Discontinuous Active Short Circuit Strategy for Improved Safe State of PMSMs

A closed-loop active short circuit (ASC) method is developed for permanent magnet synchronous motor (PMSM) to suppress the transient oscillating current and torque. ASC inherently shuts down the inverter and motor side and is used as a safe state in electric drive systems based on PMSM. However, when the motor has an ASC at medium/high speeds, the system has insufficient damping, resulting in overcurrent and oscillating currents. To mitigate it, another safe state, freewheeling (FW), is injected into the ASC operation. The output voltage determined by the motor current angle in FW operation was straightforwardly derived. Then, a modulation method with two safe states is proposed by combining ASC and FW operation. An appropriate FW time should be calculated to avoid dc-link overvoltage due to FW. For this reason, a d-axis current feedback algorithm with a high-pass filter (HPF) was implemented. The proposed algorithm was analyzed by a root locus method to improve the damping of the system. In addition, the unstable FW voltage angle region was calculated using the Routh–Hurwitz criterion. The proposed method is demonstrated by simulations and experimental results at 2400 rev/min.