Abstract: This paper briefly reviews the development process of power electronics technology and its devices, introduces the working principles, application scope, advantages and disadvantages of mainstream power electronic devices, and discusses the application prospects of new power electronic devices in the 21st century. Keywords: Power electronics technology; Thyristor; Power integrated circuit; Application Introduction Power electronics technology includes several aspects such as power semiconductor devices and IC technology, power conversion technology, and control technology. Among them, power electronic devices are an important foundation of power electronics technology and the "leading force" in its development. Since GE developed the world's first industrial-grade thyristor in 1958, the conversion and control of electrical energy has moved from rotating converter units and static ion converters to the era of converters composed of power electronic devices, marking the birth of power electronics technology. By the 1970s, thyristors began to form a series of products ranging from low voltage and low current to high voltage and high current. At the same time, thyristor-derived devices such as asymmetric thyristors, reverse-conducting thyristors, bidirectional thyristors, and light-controlled thyristors were successively introduced and widely used in various converter devices. Due to their advantages such as small size, light weight, low power consumption, high efficiency, and fast response, their research and application have developed rapidly. Because ordinary thyristors cannot self-turn off and are considered semi-controlled devices, they are called first-generation power electronic devices. Driven by practical needs, and with continuous improvements in theoretical research and manufacturing processes, power electronic devices have greatly developed in terms of capacity and types, leading to the emergence of self-turn-off and fully controlled devices such as GTRs, GTOs, and power MOSETs, which are called second-generation power electronic devices. In recent years, power electronic devices have been developing towards composite, modular, and power integration directions; for example, IGBTs, MCTs, and HVICs are products of this development. Power Rectifiers Rectifiers originated in the 1940s and are the simplest and most widely used type of power electronic device. Currently, they have formed three main types: ordinary rectifiers, fast recovery rectifiers, and Schottky rectifiers. The characteristics of ordinary rectifier diodes are: low leakage current, high on-state voltage drop (10-18V), long reverse recovery time (tens of microseconds), and the ability to achieve very high voltage and current ratings. They are mostly used in devices such as traction, charging, and electroplating where high conversion speed is not required. Fast recovery rectifier diodes are characterized by their fast reverse recovery time (hundreds of nanoseconds to a few microseconds), but their on-state voltage drop is very high (16-40V). They are mainly used in chopper and inverter circuits as bypass diodes or blocking diodes. Schottky rectifier diodes combine the advantages of fast reverse recovery time (almost zero) and low on-state voltage drop (0.3-0.6V), but they have higher leakage current and lower withstand voltage, and are commonly used in high-frequency low-voltage instruments and switching power supplies. Current research and development levels include: ordinary rectifier tubes (8000V/5000A/400Hz); fast recovery rectifier tubes (6000V/1200A/1000Hz); and Schottky rectifier tubes (1000V/100A/200kHz). Power rectifier tubes play a crucial role in improving the performance of various power electronic circuits, reducing circuit losses, and increasing power supply efficiency. With the emergence of various high-performance power electronic devices, the development of power rectifier tubes with good high-frequency performance has become essential. Currently, through novel structural designs and the application of large-scale integrated circuit manufacturing processes, new high-voltage fast recovery rectifier tubes with MPS, SPEED, and SSD structures have been developed, combining the advantages of PIN rectifier tubes and Schottky rectifier tubes. Their on-state voltage drop is approximately 1V, their reverse recovery time is half that of PIN rectifier tubes, and their reverse recovery peak current is one-third that of PIN rectifier tubes. Ordinary Thyristors and Their Derivatives After the invention of the thyristor, improvements in its structure and manufacturing processes paved the way for the continuous emergence of new devices. In 1964, the bidirectional thyristor was successfully developed by GE and applied to dimming and motor control. In 1965, the low-power optically triggered thyristor appeared, laying the foundation for subsequent optocouplers. In the late 1960s, high-power inverter thyristors were introduced, becoming a fundamental component of inverter circuits at the time. In 1974, the reverse-conducting thyristor and asymmetric thyristors were developed. Ordinary thyristors are widely used in low-frequency (below 400Hz) applications such as AC/DC speed regulation, dimming, and temperature control. Using circuits constructed with thyristors to control and transform the power grid is a simple and economical method. However, the operation of such devices can cause waveform distortion and reduce the power factor, affecting the quality of the power grid. Current levels are 12kV/1kA and 6500V/4000A. A bidirectional thyristor can be considered as an integrated pair of anti-parallel ordinary thyristors and is commonly used in AC voltage and power regulation circuits. It can be triggered by both positive and negative pulses, making its control circuit relatively simple. Its disadvantages include poor commutation capability, low trigger sensitivity, and long turn-off time; its performance has exceeded 2000V/500A. A light-controlled thyristor is a device that uses optical signals to control the thyristor's conduction. It has strong anti-interference capabilities, good high-voltage insulation performance, and high transient overvoltage withstand capability, and is therefore used in high-voltage direct current transmission (HVDC), static var compensator (SVC), and other fields. Its development level is approximately 8000V/3600A. Inverter thyristors, due to their short turn-off time (10-15s), are mainly used for medium-frequency induction heating. In inverter circuits, they have been superseded by newer devices such as GTRs, GTOs, and IGBTs. Currently, its maximum capacity ranges from 2500V/1600A/1kHz to 800V/50A/20kHz. An asymmetric thyristor is a thyristor with asymmetrical forward and reverse voltage withstand capabilities. A reverse-conducting thyristor is simply a special case of an asymmetric thyristor, a power integrated device that integrates a thyristor with a diode connected in anti-parallel on the same die. Compared to ordinary thyristors, it has advantages such as short turn-off time, low forward voltage drop, high rated junction temperature, and good high-temperature characteristics, and is mainly used in inverters and rectifiers. Currently, some domestic manufacturers produce 3000V/900A asymmetric thyristors. Fully Controllable Power Electronic Devices Gate Turn-Off Thyristor (GTO): In 1964, the United States successfully prototyped a 500V/10A GTO for the first time. For nearly 10 years afterward, the capacity of GTOs remained at a relatively small level, only being tested in automotive ignition systems and television horizontal scanning circuits. Since the mid-1970s, breakthroughs have been achieved in the development of GTOs, with products of 1300V/600A, 2500V/1000A, and 4500V/2400A successively emerging. Currently, they have reached the levels of 9kV/25kA/800Hz and 6Hz/6kA/1kHz. GTOs come in three types: symmetrical, asymmetrical, and reverse-conducting. Compared with symmetrical GTOs, asymmetrical GTOs have lower on-state voltage drop, stronger surge current resistance, and are easier to improve in terms of withstand voltage (above 3000V). Reverse-conducting GTOs are integrated devices made by connecting a GTO and a rectifier diode in anti-parallel on the same chip. They cannot withstand reverse voltage and are mainly used in medium-capacity traction drives. Among various self-turn-off devices, GTOs have the largest capacity and the lowest operating frequency (1-2kHz). GTOs are current-controlled devices, therefore requiring a large reverse drive current during turn-off; GTOs have a large on-state voltage drop and low dV/dT and di/dt withstand capabilities, requiring a large absorption circuit. Currently, although GTOs have been replaced by GTRs and IGRTs in some areas below 2000V, they have significant advantages in high-power electric traction; in the future, they will inevitably occupy a place in the high-voltage field. High-power transistors (GTRs) are current-controlled bipolar double-junction power electronic devices that originated in the 1970s, with rated values ​​reaching 1800V/800A/2kHz, 1400V/600A/5kHz, and 600V/3A/100kHz. They possess the inherent characteristics of transistors while increasing power capacity; therefore, circuits composed of GTRs are flexible, mature, have low switching losses, and short switching times, making them widely used in medium-capacity, medium-frequency circuits such as power supplies, motor control, and general-purpose inverters. The disadvantages of GTRs are high drive current, poor surge current tolerance, and susceptibility to secondary breakdown damage. In switching power supplies and UPS systems, GTRs are gradually being replaced by power MOSFETs and IGBTs. Power MOSFETs are voltage-controlled unipolar transistors that control the drain current through the gate voltage. Their key features include simple drive circuitry and low drive power. They conduct only through majority carriers, eliminating minority carrier storage effects, resulting in excellent high-frequency characteristics. Operating frequencies exceeding 100kHz are the highest among all power electronic devices, making them ideal for high-frequency applications such as switching power supplies and high-frequency induction heating. They also have no secondary breakdown issues, a wide safe operating area, and strong resistance to damage. The disadvantages of power MOSFETs include low current capacity, low voltage withstand, and large on-state voltage drop, making them unsuitable for high-power devices. Current manufacturing levels are approximately 1kV/2A/2MHz and 60V/200A/2MHz. Composite Power Electronic Devices Insulated Gate Bipolar Transistors (IGBTs) were first developed by GE and RCA in 1983, with an initial capacity of only 500V/20A and some technical issues. After several years of improvements, IGBTs began formal production in 1986 and gradually became standardized. By the early 1990s, the second generation of IGBTs had been developed. Currently, the third generation of intelligent IGBTs has emerged, and scientists are working on the fourth generation of trench gate IGBTs. An IGBT can be considered a combination of a bipolar junction transistor (BJT) and a power MOSFET. Applying a forward gate voltage forms a channel, providing base current to the transistor to turn the IGBT on; conversely, applying a reverse gate voltage eliminates the channel, causing the IGBT to turn off due to the reverse gate current. The IGBT combines the advantages of a bipolar junction transistor (BJT) (low on-state voltage drop, high current density, high voltage withstand) with a power MOSFET (low drive power, fast switching speed, high input impedance, good thermal stability), making it highly popular. Its successful development has provided favorable conditions for improving the performance of power electronic devices, especially for the miniaturization, efficiency improvement, and noise reduction of inverters. Comparatively, the switching speed of an IGBT is lower than that of a power MOSFET but significantly higher than that of a BJT; the on-state voltage drop of an IGBT is similar to that of a BJT but much lower than that of a power MOSFET; the current and voltage ratings of an IGBT are close to those of a BJT but higher than those of a power MOSFET. Currently, its research and development level has reached 4500V/1000A. Due to the aforementioned characteristics, IGBTs have gradually replaced GTRs as core components in medium-power capacity (above 600V) UPS, switching power supplies, and PWM inverters for AC motor control. Furthermore, IR has designed the WARP series 400-600VIGBTs with switching frequencies up to 150kHz. Their switching characteristics are close to those of power MOSFETs, but their conduction losses are much lower. This series of IGBTs is expected to replace power MOSFETs in high-frequency 150kHz rectifiers and significantly reduce switching losses. The development direction of IGBTs is to improve voltage withstand capability and switching frequency, reduce losses, and develop intelligent products with integrated protection functions. MOS-controlled thyristors (MCTs) were first developed by GE in the United States. They are a new type of device composed of MOSFETs and thyristors. Each MCT device consists of thousands of MCT elements, and each element consists of a PNPN thyristor, a MOSFET controlling the MCT's conduction, and a MOSFET controlling the MCT's turn-off. The MCT operates in an over-blocking state, making it a true PNPN device, which is the primary reason why its on-state resistance is significantly lower than other field-effect devices. The MCT combines the high input impedance, low drive power, and fast switching speed of a power MOSFET with the high voltage, high current, and low voltage drop of a thyristor. Its continuous current density is the highest among various devices, its on-state voltage drop is only 1/3 that of an IGBT or GTR, while its switching speed exceeds that of a GTR. Furthermore, because the MOSFETs in the MCT can control the entire area of ​​the MCT chip's switching, the MCT has very strong conduction di/dt and blocking dV/dt capabilities, reaching values ​​as high as 2000 A/s and 2000 V/s, respectively. Its operating junction temperature is also high, reaching 150–200°C. MCTs with a blocking voltage of up to 4000V have been developed, and the 75A/1000VMCT has been applied to series resonant converters. With the continuous optimization of performance-price ratio, MCTs will gradually enter the application field and may replace high-voltage GTOs, while competition with IGBTs will also unfold in the medium-power field. Power Integrated Circuits (PICs) are a product of the combination of power electronic device technology and microelectronics technology, and are key interface components of mechatronics. A PIC is made by integrating power devices and their drive circuits, protection circuits, interface circuits, and other peripheral circuits onto one or more chips. Generally, the rated power of a PIC should be greater than 1W. Power integrated circuits can also be divided into high-voltage power integrated circuits (HVICs), smart power integrated circuits (SPICs), and smart power modules (IPMs). HVICs integrate multiple high-voltage devices with low-voltage analog devices or logic circuits on a single chip. Because its power devices are lateral and have a small current capacity, while the control circuit has a large current density, it is often used in high-voltage, low-current applications such as small motor drives, flat panel display drives, and long-distance telephone communication circuits. HVICs with current ratings of 110V/13A, 550V/0.5A, 80V/2A/200kHz, and 500V/600mA are already used in the aforementioned devices. SPIC (Sequentially Variable Input/Output) integrates one or more vertically oriented power devices with control and protection circuits. It has a large current capacity but poor voltage withstand capability, making it suitable for motor drives, automotive power switches, and voltage regulators. IPM (Integrated Power Device) integrates power devices and drive circuits, as well as overvoltage, overcurrent, and overheat fault monitoring circuits, and can transmit monitoring signals to the CPU to ensure the IPM itself is not damaged under any circumstances. Currently, IGBTs are generally used as power devices in IPMs. Due to their small size, high reliability, and ease of use, IPMs are popular among users. IPMs are mainly used for AC motor control and household appliances. 400V/55kW/20kHz IPMs are already available. Since the first PIC was prototyped in the United States in 1981, PIC technology has developed rapidly; in the future, PICs will undoubtedly develop even faster towards higher voltage and intelligence, and enter a stage of widespread practical application. Prospects for the Development of Power Electronic Devices Application of New Materials The various power electronic devices mentioned above are generally made of silicon (Si) semiconductor materials. In addition, many new compound semiconductor materials with excellent performance have emerged in recent years, such as gallium arsenide (GaAs), silicon carbide (SiC), indium phosphide (InP), and silicon germanide (SiGe). Power electronic devices made from these materials are constantly emerging. Gallium arsenide (GaAs) is a promising semiconductor material. Compared with Si, GaAs has two unique advantages: ① Its bandgap energy is 1.4 eV, higher than Si's 1.1 eV. Therefore, GaAs rectifiers can operate at temperatures up to 350℃ (Si rectifiers can only reach 200℃), exhibiting excellent high-temperature resistance, which is beneficial for module miniaturization; ② GaAs has an electron mobility of 8000 cm²/Vs, five times that of Si, resulting in smaller device dimensions for the same capacity, thereby reducing parasitic capacitance and increasing switching frequency (above 1 MHz). Of course, the large bandgap of GaAs material also brings the disadvantage of a relatively large forward voltage drop, but its electron mobility can compensate for this effect to some extent. GaAs rectifier components are widely used by some long-term customers of Motorola to manufacture DC power supplies with various output voltages (12V, 24V, 36V, 48V) for use in communication equipment and computers. It is expected that with the improvement of the manufacturing process technology for 200V withstand voltage GaAs rectifier devices, the devices will be optimized, and the application fields will continue to expand. Silicon carbide (SiC) is currently the most mature wide bandgap semiconductor material. As an important complement to Si and GaAs, it can be used to manufacture high-temperature (300-500℃), high-frequency, high-power, high-speed, and radiation-resistant devices with superior performance. High-power, high-voltage SiC devices are of great significance for energy conservation in public power transmission and electric vehicles. SiC has been used to fabricate general-purpose thyristors, bipolar junction transistors (BJTs), IGBTs, power MOSFETs (175V/2A, 600V/18A), SiTs (600MHz/225W/200V/fmax=4GHz), PN junction diodes (with a withstand voltage of 4.5kV at 300K), and Schottky barrier diodes (with a withstand voltage of 1kV at 300K), which are widely used in locomotives, trams, industrial generators, and high-voltage power transmission and transformation equipment. Indium phosphide (InP) is a group III-V compound semiconductor material, a new generation of electronic functional materials following Si and GaAs. It has a higher breakdown electric field, higher thermal conductivity, and a higher average electron velocity at high fields. Furthermore, its surface recombination rate is almost three orders of magnitude lower than that of GaAs, allowing InPHBTs to operate at low currents and making them suitable as materials for high-speed, high-frequency microwave devices up to 340GHz. Silicon Germanium (SiGe) Materials According to reports, the German company Tenic Telefunken Microelectronics plans to begin mass production of SiGe chips for wireless applications in the first quarter of 1998, with a cutoff frequency of 50GHz to 110GHz. This marks the official entry of SiGe devices into the application field. Conclusion The application of power electronic devices has penetrated into all aspects of industrial production and social life, and practical needs will greatly drive continuous innovation in these devices. Very large-scale integrated circuit (VLSI) technology in microelectronics will find wider application in the fabrication of power electronic devices; the use of new semiconductor materials with high carrier mobility, strong thermoelectric conductivity, and wide bandgap, such as gallium arsenide, silicon carbide, and synthetic diamond, will help develop a new generation of devices with high junction temperatures, high frequencies, and high dynamic parameters. Structurally, devices will become more composite and modular; in terms of performance, the development direction will be to increase capacity and operating frequency, reduce on-state voltage drop, reduce drive power, improve dynamic parameters, and increase multifunctionality; in terms of application, MPS power rectifiers, MOSFETs, IGBTs, and MCTs are the most promising devices. Future research and development will focus on further improving the soft reverse recovery characteristics of MPS, increasing the switching frequency and rated capacity of IGBTs and MCTs, developing intelligent MOSFETs and IGBT modules, and advancing power integrated circuits and other power devices. GTOs will continue to play a role in ultra-high voltage and high-power fields; power MOSFETs will have a competitive advantage in high-frequency, low-voltage, and low-power fields; ultra-high voltage (above 8000V) and high-current ordinary thyristors will continue to play a role in high-voltage DC transmission and static var compensators, while low-voltage ordinary thyristors and GTRs will be gradually replaced by power MOSFETs (below 600V) and IGBTs (above 600V); MCTs have the most promising future. It is foreseeable that the development of power electronic devices will be rapid, and the future of power electronic devices will be full of vitality.