Aiming at the problems of system chattering and low observation accuracy of the traditional full order sliding mode observer during operation, a full order sliding mode control strategy with controllable boundary layer is proposed. A normalized phase-locked loop is introduced for rotational speed estimation to avoid the effect of parameter variations on the estimated value and to make the rotor position identification more accurate. The stability of the algorithm is demonstrated using the Lyapunov equation. Finally, the reliability and accuracy of the improved full order sliding mode observer sensorless control strategy are verified through simulation and experiments.