Careful people will find that when we check some refrigerators, air conditioners or washing machines, we can see keywords like "frequency conversion" in the title. Of course, the frequency conversion mentioned here is the product of the VFD electric motor, so compared with the motors used in our household appliances before, what are the characteristics of the VFD electric motor? What special experience can it bring us?
All household appliances generate different levels of harmonic voltage and current when the motor is running, making the motor run under non-sinusoidal voltage and current. Higher harmonics will cause the increase of motor stator copper loss, rotor copper (aluminum) loss, iron loss and additional loss, the most significant is the rotor copper (aluminum) loss. Because the ordinary AC asynchronous motor rotates at a synchronous speed close to the fundamental frequency, therefore, after the high-order harmonic voltage cuts the rotor bar with a large slip, a large rotor loss will be generated. In addition, additional copper loss due to skin effect needs to be considered. These losses will cause the motor to generate extra heat, reduce efficiency, and reduce output power. However, if a variable frequency motor is used, its energy consumption can be reduced by about 20% to 30%.
When the motor is running, the carrier frequency is about several thousand to tens of thousands of hertz, which makes the motor stator winding to withstand a high voltage rise rate, which is equivalent to applying a steep impulse voltage to the motor, so that the inter-turn insulation of the motor can withstand more severe test. The variable frequency motor can work under the rectified and filtered voltage, the performance can be more stable, and the life span is longer.
The vibration and noise of ordinary asynchronous motors due to electromagnetic, mechanical, ventilation and other factors become more complicated. The various time harmonics contained in the variable frequency power supply interfere with the inherent space harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces. When the frequency of the electromagnetic force wave is the same as or close to the natural vibration frequency of the motor body, a resonance phenomenon will occur, thereby increasing the noise. Due to the wide operating frequency range of the motor and the large range of speed variation, it is difficult for the frequency of various electromagnetic force waves to avoid the natural vibration frequency of each component of the motor. But VFD electric motor can effectively solve these problems.