20304726 power electronics chapter 1

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Overview to

Power Electronics

Mohd Shawal Bin Jadin

Ext : 2321A01-2074

[email protected]



Learning OutcomesLearning Outcomes At the end of the lecture, student

should be able to:

± Identify the function of electronics

switches, hence to select a proper

switching for certain applications.

± Outline the principles of energy recovery

and also to calculate the power for non-

sinusoidal periodic waveform



Definition of PowerDefinition of Power

ElectronicsElectronics

Multidisciplinary Nature of Multidisciplinary Nature of

the Fieldthe Field Block Diagrams of PowerBlock Diagrams of Power

Electronic SystemsElectronic Systems

The Need for PowerThe Need for Power

ElectronicsElectronics

Future TrendsFuture Trends Types of Power ConversionTypes of Power Conversion

Electronic SwitchElectronic Switch

Switch SelectionSwitch Selection

Energy RecoveryEnergy Recovery

Chapter 1Chapter 1Power Electronic

"Power" Circuit

Feedback

"Control Circuit"

Load1

Load2

Loadn

ElectricalInputs

"Sources"

Electrical or Mechanical

Output "Loads"

x1

x2

xm

y1

y2

yn

f 1 f 2 f k

Power

Processing

circuit

(Ploss

)

(input)

Source Side

(output)

Load Side

Load



What is Power Electronics? Generally:

± Electronics: Solid State Electronics Devices and their

Driving Circuits. ± Power: Static and Dynamic Requirements for Generation,

Conversion and Transmission of Power.

± Control: The Steady State and Dynamic Stability of the

Closed Loop system.

POWER ELECTRONICS may be defined as the

application of Solid State Electronics for the

Control and conversion of Power.



Definition of Power ElectronicsDefinition of Power Electronics DEFINITION:

To convert, i.e to process and control the flow of

electric power by supplying voltages and currentsin a form that is optimally suited for user loads.



Power Electronics (PE) SystemsPower Electronics (PE) Systems To convert electrical energy from one form to

another, i.e. from the source to load with:

highest efficiency,

highest availability

highest reliability

lowest cost,

smallest size

least weight



Detailed Block Diagram of PowerDetailed Block Diagram of Power

Electronics SystemElectronics System

Filter

&

Recti y

ircuit oad

Filter

&

Recti y

ontrolircuitechanical Variable

Feedback

lectrical Variable

Feedback

Input

Form oelectrical

energy

lectrical

echanical

re-stageo er proc. stage ost stage

utput

Form o elec. or

mechan. energy

i t c h

D r

i v

e s

rocess eedback

signals and decide

on control

ould generate

undesirable

ave orms

ostly ac line

voltage (single

or three phase)

ostly

unregulate

d dc

voltage

Inter ace bet een

control and po er

circuits



Applications Static applications

± involves non-rotating or moving mechanical

components.

± Examples:

DC Power supply

Un-interruptible power supply, Power generation and

transmission

(HVDC), Electroplating, Welding, Heating,

Cooling, Electronic ballast



Applications Drive applications

± intimately contains moving or rotating

components such as motors.

± Examples:

Electric trains, Electric vehicles, Air-conditioning

System, Pumps, Compressor,

Conveyer Belt (Factory automation).



Application examples Static Application: DC Power Supply



Application examples Drive Application: Air-Conditioning System



Other ApplicationsOther Applications

Heating, cooling, CFLHeating, cooling, CFLElectroplating, WeldingElectroplating, Welding

Photovoltaic Systems.Photovoltaic Systems.eV (fuel cell, Solar)eV (fuel cell, Solar)

WindWind--electric systems.electric systems.



Conversion concept: exampleConversion concept: example11

Supply from TNB: 50Hz, 240V RMS (340V peak).Customer need DC voltage for welding purpose, say.

TNB i - v ly

iv z DCm !

Av v l

W im l h lf-

v ifi . A fix DC

v l i b i .Thi i im l E y m.

1 El i , M D Z i l l m, UTM



Conversion concept: example (Cont)Conversion concept: example (Cont)11

How about if customer wants variable DC voltage?

± More complex circuit using SCR is required.

By lli h fi i l , , h DC v l

f v i b v i .

1 El i , M D Z i l l m, UTM

Av V l



Advantages of Advantages of Power ElectronicsPower Electronics

High energy conversion efficiencyHigh energy conversion efficiency

± Instead of using 50/60Hz motor-generator

Higher Reliability and cost effective

± Less maintenance, longer lifetime, light and small size, fast recovery time, unlimitedrange of conversion

Environmentally clean and safeEnvironmentally clean and safe

± produce no hazardous waste products

± Burning of fossil fuel emits gases such as C,0,, CO (oil burning), S02, NOx (coalburning) etc. Creates global warming (green house effect), acid raill and urbanpollution h-oll)

Q uite operationQ uite operation

± has no moving parts, suitable for residential, hotels etc

reduce dependence on fossil fuel (coal, natural gas, oil) and nuclear power resourcereduce dependence on fossil fuel (coal, natural gas, oil) and nuclear power resource(uranium).(uranium). ± Effort to tap renewable energy resources such as solar, wind, fuel-cell etc. need to be increased.

Special effort is needed to reduce pollution in cities by enforcing the use of electricvehicle.



PE growth

PE growth

PE rapid growth due to:PE rapid growth due to:

± Advances in power (semiconductor) switches

Advances in microelectronics(DSP, VLSI, microprocessor /

microcontroller, ASIC)

New ideas in control algorithms

Demand for new applications



PE is an interdisciplinary field: ± ± Digital/analogue electronicsDigital/analogue electronics

± ± Power and energyPower and energy

± ± MicroelectronicsMicroelectronics

± ± Control systemControl system

± ± Computer, simulation and softwareComputer, simulation and software

± ± SolidSolid--state physics and devicesstate physics and devices

± ± PackagingPackaging

± ± Heat transferHeat transfer



Power Electronics ConvertersPower Electronics Converters

AC to DC: RECTIFIERAC to DC: RECTIFIER

DC to DC: CHOPPERDC to DC: CHOPPER

DC toA

C: INVERTERDC toA

C: INVERTER

AC to AC: CYCLOCONVERTERAC to AC: CYCLOCONVERTER



Power semiconductor devicesPower semiconductor devices

(Power switches)(Power switches)

C b i i h :

± Uncontrolled: Diode

± Semi-controlled: Thyristor (SCR)

± Fully controlled: Power transistors e.g.

BJT,MO FET, IGBT, GTO, IGCT



Photos of Power SwitchesPhotos of Power Switches (From(From PowerexPowerex Inc.)Inc.)



Power Electronics ConvertersPower Electronics Converters

AC to DC: RECTIFIERAC to DC: RECTIFIER

DC to DC: CHOPPERDC to DC: CHOPPER

DC toA

C: INVERTERDC toA

C: INVERTER

AC to AC: CYCLOCONVERTERAC to AC: CYCLOCONVERTER



The Need For Switching In Power Electronic CircuitsThe Need For Switching In Power Electronic Circuits

The need to use semiconductor switching devices inpower electronic circuits is based on their ability tocontrol and manipulate very large amounts of power from

the input to the output with relatively very low powerdissipation in the switching device.

Implication of low efficiency:

1. The cost of energy increasescost of energy increases due to increasedconsumption.

2. Additional design complications might be imposed,especially regarding the design of device heat sinksdesign of device heat sinks



ExampleExampleInvestigate the efficiency of four different power electronic

circuits whose function is to take power from a 2424 VV dcdc sourcesourceandand deliverdeliver aa 1212 VV dcdc outputoutput toto aa 66;; resistiveresistive loadload. In otherwords, the task of these circuits is to serve as dc transformerswith a ratio of 2 : 1. The four circuits are shown in Fig. 1 (a), (b),(c), and (d) representing a voltagevoltage dividerdivider circuit,circuit, zenerzener regulatorregulator((assumeassume IIZZ isis 1010%% of of loadload current)current),, transistortransistor linearlinear regulator,regulator, andandswitchingswitching circuit,circuit, respectivelyrespectively. [Hint: For circuit (d), Vo=Vin*D]



(e) Zener diode i-v switching characteristics. (f) Switching waveforms for circuit

Example (Cont)Example (Cont)




Cicuit (a) : VoltageDivider dc RegulatorCicuit (a) : VoltageDivider dc Regulator Since Vin=24V and RL=6; and desired Vo=12V.

Hence, R =R = RRLL=6=6;;.

Thus,%50%

66

6%

%%

!

!

!

!!

R R

R

P

P

P

P

L

L

in

L

in

out L

CicuitCicuit (b) :(b) : Zener Zener dc Regulator dc Regulator

i i V =12V, h h bl ki v l f z i , VZ

= 12V.

i , R =6;. Th I =2A. A m h , I A m h , IZZ = 0.2A= 0.2A

10% f l10% f l

Th ,

%5.45%8

.52

24%

24122

8.52242.2

2.22.02

!!!

!v!

!v!

!!

!

in

out

out

in

z

T

W

W

A

I I I

L




CicuitCicuit (c) : Transistor dc Regulator(c) : Transistor dc Regulator

For Vo=12V, it is clear that VCE must be around 12V.

Hence, the control circuit must provide base current, IB to put

transistor in active mode with VCE=12V. For given Vo=12V andRL=6;, thus IILL=2A=2A.

Thus, IICC = 2A= 2A since IB too small in such that to turn on transistor.

%50%48

24%

24212

48)24(2

!!!@

!v}}

!

!!!

in

out

C CE

B BE C CE diss

cinin

P

P

W I V

I V I V P

W I V P

L




CicuitCicuit (d) : Switching dc Regulator (d) : Switching dc Regulator A m h i h i i l i i lly ff.

F m fi f , V i iv by

%100%48

48%,

),(

48242,24

!!!!

!v!v!!

in

out inout

in Linin

P

P P P

ideal assume switching to Due

W V I P V V Since

L

´ !!

DT

inin

s

aveo

s

DV dt V T V 0

,

1

F V , v =12V, h D=0.5D=0.5 VV , v, v =24 x 0.5 =12V=24 x 0.5 =12V



Ideal Switch

ingCh

aracteristicsIdeal Switch

ingCh

aracteristics1. No limit on the amount of current that the device can

carry when in the conduction state (on-state)

2. No limit on the amount of device voltage (known as

blocking voltage) when the device is in the non-

conduction state (off-state)

3. Zero on-state voltage drop when in the conduction

state

4. Zero leakage current when in the nonconduction

state

5. No limit on the operating speed of the device when it

changes state, i.e., zero rise and fall times



Ideal Switch

ingCh

aracteristicsIdeal Switch

ingCh

aracteristics

Power lossPower loss



Th

e Practical Switch

Th

e Practical Switch

The practical switch has the following switchingand conduction characteristics:

1.1. Limited powerLimited power--handling capabilitieshandling capabilities

2.2. Limited switching speedLimited switching speed

3.3. TheThe existence of forward voltage drop in the onexistence of forward voltage drop in the onstate, and reverse current flow (leakage) in thestate, and reverse current flow (leakage) in theoff stateoff state

4. Because of characteristics 2 and 3, the practicalswitch experiences power losses in the on andswitch experiences power losses in the on andoff states (known as conduction loss) and duringoff states (known as conduction loss) and duringswitching transitions (known as switching loss)switching transitions (known as switching loss)



PowerD

iodesPowerD

iodes

When diode is forward biased, it conducts current with asmall forward voltage (V f ) across it (0.2-3V)

When reversed (or blocking state), a negligibly small leakagecurrent (uA to mA) flows until the reverse breakdownoccurs. Diode should not be operated at reverse voltagegreater than V r . Thus, higher voltage blocking is needed.Thus, higher voltage blocking is needed.



PowerPower Diode (ReverseDiode (Reverse Recovery)Recovery)

When a diode is switched quickly from forward toreverse bias, itit continuescontinues toto conductconduct due to themi nor i ty carr i ers which remains in the p-n

junction.

The minority carriers require finite time, i.e, t rr (reverse recovery time) to recombine withopposite charge and neutralize.

Effects of reverse recovery are increase inswitching losses, increase in voltage rating, over-voltage (spikes) in inductive loads



PowerPower Diode (ReverseDiode (Reverse Recovery)Recovery)



Types of Power DiodesTypes of Power Diodes

Line frequency (general purposeLine frequency (general purpose) :) :

on state voltage very low(below 1V)

large t rr (about 25us)

very high current (up to 5kA)and voltage (5kV) ratings

Used in line-frequency(50/60Hz)

applications such as rectifiers

Fast recoveryFast recovery ver y low trr (<1 s). Power levels at several

h red volts and several

h ndred am s Nor mally used in hi h f requency circuits

SchottkySchottky ver y low f orward voltage drop (typical 0.3V) limited blocking voltage (50-100V) Used in low voltage, high current application such as switched mode power

supplies.



Thyristor basedThyristor based Thyristor refers to the family of power semiconductor

devices made of threethree pnpn junctions junctions (fourfour layerslayers of of pnpnpnpn)that cancan bebe latchedlatched intointo thethe onon statestate throughthrough anan externalexternalgategate signalsignal that causes a regeneration mechanism in thedevice.

Thyristor family currently used in power electroniccircuits:

± ± TheThe siliconsilicon--controlledcontrolled rectifierrectifier (SCR),(SCR),

± ± gategate turnturn--off off thyristorthyristor (GTO),(GTO), ± ± triodetriode acac switchswitch (triac),(triac),

± ± staticstatic inductioninduction transistortransistor (SIT),(SIT),

± ± staticstatic inductioninduction thyristorthyristor (SITH),(SITH),

± ± andand MOSMOS--controlledcontrolled thyristorthyristor (NICT)(NICT)..



Thyristor (SCR)Thyristor (SCR)

Unlike the diode, the SCRUnlike the diode, the SCR has a third terminal called the "gate" used"gate" usedfor control purposes.for control purposes.

The holding currentholding current is the minimum forward currentminimum forward current the SCR can carryin the absence of a gate drive.

The forward breakover voltage, VVBOBO, is the voltage across the anode-cathode terminal that causes the SCR to turn on without thecauses the SCR to turn on without theapplication of a gate currentapplication of a gate current.

Reverse avalanche (breakdown) occurs when VAK is negatively large.



Thyristor (SCR)Thyristor (SCR)

Thyristors can only be turned on with two conditions:

thethe devicedevice isis inin forwardforward blockingblocking statestate ((ii..ee V V ak ak isis positive)positive)

aa positivepositive gategate currentcurrent ((IIgg)) isis appliedapplied atat thethe gategate

Once conducting, the anode current is LATCHED (continuously flowing).

In reversereverse -- biasedbiased mode,mode, thethe SCRSCR behavesbehaves likelike aa diodediode.. It conducts a smallleakage current which is almost dependent of the voltage, but increases withtemperature.

When the peak reverse voltage is exceeded, avalancheavalanche breakdownbreakdown occursoccurs, andthe large current will flow.

In the forward biased mode, with no gate current present (i.e. in theuntriggered state), the device exhibits a leakage current.

If the forward breakover voltage (VBO) is exceeded, the SCR self-triggers intothe conducting state and the voltage collapses to the normal forward volt-drop,typically 1.5-3V. The presence of any gate current will reduce the forwardbreakover voltage.



Thyristor ConductionThyristor Conduction

How to turn off thyristor ?



Thyristor ConductionThyristor Conduction

Thyristor cannot be turned off by applying negativenegative

gategate currentcurrent. It can only be turned off if I A goes

negative (reverse)

ThisThis happenshappens whenwhen negativenegative portionportion of of thethe of of

sinesine--wavewave occursoccurs (natural commutation).

Another method of turning off is known as forcedcommutation,

TheThe anodeanode currentcurrent isis diverteddiverted toto anotheranother

circuitrycircuitry..



ControllableControllable switches (powerswitches (power transistors)transistors)

Can be turned ONand OFF by relatively very small controlsignals.

Operated in SATURATION and CUTOFF modes onlySATURATION and CUTOFF modes only. No linear

region operation is allowed due to excessive power loss.

In general, power transistors do not operate in latched modepower transistors do not operate in latched mode.

T rad i t i onal dev i ces: Bipolar junction transistors (BJT), Metal oxideBipolar junction transistors (BJT), Metal oxidesilicon field effect transistor ( MOSFET), Insulated gate bipolarsilicon field effect transistor ( MOSFET), Insulated gate bipolartransistors (IGBT), Gate turntransistors (IGBT), Gate turn--off off thyristorsthyristors (GTO)(GTO)

E mergi ng (new) dev i ces: Gate controlled thyristors (GCT).



Bipolar Junction Transistor (BJT)Bipolar Junction Transistor (BJT)

Ratings: Voltage: V V C E C E

<<10001000,, CurrentCurrent:: IIC C <<400400AA.. SwitchingSwitching

frequencyfrequency upup toto 55kHzkHz.. LowLow onon--statestate voltagevoltage:: V V C E (sat)C E (sat) :: 22--33VV..

Low current gain (). Need high base current to obtainreasonable I

C . (Current driven).(Current driven). Expensive and complexExpensive and complex

base drive circuit.base drive circuit.

Not popular in new productsNot popular in new products.



BJT ConductionBJT Conduction

sat ¡

sat ¡

¢

sat I

!

The level of IB in the active region just bef ore saturation

must be

At saturation, the current IC is quite high and the voltage

VCE ver y low. The resistance across the ter minals

deter mined by

d c

sat c£

I I

F"

max

Saturation conditions andSaturation conditions and

the resulting ter minal resistancethe resulting ter minal resistance

Cutoff conditions andCutoff conditions and

the resulting ter minal resistancethe resulting ter minal resistance



Metal Oxide SiliconMetal Oxide Silicon Field EffectField Effect Transistor (MOSFET)Transistor (MOSFET)

Ratings: VoltageVoltage V V DSDS

<500V, current<500V, current IIDSDS

<300A.<300A. (Voltage(Voltage

driven)driven)

Very fast device: >100KHz. For some low power devices (few

hundred watts) may go up to MHz range.



MOSFET characteristicsMOSFET characteristics Turning on and off is very simpleTurning on and off is very simple. Only need to provide V

GS

=+15V to turn on and 0V to turn off. Gate drive circuit isGate drive circuit issimple.simple.

Basically low voltage device. High voltage device areBasically low voltage device. High voltage device areavailable up to 600V but with limited currentavailable up to 600V but with limited current. Can beparalleled quite easily for higher current capability.

Internal (dynamic) resistance between drain and sourceresistance between drain and sourceduring on state,during on state, RR

DS(ON)DS(ON) , , limits the power handling capabilitylimits the power handling capability

of MOSFETof MOSFET. High losses especially for high voltage device dueto R

DS(ON) .

Dominant in high frequency applicationhigh frequency application (>100kHz). Biggestapplication is in switchedapplication is in switched--mode power suppliesmode power supplies.



Insulated GateInsulated Gate Bipolar TransistorBipolar Transistor (IGBT)(IGBT)

Combination of BJT and MOSFET characteristics.

Compromises include:

Gate behaviour similar to MOSFET - easy to turn on and off.

Low losses like BJT due to low on-state Collector-Emitter

voltage (2-3V).



Ratings: Voltage: VCE<3.3kV, Current,: IC<1.2kA currentlyavailable. Work in under progress for 4.5kV/1.2kA device.Constant improvement in voltage and current ratings.

Good switching capability (up to 100KHz) for newer devices.

Typical application, IGBT is used at 20-50KHz.

For very high power devices and applications, frequency islimited to several KHz.

Very popular in new products; practically replacing BJT inmost new applications.

Snubberless operation is possible. Most new IGBTs do notrequire snubbers.

Insulated GateInsulated Gate Bipolar TransistorBipolar Transistor (IGBT)(IGBT)



Gate turnGate turn--off off thyristorthyristor (GTO)(GTO)

Behave like normal thyristor, but can be turned off usingbut can be turned off using

gate signalgate signal

However turning off is difficultturning off is difficult. Need very large reverse

gate current (normally 1/5 of anode current)



Ratings: Voltage:Voltage: V V ak ak <5kV; Current:<5kV; Current: IIaa<5kA.<5kA. Highest power ratingsswitch. Frequency<5KHz.

Gate drive design is very difficultGate drive design is very difficult. Need very large reverse gatecurrent to turn off. Often custom-tailored to specific application.

Currently getting very stiff competition from high power IGBTCurrently getting very stiff competition from high power IGBT. Thelatter has much simpler and cheaper drivers.

GTO normally requires snubbers. High power snubbers areexpensive.

In very high power region (>5kV, >5kA), development in gate-controlled thyristor (GCT) may effectively end the future of GTO

Gate turnGate turn--off off th

yristorth

yristor (GTO)(GTO)



Switches comparisons (2000)Switches comparisons (2000)

Device Type Year made Rated Voltage Rated Current Switching Frequency Rated Power Drive Circuit Comments

SCR 1957 6kV 3.5kA 500Hz 100s MW Simple Cannot turn-off using gate signal

GTO 1962 4.5kV 3kA 2kHz 10s MW Ver y Difficult King in ver y high power

BJT 1960s 1.2kV 400A 5kHz 1 MW Difficult Phasing out in new product

MOSFET 1976 500V 200A 1MHz 100 kW Ver y Simple Good per f or mance in high f requency

IGBT 1983 3.3kV 1.2kA 100kHz 100s kW Ver y Simple Best overall per f or mance



Application examplesApplication examples

For each of the following application, choose the best powerswitches and reason out why.

1. An inverter for the light-rail train (LRT) locomotive operating from a DCsupply of 750 V. The locomotive is rated at 150 kW. The induction motor

is to run from standstill up to 200 Hz, with power switches frequenciesup to 10KHz.

2. A switch-mode power supply (SMPS) for remote telecommunicationequipment is to be developed. The input voltage is obtained from aphotovoltaic array that produces a maximum output voltage of 100 V

and a minimum current of 200 A. The switching frequency should behigher than 100kHz.

3. A HVDC transmission system transmitting power of 300 MW from oneac system to another ac system both operating at 50 Hz, 230 kV rmsline to line and the DC link voltage operating at 200 kV.



Q uestions?????

20304726 power electronics chapter 1

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