Power Electronic Circuits - Fall 2006 1

POWER ELECTRONIC CIRCUITSPOWER ELECTRONIC CIRCUITS

FALL 2006FALL 2006Özgür ÜSTÜN

Power Electronic Circuits - Fall 2006 2

Syllabus• Introduction to Power Electronics• Switching circuits (DC – AC)• Rectifiers• AC Choppers• DC Choppers• Inverters• Cycloconverters• Triggering and control circuits• Snubber circuits and protection• Some design issues

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What is Power Electronics?

In the broadest sense, the task of power electronics is to process and control the flow of electric energy by supplying voltages and currents in a form that is optimally suited for user loads.

LoadPower Processor(Power Electronic Circuit)

ControllerReference

Control Signals

Power Input

Power Output

Measurements

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In power electronic concept, power electronic devices are shown as switches. Every type of semiconductor device is operating in switching mode. This is important for high efficient power transfer from one type of electrical energy to another. Devices which operate in linear mode are not useful in high efficient power transfer because of their relatively higher losses .

Power Electronics versus Linear Electronics

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PowerElectronics

Systems andcontrol theory

Signalprocessing

Electronics

Circuittheory

Solid-statephysics

Simulation and computing

Electricmachines

Powersystems

Electromagnetics

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Electronic Circuits and

Networks

Digital electronics

Power electronics

Analog electronics

R.F. electronics

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∼ =

∼ =

Rectifying

Inverting

D.C. Chopping

A.C. Chopping

Power Electronic Converters

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Power Electronic Applications

• Residential: Refrigeration and freezers, Space heating, Air conditioning, Cooking, Lighting, Electronics (PCs, other entertainment equipment).

• Commercial: Heating, ventilating and air conditioning, Central refrigeration, Lighting, Computers and office equipment, Uninterruptible Power Supplies (UPSs), Elevators.

• Industrial: Pumps, Compressors, Blowers and fans, Machine tools (robots), Arc furnaces, induction furnaces, Lighting, Industrail lasers, Induction heating, Welding.

• Transportation: Traction control of electric vehicles, Battery charges for electric vehicles, Electric locomotives, Street cars, trolley buses, Subways, Automotive electronics.

• Utility Systems: High-voltage dc transmission (HVDC), Static var compensation (SVC), Supplemental energy sources (wind, photovoltaic), fuel cells, energy storage systems, Induced-draft fans and boiler feedwater pumps.

• Aerospace: Space shuttle power supply systems, Satellite power systems, aircraft power systems.

• Telecommunications: Battery chargers, Power supplies (dc and UPS)

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Ideal Switch

i : switch current

+ v -

Switch voltageWhile open:

v = V ; i = 0

While closed:

v = 0 ; i = I

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VS IS

Time, t

P P

Turn-on and turn-off losses

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The power diode (PN junction)

a) Structure

b) Symbol

Diode characteristics

Power Diode

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Thyristor

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Thyristor

a) Structure

b) Symbol

Thyristor

Thyristor characteristics

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Turning on of the thyristor

=

Load

+

The problem is how to turn off thyristor.The gate is no use of this.

ig

iload

Time, t

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Methods of turning off the thyristor

=

Load

+

=

Load

++

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The GTO: Gate Turn-off Thyristor

Its difference from normal thyristor is the possibility to turn-off by applying a reversal gate current.

The GTO symbol

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=

Load

+ig

iload

Time, t

Operation of the GTO

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NPN Bipolar junction Transistor

a) Structure

b) Symbol

BJT characteristics

Power Transistor

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Transistor Controlled load Transistor as a switch

Operation of BJT

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SOA (Safe Operating Area of BJT)

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MOSFET (Metal Oxide Semiconductor Field Effect Transistor)

+

-VGS

G

D

S

+

VDS

-

iDMOSFET is a voltage controlled device, gate current is very low capasitic current.

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+

-VGS

G

D

S

+

VDS

-

iD

IGBT (Insulated Gate Bipolar Transistor)

C

E

G

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Device Power Capability

SwitchingSpeed

BJT/MD Medium Medium

MOSFET Low Fast

GTO High Slow

IGBT Medium Medium - Fast

MCT Medium Medium

Relative Properties of Controllable Switches