The inverter includes a rectifier circuit and an inverter circuit. The input AC power is converted into a DC voltage through the rectifier circuit and the flat circuit, and then the DC voltage is converted into pulses of different widths through the inverter. Voltage (called pulse width modulation voltage, PWM). By using this PWM voltage to drive the motor, the motor torque and speed can be adjusted.
This working principle leads to the following three kinds of electromagnetic interference:
1, harmonic interference:
Rectifier circuits generate harmonic currents that produce a voltage drop across the impedance of the power supply system, causing distortion of the voltage waveform. This distorted voltage interferes with many electronic devices (because most electronic devices only work. In the case of a sinusoidal voltage, the common voltage distortion is that the top of the sine wave flattens. When the harmonic current is constant, the voltage distortion is more serious in the case of a weak power supply. The characteristic of this type of interference is that it will interfere with the equipment that uses the same power grid, and has nothing to do with the distance between the equipment and the frequency converter;
2, RF conducted emission interference:
Since the load voltage is pulsed, the frequency converter draws current from the power grid also in the form of a pulse. This type of pulsed current contains a large number of high-frequency components that form radio frequency interference. This type of interference is characteristic of devices that use the same power grid. Interference, independent of the distance between the equipment and the frequency converter;
3, radio frequency radiation interference:
RF emissions interfere with the input and output cables from the frequency converter. In the above-mentioned case of radio frequency conducted emission interference, when there is radio frequency interference current on the input and output cables of the frequency converter, since the cable is equivalent to the antenna, electromagnetic wave radiation will inevitably occur and radiation interference will occur. The PWM voltage transmitted on the output cable of the inverter also contains rich high-frequency components, which will generate electromagnetic wave radiation and form radiated interference. The characteristic of radiated interference is that the interference phenomenon becomes serious when other electronic devices are close to the inverter.