Suppression of Current Fluctuations and the Brake Torque for PMSM Shutoff in Electric Vehicles

When a safety-related fault in the motor controller is detected, the torque output of the motor cannot be effectively shut off in time and an overcurrent occurs at the moment of switching. The advantages and disadvantages of the open circuit and active short-circuit methods are analyzed. Combining the advantages of these two operations, this paper proposes a new mixed voltage modulation method. It introduces a voltage modulation ratio that represents the duty cycle of the open circuit operation during a PWM period. This ratio is first set to a fixed value and gradually reduced to zero. The inverter is switched at a mixed operation and finally remains in the active short-circuit mode. The current can be quickly converged by a freewheeling diode of open circuit. After switching to active circuit, the brake torque is safety. The effectiveness of this shutoff method was verified by simulations and experiments. It shows that current fluctuations are suppressed and the torque output is also within a safety range. In addition, this shutoff method does not require any additional sensor information and is simple to implement.