Abstract: Aiming at the problem of speed fluctuation caused by periodic torque ripple and parameter sensitivity of permanent magnet synchronous motor at low speed, a compound suppression strategy of speed fluctuation is proposed. An improved linear active disturbance rejection controller combining an improved linear extended state observer and a second-order infinite impulse response Butterworth high-pass filter is designed in the speed loop. Among them, the improved linear extended state observer effectively compensates the lag problem of traditional linear extended state observer for medium and high frequency periodic disturbance observation by using the phase advance characteristic of differential. The second-order infinite impulse response Butterworth high-pass filter can accurately separate and filter out the high-frequency measurement noise in the improved linear extended state observer speed observation value, and compensate the design through the linear error feedback control law, which solves the contradiction between the observer bandwidth improvement and noise amplification in the traditional active disturbance rejection control. The current loop adopts a model-free predictive control strategy based on the ultra-local model extended state observer, which effectively reduces the dependence on the accurate value of the motor parameters, reduces the current tracking error, and improves the robustness of the system. The experimental results show that compared with the traditional proportional integral double closed-loop control and the speed loop linear active disturbance rejection control, the composite control method reduces the speed fluctuation amplitude by about 88.8% and 37% respectively, which verifies its superiority in improving the stability of permanent magnet synchronous motor at low speed.