Discussion on the development of modern power electronics and power technology

Abstract: This paper expounds the development process of modern power electronics technology, describes the application fields of power electronics technology, and discusses the development trend of modern power technology.

Keywords: power electronic technology switching power supply

Modern power technology is a multidisciplinary edge-crossing technology that uses power electronics semiconductor devices, integrated automatic control, computer (microprocessor) technology and electromagnetic technology. It plays a key role in various high-quality and high-efficiency high-reliability power supplies and is the specific application of modern power electronics technology.

At present, power electronics, as the foundation of energy saving, saving, automation, intelligence and mechatronics is developing in the direction of high-frequency application technology, modular hardware structure, and green product performance. In the near future, power electronics technology will make power supply technology more mature, economical and practical, and achieve high efficiency and high quality power.

1. Development of power electronics technology

The development direction of modern power electronics technology is from the traditional power electronics with low-frequency technology processing topics to the modern power electronics with high-frequency technology processing topics. Power electronics technology began in the late 1950s and early 1960s, and its development has experienced the era of rectifiers, inverters and inverters, and promoted the application of power electronics in many new fields. The power semiconductor composite devices, which are developed in the late 1980s and early 1990s and represented by power MOSFETs and IGBTs, which combine high-frequency, high-voltage and high-current, show that traditional power electronics technology has entered the modern power electronics era. .

1.1 rectifier era

High-power industrial electricity is provided by power frequency (50Hz) alternators, but about 20% of the electricity is consumed in direct current, the most typical of which is electrolysis (non-ferrous metals and chemical materials require DC electrolysis), traction (electrical Locomotives, electric drive diesel locomotives, subway locomotives, urban trolley buses, etc.) and DC transmission (rolling steel, papermaking, etc.) three major areas. High-power silicon rectifiers can efficiently convert power-frequency AC to DC power. Therefore, in the 1960s and 1970s, the development and application of high-power silicon rectifiers and thyristors were greatly developed. At that time, China had set off a climax of the large-scale silicon rectifier factory in various places. At present, the semiconductor manufacturers of large and small silicon rectifiers in China are the products of that time.

1.2 Inverter era

In the 1970s, there was a worldwide energy crisis, and AC motor frequency conversion idling developed rapidly due to the obvious energy saving effect. The key technology of frequency conversion speed regulation is to invert DC power to 0~100Hz AC. In the 1970s and 1980s, with the popularization of frequency converters, thyristors, giant power transistors (GTRs) and gate turn-off thyristors (GT0) for high-power inverters became the protagonists of power electronics at that time. Similar applications include high voltage DC output, static reactive power dynamic compensation, and more. At this time, power electronics technology has been able to achieve rectification and inverter, but the operating frequency is low, only limited to the low-mid frequency range.

1.3 inverter era

In the 1980s, the rapid development of large-scale and ultra-large-scale integrated circuit technology laid the foundation for the development of modern power electronics technology. Combining the fine processing technology of integrated circuit technology with the high-voltage and high-current technology, a new batch of fully-controlled power devices, first of all, the emergence of power MOSFETs has emerged, which has led to the development of medium- and small-power power supplies to high-frequency, and then the door The emergence of extremely bipolar transistors (IGBTs) has brought opportunities for high-frequency development of large and medium-sized power supplies. The successive introduction of MOSFETs and IGBTs is a sign of the transformation of traditional power electronics into modern power electronics. According to statistics, by the end of 1995, power MOSFETs and GTRs had reached a level of equalization in the power semiconductor device market, and the replacement of GTRs with IGBTs was conclusive in the field of power electronics. The development of new devices not only provides high frequency for AC motor frequency conversion speed regulation, but also makes its performance more perfect and reliable, and makes modern electronic technology continue to develop at high frequency, which is energy efficient and energy-saving for electric equipment. Quantification, mechatronics and intelligence provide an important technical foundation.

2. Application fields of modern power electronics

2.1 computer high efficiency green power supply

The rapid development of computer technology has led humans into the information society, and has also promoted the rapid development of power technology. In the 1980s, the computer fully adopted the switching power supply, and took the lead in completing the computer power generation. Then switching power supply technology has entered the field of electronics and electrical equipment.

The development of computer technology has proposed green computers and green power supplies. Green computers refer to personal computers and related products that are harmless to the environment. Green power refers to efficient power-saving power supplies related to green computers. According to the US Environmental Protection Agency's June 17, 1992 "Energy Star" program, the table Type PCs or related peripheral devices, if the power consumption in the sleep state is less than 30 watts, it meets the requirements of green computers, and improving power efficiency is the fundamental way to reduce power consumption. For a current 200 watt switching power supply with 75% efficiency, the power supply itself consumes 50 watts of energy.

2.2 Communication high frequency switching power supply

The rapid development of the communication industry has greatly promoted the development of communication power. The high-frequency miniaturized switching power supply and its technology have become the mainstream of modern communication power supply systems. In the field of communications, a rectifier is often referred to as a primary power source, and a direct current-direct current (DC/DC) converter is referred to as a secondary power source. The function of the primary power supply is to convert the single-phase or three-phase AC power grid into a DC power source with a nominal value of 48V. At present, in the primary power supply for the program-controlled switch, the traditional phase-controlled regulated power supply has been replaced by the high-frequency switching power supply. The high-frequency switching power supply (also called the switching rectifier SMR) operates at high frequency through the MOSFET or IGBT, and the switching frequency generally controlled in the range of 50-100 kHz, achieving high efficiency and miniaturization. In recent years, the power capacity of switching rectifiers has been continuously expanded, and the stand-alone capacity has been expanded from 48V/12.5A and 48V/20A to 48V/200A and 48V/400A.

Due to the wide variety of integrated circuits used in communication equipment, the power supply voltage is also different. In the communication power supply system, a high-power density high-frequency DC-DC isolated power supply module is used, which is converted from the intermediate bus voltage (generally 48V DC). Various DC voltages are required, which can greatly reduce the loss, facilitate maintenance, and is very convenient to install and increase. Generally, it can be directly mounted on the standard control board. The requirement for the secondary power supply is high power density. As communication capacity continues to increase, communication power capacity will continue to increase.

2.3 DC-DC converter

The DC/DC converter converts a fixed DC voltage into a variable DC voltage. This technology is widely used in the continuously variable transmission and control of trolley buses, subway trains, electric vehicles, and at the same time, the above control is accelerated and stable. Responsive performance and at the same time receive the effect of saving energy. Replacing the varistor with a DC chopper saves energy (20~30)%. The DC chopper can not only function as a voltage regulator (switching power supply), but also effectively suppress the harmonic current noise of the grid side.

The secondary power supply DC/DC converter of the communication power supply has been commercialized, and the module adopts high frequency PWM technology. The switching frequency is about 500 kHz and the power density is 5W~20W/in3. With the development of large-scale integrated circuits, power modules are required to be miniaturized. Therefore, it is necessary to continuously improve the switching frequency and adopt a new circuit topology. At present, some companies have developed and produced two technologies using zero current switching and zero voltage switching technology. The secondary power module has a significant improvement in power density.

2.4 uninterruptible power supply (UPS)

Uninterruptible power supplies (UPS) are high-reliability, high-performance power supplies that are required for computers, communication systems, and where uninterrupted applications are required. The AC mains input is converted to DC by the rectifier, part of the energy is charged to the battery pack, and the other part of the energy is converted into AC through the inverter, and sent to the load via the transfer switch. In order to still provide energy to the load in the event of an inverter failure, another alternate power source is implemented by a power transfer switch.

Modern UPS generally adopts pulse width modulation technology and modern power electronic devices such as power MOSFETs and IGBTs, and the noise of the power supply is reduced, and the efficiency and reliability are improved. The introduction of microprocessor hardware and software technology can realize intelligent management of UPS, remote maintenance and remote diagnosis.

At present, the maximum capacity of online UPS can be made up to 600kVA. The development of ultra-small UPS is also very fast, and there are already various specifications of products such as 0.5kVA, 1kVA, 2kVA, 3kVA.

2.5 inverter power supply

The inverter power supply is mainly used for frequency conversion speed regulation of AC motors, and its position in the electric drive system is becoming more and more important, and huge energy-saving effects have been obtained. The main circuit of the inverter power supply adopts the AC-DC-AC scheme. The power frequency power supply is turned into a fixed DC voltage through a rectifier, and then a PWM high frequency converter composed of a high power transistor or an IGBT converts the DC voltage into a voltage and variable frequency AC output, and the power output waveform is approximated to a sine wave. It is used to drive AC asynchronous motor to achieve stepless speed regulation.

International inverter power supply products below 400kVA have been introduced. In the early 1980s, Toshiba Corporation of Japan first applied AC variable frequency speed control technology to air conditioners. By 1997, its market share had reached more than 70% of Japanese household air conditioners. Inverter air conditioners have the advantages of comfort and energy saving. In the early 1990s, China began to research inverter air conditioners. In 1996, it introduced production lines to produce inverter air conditioners, and gradually formed the development and production of inverter air conditioners. It is expected that a climax will be formed by around 2000. In addition to the variable frequency power supply, the inverter air conditioner also requires a compressor motor suitable for variable frequency speed regulation. Optimizing the control strategy and selecting functional components is the further development direction of the development of air conditioner variable frequency power supply.

2.6 high frequency inverter type rectifier welding machine power supply

The high-frequency inverter rectifier welding machine power supply is a new type of welding machine power supply with high performance, high efficiency and low cost, which represents the development direction of today's welding machine power supply. Due to the commercialization of IGBT high-capacity modules, this power supply has a broad application prospect.

Most of the inverter welding machine power supply adopts the AC-DC-AC-DC (AC-DC-AC-DC) conversion method. The 50Hz AC power is converted into DC by full-bridge rectification. The PWM high-frequency conversion part composed of IGBT inverts the DC power into a high-frequency rectangular wave of 20k Hz. After high-frequency transformer coupling, it is stabilized and filtered by the high-frequency transformer, and the power supply arc is used.

Due to the harsh working conditions of the welding machine power supply, frequent short-circuit, arcing, and open circuit changes, the work reliability problem of the high-frequency inverter type rectifying machine power supply has become the most critical issue, and it is also the most concerned topic for users. . The microprocessor is used as the pulse width modulation (PWM) related controller. Through the extraction and analysis of multi-parameters and multiple- information, the purpose of predicting various working states of the system is achieved, and then the system is adjusted and processed in advance to solve the problem. The current high-power IGBT inverter power supply reliability.

The foreign inverter welding machine can achieve rated welding current of 300A, load duration of 60%, full load voltage of 60~75V, current adjustment range of 5~300A and weight of 29kg.

2.7 high power switching type high voltage DC power Supply

High-power switch-type high-voltage DC power supplies are widely used in large-scale equipment such as electrostatic precipitator, water quality improvement, medical X-ray machines and CT machines. The voltage is as high as 50~l59kV, the current reaches 0.5A and the power can reach 100kW.

Since the 1970s, some companies in Japan have adopted inverter technology to rectify the mains to a medium frequency of about 3 kHz and then boost. In the 1980s, high-frequency switching power supply technology developed rapidly. Siemens Germany uses power transistors as the main switching components to increase the switching frequency of the power supply to more than 20 kHz. The dry-type transformer technology was successfully applied to the high-frequency high-voltage power supply, and the high-voltage transformer fuel tank was eliminated, so that the volume of the transformer system was further reduced.

The domestic research on electrostatic precipitator high-voltage DC power supply has been developed. The mains is rectified into DC, and the full-bridge zero-current switch series resonant inverter circuit is used to invert the DC voltage into a high-frequency voltage, which is then boosted by a high-frequency transformer and finally rectified. It is DC high voltage. Under resistive load conditions, the output DC voltage reaches 55kV, the current reaches 15mA, and the operating frequency is 25.6k Hz.

2.8 Power Active Filter

When the conventional AC-DC converter is put into operation, a large amount of harmonic current will be injected into the grid, causing harmonic loss and interference, and the phenomenon that the power factor of the device network side deteriorates, that is, the so-called " Power pollution, for example, when uncontrolled rectification plus capacitor filtering, the third harmonic content of the network side can reach (70~80)%, and the power factor of the grid side is only 0.5~0.6.

The active power filter is a new type of power electronic device capable of dynamically suppressing harmonics. It can overcome the shortcomings of traditional LC filters and is a promising harmonic suppression method. The filter consists of a bridge switching power converter and a specific control circuit. The difference from the traditional switching power supply is: (1) not only feedback output voltage, but also feedback input uniform current; (2) current loop reference signal is the product of voltage loop error signal and full-wave rectified voltage sampling signal.

2.9 Distributed Switching Power Supply System

The distributed power supply system uses small power modules and large-scale control integrated circuits as basic components, and uses the latest theoretical and technical achievements to form a modular and intelligent high-power power supply, so that the strong and weak powers are tightly combined to reduce high power. The development pressure of components and high-power devices (centralized) to improve production efficiency.

In the early 1980s, research on distributed high-frequency switching power supply systems focused on the research of converter parallel technology. In the mid-to-late 1980s, with the rapid development of high-frequency power conversion technology, various converter topologies have emerged, combining large-scale integrated circuits and power component technologies to enable the integration of small and medium-sized power devices, thus rapidly Promoted the development of distributed high frequency switching power supply systems. Since the late 1980s, this direction has become a hot research topic in the international power electronics industry. The number of papers has increased year by year, and the application field has been expanding.

The distributed power supply mode has the advantages of energy saving, reliability, high efficiency, economy and convenient maintenance. It has been gradually adopted by large computers, communication equipment,special, industrial control systems, etc. It is also the most ideal power supply for low-voltage power supplies (3.3V) of ultra-high-speed integrated circuits. In high-power applications, such as electroplating, electrolysis power supply, electric locomotive traction power supply, intermediate frequency induction heating power supply, motor drive power supply and other fields also have broad application prospects.

3. The development trend of high frequency switching power supply

In the application of power electronics technology and various power systems, switching power supply technology is at the core. For large electrolytic plating power supplies, the traditional circuit is very large and bulky. If the high-voltage switching power supply technology is adopted, the volume and weight will be greatly reduced, and the power utilization efficiency, material saving, and cost reduction can be greatly improved. In electric vehicles and variable frequency drives, switching power supply technology is indispensable, and the power frequency is changed by the switching power supply to achieve near-optimal load matching and drive control. High-frequency switching power supply technology is the core technology of various high-power switching power supplies (inverter welding machine, communication power supply, high-frequency heating power supply, laser power supply, electric power supply, etc.).

3.1 High frequency

Theoretical analysis and practical experience show that the volumetric weight of transformers, inductors and capacitors of electrical products is inversely proportional to the square root of the supply frequency. Therefore, when we increase the frequency from 50Hz to 20kHz and increase 400 times, the volumetric weight of the electrical equipment is roughly reduced to 5~10% of the power frequency design. Both the inverter rectification welder and the switching rectifier for communication power supply are based on this principle. Similarly, various DC power supplies such as electroplating, electrolysis, electric processing, charging, floating charging, and power closing for the traditional "rectification industry" can be modified according to this principle to become a "switching conversion type power supply", and its main materials can be Save 90% or more and save 30% or more. Due to the gradual progress of the upper limit of the operating frequency of power electronic devices, many traditional high-frequency devices that originally used electron tubes have been solidified, which has obvious economic benefits of energy saving, water-saving and material saving, and can reflect the value of technical content.

3.2 Modular

Modularity has two meanings, one of which refers to the modularization of power devices, and the other refers to the modularization of power supply units. Our common device modules, consisting of one unit, two units, six units up to seven units, including switching devices and their anti-parallel freewheeling diodes, are essentially "standard" power modules (SPM). In recent years, some companies have installed the drive protection circuit of the switching device into the power module to form an "intelligent" power module (IPM), which not only reduces the size of the whole machine, but also facilitates the design and manufacture of the whole machine. In fact, due to the continuous improvement of the frequency, the influence of lead parasitic inductance and parasitic capacitance is more serious, causing greater electrical stress on the device (expressed as overvoltage, over-current glitch). In order to improve the reliability of the system, some manufacturers have developed a "user-specific" power module (ASPM), which installs almost all the hardware of a complete machine into a module in the form of a chip, so that components are no longer With traditional lead connections, such modules have undergone rigorous and fair thermal, electrical and mechanical design to achieve optimal and perfect conditions. It is similar to an application specific integrated circuit (ASIC) in microelectronics. As long as the control software is written into the microprocessor chip in the module, and then the entire module is fixed on the corresponding heat sink, it constitutes a new type of switching power supply device. It can be seen that the purpose of modularization is not only to facilitate the use, but also to reduce the size of the whole machine. What is more important is to eliminate the traditional connection and minimize the parasitic parameters, thereby minimizing the electrical stress on the device and improving the reliability of the system. . In addition, high-power switching power supplies, due to device capacity limitations and increased reliability and reliability considerations, generally use multiple independent modular units to work in parallel, using current sharing technology, all modules share the load current, once one of them the modules fail, and the other modules evenly share the load current. In this way, not only the power capacity is improved, the high current output is satisfied in the case of limited device capacity, and the system power is greatly improved by increasing the redundant power supply module with a small power relative to the entire system, even if In the event of a single module failure, it will not affect the normal operation of the system and provide sufficient time for repair.

3.3 Digitization

In traditional power electronics, the control section is designed and operated as an analog signal. In the 1960s and 1970s, power electronics technology was based entirely on analog circuits. However, digital signals and digital circuits are becoming more and more important nowadays. Digital signal processing technology is becoming more and more mature, showing more and more advantages: easy computer processing control, avoiding distortion of analog signals, and reducing spurious signals. Interference (progressive anti-interference ability), easy package debugging and remote sensing far-distance adjustment, and also facilitate the self-diagnosis, fault tolerance and other technologies. Therefore, in the 1980s and 1990s, analog technology was useful for the design of various circuits and systems, especially: layouts such as printed plates, electromagnetic compatibility (EMC) problems, and power factor correction (PFC). The solution to the problem is inseparable from the knowledge of analog technology, but for intelligent switching power supplies, when digital control is required, digital technology cannot be separated.

3.4 Green

The greening of the power system has two meanings: firstly, it is obviously saving electricity, which means saving power generation capacity, and power generation is an important cause of environmental pollution, so power saving can reduce environmental pollution; secondly, these power sources cannot ( Or less) pollution to the power grid, the International Electrotechnical Commission (IEC) has developed a series of standards, such as IEC555, IEC917, IECl000 and so on. In fact, many power electronic power-saving devices often become sources of pollution to the power grid: injecting severe high-order harmonic currents into the grid, causing the total power factor to drop, causing the grid voltage to couple many burr spikes and even cornering and distortion. At the end of the 20th century, various active filter and active compensator solutions were born, with a variety of methods to correct the power factor. These laid the foundation for the mass production of various green switching power products in the 21st century.

Modern power electronics technology is the basis for the development of switching power supply technology. With the emergence of new power electronics and circuit topologies for higher switching frequencies, modern power technologies will grow rapidly with real-world needs. Under the traditional application technology, the performance of the switching power supply is affected due to the limitation of the performance of the power device. In order to maximize the characteristics of various power devices and minimize the impact of device performance on the performance of switching power supplies, the new power circuit topology and new control technology can make the power switch work in zero voltage or zero current state. Greatly improve the working frequency, improve the working efficiency of the switching power supply, and design a switching power supply with excellent performance.

All in all, power electronics and switching power supply technology continue to advance due to application requirements. The emergence of new technologies will lead to the replacement of many application products, and will open up more updated application areas. The realization of high-frequency switching, modularization, digitization and greening of switching power supplies will mark the maturity of these technologies and realize the combination of high-efficiency electricity and high-quality electricity. In recent years, with the development of the communication industry, the switching power supply for communication with the switching power supply technology as the core has only a market demand of more than 2 billion RMB in China, attracting a large number of scientific and technical staff at home and abroad to carry out research and development. Switching power supplies are the main trend in place of linear power supplies and phase-controlled power supplies. Therefore, the domestic markets for power-operated power systems that also have billions of output requirements is starting and will soon develop. There are many other dedicated power supplies and industrial power supplies with switching power supply technology as the core, which are waiting for people to develop.

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