chapter 5 diode rectifiers - unob.cz · • power electronics load is represented by an equivalent...

Copyright © 2003 by John Wiley & Sons, Inc.

Chapter 5 Line-Frequency Diode Rectifiers

5-1

Chapter 5

Diode Rectifiers



5-2

Diode Rectifier Block Diagram

• Uncontrolled utility interface (ac to dc)



5-3

A Simple Circuit

• Resistive load



5-4

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

Single-Phase Diode Rectifier Bridge

• Large capacitor at the dc output for filtering and energy storage



5-7

Diode-Rectifier Bridge Analysis

• Two simple (idealized) cases to begin with



5-8

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



5-10

Diode-Rectifier Bridge Input Current

• Idealized case with a purely dc output current



5-11

Diode-Rectifier Bridge Analysis with AC-Side Inductance

• Output current is assumed to be purely dc



5-12

Understanding Current Commutation

• Assuming inductance in this circuit to be zero



5-13

Understanding Current Commutation (cont.)

• Inductance in this circuit is included



5-14

Current Commutation Waveforms

• Shows the volt-seconds needed to commutate current



5-15

Current Commutation in Full-Bridge Rectifier

• Shows the necessary volt-seconds



5-16

Understanding Current Commutation

• Note the current loops for analysis



5-17

Rectifier with a dc-side voltage



5-18

DC-Side Voltage and Current Relationship

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



5-19

Effect of DC-Side Current on THD, PF and DPF

• Very high THD at low current values



5-20

Crest Factor versus the Current Loading

• The Crest Factor is very high at low values of current



5-21

Diode-Rectifier with a Capacitor Filter

• Power electronics load is represented by an equivalent load resistance



5-22

Diode Rectifier Bridge

• Equivalent circuit for analysis on one-half cycle basis



5-23

Diode-Bridge Rectifier: Waveforms

• Analysis using MATLAB



5-24

Diode-Bridge Rectifier: Waveforms

• Analysis using PSpice



5-25

• Analysis using PSpice

Input Line-Current Distortion



5-26

Line-Voltage Distortion

• PCC is the point of common coupling



5-27

• Distortion in voltage supplied to other loads

Line-Voltage Distortion



5-28

Voltage Doubler Rectifier

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



5-29

A Three-Phase, Four-Wire System

• A common neutral wire is assumed



5-30

Current in A Three-Phase, Four-Wire System

• The current in the neutral wire can be very high



5-31

Three-Phase, Full-Bridge Rectifier

• Commonly used



5-32

Three-Phase, Full-Bridge Rectifier: Redrawn

• Two groups with three diodes each



5-33

Three-Phase, Full-Bridge Rectifier Waveforms

• Output current is

assumed to be dc



5-34

Three-Phase, Full-Bridge Rectifier: Input Line-Current

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



5-35


• Including the ac-side inductance



5-36

3-Phase Rectifier: Current Commutation

• output current is assumed to be purely dc



5-37

Rectifier with a Large Filter Capacitor

• Output voltage is assumed to be purely dc



5-38


• THD, PF and DPF as functions of load current



5-39

Crest Factor versus the Current Loading

• The Crest Factor is very high at low values of current



5-40

Three-Phase Rectifier Waveforms

• PSpice-based analysis

chapter 5 diode rectifiers - unob.cz · • power electronics load is represented by an equivalent...

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