An Online Optimal Phase Current Derating Method With Arbitrary Current Limits for Multiphase Motors in Subnormal Health

Abstract

Existing fault-tolerant control methods for multiphase motors mainly focus on motor operation postopen circuit fault but fail to sufficiently address the subhealthy state of the motor, such as detecting over-temperature of specific phase windings or inverter bridge legs. Hence, we propose an active phase current derating (PCD) fault-tolerant control method, capable of proactively reducing phase currents of subhealthy phases upon detection of over-temperature of the motor's windings or the inverter arms to delay or even prevent the onset of irreversible thermal damage. Compared to the conventional three-phase-based derating method, this approach permits individual derating of subhealthy phases, enhances torque output range, reduces stator copper losses, and offers greater versatility for multiphase motors with different number of phases, especially for motors where the number of phases is not a multiple of three. Additionally, we propose an online algorithm for calculating current references during derating, tackling the challenge of extensive offline storage in microcontrollers. The proposed method is experimentally validated using a nine-phase motor.