UNIT III AC voltage controller and cycloconverter.
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Transcript of UNIT III 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 ≤α ≤ π
04/20/23 2
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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
2sin
2
1dsin2
11
2
1o UttUU (4-1)
(4-2) R
UIoo
(4-3) )2
2sin1(
2
1sin2
2
1 1
2
1
R
Utd
R
tUIT
(4-4)
2sin2
1
1
o
o1
oo
U
U
IU
IU
S
P
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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:
φ ≤α ≤ π
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4.2 Other AC controllers
4.2.1 Integral cycle control—AC 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
M
Line period
Control period
= M *Line period
= 2
4
M O
Conduction
angle
=
2 N M
3
M
2
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
π Output
voltage
ap=0
Average
output voltage
ap= 2
π
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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
bl ocki ng P
N
Rectifi
cation
Inver
sion
bl ocki ng Rectifi
cation
Inver
sion
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• Modulation methods for firing delay angle
Calculation method
– For the rectifier circuit
ω t
ω t
cosd0o Uu
tUu oomo sin
ttU
Uoo
d0
om sinsincos
)sin(cos o1 t
( 4 - 1 5 )
– F o r t h e c y c l o c o n v e r t e r
o u t p u t
( 4 - 1 6 )
– E q u a t i n g ( 4 - 1 5 ) a n d ( 4 - 1 6 )
– t h e r e f o r e
( 4 - 1 7 )
( 4 - 1 8 )
P r i n c i p l e o f c o s i n e
w a v e - c r o s s i n g m e t h o d
u 2 u 3 u 4 u 5 u 6 u 1
a p 3 a p 4
u o
u s 2 u s 3 u s 4 u s 5 u s 6 u s 1
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O u t p u t v o l t a g e r a t i o
( M o d u l a t i o n f a c t o r )
)10(0
d
om
U
U
2
2 t 3
2
0
3 0
6 0
9 0
1 2 0
1 5 0
Ou t p u t v o l t a g e p h a s e a n g l e
/ ( º ) γ
γ
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4.3.2 Three- phase thyristor-cyclo converter
• The configuration with common input line
4-24图04/20/23 11
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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 characteristicsThe 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 conversion—high efficiency –Bidirectional energy flow, easy to realize 4- quadrant operation –Very complicated—too 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
i nput
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 conversion—high efficiency can realize good input and output waveforms, low harmonics, and nearly unity displacement factor
Bidirectional energy flow, easy to realize 4- quadrant operationOutput frequency is not limited by input frequencyNo need for bulk capacitor (as compared to indirect frequency converter)Very complicated—too many power semiconductor devicesOutput voltage magnitude is a little lower as compared to indirect
frequency converter.
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