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

AC frequency conversion speed regulation technology represents a significant advancement in modern electric drive systems. By integrating power electronics, microelectronics, and advanced control theories into AC speed control systems, frequency conversion has largely replaced traditional methods like slip control, variable-pole speed control, and DC speed control. This technology is now extensively utilized across industries and daily life applications. With the widespread adoption of frequency converters, many engineers and technicians have gained familiarity with their functionality. A general-purpose inverter typically consists of four primary components: the rectifier circuit, the DC intermediate circuit, the inverter circuit, and the control circuit. The inverter circuit, which generates both adjustable voltage and frequency outputs, stands as the core technology within each inverter component. The inverter circuit comprises an inverter module and a drive circuit. Due to advancements in processing techniques, packaging technologies, and high-power transistor components, most current inverter modules originate from Japan (such as Toshiba, Mitsubishi, Sanshe, Fuji, and Sanken) or a few manufacturers in Europe and America (like Siemens, Ximenkang, Motorola, and IR). As a critical part of the inverter circuit, the drive circuit significantly influences the three-phase output of the inverter. There are several design approaches for drive circuits, including discrete pin-type component circuits, optocoupler-based drive circuits, thick-film drive circuits, and dedicated integrated block drive circuits. Discrete pin-type component drive circuits were commonly used in Japanese and Taiwanese inverters during the 1980s. These included series from Japan (Fuji: G2, G5; Sanken: SVS, SVF, MF; Kasuga; Mitsubishi Z series, K series, etc.) and Taiwan (Olin, Pu Chuan, Taian). However, with the rise of large-scale integrated circuits and chip technology, these designs became overly complex and were gradually phased out due to their low integration levels. Optocoupler drive circuits represent a widely adopted solution in modern inverter designs. Known for their simplicity, reliability, and excellent switching capabilities, they are favored by numerous inverter manufacturers globally. With many models available, the selection process can be extensive. Toshiba's TLP series, Sharp's PC series, and HP's HCPL series are prominent examples. Taking Toshiba’s TLP series as an example, the main IGBT modules are driven by two models: TLP250 and TLP251. For smaller current (15A) modules, TLP251 is typically used, complemented by drive power and current-limiting resistors to create the simplest drive circuit. For medium current (50A) modules, the TLP250 model is generally employed. For larger current modules, a first-stage amplifier circuit is usually added post-optocoupler to ensure safe driving of the IGBT module. Thick-film driver circuits, developed based on RC components and semiconductor technology, utilize thick-film technology to fabricate pattern components and connecting wires on ceramic substrates. These components are then integrated onto the ceramic substrate, forming a cohesive unit. Thick-film drivers offer significant design and wiring convenience, enhancing the overall reliability of the system and ensuring consistent mass production while bolstering technological confidentiality. Today, thick-film drivers frequently integrate various protection and detection circuits, indicating that their technical complexity continues to grow. In addition, there are specialized integrated block driver circuits, such as IR IR1111, IR2112, IR2113, and other Mitsubishi EXB series thick-film drives. Mitsubishi M57956 and M57959 thick-films are also notable examples. Moreover, some European and American inverters now incorporate high-frequency isolation transformers within their drive circuits (e.g., Danfoss VLT series inverters). Adding high-frequency transformers enhances the isolation between power and signals in the drive circuit, improving the reliability of the circuit and safeguarding the weak current circuit from potential damage caused by failures in the high-voltage section. During practical maintenance, we’ve observed that this drive circuit configuration exhibits a very low failure rate, minimizing issues with high-power modules. High-power module failure remains a common occurrence in our daily production environments. Possible causes include motor short circuits, poor ground insulation, motor blockage, or excessively high external power supply voltages, all of which can lead to damage of the inverter’s high-power module. When replacing a high-power module during maintenance, it’s crucial to confirm the drive circuit is functioning correctly; otherwise, the new module may quickly fail. Additionally, understanding the differences between GTR module and IGBT module drive circuits is essential. While the former requires current drive for both power modules, the latter combines current and voltage-driven mechanisms. With the evolution of electronic components and large-scale integrated circuits, drive circuits continue to evolve towards greater integration, expanding functionality and improving performance. Consequently, those involved in frequency converter maintenance face increasingly stringent demands. The above insights represent some of my experiences in frequency converter maintenance, and I hope this fosters further communication among professionals in this field.