Power electronics is the applications of solid-state electronics for the control and conversion of electric power
Introductions
Power electronic converters can be found wherever there is a need to modify the electrical energy form (i.e modify its voltage, current or frequency). Therefore, their power range is from some milliwatts (as in a mobile phone) to hundreds of megawatts (e.g in a HVDC transmission system). With "classical" electronics, electrical currents and voltage are used to carry information, whereas with power electronics, they carry power. Therefore the main metric of power electronics becomes the efficiency.
The first very high power electronic devices were
mercury arc valveA mercury arc valve is a type of electrical rectifier which converts alternating current into direct current. Rectifiers of this type were used in electric motor power supplies for industry, in electric railways,...
s. In modern systems the conversion is performed with
semiconductorA semiconductor is a material that has an electrical resistivity between that of a conductor and an insulator, that is, generally in the range 10
3 Siemens/cm to 10
−8 S/cm. Devices made from semiconductor materials are the foundation of modern electronics, including radio,...
switching devices such as
diodeIn electronics a diode is a two-terminal electronic component which conducts electric current asymmetrically or unidirectionally; that is, it conducts current more easily in one direction than in the opposite direction. The term usually refers to a semiconductor diode, the most common type today,...
s, thyristors and transistors. In contrast to electronic systems concerned with transmission and processing of signals and data, in power electronics substantial amounts of electrical energy are processed. An
AC/DCAC/DC are an Australian rock band formed in Sydney in 1973 by Scottish-born brothers Malcolm and Angus Young. Although the band are commonly classified as hard rock and are considered pioneers of heavy metal, they have always classified their music as "rock and roll".AC/DC underwent several line-up...
converter (
rectifierA rectifier is an electrical device that converts alternating current to direct current , a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals...
) is the most typical power electronics device found in many consumer electronic devices, e.g.,
televisionTelevision is a widely used telecommunication medium for transmitting and receiving moving images, either monochromatic or color, usually accompanied by sound. "Television" may also refer specifically to a television set, television programming or television transmission...
sets, personal
computerA computer is a machine that manipulates data according to a set of instructions.Although mechanical examples of computers have existed through much of recorded human history, the first electronic computers were developed in the mid-20th century . These were the size of a large room, consuming as...
s,
battery chargerA battery charger is a device used to put energy into a secondary cell or battery by forcing an electric current through it.The charge current depends upon the technology and capacity of the battery being charged...
s, etc. The power range is typically from tens of
wattThe watt is a derived unit of power in the International System of Units . It measures rate of energy conversion. One watt is equivalent to 1 joule of energy per second....
s to several hundred watts. In
industryAn industry is the manufacturing of a good or service within a category. Although industry is a broad term for any kind of economic production, in economics and urban planning industry is a synonym for the secondary sector, which is a type of economic activity involved in the manufacturing of raw...
the most common application is the variable speed drive (VSD) that is used to control an
induction motorAn induction motor is a type of alternating current motor where power is supplied to the rotating device by means of electromagnetic induction. It is also called asynchronous motor....
. The power range of VSDs start from a few hundred watts and end at tens of megawatts.
The power conversion systems can be classified according to the type of the input and output power
- AC
In alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again...
to DCDirect current is the undirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through...
(rectificationA rectifier is an electrical device that converts alternating current to direct current , a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals...
)
- DC
Direct current is the undirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through...
to ACIn alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again...
(inversionAn inverter is an electrical device that converts direct current to alternating current ; the resulting AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
)
- DC
Direct current is the undirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through...
to DCDirect current is the undirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through...
(choppingIn electronic engineering, a DC to DC converter is an electronic circuit which converts a source of direct current from one voltage level to another. It is a class of power converter.- Usage :...
)
- AC to AC
AC/AC conversion converts an AC waveform such as the mains supply, to another AC waveform, where the output voltage and frequency can be set arbitrarily.AC/AC converters can be categorized into* Converters with a DC-link.* Hybrid Matrix Converters....
Principle
As efficiency is at a premium in a power electronic converter, the losses that a power electronic device generates should be as low as possible. The instantaneous dissipated power of a device is equal to the product of the voltage across the device and the current through it . From this, one can see that the losses of a power device are at a minimum when the voltage across it is zero (the device is in the On-State) or when no current flows through it (Off-State). Therefore, a power electronic converter is built around one (or more) device operating in switching mode (either On or Off). With such a structure, the energy is transferred from the input of the converter to its output by bursts.
To convert the power electronics by using rectifier
Applications
Power electronic systems are virtually in every electronic device. For example, around us:
- DC/DC converters are used in most mobile devices (mobile phone, pda...) to maintain the voltage at a fixed value whatever the charge level of the battery is. These converters are also used for electronic isolation and power factor correction.
- AC/DC converters (rectifiers) are used every time an electronic device is connected to the mains (computer, television,...)
- AC/AC converters are used to change either the voltage level or the frequency (international power adapters, light dimmer). In power distribution networks AC/AC converters may be used to exchange power between utility frequency
The line frequency or mains frequency is the frequency at which alternating current is transmitted from a power plant to the end user. In most parts of the world this is 50 Hz, although in the Americas it is typically 60 Hz...
50 Hz and 60 Hz power grids.
- DC/AC converters (inverters) are used primarily in UPS
An Uninterruptible power supply , also known as a battery backup, provides emergency power and, depending on the topology, line regulation as well to connected equipment by supplying power from a separate source when utility power is not available...
or emergency lightAn emergency light is a battery-backed lighting device that comes on automatically when a building experiences a power outage. Emergency lights are standard in new commercial and high occupancy residential buildings, such as college dormitories...
. During normal electricity condition, the electricity will charge the DC battery. During blackout time, the DC battery will be used to produce AC electricity at its output to power up the appliances.