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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 Power Definition of Power ElectronicsElectronics
• Multidisciplinary Nature of Multidisciplinary Nature of the Fieldthe Field
• Block Diagrams of Power Block Diagrams of Power Electronic SystemsElectronic Systems
• The Need for Power The 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 orMechanical
Output "Loads"
x1
x2
xm
y1
y2
yn
f1 f2 fk
PowerProcessing
circuit(P loss )
(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 currents in 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 Power Detailed Block Diagram of Power Electronics System Electronics System
Filter&
RectifyPE Circuit Load
Filter&
Rectify
ControlCircuit
Mechanical VariableFeedback
Electrical VariableFeedback
Input
Form ofelectrical
energy
ElectricalMechanical
Pre-stage Power proc. stage Post stageOutput
Form of elec. ormechan. energy
Switc
hD
rives
Process feedbacksignals and decide
on control
Could generateundesirablewaveforms
Mostly ac linevoltage (singleor three phase)
Mostlyunregulate
d dcvoltage
Interface betweencontrol and power
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)
Wind-electric systems.Wind-electric systems.
Conversion concept: exampleConversion concept: example11
• Supply from TNB: 50Hz, 240V RMS (340V peak). Customer need DC voltage for welding purpose, say.
• TNB sine-wave supply gives zero DC component!
• Average output voltage
• We can use simple half-wave rectifier. A fixed DC voltage is now obtained. This is a simple PE system.
1 Power Electonics, PM Dr Zainal Salam, 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 controlling the firing angle, α, the output DC voltage (after conversion) can be varied.
1 Power Electonics, PM Dr Zainal Salam, UTM
Average output Voltage
Advantages of Power ElectronicsAdvantages of Power 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, unlimited
range 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 (coal
burning) etc. Creates global warming (green house effect), acid raill and urban pollution h-oll)
• Quite operationQuite operation– has no moving parts, suitable for residential, hotels etc
• reduce dependence on fossil fuel (coal, natural gas, oil) and nuclear power resource reduce 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 electric vehicle.
PE growthPE 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– – – Solid-state physics and devicesSolid-state 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 to AC: INVERTERDC to AC: INVERTER
AC to AC: CYCLOCONVERTERAC to AC: CYCLOCONVERTER
Power semiconductor devicesPower semiconductor devices(Power switches)(Power switches)
• Can be categorised into three groups:
– Uncontrolled: Diode
– Semi-controlled: Thyristor (SCR)
– Fully controlled: Power transistors e.g. BJT,MOSFET, IGBT, GTO, IGCT
Photos of Power Switches Photos of Power Switches (From Powerex Inc.)(From Powerex Inc.)
Power Electronics ConvertersPower Electronics Converters
AC to DC: RECTIFIERAC to DC: RECTIFIER
DC to DC: CHOPPERDC to DC: CHOPPER
DC to AC: INVERTERDC to AC: 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 in power electronic circuits is based on their ability to control and manipulate very large amounts of power from the input to the output with relatively very low power dissipation in the switching device.
• Implication of low efficiency:1. The cost of energy increasescost of energy increases due to increased
consumption.2. Additional design complications might be imposed,
especially regarding the design of device heat sinks design of device heat sinks
ExampleExampleInvestigate the efficiency of four different power electronic circuits whose function is to take power from a 24 V dc source 24 V dc source and deliver a 12 V dc output to a 6and deliver a 12 V dc output to a 6 resistive load resistive load. In other words, the task of these circuits is to serve as dc transformers with a ratio of 2 : 1. The four circuits are shown in Fig. 1 (a), (b), (c), and (d) representing a voltage divider circuit, zener regulator voltage divider circuit, zener regulator ((assume Iassume IZ Z is 10% of load current)is 10% of load current), transistor linear regulator, and , transistor linear regulator, and switching circuit, respectivelyswitching circuit, respectively. [Hint: For circuit (d), Vo=Vin*D]
(e) Zener diode i-v switching characteristics. (f) Switching waveforms for circuit
Example (Cont)Example (Cont)
Example (Cont)Example (Cont)• Cicuit (a) : Voltage Divider dc RegulatorCicuit (a) : Voltage Divider dc Regulator• Since Vin=24V and RL=6 and desired Vo=12V.
Hence, R = RR = RLL=6=6.
Thus,
%50%66
6%
%%
RR
R
P
P
P
P
L
L
in
L
in
out
• Cicuit (b) : Zener dc RegulatorCicuit (b) : Zener dc Regulator
• Since desired Vo=12V, hence the blocking voltage for zener diode, VZ
= 12V.
Since, RL=6. Thus IL=2A.
Assume that, IAssume that, IZZ = 0.2A = 0.2A
(10% of load current)(10% of load current)
Thus, %5.45%
8.52
24%
24122
8.52242.2
2.2
2.02
in
out
out
in
zLT
P
P
WP
WP
A
III
Example (Cont)Example (Cont)• Cicuit (c) : Transistor dc RegulatorCicuit (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 and RL=6, thus IILL=2A=2A.
Thus, IIC C = 2A= 2A since IB too small in such that to turn on transistor.
%50%48
24%
24212
48)24(2
in
out
CCE
BBECCEdiss
cinin
P
P
WIV
IVIVP
WIVP
Example (Cont)Example (Cont)
• Cicuit (d) : Switching dc RegulatorCicuit (d) : Switching dc Regulator
Assume the switch is ideal and periodically turn on and off. From figure (f), Vo is given by
%100%48
48%,
),(
48242,24
in
outinout
inLinin
P
PPP
idealassumeswitchingtoDue
WVIPVVSince
DT
inins
aveo
s
DVdtVT
V0
,
1
• For Vo,ave=12V, hence D=0.5D=0.5 (VVo,aveo,ave=24 x 0.5 =12V=24 x 0.5 =12V)
Ideal Switching CharacteristicsIdeal Switching Characteristics 1. 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 state5. No limit on the operating speed of the device when it
changes state, i.e., zero rise and fall times
Ideal Switching CharacteristicsIdeal Switching Characteristics
Power lossPower loss
The Practical SwitchThe Practical Switch • The practical switch has the following switching and conduction
characteristics:1.1. Limited power-handling capabilitiesLimited power-handling capabilities2.2. Limited switching speedLimited switching speed3.3. The existence of forward voltage drop in the on state, and reverse The existence of forward voltage drop in the on state, and reverse
current flow (leakage) in the off statecurrent flow (leakage) in the off state4. Because of characteristics 2 and 3, the practical switch experiences switch experiences
power losses in the on and off states (known as conduction loss) and power losses in the on and off states (known as conduction loss) and during switching transitions (known as switching loss)during switching transitions (known as switching loss)
Power DiodesPower Diodes
• When diode is forward biased, it conducts current with a small forward voltage (Vf) across it (0.2-3V)
• When reversed (or blocking state), a negligibly small leakage current (uA to mA) flows until the reverse breakdown occurs. Diode should not be operated at reverse voltage greater than Vr. Thus, higher voltage blocking is needed.Thus, higher voltage blocking is needed.
Power Diode (Reverse Recovery)Power Diode (Reverse Recovery)
• When a diode is switched quickly from forward to reverse bias, it continues to conductit continues to conduct due to the minority carriers which remains in the p-n junction.
• The minority carriers require finite time, i.e, trr (reverse recovery time) to recombine with opposite charge and neutralize.
• Effects of reverse recovery are increase in switching losses, increase in voltage rating, over-voltage (spikes) in inductive loads
Power Diode (Reverse Recovery)Power Diode (Reverse Recovery)
Types of Power DiodesTypes of Power Diodes
• Line frequency (general purpose) :Line frequency (general purpose) :• on state voltage very low
(below 1V)• large trr (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• very low trr (<1us).• Power levels at several
hundred volts and several hundred amps
• Normally used in high frequency circuits
• SchottkySchottky• very low forward 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 three pn junctionsthree pn junctions (four layers of pnpnfour layers of pnpn) that can be latched into the on state through an external can be latched into the on state through an external gate signalgate signal that causes a regeneration mechanism in the device.
• Thyristor family currently used in power electronic circuits: – The silicon-controlled rectifier (SCR), The silicon-controlled rectifier (SCR), – gate turn-off thyristor (GTO), gate turn-off thyristor (GTO), – triode ac switch (triac), triode ac switch (triac), – static induction transistor (SIT), static induction transistor (SIT), – static induction thyristor (SITH), static induction thyristor (SITH), – and MOS-controlled thyristor (NICT).and MOS-controlled thyristor (NICT).
Thyristor (SCR)Thyristor (SCR)
• Unlike the diode, the SCR Unlike the diode, the SCR has a third terminal called the "gate" used "gate" used for control purposes.for control purposes.
• The holding currentholding current is the minimum forward currentminimum forward current the SCR can carry in 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 the causes the SCR to turn on without the application 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:
– – the device is in forward blocking state (i.e the device is in forward blocking state (i.e VVakak is positive)is positive) – – a positive gate current (a positive gate current (IIgg) is applied at the gate) is applied at the gate
• Once conducting, the anode current is LATCHED (continuously flowing).
• In reverse - biased mode, the SCR behaves like a diodereverse - biased mode, the SCR behaves like a diode.. It conducts a small leakage current which is almost dependent of the voltage, but increases with temperature.
• When the peak reverse voltage is exceeded, avalanche breakdown occursavalanche breakdown occurs, and
the large current will flow.
• In the forward biased mode, with no gate current present (i.e. in the untriggered state), the device exhibits a leakage current.
• If the forward breakover voltage (VBO) is exceeded, the SCR “self-triggers” into the 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 forward breakover voltage.
Thyristor ConductionThyristor Conduction
How to turn off thyristor ?
Thyristor ConductionThyristor Conduction• Thyristor cannot be turned off by applying negative gate negative gate
currentcurrent. It can only be turned off if IA goes negative (reverse)– This happens when negative portion of the of sine-This happens when negative portion of the of sine-wave occurswave occurs (natural commutation).
• Another method of turning off is known as “forced commutation”,– The anode current is “diverted” to another circuitry.The anode current is “diverted” to another circuitry.
Controllable switches (power transistors)Controllable switches (power transistors)• Can be turned “ON”and “OFF” by relatively very small control signals.
• 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.
• Traditional devices: Bipolar junction transistors (BJT), Metal oxide silicon field Bipolar junction transistors (BJT), Metal oxide silicon field effect transistor ( MOSFET), Insulated gate bipolar transistors (IGBT), Gate effect transistor ( MOSFET), Insulated gate bipolar transistors (IGBT), Gate turn-off thyristors (GTO)turn-off thyristors (GTO)
• Emerging (new) devices: Gate controlled thyristors (GCT).
Bipolar Junction Transistor (BJT)Bipolar Junction Transistor (BJT)
• Ratings: Voltage: VVCECE<1000, Current: <1000, Current: IICC<400A. Switching <400A. Switching frequency up to 5kHz. Low on-state voltage: frequency up to 5kHz. Low on-state voltage: VVCE(sat)CE(sat) : 2-3V.: 2-3V.
• Low current gain (β). Need high base current to obtain reasonable IC . (Current driven).(Current driven). Expensive and complex Expensive and complex base drive circuit.base drive circuit.
• Not popular in new productsNot popular in new products.
BJT ConductionBJT Conduction
satC
satCEsat I
VR
• The level of IB in the active region just before saturation must be
• At saturation, the current IC is quite high and the voltage VCE very low. The resistance across the terminals determined by
dc
satcB
II
max
Saturation conditions and Saturation conditions and the resulting terminal resistancethe resulting terminal resistance
Cutoff conditions and Cutoff conditions and the resulting terminal resistancethe resulting terminal resistance
Metal Oxide Silicon Field Effect Transistor (MOSFET)Metal Oxide Silicon Field Effect Transistor (MOSFET)
• Ratings: Voltage Voltage VVDSDS<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 VGS
=+15V to turn on and 0V to turn off. Gate drive circuit is Gate drive circuit is simple.simple.
• Basically low voltage device. High voltage device are Basically low voltage device. High voltage device are available up to 600V but with limited currentavailable up to 600V but with limited current. Can be paralleled quite easily for higher current capability.
• Internal (dynamic) resistance between drain and source resistance between drain and source during on state, during on state, RRDS(ON)DS(ON), , limits the power handling capability limits the power handling capability of MOSFETof MOSFET. High losses especially for high voltage device due to RDS(ON) .
• Dominant in high frequency applicationhigh frequency application (>100kHz). Biggest application is in switched-mode power suppliesapplication is in switched-mode power supplies.
Insulated Gate Bipolar Transistor (IGBT)Insulated Gate Bipolar Transistor (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 currently available. 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 is limited to several KHz.
• Very popular in new products; practically replacing BJT in most new applications.
• “Snubberless” operation is possible. Most new IGBTs do not require snubbers.
Insulated Gate Bipolar Transistor (IGBT)Insulated Gate Bipolar Transistor (IGBT)
Gate turn-off thyristor (GTO)Gate turn-off thyristor (GTO)
• Behave like normal thyristor, but can be turned off using but 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: VVakak<5kV; Current: <5kV; Current: IIaa<5kA.<5kA. Highest power ratings switch. Frequency<5KHz.
• Gate drive design is very difficultGate drive design is very difficult. Need very large reverse gate current 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. The latter has much simpler and cheaper drivers.
• GTO normally requires snubbers. High power snubbers are expensive.
• In very high power region (>5kV, >5kA), development in gate-controlled thyristor (GCT) may effectively end the future of GTO
Gate turn-off thyristor (GTO)Gate turn-off thyristor (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 Very Difficult King in very high power
BJT 1960s 1.2kV 400A 5kHz 1 MW Difficult Phasing out in new product
MOSFET 1976 500V 200A 1MHz 100 kW Very SimpleGood performance in high frequency
IGBT 1983 3.3kV 1.2kA 100kHz 100s kW Very Simple Best overall performance
Application examplesApplication examples• For each of the following application, choose the best
power switches and reason out why.
1. An inverter for the light-rail train (LRT) locomotive operating from a DC supply 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 frequencies up to 10KHz.
2. A switch-mode power supply (SMPS) for remote telecommunication equipment is to be developed. The input voltage is obtained from a photovoltaic array that produces a maximum output voltage of 100 V and a minimum current of 200 A. The switching frequency should be higher than 100kHz.
3. A HVDC transmission system transmitting power of 300 MW from one ac system to another ac system both operating at 50 Hz, 230 kV rms line to line and the DC link voltage operating at 200 kV.
Questions?????
