PI controller relay auto-tuning using delay and phase margin in PMSM drives

This paper presents an auto-tuning method for a proportion plus integral (PI) controller for permanent magnet synchronous motor (PMSM) drives, which is supposed to be embedded in electro-mechanical actuator (EMA) control module in aircraft. The method, based on a relay feedback with variable delay time, explores different critical points of the system frequency response. The Nyquist points of the plant can then be derived from the delay time and filter time constant. The coefficients of the PI controller can then be obtained by calculation while shifting the Nyquist point to a specific position to obtain the required phase margin. The major advantage of the auto-tuning method is that it can provide a series of tuning results for different system bandwidths and damping ratios, corresponding to the specification for delay time and phase margin. Simulation and experimental results for the PMSM controller verify the performance of both the current loop and the speed loop auto-tuning.