Research on Sensorless Control Technology of Brushless DC Motor with Delta Winding for Cooling Fan in Electric Reactor

The cooling fan of the electric reactor is based on the brushless DC motor with delta winding and the commutation point of sensorless drive is 60° after the back electromotive force (EMF) passes through zero point. In this paper, the mechanism of back EMF zero-crossing detection method for delta winding is deduced and the starting problem at low speed and the commutation error caused by diode freewheeling at high speed and large current are analyzed. On this basis, combining I/f constant current up-frequency starting and the back EMF zero-crossing detection method and performing the commutation angle compensation, a full-speed range sensorless control strategy is proposed. Based on this strategy, an electric reactor cooling fan with rated speed of 4750(r/min) and rated power of 800W under low voltage and large current conditions is verified by simulations and experiments. The results show that the sensorless control strategy proposed can ensure the stable operation of the cooling fan of the electric reactor in the full-speed range, which has good feasibility and robustness.