Sensorless direct torque control for PM-assisted synchronous motors with injection high-frequency signal into stator flux reference frame

A new sensorless direct torque control method for PM-Assisted synchronous motor drives is proposed in this paper. The stator flux linkage amplitude and electromagnetic torque are the two controlled variables which are regulated in stator flux frame. Unlike the two most conventional sensorless methods at low speeds, high frequency (HF) rotating carrier voltage injection into stationary reference frame and HF pulsating carrier voltage injection into estimated rotor reference frame, in this presented method, a HF flux signal is superimposed into the amplitude of the flux reference, i.e., to the stator flux reference, and then rotor position is estimated by demodulating the flux responses coming from flux observer. The advantage of the proposed method is that the HF signal is closed loop controlled thanks to the high bandwidth of the flux loop and that low pass filter (LPF) in torque and flux feedback loop is not required. Experimental results validate the feasibility of the proposed sensorless control technique and prove that the rotor position can be estimated accurately in both steady states and dynamics.