Robust field weakening algorithm for vector-controlled induction machine traction drives

This paper focuses on the field weakening operation of the vector-controlled induction machine drive intended for traction application (trams and trolley-buses). New field weakening strategy based on the modulation depth control is presented. This strategy makes possible operation of the converter in the linear modulation area as well as in the overmodulation area (close to the six-step mode), even if the common carrier-based PWM is employed. The proposed algorithm is simple, independent of the machine parameter variations and provides maximum output torque. Very important contribution is that this method does not use feedback from the dc-link voltage. It significantly improves the immunity of the traction drive against the oscillations of the input dc-link filter. The simulation results presenting behaviour of the traction drive prototype of power of 160kW and the experiments performed on the laboratory prototype confirm the proper function of the proposed field weakening strategy.