Approaching the motor | Silicon-based power brushless motor noise reduction
Why does the motor make noise?
01What are the types of motor noise? ——Ventilation noise, electromagnetic noise, mechanical noise
Ventilation noise: it includes the fan or other ventilation components and the gas eddy current noise formed by the rotation of the rotor of the three-phase asynchronous motor, the single-frequency noise generated by the periodic pulsation of the cooling gas or the gas hitting the obstacle due to the rotation of the fan, and the resonance of the thin-walled parts in the air path Or the "flute sound" produced by the unreasonable design of the air duct. The intensity of ventilation noise is not only related to the type of fan, the diameter of the fan and the speed of the motor, but also to whether the design is reasonable.
Electromagnetic noise: It is generated by the interaction of the stator and rotor magnetic fields in the air gap of the motor. The radial force that changes with time and space causes the stator core and the frame to deform periodically over time, causing vibration and noise. The magnitude of the electromagnetic noise intensity limit is related to the magnitude of the radial force and the stiffness of the stator core and rotor.
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Mechanical noise: it includes mechanical vibration and noise generated by centrifugal force caused by rotor mechanical imbalance; bearing vibration noise; brush and slip ring or commutator sliding contact noise; end cover axial vibration noise excited by bearing vibration .
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02How does the electromagnetic noise of the motor come from?
Electromagnetic noise is mainly due to the periodically changing radial force or unbalanced magnetic field force generated by the magnetic field in the air gap (including the fundamental wave magnetic field and various high-order harmonic magnetic fields), which causes the stator and rotor cores to produce hysteresis contraction and vibration. The electromagnetic noise accounts for about 20% of the total motor noise. The specific reasons are as follows:
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The stator and rotor slots are not properly matched, the iron core is not tightly laminated, the length of the stator and the rotor is not well matched, the radial vibration of the rotor iron core, the winding pitch is incorrect, the inclination of the rotor slot is not enough, the coils in a certain pole phase group are connected reversely, There are branch circuit breakages in the parallel windings, the stator windings are asymmetrical or short-circuited between turns, the cage bars of the cage rotor are welded or disconnected, and the voltage and frequency vary greatly. The voltage is seriously unbalanced, and the frequency is too high, causing the electromagnetic sound to increase.
03How does the mechanical noise of the motor come from?
Motor stator and rotor friction, dynamic balance damage, bearing and bearing sleeve wear, and motor body resonance form mechanical noise. The detailed reasons are as follows:
The bearing is damaged or poorly assembled. When the motor rotates, place one end of the listening rod on the bearing end cover, and place the other end on the earlobe with your fingers to listen to whether the sound of the bearing rotation is uniform and whether there are periodic "clunks, clunks". If there is any abnormal sound, it means that there is a problem with the bearing, which is generally caused by a serious lack of oil in the bearing, impurities in the oil, unqualified product quality or bearing wear. For large high-voltage motors, such as improper assembly of motor bearings, wear of bearing sleeves, and loosening of bearing lock nuts will cause abnormal noises from the bearings.
The dynamic balance of the motor rotor is destroyed, the rotor is not stable or the rotating shaft is bent, causing the rotor to vibrate, and at the same time, the machine base vibrates and generates noise.
The stator and rotor cores are loose. .The uneven air gap between stator and rotor leads to mutual friction.
In a newly wound motor, the interphase insulating paper or slot protrudes out of the slot and rubs against the rotor. . Vibration of components (end shields, hoods, outlet box covers, etc.). The iron core is loose or the short circuit between the pieces, and the groove teeth are damaged. The fan is rubbing against the hood or the fan is unbalanced and the wind is loose. There are foreign objects in the machine entering the motor. Coupling connections are loose. Poor bearing installation or bearing damage. Fasteners are loose. The carbon brush commutator rubs against each other. The foundation is uneven or the installation is not good, the footing is unstable, the motor is not aligned during installation, and the motor shaft is not concentric with the mechanical load shaft. 04How does the motor ventilation noise come from?
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When the motor rotates, some protruding parts on the fan and rotor make the air impact and friction to form aerodynamic noise. It increases with the peripheral speed of the fan and rotor. The rotation of the fan forms a wide-band continuous noise, which accounts for a large proportion of this noise (especially for high-speed motors with a speed of more than 1500r/min). The intensity of fan noise is determined by the improper design of the fan (blade angle, width, motor speed), air inlet and outlet and air duct.
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05Brushless motor for ultimate noise reduction
The silicon-based power brushless DC motor technology uses the sine wave control of the brushless DC motor, that is, by applying a certain voltage to the motor winding, a sinusoidal current is generated in the motor winding, and the motor torque is controlled by controlling the amplitude and phase of the sinusoidal current. the goal of. Compared with the traditional square wave control, the motor phase current is sinusoidal and changes continuously, and there is no sudden change in the commutation current, so the motor noise is low. In the specific solution, the silicon-based power brushless motor performs well in noise reduction. For example, in the purifier solution, Si-based Power has developed inductive sine and FOC control strategies in terms of control, and can adopt various speed regulation methods such as analog speed regulation, PWM speed regulation, and frequency modulation speed regulation to achieve low noise and high speed of the motor. Efficient smooth operation. In the vacuum cleaner motor scheme, silicon-based power reduces noise through structural design and the selection of moving impellers and fixed impellers. At the same time, silicon-based power is also committed to researching and improving the noise of motors at high speeds, and constantly improving products. , to provide customers with better product customization.
