chapter5
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Power ElectronicsPower Electronics
Chapter 5 DC to AC Converters
( Inverters )
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Applications of InvertersApplications of Inverters
Conversion of electric power from DC type energy Conversion of electric power from DC type energy sources to AC type loadsources to AC type load–– BatteryBattery
–– Photovoltaic cell (Solar cell)Photovoltaic cell (Solar cell)
–– Fuel cellFuel cell
As a part of composite converterAs a part of composite converter–– ACAC--DCDC--AC frequency converter (for AC motor drive)AC frequency converter (for AC motor drive)
–– ACAC--DCDC--AC constantAC constant--voltage constantvoltage constant--frequency converter (for frequency converter (for uninterruptableuninterruptable power supplies)power supplies)
–– ACAC--DCDC--AC Converters for induction heatingAC Converters for induction heating
–– ACAC--DCDC--ACAC--DC switching power suppliesDC switching power supplies
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OutlineOutline5.1 Commutation5.1 Commutation
5.2 Voltage source inverters5.2 Voltage source inverters
5.3 Current source inverters5.3 Current source inverters
5.4 Multiple5.4 Multiple--inverter connections and multiinverter connections and multi--level inverterslevel inverters
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5.1 Commutation types5.1 Commutation types
A classification of invertersA classification of inverters–– SquareSquare--wave inverters (are discussed in this chapter)wave inverters (are discussed in this chapter)
–– PWM inverters ( will be discussed in Chapter 6)PWM inverters ( will be discussed in Chapter 6)
The concept of commutationThe concept of commutation
Basic operation principle of invertersBasic operation principle of inverters
LoadS
1
S2
S3
S4
io
uo
Ud
t
uo
iot1 t2
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4 types of commutation4 types of commutation
Device commutation: Device commutation: FullyFully--controlled devices: GTO, IGBT, MOSFETcontrolled devices: GTO, IGBT, MOSFET
Line commutationLine commutationPhasePhase--controlled rectifiercontrolled rectifierPhasePhase--controlled AC controllercontrolled AC controllerThyristorThyristor cycloconvertercycloconverter
Load commutationLoad commutation
Forced commutationForced commutation
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Load commutationLoad commutation
Condition: Load current is leading load voltageCondition: Load current is leading load voltageApplication: capacitive load, synchronous motorApplication: capacitive load, synchronous motor
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Forced commutation Forced commutation (capacitance commutation)(capacitance commutation)
DirectDirect--CoupledCoupled With CouplingWith Coupling--InductorInductor
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Another classification of commutationsAnother classification of commutations
SelfSelf--commutationcommutation
Device commutation
Forced commutation
Line commutation
Load commutation
4 types of Commutations4 types of Commutations
External External commutationcommutation
For fully-controlled devices
For thyristors
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2 classes of inverters2 classes of inverters
Voltage Source Inverter(VSI)
Current Source Inverter(CSI)
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5.2 Voltage source inverter (VSI)5.2 Voltage source inverter (VSI)
DC side is constant voltage, low impedance (voltage DC side is constant voltage, low impedance (voltage source, or bulk cap)source, or bulk cap)
AC side voltage is square wave or quasiAC side voltage is square wave or quasi--square wave. square wave. AC side current is determined by the load.AC side current is determined by the load.
AntiAnti--parallel diodes are necessary to provide energy parallel diodes are necessary to provide energy feedback path.feedback path.(freewheeling diodes , feedback diodes)(freewheeling diodes , feedback diodes)
+
-
C R LUd
V1
V2
V3
V4
VD 1
VD 2
VD3
VD4
uo
io
FeaturesFeatures
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SingleSingle--phase half bridge VSIphase half bridge VSI
The current conducting path is determined by the The current conducting path is determined by the polarity of load voltage and load current. (This is true polarity of load voltage and load current. (This is true for analysis of many power electronics circuits.)for analysis of many power electronics circuits.)
The magnitude of output squareThe magnitude of output square--wave voltage is Uwave voltage is Udd/2./2.
-
R LUd
io
uo
V1
V2
VD1
VD2
Ud2
Ud2
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SingleSingle--phase full bridge VSIphase full bridge VSIOperation principleOperation principle
+
-
CR L
Ud
V1
V2
V3
V4
VD1
VD2
VD3
VD 4
uo
io
The magnitude of output squareThe magnitude of output square--wave voltage is wave voltage is UUdd..
The effective value of output voltage (or fundamental The effective value of output voltage (or fundamental output voltage) can be changed by changing output voltage) can be changed by changing UUdd..
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Fourier series extension of output voltageFourier series extension of output voltage
Magnitude of output voltage fundamental component Magnitude of output voltage fundamental component
Effective value of output voltage fundamental component Effective value of output voltage fundamental component
SingleSingle--phase full bridge VSIphase full bridge VSIQuantitative analysisQuantitative analysis
⎟⎠⎞
⎜⎝⎛ +++= tttUu ωωω
π5sin
513sin
31sin4 d
o
dd
o1m 27.14 UUU ==π
dd
1o 9.022 UUU ==π
(5(5--1)1)
(5(5--2)2)
(5(5--3)3)
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SingleSingle--phase full bridge VSIphase full bridge VSIOutput voltage control by phaseOutput voltage control by phase--shiftshift
tO
tO
tO
tO
tO
θ
uG1
uG2
uG3
uG4
uoio
t1 t2
t3io
uo
+
-
C R LUd
V1
V2
V3
V4
VD1
VD2
VD 3
VD 4
uo
io
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Inverter with centerInverter with center--tapped transformertapped transformer——pushpush--pull inverterpull inverter
Load
+
-
io uo
UdV1 V2
VD1VD2
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ThreeThree--phase VSIphase VSI
180180oo conductionconduction
Dead time (blanking time) to Dead time (blanking time) to avoid avoid ““shoot throughshoot through””
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ThreeThree--phase VSIphase VSIBasic equations to obtain voltage waveformsBasic equations to obtain voltage waveforms
For line voltage For phase voltage of the load
0=++ WNVNUN UUU
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ThreeThree--phase VSIphase VSI
Fourier series extension of output lineFourier series extension of output line--toto--line voltageline voltage
Magnitude of output voltage (lineMagnitude of output voltage (line--toto--line) fundamental component line) fundamental component
Effective value of output voltage (lineEffective value of output voltage (line--toto--line) fundamental line) fundamental componentcomponent
Quantitative analysisQuantitative analysis
⎥⎦
⎤⎢⎣
⎡−+=
⎟⎠⎞
⎜⎝⎛ −++−−=
∑n
k tnn
tU
tttttUu
ωωπ
ωωωωωπ
sin)1(1sin32
13sin13111sin
1117sin
715sin
51sin32
d
dUV
dd
UV1m 1.132 UUU ==π
ddUV1m
UV1 78.062
UUUU ===π
(5(5--8)8)
(5(5--10)10)
(5(5--11)11)
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5.3 Current source inverter (CSI)5.3 Current source inverter (CSI)
DC side is constant current, high impedance(current source, or largeinductor)
AC side current is quasi-square wave. AC side voltage is determined by the load.
No anti-parallel diodes are needed. sometimes series diodes are needed to block reverse voltage for other power semiconductor devices.
FeaturesFeatures
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SingleSingle--phase bridge CSIphase bridge CSIParallel Resonant Inverter Parallel Resonant Inverter
A
C
R L
Ld
Id VT1
VT2
VT3
VT4
LT1
LT2
LT3
LT4
uo
io
Switching frequency is a little higher Switching frequency is a little higher than the resonant frequency so that the than the resonant frequency so that the load becomes capacitive and load load becomes capacitive and load current is leading voltage to realize current is leading voltage to realize load commutation.load commutation.
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ThreeThree--phase selfphase self--commutated CSIcommutated CSI
120120oo conductionconduction
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ThreeThree--phase forcephase force--commutated CSIcommutated CSI
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ThreeThree--phase loadphase load--commutated CSIcommutated CSI
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5.4 5.4 MultipleMultiple--inverter connections inverter connections and multiand multi--level inverterslevel inverters
Series connection of 2 singleSeries connection of 2 single--phase phase VSIsVSIs
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Series connection of 2 3Series connection of 2 3--phase phase VSIsVSIs
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MultiMulti--level Inverterslevel Inverters33--level inverterlevel inverter
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