Analysis and improvement of pulsating current injection based sensorless control of permanent magnet synchronous motor

In the paper performances of the pulsating current injection based sensorless control of permanent magnet synchronous motor (PMSM) are analyzed theoretically and investigated by simulations. In the analyses, the effects of the speed EMF terms and the deviations between the actual high-frequency carrier currents and the commands, which results from the limited gain and bandwidth of the current controller, are all taken into account. It is shown that the pulsating current injection method can achieve stable position estimation in a wide speed range. But appreciable position errors will result at high speeds due to the cross-coupling effects of the speed EMFs and the tracking errors between the actual and command carrier currents. In order to improve the position estimation accuracy, three modified schemes are proposed and analyzed. Their validities are confirmed by simulations.