Power Electronics Unit V Ppt

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

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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

21dsin21

1

2

1o UttUU (4-1)

(4-2) RUIoo

(4-3) )22sin1(

21sin2

21 1

2

1

R

UtdR

tUIT

(4-4)

2sin21

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:

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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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

ω t

ω t

cosd0o Uu

tUu oomo sin

ttUU

ood0

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

UU

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04/27/23 11


• 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 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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Documents

Power Electronics Unit V Ppt