Variable Conduction Mode Control Method to Reduce Torque Ripple for Symmetrical Winding Multiphase Brushless DC Motor

Increasing the number of phases in a motor can enhance control freedom, offering more possibilities for high-performance motor drives. For the symmetrical winding multiphase brushless dc motor (BLDCM), this article proposes a variable conduction mode control method to reduce torque ripple. The proposed method divides the torque intervals based on two types of constraints: 1) equal copper loss and 2) equal phase current amplitude. It utilizes the torque reference value to identify the torque interval and selects the conduction mode that minimizes torque ripple within that interval. During motor operation, the conduction mode can be dynamically switched with load variations. By optimally arranging and combining different conduction modes based on the motor's torque output characteristics, this method significantly reduces torque ripple within each torque interval. This method does not require additional hardware circuits in general multiphase motor systems, making it simple and easy to implement. The validity of the proposed method is verified through experiments using a nine-phase BLDCM as a prototype.