Transcript V d
Chapter 6
Thyristor Converters
• Thyristor circuits and their control
• Line-frequency phase-controlled rectifiers and inverters
• line-frequency ac <-> controlled dc
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-1
Thyristor Converters
• Two-quadrant conversion
• positive Vd implies rectification
• negative Vd implies inverter mode
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-2
Primitive circuits with thyristors (1)
R load
• The current is zero until t=
• The current and voltage vd are in phase
• Average voltage of load R controlled by adjusting
vd
Copyright © 2008
by Jose Bastos
1
V
V sin x dx
(1 cos)
2
2
Chapter 6 Thyristor Converters
6-3
Primitive circuits with thyristors (2)
R L load
v
R
• The current is zero until t=
• The current lags voltage vd
• At Instant 2 current becomes zero
di
vL L
vd v R
dt
t
1
vd () vR ()d
i (t )
L
1
i ( 2 )
L
Copyright © 2008
by Jose Bastos
1
1
v
(
)
v
(
)
d
R
d
L
2
v
d
() vR ()d 0
1
Chapter 6 Thyristor Converters
6-4
Primitive circuits with thyristors (3)
L Load with dc voltage
di
v L L vd E d
dt
i(t )
t
v
d
( ) Ed d
2
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by Jose Bastos
Chapter 6 Thyristor Converters
6-5
Thyristor Gate Triggering
Delay angle is
vcontrol
180
Vˆst
o
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by Jose Bastos
Chapter 6 Thyristor Converters
6-6
Full-Bridge Thyristor Converters (1)
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by Jose Bastos
Chapter 6 Thyristor Converters
6-7
Full-Bridge Thyristor Converters (2)
• constant dc current load
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-8
Thyristor Converter Waveforms (1)
0
• Assuming zero ac-side inductance
• at t=0 thyristors 1,2 are triggered
•At t= thyristors 3,4 are triggered
vd
Copyright © 2008
by Jose Bastos
1
V sin(t )d (t )
0
2V
2 2
VRMS 0.9VRMS
Chapter 6 Thyristor Converters
6-9
Thyristor Converter Waveforms (2)
0
vd
1
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by Jose Bastos
V sin(t )d (t )
2V
cos
2 2
VRMS cos 0.9VRMS cos
Chapter 6 Thyristor Converters
6-10
Thyristor Converter Waveforms (3)
• The drop in the average value due to is
vd vd vd 0.9 VRMS (1 cos )
• The average power in the converter is
T
1
P vd id dt
T 0
T
1
I d vd dt I d vd 0.9 I d VRMS cos
T 0
• Average power becomes negative when > 90º ; this is inverter mode
of operation
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-11
Inverter mode
• 90º < < 180º
• average vd is a negative value
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-12
Average DC Output Voltage
• Assuming zero ac-side inductance
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-13
Input Line-Current Waveform
• input line current is harmonics
is (t ) I s1 (sin t ) I s 3 (sin 3t ) I s 5 (sin 5t ) K
with
I s1
2
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by Jose Bastos
2 I d 0.9 I d
I sh
I s1
h
Chapter 6 Thyristor Converters
6-14
THD, Power Factor, Power
• THD
I s2 I s21
THD 100
48.31%
I s1
• Power
P Vs _ RMS I s1_ RMS cos 0.9 Vs _ RMS I d cos
• Power Factor PF
PF
Copyright © 2008
by Jose Bastos
I
I
P
s1 DPF s1 cos 0.9 cos
Vs _ RMS I s _ RMS I s
Is
Chapter 6 Thyristor Converters
6-15
Effect of Ls
• Finite ac-side inductance; constant dc output
current
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by Jose Bastos
Chapter 6 Thyristor Converters
6-16
Finite ac-side inductance (1)
• finite comutation interval u
• during u all thyristors conduct (vd=0)
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-17
Finite ac-side inductance (2)
dis
dt
to find u, integrateover thecomutationinterval:
vd 0 v s v L L
Id
u
V sin(t ) d (t ) L di
s
2 L Id
Id
u
Au
V sin(t ) d (t ) 2 L I
d
Au V cos( ) cos( u ) 2 L I d
2 L Id
V
vd can be obtainedby
cos( u ) cos( )
u
1
vd V sin (t ) d (t ) V sin(t ) d (t )
2 L Id
2V
cos
2 2 VRMS cos 2 L I d
2
0.9 VRMS cos L I d
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-18
Input line current is
• Is has a trapezoidal waveform
• DPF is
DPF cos1 cos( u / 2)
• The RMS value of fundamental frequency is
Vs RMS I s1 RMS DPF vd I d
I s1 RMS
Copyright © 2008
by Jose Bastos
0.9 Vs RMS I d cos 2 / L I d2
Vs RMS cos( u / 2)
Chapter 6 Thyristor Converters
6-19
Practical Thyristor Converter
• waveform for =45º
• average value of vd
Copyright © 2008
by Jose Bastos
vd 0.9 Vs RMS cos
Chapter 6 Thyristor Converters
2
L I d ,min
6-20
Thyristor Converter Waveforms:
Discontinuous Conduction Mode
• PSpice-based simulation
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by Jose Bastos
Chapter 6 Thyristor Converters
6-21
DC Voltage versus Load Current
• at constant , if Id falls below a certain value, Vd
increases sharply
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-22
Inverter mode
• 90º < < 180º
• average vd is a negative value
• on dc side average power <vd>Id is negative
• on ac side average power VS RMS Is1 RMS cos 1 is negative
Copyright © 2008
by Jose Bastos
Chapter 6 Thyristor Converters
6-23