Sensorless control of PMSM based on low frequency voltage injection at low speeds and standstill

Most sensorless control methods have problems when they are used in surface-mounted permanent magnet synchronous motor (PMSM) that has little salient effect. To solve this problem, a novel low frequency voltage injection method is developed in this paper. Low frequency rotating voltage vectors are imposed on the stator, and the current responses are analyzed to get the rotor position information. Different from high frequency voltage injection, electric torque produced by low frequency voltage would has enough time to move the rotor a little but not big enough to rotate the rotor. The electric torque, friction torque and the cogging torque together will make the rotor oscillate around an equilibrium point. The back electromotive force produced by the rotor movement would have effect in the current response, which is finally used in the rotor position estimation. A rotor position estimation structure based on phase lock loop (PLL) is designed to continuously estimate the rotor position at low speeds and some offline experiments and compensation are added to get more accuracy estimation results. Experiments have been finished on a 1.25 kW PMSM at low speeds and standstill, the correctness of the proposed method has been demonstrated.