Reduced order observers for rotor position estimation of nonsalient PMSM

The paper discusses the problem of rotor position estimation for the nonsalient permanent magnet synchronous motor (PMSM) and presents two reduced order observers that are based on the machine´s model in the stationary reference frame. The first observer estimates the machine´s stator flux linkages and then computes the rotor fluxes and the rotor position. The second observer estimates the back emfs of the PMSM and allows for direct calculation of the rotor angle. Both methods are developed under the assumption that the speed of the motor is known (the motor´s speed is an input into the observers). The observers are designed in the framework of nonlinear control; their stability and rate of convergence is discussed. The methods proposed are directly applicable to rotor position estimation for sensorless nonsalient PMSM drives.