Abstract: With the purpose of improving the performance of sensorless control system of permanent magnet synchronous motor (PMSM), an improved sliding mode observer based on stator resistance online identification is proposed. These ctional hyperbolic tangent function is adopted as switching function, combined with variable sliding mode gain to weaken the high frequency chattering. Through the use of Lyapunov stability theory, the stator resistance online identification is adapted for improving the estimation accuracy of observer. Fractional order phase-locked loop is employed to estimate the rotor position and speed information from observed back EMF so that computing complexity caused by traditional phase compensation can be effectively avoided. The experimental simulation results indicate that the improved sliding mode observer can effectively inhibit the system chattering as well as accurately estimate the information of motor speed and rotor position.

Key words: sliding mode observer, variable sliding mode gain, sectional hyperbolic tangent function, fractional order phase-locked loop