Common drive circuit form and analysis of general-purpose inverter - Power Circuit - Circuit Diagram

AC frequency conversion speed regulation technology represents a key advancement in modern electric drive systems. By integrating power electronics, microelectronics, and modern control theories into AC speed control systems, frequency conversion has increasingly replaced traditional methods like slip-speed control, variable-pole speed control, and DC speed control. This technology is now widely applied across industries and everyday life. As frequency converters become more prevalent, many engineers and technicians are gaining familiarity with them. A general-purpose inverter typically consists of four main parts: 1) a rectifier circuit, 2) a DC intermediate circuit, 3) an inverter circuit, and 4) a control circuit. Among these, the inverter circuit—responsible for generating both adjustable voltage and frequency—is arguably the most crucial aspect of the entire inverter. The inverter circuit primarily includes an inverter module and a drive circuit. Owing to advancements in processing techniques, packaging technologies, and high-power transistor components, current inverter modules mostly come from Japan (like Toshiba, Mitsubishi, Sanshe, Fuji, and Sanken) or a few European and American manufacturers (Siemens, Infineon, Motorola, and IR). As part of the inverter circuit, the drive circuit significantly impacts the three-phase output. Drive circuit designs generally fall into several categories: 1) discrete pin-type component circuits, 2) optocoupler drive circuits, 3) thick-film drive circuits, and 4) dedicated integrated block drive circuits. Discrete pin-type component circuits were commonly used in Japanese and Taiwanese inverters during the 1980s, including brands like Fuji (G2, G5), Sanken (SVS, SVF, MF), and Mitsubishi's Z and K series. However, due to the rise of large-scale integrated circuits and chip technology, these designs became overly complex and were gradually phased out. Optocoupler drive circuits are now widely adopted in modern inverter designs. Their simplicity, reliability, and excellent switching performance make them popular among manufacturers worldwide. Optocouplers are available in numerous models, providing plenty of choices. For instance, Toshiba’s TLP series, Sharp’s PC series, and HP’s HCPL series are commonly used. As an example, Toshiba’s TLP250 and TLP251 are frequently employed for driving IGBT modules. TLP251 is typically used for smaller current (15A) modules, complemented by drive power and current-limiting resistors for a basic drive circuit. Medium current (50A) modules often utilize TLP250, while larger current modules usually require an additional first-stage amplifier circuit post-optocoupler to ensure safe IGBT module operation. Thick-film driver circuits represent hybrid integrated circuits developed using RC components and semiconductor technology. These circuits employ thick-film technology to fabricate pattern components and connecting wires on ceramic substrates, integrating all driver circuit components onto the substrate. This approach simplifies design and wiring, enhances overall machine reliability, ensures consistency in mass production, and boosts technological confidentiality. Nowadays, thick-film drivers often incorporate extensive protection and detection circuits, indicating their growing complexity and sophistication. Additionally, specialized integrated block driver circuits exist, such as IR's IR1111, IR2112, IR2113, and Mitsubishi’s EXB series thick-film drivers, along with M57956 and M57959. Some European and American inverters now incorporate high-frequency isolation transformers within their drive circuits (e.g., Danfoss VLT series inverters). This addition enhances the separation of power and signals in drive circuits, improving reliability and safeguarding the weak current circuit from potential damage caused by failures in the high-voltage portion. In practice, this drive circuit design shows remarkably low failure rates, even under high-power conditions. High-power module failure remains a frequent occurrence in daily industrial usage. Possible causes include motor short circuits, poor ground insulation, mechanical blockages, or excessively high external voltages—all of which could damage the inverter's high-power modules. When replacing these modules in maintenance, it's essential to confirm the drive circuit's functionality; otherwise, newly installed modules may fail shortly afterward. Additionally, one must understand the distinction between GTR module and IGBT module drive circuits. The former relies on current-driven power modules, whereas the latter combines current and voltage-driven approaches. With ongoing progress in electronic components and large-scale integrated circuits, drive circuits continue to evolve toward greater integration, expanded functionality, and improved performance. These developments also impose higher expectations on professionals in the frequency conversion repair field. The above insights merely scratch the surface of my practical experience in frequency conversion maintenance, and I hope they spark further dialogue within this dynamic industry.