The permanent magnet brushless DC motor is essentially an AC motor, and its stator has multi-phase AC windings. Because its operating mechanism is different from ordinary AC motors, the number of winding phases can have a variety of options, in principle, it can be single-phase, 2, 3, 4, 5, 6, 7, ... to more than ten phases.

　　The common connection modes between the windings of each phase of the brushless DC motor are star windings and enclosed windings. The star winding is to connect the tails of each phase winding together (called the midpoint of the winding), and then connect the head of each phase winding to an electronic commutation switch. The closed winding is to connect the tail of a phase winding to the head of the next group of windings, all windings are connected end to end to form a closed loop, and then each connection point is connected to an electronic commutation switch. However, due to the possibility of harmonic current circulating in the closed winding when the motor is running, the loss increases and the motor efficiency is reduced, so most of the brushless motors adopt the star winding connection method.

　　This article is taken from ------"Permanent Magnet Brushless DC Motor Technology"