New field weakening strategy for AC machine drives for light traction vehicles

This paper presents new control strategy of vector-controlled ac machine traction drives intended for light traction vehicles in the field weakening region. Important contribution of the proposed field weakening method is improved drive immunity against oscillations of the input dc trolley wire filter, because our approach does not use the converter dc-link voltage feedback, as well as possible operation of the traction converter in the overmodulation (close to the six-step mode) with the conventional PWM. Theoretical conclusions and simulation results of both traction drive prototype and laboratory set-up are verified by experiments performed on the designed laboratory prototype of the induction machine trolley-bus drive. The proposed field weakening algorithm is in this paper generalized also for other control strategies - e.g. DTFC with constant switching frequency.