The principle of frequency converter is that the main circuit is the power conversion part that provides voltage regulation and frequency modulation power supply for asynchronous motor. The main circuit of the frequency converter can be roughly divided into two types: the voltage type is a frequency converter that converts the DC of the voltage source into alternating current, and the filtering of the DC loop is a capacitor. Current mode is a frequency converter that converts DC of current source into AC, and its DC loop filter is inductance. It consists of three parts, namely, a rectifier that converts power frequency power supply into DC power supply, a smoothing circuit that absorbs voltage pulsation generated by converter and inverter, and an inverter that converts DC power supply into AC power supply.

Basic components of frequency converter:

1, frequency converter is usually divided into four parts: rectifier unit, large-capacity capacitor, inverter and controller.

2. Rectifier unit: Convert alternating current with fixed working frequency into direct current.

3. Large-capacity capacitor: store the converted electric energy.

4. Inverter: an electronic switch consisting of a high-power switching transistor array, which converts direct current into square waves with different frequencies, widths and amplitudes.

5. Controller: Work according to the set program, control the amplitude and pulse width of the output square wave, so that it can be superimposed into alternating current which is similar to sine wave to drive the AC motor.

Frequency converter is a kind of power control equipment which uses frequency conversion technology and microelectronics technology to control AC motor by changing the frequency mode of motor working power supply. The frequency converter is mainly composed of rectifier (AC to DC), filter, inverter (DC to AC), braking unit, driving unit, detection unit and microprocessor unit. The inverter can adjust the voltage and frequency of the output power supply by switching the internal IGBT, and provide the required power supply voltage according to the actual needs of the motor, so as to achieve the purpose of energy saving and speed regulation. In addition, the inverter also has over-current, over-voltage, overload protection and other protection functions. With the continuous improvement of industrial automation, frequency converters have been widely used.