Robust initial phase correction strategy for zero sequence back EMF based sensorless drive under transition from current regulation control

This paper proposes a phase correction strategy for the zero sequence back EMF based sensorless drive under current regulation control (viz., I/f control). The straightforward phase correction process based on the nearest principle might lead to false correction under different load conditions. The proposed strategy can achieve robust phase correction by injecting transitory high frequency (HF) signal into the stator winding to track the secondary saliency information without polarity identification. Then the estimation position angle, which can be inphase or π rad shifted to the real position angle, is used in tandem with the estimation position angle from zero sequence back EMF based sensorless method to deduce the required phase correction values which can be 0, 2/3π or 4/3π. The proposed strategy is suitable for zero sequence back EMF based sensorless drive with I/f startup. The transitory HF injection imposed during the transient switching process from I/f control to sensorless mode induces negligible audible noise due to the short injection duration. Hence, the proposed strategy keeps the merits of the conventional method and provides robust phase correction as well.