The number of pole pairs of the brushless motor is distinguished by detecting the change in the magnetic field of the rotor magnetic pole. The rotor magnets are arranged alternately according to the N pole and S pole. When the Hall of the brushless motor detects that the magnet jumps from the N pole to the S pole, Or when the S pole jumps to the N pole, the output of the Hall will have a corresponding high and low level change, which means that the position of the rotor has changed. Whether the windings of the brushless motor are energized or not will not affect the Hall detection.
The rotation speed of the magnetic field of the brushless motor is also called synchronous speed, which is related to the frequency of the three-phase current and the number of magnetic pole pairs p. If the stator winding has only one pair of magnetic poles (the number of magnetic pole pairs p=1), that is, there are only two magnetic poles. For a rotating magnetic field with only one pair of magnetic poles, the three-phase current changes one cycle, and the combined magnetic field also follows For one revolution, if it is a 50hz alternating current, the synchronous speed of the rotating magnetic field is 50 rpm or 3000 rpm. In engineering technology, revolutions per minute (r/min) are often used to express the speed. If the composite magnetic field of the stator winding of the brushless motor has two pairs of magnetic poles (the number of magnetic pole pairs p=2), that is, there are four magnetic poles, it can be proved that the current changes one cycle and the composite magnetic field rotates 180 degrees in space, which can be calculated : The synchronous speed per minute of the rotating magnetic field of p to the magnetic pole is n=60f/p.
When the number of pole pairs of the brushless motor is constant, if the frequency of the alternating current is changed, the synchronous speed of the rotating magnetic field can be changed, which is the basic principle of frequency conversion speed regulation. Since the magnetic poles of the motor appear in pairs, the number of pole pairs is also often expressed.
The brushless motor senses the change of the magnetic steel through the Hall element to determine the position of the pole pair of the brushless motor, and drives the rotor of the brushless motor to achieve the detection of the magnetic field speed and the number of pole pairs through the controller.
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