A novel approach for sensorless control of PM machines down to zero speed without signal injection or special PWM technique

A novel approach for sensorless control of PM machines down to zero speed without signal injection or special PWM techniques is developed in this paper. Taking advantage of the low inductance, the current ripples of a PM machine under a conventional PWM excitation are measured to derive the information about the rotor position by inductance calculation or back-EMF estimation. This approach can be used to estimate the rotor position at standstill if the rotor saliency exists. No prior knowledge about the machine parameters is needed and no special detecting signal is injected to the machine in this approach. Sensorless control of a PM machine based on the proposed strategy has been investigated by comprehensive computer simulation. The experimental testing results verify the effectiveness of the proposed approach.