[Abstract] This article mainly introduces the current development status of high voltage frequency converters at home and abroad, and focuses on its important role in the national economy and its future development trend.
[Keywords] Modern power electronics; power semiconductors; high-voltage frequency converters
1. Introduction
In the 11th Five-Year Plan, building a resource-conserving society is an important aspect of future development. Effectively utilizing and conserving energy are concrete manifestations of building a resource-conserving society.
Electric motors are recognized as major electricity consumers, accounting for over 60% of the total electricity consumption of the national economy, indicating enormous potential for energy-saving retrofitting. Building a resource-conserving society is an essential task. Vigorously promoting variable frequency speed control technology is a necessary means to achieve this goal and is also a key focus of energy-saving retrofitting of AC motors.
2. Development Background and Significance of High Voltage Frequency Converters
With the rapid development of modern power electronics and computer control technologies, a technological revolution in electrical drives has been promoted. AC speed regulation replacing DC speed regulation, and computer digital control replacing analog control, have become development trends. AC motor variable frequency speed regulation is a major means of saving energy, improving production processes, enhancing product quality, and improving the operating environment. Variable frequency speed regulation is widely recognized both domestically and internationally as the most promising speed regulation method due to its high efficiency, high power factor, and excellent speed regulation and braking performance.
Traditional high-voltage frequency converters, composed of thyristor rectifiers and thyristor inverters, have many drawbacks, including high harmonic emissions that negatively impact both the power grid and motors. In recent years, the development of new devices such as IGBTs, IGCTs, and SGCTs has changed this situation. High-voltage frequency converters constructed from these devices offer superior performance, enabling PWM inversion and even PWM rectification. They not only feature low harmonic emissions but also significantly improved power factors.
3. Current Development Status of Domestic High Voltage Frequency Converters
Currently, there are numerous low-voltage frequency converter manufacturers in China, most of which produce small to medium-power AC 380V products. However, there are very few manufacturers specializing in high-voltage, high-power frequency converters. Only a handful of companies with research capabilities or financial strength are capable of developing, manufacturing, and providing services for high-voltage frequency converters.
Only a small number of medium and high-voltage motors in China have undergone frequency conversion speed regulation retrofitting, and they generally use V/f control. The variety and performance of high-voltage frequency converters are still under development, and the market still needs to import a large amount each year. These situations are mainly reflected in the following aspects:
① Major international brands are aggressively expanding their presence in the domestic market and accelerating their localization efforts.
② There are few enterprises with R&D capabilities and industrialization scale.
③ The power rating of domestically produced high-voltage frequency converters is relatively low, currently not exceeding 3500KW.
④ The technical standards for high-voltage frequency converters in China still need to be standardized.
⑤ The industry supporting high-voltage frequency converters is underdeveloped.
⑥ The production process is outdated, barely meeting the technical requirements of frequency converter products, but the price is low.
⑦ The key components used in frequency converters, such as power semiconductors, drive circuits, and electrolytic capacitors, are entirely dependent on imports.
⑧ The technological gap with developed countries is narrowing, and products with independent intellectual property rights are being used in the national economy.
⑨ A frequency converter with functions such as instantaneous power failure recovery and fault recovery has been developed.
⑩ High-voltage frequency converters capable of four-quadrant operation are still under research and development.
4. Current Status of High Voltage Frequency Converter Development Abroad
Major international inverter manufacturers have developed product lines, and their control systems are fully digital. Almost all products feature vector control capabilities, and sophisticated manufacturing processes are a key characteristic of international brands. Currently, in developed countries, inverters are present wherever motors are used. Their current development is mainly reflected in the following:
① Technological development started early and has a considerable scale of industrialization.
② It can provide inverters with extremely high power, currently exceeding 10,000 KW.
③ The technical standards for variable frequency speed control products are relatively complete.
④ The supporting industries and sectors related to frequency converters have begun to take shape.
⑤ Capable of producing power devices for frequency converters, such as IGBTs, IGCTs, and SGCTs.
⑥ High-voltage frequency converters are widely used in various industries and have achieved significant economic benefits.
⑦ Product internationalization is intensifying, while localization is becoming more pronounced.
⑧ New technologies and processes are emerging one after another and being applied to products in large quantities and rapidly.
⑨ Currently, there are no 10KV products.
5. Future Development Trends of High Voltage Frequency Converters
AC variable frequency speed control technology is a comprehensive technology integrating strong and weak currents and electromechanical systems. It must handle both the conversion of massive electrical energy (rectification and inversion) and the collection, transformation, and transmission of information. Therefore, it inevitably consists of two main parts: power control and control. The former addresses technical issues related to high voltage and high current, while the latter addresses hardware and software control issues. Therefore, future high-voltage variable frequency speed control technology will also develop in these two areas, mainly manifested in:
① High-voltage frequency converters will develop towards higher power, smaller size, and lighter weight.
② High-voltage frequency converters will develop in two directions: direct high voltage of devices and multiple superposition (device series and unit series).
③ New types of power semiconductor devices with higher voltage and greater current will be used in high-voltage frequency converters.
④ At present, IGBT, IGCT, and SGCT will still play the main roles, while SCR and GTO will be phased out of the frequency converter market.
⑤ The application of sensorless vector control, flux control and direct torque control technologies will become more mature.
⑥ Fully realize digitalization and automation: parameter self-setting technology; process self-optimization technology; fault self-diagnosis technology.
⑦ By using 32-bit MCU, DSP and ASIC devices, the frequency converter achieves high precision and multiple functions.
⑧ Related supporting industries are developing towards specialization and large-scale operation, and the social division of labor will become more obvious.
6. Conclusion
Building a resource-conserving society is a cause for all humankind, and the efficient use of energy is a problem that must be solved in this century. Paying attention to the development of high-voltage frequency converters is paying attention to the development of energy conservation.
