Stator: The stationary part of the motor
Rotor: The part that the motor turns
Number of poles: the number of magnets on the rotor, there are 6 poles in the picture below
Number of pole pairs: every 2 poles constitute a pair of magnetic poles, the figure below has 3 pole pairs
KV value: When the voltage increases by 1V, the motor speed increases by k, for example: KV=1000, when the voltage increases by 1V, the motor speed increases by 1000 rpm
Speed: Speed = KV value × voltage
No-load current: When there is no load, the current of the motor
Torque: The driving torque of the motor to drive the load, commonly understood as the "power" of the motor
The relationship between torque and speed: one trade-off, torque ↑ speed ↓ torque ↓ speed ↑
Slot pole structure (N: number of slots, P: number of poles)
The common inner rotor brushless motor structures in the model are: 3N2P (commonly used in induction motors), 12N4P (most inner rotor motors) The common outer rotor brushless motor structures in the model are: 9N6P, 9N12P, 12N8P, 12N10P, 12N14P, 18N16P, 24N20P
Actual speed = motor speed / number of pole pairs
Coil winding: 2 ways, fractional slot, integer slot
Fractional slots: number of slots ÷ 3 (number of phases) ÷ number of poles = fraction
Integer: number of slots ÷ 3 (number of phases) ÷ number of poles = integer
Why use fractional slots so heavily?
Permanent magnet motors all have the problem of cogging torque. Many people even mistakenly believe that a motor with a strong slam-sensing and strong magnetism is an excellent performance of the motor. No, cogging torque is a natural disadvantage of permanent magnet motors. It is an indicator that motor design needs to overcome and minimize. It will cause motor speed fluctuations (the professional term is ripple torque), running noise, and running vibration. The cogging torque and the number of slots of fractional slots are related to the least common multiple of the number of poles.
Permanent magnet synchronous motor current waveform:
1. Square wave
Simple control and small torque ripple
2. Sine wave
Complex control and large torque fluctuation