Improved Switching Strategy for a Single-Phase Brushless Direct Current Fan Drive and its Impact on Efficiency

Advancing the turn-off angle of the phase current of brushless direct current (BLDC) motors is a common control practice to improve the operating behavior and energy conversion efficiency of such drives by, e.g., reduction of current peaks, copper losses, and breaking torques. This paper investigates a refined switching strategy for a single-phase BLDC motor with bifilar winding to increase the energy conversion efficiency of the system. In addition to advancing the phase current turn-off angle, the turn-on angle is delayed to improve the drive's performance and increase the efficiency even further. This efficiency increase of up to 20.6 % is verified experimentally for a speed range from 3000 to 8000 rpm, translating into a reduction of copper losses of up to 37.4 % or a decrease of current peaks by 27.4 %. The focus is on sub-fractional horsepower single-phase BLDC motors with bifilar winding which, concerning this matter, have not drawn much attention in the literature yet. The findings show that the improved switching strategy can reduce current peaks, breaking torques, copper losses, and therefore increase efficiency over the speed range of interest for fan applications.