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With the continuous development of industrial automation, the frequency converter has also been recognized by more users. At the same time, users have more questions. The following briefly describes the circuit composition of the inverter.
The main circuit of the frequency converter is mainly composed of a rectifier circuit, an inverter circuit and a DC intermediate circuit and the related auxiliary circuits.
1. Rectifier circuit The main function of the rectifier circuit is to rectify the AC power supply of the power grid and provide the required DC power to the inverter circuit and control circuit. In a current-type inverter, the rectifier circuit acts as a DC current source, and in a voltage-type inverter, the rectifier circuit acts as a DC voltage source. Depending on the rectifier components used, the rectifier circuit also takes many forms.
2. The inverter circuit of the inverter circuit is one of the most important parts of the inverter. Its main function is to convert the DC voltage (current) output from the DC intermediate circuit into an AC voltage (current) having the required frequency under the control of the control circuit. The output of the inverter circuit is the output of the frequency converter and it is used to realize the speed control of the asynchronous motor.
3. DC intermediate circuit Although a rectifier circuit can be used to obtain a DC voltage or a DC current from an AC power source of a power grid, the voltage or current contains a voltage or current ripple whose frequency is six times the frequency of the power source. In addition, the inverter inverter circuit will also produce ripple voltage and current due to the output and carrier frequency and other factors, and in turn affect the quality of the DC voltage or current. Therefore, in order to ensure that the inverter circuit and the control power supply can obtain higher quality DC current or voltage, the output of the rectifier circuit must be smoothed to reduce voltage or current fluctuations. This is the role of the DC intermediate circuit. Because of this, the DC intermediate circuit is also called a smoothing circuit.
For a voltage-type inverter, the output of the rectifier circuit is a DC voltage, and the DC intermediate circuit smoothes the output voltage through a large-capacity capacitor. For the current-type inverter, the output of the rectifier circuit is a DC current, and the DC-intermediate circuit smoothes the output current through a large-capacity inductor.
The DC capacitor used in the DC intermediate circuit of the voltage-type inverter is a large-capacity aluminum electrolytic capacitor. In order to obtain the required pressure value and capacity, the capacitors are often used in series and in parallel according to the requirements of voltage and frequency converter capacity.
When the rectifier circuit is a diode rectifier circuit, since the capacitor will have a large charging current (surge current) flowing when the power supply is turned on, there is a possibility that the diodes may be burned out and other devices in the same power supply system may work properly. Take corresponding measures.