Direct Torque Control of PMSM Drives for Common- Mode Voltage Reduction and Steady State Performance Improvement

Direct torque control (DTC) is characterized by the advantages of simple control structure, insensitivity to motor parameters and good dynamic performance. However, two key challenges have limited the control development. One is the relatively large torque fluctuation and high current distortion; the other is the high common mode voltage (CMV) generated by zero voltage vectors, which may cause damage to the motor and deteriorate the reliability of the motor system. To address these two main concerns, a new virtual vector- based DTC method is proposed in this paper. Firstly, two adjacent or opposite active vectors are used to synthesize discrete virtual vectors, and their sequence is uniformly arranged so as to avoid the CMV spikes resulting from dead-time effect. Then, the vector plane is divided into several subregions, and a look-up table is established to select a voltage vector according to the location of the reference voltage vector. The proposed control method not only inherited the simple control structure of DTC, but also demonstrated the merits of simultaneously improving the steady state performance of the motor and reducing CMV. Finally, comparative experiments verified the effectiveness of the proposed DTC method.