Reasearch on Sensorless PM Brushless DC Motor Starting Control

Aiming at the starting problem of sensorless permanent magnet brushless DC motor (BLDCM), an interpolation start-up strategy is proposed according to the direct relation between the source voltage and the commutating instant. In this strategy, different start-up commutating instant under different source voltages are collected first. Then, cubic spline interpolation functions are fitted off line using source voltages as the inputs and commutating instant as the outputs. During open loop starting, these functions can provide accurate start-up commutating instant under any given source voltage; During closed-loop starting, with the variation of the effective value of the source voltage controlled by PI regulator, interpolation functions can adjust the commutating instant on line to make sure they are accurate. When start-up procedure is over, the system is switched to back EMF running by software. Simulation and experiment results show that the interpolation start-up strategy proposed in this paper is widely applicable for sensorless BLDCM in open loop starting, closed-loop starting and the corresponding starting in loading.