The control circuit of a frequency converter is composed of which parts?

The control circuit of a frequency converter is centered around an MCU (Microcontroller Unit), and consists of five main parts: the working power supply (switching power supply circuit), voltage and current detection (fault alarm, protection) circuits, IGBT drive circuit, operation control circuit, and the basic MCU circuit.
(1)  Switching power supply circuit. Typically, it obtains a 530V DC power supply from the DC circuit (across C1 and C2) of the main circuit. Through DC-AC-DC conversion, it produces several stable DC voltages such as +5V, +15V, -15V, and 24V to power the control circuit. The 4 or 6 channels of drive power required by the IGBT drive circuit are also supplied by the switching power supply.
(2)  Drive circuit. The six pulse signals output from the MCU pins are input to the drive circuit through a buffer circuit. After photoelectric conversion, isolation, and power amplification, they are used to drive the IGBTs to turn on and off according to a certain pattern, inverting the DC530V power supply into a three-phase AC voltage output.
(3)  (3) Detection circuits for current, voltage, power module temperature, OC fault (overcurrent fault), etc. The voltage detection signal is obtained from the DC circuit to display the DC voltage value, as well as for overvoltage and undervoltage alarms and shutdown protection. Current transformers (Hall effect components and circuits) are connected in series at the U, V, and W output terminals to detect the output current, which is used for displaying the operating current, output control, overload alarm, and shutdown protection. Temperature sensors are installed on the heatsink to detect temperature changes in the inverter power module, and to trigger over-temperature alarms and shutdown protection in case of abnormalities, as well as to control the operation of the cooling fan. The drive circuit typically includes a fault detection function for the IGBTs, which generates an OC signal when the inverter power circuit operates abnormally, for alarming and shutdown protection.
(4)  Operation control circuit. The internal circuits of the control terminals of the frequency converter (including auxiliary power supply, digital/analog input/output circuits), as well as the operation display panel and other circuits, are responsible for controlling the start, stop, communication, and other functions of the frequency converter. The panel also provides real-time monitoring of the operating status.
(5)  MCU basic circuit. The detection signals and control signals from the circuits mentioned in (3) and (4) are ultimately input into the MCU, where they undergo software processing before outputting six pulse signals and relevant control signals. As the "command center", the MCU coordinates the orderly operation of the entire machine and centrally processes input and output signals. The basic working conditions for the MCU, including a +5V power supply, reset circuit, crystal oscillator circuit, and external memory circuit, collectively form the MCU base circuit. From the perspective of maintenance and supervision, the MCU's interface circuit and operation display circuit are also considered part of its basic circuit. In fault troubleshooting, confirming the normality of this part of the circuit is a prerequisite for diagnosing other faulty circuits.

Frequency converters are products that closely combine power electronics (high reverse voltage, high current) components with microelectronics (microcontroller) technology, reflecting the current level of electronic technology to a certain extent. They represent an organic integration of weak and strong electricity, as well as software and hardware. With their powerful functions, comprehensive detection and protection circuits, and intelligent and flexible control, they apply a combination of microelectronics technology and power semiconductor devices. The non-standard nature and special requirements of their circuit components highlight the characteristics of these intelligent electrical devices, resulting in unique troubleshooting approaches and methods.