Abstract : This paper mainly analyzes the drive circuit of general-purpose frequency converters to understand some common forms and development trends of drive circuits, meeting the needs of solving practical problems in the field. 1 Introduction AC variable frequency speed control technology is an important development direction of modern electric drive technology. With the application of power electronics technology, microelectronics technology and modern control theory in AC speed control systems, variable frequency AC speed control has gradually replaced the past slip speed control, pole changing speed control, DC speed control and other speed control systems, and is increasingly widely used in many fields of industrial production and daily life. With the widespread application of variable frequency speed controllers, many engineering technicians have gained a considerable understanding of them. A general-purpose frequency converter generally includes the following parts: 1. Rectifier circuit, 2. DC intermediate circuit, 3. Inverter circuit, 4. Control circuit. The inverter circuit, which generates adjustable voltage and adjustable frequency, should be the core technology of each component of the frequency converter. 2 Drive Circuit The inverter circuit mainly includes: inverter module and drive circuit. Due to factors such as processing technology, packaging technology, and high-power transistor components, inverter modules are currently mainly produced by a few manufacturers in Japan (Toshiba, Mitsubishi, Sansha, Fuji, Sanken) and Europe and the United States (Siemens, Semikron, Motorola, IR). As part of the inverter circuit, the drive circuit has a huge impact on the three-phase output of the frequency converter. The design of the drive circuit generally includes several methods: (1) drive circuit composed of discrete pin-type components; (2) optocoupler drive circuit; (3) thick film drive circuit; (4) dedicated integrated circuit drive circuit. (1) Drive circuit composed of discrete pin-type components Drive circuit composed of discrete pin-type components was widely used in frequency converters in Japan and Taiwan in the 1980s, mainly including a series of frequency converters from Japan (Fuji: G2, G5, Sanken: SVS, SVF, MF, Kasuga, Mitsubishi Z series K series, etc.) and Taiwan (Olin, Puchuan, Taian, etc.). With the development of large-scale integrated circuits and the emergence of surface mount technology, such complex and low-integration drive circuits have been gradually phased out. (2) Optocoupler drive circuit Optocoupler drive circuit is a type of drive circuit widely used in modern frequency converter design. Due to its simple circuit, high reliability, and good switching performance, it is adopted by many frequency converter manufacturers in Europe, America and Japan. Since there are many models of drive optocouplers, there is a lot of room for selection. The drive optocouplers used most often are Toshiba's TLP series, Sharp's PC series, HP's HCPL series, etc. Take Toshiba's TLP series optocouplers as an example. The drive optocouplers used for driving IGBT modules are mainly TLP250 and TLP251. For modules with small current (around 15A), TLP251 is generally used. With the help of drive power supply and current limiting resistor, the simplest drive circuit is formed. For modules with medium current (around 50A), TLP250 optocouplers are generally used. For modules with larger current, when designing the drive circuit, it is generally adopted to add an amplifier circuit after the optocoupler drive to achieve the purpose of safely driving the IGBT module. (3) Thick film drive circuit The thick film drive circuit is a hybrid integrated circuit developed on the basis of resistor-capacitor components and semiconductor technology. It uses thick film technology to make mode components and connecting wires on a ceramic substrate, and integrates the various components of the drive circuit on a ceramic substrate to make it a whole component. Using thick film drive has greatly facilitated the design and wiring, improved the reliability of the whole machine and the consistency of mass production, and also strengthened the confidentiality of the technology. The current thick film drive often integrates many protection circuits and detection circuits. It should be said that the technical content of thick film drive is getting higher and higher. (4) Dedicated integrated block drive circuit Now there are also dedicated integrated block drive circuits, mainly IR's IR2111, IR2112, IR2113, etc., and Mitsubishi's EXB series thick film drive. Mitsubishi's M57956, M57959, etc. thick film drive. Furthermore, some European and American frequency converters now incorporate high-frequency isolation transformers into their drive circuits (such as the Danfoss VLT series frequency converters). It should be said that by isolating the power supply and signals of the drive circuit through high-frequency transformers, the reliability of the drive circuit is enhanced, and it also effectively prevents damage to the low-voltage circuits when the high-voltage circuit fails. In actual maintenance, we have also found that the failure rate of this drive circuit is very low, and high-power modules rarely have problems. In our daily production use, high-power module failure is a common fault phenomenon. 3. Fault Phenomenon Analysis The causes of damage can be varied. Motor short circuits, poor insulation to ground, motor stall, and excessively high external power supply voltage can all cause damage to the high-power module of the frequency converter. In actual maintenance, when replacing a high-power module, we must ensure that the drive circuit is working properly. Otherwise, replacement can easily cause the high-power module to fail again. In addition, we must understand the difference between the drive circuits of GTR modules and IGBT modules; the former is current-driven, while the latter is voltage-driven. With the development of electronic components and large-scale integrated circuits, drive circuits are also constantly evolving towards higher integration, with expanding functions and improving performance. This also places higher demands on those of us in the frequency converter repair industry. The above are just some of my personal experiences in frequency converter repair, and I hope to exchange ideas and insights with others in this field.