A novel smooth transition strategy for BEMF-based sensorless drive startup of PMSM

This paper proposes a novel smooth transition method, which can be applied to back electromotive force (BEMF)-based permanent magnet synchronous motors (PMSM) sensorless vector control drive. The problem with BEMF-based sensorless control of PMSM control is the inherent BEMF estimation precision before reaching a certain rotation velocity. A position open loop constant current (I-F) method, which is compared with the classical voltage-frequency (V-F) method of asynchronous motors control, is employed by applying the torque current feedback control technique to drive the motor from standstill to switch frequency. I-F strategy is analyzed first, the critical element load angle, which can influence motors switch process performance, is studied. To eliminate the switch physical parameters disturbance and achieve smooth transition, a novel strategy, that can transit the PMSM drive state from I-F, which is used during standstill and low speed rotation region, to BEMF-based sensorless FOC control smoothly, are presented. The transition strategy is furnished and its performance is shown and analyzed based on the PMSM dynamic model. At the end, an experimental platform, which is built by a high speed PMSM spindle and corresponding sensorless drive, is introduced to realize the supposed method, which can show the switch smoothness and illustrate the theoretical analysis rationality.