Power electronics

Power electronics

·        Introduction

Power physics is that the application of solid-state physics to the management and conversion of electrical power.

The first high power electronic devices were mercury-arc valves. In trendy systems the conversion is performed with semiconductor switch devices like diodes, thyristors and transistors, pioneered by R. D. Middlebrook and others beginning in the 1950s. In distinction to electronic systems involved with transmission and process of signals and information, in power physics substantial amounts of electricity area unit processed. An AC/DC device (rectifier) is that the commonest power physics device found in several shopper electronic devices, e.g. television sets, personal computers, battery chargers, etc. The power vary is usually from tens of watts to many hundred watts. In trade a typical application is that the variable speed drive (VSD) that's accustomed management AN induction motor. The power vary of VSDs begin from a couple of hundred watts and finish at tens of megawatts.

The power conversion systems are often classified consistent with the sort of the input and output power

• History

Power physics started with the event of the mercury arc rectifier. Invented by altruist Hewitt in 1902, it had been accustomed convert electricity (AC) into electrical energy (DC). From the Nineteen Twenties on, analysis continued  on applying thyratrons and grid-controlled mercury arc valves to power transmission. Uno Lamm developed a mercury valve with grading electrodes creating them appropriate for prime voltage electricity power transmission. In 1933 selenium rectifiers were invented.

In 1947 the bipolar point-contact semiconductor was fancied by director H. Brattain and John Bardeen under the direction of William Shockley at Bell Labs. In 1948 Shockley's invention of the bipolar semiconductor device (BJT) improved the soundness and performance of transistors, and reduced prices. By the Fifties, higher power semiconductor diodes became offered and began exchange vacuum tubes. In 1956 the chemical element controlled rectifier (SCR) was introduced by General electrical, greatly increasing the range of power electronics applications.

By the Sixties the improved change speed of bipolar junction transistors had allowed for top frequency DC/DC converters. In 1976 power MOSFETs became commercially available. In 1982 the Insulated Gate Bipolar semiconductor unit (IGBT) was introduced.

• Devices

The capabilities and economy of power physics system area unit determined by the active devices that area unit accessible. Their characteristics and limitations area unit a key component within the style of power physics systems. Formerly, the mercury arc valve, the high-vacuum and gas-filled diode particle rectifiers, and triggered devices such as the thyratron and ignitron were widely used in power electronics. As the ratings of solid-state devices improved in each voltage and current-handling capability, vacuum devices are nearly entirely replaced by solid-state devices.

Power electronic devices may be used as switches, or as amplifiers. An ideal switch is either open or closed and so dissipates no power; it withstands an applied voltage and passes no current, or passes any amount of current with no voltage drop. Semiconductor devices used as switches will approximate this ideal property then most power electronic applications believe switch devices on and off, that makes systems terribly economical as very little power is wasted in the switch. By contrast, in the case of the amplifier, the current through the device varies continuously according to a controlled input. The voltage and current at the device terminals follow a water level, and the power dissipation inside the device is large compared with the power delivered to the load.

Several attributes dictate how devices are used. Devices like diodes conduct once a forward voltage is applied and haven't any external management of the beginning of physical phenomenon. Power devices like Si management led rectifiers and thyristors (as well because the mercury valve and thyratron) permit control of the beginning of physical phenomenon, but rely on periodic reversal of current flow to turn them off. Devices such as gate turn-off thyristors, BJT and MOSFET transistors provide full switching control and can be turned on or off without regard to the current flow through them. Transistor devices additionally permit proportional amplification, but this is rarely used for systems rated more than a few hundred watts. The management input characteristics of a tool additionally greatly have an effect on design; generally, the management input is at a awfully high voltage with regard to ground and should be driven by an isolated source.

As potency is at a premium during a power converter, the losses that an influence device generates ought to be as low as potential.