Author: Wang Class: Mechanical Design 09 18 Major: Mechanical and Electrical Equipment Maintenance and ManagementNo.: 09 183 16 College: Anhui Institute of Hydropower Date: 2010 65438+February.

Nowadays, the energy consumption in the world is growing very rapidly. At present, electric energy accounts for about 40% of all energy sources, and 40% of electric energy comes to users through the conversion of power electronic equipment. It is predicted that after ten years, 80% of power energy will be converted by power electronic equipment, and power electronic technology will play a greater role in 2 1 century.

Power electronics technology is a subject that uses power electronic devices to control and convert electric energy. It includes three parts: power electronic devices, converter circuits and control circuits, and is an interdisciplinary subject among the three electrical engineering technical fields of power, electronics and control. With the development of science and technology, power electronics technology is closely related to modern control theory, material science, electrical engineering, microelectronics technology and many other fields, and has gradually developed into a comprehensive technical discipline with multi-disciplinary infiltration.

Modern power supply technology is a multidisciplinary edge crossing technology which applies power electronic semiconductor devices and integrates automatic control, computer (microprocessor) technology and electromagnetic technology. It plays a key role in various high-quality, high-efficiency and high-reliability power supplies, and is a concrete application of modern power electronics technology. At present, power electronics, as the basis of energy saving, talent saving, automation, intelligence and mechatronics, is developing towards high-frequency application technology, modular hardware structure and green product performance. In the near future, power electronics technology will make power technology more mature, economical and practical, and realize the combination of high efficiency and high quality electricity consumption.

First, the development history of power electronics technology

1. rectifier era

High-power industrial electricity is provided by power frequency (50Hz) alternator, but about 20% of the electricity is consumed in the form of DC. The most typical ones are electrolysis (non-ferrous metals and chemical raw materials need DC electrolysis) and traction (electric locomotives, electric diesel locomotives, subway locomotives, urban trolleybuses, etc.). ) and DC drive (steel rolling, paper making, etc. High-power silicon rectifiers can efficiently convert power frequency alternating current into direct current, so the development and application of high-power silicon rectifiers and thyristors have been greatly developed in the 1960s and 1970s. At that time, there was an upsurge of running large-scale silicon rectifier plants in various parts of China. At present, large and small semiconductor manufacturers of silicon rectifiers in China are the products of that era.

2. Inverter era

In 1970s, there was an energy crisis all over the world, and the variable frequency speed regulation of AC motor developed rapidly because of its remarkable energy-saving effect. The key technology of variable frequency speed regulation is to convert direct current into alternating current of 0~ 100Hz. In 1970s and 1980s, with the popularization of frequency conversion speed regulating devices, thyristors, high-power transistors (GTR) and high-power inverter gate turn-off thyristors (GT0) became the protagonists of power electronic devices at that time. Similar applications include high voltage DC output, static reactive power dynamic compensation and so on. At this time, power electronics technology has been able to achieve rectification and inverter, but the working frequency is low, limited to the middle and low frequency range.

3. Frequency converter era

In 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 precision machining technology of integrated circuit technology with high voltage and high current technology, a number of brand-new fully controlled power devices have emerged. First, the appearance of power M0SFET has driven the development of medium and small power supplies to high frequency, and then the appearance of insulated gate bipolar transistors (IGBT) has brought opportunities for the development of medium and large power supplies to high frequency. The appearance of MOSFET and IGBT marks the transformation from traditional power electronics to modern power electronics. According to statistics, by the end of 1995, power M0SFET and GTR have reached the same level in the market of power semiconductor devices, and it has been concluded that IGBT will replace GTR in the field of power electronics. The development of new devices not only provides high frequency for AC motor variable frequency speed regulation, which makes its performance more perfect and reliable, but also makes modern electronic technology develop to high frequency, which provides an important technical basis for efficient material saving and energy saving of electrical equipment, and realizes small, lightweight, electromechanical integration and intelligence.

2. Application fields of modern power electronics

2. 1 Efficient green computer power supply

The rapid development of computer technology has led mankind into the information society and promoted the rapid development of power technology. In the 1980s, computers adopted switching power supply in an all-round way, taking the lead in replacing computer power supply. So switching power supply technology has entered the field of electronic and electrical equipment.

With the development of computer technology, green computer and green power supply are put forward. Green computer generally refers to personal computers and related products that are harmless to the environment, and green power supply refers to high-efficiency and energy-saving power supply related to green computers. According to the "Energy Star" plan of the United States Environmental Protection Agency on June, l992 17, if the power consumption of desktop personal computers or related peripherals is less than 30 watts, the requirements will be met.

To meet the requirements of green computers, improving power efficiency is the fundamental way to reduce power consumption. As far as the current 75% efficient 200-watt switching power supply is concerned, the power supply itself consumes 50 watts of energy.

2.2 High frequency switching power supply for communication

The rapid development of communication industry has greatly promoted the development of communication power supply. High-frequency miniaturized switching power supply and its technology have become the mainstream of modern communication power supply system. In the field of communication, rectifier is usually called primary power supply, while DC/DC converter is called secondary power supply. The primary power supply is used to convert a single-phase or three-phase AC power grid into a DC power supply with a nominal value of 48V. At present, the traditional phase-controlled stabilized power supply has been replaced by high-frequency switching power supply in the primary power supply of program-controlled switches. High-frequency switching power supply (also known as 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, which realizes high efficiency and miniaturization. In recent years, the power capacity of switching rectifiers has been continuously expanded, and the single-machine capacity has been expanded from 48V/ 12.5A and 48V/20A to 48V/200A and 48V/400A.

Because there are many kinds of integrated circuits used in communication equipment, their power supply voltages are also different. In the communication power supply system, the high-frequency DC-DC isolated power supply module with high power density is used to convert the intermediate bus voltage (generally 48V DC) into various DC voltages, which can greatly reduce the loss and facilitate maintenance, installation and increase. Generally, it can be directly installed on the standard control panel, and the requirement for secondary power supply is high power density. Due to the continuous increase of communication capacity, the capacity of communication power supply will also increase.

2.3 DC-DC converter

A 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. At the same time, the above control can achieve the performance of acceleration, stability and rapid response, and at the same time, it can save electricity. Replacing rheostat with DC chopper can save energy by 20 ~ 30%. DC chopper can not only adjust the voltage (switching power supply), but also effectively suppress the harmonic current noise on the grid side.

The secondary DC/DC converter of 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 miniaturization of power modules is required, so it is necessary to continuously improve the switching frequency and adopt a new circuit topology. At present, some companies have developed and produced secondary power modules with 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 kind of high reliability and high performance power supply, which is suitable for computers, communication systems and occasions requiring uninterrupted power supply. The AC mains input is converted into DC through the rectifier, and part of the energy is used to charge the battery, and the other part is converted into AC through the inverter and sent to the load through the transfer switch. In order to provide energy to the load when the inverter fails, another standby power supply is realized through the power transfer switch.

Modern UPS generally adopts pulse width modulation technology and modern power electronic devices such as M0SFET and IGBT, which reduces power supply noise and improves efficiency and reliability. The introduction of microprocessor software and hardware technology can realize intelligent management, remote maintenance and remote diagnosis of UPS.

At present, the maximum capacity of online UPS has reached 600kVA. Ultra-small UPS has also developed rapidly, and its products have specifications such as 0.5kVA, lkVA, 2kVA and 3kVA.

2.5 inverter power supply

Inverter power supply is mainly used for variable frequency speed regulation of AC motor, which plays an increasingly important role in electric drive system and has achieved great energy-saving effect. The main circuit of inverter power supply adopts AC -DC- AC scheme. The power frequency power supply is converted into a fixed DC voltage through a rectifier, and then the DC voltage is converted into an AC output with variable voltage and frequency by a PWM high-frequency converter composed of high-power transistors or IGBT. The output waveform of power supply is similar to sine wave, which is used to drive AC asynchronous motor to realize stepless speed regulation.

The series products of inverter power supply below 400kVA in the world have come out. In the early 1980s, Toshiba Corporation of Japan first applied AC variable frequency speed regulation technology to air conditioners. By 1997, its share has reached more than 70% of Japanese household air conditioners. Frequency conversion air conditioner has the advantages of comfort and energy saving. Domestic research on inverter air conditioners began in the early 1990s. 1996 introduced a production line to produce inverter air conditioners, which gradually became a hot spot in R&D and production of inverter air conditioners. It is expected to reach its climax around 2000. In addition to variable frequency power supply, variable frequency air conditioner also needs a compressor motor suitable for variable frequency speed regulation. Optimizing control strategy and selecting functional components are the further development direction of air conditioning variable frequency power supply.

2.6 high frequency inverter rectifier welding machine power supply

High frequency inverter rectifier welding machine power supply is a new welding machine power supply with high performance, high efficiency and material saving, which represents the development direction of welding machine power supply today. Because of the commercialization of IGBT large-capacity module, the power supply has a broader application prospect.

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

Due to the harsh working conditions of welding machine power supply, short circuit, arc and open circuit frequently occur, so the working reliability of high frequency inverter rectifier welding machine power supply has become the most critical issue, and it is also the most concerned issue for users. The microprocessor is used as the relevant controller of pulse width modulation (PWM). Through the extraction and analysis of various parameters and 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 reliability problem of the current high-power IGBT inverter power supply.

Foreign inverter welding machines have achieved 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 high-voltage DC power supply

High-power switching high-voltage DC power supply is widely used in electrostatic dust removal, water quality improvement, medical X-ray machine and CT machine and other large equipment. The voltage is as high as 50~l59kV, the current is above 0.5A, and the power can reach 100kW.

Since the 1970s, some Japanese companies have started to adopt inverter technology, which rectifies the commercial power and inverts it to an intermediate frequency of about 3kHz, and then boosts it. In 1980s, the technology of high-frequency switching power supply developed rapidly. Siemens Company of Germany adopts power transistor as the main switching element, which increases the switching frequency of power supply to above 20kHz. Dry-type transformer technology has been successfully applied to high-frequency and high-voltage power supply, eliminating the oil tank of high-voltage transformer and further reducing the volume of transformer system. China has developed a high voltage DC power supply for electrostatic precipitator. The mains electricity is converted into DC after rectification. DC voltage is converted into high-frequency voltage by full-bridge zero-current switch series resonant inverter circuit, then boosted by 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 working frequency is 25.6kHz.

2.8 Power Active Filter

When the traditional AC DC converter is put into operation, it will inject a lot of harmonic current into the power grid, causing harmonic loss and interference, and at the same time, the power factor of the equipment network side will deteriorate, which is called "power pollution". For example, with uncontrolled rectification and capacitive filtering, 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 (APF) is a new type of power electronic device which can dynamically suppress harmonics. It can overcome the shortcomings of traditional LC filter and is a promising harmonic suppression method.

2. The application of modern power electronics technology in power system.

1. Power generation link

The power generation link of power system involves all kinds of equipment of generator set, and the main purpose of power electronic equipment application is to improve the operating characteristics of these equipment.

(l) Static excitation control of large generators

Static excitation adopts thyristor rectifier self-shunt excitation mode, which has the advantages of simple structure, high reliability and low cost, and is widely used in major power systems in the world. Because the intermediate inertia link of vibration exciter is omitted, it has its unique rapid adjustment, which provides favorable conditions for the advanced control law to give full play and produce good control effect.

(2) Variable-speed constant-frequency excitation of hydro-generator and wind-driven generator.

The effective power of hydropower generation depends on the dry head pressure and flow. When the water head changes greatly (especially for pumped storage units), the optimal speed of the units will also change accordingly. The effective power of wind power generation is directly proportional to the cubic power of wind speed, and the speed at which windmills capture the maximum wind energy varies with the wind speed. In order to obtain the maximum effective power, the unit can run at variable speed. By adjusting the frequency of the rotor excitation current, the stator frequency, that is, the output frequency, remains constant after being superimposed with the rotor speed. The technical core of this application is frequency conversion power supply.

(3) Frequency conversion speed regulation of fans and pumps in power plants.

The average auxiliary power consumption rate of power plant is 8%, and the power consumption of fans and pumps accounts for about 65% of the total power consumption of thermal power equipment, so the operation efficiency is low. Using low-voltage or high-voltage frequency converter to implement frequency conversion speed regulation for fans and pumps can achieve the purpose of energy saving. Low-voltage inverter technology has been very mature. There are many manufacturers at home and abroad, but there is not a complete series of products. However, there are not many enterprises with high-voltage and large-capacity inverter design and production capacity, and many domestic universities and enterprises are stepping up joint development.

2. Transmission link

The application of power electronic devices in high voltage transmission system is called "the second revolution caused by silicon wafer", which greatly improves the stable operation characteristics of power grid.

(1) HVDC and HVDC L i g ht technology HVDC has the advantages of large transmission capacity, good stability and flexible control and adjustment, and has unique advantages for long-distance transmission, submarine cable transmission and networking of different frequency systems. 1970 The appearance of the first thyristor converter in the world marks the formal application of power electronics technology in DC transmission. Since then, all new DC transmission projects in the world have adopted thyristor converter valves.

(2) FA CTs technology The concept of FA CTs technology came out in the late 1980s. Based on power electronics technology and modern control technology, it can flexibly and quickly adjust the impedance, voltage and phase of AC transmission system, which can realize flexible control of AC transmission power flow and greatly improve the stability level of power system. Since 1990s, FA CTS technology has been applied to practical power system engineering on the basis of research and development abroad. Its output reactive power is large, the equipment structure is simple, the control is convenient and the cost is low, so it is applied earlier.

3. Distribution link

How to strengthen the reliability of power supply and improve power quality is an urgent problem for distribution system. Power quality control should not only meet the requirements of voltage, frequency, harmonics and asymmetry, but also suppress various transient fluctuations and interference. The application of power electronics technology and modern control technology in distribution system, namely, customer power (Cu s t o m Po we r) technology or DF ACTS technology, is a new type of power quality control technology developed on the basis of mature F ACTS technology. It can be understood that DFACTS equipment is a miniature version of FACTS equipment, with the same principle, structure and similar functions. Due to the huge potential demand, relatively easy market intervention, relatively low development investment and production cost, with the continuous reduction of the price of power electronic devices, it can be expected that D F A C TS equipment products will enter a period of rapid development.

Three. Development prospect of power electronics technology

1. New power electronic equipment

Among the power devices made of new semiconductor materials, the most promising one is silicon carbide (SiC). Its performance index is one order of magnitude higher than that of GaAs devices. Compared with other semiconductor materials, silicon carbide has the following excellent physical properties: high band gap, high saturated electron drift velocity, high breakdown strength, low dielectric constant and high thermal conductivity. These excellent physical properties determine that silicon carbide is an ideal semiconductor material for high temperature, high frequency and high power applications. At the same withstand voltage and current level, the drift resistance of SiC devices is only 1/200 of that of silicon devices, and even the on-voltage drop of high withstand voltage SiC field effect transistors is much lower than that of unipolar and bipolar silicon devices. Moreover, the switching time of SiC devices can reach the order of 10ns, and it has excellent FBSOA. SiC can be used to manufacture RF and microwave power devices, various high-frequency rectifiers, MESFETs, MOSFETs and JFETs. Silicon carbide high frequency power devices have been successfully developed in Motorola and applied to microwave and RF devices. GE company is developing SiC power devices and high temperature devices (including sensors for jet engines). Westinghouse has manufactured a VHF MESFET operating at 26GHz. ABB is developing high-power, high-voltage silicon carbide rectifiers and other silicon carbide low-frequency power devices for industrial and power systems. Theoretical analysis shows that SiC power devices are very close to ideal power devices. It can be predicted that the research and development of various SiC devices will become one of the main trends in the research field of power devices. However, there are still many problems to be solved in the mechanism, theory and manufacturing technology of SiC materials and power devices. It is estimated that it will take them at least 10 years to really bring another revolution to the field of power electronics technology.

2. New energy sources

Power electronics technology has broad development prospects in new energy generation technology, power quality control technology and energy saving technology. Among them, wind power generation and solar power generation are the most concerned, and power electronics technology is one of the core technologies of wind power generation and solar power generation, which provides a golden opportunity for power electronics engineers. The majority of power electronics engineers can seize this opportunity to promote the development of power electronics technology. At the same time, due to the wide application of power electronic devices and electric arc furnaces, the power quality is declining day by day. On the other hand, users have higher requirements for power quality. People pay more and more attention to the power quality control device represented by active power filter, and more and more research and development have been carried out. In addition, power electronic devices can compensate reactive power and power harmonics well because motors (accounting for more than 60% of power generation) and lighting power sources (accounting for about 10 ~ 15% of power generation) are widely used in power systems, so power electronic technology is called energy-saving technology. At present, due to the exhaustion of fossil energy, power electronics technology has received great attention in energy saving and has developed rapidly.

3. Electric cars

China has a large population and little oil. Now China imports a lot of oil every year. 2/kloc-0 in the first half of the century, the oil and gas resources on the earth are decreasing day by day, and even will be exhausted sooner or later. Especially in the national conditions of China, it is an inevitable trend to focus on the development of electric vehicles in urban transportation. Maglev trains between big cities, electric elevated trains and subway trains in cities, personal electric bicycles and electric cars will be the protagonists of the future transportation network. Among them, power electronic products are of great use. Frequency conversion speed regulation of magnetic suspension power supply and linear motor of maglev train: frequency conversion speed regulation of asynchronous motor in urban elevated train and subway train: the external rotor speed regulation of permanent magnet brushless motor in electric bicycle and electric vehicle will have great development in the next decade. Here, the popularization of electric bicycles and electric vehicles must solve the problems of brushless motors and their controllers, environmental protection batteries, fast chargers and network services of charging stations. Now it seems that the technology of promoting electric bicycles instead of motorcycles as a means of transportation in China has matured. Nickel-hydrogen batteries and lithium-ion batteries must be used here to eliminate the environmental pollution caused by traditional lead-acid batteries. This kind of battery pack, which is still expensive, can be rented to electric bicycle users, and the method of charging by battery charging stations with reasonable spacing and charging by users themselves is implemented. Compared with lithium-ion batteries (such as 36V and 10AH), lead-acid batteries weigh 12 kg, while the latter only weighs 2.4kg. ..

The development of electric vehicles is a potential big market for power electronics in the future. The first is the breakthrough of clean batteries with high energy density. The most promising is the fuel cell, which needs power electronic products for its start-up and stable operation. The most interesting and promising traction system scheme is driven by an external rotor disk permanent magnet brushless DC motor mounted on four wheels. The optimal design of this motor structure, high-performance control and speed regulation drive, and the coordinated operation of four motors will provide technical support for the comfortable operation and zero-radius turning of electric vehicles. The next decade will be a crucial period for the practical development of electric vehicles, and the power electronics industry can and should make corresponding research and development work to actively meet the arrival of this huge market.

Conclusion:

Power electronics technology has rapidly developed into an independent technical and disciplinary field. Its application field involves almost all industrial sectors of the national economy. Undoubtedly, it will become one of the key supporting technologies in the new century. Power electronics technology has many characteristics, such as rapid development of microelectronics technology, strong penetration and vigorous vitality, and can be integrated with other disciplines.

Take the exam and contribute.

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