Improved Sensorless Control Method and Asymmetric Phase Resistances Determination for Permanent Magnet Synchronous Machines

This article proposes an improved sensorless control method for permanent magnet synchronous machines under phase resistance asymmetry. The proposed method acquires positive sequence current and voltage signals by applying a sequence component extractor and a double synchronous reference frame current control strategy. These signals can, then, be applied to improve the extended electromotive force based sensorless observer to eliminate the undesired second-order fluctuation in position and speed estimation due to asymmetric phase resistances. In addition, the resistance deviations, which may be due to asymmetric resistances and temperature variation, could introduce dc offset error in rotor position estimation. Therefore, a model reference adaptive system based resistance estimation is employed to compensate for inaccuracy of resistances. Moreover, from the information contained in the negative sequence voltages, the specific values of all asymmetric phase resistances can be estimated as well. Experimental and simulation results are provided to validate the proposed method.