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Chapter 6 AC to AC Converters( AC Controllers and Frequency Converters )

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Power Electronics Power Electronics

Chapter 6 AC to AC Converters

( AC Controllers and

Frequency Converters )

(2)

Classification of AC to AC converters Classification of AC to AC converters

Same frequency Same frequency variable magnitude variable magnitude

AC power

AC power AC powerAC power

Variable Variable frequency frequency AC power AC power

AC controllers Frequency converters (Cycloconverters)

AC to AC converters

P ow e r E le ct ro ni cs

(3)

P ow e r E le ct ro ni cs

Classification of AC controllers Classification of AC controllers

AC controller AC controller

Phase control:

Phase control: AC voltage controllerAC voltage controller (Delay angle control)

(Delay angle control) Integral cycle control:

Integral cycle control: AC power controllerAC power controller

PWM control:

PWM control: AC chopperAC chopper (Chopping control)

(Chopping control) On/off switch:

On/off switch: electronic AC switchelectronic AC switch PWM: Pulse Width Modulation

PWM: Pulse Width Modulation

(4)

Classification of frequency converters Classification of frequency converters

Frequency converter Frequency converter

(Cycloconverter) (Cycloconverter)

Phase control:

Phase control: thyristor cycloconverterthyristor cycloconverter (Delay angle control)

(Delay angle control) PWM control:

PWM control: matrix convertermatrix converter (Chopping control)

(Chopping control)

P ow e r E le ct ro ni cs

Cycloconverter is sometimes referred to Cycloconverter is sometimes referred to

in a broader sensein a broader sense—any ordinary AC to AC converter—any ordinary AC to AC converter in a narrower sense—thyristor cycloconverterin a narrower sense—thyristor cycloconverter

(5)

P ow e r E le ct ro ni cs

Outline Outline

6.1 AC voltage controllers 6.1 AC voltage controllers

6.2 Other AC controllers 6.2 Other AC controllers

6.3 Thyristor cycloconverters 6.3 Thyristor cycloconverters

6.4 Matrix converters 6.4 Matrix converters

(6)

P ow e r E le ct ro ni cs

6.1 AC voltage controllers 6.1 AC voltage controllers

6.1.1 Single-phase AC voltage controller 6.1.1 Single-phase AC voltage controller 6.1.2 Three-phase AC voltage controller 6.1.2 Three-phase AC voltage controller

Applications Applications

Lighting control Lighting control

Soft-start of asynchronous motors Soft-start of asynchronous motors

Adjustable speed drive of asynchronous motors Adjustable speed drive of asynchronous motors

Reactive power control Reactive power control

(7)

6.1.1 Single-phase AC voltage controller 6.1.1 Single-phase AC voltage controller

The phase shift range The phase shift range

(operation range of phase (operation range of phase delay angle):

delay angle):

Resistive load Resistive load

P ow e r E le ct ro ni cs

u1 uo R

io

VT1

VT2

O u1

uo

io

uVT

t

O t

O t

O t

(8)

P ow e r E le ct ro ni cs

RMS value of output voltageRMS value of output voltage RMS value of output current RMS value of output current

RMS value of thyristor current RMS value of thyristor current

Power factor of the circuit Power factor of the circuit

Resistive load, quantitative analysis Resistive load, quantitative analysis

 

1

2 1 sin 2 d 1 21 sin2

o U t t U

U

R Io Uo

 

)

2 2 1 sin

2( sin 1

2 2

1 1 2 1

U R t d t UR IT

 

sin2 2

1

1 o o

1 o o

U U I

U I U S

P

(6-1) (6-1)

(6-2) (6-2)

(6-3) (6-3)

(6-4) (6-4)

(9)

P ow e r E le ct ro ni cs

Inductive (Inductor-resistor) load, Inductive (Inductor-resistor) load, operation principle

operation principle

The phase shift The phase shift

range:

range:



   

u

1

u

o

R

i

o

VT

1

VT

2

(10)

P ow e r E le ct ro ni cs

Differential equationDifferential equation Solution

Solution

Considering

Considering iioo=0 when =0 when tt==++



We have We have

Inductive load, quantitative analysis Inductive load, quantitative analysis

The RMS value of output voltage, output current, and thyristor The RMS value of output voltage, output current, and thyristor current can then be calculated.

current can then be calculated.

0

sin d 2

d

o

1 o

o



i t

t U

t Ri L i

(6-5) (6-5)

0 20 60 100 140 180

20 100

4-3 60

/(°)

180

140

 / (° )

(6-6) (6-6)

) sin( ) tg

sin(

e (6-7)(6-7)

2 1

[sin( ) sin( ) ]

t

o U tg

i t e

Z t

 

   

   

 

 

(11)

P ow e r E le ct ro ni cs

Inductive load, when

Inductive load, when   < <  

The circuit can still work.

The circuit can still work.

The load current will be co The load current will be co ntinuous just like the thyrist ntinuous just like the thyrist ors are short-circuit, and th ors are short-circuit, and th e thyristors can no longer c e thyristors can no longer c ontrol the magnitude of out ontrol the magnitude of out

put voltage.

put voltage.

The start-up transient will b The start-up transient will b e the same as the transient e the same as the transient

when a RL load is connect when a RL load is connect

ed to an AC source at

ed to an AC source at t t ==



 < < 

 t

 t

 t

 t

4-5

  

  O O O O u 1

iG1

iG2

io iT1

iT2

Start-up transient Start-up transient

(12)

Harmonic analysis Harmonic analysis

There is no DC component There is no DC component

and even order harmonics in and even order harmonics in

the current.

the current.

The current waveform is half-The current waveform is half- wave symmetric.

wave symmetric.

The higher the number of The higher the number of

harmonic ordinate, the lower harmonic ordinate, the lower

the harmonic content.

the harmonic content.

is when harmonics is is when harmonics is the most severe.

the most severe.

The situation for the inductive The situation for the inductive

load is similar to that for the load is similar to that for the

resistive load except that the resistive load except that the

corresponding harmonic corresponding harmonic

content is lower and is even content is lower and is even

lower as

lower as is increasing. is increasing.

P ow e r E le ct ro ni cs

Current harmonics Current harmonics for the resistive load for the resistive load

0 60 120 180

Fundamental

3 5 7

/ ( °) In/I* /%

20 40 60 80 100

(13)

P ow e r E le ct ro ni cs

6.1.2 Three-phase AC voltage controller 6.1.2 Three-phase AC voltage controller

Classification of three-phase circuits Classification of three-phase circuits

Y connection

Y connection Line-controlled Line-controlled ∆ connection∆ connection

Branch-controlled

Branch-controlled ∆ connection∆ connection Neutral-point-controlled ∆ connectionNeutral-point-controlled ∆ connection

(14)

P ow e r E le ct ro ni cs

3-phase 3-wire Y connection 3-phase 3-wire Y connection AC voltage controller

AC voltage controller

For a time instant, there are 2 possible conduction states:

For a time instant, there are 2 possible conduction states:

Each phase has a thyristor conducting. Load voltages are the saEach phase has a thyristor conducting. Load voltages are the sa me as the source voltages.

me as the source voltages.

There are only 2 thyristors conducting, each from a phase. The lThere are only 2 thyristors conducting, each from a phase. The l oad voltages of the two conducting phases are half of the corresp oad voltages of the two conducting phases are half of the corresp onding line to line voltage, while the load voltage of the other pha onding line to line voltage, while the load voltage of the other pha se is 0.

se is 0.

n n '

a

b

c u

u aa

uu

b b

uu

cc

iiaa Ua0'

VT5 VT3

VT6 VT4

VT2 VT1

(15)

P ow e r E le ct ro ni cs

3-phase 3-wire Y connection 3-phase 3-wire Y connection AC voltage controller

AC voltage controller

Resistive load, 0

Resistive load, 0  < 60< 60

4 

3 2 

3

5  3

3

0 2 

u ao'

u a u ab

2 u ac

2

t1 t

2 t

3

VT 1

VT3 VT 6

VT4 VT 6

VT 2 VT 5

VT 5

VT1

(16)

P ow e r E le ct ro ni cs

3-phase 3-wire Y connection 3-phase 3-wire Y connection AC voltage controller

AC voltage controller

Resistive load, 60

Resistive load, 60  < 90< 90

4  3 2 

3

5  3

3

0 2 

u ao'

u a

u ab

2 u

ac

2

t1 t

2 t

3

VT 5 VT

1 VT

3

VT 4 VT

VT 6

VT 2 6

VT 5

(17)

P ow e r E le ct ro ni cs

3-phase 3-wire Y connection 3-phase 3-wire Y connection AC voltage controller

AC voltage controller

Resistive load, 90

Resistive load, 90  < 150< 150

4  3 2 

3

5  3

3

0 2 

uao'

ua

u ab

2

uac

2

VT 5 VT

1 VT

3

VT 4 VT VT 6

VT 2 6

VT 5

VT 5 VT

1 VT

3 VT

5

VT 4

VT 2

VT 4VT

6

(18)

P ow e r E le ct ro ni cs

6.2 Other AC controllers 6.2 Other AC controllers

6.2.1 Integral cycle control

6.2.1 Integral cycle control—AC power controller—AC power controller

6.2.2 Electronic AC switch 6.2.2 Electronic AC switch

6.2.3 Chopping control

6.2.3 Chopping control—AC chopper—AC chopper

(19)

P ow e r E le ct ro ni cs

6.2.1 Integral cycle control 6.2.1 Integral cycle control —AC power controller —AC power controller

Circuit topologies are the same as AC voltage contr Circuit topologies are the same as AC voltage contr

ollers. Only the control method is different.

ollers. Only the control method is different.

Load voltage and current are both sinusoidal when t Load voltage and current are both sinusoidal when t

M

Line period Line period

Control period=M *Line period=2

4M O

Conduction Conduction angle

angle =2N

M

3M 2M

uo

u1 uo,io

t U1

2

u

1

u

o

R i

o

VT1

VT2

(20)

P ow e r E le ct ro ni cs

Spectrum of the current in Spectrum of the current in

AC power controller AC power controller

There is NO There is NO

harmonics in the harmonics in the ordinary sense.

ordinary sense.

There is harmonics There is harmonics

as to the control as to the control

frequency. As to the frequency. As to the line frequency, these line frequency, these components become components become fractional harmonics.

fractional harmonics.

Harmonic order as to control frequency

Harmonic order as to line frequency

0 1 2 3 4 5

0 2 4 6 8 1012 14 0.6

0.5 0.4 0.3 0.2 0.1 I n/I 0m

(21)

P ow e r E le ct ro ni cs

6.2.2 Electronic AC switch 6.2.2 Electronic AC switch

Circuit topologies are the same as AC voltag Circuit topologies are the same as AC voltag

e controllers. But the back-to-back thyristors e controllers. But the back-to-back thyristors

are just used like a switch to turn the equipm are just used like a switch to turn the equipm

ent on or off.

ent on or off.

(22)

P ow e r E le ct ro ni cs

6.2.3 Chopping control

6.2.3 Chopping control —AC chopper —AC chopper

Principle of chopping control Principle of chopping control

The mean output voltage over The mean output voltage over one switching cycle is

one switching cycle is

proportional to the duty cycle in proportional to the duty cycle in that period. This is also called that period. This is also called Pulse Width Modulation

Pulse Width Modulation (PWM)

(PWM)..

Advantages Advantages

Much better output waveforms, Much better output waveforms, much lower harmonics

much lower harmonics For resistive load, the For resistive load, the

displacement factor is always displacement factor is always 1.1.

Waveforms when the load Waveforms when the load

is pure resistor is pure resistor

(23)

P ow e r E le ct ro ni cs

AC chopper AC chopper

Modes of operation Modes of operation

   >0, >0, iioo>0: V>0: V11 charging, V charging, V33 freewheeling freewheeling    >0, >0, iioo<0: V<0: V44 charging, V charging, V22 freewheeling freewheeling    <0, <0, ii >0: V>0: V charging, V charging, V freewheeling freewheeling u

uo

uo

(24)

P ow e r E le ct ro ni cs

6.3 Thyristor cycloconverters 6.3 Thyristor cycloconverters

(Thyristor AC to AC frequency converter) (Thyristor AC to AC frequency converter)

Another name—direct frequency converter (as com Another name—direct frequency converter (as com pared to AC-DC-AC frequency converter which is di pared to AC-DC-AC frequency converter which is di

scussed in Chapter 8) scussed in Chapter 8)

Can be classified into single-phase and three-phase Can be classified into single-phase and three-phase

according to the number of phases at output according to the number of phases at output

6.3.1 Single-phase thyristor-cycloconverter 6.3.1 Single-phase thyristor-cycloconverter 6.3.2 Three-phase thyristor-cycloconverter 6.3.2 Three-phase thyristor-cycloconverter

(25)

P ow e r E le ct ro ni cs

6.3.1 Single-phase thyristor-cycloconverter 6.3.1 Single-phase thyristor-cycloconverter

Circuit configuration and operation principle Circuit configuration and operation principle

Z

P N

uo

O

uo P= 2 P=0 P= 2

t

Output v oltage

Average output voltage

(26)

P ow e r E le ct ro ni cs

Single-phase thyristor-cycloconverter Single-phase thyristor-cycloconverter

Modes of operation Modes of operation

t t t t t

O O O O O uo,io uo

io

t1 t2 t3 t4 t5 uo

uP

uN

uo iP

iN

Rectifi Rectifi cation cation InverInver

sion sion

Blocking Blocking PP

N N

Inver Inver sionsion

Blocking Blocking

Rectifi Rectifi cation cation

u P u o u N

io

iN iP

(27)

P ow e r E le ct ro ni cs

Single-phase thyristor-cycloconverter Single-phase thyristor-cycloconverter

Typical waveforms Typical waveforms

1 O

O

2

3 4

5

6 u o

io

 t

 t

(28)

P ow e r E le ct ro ni cs

Calculation methodCalculation method

For the rectifier circuitFor the rectifier circuit

For the cycloconverter outputFor the cycloconverter output

Equating (6-15) and (6-16)Equating (6-15) and (6-16)

ThereforeTherefore

Cosine wave-crossing met Cosine wave-crossing met hodhod

Modulation methods for firing delay angle Modulation methods for firing delay angle

Principle of cosine wave-crossing method

4-21

u2 u 3 u 4 u 5 u6 u 1

us2 u s3 u s4 u s5 u s6 u s1

u o

P3 P4

 t

 t

d0 cos

o U

u

t U

uo om sino

t U t

U

o o

d0

om sin sin

cos

) sin (

cos 1 ot

(6-(6- 15)15)

(6-(6- 16)16)

(6-(6- 17)17) (6-(6- 18)18)

(29)

P ow e r E le ct ro ni cs

Calculated results for firing delay angle Calculated results for firing delay angle

Output voltage ratio Output voltage ratio

(Modulation factor) (Modulation factor)

) 1 0

(

d0

om

r

U

U  = 0  = 0.1

/(°)

Output voltage phase angle

0 t 120

150 180

30 60 90

0

0.1 0.2 0.3 0.8 0.9 1.0

0.8 0.2 0.3 0.91.0

2

2

32

(30)

P ow e r E le ct ro ni cs

Input and output characteristics Input and output characteristics

Maximum output Maximum output

frequency: 1/3 or 1/2 of the frequency: 1/3 or 1/2 of the

input frequency if using 6- input frequency if using 6-

pulse rectifiers pulse rectifiers

Input power factor Input power factor

Harmonics in the output Harmonics in the output

voltage and input current voltage and input current

are very complicated, and are very complicated, and

both related to input both related to input

frequency and output frequency and output

frequency.

frequency.

0.8 0.6 0.4 0.2 0

=1.0 Input displacement factor Input displacement factor

Load power factor Load power factor

(lagging) (lagging) Load power factor

Load power factor (leading

(leading))

0 0.8 1.0 0.6 0.4 0.2 0

0.8 0.6 0.4 0.2

0.60.8 0.4 0.2

(31)

P ow e r E le ct ro ni cs

6.3.2 Three-phase thyristor-cycloconverter 6.3.2 Three-phase thyristor-cycloconverter

The configuration with common input line The configuration with common input line

(32)

P ow e r E le ct ro ni cs

Three-phase thyristor-cycloconverter Three-phase thyristor-cycloconverter

The configuration with star-connected output The configuration with star-connected output

(33)

P ow e r E le ct ro ni cs

Three-phase thyristor-cycloconverter Three-phase thyristor-cycloconverter

Typical waveforms Typical waveforms

200 t/ms

Output voltage Output voltage

Input current with Input current with 3-phase output 3-phase output

200 t/ms

200 t/ms

Input current with Input current with Single-phase output Single-phase output

0

0

0

(34)

P ow e r E le ct ro ni cs

Input and output characteristics Input and output characteristics

The maximum output frequency and the harmonics The maximum output frequency and the harmonics

in the output voltage are the same as in single- in the output voltage are the same as in single-

phase circuit.

phase circuit.

Input power factor is a little higher than single- Input power factor is a little higher than single-

phase circuit.

phase circuit.

Harmonics in the input current is a little lower than Harmonics in the input current is a little lower than

the single-phase circuit due to the cancellation of the single-phase circuit due to the cancellation of

some harmonics among the 3 phases.

some harmonics among the 3 phases.

To improve the input power factor:

To improve the input power factor:

Use DC bias or 3k order component bias on each of the 3 Use DC bias or 3k order component bias on each of the 3 output phase voltages

output phase voltages

(35)

P ow e r E le ct ro ni cs

Features and applications Features and applications

Features Features

Direct frequency conversion—high efficiencyDirect frequency conversion—high efficiency

Bidirectional energy flow, easy to realize 4-quadrant Bidirectional energy flow, easy to realize 4-quadrant operation

operation

Very complicated—too many power semiconductor devicesVery complicated—too many power semiconductor devices Low output frequencyLow output frequency

Low input power factor and bad input current waveformLow input power factor and bad input current waveform

Applications Applications

High power low speed AC motor driveHigh power low speed AC motor drive

(36)

P ow e r E le ct ro ni cs

6.4 Matrix converter 6.4 Matrix converter

Circuit configuration Circuit configuration

a) b)

Input Input

Output Output

a b c

u v w S11 S12 S13

S21 S22 S23 S31 S32 S33

Sij

(37)

P ow e r E le ct ro ni cs

Matrix converter Matrix converter

Usable input voltage Usable input voltage

a ) b ) c )

U m

U 1 m

U 1 m

2 3

U m

12

a) Single-phase input a) voltage

b) Use 3 phase voltages b) to construct output voltag

e

c) Use 3 line-line voltages c) to construct output voltag

e

(38)

P ow e r E le ct ro ni cs

Features Features

Direct frequency conversion—high efficiency Direct frequency conversion—high efficiency

Can realize good input and output waveforms, low Can realize good input and output waveforms, low

harmonics, and nearly unity displacement factor harmonics, and nearly unity displacement factor

Bidirectional energy flow, easy to realize 4-quadrant Bidirectional energy flow, easy to realize 4-quadrant

operation operation

Output frequency is not limited by input frequency Output frequency is not limited by input frequency

No need for bulk capacitor (as compared to indirect No need for bulk capacitor (as compared to indirect

frequency converter) frequency converter)

Very complicated—too many power semiconductor Very complicated—too many power semiconductor

devices devices

Output voltage magnitude is a little lower as Output voltage magnitude is a little lower as

compared to indirect frequency converter.

compared to indirect frequency converter.

Referanslar

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