ch5pontedio-2014set

5-1 Copyright 2003

by John Wiley & Sons, Inc. Chapter 5 Line-Frequency Diode

Rectifiers

Chapter 5

Diode Rectifiers

5-2 Copyright 2003


Rectifiers

Diode Rectifier Block Diagram

Uncontrolled utility interface (ac to dc)

5-3 Copyright 2003


Rectifiers

A Simple Circuit

Resistive load

A Simple Circuit (R-L Load)

Current continues to flows for a while even

after the input voltage

has gone negative

5-5

A Simple Circuit (Load has a dc back-emf)

Current begins to flow when the input voltage exceeds

the dc back-emf

Current continues to flows for a while even after the

input voltage has gone

below the dc back-emf

5-6 Copyright 2003


Rectifiers

Single-Phase Diode Rectifier Bridge

Large capacitor at the dc output for filtering and energy storage

5-7 Copyright 2003


Rectifiers

Diode-Rectifier Bridge Analysis

Two simple (idealized) cases to begin with

5-8 Copyright 2003


Rectifiers

Redrawing Diode-Rectifier Bridge

Two groups, each with two diodes

5-9

Waveforms with a purely

resistive load and a purely

dc current at the output

In both cases, the dc-side voltage waveform is the same:

2

0

0

2

12 sin

2

12 cos

2

22

2 2

T

do S

ST

do S

V V t dtT

V tT

fT

V V

5-10 Copyright 2003


Rectifiers

Diode-Rectifier Bridge Input Current Idealized case with a purely dc output current

11

2 2; ; ( )

SS d S d Sh

II I I I I h mpar

h

1 1cosdo d S SV I V I

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Rectifiers

Diode-Rectifier Bridge Analysis with

AC-Side Inductance

Output current is assumed to be purely dc

5-12 Copyright 2003


Rectifiers

Understanding Current Commutation

Assuming inductance in this circuit to be zero

5-13 Copyright 2003


Rectifiers

Understanding Current Commutation (cont.)

2 sin ; 0

2 sin ( )

SL S S

S S S

div V t L t

dt

V t d t L di

Current Commutation Waveforms

0 0

2 sin ( )

2 1 cos cos 12

dI

S S S

S dS S d

S

A V t d t L di

L IV L I

V

Current Commutation in Full-Bridge Rectifier

0

2 sin

2 sin ( )

d S d

SL S S

S S S

t I i I

d iv V t L

dt

V t d t L d i

0

2 sin ( )

d

d

S

I

S S

I

A V t d t

A L di

iD1 iD3

Understanding Current Commutation

2 2 2 Sd do S d

A LV V V I

1

3

0 0

2

d

D

D d

S d

t i

t i I

i i

i I i

i i I

0

2 sin ( ) 2 1 cos

2d

d

S S

I

S S S d

I

A V t d t V

A L di L I

5-17

Rectifier with a

dc-side voltage

5-18 Copyright 2003


Rectifiers

DC-Side Voltage and Current Relationship

Zero current corresponds to dc voltage equal to the peak of the input ac voltage

5-19 Copyright 2003


Rectifiers

Effect of DC-Side Current on

THD, PF and DPF

Very high THD at low current values

5-20 Copyright 2003


Rectifiers

Crest Factor versus the Current Loading

The Crest Factor is very high at low values of current

5-21 Copyright 2003


Rectifiers

Diode-Rectifier with a Capacitor Filter

Power electronics load is represented by an equivalent load resistance

5-22 Copyright 2003


Rectifiers

Diode-Bridge Rectifier: Waveforms

Analysis using PSpice

5-23 Copyright 2003


Rectifiers

Analysis using PSpice

Input Line-Current Distortion

5-24 Copyright 2003


Rectifiers

Line-Voltage Distortion

PCC is the point of common coupling

5-25 Copyright 2003


Rectifiers

Distortion in voltage supplied to other loads

Line-Voltage Distortion

5-26 Copyright 2003


Rectifiers

Voltage Doubler Rectifier

In 115-V position, one capacitor at-a-time is charged from the input.

5-27 Copyright 2003


Rectifiers

A Three-Phase, Four-Wire System

A common neutral wire is assumed

5-28 Copyright 2003


Rectifiers

Current in A Three-Phase, Four-Wire

System

The current in the neutral wire can be very high

5-29 Copyright 2003


Rectifiers

Three-Phase, Full-Bridge Rectifier

5-30 Copyright 2003


Rectifiers

Three-Phase, Full-Bridge Rectifier: Redrawn

Two groups with three diodes each

Three-Phase,

Full-Bridge Rectifier

Waveforms

5-32 Copyright 2003


Rectifiers

Three-Phase, Full-Bridge Rectifier Waveforms

6

6

2

3 322

0

3

1 1

1

1

1 3 22 cos ( )

3

1 2

3

3 cos

6

( 5,7,11,13, )

do LL LL

T T

S d d d

T

LL S do d

S d

SSh

V V t d t V

I I dt I dt IT

V I V I

I I

II h

h

Three-Phase, Full-Bridge Rectifier:

Input Line-Current

Assuming output current to be purely dc and zero ac-side inductance:

11

1 1

2 6; ; ( 5,7,11,13, )

3

3 cos 30.955

3

SS d S d Sh

LL S

LL S

II I I I I h

h

P V I

S V I

5-34 Copyright 2003


Rectifiers


Including the ac-side inductance:

3-Phase Rectifier: Current Commutation

0

0

( )

( )

Pn an La

La S

an Pn

La

v v v

div L

dt

A v v d t

A v d t

3

d do

AV V

3-Phase Rectifier

;

;

0

2

2 2

a c d

La S Lc S

an La Lc cn

an cnLa

Pn an La

an cn bnPn an

i i i I i

di div L v L

dt dt

v v v v

v vv

v v v

v v vv v

0 0

0 0

( ) ( )

( )

3

3 2 3

d

an Pn La

I

La S

S d

d do

Sd LL d

A v v d t v d t

v d t L di

A L I

AV V

LV V I

3-Phase Rectifier: Current Commutation

0 0

0

;

;

2

( ) 2

2 sin ( ) 2

2cos 1

2

d

a c d

La S Lc S

an cn La Lc S

I

an cn S

LL S d

S d

LL

i i i I i

di div L v L

dt dt

div v v v L

dt

v v d t L di

V t d t L I

L I

V

Rectifier with a Large Filter Capacitor

Output voltage is assumed to be purely dc

5-39 Copyright 2003


Rectifiers


THD, PF and DPF as functions of load current

5-40 Copyright 2003


Rectifiers

Crest Factor versus the Current Loading

The Crest Factor is very high at low values of current

5-41 Copyright 2003


Rectifiers

Three-Phase Rectifier Waveforms

UF

RJ

Maurcio Aredes

ch5pontedio-2014set

Documents

dc current

john wiley sons

dc output current

load current

v t ldtv t d t

emf current

tdtv t d t

current loading