UNIT V AC voltage controller and
cycloconverter
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4.1.1 Single-phase AC voltage controller
R u 1 u o
i o VT 1
VT 2
u
O
u 1
u o
i o
VT
t
O t
O t
O t
The phase shift range (operation range of phase delay angle):
0
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Resistive load, quantitative analysis
RMS value of output voltage
RMS value of output current
RMS value of thyristor current
Power factor of the circuit
( ) ( )pi
pi
pi
pi
pi
+== 2sin21dsin21 1
2
1o UttUU (4-1)
(4-2) RUI oo =
(4-3) ( ) )2
2sin1(21sin2
21 1
2
1
pi
pi
pi
pi
+=
= R
Utd
RtUIT
(4-4) pi
pi
pi +==== 2sin
21
1
o
o1
oo
UU
IUIU
SP
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Inductive (Inductor- resistor) load , operation principle
R
L
u 1 u o
i o
VT 1
VT 2
O
u 1
u o
i o
u VT
O
O
t
O
u G1
u G2
O
O
t
t
t
t
t
The phase shift range:
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4.2 Other AC controllers
4.2.1 Integral cycle controlAC power controller
Circuit topologies are the same as AC voltage controllers. Only the control method is different. Load voltage and current are both sinusoidal when thyristors are conducting.
R u 1 u o
i o VT
1
VT 2
pi M
Line period
Control period
= M *Line period
= 2 pi
4
pi
M
O
Conduction angle =
2
pi N M
3
pi M
2
pi
M
u o
u
1 u o , i o
t
U 1 2
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4.3 Thyristor cycloconverters
4.3.1 Single- phase thyristor-cycloconverter Circuit configuration and operation principle
P N
Z
t
uo ap= 2 Output
voltage
ap=0 Average
output voltage
ap= 2
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Single- phase thyristor-cycloconverter Modes of operation
t
t
t
t
t
O
O
O
O
O
u o
, i o
u o
i o
t 1
t 2
t 3
t 4 t 5
u o u P
u N
u o
i P
i N
u P u N u o
i o i N i P
blocking
P
N
Rectifi
cation
Inver
sion
blocking Rectifi cation
Inver
sion
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Typical waveforms
1
O
O
2
3 4 5
6
u o
i o
t
t
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Modulation methods for firing delay angle Calculation method For the rectifier circuit
t
t
cosd0o Uu =
tUu oomo sin=
ttUU
oo
d0
om sinsincos ==
)sin(cos o1 t =
(4-15) For the cycloconverter
output
(4-16) Equating (4- 15) and (4-16)
therefore (4-17)
(4-18)
Principle of cosine
wave-crossing method
u2 u3 u4 u5 u6 u1
ap3 ap4
uo
us2 us3 us4 us5 us6 us1
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Output voltage ratio
(Modulation factor)
)10(0
= d
om
UU
pi 2
2 pi pi t 3 pi 2
0 30
60 90
120
150
Output voltage phase angle
/ ( ) =0 =0.1 0.2
0.3 0.8 0.9 1.0
0.1 0.2 0.3
0.8 0.9 1.0
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4.3.2 Three- phase thyristor-cyclo converter
The configuration with common input line
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The configuration with star-connected output
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Typical waveforms
200
t
/
ms
Output voltage
Input current with Single-phase output
Input current with 3-phase output
200
t
/
ms
200
t
/
ms
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Input and output characteristics The maximum output frequency and the harmonics in the output voltage
are the same as in single-phase circuit. Input power factor is a little higher than single-phase circuit. Harmonics in the input current is a little lower thanthe single- phase circuit due to the cancellation of some harmonics among the 3 phases.
To improve the input power factor: Use DC bias or 3k order component bias on each of the 3 output
phase voltages Features and applications Features: Direct frequency conversionhigh efficiency Bidirectional energy flow, easy to realize 4- quadrant operation Very complicatedtoo many power semiconductor devices Low output frequency Low input power factor and bad input current waveform Applications: High power low speed AC motor drive
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4.4 Matrix converter
Circuit configuration input
output
a) b)
a b c
u
v
w
S
1
1
S
1
2
S
1
3
S
2
1
S
2
2
S
2
3
S 3 1
S 3 2
S 3 3
S ij
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Usable input voltage
a) b) c) a) Single-phase input
voltage
b) Use 3 phase voltages to construct output
voltage
c) Use 3 line-line voltages to construct output
voltage
Um U1m Um 1 2
3 2 U1m
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Features
Direct frequency conversionhigh efficiency can realize good input and output waveforms, low harmonics, and nearly unity displacement factor
Bidirectional energy flow, easy to realize 4- quadrant operation Output frequency is not limited by input frequency No need for bulk capacitor (as compared to indirect frequency converter) Very complicatedtoo many power semiconductor devices Output voltage magnitude is a little lower as compared to indirect
frequency converter.
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