Objective To achieve high-efficiency vector control of permanent magnet synchronous motors PMSMs obtaining accurate rotor angle and speed information is essential as these two parameters are critically important. However sensor installation is often impractical necessitating the use of sensorless algorithms to estimate these parameters. Methods A sliding mode observer SMO known for its robustness and insensitivity to motor parameter variations was employed for angle and speed estimation. An improved SMO building upon the super-twisting sliding mode observer ST-SMO was proposed. This improved version employed a novel switching function sin arctan nx to replace the conventional switching function. The stabiliity of the system was proven using the Lyapunov stability criterion. Results The proposed improved SMO was simulated and evaluated. Results indicate that when the desired speed is set to 1 200 rad / min the steady-state speed oscillation range of the improved observer is confined between 1 199. 7 rad / min and 1 200. 2 rad / min. Conclusion The improved super-twisting sliding mode observer demonstrates faster response more effective chattering suppression and more accurate angle estimation. It offers a promising new approach for sensorless control strategies in PMSMs.