In a permanent magnet brushless motor, airgap field excited by a 2-pole magnet ring with parallel magnetisation is sinusoidal.
永磁无刷电机中，平行充磁的2极磁环产生的气隙磁场是正弦分布的。
2
The output power mechanism of a separately excited DC motor can be equivalent to a variable resistance, which is parallel with the armature winding of the motor.