Power electronic devices are high-power (typically referring to currents ranging from tens to thousands of amperes and voltages exceeding hundreds of volts) electronic devices used in power conversion and control circuits; they are also known as power electronic devices. In the 1950s, power electronic devices mainly consisted of mercury thyristors and high-power vacuum tubes. Thyristors, developed in the 1960s, gained widespread use in power electronic circuits due to their reliable operation, long lifespan, small size, and fast switching speed. By the early 1970s, thyristors had gradually replaced mercury thyristors.
The development of power electronics technology not only requires increasing the control power capacity and operating frequency of power electronic devices, but also reducing power losses and minimizing the size of devices and their control circuits. New achievements in semiconductor technology have provided the necessary material foundation for this. In the 1980s, ordinary thyristors could already switch currents of several thousand amperes and withstand forward and reverse operating voltages of several thousand volts. Based on this, a series of derived devices were developed, including bidirectional thyristors, light-controlled thyristors, gate-turn-off thyristors, and reverse-conducting thyristors. At the same time, new power electronic devices such as unipolar MOS power field-effect transistors, bipolar power transistors, electrostatic induction thyristors, functional combination modules, and power integrated circuits were also developed.
II. Classification of Power Electronic Devices
Power electronic devices can generally be divided into three categories:
① Power diodes, including power rectifier diodes, Schottky diodes, Zener diodes, and diode assemblies.
② Power transistors, including power Darlington transistors, MOS power field-effect transistors, isolated gate transistors, and power electrostatic induction transistors.
③ Thyristor series, mainly thyristors and their derivative devices, including ordinary thyristors, bidirectional thyristors, reverse-conducting thyristors, asymmetric thyristors, gate-assisted turn-off thyristors, light-controlled thyristors, turn-off thyristors, and electrostatic induction thyristors. Of course, other classifications are possible, but this is a simplified classification method.
III. Operating Characteristics of Power Electronic Devices
All power electronic devices possess two operating characteristics: conduction and blocking. Power diodes are two-terminal devices (referring to the cathode and anode terminals). Their current is determined by their volt-ampere characteristics; aside from changing the voltage applied between the two terminals, their anode current cannot be controlled, hence they are called uncontrollable devices. Ordinary thyristors are three-terminal devices; their gate signal can control the device's conduction but not its turn-off, hence they are called semi-controlled devices. Turn-off thyristors, power transistors, and other devices have gate signals that can control both conduction and turn-off, hence they are called fully controlled devices. Semi-controlled and fully controlled power electronic devices offer flexible control, simple circuits, and fast switching speeds. They are widely used in rectifier, inverter, and chopper circuits and are core components in power electronic devices such as motor speed control, generator excitation, induction heating, electroplating, electrolysis, and DC power transmission.
IV. Development of Power Electronic Devices
Power electronic devices are developing towards higher power, higher frequency, and greater integration. In the 1980s, thyristors had current capacities reaching 6000 amps and blocking voltages as high as 6500 volts. However, these devices operated at relatively low frequencies. Increasing their operating frequency depends on accelerating the recombination rate of minority carriers in the base region and extracting more carriers through the gate during the device's turn-off period. While reducing minority carrier lifetime can effectively shorten the turn-off current process, it leads to an increase in the forward voltage drop during the device's conduction period. Therefore, it is necessary to balance the requirements of switching speed and on-state power loss. In the 1980s, the highest operating frequency of these devices was below 10 kHz. Bipolar high-power transistors can operate at 100 kHz, with control current capacities reaching hundreds of amps and blocking voltages exceeding 1000 volts, but maintaining the on-state requires a larger base drive current than other power controllable devices. The presence of thermally excited secondary breakdown limits their surge protection capability. Further increasing their operating frequency is still affected by the minority carrier storage effect in the base and collector regions. The unipolar MOS power field-effect transistor, developed in the mid-1970s, is an electronic power device that, due to its immunity to minority carrier storage effects, can operate at frequencies above megahertz. This device exhibits a negative temperature characteristic in its on-state current, making it less prone to thermally triggered secondary breakdown. When increased current capacity is required, parallel connection of the devices is simple, and it possesses good linear output characteristics and low drive power. Furthermore, it is easy to integrate on a large scale in manufacturing processes. However, its on-state voltage drop is relatively large, requiring high consistency in materials and device processes during manufacturing. By the mid-to-late 1980s, its current capacity had decreased to only tens of amperes, while its blocking voltage approached kilovolts.
The electrostatic induction thyristors, isolated-gate transistors , and various combined devices developed in the 1980s integrated the advantages of thyristors, MOS power MOSFETs, and power transistors, achieving new performance advancements. For example, the isolated-gate transistor possesses both the gate control characteristics of a MOS power MOSFET and the current conduction performance of a bipolar power transistor, allowing for a current density several times higher than that of a bipolar power transistor. The electrostatic induction thyristor retains the advantage of low on-state voltage of the thyristor, and its structure avoids the process required by conventional thyristors where conduction must first occur around the gate and then gradually expand laterally upon gate triggering. Therefore, it has a higher switching speed than conventional thyristors, and its allowable junction temperature rise is also higher. These new devices meet the requirements of power electronics technology at higher frequency ranges.
Power integrated circuits (ICs) integrate multiple devices and their control circuits onto a single chip. Their manufacturing process combines the experience gained from the development of first-generation power electronic devices towards higher current and higher voltage, with the technological characteristics of large-scale integrated circuits. Because these devices significantly reduce the size of the components and their control circuits, they effectively minimize the impact of parasitic parameters when operating at high frequencies. This is crucial for increasing circuit operating frequencies and suppressing external interference.
From the 1960s to the early 1970s, power electronic devices , represented by semi-controlled ordinary thyristors, were mainly used in phase-controlled circuits. These circuits were widely used in rectifier devices such as electrolysis, electroplating, DC motor drives, and generator excitation. Compared with traditional mercury arc rectifiers, they were not only smaller and more reliable, but also achieved significant energy savings (generally 10-40% energy savings; in China, where fans and pumps account for about one-third of the country's electricity consumption, AC motor speed control could save an average of over 20%, amounting to 40 billion kilowatt-hours annually). Therefore, the development of power electronics technology received increasing attention. In the mid-1970s, fully controlled turn-off thyristors and power transistors emerged, offering fast switching speeds and simple control. Reverse-conducting turn-off thyristors further combined the functions of turn-off thyristors and fast rectifier diodes. These advancements propelled the application of power electronics technology into new areas centered on inversion and chopping. These devices are now widely used in power electronic devices such as variable frequency drives, switching power supplies, and static frequency converters.
In the early 1980s, MOS power field-effect transistors and power integrated circuits emerged, operating at frequencies in the megahertz range. Integrated circuit technology facilitated the miniaturization and functionalization of devices. These new achievements provided the conditions for the development of high-frequency power electronics technology, driving power electronic devices towards intelligence and higher frequencies.
