What is the principle of three-phase inverter

1. The main circuit is the power conversion part that provides voltage regulation and frequency regulation power supply for the asynchronous motor. The main circuit of the inverter can be roughly divided into two categories: the voltage type is the inverter that converts the DC of the voltage source into alternating current, and the filter of the DC circuit is the capacitor.

2. The current type is a frequency converter that converts the DC of the current source into alternating current, and its DC loop filter is an inductor. It consists of three parts: a rectifier that converts power frequency power to DC power, a smoothing circuit that absorbs the voltage pulsation generated by the current transformer and inverter, and an inverter that converts DC power to AC power.

One, the rectifier:

Diode converters are widely used, which convert power frequency power into DC power. Two sets of transistor converters can also be used to form a reversible converter, and since its power direction is reversible, regenerative operation can be performed.

Second, the 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 the voltage fluctuation, 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 loop can be used.

Third, the inverter:

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.

The control circuit is a loop that provides control signals to the main circuit that supplies power to the asynchronous motor (adjustable voltage and frequency). It consists of a “drive circuit” that amplifies the control signal of the arithmetic circuit, and a “protection circuit” of the inverter and the motor.

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