Switching power supply history

1. Development of power electronics technology

The development direction of modern power electronics technology is to change from traditional power electronics, which mainly uses low-frequency technology to solve problems, to modern power electronics, which mainly uses high-frequency technology to solve problems. Power electronics technology started with silicon rectifier devices in the late 1950s and early 1960s. Its development has gone through the rectifier era, inverter era and frequency converter era, and promoted the application of power electronics technology in many new fields. The power semiconductor composite devices represented by power MOSFET and IGBT, which were developed in the late 1980s and early 1990s and integrate 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 industrial frequency (50Hz) AC generators, but about 20% of the electricity is consumed in the form of DC, the most typical of which are electrolysis (non-ferrous metals and chemical raw materials require DC electrolysis), traction (electric locomotives, electric-driven diesel locomotives, subway locomotives, urban trolleybuses, etc.) and DC transmission (steel rolling, papermaking, etc.). High-power silicon rectifiers can efficiently convert industrial frequency AC into DC, so in the 1960s and 1970s, the development and application of high-power silicon rectifiers and thyristors were greatly developed. At that time, there was a wave of silicon rectifier factories in various places in China. The current semiconductor manufacturers of large and small silicon rectifiers in the country are the products of that time.

1.2 The inverter era

In the 1970s, there was a worldwide energy crisis, and AC motor variable frequency speed regulation developed rapidly due to its significant energy-saving effect. The key technology of variable frequency speed regulation is to invert DC power into 0~100Hz AC power. From the 1970s to the 1980s, with the popularization of variable frequency speed regulation devices, thyristors, giant power transistors (GTR) and gate turn-off thyristors (GT0) for high-power inverters became the protagonists of power electronic devices at the time. Similar applications also include high-voltage DC output, static reactive power dynamic compensation, etc. At this time, power electronic technology was able to achieve rectification and inversion, but the operating frequency was low and limited to the medium and low frequency range.

1.3 The inverter era

Entering 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. The organic combination of fine processing technology of integrated circuit technology and high-voltage and high-current technology has led to the emergence of a number of new fully controlled power devices. First, the advent of power MOSFET has led to the development of small and medium-sized power supplies towards high frequency, and then the emergence of insulated gate bipolar transistors (IGBT) has brought opportunities for the development of large and medium-sized power supplies towards high frequency. The emergence of MOSFET and IGBT is a sign of the transformation of traditional power electronics to modern power electronics. According to statistics, by the end of 1995, power MOSFET and GTR had reached an equal point in the power semiconductor device market, and the use of IGBT to replace GTR has become a conclusion in the field of power electronics. The development of new devices not only provides a higher frequency for AC motor variable frequency speed regulation, making its performance more perfect and reliable, but also enables modern electronic technology to continue to develop towards high frequency, providing an important technical foundation for efficient material and energy saving of electrical equipment, small and lightweight, mechatronics and intelligence.

2. Application fields of modern power electronics

2.1 High-efficiency green power supply for computers

The rapid development of computer technology has led mankind into the information society, and has also promoted the rapid development of power supply technology. In the 1980s, computers fully adopted switching power supplies, taking the lead in completing the replacement of computer power supplies. Then switching power supply technology has successively entered the field of electronic and electrical equipment.

With the development of computer technology, green computers and green power supplies have been proposed. Green computers refer to personal computers and related products that are harmless to the environment. Green power supplies refer to high-efficiency and energy-saving power supplies related to green computers. According to the "Energy Star" program of the U.S. Environmental Protection Agency on June 17, 1992, desktop personal computers or related peripherals meet the requirements of green computers if the power consumption in sleep mode is less than 30 watts. Improving power efficiency is the fundamental way to reduce power consumption. For a 200-watt switching power supply with an efficiency of 75%, the power supply itself consumes 50 watts of energy.

2.2 High-frequency switching power supply for communication

The rapid development of the communications industry has greatly promoted the development of communications power supplies. High-frequency and miniaturized switching power supplies and their technologies have become the mainstream of modern communications power supply systems. In the field of communications, rectifiers are usually called primary power supplies, and DC-DC (DC/DC) converters are called secondary power supplies. The function of the primary power supply is to convert a single-phase or three-phase AC power grid into a DC power supply with a nominal value of 48V. At present, in the primary power supply used in programmable switches, the traditional phase-controlled voltage-stabilized power supply has been replaced by a high-frequency switching power supply. The high-frequency switching power supply (also called a switching rectifier SMR) works through the high frequency of MOSFET or IGBT, and the switching frequency is generally controlled in the range of 50-100kHz to achieve high efficiency and miniaturization. In recent years, the power capacity of switching rectifiers has been continuously expanded, and the capacity of a single machine has been expanded from 48V/12.5A, 48V/20A to 48V/200A, 48V/400A.

Since there are many types of integrated circuits used in communication equipment, their power supply voltages are also different. In the communication power supply system, a high-power-density high-frequency DC-DC isolated power supply module is used to convert the intermediate bus voltage (generally 48V DC) into various required DC voltages, which can greatly reduce losses, facilitate maintenance, and is very convenient to install and increase. Generally, it can be directly installed on the standard control board, and the requirement for the secondary power supply is high power density. As the communication capacity continues to increase, the communication power supply capacity will also 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 stepless speed change and control of trolleybuses, subway trains, and electric vehicles, and enables the above control to achieve smooth acceleration and fast response performance, while also achieving the effect of saving energy. Using a DC chopper instead of a rheostat can save (20~30)% of energy. The DC chopper can not only play the role of voltage regulation (switching power supply), but also effectively suppress the harmonic current noise on the grid side.

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

2.4 Uninterruptible Power Supply (UPS)

Uninterruptible power supply (UPS) is a highly reliable and high-performance power supply required for computers, communication systems and other occasions that require uninterrupted power. The AC mains input is converted into DC by a rectifier, part of the energy is used to charge the battery pack, and the other part of the energy is converted into AC by an inverter and sent to the load through a conversion switch. In order to still provide energy to the load when the inverter fails, another backup power supply is realized through a power conversion switch.

Modern UPS generally adopts pulse width modulation technology and modern power electronic devices such as power MOSFET and IGBT, which can reduce the noise of power supply and improve efficiency and reliability. 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 reach 600kVA. The ultra-small UPS is also developing rapidly, and there are already products with various specifications such as 0.5kVA, 1VA, 2kVA, and 3kVA.

2.5 Inverter power supply

The inverter power supply is mainly used for variable frequency speed regulation of AC motors. It occupies an increasingly important position in the electrical transmission system and has achieved great energy-saving effects. The main circuit of the inverter power supply adopts the AC-DC-AC scheme. The industrial frequency power supply is converted into a fixed DC voltage through a rectifier, and then the PWM high-frequency converter composed of high-power transistors or IGBTs inverts the DC voltage into an AC output with variable voltage and frequency. The power output waveform is similar to a sine wave, which is used to drive AC asynchronous motors to achieve stepless speed regulation.

Internationally, inverter power supply series products below 400kVA have been launched. In the early 1980s, Japan's Toshiba Corporation first applied AC variable frequency speed regulation technology to air conditioners. By 1997, its market share had reached more than 70% of Japan's household air conditioners. Variable frequency air conditioners have the advantages of comfort and energy saving. China began to study variable frequency air conditioners in the early 1990s, and introduced production lines to produce variable frequency air conditioners in 1996, gradually forming a hot spot for the development and production of variable frequency air conditioners. It is expected to reach a climax around 2000. In addition to variable frequency power supplies, variable frequency air conditioners also require compressor motors suitable for variable frequency speed regulation. Optimizing control strategies and selecting functional components are the further development directions of the research and development of variable frequency power supplies for air conditioners.

2.6 High frequency inverter rectifier welding power supply

High frequency inverter rectifier welding power supply is a new type of welding power supply with high performance, high efficiency and material saving, which represents the development direction of welding power supply today. Due to the commercialization of IGBT large capacity modules, this power supply has a broader application prospect.

Most inverter welding machine power supplies use the AC-DC-AC-DC conversion method. 50Hz AC is converted into DC through full-bridge rectification, and the PWM high-frequency conversion part composed of IGBT converts DC into a 20kHz high-frequency rectangular wave, which is coupled by a high-frequency transformer, rectified and filtered to become a stable DC for arc power supply.

Due to the harsh working conditions of the welding power supply, which is frequently in the alternating changes of short circuit, arcing and open circuit, the working reliability of the high-frequency inverter rectifier welding power supply has become the most critical issue and the issue that users are most concerned about. The microprocessor is used as the relevant controller of pulse width modulation (PWM). Through the extraction and analysis of multiple 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, which solves the current high-power IGBT inverter power supply reliability.

Foreign inverter welding machines can already achieve a rated welding current of 300A, a duty cycle of 60%, a full-load voltage of 60~75V, a current adjustment range of 5~300A, and a weight of 29kg.

2.7 High-power switching high-voltage DC power supply

High-power switching high-voltage DC power supplies are widely used in large equipment such as electrostatic dust removal, water quality improvement, medical X-ray machines and CT machines. The voltage is as high as 50~159kV, the current reaches more than 0.5A, and the power can reach 100kW.

Since the 1970s, some Japanese companies have begun to use inverter technology to convert the city power into a medium frequency of about 3kHz after rectification, and then boost the voltage. In the 1980s, high-frequency switching power supply technology developed rapidly. Siemens of Germany used power transistors as the main switching element to increase the switching frequency of the power supply to more than 20kHz. It also successfully applied dry-type transformer technology to high-frequency high-voltage power supplies, eliminated the high-voltage transformer oil tank, and further reduced the size of the transformer system.

The domestic electrostatic precipitator high-voltage DC power supply has been developed. The city power is rectified into DC, and the DC voltage is inverted into high-frequency voltage by a full-bridge zero-current switch series resonant inverter circuit, which is then boosted by a high-frequency transformer and finally rectified into DC high voltage. Under the condition of resistive load, the output DC voltage reaches 55kV, the current reaches 15mA, and the operating frequency is 25.6kHz.

2.8 Active Power Filter

When traditional AC-DC converters are put into operation, they will inject a large amount of harmonic current into the power grid, causing harmonic losses and interference. At the same time, the power factor on the grid side of the device will deteriorate, which is the so-called "power pollution". For example, when uncontrolled rectification and capacitor filtering are used, the third harmonic content on the grid side can reach (70~80)%, and the power factor on the grid side is only 0.5~0.6.

The power active filter is a new type of power electronic device that can dynamically suppress harmonics. It can overcome the shortcomings of traditional LC filters and is a very 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: (l) not only the output voltage is fed back, but also the input average current is fed back;

(2) The current loop reference signal is the product of the voltage loop error signal and the 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 technological achievements to form a building block-type, intelligent high-power power supply, thereby closely combining strong electricity with weak electricity, reducing the research and development pressure of high-power components and high-power devices (centralized), and improving production efficiency.

In the early 1980s, the research on distributed high-frequency switching power supply systems was basically 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 emerged one after another. Combined with large-scale integrated circuits and power component technology, the integration of small and medium power devices became possible, which rapidly promoted the development of distributed high-frequency switching power supply system research. Since the late 1980s, this direction has become a research hotspot in the international power electronics community, with the number of papers increasing year by year and the application field expanding continuously.

Distributed power supply has the advantages of energy saving, reliability, high efficiency, economy and easy maintenance. It has been gradually adopted by large computers, communication equipment, aerospace, industrial control and other systems, and is also the most ideal power supply for low voltage power supply (3.3V) of ultra-high-speed integrated circuits. It also has broad application prospects in high-power occasions such as electroplating, electrolysis power supply, electric locomotive traction power supply, medium-frequency induction heating power supply, motor drive power supply and other fields.

3. Development trend of high-frequency switching power supply

In the application of power electronics technology and various power supply systems, switching power supply technology is at the core. For large electrolytic and electroplating power supplies, traditional circuits are very large and bulky. If Gaodun switching power supply technology is used, its volume and weight will be greatly reduced, and it can greatly improve the efficiency of power supply utilization, save materials and reduce costs. In electric vehicles and variable frequency drives, switching power supply technology is indispensable. By changing the power frequency through switching power supply, nearly ideal load matching and drive control can be achieved. High-frequency switching power supply technology is the core technology of various high-power switching power supplies (inverter welding machines, communication power supplies, high-frequency heating power supplies, laser power supplies, power operation power supplies, etc.).

3.1 High frequency

Theoretical analysis and practical experience show that the volume weight of transformers, inductors and capacitors of electrical products is inversely proportional to the square root of the power supply frequency. So when we increase the frequency from 50Hz to 20kHz, which is 400 times higher, the volume weight of electrical equipment will drop to 5-10% of the power frequency design. Whether it is an inverter rectifier welding machine or a switch rectifier for communication power supply, it is based on this principle. Similarly, various DC power supplies such as electroplating, electrolysis, electrical processing, charging, floating charging, and power closing in the traditional "rectifier industry" can also be transformed according to this principle to become "switching conversion power supplies", and their main materials can be saved by 90% or more, and electricity can be saved by 30% or more. Due to the gradual increase in the upper limit of the operating frequency of power electronic devices, many traditional high-frequency devices that originally used electron tubes have been solidified, bringing significant economic benefits of energy saving, water saving, and material saving, and can also reflect the value of technical content.

3.2 Modularity

Modularization has two meanings. One is the modularization of power devices, and the other is the modularization of power supply units. Our common device modules contain one unit, two units, six units, and even seven units, including switching devices and freewheeling diodes connected in antiparallel with them. In fact, they all belong to "standard" power modules (SPM). In recent years, some companies have also installed the driving protection circuit of the switching device into the power module, forming 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 increase in frequency, the influence of lead parasitic inductance and parasitic capacitance has become more serious, causing greater electrical stress on the device (manifested as overvoltage and overcurrent burrs). 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 whole machine into a module in the form of a chip, so that there is no traditional lead connection between components. Such a module has been strictly and reasonably designed in terms of heat, electricity, and machinery to achieve the state of optimization and perfection. It is similar to the user-specific integrated circuit (ASIC) in microelectronics. As long as the control software is written into the microprocessor chip in the module and the entire module is fixed on the corresponding heat sink, a new type of switching power supply device is formed. It can be seen that the purpose of modularization is not only to facilitate use and reduce the size of the whole machine, but more importantly, to cancel the traditional connection, reduce the parasitic parameters to a minimum, thereby reducing the electrical stress of the device to a minimum and improving the reliability of the system. In addition, due to the limitation of device capacity and the consideration of increasing redundancy to improve reliability, high-power switching power supplies generally use multiple independent module units to work in parallel, using current balancing technology, all modules share the load current together, and once one of the modules fails, the other modules will share the load current evenly. In this way, not only the power capacity is improved, and the requirements of high current output are met under the condition of limited device capacity, but also the system reliability is greatly improved by adding redundant power supply modules with very small power relative to the entire system. Even if a single module fails, it will not affect the normal operation of the system and provide sufficient time for repair.

3.3 Digitalization

In traditional power electronics technology, the control part is designed and works according to analog signals. In the 1960s and 1970s, power electronics technology was completely based on analog circuits. However, digital signals and digital circuits are becoming more and more important, and digital signal processing technology is becoming more and more mature, showing more and more advantages: it is easy to process and control by computers, avoid distortion of analog signals, reduce interference from stray signals (improve anti-interference ability), facilitate software package debugging and remote sensing, telemetry and remote adjustment, and also facilitate the implantation of self-diagnosis, fault tolerance and other technologies. Therefore, in the 1980s and 1990s, analog technology was still useful for the design of various circuits and systems, especially: the solution of problems such as printed circuit layout, electromagnetic compatibility (EMC) and power factor correction (PFC) cannot be separated from the knowledge of analog technology, but for intelligent switching power supplies, when computer control is required, digital technology cannot be separated.

3.4 Greening

The greening of power supply system has two meanings: first, it can significantly save electricity, which means saving power generation capacity. Power generation is an important cause of environmental pollution, so saving electricity can reduce pollution to the environment; second, these power supplies cannot (or less) pollute the power grid. The International Electrotechnical Commission (IEC) has formulated a series of standards for this, such as IEC555, IEC917, IEC1000, etc. In fact, many power electronic power-saving devices often become a source of pollution to the power grid: injecting serious high-order harmonic currents into the power grid, reducing the total power factor, coupling many burrs and spikes to the power grid voltage, and even causing missing corners and distortion. At the end of the 20th century, various active filter and active compensator solutions were born, and there were many methods to correct the power factor. These laid the foundation for the mass production of various green switching power supply products in the 21st century.

Modern power electronics technology is the foundation of the development of switching power supply technology. With the continuous emergence of new power electronic devices and circuit topologies suitable for higher switching frequencies, modern power supply technology will develop rapidly driven by practical needs. Under traditional application technology, the performance of the switching power supply is affected due to the limitation of power device performance. In order to maximize the characteristics of various power devices and minimize the impact of device performance on the performance of the switching power supply, new power supply circuit topologies and new control technologies can make the power switch work in a zero voltage or zero current state, thereby greatly increasing the operating frequency, improving the working efficiency of the switching power supply, and designing a switching power supply with excellent performance.

In short, power electronics and switching power supply technology are constantly developing due to application needs. The emergence of new technologies will enable many application products to be updated and replaced, and will also open up more and newer application fields. The realization of high frequency, modularization, digitization, and greening of switching power supplies will mark the maturity of these technologies and achieve the combination of high-efficiency and high-quality electricity use. In recent years, with the development of the communications industry, the switching power supply for communications with switching power supply technology as the core has a market demand of more than 2 billion yuan in China alone, attracting a large number of scientific and technological personnel at home and abroad to develop and research it. It is a general trend for switching power supplies to replace linear power supplies and phase-controlled power supplies. Therefore, the domestic market for power-operated power supply systems, which also have a demand for billions of output value, is starting and will soon develop. There are also many other special power supplies and industrial power supplies with switching power supply technology as the core waiting for people to develop.