Background knowledge:
Basic principle:
According to the application fields of modern power electronics, we divide power sources as follows:
1. High efficiency green power supply for computers
The rapid development of computer technology has led humanity into the information society, while also promoting the rapid development of power technology. In the 1980s, computers fully adopted switch mode power supplies, taking the lead in completing the replacement of computer power supplies. Subsequently, switch mode power supply technology has entered the fields of electronics and electrical equipment.
The development of computer technology has led to the proposal of green computers and green power sources. Green computers generally refer to personal computers and related products that are harmless to the environment. Green power refers to high-efficiency and energy-saving power sources related to green computers. According to the Energy Star program of the US Environmental Protection Agency on June 17, 1992, desktop personal computers or related peripheral devices that consume less than 30 watts of power during sleep meet the requirements of green computers. Improving power efficiency is the fundamental way to reduce power consumption. For the current 200 watt switching power supply with an efficiency of 75%, the power supply itself consumes 50 watts of energy.
High frequency switching power supply for communication
The rapid development of the communication industry has greatly promoted the development of communication power supply. High frequency miniaturized switching power supplies and their technologies have become the mainstream of modern communication power supply systems. In the field of communication, rectifiers are commonly referred to as primary power sources, while DC-DC converters are referred to as secondary power sources. The function of a 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primary power supply used in program-controlled switches, traditional phase controlled regulated power supplies have been replaced by high-frequency switching power supplies. High frequency switching power supplies (also known as switch mode rectifiers SMR) operate at high frequencies through MOSFETs or IGBTs, with switching frequencies generally controlled within the range of 50-100kHz, achieving high efficiency and miniaturization. In recent years, the power capacity of switch rectifiers has been continuously expanding, with single machine capacity increasing 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 and their varying power supply voltages, high-power density high-frequency DC-DC isolated power modules are used in communication power supply systems to convert the intermediate bus voltage (usually 48V DC) into various required DC voltages. This greatly reduces losses, facilitates maintenance, and is very easy to install and add. Generally, it can be directly installed on a standard control board, and the requirement for the secondary power supply is high power density. Due to the continuous increase in communication capacity, the capacity of communication power supply will also continue to increase.
3 DC-DC converters
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 trolleybus, subway trains, and electric vehicles, while achieving smooth acceleration, fast response performance, and energy-saving effects. Replacing the variable resistor with a DC chopper can save energy by 20-30%. DC chopper can not only regulate voltage (switching power supply), but also effectively suppress harmonic current noise on the grid side.
The secondary power DC/DC converter for communication power supply has been commercialized, and the module adopts high-frequency PWM technology with a switching frequency of around 500kHz and a power density of 5W~20W/n3. With the development of large-scale integrated circuits, there is a demand for miniaturization of power modules. Therefore, it is necessary to continuously increase the switching frequency and adopt new circuit topologies. Currently, some companies have developed and produced secondary power modules using zero current switching and zero voltage switching technologies, which have significantly improved power density.
4 Uninterruptible Power Supply (UPS)
Uninterruptible power supply (UPS) is a highly reliable and high-performance power source necessary for computers, communication systems, and applications that require uninterrupted power supply. The AC mains input is converted into DC through a rectifier, and a portion of the energy is used to charge the battery pack. The other portion of the energy is converted into AC through an inverter and sent to the load through a conversion switch. In order to provide energy to the load in case of inverter failure, another backup power supply is implemented through a power conversion switch.
Modern UPS commonly uses pulse width modulation technology and modern power electronic devices such as M0SFET and IGBT, which reduces power noise and improves efficiency and reliability. The introduction of microprocessor software and hardware technology can achieve intelligent management, remote maintenance, and remote diagnosis of UPS.
At present, the maximum capacity of online UPS can reach 600kVA. The development of ultra small UPS is also very rapid, with various specifications of products such as 0.5kVA, lVA, 2kVA, 3kVA, etc.
5. Inverter power supply
Variable frequency power supply is mainly used for variable frequency speed regulation of AC motors, and its position in electrical transmission systems is becoming increasingly important, achieving significant energy-saving effects. The main circuit of the frequency converter power supply adopts the AC-DC-AC scheme. The power supply is converted into a fixed DC voltage through a rectifier, and then a 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 output waveform of the power supply is similar to a sine wave, which is used to drive AC asynchronous motors to achieve stepless speed regulation.
Internationally, a series of frequency converter power supply products below 400kVA have been launched. In the early 1980s, Toshiba Corporation of Japan was the first to apply AC variable frequency speed regulation technology to air conditioners. By 1997, its market share had reached over 70% of Japan’s household air conditioners. Variable frequency air conditioning has advantages such as comfort and energy efficiency. In the early 1990s, research on variable frequency air conditioners began in China. In 1996, production lines were introduced to produce variable frequency air conditioners, gradually forming a hot spot in the development and production of variable frequency air conditioners. It is expected to reach a climax around the year 2000. In addition to the variable frequency power supply, the variable frequency air conditioner also requires a compressor motor suitable for variable frequency speed regulation. Optimizing control strategies and selecting functional components are further development directions for the research and development of air conditioning variable frequency power supplies.
6 High frequency inverter rectifier welding machine power supply
High frequency inverter rectifier welding machine power supply is a new type of welding machine power supply with high performance, high efficiency, and material saving, representing the development direction of welding machine power supply today. Due to the commercialization of IGBT high-capacity modules, this power supply has broad application prospects.
Most inverter welding machine power supplies use the AC-DC-AC-DC conversion method. 50Hz AC power is rectified by a full bridge and converted into DC power. The PWM high-frequency conversion part composed of IGBT reverses the DC power into a 20kHz high-frequency rectangular wave, which is coupled by a high-frequency transformer, rectified and filtered to become a stable DC power for arc supply.
Due to the harsh working conditions of the welding machine power supply, which frequently alternates between short circuits, arcing, and open circuits, the reliability of the high-frequency inverter rectifier welding machine power supply has become the most critical issue and the most concerned issue for users. Using a microprocessor as the relevant controller for pulse width modulation (PWM), by extracting and analyzing multiple parameters and information, the goal of predicting various working states of the system can be achieved, and the system can be adjusted and processed in advance to solve the reliability of high-power IGBT inverter power sources.
Foreign inverter welding machines can achieve a rated welding current of 300A, a load duration of 60%, a full load voltage of 60-75V, a current regulation range of 5-300A, and a weight of 29kg.
7 high-power switch type high-voltage DC power supply
High power switch type high-voltage direct current power supplies are widely used in large equipment such as electrostatic precipitators, water quality improvement, medical X-ray machines, and CT machines. The voltage can reach up to 50~159kV, the current can exceed 0.5A, and the power can reach 100kW.
Since the 1970s, some Japanese companies have adopted inverter technology, which rectifies the mains power and converts it into a medium frequency of around 3kHz, and then boosts it. In the 1980s, high-frequency switching power supply technology developed rapidly. Siemens AG in Germany uses power transistors as the main switching element to increase the switching frequency of the power supply to over 20kHz. And the dry-type transformer technology has been successfully applied to high-frequency and high-voltage power supplies, eliminating the high-voltage transformer oil tank and further reducing the volume of the transformer system.
A high-voltage DC power supply for electrostatic precipitator has been developed domestically. The mains power is rectified into DC, and a full bridge zero current switch series resonant inverter circuit is used to invert the DC voltage into high-frequency voltage, which is then stepped up by a high-frequency transformer and finally rectified into DC high voltage. Under resistive load conditions, the output DC voltage reaches 55kV, the current reaches 15mA, and the operating frequency is 25.6kHz.
8. Active power filter
Traditional AC-DC converters inject a large amount of harmonic current into the power grid during operation, causing harmonic losses and interference. At the same time, there is also a phenomenon of deterioration of the power factor on the grid side, known as “power pollution”. For example, when uncontrolled rectification and capacitor filtering are added, 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.
Active power filter is a new type of power electronic device that can dynamically suppress harmonics, overcome the shortcomings of traditional LC filters, and is a promising harmonic suppression method. The filter consists of a bridge switch power converter and a specific control circuit. The difference from traditional switching power supplies is that: (l) it not only feeds back the output voltage, but also feeds back the average input current; (2) The current loop reference signal is the product of the voltage loop error signal and the full wave rectified voltage sampling signal.
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 utilizes the latest theories and technological achievements to form a modular and intelligent high-power power supply. This tightly integrates strong and weak electricity, reduces the development pressure of high-power components and high-power devices (centralized), and improves production efficiency.
In the early 1980s, research on distributed high-frequency switching power supply systems mainly focused on the study 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-sized power devices became possible, which quickly promoted the research of distributed high-frequency switching power supply systems. Since the late 1980s, this field has become a research hotspot in the international power electronics industry, with an increasing number of papers and expanding application areas year by year.
The distributed power supply method 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 method for low voltage power (3.3V) of ultra high speed integrated circuits. In high-power applications, such as electroplating, electrolytic power supply, electric locomotive traction power supply, intermediate frequency induction heating power supply, electric motor drive power supply, etc., there are also broad application prospects.
Current situation and development:
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 technology will rapidly develop under the driving force of practical needs. Under traditional application technologies, the performance of switching power supplies is affected due to limitations in power device performance. In order to maximize the characteristics of various power devices and minimize the impact of device performance on the performance of switching power supplies, new power circuit topologies and control technologies can enable power switches to operate in zero voltage or zero current states, thereby greatly increasing the operating frequency and efficiency of switching power supplies, and designing high-performance switching power supplies. Power electronics and switching power supply technology are constantly advancing due to application demands, and the emergence of new technologies will lead to the upgrading of many application products and the exploration of more new application areas. The realization of high-frequency, modular, digital, and green switching power supplies will mark the maturity of these technologies, achieving a combination of high-efficiency and high-quality electricity consumption. In recent years, with the development of the communication industry, there has been a market demand of over 2 billion yuan for communication switch power supplies with switch power supply technology as the core, which has attracted a large number of domestic and foreign scientific and technological personnel to develop and research them. The replacement of linear and phase controlled power supplies with switch mode power supplies is the trend, therefore, the domestic market for power operation power supply systems with billions of output value demand is starting to emerge and will soon develop. There are many other specialized power supplies and industrial power supplies with switch mode power supply technology as the core waiting for people to develop.