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       the main noise sources of micro and special motors can be divided into ventilation noise, electromagnetic noise and mechanical noise. the electromagnetic noise is the most complex and main noise source in the motor. the interaction between the stator and rotor magnetic fields in the air gap of the motor produces radial force that changes with time and space, which makes the stator core and base periodically deform with time and causes vibration, which is caused by the ambient air pulsation.

       1. radial electromagnetic force wave the lower the order of the radial force wave, the longer the distance between the two adjacent fulcrums where the core produces bending deformation, and the greater the radial deformation. the deformation of stator core is approximately inversely proportional to the fourth power of force wave order m, and is directly proportional to the amplitude of force wave. therefore, low order radial force wave with large amplitude is the main source of electromagnetic noise. in addition, it should be noted that when the frequency of radial force wave is close to or even the same as the natural vibration frequency of stator core and frame, resonance will occur, and then the core vibration and radiated noise will greatly increase. 2. electromagnetic noise generated by fundamental magnetic field the amplitude of air gap magnetic flux density is b δ the order of the radial force wave generated by the pole-to-pole fundamental wave magnetic field is m=2p, and the frequency is 2f1 (f1 is the current frequency of the magnetic field, that is, the power frequency for the motor). the amplitude of the force wave is the same as b2 δ in direct proportion, that is, the fundamental magnetic field can produce vibration noise twice as high as the current frequency. for motors with more than four poles, the force wave order generated by the fundamental magnetic field is m>4, and the core deformation will be small, so the frequency doubling noise is common in two-pole motors.

       3. electromagnetic noise generated by harmonic magnetic field the air gap magnetic field of the motor contains a series of stator magnetic field harmonics and a series of rotor magnetic field harmonics. the interaction between one stator harmonic magnetic field and the other rotor harmonic magnetic field may produce lower order force waves, which will produce larger electromagnetic noise. 4. electromagnetic noise caused by unbalanced magnetic circuit for many reluctance motors, such as stepper motors, switched reluctance motors, doubly salient motors, etc., the transient magnetic circuit is unbalanced due to large changes in reluctance during operation. the unbalanced radial and tangential forces of the motor cause vibration and noise; for the servo motor with fractional slot concentrated winding, when the number of stator slots is odd and the ratio of stator slots to rotor slots is selected as unit motor, unbalanced radial magnetic pull will also be generated, which will cause vibration noise. in addition, the cogging effect of the motor is obvious, the cogging torque component is large, and the noise of higher frequency is also generated.

       5. noise caused by torque fluctuation servo driven motors, due to their own torque fluctuations, make the motor in a certain speed range or in the process of speed change, the system torque imbalance causes noise, as well as the electromagnetic noise caused by sudden load changes and the increase in the rate of change of the regulating quantity in the process of system dynamic response. 6. noise generated by power electronic power supply many micro and special motors often use power electronics for power supply due to the high requirements of control performance, and often generate electromagnetic noise due to the carrier frequency of pwm. for more knowledge about micro motors, you can continue to pay attention to jinli variable speed. jinli transmission provides core transmission scheme for ai!