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Decrypt The Inverter Anti-interference Problem
Jul 27, 2018

At the scene, the interference of the inverter appears more and more serious, and even the control system can not be put into use. The working principle of the inverter is destined to generate strong electromagnetic interference.

The inverter includes a rectifier circuit and an inverter circuit. The input AC power is converted into a DC voltage through a rectifier circuit and a smooth wave circuit, and then the DC voltage is converted into a pulse voltage of a different width by the inverter (referred to as a pulse width modulation voltage, PWM). . By using this PWM voltage to drive the motor, it is possible to adjust the torque and speed of the motor. This principle of operation leads to the following three types of electromagnetic interference:

1.Harmonic interference

 The rectifier circuit generates a harmonic current that causes a voltage drop across the impedance of the power supply system, causing distortion of the voltage waveform that interferes with many electronic devices (since most electronic devices only work) Under sinusoidal voltage conditions, the common voltage distortion is the flattening of the top of the sine wave. When the harmonic current is constant, the voltage distortion is more serious in the case of a weak power supply, which is characterized by interference with equipment using the same power grid, regardless of the distance between the equipment and the frequency converter;

2. RF conducted emission interference

 Since the load voltage is pulsed, the inverter draws current from the grid as a pulse. This pulse current contains a large amount of high-frequency components, which form radio frequency interference. This interference is characterized by the use of equipment using the same grid. Interference, regardless of the distance between the device and the frequency converter;

3. Radio frequency interference

 RF emissions interfere with the input and output cables from the drive. In the case of the above-mentioned radio frequency conducted emission interference, when there is radio frequency interference current on the input and output cable of the frequency converter, since the cable is equivalent to the antenna, electromagnetic wave radiation is inevitably generated, and radiation interference is generated. The PWM voltage transmitted on the output cable of the inverter also contains abundant high-frequency components, which will generate electromagnetic wave radiation and form radiation interference. The characteristic of radiated interference is that the interference phenomenon becomes serious when other electronic devices are close to the inverter.

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