Position estimation capability on saliency-based sensorless drive of permanent magnet machine using different injection signals

This paper analyzes the position estimation capability on the saliency-based positon sensorless drive of permanent magnet (PM) machine. To obtain the rotor position information, high frequency (HF) voltage is persistently injected to provide the measurable spatial saliency signal. Although many saliency-based sensorless drives have demonstrated the comparable performance with low-end encoder-based drives, very few researches related to the position estimation accuracy based on different injection signals have published at this time. In general, saliency-based position estimation errors are primarily caused by the machine flux saturation and inverter dead-time. In this paper, both sine-wave and square-wave HF injection voltages are compared to evaluate the saliency-based position estimation error. It is shown that the sine-wave voltage injection results in the reduced effect on the inverter dead-time. By contrast, the square-wave voltage injection induces a higher saliency signal for the position estimation which is suited for the machines with low saliencies. A PM machine with the saliency ratio (L
_q
/L
_d
) of 1.41 is tested to verify all the analytical results based on two different injection voltage signals.