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LECTURE 23

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SINGLE PHASE

CONTROLLED RECTIFIER The rectifier converts the ac voltages to dc voltage.

The most frequent applications are: Battery charger

DC motor drive (speed and torque control)

Power supplies for appliances, computers e.t.c.

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SINGLE PHASE

CONTROLLED RECTIFIER The rectifier converts the ac voltages to dc voltage.

The rectifier is supplied by an ac source, which isrepresented by its thevenin equivalent: AC voltagesource and a reactance connected in series

At the dc side the load can be:

Inductive load, which is represented by a constant currentsource

Capacitive, which is represented by a voltage source

Resistive, represented by a resistance

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SINGLE PHASE

CONTROLLED RECTIFIER Basic single phase rectifier circuit contains:

AC Supply

Switch

Load ( inductive, resistive or capacitive)

Supply:

Voltage source

and Reactance

Switch

Load

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SINGLE PHASE

CONTROLLED RECTIFIER The most frequently

used circuit is the

single phase bridge.

This circuit has four

switching devices

The circuit providesfull-wave rectification

DC

AC

Load

Switch 1

Switch 2

Switch 3

Switch 4

AC

DC

0 60 120 180 240 300 360120

80

40

0

40

80

120120

120

V ac t( )

0

V dc t( )

3600 t

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SINGLE PHASE

CONTROLLED RECTIFIER The main element of the rectifier is the directional

switch.

The most frequently used switches are:

Thyristor,

GTO (Gate Turn off- Thyristor),

IGBT (Insulated Gate Bipolar Transistor),

Power MOSFET

The rectifier operation will be demonstrated using

thyristor switches

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THYRISTOR

Thyristor, is a switch that conduct only in one

direction when:

The voltage between anode and cathode is positive

The gate is triggered, by a short pulse

This is illustrated on the next slide

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SINGLE PHASE RECTIFIER

WITH THYRISTOR SWITCH

In the circuit above the thyristor is triggered by a shortsquare pulse, during the positive cycle

The turn on the devices switches the ac voltage to theload and drives current through the resistance

The turn on delay controls the average dc voltage

Vac

Thyristor

Simplified rectifier

circuit, supply and

load reactance is zero

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WITH THYRISTOR SWITCH

0 60 120 180 240 300 360 420 480 5400

20

40

60

80

100

120120

0

V dc t( )

V dcc t( )

5400 t

deg

0 60 120 180 240 300 360 420 480 5400

20

40

60

80

100

120120

0

V dc t( )

V g t( )

5400 t

deg

DC voltage with

gate control

DC voltage

without gate

control

Gate control

pulse

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WITH THYRISTOR SWITCH The turn on delay (a) controls the average dc

voltage.

The average voltage is the integral of the bleu

curve for a cycle

)cos(V)t(d)tsin(VV

ac

acaver_dc

a

a

12

2

22

1

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WITH THYRISTOR SWITCH Effect of supply and load inductance

The loop equation for the simplified circuit, if the

thyristor conducts, is:

Vac

ThyristorLs

RloadThis differential equation is

solved by using MATCAD.

Student switch to MATCAD

LoadsacRI

dt

dIL)tsin(V 2

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WITH THYRISTOR SWITCH The MATCAD solution of the differential

equation produced the following results

0 1 2 3 4 5 6 7 8 9 100

4

8

12

16

2015.556

0

I1i

V1i10

100 t1i

ms

Voltage Current

The current flows

after the voltage

zero in case ofinductive load

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WITH THYRISTOR SWITCH The method of analytical solution has been

demonstrated

The analytical solution for capacitive and

inductive or other loads are complicated.

The PSPICE simulation is used to analyze the

rectifier operation

Student switch to PSPICE

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WITH THYRISTOR SWITCH PSPICE simulation of inductive loaded rectifier

Circuit diagram Vac

= 120V (peek), 60Hz

Ls = 0.1mH

Lload = 10H

Rload = 20 ohmCo = 10F,

Initial voltage Vc_in = 100V

RloadVac

ThyristorLs

Lload

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WITH THYRISTOR SWITCH PSPICE simulation inductive load

Voltage source and

inductance supply thethyristor

The thyristor is

represented by an ideal

switch, diode and a gatepulse generator

The load is a resistance

and reactance

The firing signal can be delayed

by software command

0

0

V1

state = 0 R1

20

L1

{L}

V2

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WITH THYRISTOR SWITCH The result of the transient run

The firing pulse starts the current flow.

The current is intermittent and flows only one direction. Nonegative current flows in this circuit

Because of inductance the current flows after the voltage

zero crossing.

The firing delay controls the average dc voltage. The next figure shows the increase of inductance increases

the duration of the current pulse, but reduces the amplitude

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WITH THYRISTOR SWITCH The effect of increasing inductance

VoltageCurrent

Time

0s 5ms 10ms 15ms 20ms 25ms 30ms 35ms 40ms 45ms 50msV(V1:+) V(R1:1)

-200V

-100V

0V

100V

200V

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WITH THYRISTOR SWITCH PSPICE simulation of capacitive loaded

rectifier

Circuit diagram

Vac

ThyristorLs

RloadCo

Vac

= 120V (peek), 60Hz

Ls =0.01uH

Rload = 20 ohm

Co = 10F,Initial voltage Vc_in = 100V

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WITH THYRISTOR SWITCH PSPice simulation capacitive load

Voltage source and

inductance supply thethyristor

The thyristor is

represented by an ideal

switch, diode and a gatepulse generator

The load is a resistance

and capacitor

The current flows only if the AC

voltage is higher than the capacitor

voltage and the tyristor is triggered

0

0

V1

state = 0 R1

20

L1

{L}

V2

C1

1000uF

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WITH THYRISTOR SWITCH The result of the transient run, capacitive load

AC Voltage Current

Firing Pulse

Capacitor voltage

Time

60ms 65ms 70ms 75ms 80ms 85ms 90ms 95ms 100ms

I(L1)*12 V(V2:+)*100-200 V(V1:+) V(R1:1)

-200

0

200

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TEST 5

DC Machine

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LECTURE 24

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SINGLE PHASE

CONTROLLED RECTIFIER The single phase

bridge circuit provides

full-wave rectification. This circuit has four

thyristors

The delay of firing

controls the average dcvoltage

DC

AC

Load

Switch 1

Switch 2

Switch 3

Switch 4

AC

DC

0 60 120 180 240 300 360120

80

40

0

40

80

120

120

120

V ac t( )

0

V dc t( )

3600 t

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SINGLE PHASE CONTROLLED

BRIDGE RECTIFIER The single phase

bridge circuit operationis demonstrated using

a simplified circuit.

Zero sourceimpedance and pureresistive load is

assumed The voltage is

controlled by the firingdelay angle

VDC RLoadVac

Th 1

Th 2Th 4

Th 3

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BRIDGE RECTIFIER In the positive cycle

Th1 and Th2 conduct.

The current path isshown in the figure.

VDC

RLoad

Vac

Th 1

Th 2Th 4

Th 3I

0 6 0 1 2 0 1 8 0 2 4 0 3 0 0 3 6 0 4 2 0 4 8 0 5 4 012 0

80

40

0

40

80

12 012 0

12 0

V dc t( )

V dcc t( )

V g t( )

54 00 t

de g

The current and DCvoltage is controlled

by the firing delay

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BRIDGE RECTIFIER In the negative cycle

Th3 and Th4 conduct.

The current path isshown in the figure.

VDC RLoadV

ac

Th 1

Th 2Th 4

Th 3I

0 6 0 1 2 0 1 8 0 2 4 0 3 0 0 3 6 0 4 2 0 4 8 0 5 4 012 0

80

40

0

40

80

12 012 0

12 0

V dc t( )

V dcc t( )

V g t( )

54 00 t

de g

Load current andvoltage is positive.

Full wave rectifier

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BRIDGE RECTIFIER

0

vs

vs

vs

c Gp1Gp1 Gp3

Gp4 Gp2Gp4c

Gp4 Gp3

Gp1 Gp2

0 0

0 0

c

A

GK

A

GK

A

GK

+ - Ld

5mH200k

Rs

1m

-

++

-

E2

ENOM

-

++

-

E1

ENOM

-1

THY_TRIG_SUBCKT2

f = 60

C PV

THY_TRIG_SUBCKT1

f = 60

C PV

A

GK

0.25

RLoad5.0

+ -

Ls2

1mH

10k

+ -

Ls1

0.2mH2k

Vs

control voltage

1

2

3

4

PSPICE simulation of the operation. Inductive load

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BRIDGE RECTIFIERInductive load with small inductance.

Time

20ms 25ms 30ms 35ms 40ms 45ms 50msV(RLoad:1,SCR_SUBCKT3:A) V(vs) V(SCR_SUBCKT1:G)*100-200

V(SCR_SUBCKT2:G)*100-200

-200V

0V

200V

Firing pulseAC voltage

DC voltage and current

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BRIDGE RECTIFIERInductive load with small inductance.

The firing pulse initiates the current. Thecurrent flows only positive direction.

The current flow stops when the currentbecomes zero

Because of the inductive load the current

flows after voltage zero crossing. The firing delay controls the dc current and

voltages.

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BRIDGE RECTIFIERInductive load with large inductance.

Time

20ms 25ms 30ms 35ms 40ms 45ms 50ms

V(RLoad:1,SCR_SUBCKT3:A) V(vs) V(SCR_SUBCKT1:G)*100-200V(SCR_SUBCKT2:G)*100-200

-200V

0V

200V

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BRIDGE RECTIFIERInductive load with large inductance.

The firing pulse initiates commutation fromT1&T2 to T3&T4 or T3&T4 to T1&T2.

The commutation occurs after voltage zerocrossing

The dc current flows continuously, but ac

modulation, ripples can be observed Firing delay controls the dc voltage across

the resistance.

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BRIDGE RECTIFIERPSPICE simulation of the operation. Capacitive load

vs

vs

vs

c Gp1 Gp1

Gp4 Gp2Gp4

c

Gp4

Gp1 Gp2

c

0

0

00

0

Gp3

Gp3

A

GK

A

GK

A

GK

-

++

-

E2

ENOM

A

GK

THY_TRIG_SUBCKT1

f = 60

C PV

THY_TRIG_SUBCKT2

f = 60

C PV

-1

Rs

1m-

++

-

E1

ENOM

RLoad5.0

0.25

Vs

+ -

Ls1

0.2mH2k

+ -

Ls2

0.5mH

10k

C1

100uF

control voltage

1

2

3

4

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BRIDGE RECTIFIERCapacitive & Resistance load.

The current flows only if the AC voltage is higher than the capacitor

voltage and the thyristor is fired

Time

100ms 110ms 120ms 130ms 140ms 150ms

I(L1) V(V2:+)*100-200 V(V1:+) V(R1:1)*2

-400

0

400

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BRIDGE RECTIFIERCapacitive & Resistance load.

The firing pulse initiates the current, if the AC

voltage is larger than the capacitor dc voltage

The current flows till the AC voltage is higher than

the capacitor voltage

The intermittent current charges the capacitor and

increases the dc voltage.

DC capacitor voltage is continuous and controlled

by the firing delay.

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BRIDGE RECTIFIERSource inductance effect.

The source inductance delays the commutation

from Th1 to Th3

Th1 current decreases slowly as Th3 increases. The

total current is constant.

The simultaneous conduction of Th1 and Th3

produces a short circuit. The circulating current

increases Th3 and decreases Th1

The circulating current is limited by the source

inductance

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BRIDGE RECTIFIERSource inductance effect.

VDC RLoadVac

Th 1

Th 2Th 4

Th 3 I

Icirc

IThe voltage is negative

whenTh3 is triggeredThis negative voltage

drives a circulating

current in the short

circuited loop

The circulating current reduces the current of Th1

and increases of the current Th3

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BRIDGE RECTIFIERPSPICE simulation effect of source inductanceLoad is : resistance and inductance, source inductance varies

vs

vs

vs

c Gp1 Gp1

Gp4 Gp2Gp4

c

Gp4

Gp1 Gp2

c

0

0

00

0

Gp3

Gp3

+ -Ld

0.1H200k

A

GK

A

GK

A

GK

-

++

-

E2

ENOM

A

GK

THY_TRIG_SUBCKT1

f = 60

C PV

THY_TRIG_SUBCKT2

f = 60

C PV

-1

Rs

1m-

++

-

E1

ENOM

RLoad5.0

0.25

Vs

+ -

Ls1

0.2mH2k

+ -

Ls2

0.5mH

10k

control voltage

1

2

3

4

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BRIDGE RECTIFIERSource inductance effect. Lsource = 0.2mH

Time

125ms 130ms 135ms 140ms 145ms 150ms

I(Rs)*2 I(R3) I(R6)

-40A

0A

40A

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BRIDGE RECTIFIERSource inductance effect. Lsource = 12mH

Time

125ms 130ms 135ms 140ms 145ms 150msI(Rs)*2 I(R3) I(R6)

-40A

0A

40A

Large inductance causes long commutation time

Th3

Th1IAC

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LECTURE 25

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SINGLE PHASE BRIDGE RECTIFIER

INVERTER OPERATION The inverter converts the DC voltage to AC

In inverter operation the DC source supply power to

the AC source.

Solar power generated by photovoltaic cells is

inverted to supply the ac network

In an un-interruptible power supply stores theenergy in a battery. Energy stored in this battery is

inverted to supply the ac network

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INVERTER OPERATION The adjustment of firing angle delay between 90-

180deg in a thyristor bridge rectifier results ininverter operation

Inverter operation requires large inductanceconnected in series with the converter at the dc side

The large inductance maintains more or lessconstant dc current

The inverter operation requires an AC source at theAC side to generate sinusoidal voltage

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INVERTER OPERATION The inverter operation is simulated by PSPICE by

adjusting the firing delay angle between 90-180 deg.

0

vs

vs

vs

c Gp1Gp1 Gp3

Gp4 Gp2Gp4

c

Gp4 Gp3

Gp1 Gp2

0 0

0 0

c

A

GK

A

GK

A

GK

+ -

Ld0.1H200k

Rs

1m

-

++

-

E2

ENOM

-

++

-

E1

ENOM

-1

THY_TRIG_SUBCKT2

f = 60

C PV

THY_TRIG_SUBCKT1

f = 60

C PV

A

GK

135/180

+ -

Ls21mH

10k

+ -

Ls1

0.2mH2k

VsV1

88V

control voltage

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INVERTER OPERATION Inverter operation firing delay angle is 135 degree

Time

45ms 50ms 55ms 60ms 65ms 70ms 73ms

I(Rs)*20 V(vs)

-200

0

200

AC Voltage AC Current

Delay angle

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INVERTER OPERATION The simulation shows that the AC voltage

and current polarity is opposite. When the voltage is positive current is negative

and vice versa

This indicates generator operation, the powertransferred from DC to AC

The power is negative, because the power factor(cos f) is negative between 90 and 180 degrees

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INVERTER OPERATION The nearly square shape current produces

undesirable harmonics in the ac system

The FFT analyses shows 3th,5th,7thharmonics

Frequency

0Hz 0.2KHz 0.4KHz 0.6KHz 0.8KHz 1.0KHz

I(Rs)

0A

5A

10A

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SINGLE PHASE BRIDGE

RECTIFIER WITH PULSE WIDTH

MODULATION

The bridge rectifier is controlled by the firing

delay

The firing delay cuts out a part of the voltage

wave. This reduces the average dc voltage.

Similar effect can be achieved by distributing the

off periods along the half cycle The distribution of the delay improves

performance, reduces the harmonics

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WITH PW MODULATION

Demonstration of delayed firing and the distributedfiring delay

The system performance can be further improvedby changing the width of the on and off periods.

Delayed firing Distributed firing delay

0 6 0 1 2 0 1 8 0 2 4 0 3 0 0 3 6 0 4 2 0 4 8 0 5 4 012 0

80

40

0

40

80

12 012 0

12 0

V pw t( )

V d t( )

54 00 t

de g

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SINGLE PHASE BRIDGE


MODULATION

Concept of Pulse-Width modulation: The firingdelay is distributed along period and the on

and off times are varied to reduce harmonics The most frequently used PW method is the

sinusoidal PW modulation

The switches in the converter are controlled by

pulses. The width of each pulse is varied in proportion

to the amplitude of a sine wave

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SINGLE PHASE BRIDGE


MODULATION

Generation of the PWM waveform

A triangular carrier wave is generated

A sinusoidal reference signal is generated

The two signals are compared, when the carrierwave is larger than the reference signal the gatesignal is positive

When the carrier wave is smaller than thereference signal the gate signal is zero

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SINGLE PHASE BRIDGE

CONVERTER WITH PULSE WIDTH

MODULATION

Gate signal generation for PWM converter

Time

0s 5ms 10ms 15ms 20ms 25ms

V(PWM_TRI1.E1:IN+) V(PWM_TRI1.Vtri:+)

-1.0V

0V

1.0V

Carrier wave Reference signal

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SINGLE PHASE BRIDGE


MODULATION

Gate signal generation for PWM converter.

Firing pulse with variable width

Time


V(PWM_TRI1:s)

-1.0V

0V

1.0V

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SINGLE PHASE BRIDGE


MODULATION

PWM Converter

The generated firing signal controls the converter switches

The converter switches have to switch on and off the current

This can be achieved by GTO (Gate turn on transistor) or

GTO, gate turn off thyristor, or MOSFET

The switches have to be shunted by a diode to avoid the over

voltages generated by the interruption of inductive current

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SINGLE PHASE BRIDGE


MODULATION

PWM Converter

The converter can operate both in inverter or in

rectifier mode

Advantage of this circuit are :

in inverter mode it can supply passive load.

significant reduction of current and voltage

harmonics

S G S G

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SINGLE PHASE BRIDGE


MODULATION

PWM Converter

D1

IGBT1

IGBT2D2

Vdc

Vac

SINGLE PHASE BRIDGE

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SINGLE PHASE BRIDGE


MODULATION

Operation analysis with PS SPICE

The students are provided with the model, theychange the parameters and observe the results:

Load inductance and resistance

Switching frequency

Calculate harmonics and RMS values

SINGLE PHASE BRIDGE

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SINGLE PHASE BRIDGE


MODULATIONOperation analysis with PS SPICE

PWM Inverter supplies AC network with voltage source

0

P1

P1

P2

P2

R1

2.0

L1

10mH

IC = -7AV1

271V

D2

D3

1-V(%IN)

PWM_TRI1

fs = 1kHz

c s

D5

D4

V4

V5

in

out

SINGLE PHASE BRIDGE

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SINGLE PHASE BRIDGE


MODULATION

Time


I(V5)*10 V(L1:1,VOUT-) V(V5:+,V5:-)

-400

0

400

PWM Output

Voltage Load Current Load Voltage

Current, voltage waveforms in bipolar operation.

SINGLE PHASE BRIDGE

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SINGLE PHASE BRIDGE


MODULATION

Time

50ms 55ms 60ms 65ms 70ms 75ms 80ms 85ms 90ms 95ms 100ms

V(L1:1,PWR_SWITCH4:in) V(C2:1,PWR_SWITCH4:in) I(L1)*5

-400

-200

0

200

400

L1 = 10mH, C =

100uF, R1 (in serieswith L1) = 0.1ohm

and load resistance

(across C) = 10

ohm.. (fundamental

- 40 Hz, sw.

frequency 1kHz).

Current and voltage waveforms in

mono-polar operation mode

SINGLE PHASE BRIDGE

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SINGLE PHASE BRIDGE


MODULATION

Time

0s 5ms 10ms 15ms 20ms 25ms 30ms

V(L1:1,PWR_SWITCH4:in)*0.6-500 V(V5:+,V5:-) V(P1) I(L1)*20 -I(L1)

-800

-400

0

400

Monopolar operation Loading increases the current ripples

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MOTOR DRIVE CONCEPT WITH

PWM INVERTER

Rectifier

Inverter

DC linkMotor

M

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MOTOR DRIVE CONCEPT WITH

PWM INVERTER

The ac voltage of the supply is rectified

The dc link filters the harmonics and produces smooth DC

The PW inverter produces a variable frequency and voltage

sine wave that drives the motor

The frequency regulates the motor speed.

The voltage and frequency ratio is kept constant to avoid

saturation at low frequencies

1 phase scr

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