Improved speed control of Permanent Magnet Synchronous Machine at overmodulation region

In Permanent Magnet Synchronous Machine (PMSM) drives, linear region, which is inside the inscribed circle of the voltage hexagon in the voltage plane, is mainly used for the stable operation. To enhance torque capability under the limited input DC link voltage, the region outside the inscribed circle of the voltage hexagon, known as overmodulation region, can be exploited in the flux-weakening operation. However, the operation of drive system in the overmodulation region cannot be free from the degradation of speed control performance. This paper presents investigations on control issues in the overmodulation region and proposes an algorithm for improving the speed control performance in the overmodulation region. The effectiveness of the proposed method is verified by computer simulations and experiments.