Chapter 5 Diode Rectifiers Basic rectifier concepts SinglePhase

Chapter 5 Diode Rectifiers • Basic rectifier concepts • Single-Phase diode bridge rectifiers • Voltage-Doubler rectifiers 5 -1

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

A Simple Circuit (R Load) • 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 (R-L Load) 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 R load I load • Two simple (idealized) cases to begin with: (a) R load (b) current load 5 -8

Waveforms with a purely resistive load at the output 5 -9

Diode-Rectifier Bridge Input Current THD=48. 43% DPF=1. 0 PF=DPF x Is 1/Is=0. 9 • Idealized case with a purely dc output current 5 -10

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

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

Understanding Current Commutation #2 • Assuming inductance to be zero 5 -13

Understanding Current Commutation #3 • Assuming inductance to be zero 5 -14

Understanding Current Commutation #4 • Inductance is included 5 -15

Current Commutation Waveforms vd u v. L Id is 5 -16

Current Commutation Waveforms 5 -17

Average voltage <Vd> When L=0 With finite L Reduction in average output voltage 5 -18

Current Commutation in Full-Bridge Rectifier 5 -19

Current Commutation in Full-Bridge Rectifier 5 -20

Current Commutation Waveforms 5 -21

Average voltage <Vd> When L=0 With finite L Reduction in average output voltage 5 -22

Conclusions Average output voltage drops with 1. increased current 2. increased frequency 3. Increased L Load Regulation is a major consideration in most rectifier systems because • voltage changes with load (IL) 5 -23

Diode-Rectifier with a Capacitor Filter • Power electronics load is represented by an equivalent load resistance 5 -24

Diode-Bridge Rectifier: Waveforms DV=I/C T/2 • Analysis using PSpice 5 -25

Voltage Doubler Rectifier input • In 115 -V position, one capacitor at-a-time is charged from the input. 5 -26