Sensorless control of PMSMs based on an adaptive ST-SMO and suppressing zero-current clamp phenomenon

Sliding mode observer (SMO) is popular in the sensorless control of permanent magnet synchronous motors (PMSMs), and as the recent advances, the super-twisting SMO (ST-SMO) reduces chattering and retains a decent robustness, however, inappropriate coefficient choice of a ST-SMO can contribute to chattering particularly at low speed. In this work, an adaptive ST-SMO is proposed, where the coefficient is designed to change with the speed, and thus the ST-SMO can fit a wide speed range in the sensorless mode. In addition, a dead time compensation method is adopted to improve the steady-state sensorless drive performance, and specifically, a phase current polarity judgement method under a fuzzy rule and predicted current is proposed to cope with the zero-current clamp phenomenon. Finally, the proposed method is validated by the experimental results.