Restarting control of free-running interior permanent magnet synchronous motor under position sensorless control

In some practical interior permanent magnet synchronous motor (IPMSM) traction applications, it is essential for the free-running IPMSM to fast and smoothly return to its normal operation after intermittent power interruption. In this paper, a creative restarting strategy for free-running IPMSM under position sensorless control is proposed, in which a reasonable restarting process based on three steps is designed. In the restarting process for position sensorless control, the initial rotor speed and position are needed. In first step, a proportional resonant (PR) based controller is applied to regulate the stator current to zero, then initial rotor speed and position are estimated with a PLL-based observer for the subsequent position sensorless control. Next, a zero-torque control method is used to refine the estimated results in the first step to improve the estimation accuracy. Finally, a hybrid position sensorless control method is utilized to restore the IPMSM to normal operation. Compared with current control techniques, the proposed strategy is more parameters robust and can suppress the inrush current during the restarting process, and is able to fast restore a free-running IPMSM to normal operation within 350 ms. Simulation and experimental research have been conducted to validate the effectiveness of the proposed solution.