The function of the inverter's main circuit. In the inverter's circuit structure, the main circuit is a unit circuit. This circuit converts 220VAC or 380VAC AC power into pulsating DC power through rectifier elements. The AC component in the pulsating DC power is then filtered out by a filter circuit, and the DC power is further amplified. After processing by a braking circuit, the inverter circuit converts the DC power into AC power of a specific frequency, which is then sent to the motor to achieve the desired motor speed. This is the function of the inverter's main circuit.
The main circuit structure of a frequency converter. By observing the circuit composition of frequency converters from various brands such as Siemens, Schneider Electric, ABB, Danfoss, Yaskawa, Fuji, and Delta, the main circuit structure can be summarized into several major parts: input power supply anti-interference circuit, rectifier circuit, filter circuit, braking circuit, inverter circuit, and current sensor circuit.
The input power supply anti-interference circuit is mainly composed of resistive, capacitive, and inductive components. It filters out some interference components in the 220VAC or 380VAC AC power input to the frequency converter, ensuring that the power input to the frequency converter is pure AC power with a frequency of 50HZ and a voltage of 220VAC or 380VAC.
The rectifier circuit consists of a single-phase rectifier bridge or a three-phase rectifier bridge. For low-power frequency converters, the rectifier circuit is mostly integrated together, which is called a rectifier module in the industry. For high-power frequency converters, the rectifier circuit usually uses six independent rectifier diodes for rectification.
The filter circuit is composed of capacitors and inductors. For low-power frequency converters, two to six electrolytic capacitors are usually used. For high-power frequency converters, a separate capacitor filter board is made, which is combined with a large filter inductor.
The braking and inverter circuits consist of 7 IGBTs. For low-power inverters, the 7 IGBTs are usually integrated together, which is called an IGBT module in the industry. For high-power inverters, manufacturers will use 7 independent high-power IGBTs. Some manufacturers also integrate the rectifier circuit, braking circuit, and inverter circuit into one module to make an IPM intelligent module.
The current sensor circuit mainly consists of two current sensors. The manufacturer connects the current sensors in series in two phases of the three-phase output circuit of the frequency converter to detect the output current of the frequency converter.
