How to solve the noise problem of brushless motor

With the wide application of brushless motor, users pay more and more attention to the running performance and sound of the motor, and put forward stricter requirements on the noise of the motor, requiring the motor to be low noise and provide more advantageous performance.

The noise sources of brushless motors are divided into two categories, one is mechanical noise, the other is electromagnetic noise. 

Source of noise 

The electromagnetic noise comes from the electromagnetic vibration, which is excited by the electromagnetic force generated by the air-gap magnetic field of the motor acting on the motor core. The air-gap magnetic field of the permanent magnet brushless motor determines the magnetic potential of the stator winding, and the permanent magnet magnetic potential and the air-gap magnetic conduction start. Then, the established magnetic field and the electromagnetic force generating the vibration are analyzed. 

In the brushless motor, the permanent magnet enters the air gap roughly along the radial direction, and generates radial force on the stator and rotor, thus causing electromagnetic vibration and noise. At the same time, it generates tangential torque and axial force, which causes tangential vibration and axial vibration. In many occasions, such as asymmetric or single-phase motors, the tangential vibration produced is very large, which easily causes the components connected with the motor to resonate and generate radiation noise. In order to calculate electromagnetic noise, analyze and control these noises, we must know their sources, that is, force waves that produce vibration and noise. Therefore, the distribution of magnetic flux density in the air gap should be divided first, and the product table of magnetic potential and magnetic morality is usually used. 

Methods of reducing noise 

1. The main methods to reduce the mechanical noise are to improve the machining accuracy, reduce the form and position tolerance of the flange and shaft, and improve the fit clearance of the bearing, etc.

2. Methods to reduce electromagnetic noise: A. Change the matching number of polar slots to reduce cogging torque B. Change the polar arc coefficient to reduce cogging torque. 

3. If the electrical angle of the brushless motor lags far behind the mechanical angle when it is commutated, resulting in noise, then the delay time between the electrical angle and the mechanical angle should be shortened. 

4. If it is the pulsation problem of the brushless motor, it is necessary to compensate the current of the brushless motor. 

5. Could also soak the coil of brushless motor in insulating paint, then dry it at high temperature, and finally fully soak the bearing of the rotor to reduce the noise. 

Of course, the noise of brushless motor can not be completely eliminated, but can only be reduced by all means. By contrast, the overall running noise of PMSM with sine wave band design will be less than that of square wave motor.