Analysis of Electromagnetic Noise of Motor
Noise is a combination of cluttered sounds of various frequencies and intensities, and the dangers of such annoying noise to humans are well known. Noise is often accompanied by vibration, which can damage other equipment. The level of vibration and noise reflects the level of product design and manufacturing and is an important indicator for measuring product quality. The importance of reducing noise is now widely recognized. Motor design, manufacturing and operation personnel need more knowledge about motor noise. For example, it is necessary to find out how the motor noise is generated, and what factors are involved. It is desirable to predict the noise generated during the actual operation of the motor during the design phase, and to know the method of reducing the noise.
Electromagnetic noise is generated by alternating electromagnetic fields that cause some mechanical components or space volume to vibrate. For the electric motor, the stator vibration can be excited to generate noise due to the unstable power supply. The main characteristics of electromagnetic noise are related to the characteristics of the alternating electromagnetic field, the size of the forced vibrating parts and the size of the space. Higher frequency electromagnetic noise, also known as electromagnetic howling.
Analysis of the causes of electromagnetic noise
When the motor is running, there is a fundamental magnetic field and a series of harmonic magnetic fields. These magnetic fields interact to generate a tangential force, which in addition to the tangential electromagnetic torque, and also produces radial forces that vary with time and space.
In general, there are various kinds of rotating radial electromagnetic force waves of various frequencies and frequencies in the air gap of the motor. Each radial force wave acts on the stator and rotor cores respectively, causing the stator core and the base and the rotor to have radial deformation that changes periodically with time, that is, vibration occurs, and the vibration frequency is the frequency of the force wave action. Since the rotor core is very rigid and the amount of vibration generated is small, only the vibration of the stator core and the base is generally considered. Electromagnetic noise is mainly caused by airborne noise caused by the vibration of the stator causing the surrounding air to pulsate.
The lower the order of the radial force wave, the farther the distance between the adjacent two points of the bending deformation of the core, the rigidity of the core is relatively poor, and the radial deformation is also larger. The deformation of the stator core is inversely proportional to the fourth power of the force wave number, and is proportional to the amplitude of the force wave. Therefore, the low-order radial force wave with a large amplitude is the main source of electromagnetic noise. In addition, special attention should be paid. Yes, both the core and the base have a certain natural vibration frequency. When the radial force wave frequency is close to or even the same as the natural frequency, resonance will occur, and the core vibration and radiation noise will increase greatly.
Since the amplitude of the fundamental magnetic field is large, and if there is no fundamental magnetic field, the motor cannot work, so the frequency doubling noise generated by it cannot be avoided. However, due to its high frequency of power waves (except for 2-pole motors), the frequency is lower and the noise radiation efficiency is lower. Therefore, in addition to the 2-pole motor with higher power, the frequency-doubled noise is generally small.
