Analysis and suppression of high-frequency inverter modulation in sensorless position-controlled induction machine drives

This paper focuses on the modulation of high-frequency (HF) currents required for sensorless position control of induction machine drives. Such drives can be realized by using the modulating effect of the rotor slots or from an engineered rotor saliency. Distortion due to saturation is known to cause a deterioration in the rotor position estimate. This paper reports a hitherto unreported distortion arising from inverter deadtime that will affect all sensorless drives using HF injection techniques. The deadtime distortion behaves in a similar way to that of saturation but has some specific characteristics that are presented in this work. Standard deadtime compensation techniques reduce but do not eliminate the distorting modulation. The residual distortion should be suppressed for good position estimation. The paper presents a new compensation strategy termed space modulation profiling which is effective in suppressing the HF modulations due to inverter deadtime and saturation saliencies. Experimental results show the sensorless drive under heavy load for zero-speed and transient operation.