Sensorless control of surface-mounted permanent-magnet synchronous machines for low-speed operation based on high-frequency square-wave voltage injection

This paper proposes a high-frequency signal injection-based position estimation scheme for surface-mounted permanent-magnet synchronous machines (SPMSM) operating in the low-speed range. A square-wave voltage vector is injected in the estimated rotating reference frame. The rotor position information is then extracted from the envelopes of the resulting induced high-frequency currents in the stationary reference frame. The proposed position estimation method has almost no dependence on machine asymmetric properties and, therefore, is well suited for SPMSM applications. Simulation results are provided to verify the effectiveness of the proposed method from 1 Hz to 50 Hz electric fundamental frequency under all load conditions. Experimental results on a 2.4-kW SPMSM in both sensorless speed and torque controls are also provided to validate the proposed method. The sensorless speed control can be achieved as low as 0.3 Hz electric fundamental frequency.