New approach for the low-speed operation of PMSM drives without rotational position sensors

A new approach to the position sensor elimination of permanent magnet synchronous machine (PMSM) drives for low-speed operation is presented in this paper. Using the position sensing characteristics of the PMSM itself, the actual rotor position, as well as the machine speed, can be obtained even in the transient state. Since the essential back-EMF information is obtained from direct measurement during a special test cycle called MCDI, the operating speed range of the sensorless drives can be extended to 10 RPM. Moreover, the chronic starting problem of PMSM drives can be simply settled by the proposed algorithm. In order to verify the feasibility of the proposed scheme, experimental results in the low-speed range of about 10~100 RPM are also presented