Switching Components For Medium Voltage Drives Engineering Essay

Nowadays power electronics is likely the most developed portion of the market of equipment for energy sector. Permanently turning power of air current turbines, overvoltage lines, power thrusts and accordingly supplied energy, demands growing of the market of power electronics.

The immense progress of power electronics for the last several decennaries gives the possibility for right pick of semiconducting material devices for specific use, seeking to utilize best features of each switch depending on proficient demands and restraints. This inquiry is particularly topical in the medium electromotive force scope, where many devices can replace for each other and in order to increase the efficiency and cut down costs the pick of switches should be done every bit accurate as possible.

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Medium electromotive force scope is upper than 1 kilovolts in classical vision, but it is conventional distinction and it does n’t ever work in power electronics. For illustration power MOSFET, for which high electromotive force scope already corresponds 500 V. Therefore the boundary line between medium electromotive force and high electromotive force ranges in power electronics is being smoothed presents, so this thesis pays attending on devices which can be rated either to medium or high electromotive force evaluations.

Medium electromotive force exchanging constituents
Thyristor is a semiconducting material device executed on the footing of a monocrystal of the semiconducting material with three or more junctions by passages and holding two steady conditions: turn off – status of low conduction, and turn-on – status of high conduction. There are assorted sorts of thyristors which are subdivided, chiefly, on a manner of direction and on conduction. Differentiation on conduction means that some thyristors conduct a current in one way and other in two waies ( the triode ac the switch – TRIAC, diacs ) .

Figure 1 Simplified cross subdivision of a thyristor. [ 3 ]

Thyristor can be switched on, holding put a short positive urge to gate. The forward electromotive force bead in the turn-on status is a few Vs ( as a regulation 1-3 V depending on the blocking electromotive force of the device ) .

Equally shortly as the device starts to carry on, it is latched in the turn-on status, and the current of gate can be removed. Thyristor ca n’t be switched off by the gate, and thyristor plants as the rectifying tube. Merely when the anode current attempts to go negative under the influence of a circuit to which it is connected, thyristor is switched away, and the current goes to a nothing. It allows gate to recover control to exchange on the device in some governable clip after it has once more entered the forward barricading status.

In contrary prejudice electromotive forces, merely little electric current of leak flows in the thyristor. Forward- and reverse- blocking electromotive forces of the thyristor are normally the same. [ 1 ]

Figure 1 A thyristor: ( a ) electrotechnical symbol, ( B ) i-u features. [ 2 ]

Gate turn-off thyristor ( GTO )
GTO can be switched on by a short urge of a gate current, and being in turn-on status GTO can stay without a gate current. However, unlike the thyristor, GTO can be switched off, seting negative gate-cathode electromotive force, thereby doing plenty large negative current through the gate. This negative gate current amplitude depends on the anode current which should be switched off. Turn-off is provided by short-circuiting bearers straight to the gate circuit, its turn-off clip is short, therefore giving it more capableness for high frequence operation than thyristors. [ 1 ] , [ 2 ]

Figure 2 A GTO: ( a ) electrotechnical symbol, ( B ) i-u features. [ 1 ]

Integrated Gate-Commutated Thyristor ( IGCT )
IGCT is a type of thyristor which is similar GTO. Turn-on and turn-off provinces can be achieved by using a gate signal. In comparing to GTO, IGCTs have lower conductivity loss and withstand higher rates of electromotive force rise ( dv/dt ) .

The construction of an IGCT is really similar to a GTO thyristor. In an IGCT, the gate turn off current is greater than the anode current. This fact follows to halt the expulsion of minority current bearers from the lower PN junction, which leads to the faster turn-off. The chief differences from the GTO are the lower size of the cell and presence of gate thrust in the organic structure of IGCT. The integrating of thrust circuit into the frame of device causes decrease of opposition and induction of the connexion.

Turn-off times of IGCT are much faster in comparing to GTO ‘s. That allows them to work at higher frequencies-up to several of kilohertz. But higher losingss appear on high frequences. Consequently typical operating frequence is about 500 Hz.

There are devices with contrary barricading capableness and without that is symmetrical and asymmetrical IGCTs. [ 3 ]

Metal-oxyde-semiconductor field consequence transistor ( MOSFET )
MOSFET is a electromotive force controlled device. It is to the full on and approaches a closed switch when the gate-source electromotive force is below the threshold value Vgs ( Thursday ) .

MOSFET requires the uninterrupted application of gate-source electromotive force of appropriate magnitude in order to be in the on province.

The shift times are really abruptly, being in the scope of a few 10s of nanoseconds to a few hundred nanoseconds depending on the device type. [ 1 ]

Figure 4 A MOSFET: ( a ) electrotechnical symbol, ( B ) i-u features. [ 1 ]

Figure 4 Simplified cross subdivision of a MOSFET. [ 3 ]

Insulated gate bipolar transistor ( IGBT )
The IGBT has some advantages of the MOSFET and GTO combined. Similar to the MOSFET, the IGBT has a high electric resistance gate, which requires merely a little sum of energy to exchange the device. Similar to GTO, the IGBT can be designed to barricade negative electromotive forces.

Figure 4 An IGBT: ( a ) electrotechnical symbols, ( B ) i-u features. [ 1 ]

The basic application IGBT are inverters, pulse regulators of the current, frequency-regulated thrusts. Wide application IGBT have found in current beginnings for a welding, in direction of the powerful electrical thrusts, including metropolis electric conveyance.

Application of IGBT faculties in control systems of grip engines allows ( in comparing with thyristor devices ) to supply high efficiency, high smoothness of an operation of the machine and possibility of application of restorative braking about at any velocity. IGBT is applied in high electromotive force devices ( more than 1000 V ) , high temperature ( more than 100 & A ; deg ; C ) and high end product power ( more than 5 kilowatt ) .

Figure 4 Simplified cross subdivision of an IGBT cell. [ 3 ]

IGBT and MOSFET occupy a scope of mean capacities and frequences, partly replacing of each other. Generally, for high-frequency low-tension Cascadess most applicable MOSFET, and for high-voltage is most appropriate powerful IGBT.

In certain instances IGBT and MOSFET – are wholly interchangeable. The feature of operating signals of both devices – are indistinguishable. IGBT and MOSFET demand 12 – 15 V for exchanging on. [ 1 ]

Comparison of power switches
The to the full controlled GTO was traditionally used in high power systems, because of its off-state electromotive force capableness and on-state current capableness. IGBT was really popular in medium power applications and the lower portion of high power, particularly when electromotive force is less than 1.5 kilovolts. With visual aspect of HVIGBT, IGBT is presented a challenge to predomination of the GTO in high power country. Switch overing public presentation of IGBT engineering is much better than GTO ‘s, but exchanging public presentation of GTO can be significantly improved by driving the gate current to be greater than or equal to the anode current during turn-off. Thus the IGCT appeared. Another of import feature of the GTO and the IGCT that they allow merely ON and OFF provinces. These switches are latching devices, while IGBT can ever be controlled in the whole scope from OFF to ON.

MOSFETs are normally used when there is necessity in really high shift frequence, but these switches are merely for comparatively low power applications. These devices are non applicable in high power circuits, but belongingss of MOSFETs are interesting, because the construction of IGBT contains it. [ 12 ] , [ 13 ]

Main features of the above semiconducting material switches are presented in the tabular array below.

Table 1 Comparison of the semiconducting material switches. [ 5 ] – [ 11 ]

Type of the device



Voltage scope ( VDRM ) , kV

Switch overing frequence scope, kHz

Scope of application


Lowest losingss in the turn-on province. The highest overload capacity in comparing to other switches. High dependability.

It is non capable for compulsory latching on an operating electrode.


& A ; lt ; 10

DC thrusts, power providers, equipment for welding, runing and warming, inactive volt-ampere compensators, HVDC, AC switches.


Controlled turn-off ability. Relatively high overload capacity. The dependability and cost effectivity.

High losingss in the turn-on province, really high losingss in the control system. Difficult and expensive turn-off snubbers. High shift losingss.

Slow switching- 10 – 30 µs


0.2 – 0.5

Adjustable velocity thrusts, inactive volt-ampere compensators, HVDC, uninterruptible power supply ( UPS ) , equipment for inductive warming.


Controlled turn-off ability. Relatively high overload capacity. Low losingss in the turn-on province during the shift. Snubberless turn-off.

Disadvantages are n’t good known, because nowadays IGCTs are n’t widely used.


& A ; gt ; 25 ( limited merely by thermic conditions of the device ) .

Power supplies, inverters, convertors, HVDC, power thrusts.


High working frequence,

Low power of devices


& A ; lt ; 1000

Switch Mode Power Supplies ( SMPS ) , uninterruptable power supplies ( UPS ) , inverters and DC motor thrusts


Controlled turn-off ability. Simple control system with incorporate driver.

Very high losingss in the turn-on province.



Power thrusts, uninterruptible power supply ( UPS ) , inactive volt-ampere compensators, HVDC, active filters.

Semiconductor stuffs:
Silicon ( Si )
Hyperpure Si is largely used for fabrication of individual faculties of nonlinear semiconducting material devices. It is the primary merchandise for the photovoltaic elements.

Silicon carbide ( SiC )
Silicon carbide is used in fast Schottky rectifying tubes, field transistors and high-temperature thyristors. In opposite to switches based on GaAs, devices on SiC have following advantages:

out zone GaAs is several times wider ;

field strength of electrical dislocation is 10 times bigger ;

high admissible working temperatures ( to 600 & A ; deg ; C ) ;

heat conduction is 3 times more over Si and about 10 times more over GaAs ;

stableness at radiation influence ;

stableness of electrical features while temperature is altering ;

Germanium ( Ge )
In wireless technology, transistors and rectifying tubes made from Ge have features which are differ from Si, in position of smaller unlocking electromotive forces of pn-junction of Ge – 0.4V against 0.6?’ of Si devices. Besides, back currents of Ge devices on some orders are more than those at Si.

Gallium arsenide ( GaAs )
Some electronic belongingss of GaAs exceed belongingss of Si. Gallium arsenide possesses higher mobility of negatrons which allows devices to work on frequences to 250 GHz. Semiconductor devices on the footing of GaAs generate less noise, than silicon devices on the same frequence. Because of more high tenseness of electric field of dislocation in GaAs in comparing with Si, devices from Ga arsenide can work at higher power.


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