The working magnetic flux of the DC brushless motor should be based on the air gap magnetic flux formed by the average magnetic flux density of the magnetic steel in the magnetic field of the coil. The maximum value of the magnetic flux density of each pole of the magnetic steel should be the remanence of the magnetic steel, and the magnetic flux density in various places of the magnetic steel will not exceed the maximum magnetic flux density of the magnetic steel.
(1) The influence of the mechanical pole arc coefficient of the magnet. If the mechanical included angle of the surface-mounted magnet is smaller than the pole pitch of the magnet, then the magnetic flux of the magnet must be affected and reduced. This coefficient is the ratio of the width of the magnetic flux pole arc to the pole pitch of the magnet, which is called Mechanical pole arc coefficient.
(2) The influence of the magnetic pole arc coefficient of the magnetic steel. Because the magnetic flux density distribution waveform of the magnetic steel is not necessarily a square wave, it may be a sine wave, a saddle wave, a trapezoidal wave, etc., so the coefficient of the average magnetic flux density must be different. For this reason, a coefficient must be used. Multiplied by the maximum magnetic flux density of the magnetic steel, it represents the actual average magnetic flux density of the magnetic steel. This coefficient can be called the magnetic pole arc coefficient of the magnet.
(3) The thickness of the magnetic steel is the length of the magnetic steel. The air gap length of the motor will all reduce the magnetic flux density of the magnetic steel into the air gap magnetic flux density of the motor, resulting in an air gap lower than the maximum magnetic flux density of the magnetic steel. Average magnetic flux density.
(4) The average magnetic flux density of the air gap is the product of various discount factors multiplied by the maximum magnetic flux density of the magnetic steel. As the calculation basis and method for converting the magnetic steel magnetic flux density of the DC brushless motor into the average magnetic flux density of the motor air gap. From another perspective, since the air gap flux is an average value, it should be considered that the distribution of the air gap flux in the air gap circumference of the DC brushless motor is uniform, so the air gap flux of the motor and the magnetic flux of the motor rotor The number of pass poles is irrelevant. If the magnetic properties of the magnetic steel are the same and the waveform of the magnetic flux density distribution is the same, then the number of magnetic steel on the circumference of the air gap has nothing to do with the average magnetic flux density and air gap magnetic flux generated. A uniform air gap flux concept is used to consider the effect on the motor, which facilitates the design and calculation of future brushless DC motors.
www.dw-motor.com