An Initial States Recognition (ISR) Method for Start-Up of 1Ф BLDC Motor in Hall-Sensor-Less Fan Applications

The initial state is very important for a single-phase brushless DC (BLDC) fan motor when starting, especially in fan application with a nonstatic motor. The direction of self-rotation caused by the external thrust needs to be considered to avoid the starting fail or wrong running direction. This article proposes an initial states recognition (ISR) method to smartize the starting procedure. However, the self-rotation direction identification of single-phase BLDC motors is a challenge, which is even more difficult in some applications without rotor position sensors. The unequal air gap, which is designed by the geometric variation on the pole shoe to form the asymmetric stator, is generally the necessary design for the single-phase BLDC motor to dodge the null torque position (dead point) and determine the operation direction; and it will further form the asymmetrical waveform of the back electromotive force (EMF) voltage. The asymmetric distribution of back EMF waveform will be opposite in half cycle (positive or negative half cycle) with the rotation direction. The proposed ISR method utilizes this trait to achieve the self-rotation direction recognition before starting a dynamic single-phase BLDC fan motor. Finally, under the architecture of Hall-sensor-less control, the experimental results prove that the proposed method is reliable and feasible.