Chapter 5 Diode Rectifiers 5 1 Diode Rectifier

Chapter 5 Diode Rectifiers 5 -1

Diode Rectifier Block Diagram • Uncontrolled utility interface (ac to dc) 5 -2

A Simple Circuit • Resistive load 5 -3

A Simple Circuit (R-L Load) • Current continues to flows for a while even after the input voltage has gone negative 5 -4

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 -5

Single-Phase Diode Rectifier Bridge • Large capacitor at the dc output for filtering and energy storage 5 -6

Diode-Rectifier Bridge Analysis • Two simple (idealized) cases to begin with 5 -7

Redrawing Diode-Rectifier Bridge • Two groups, each with two diodes 5 -8

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 -9

Diode-Rectifier Bridge Input Current • Idealized case with a purely dc output current 5 -10

Diode-Rectifier Bridge Analysis with ACSide Inductance • Output current is assumed to be purely dc 5 -11

Understanding Current Commutation • Assuming inductance in this circuit to be zero 5 -12

Understanding Current Commutation (cont. ) • Inductance in this circuit is included 5 -13

Current Commutation Waveforms • Shows the volt-seconds needed to commutate current 5 -14

Current Commutation in Full-Bridge Rectifier • Shows the necessary volt-seconds 5 -15

Understanding Current Commutation • Note the current loops for analysis 5 -16

Rectifier with a dcside voltage 5 -17

DC-Side Voltage and Current Relationship • Zero current corresponds to dc voltage equal to the peak of the input ac voltage 5 -18

Effect of DC-Side Current on THD, PF and DPF • Very high THD at low current values 5 -19

Crest Factor versus the Current Loading • The Crest Factor is very high at low values of current 5 -20

Diode-Rectifier with a Capacitor Filter • Power electronics load is represented by an equivalent load resistance 5 -21

Diode Rectifier Bridge • Equivalent circuit for analysis on one-half cycle basis 5 -22

Diode-Bridge Rectifier: Waveforms • Analysis using MATLAB 5 -23

Diode-Bridge Rectifier: Waveforms • Analysis using PSpice 5 -24

Input Line-Current Distortion • Analysis using PSpice 5 -25

Line-Voltage Distortion • PCC is the point of common coupling 5 -26

Line-Voltage Distortion • Distortion in voltage supplied to other loads 5 -27

Voltage Doubler Rectifier • In 115 -V position, one capacitor at-a-time is charged from the input. 5 -28

A Three-Phase, Four-Wire System • A common neutral wire is assumed 5 -29

Current in A Three-Phase, Four-Wire System • The current in the neutral wire can be very high 5 -30

Three-Phase, Full-Bridge Rectifier • Commonly used 5 -31

Three-Phase, Full-Bridge Rectifier: Redrawn • Two groups with three diodes each 5 -32

Three-Phase, Full-Bridge Rectifier Waveforms • Output current is assumed to be dc 5 -33

Three-Phase, Full-Bridge Rectifier: Input Line-Current • Assuming output current to be purely dc and zero ac-side inductance 5 -34

Three-Phase, Full-Bridge Rectifier • Including the ac-side inductance 5 -35

3 -Phase Rectifier: Current Commutation • output current is assumed to be purely dc 5 -36

Rectifier with a Large Filter Capacitor • Output voltage is assumed to be purely dc 5 -37

Three-Phase, Full-Bridge Rectifier • THD, PF and DPF as functions of load current 5 -38

Crest Factor versus the Current Loading • The Crest Factor is very high at low values of current 5 -39

Three-Phase Rectifier Waveforms • PSpice-based analysis 5 -40