Zhejiang Shuyi Electric Co. Ltd

The #frequencyconverter is a power conversion device, which converts the three-phase alternating current of fixed frequency and fixed voltage input to the frequency converter into three-phase alternating current with adjustable frequency and adjustable voltage. It is composed of #inverter (DC to AC), braking unit, drive unit, detection unit and micro-processing unit. It can be roughly divided into four parts. They are the main circuit, rectifier, smoothing circuit and #inverter.


A diode-based converter is widely used, which converts power frequency power into DC power. Two sets of transistor converters can also be used to form a reversible converter, which can perform regenerative operation because its power direction is reversible.

2.smoothing circuit

The DC voltage rectified by the rectifier includes a pulsating voltage six times the frequency of the power supply, and the pulsating current generated by the inverter also fluctuates the DC voltage. In order to suppress voltage fluctuations, inductors and capacitors are used to absorb the pulsating voltage (current). If the capacity of the device is small, if the power supply and the main circuit components have margins, the inductor can be omitted and a simple smoothing circuit can be used.


Contrary to the rectifier, the inverter converts the DC power into the AC power of the required frequency, and turns on and off the 6 switching devices at the determined time to obtain a 3-phase AC output. Taking the voltage type pwm inverter as an example, the switching time and voltage waveform are shown.

4.The main circuit

The main circuit is the power conversion part that provides the voltage regulation and frequency regulation power supply for the asynchronous motor. The main circuit of the frequency converter can be roughly divided into two categories: the voltage type is the frequency converter that converts the DC of the voltage source into the AC, and the filter of the DC circuit is the capacitor. . The current type is a frequency converter that converts the DC of the current source into an AC, and its DC loop filter is an inductance. It consists of three parts, a “rectifier” that converts power frequency power into DC power, a “smoothing loop” that absorbs the voltage pulsation generated by the converter and #inverter, and an “inverter” that converts DC power to AC power transformer”.

These parts also undertake their own tasks. Through cooperation, the inverter can realize the corresponding operation and change the current of the motor, so as to realize the control of the equipment. Of course, the role of the #inverter is also very significant, which also makes its application More generally。


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