Transcript V d
Chapter 5
Diode Rectifiers
• Basic rectifier concepts
• Single-Phase diode bridge rectifiers
• Voltage-Doubler rectifiers
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-1
Diode Rectifier Block Diagram
• Uncontrolled utility interface (ac to dc)
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-2
A Simple Circuit (R Load)
• Resistive load
Copyright © 2008
by Jose Bastos
1
V
vR
V sin(x)dx
2 0
Chapter 5 Line-Frequency Diode
Rectifiers
5-3
A Simple Circuit (R-L Load)
• Current continues to flows for a while even after the input
voltage has gone negative
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-4
A Simple Circuit (R-L Load)
di
vL L
dt
1
vL dt di
L
1
0 L vL dt
i ( t 3)
t1
t3
t3
di i(t 3) i(0) 0
i (0)
1
1
0 L vL dt t1 L vL dt 0
Area A Area B 0
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-5
A Simple Circuit (Load has a dc back-emf)
• Current begins to flow when the input voltage exceeds the dc back-emf
• Current continues to flows for a while even after the input voltage has
gone below the dc back-emf
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-6
Single-Phase Diode Rectifier Bridge
• Large capacitor at the dc output for filtering and energy
storage
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-7
Diode-Rectifier Bridge Analysis
R load
I load
• Two simple (idealized) cases to begin with: (a) R load (b)
current load
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-8
Waveforms with a purely resistive load at the output
vd
Copyright © 2008
by Jose Bastos
1
V sin(x)dx
0
2V
2
2 VRMS 0.9 VRMS
Chapter 5 Line-Frequency Diode
Rectifiers
5-9
Diode-Rectifier Bridge Input Current
I s1
2
2 I d 0.9 I d
0 h even
I sh
I s1 / h h odd
THD=48.43%
DPF=1.0
PF=DPF x Is1/Is=0.9
• Idealized case with a purely dc output current
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-10
Diode-Rectifier Analysis with AC-Side
Inductance
• Output current is assumed to be purely dc
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-11
Understanding Current Commutation
• Assuming inductance to be zero
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-12
Understanding Current Commutation #2
• Assuming inductance to be zero
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-13
Understanding Current Commutation #3
• Assuming inductance to be zero
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-14
Understanding Current Commutation #4
• Inductance is included
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-15
Current Commutation Waveforms
vd
u
vL
Id
is
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-16
Current Commutation Waveforms
di
vL V sin(t ) L
dt
V sin(t ) d (t ) L di
Id
u
V sin(t ) d (t ) L di L I
0
d
0
u
Au V sin(t ) d (t ) V (1 cosu )
0
Au V (1 cosu ) L I d
cosu 1
Copyright © 2008
by Jose Bastos
L Id
V
Chapter 5 Line-Frequency Diode
Rectifiers
5-17
Average voltage <Vd>
When L=0
1
V 1
vd
V sin(t )d (t )
2 VRMS 0.45 VRMS
2 0
With finite L
u
1
1
vd
V sin(t )d (t )
V sin(t )d (t )
2 0
2 0
L
0.45 VRMS
Id
2
Reduction in average output voltage
L
vd
Id
2
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-18
Current Commutation in Full-Bridge Rectifier
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-19
Current Commutation in Full-Bridge Rectifier
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-20
Current Commutation Waveforms
di
vL V sin(t ) L
dt
V sin(t ) d (t ) L di
Id
u
V sin(t ) d (t ) L di 2 L I
0
d
Id
u
Au V sin(t ) d (t ) V (1 cosu )
0
Au V (1 cosu ) 2 L I d
2 L Id
cosu 1
V
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-21
Average voltage <Vd>
When L=0
vd
1
V sin(t )d (t )
0
2V
2
2 VRMS 0.9 VRMS
With finite L
vd
1
1
u
V sin(t )d (t ) V sin(t )d (t )
0
0
0.9 VRMS
2 L
Id
Reduction in average output voltage
vd
Copyright © 2008
by Jose Bastos
2 L
Id
Chapter 5 Line-Frequency Diode
Rectifiers
5-22
Conclusions
Average output voltage drops with
1. increased current
2. increased frequency
3. Increased L
Load Regulation is a major consideration in
most rectifier systems because
• voltage changes with load (IL)
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-23
Diode-Rectifier with a Capacitor Filter
• Power electronics load is represented by an equivalent load
resistance
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-24
Diode-Bridge Rectifier: Waveforms
• Analysis using PSpice
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by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-25
Voltage Doubler Rectifier
input
input
• In 115-V position, one capacitor at-a-time is charged from the
input.
Copyright © 2008
by Jose Bastos
Chapter 5 Line-Frequency Diode
Rectifiers
5-26