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Power Electronics Industry
Utility systems usually generate, transmit, and distribute power at a fixed frequency such as 50 or 60 Hz, while maintaining a reasonably constant voltage at the consumer's terminal. The consumer may use many different electronic or electrical products which consume energy from a DC or AC power supply which converts the incoming AC into the required form.
In the case of products or systems running on AC, the frequency may be the same, higher, lower or variable compared to the incoming frequency. Often, power needs to be controlled with precision. A power electronics system interfaces between the utility system and consumer's load to satisfy this need.
The core of most power electronic apparatus consists of a converter using power semiconductor switching devices that works under the guidance of control electronics. The converters can be classified as rectifier (AC-to-DC converter), inverter ( DC-to-AC converter), DC-to-DC converter, or an AC power controller (running at the same frequency), etc.
Often, a conversion system is a hybrid type that mixes more than one basic conversion process. The motivation for using switching devices in a converter is to increase conversion efficiency to a high value. In few situations of power electronic systems, the devices (power semiconductors) are used in the linear mode too, even though due to reasons of efficiency it’s getting more and more limited.
Power electronics can be described as an area where anything from a few watts to over several hundred megawatt order powers are controlled by semiconductor control elements which consume only few microwatts to milliwatts in most areas. As per industry estimates indicated in an editorial of Power Conversion and Intelligent Motion Journal (2012), the power electronics industry component in the U.S. was around US$ 60 billion, from a total estimated electronics industry of around US$ 990 billion.
Power Conversion Electronics
Power conversion electronics can be described as a group of electrical and electronic components arranged to form an electric circuit or group of circuits for the purpose of modifying or controlling electric power from one form to another.
For example, power conversion electronics is employed to provide extremely high voltages to picture tubes to display the courses of aircraft approaching an airport.
In another example, power conversion electronics is employed to step up low voltage from a battery to the high voltage required by a vacuum fluorescent display to allow paramedics to display a victim's heartbeat on a screen. This also allows paramedics to gain information en route to the hospital, which may save the patient's life.
Twenty years ago, power conversion was in its infancy. High efficiency switchmode power supplies were a laboratory curiosity, not a production line reality.
Complex control functions, such as the precision control of stepper motors for robotics, microelectronics for implanted pacemakers, and harmonic-free switchmode power supplies, were not economically achievable with the limited capabilities of semiconductor components available at the time.
Importance of Power Electronics in the Modern World
At the beginning of the 20th century the world population was around 1.5 billion; by the year 2020 it’s projected to be around 7.5 billion. Rapid technology evolution coupled with the population explosion has resulted in an increase in average electrical power usage, from about one-half million MW in the year 1940 to a projected eight million MW in the year 2020. This magnitude of growth when coupled with the increasing electrical power sophistication associated with process control, communications, consumer appliances/electronics, information management, electrified transportation, medical, and other applications--results in roughly 49 percent of all electrical power delivered to user sites today being reprocessed via power electronics. This is expected to increase to about 85 percent by the year 2020. By 2020 approximately 5.8 million MW of electrical power will be processed by power electronics. Typical power electronics applications include electronic ballasts, high voltage DC transmission systems, power conditioners, UPS systems, power supplies, motor drives, power factor correction, rectifiers and, more recently, electric vehicles. With computer systems, telecom products and a plethora of electronic consumer appliances which require many power electronic sub-systems, the power electronics industry has become an important topic in the electronics industry and the information technology area.
In modem power electronics apparatus, there are essentially two types of semiconductor elements: the power semiconductors that can be defined as the muscle of the equipment, and microelectronic control chips, which provide the control and intelligence. In most situations operation of both are digital in nature. One manipulates large power up to mega or gigawatts, the other handles power only on the order of microwatts to milliwatts.
Until the 1970s, power semiconductor technology was based exclusively upon bipolar devices, which were first introduced commercially in the 1950s. The most important devices in this category were the p-i-n power rectifier, the bipolar power transistor, and the conventional power thyristor. The growth in the ratings of these devices was limited by the availability of high purity silicon wafers with large wafer diameter, and their maximum switching frequency was limited by minority carder lifetime control techniques. In the 1980s another bipolar power device, the Gate Turn-Off Thyristor (GTO), became commercially available with ratings suitable for very high power applications. Its ability to turn-on and turn-off large current levels under gate control eliminated the commutation circuits required for conventional thyristors, thus reducing size and weight in traction applications, etc.
Although these bipolar power devices have been extensively used for power electronic applications, a fundamental drawback that has limited their performance is the current controlled output characteristic of the devices. This characteristic has necessitated the implementation of high power systems with powerful discrete control circuits, which are large in size and weight.
In the 1970s, the first power Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETS) became commercially available. Their evolution represents the convergence of power semiconductor technology with mainstream CMOS integrated circuit technology for the first time.
Subsequently, in the 1980s, the Insulated Gate Bipolar Transistor (IGBT) became commercially available.
The MOSFET and IGBT require negligible steady state control power due to their Metal-Oxide-Semiconductor (MOS) gate structure. This feature has made them extremely convenient for power electronic applications resulting in a rapid growth in the percentage of their market share for power transistors.
The ratings of the power MOSFET and IGBT have improved rapidly in recent years, resulting in their overtaking the capability of bipolar power transistors. The replacement of bipolar power transistors in power systems by these devices that was predicted 15 years ago has now been confirmed. However, the physics of operation of these devices limits their ability to handle high current levels at operating voltages in excess of 2000 volts.
Consequently, for high power systems, such as traction (electric locomotives and trams) and power distribution, bipolar power devices, namely the thyristor and GTO, are the best commercially available components today. Although the power ratings for these devices continue grow, the large control currents needed to switch the GTOs has stimulated significant research around the world aimed at the development of MOS-gated power thyristor structures such as MOS Controlled Thyristors (MCT). The development of the insulated gate power devices discussed above has reduced the power required for controlling the output transistors in systems. The relatively small (less than an ampere) currents at gate drive voltages of less than 15 volts that are needed for these devices can be supplied by transistors that can be integrated with CMOS digital and bipolar analog circuitry on a monolithic silicon chip.
This led to the advent of smart power technology in the 1990s.
Smart power technology provides not only the control function in systems but also serves to provide over-current, over-voltage, and over-temperature protection, etc. At lower power levels, it enables the implementation of an entire sub-system on a monolithic chip. The computer-aided design tools that are under development will play an important role in the commercialization of smart power technology because they will determine the time-to-market as well as the cost for development of Power Application Specific Integrated Circuits (PASIC). Sometimes these devices are called Application Specific Power Integrated Circuits (ASPIC). In systems such as automotive electronics or multiplex bus networks and power supplies for computers with low operating voltages (below 100 volts), the power MOSFET provides the best performance. In systems such as electric trams and locomotives, the GTO is the best commercially available component. In the near future, MOS gated thyristor structures are likely to replace the GTO. Towards the mid-90s GaAs power diodes have entered the marketplace providing better switching characteristics as well as lower forward drop, etc. On a longer time frame, it’s possible that devices based upon wide band-gap semiconductors, such as Silicon Carbide, could replace some of these silicon devices.
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