speed range

In this paper a new stator flux estimator based on voltage model for direct torque control (DTC) is proposed. The flux estimator, with simple structure, can observe the phase angle and amplitude of stator flux accurately and is robust to machine parameters variation in whole speed range. The selection method of voltage vector and the start-up strategy are also presented to make DTC suitable for low-speed range traction. In the high-speed range, the torque is regulated under square wave condition. In order to obtain good steady state and dynamic performance, a DTC scheme under square wave condition are proposed. All of the methods and schemes are implemented on a 500 kW converter and a 190 kW induction motor, and are approved to be effective by the simulation and experiment results.