Analysis and suppression of inverter clamping saliency in sensorless position controlled induction machine drives

This paper focuses on a specific modulation that affects the high-frequency injection required for sensorless position control. Sensorless position control of induction machine drives can be realized by using the modulating effect of the rotor slots or that from an engineered rotor saliency. Saturation-induced saliencies are known to cause a deterioration of the rotor position estimate. In this paper, a new cause for the distortion of the position estimate is presented that results from the inverter deadtime. The distortion affects potentially all inverter-driven sensorless drives using high-frequency (HF) signal injection. Since the HF voltage injection is only applied in open-loop, the actual HF voltage across the machine terminals can differ significantly during the zero crossing of a fundamental current. This inverter clamping modulation behaves similar to that due to the saturation saliency but has some specific characteristics that are presented in this work. For sensorless position control, this modulation has to be suppressed since it has the potential to cause a loss of position. This paper presents a new compensation strategy termed space modulation profiling (SMP) that is effective in suppressing both clamping modulation and saturation saliency. Experimental results show the sensorless drive under heavy load for zero speed and transient operation.