Overmodulation of Constant-Switching-Frequency-Based DTC for Reluctance Synchronous Motors Incorporating Field-Weakening Operation

This paper presents a simple but effective overmodulation scheme for direct torque controlled reluctance synchronous motor (RSM) incorporating field-weakening (FW) operation. To overcome the problems of high torque ripples and variable switching frequency experienced by conventional direct torque control (DTC), constant-switching-frequency-based torque regulator is employed. By combining the proposed overmodulation scheme with this torque regulator, the dynamic torque response and constant power speed range of RSM drives are improved. Simultaneously, low torque ripples are obtained. Furthermore, an adaptive activation algorithm is proposed to activate overmodulation only when high torque output is demanded. This algorithm also contributes to ensure the stability of drives with overmodulation through effective flux regulation, which is essential for FW operations. The validity of the proposed method is verified by experimental results supplemented in this paper.