Without position sensing, determining the initial rotor position in a stationary BLDC motor is nearly impossible. Various methods have been proposed, but there have been very few studies published on the use of high-frequency signal or pulse injection methods on a single-phase BLDC motor. In the proposed method, instead of detecting the initial rotor position, the motor is energized and forced to align to a known position. The use of a ramp alignment pulse and a phase-current observer algorithm mitigate the issue of wobble during the alignment stage. Finally, start-up commutation sequence timings are calculated based on estimated initial speed.
