POWER ELECTRONICSPOWER ELECTRONICS
INTRODUCTION TO INTRODUCTION TO POWER ELECTRONICSPOWER ELECTRONICS
Dr. Adel GastliEmail: [email protected]
http://adel.gastli.net
Dr. Adel Gastli Power Electronics: Introduction 2
CONTENTSCONTENTSCONTENTS1. Definitions and History2. Applications of Power Electronics3. Power Semiconductor Devices4. Control characteristics of power devices5. Characteristics & specifications of switches6. Design of power electronics equipment7. Rms values of waveforms8. Types of power electronic circuits9. Peripheral effects10. Power modules11. Intelligent modules12. Journals & References
Dr. Adel Gastli Power Electronics: Introduction 3
DEFINITION & HISTORYDEFINITION & HISTORY
Power electronics refers to control and conversion of electrical power by power semiconductor devices wherein these devices operate as switches.
Advent of Silicon-Controlled Rectifiers, abbreviated as SCRs, led to the development of a new area of application called the Power Electronics.
Dr. Adel Gastli Power Electronics: Introduction 4
Prior to the introduction of SCRs, mercury-arc rectifiers (1900) were used for controlling electrical power, but such rectifier circuits were part of industrial electronics and the scope for applications of mercury-arc rectifiers was limited.
Once the SCRs were available (1957), the application area spread to many fields such as drives, power supplies, aviation electronics, high frequency inverters and power electronics originated.
Dr. Adel Gastli Power Electronics: Introduction 5
APPLICATIONS OF POWER APPLICATIONS OF POWER ELECTRONICSELECTRONICS
Power electronics has applications that span the whole field of electrical power systems, with the power range of these applications extending from a few VA/Watts to several MVA/MW.
The main task of power electronics is to control and convert electrical power from one form to another form.
Dr. Adel Gastli Power Electronics: Introduction 6
Power electronics is a subject of interdisciplinary nature.
Electronics Devices|Circuits
Power Equipment
Static|Rotating
ControlAnalog|Digital
Power
Electronics
Dr. Adel Gastli Power Electronics: Introduction 7
Some Applications of Power Electronics
AdvertingAir conditioningAircraft power suppliesAlarmsHousehold AppliancesBattery chargerChemical processingComputersCranes, hoists, elevatorsDimmersDisplaysElectric door openersElectric dryers, fans
Electric vehicles & tractionElectromagnetsGas turbine startingGenerator excitersHigh voltage dc (HVDC)Motor drivesMovie projectorOil well drillingPaper millsPhotograph, photocopy machinesTV, Radio, VCRSolar power supplies, etc…
Dr. Adel Gastli Power Electronics: Introduction 8
POWER SEMICONDUCTOR DEVICES
Since the first thyristor (SCR) was developed in late 1957, there has been tremendous advances in the power semiconductor devices.
Since 1970 various types of power semiconductor devices were developed and became commercially available.
Dr. Adel Gastli Power Electronics: Introduction 9
Dr. Adel Gastli Power Electronics: Introduction 10
Power semiconductor devices are made of either silicon or silicon carbide.
These devices can be divided broadly into three main types:
Power diodes
Thyristors
Transistors
Dr. Adel Gastli Power Electronics: Introduction 11
Classification of power semiconductors
Dr. Adel Gastli Power Electronics: Introduction 12
Power DiodesPower Diodes
General purposeRating up to 6000V, 4500A
High speed (or fast recovery)Rating up to 6000V, 1100A
Reverse recovery time 0.1 to 5μs
Essential for high-frequency switching
Dr. Adel Gastli Power Electronics: Introduction 13
Power Diodes (cont.)
SchottkyLow on-state voltage
Very small recover time (typically nanoseconds).
Leakage current increases with voltage rating
Rating limited to 100V, 300A
Dr. Adel Gastli Power Electronics: Introduction 14
Power Diodes (cont.)
Conducts when its anode voltage is higher then that of the cathode (VA > VC)
Forward voltage drop (when on) is very low (typically 0.5 and 1.2V)
If VC > VA the diode is said to be in blocking mode.
Anode Cathode
2 terminals
Dr. Adel Gastli Power Electronics: Introduction 15
Stud-mounted type
Disk, press pak, or hokey puck type
Dr. Adel Gastli Power Electronics: Introduction 16
ThyristorsThyristors
When a small current is passed through the gate terminal to cathode, the thyristor conducts provided that the anode terminal is at higher potential than that of the cathode:
iG >0VA > VC
3 terminals
Anode CathodeGate
Dr. Adel Gastli Power Electronics: Introduction 17
Thyristors (Cont.)
Once a Thyristor is in a conduction mode, the gate circuit has no control and the thyristor continues to conduct.In conduction mode, forward voltage is very small (0.5 to 2 V).Thyristor can be turned off by making VAC ≤ 0V
Line-commutated thyristors are turned off due to the sinusoidal nature of their input voltageForced-commutated thyristors are turned off by an extra circuit called commutation circuitry.
Dr. Adel Gastli Power Electronics: Introduction 18
Thyristors (Cont.)
Natural or line-commutated thyristors are available with rating up to 6000 V, 4500A.
Turn-off-time became very small (10 to 20 μs in 3000 V, 3600A).
Instant when the principle current has decreased to zero after external switching of the principle voltage circuit
Instant when thyristor is capable of supporting a specified voltage without turning on.
ti=0 tVAC≠0Turn-off-time
Dr. Adel Gastli Power Electronics: Introduction 19
Thyristors (Cont.)
Can be subdivided into 11 types:1. Forced-commutated
2. Line-commutated
3. Gate-Turn-Off (GTO)
4. Reverse Conducting Thyristor (RCT)
5. Static Induction Thyristor (SITH)
6. Gate-Assisted turn off Thyristor (GATT)
7. Light-activated Silicon-Controlled Rectifier (LASCR)
8. MOS Turn-Off (MTO)
9. Emitter Turn-Off (ETO)
10. Integrated Gate-Commutated Thyristor (IGCT)
11.MOS Controlled Thyristors (MCTs)
Dr. Adel Gastli Power Electronics: Introduction 20
SelfSelf--Study Study (Outcome i: a(Outcome i: a recognition of the need for, and recognition of the need for, and
an ability to engage in lifean ability to engage in life--long learning)long learning)
Page 8: main characteristics and applications of different types of thyristors.
Dr. Adel Gastli Power Electronics: Introduction 21
Power TransistorsPower TransistorsThere are 4 types:
Bipolar Junction Transistors (BJTs)
Power MOSFETS
Insulated-Gate Bipolar Transistors (IGBTs)
Static Induction Transistors (SITs)
Dr. Adel Gastli Power Electronics: Introduction 22
Power Transistors (Cont.)Power Transistors (Cont.)Bipolar Junction Transistors (BJTs)
Used in power converters at frequency below 10 kHz
Power ratings up to 1200V, 400A.
VBE> 0, IB >ITH conduction (on) mode
VBE< 0, IB <ITH nonconduction (off) mode
C
E
B
IE
ICIB
IB1
IBn IBn> IB1
IB2
VCE
IC
0saturation
Operates like a switch (on-off)
NPN-BJT
Dr. Adel Gastli Power Electronics: Introduction 23
Power Transistors (Cont.)Power Transistors (Cont.)Power MOSFETs
Used in high-speed power converters at frequency range of several tens of kHz.
Power ratings up to 1000V, 100A (relatively low power ratings).
D
S
G
ID
VGSn
VGS1> VGSn
VDS
ID
0
N-channel VGS0
Dr. Adel Gastli Power Electronics: Introduction 24
Power Transistors (Cont.)Power Transistors (Cont.)IGBTs
Voltage controlled power transistors (better drive circuit) faster than BJTs but slower than MOSFETs.
Used in power converters at frequency up to 20 kHz
Power ratings up to 1700V, 2400A (high voltage high current).
C
E
G
IE
ICVGE1
VGEn VGEn> VGE1
VCE
IC
0
VT
Dr. Adel Gastli Power Electronics: Introduction 25
Power Transistors (Cont.)Power Transistors (Cont.)SITs
Used in high-power high frequency applications (audio, VHF/UHF, and microwave amplifiers)
Power ratings up to 1200V, 300A.
Has low-noise, low-distortion, high-audio-frequency power capability.
Very short turn-on and turn-off times (typically 0.25μs)
On-characteristic and high on-state drop limit its applications for general power conversions.
D
S
G
IS
ID
VGSn
VGSn> VGS1
VDS
ID
0
VGS1=0V
Dr. Adel Gastli Power Electronics: Introduction 26
Power ranges of commercially available power semiconductor devices
100 200 500 1000 2400 4000 6000 10000 I [A]
100
200
1000
550060007500
12000
1000 V/100A(SanRex)
60 V/1000A(Semikron)
IGCT (Market)
SCR (Market)
IGBT (Market) GTO (Market)
6500V/600A(Eupec)
12000V/1500A(Mitsubishi)
7500V/1650A(Eupec) 6500V/2650A
(ABB)
5500V/2300A(ABB)
6000V/6000A GTO(Mitsubishi)
6000V/6000A IGCT(Mitsubishi announced)
4800V/5000A(Westcode)
4500V/4000A(Mitsubishi)
V [V]
Power MOSFET (Market)
Dr. Adel Gastli Power Electronics: Introduction 27
Dr. Adel Gastli Power Electronics: Introduction 28
CONTROL CHARACTERISTICS OF POWER DEVICES
+Input
voltage Vs
_
Gate signal vG
R
+Output voltage
v0_
Thyristorv0
Vs
vG
0
-1
1Thyristor switch
First pulse turns it on and stays always on
Dr. Adel Gastli Power Electronics: Introduction 29
+Input
voltage Vs
_
+vG
_
R
+Output voltage
v0_
GTO
v0Vs
vG
0
-1
1
GTO/MTO/ETO/IGCT/MCT/SITH switch
Positive pulse turns them on and negative pulse turns them off
KA
KA
SITH
KAG
MCT
t1 T t
Polarity of vG
is reversed for MCT
Dr. Adel Gastli Power Electronics: Introduction 30
+Input
voltage Vs
_
R
+Output voltage
v0_
v0Vs
vB/vGS
0
1
BJT/MOSFET/IGBT switch
Positive voltage turns them on and zero voltage turns them off
vB +
t1 T t
t1 T t
+Input
voltage Vs
_
R
+Output voltage
v0_
vGS +
C E
G
D S
Dr. Adel Gastli Power Electronics: Introduction 31
Classification1. Uncontrolled turn on and turn off (e.g. diode)
2. Controlled turn on and uncontrolled turn off (e.g. SCR)
3. Controlled turn on and off (e.g. BJT, MOSFET, IGBT, GTO, SITH, SIT, MCT)
4. Continuous gate signal requirement (e.g. BJT, MOSFET, IGBT, SIT)
5. Pulse gate requirement (e.g. SCR, GTO,MCT)
6. Bipolar voltage-withstanding capability (e.g. SCR, GTO)
7. Unipolar voltage-withstanding capability (e.g. BJT, MOSFET,GTO, IGBT, MCT)
8. Bidirectional current capability (e.g. TRIAC, RCT)
9. Unidirectional current capability (e.g. SCR, GTO, BJT, MOSFET, MCT,IGBT, SITH, SIT, Diode)
(See Table 1.4 page 15 of the textbook)
Dr. Adel Gastli Power Electronics: Introduction 32
CHARACTERISTICS & SPECIFICATIONS OF SWITCHES
On state: carry high forward current, IF= ∞Low forward voltage drop, VON=0low on-state resistance, RON=0
Off state:High forward or reverse voltage, VBR =∞Low off-state leak current, IOFF=0High off-state resistance, ROFF=∞(low off-state power losses)
Requires very low thermal impedance from internal junction to ambient, RJA=0, so that it transmits heat easily to the ambient Must have high i2t, to sustain any fault current for a long time.
Turn-on & turn-off processes:Controllable
• Must turn on with gate signal (e.g. positive)
• Must turn off with another gate signal (e.g. zero or negative)
Instantaneous (high frequency)• Low delay time, td=0• Low rise time, tr=0• Low storage time, ts=0• Low fall time, tf=0
Low gate-drive power, PG=0Low gate-drive voltage, VG=0Low gate-drive current, IG=0
Device must be capable of handling rapid voltage changes across it, dv/dt= ∞Device must be capable of handling rapid current changes across it, di/dt= ∞
Ideal SwitchIdeal Switch
Dr. Adel Gastli Power Electronics: Introduction 33
Practical DevicesPractical Devices VCC
vSW
iSW
iG
vG
PSW
VSW(sat)
ISWs
ISW0
IG(sat)
VG(sat)
Ts=1/fs
ton toff
td tr tn ts tf t0
t
t
t
t
t
+VSW
_+_
VG
IG
iSW
RL
VCC
Controlled switch
Switching power losses
GSWOND
ttt
sSW
t
sON
PPPP
pdtpdtpdtfP
pdtT
P
fsr
ON
++=
⎟⎠⎞⎜
⎝⎛ ++=
=
∫∫∫
∫
000
0
1
Conduction Switching Gate-driver power losses power losses power
Dr. Adel Gastli Power Electronics: Introduction 34
Switch SpecificationsSwitch SpecificationsVoltage ratings
Forward & reverse repetitive peak voltagesOn-state forward drop-voltage drop
Current ratingsAverage, rms, repetitive peak, nonrepetitive peak, off-state leakage
Switching speed or frequency
di/dtdv/dtSwitching lossesGate drive requirementsSafe operating area (SOA): limits on the allowable steady-state operating points in the v-icoordinatesI2t for fusingTemperaturesThermal resistance
Dr. Adel Gastli Power Electronics: Introduction 35
Device ChoicesDevice Choices
Non of the existing switching devices is ideal.
For high power applications from the ac 50-60Hz main supply, phase control and bidirectional thyristors are the most economical choices.
COOLMOS and IGBTs are potential replacements for MOSFETS and BJTs, respectively, in low and medium power applications.
Dr. Adel Gastli Power Electronics: Introduction 36
Device Choices (cont.)Device Choices (cont.)
GTOs and IGCTs are most suited for high-power applications requiring forced commutation.
With the increased advances in technology, IGBTs are increasingly employed in high-power applications and MCTs may find potential applications that require bidirectional blocking voltages.
Dr. Adel Gastli Power Electronics: Introduction 37
DESIGN OF POWER ELECTRONICS EQUIPMENT
1. Design of power circuits
2. Protection of power devices
3. Determination of control strategy
4. Design of logic and gating circuits
Dr. Adel Gastli Power Electronics: Introduction 38
In this course, power devices are assumed ideal switches unless stated otherwise.Effect of stray inductance, circuit resistances, and source inductance are usually neglected.Before prototype is built, the designer should investigate the effects of the circuit parameters and device imperfections. The design should be modified if necessary.Only after the prototype is built and tested, the designer can be confident about the validity of the design proposed and can estimate more accurately some circuit parameters (e.g. stray inductance).
Dr. Adel Gastli Power Electronics: Introduction 39
RMS VALUES OF WAVEFORMS
rms values of current waveforms must be known:
To accurately determine losses in a device
To accurately determine current ratings of the device and components
Current waveforms are rarely sinusoids or rectangles
Dr. Adel Gastli Power Electronics: Introduction 40
∫=T
rms dtiT
I0
21
Time period
If a waveform can be broken into harmonics whose rms values can be calculated individually, the rms value of the actual waveform can be approximated satisfactory as:
2)(
2)2(
2)1(
2nrmsrmsrmsdcrms IIIII +++= L
Harmonics rms valuesdc component
See page 25 (Fig. 1.17) for some rms values of commonly encountered waveforms
Dr. Adel Gastli Power Electronics: Introduction 41
Problems Solving:Problems Solving:
Find the average and rms values of the following waveforms.
vo100V
t8ms 20ms
0 π 2π
vo100V
ωt
0 π 2π
vo100V
ωt
0 π/2 π 2π
vo100V
ωt
Dr. Adel Gastli Power Electronics: Introduction 42
TYPES OF POWER ELECTRONIC CIRCUITS
Diode rectifiers
Ac-dc converters (controlled rectifiers)
Ac-ac converters (ac voltage controllers)
Dc-dc converters (dc choppers)
Dc-ac converters (inverters)
Static switches (ac or dc)
Dr. Adel Gastli Power Electronics: Introduction 43
Diode rectifiersConverts ac into a fixed dc voltage.
Input could be either single phase or three phase
tVv ms ωsin=
0 π 2π
Vm
vs
ωt
0 π 2π
voVm
ωt
Diode D1
+
_
Diode D2
+
_viac supply
Load resistance R
vs
vo+ –
tVv ms ωsin=
Find the expressions of average and rms values.
Dr. Adel Gastli Power Electronics: Introduction 44
Ac-dc convertersConverts ac into a variable dc voltage.
Input could be either single phase or three phase
vo
Thyristor T1
+
_
Thyristor T2
+
_viac supply
Load resistance R
vs
vo+ –
tVv ms ωsin=
tVv ms ωsin=
0 π 2π
Vm
vs
ωt
-Vm
α
0 π 2π
Vm
ωtα
Find the expressions of average and rms values as a function of α.
Dr. Adel Gastli Power Electronics: Introduction 45
Ac-ac convertersConverts fixed ac into a variable ac voltage.
Input could be either single phase or three phase
tVv ms ωsin=
0 π 2π
Vm
vs
ωt
-Vmac supply
Triac
Load resistance R
+
–
votVv ms ωsin=
0 π 2π
voVm
ωtα
α
Find the expressions of average and rms values as a function of α.
Dr. Adel Gastli Power Electronics: Introduction 46
Dc-dc converters (Choppers)
Converts fixed dc into a variable dc voltage.
dc supply
0 t1 Τ
vo
1vs
Vs
ωt
ωt
Load
+
–
vo
+
vs
–
TransistorQ1
+ _VGE
V0=δVs
T
t1=δ Duty cycle
Dr. Adel Gastli Power Electronics: Introduction 47
Dc-ac converters (Inverters)
Converts fixed dc into a variable ac voltage.
Output can be single phase or three phase
dc supply
0 T/2 T
vo
1vg1, vg2
vs
ωt
ωt
Load
+
vo
+
vs
–
+vg1 vg3
M1 M3
M4 M2
+ __ _
G
G G
G ωtvg3, vg4
-vs
Dr. Adel Gastli Power Electronics: Introduction 48
Static switches
Power electronic devices can operate as static switches or contactors to transmit either ac or dc power to loads.
Mains 2
Rectifier/charger Inverter Isolation transformer
Static bypassswitch
Mains 1Load
Battery
Example: Uninterruptible Power Supply (UPS)
ac supply
Dr. Adel Gastli Power Electronics: Introduction 49
PERIPHERIAL EFFECTS(Effects of Power Converters)
ProblemsProblems: Introduce current and voltage harmonics into the supply system and on converters output.
Distortion of the output voltage.
Harmonic generation into supply system
Interference with communication and signaling circuits
Dr. Adel Gastli Power Electronics: Introduction 50
SolutionsSolutions: It is normally necessary to introduce filters in the input and output of a converter system to reduce the harmonic level to an acceptable magnitude.
Input filter
Output filter
Power converter
Switching control signal
generator
PowerSource
Output
Dr. Adel Gastli Power Electronics: Introduction 51
Power quality issuesPower quality issues
Application of power electronics poses a challenge on the power quality issues and raises problems and concerns to be resolved by researchers.Important factors that measure the quality of a waveform are:
Total harmonic distortion (THD)Displacement Factor (DF)Input power factor (IPF)
Harmonic content of the waveforms is required to find these factors.
Dr. Adel Gastli Power Electronics: Introduction 52
To evaluate the performance of a converter, the input and output voltages and currents of a converter are expressed in a Fourier seriesFourier series.
The control strategycontrol strategy of a power converter play an important part on the harmonic generation and output waveform distortion, and can be aimed to minimize or reduce these problems.
Electromagnetic radiation and interference can be avoided by grounded shielding.
Dr. Adel Gastli Power Electronics: Introduction 53
POWER MODULES
Power devices are available as a single unit or a module.
A power converter often requires two, four, or six devices, depending on its topology.
Power modules with dual (in half-bridge configuration), or quad (in full bridge) or six (in three phase) are available for almost all types of power devices.
Dr. Adel Gastli Power Electronics: Introduction 54
Modules offer the advantages of
lower on-state losses,
high voltage and current switching characteristics,
high speed (switching frequency)
Some modules include transient protection and gate drive circuitry.
Gate drive circuits are commercially available to drive individual devices or modules.
Dr. Adel Gastli Power Electronics: Introduction 55
INTELLIGENT MODULES
Intelligent modules, which are the state of the art of power electronics, integrate the power module and the peripheral circuit.Peripheral circuits consists of:
Input or output isolation from, and interface with, the signal and high-voltage system, A drive circuitProtection and diagnostic circuitMicrocomputer controlControl power supply
Dr. Adel Gastli Power Electronics: Introduction 56
Users need only to connect external (floating) power supplies.
An intelligent module is also known as smart power.
Smart power technology can be viewed as a box that interfaces power source to any load.
These modules are used increasingly in power electronics.
Page 28: list of websites of some manufacturers of these modules
Dr. Adel Gastli Power Electronics: Introduction 57
JOURNAL & REFERENCES
See section 1.11 in your textbook at page 28.
Search the internet for more recent sites (keywords: power electronics, tutorials, circuits, devices,…)