If Starting Switching Strategy for Sensorless Permanent Magnet Synchronous Motor Based on New Function

When the permanent magnet synchronous motor (PMSM) switches from the IF open-loop control stage to the dual closed-loop vector control stage, a reasonable switching strategy needs to be designed to avoid current shock and speed fluctuation at the switching moment. In order to make the motor switch safely and smoothly between the two stages, this paper proposes a new transition function to achieve smooth transition of position and current during the switching process. Firstly, in the low-speed region of the motor, an IF control strategy of speed open-loop and current closed-loop is adopted, and the phase relationship between the virtual synchronous coordinate system and the rotor synchronous coordinate system is analyzed. In the medium and high speed area, a position sensorless control method based on sliding mode observer is adopted. In order to solve the problem of unstable switching process, the current and position are transformed according to the new function law in the switching interval, thereby reducing the short-term highfrequency oscillation of the current caused by the switching moment. The experimental results of the switching method based on the traditional linear weighted algorithm and the proposed new transition function switching scheme are compared to verify the effectiveness of the switching method. The results show that this method can effectively reduce the current mutation and speed oscillation after the switching is completed during the switching process, and improve the success rate of switching.