Optimization Design of MTPA Control Strategy for MMC Medium Voltage PMSM Drive

In medium-voltage Permanent Magnet Synchronous Motor (PMSM) drive systems, the Maximum Torque per Ampere (MTP A) control strategy is commonly employed under low-speed operating conditions to maximize torque per unit of current. However, traditional MTP A control neglects the impact of Back Electromotive Force (BEMF) variations when calculating the current reference value, resulting in increased stator current magnitude at low speeds and reduced efficiency. Therefore, this paper proposes an improved MTP A control method for low-speed operation in medium-voltage PMSM drive with Modular Multilevel Converter (MMC). Firstly, based on the stator voltage state equation of the PMSM and the current calculation equation of MTP A control, it is revealed that traditional MTP A control does not account for the effects of BEMF variations, leading to actual stator current magnitudes exceeding theoretical values during low-speed operation. Then, an improved MTP A control method that considers the effects of BEMF variations is proposed, achieved through the optimized design of correction factors for voltage modulation waves. By adjusting the correction factors, it ensures constant output torque while adjusting MMC output voltage, thereby reducing stator current magnitude and enhancing motor operational efficiency. Finally, the feasibility and effectiveness of the proposed method were confirmed by simulation results. The results of simulation prove that the proposed method can significantly improve the efficiency of PMSM during low-speed operation.