A novel dynamic overmodulation strategy for fast torque control of high saliency ratio AC motor

This paper describes the dynamic overmodulation strategies for the fast torque control of high saliency ratio AC motor. In the case of the high saliency ratio AC motor, the dynamic control of both d- and q-axis currents is required for the fast torque control with optimal efficiency. But because the stator inductance is designed large enough to generate desired reluctance torque, in transient operation with high current control bandwidth, the d- and q-axis current regulators are easily saturated even at low speed. By the conventional overmodulation strategies, owing to the high saliency ratio, the performance of the current regulator is more severely deteriorated than the case of the nonsalient motor. In this paper, the drawbacks of the conventional overmodulation strategies are investigated and a dynamic overmodulation strategy is proposed to improve the current response at fast transient and an algorithm for the effective implementation is given. The control performance of the proposed strategy is confirmed by the computer simulation and experiments with a 3.75 kW axially laminated synchronous reluctance motor and an IPMSM for 42 V integrated starter generator (ISG).