Sensorless rotor position estimation of PMSM by full-order and sliding mode EMF observers with speed estimate

The paper discusses the problem of rotor position estimation for the nonsalient PMSM and presents a Full-Order (FO) observer and a Sliding Mode (SM) observer; both are constructed using a speed estimate. The observers are developed using the PMSM model in the stationary reference frame and use the motor voltages, currents and speed as inputs. The PMSM is treated as a time-varying plant. Convergence is analysed assuming that the speed signal is inaccurate - this corresponds to the situation when a speed estimate is used to obtain a sensorless observer. Under improper speed, the FO observer gives errors; however, the SM observer can be forced to converge by increasing the gains. The SM structure proposed allows design of a variety of sensorless observers.