The main circuit of a high-performance frequency converter is the power conversion part that provides voltage-regulated and frequency-regulated power to the asynchronous motor.

The main circuit of the inverter can be divided into two categories: the voltage type is a high-performance inverter that converts the DC of the voltage source into AC, and the filter of the DC circuit is a capacitor. The current mode is a high-performance inverter that converts the DC of the current source into AC, and its DC loop filter is an inductor. It consists of three parts, namely the "rectifier" for converting the power frequency into DC power and the "smoothing circuit rectifier" for absorbing the voltage pulsation generated in the converter and inverter. The diode converter is widely used, which converts the power frequency into DC power. Two sets of transistor converters can also be used to form a reversible converter, because its power direction is reversible, it can be regenerated. In the DC voltage rectified by the rectifier, the smoothing circuit contains a pulsating voltage of 6 times the power frequency.

In addition, the pulsating current generated by the inverter will also change the DC voltage. In order to suppress voltage fluctuations, inductors and capacitors are used to absorb the fluctuating voltage (current). When the device capacity is small, if there is margin in the power supply and main circuit, the inductor can be omitted and a simple smoothing circuit can be used. The inverter is the opposite of the rectifier. The inverter converts DC power into AC power of the required frequency and switches 6 switching devices within a certain period of time to obtain a three-phase AC output. Taking the voltage type inverter as an example, the switching time and voltage waveform are given. The control circuit is a circuit that provides a control signal to the main circuit, which supplies power to the asynchronous motor (voltage and frequency are adjustable). It consists of a frequency voltage "operation circuit", a main circuit "voltage and current detection circuit", a motor "speed detection circuit", a drive circuit that amplifies the control signal of the operation circuit, an inverter, and a motor "protection circuit".

(1) Operation circuit: compares external instructions such as speed and torque with the current and voltage signals of the detection circuit to determine the output voltage and frequency of the inverter.

2) Voltage and current detection circuit: isolated from the main circuit potential, detects voltage and current.

3) Drive circuit: a circuit that drives the main circuit device. It is isolated from the control circuit to turn on and off the main circuit device.

4) Speed ​​detection circuit: takes the signal of the speed detector (tg, plg, etc.). Installed on the shaft of the asynchronous motor as a speed signal, and sends it to the running circuit so that the motor can run at the commanded speed according to the instructions and operations.

5) Protection circuit: detects the voltage and current of the main circuit. When overload or overvoltage is abnormal, in order to prevent damage to the high-performance inverter and asynchronous motor, the basic components of the inverter are usually divided into four parts: rectifier unit, large-capacity capacitor, high-performance inverter and controller.

Rectifier unit: converts AC power with a fixed operating frequency into DC power.

High-capacity capacitor: stores the converted electrical energy.

Inverter: an electronic switch composed of a high-power switching transistor array that converts DC power into square waves of different frequencies, widths and amplitudes.

Controller: works according to the set program, controls the amplitude and pulse width of the output square wave, and superimposes it into AC power that is close to a sine wave to drive the AC motor. Mainly used for industrial automation control.