5-1

Diode Rectifiers

EE 442-642

Fall 2012

5-2

Half-Bridge Rectifier Circuit: R and R-L Load

Current continues to flow for a while even after

the input voltage has gone negative.

5-3

Half Bridge Rectifier Circuit: Load with 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.

5-4

Full Bridge Rectifier – Simple R Load

Average value of output voltage

where Vs is the RMS value of input voltage. ssdo VVV 9.0)/22(

5-5

Full Bridge Rectifier – Simple Constant Load Current

9.0

1

%43.48]1)8/([100

,...7,5,3,/

9.0)/22(

2

1

1

PF

DPF

THD

hhII

III

II

ssh

dds

ds

RSM value of source current

RMS value of fundamental current

RMS value of harmonic current

Current THD

Displacement Power Factor

Power Factor

5-6

Diode-Rectifier Bridge with AC-Side Inductance

Commutation angle:

Average of DC-side voltage:

dssd

s

ds

ILVV

V

IL

29.0

2

21cos

5-7

Full Bridge Rectifier with dc-side Voltage

Zero current corresponds to

dc voltage equal to the peak

of the input ac voltage

Average value of DC-side current

(obtained numerically):

5-8

Diode-Rectifier with a Capacitor Filter

5-9

Voltage Distortion at PCC

• PCC is the point of common coupling

• Distorted current flow results in distorted voltage

5-10

Dual Voltage Rectifier

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

input.

5-11

Three-Phase, Four-Wire System

• A common neutral wire is assumed

• The current in the neutral wire is composed mainly of the

third harmonic and can be higher than the phase currents

5-12

Three-Phase, Full-Bridge Rectifier

LLLLdo VVV 35.123

Average value of DC-side voltage:

where VLL is the rms value of the

Line voltage

5-13

Three-Phase, Full-Bridge Rectifier

RSM value of source current

RMS value of fundamental current

RMS value of harmonic current

Current THD

Displacement Power Factor

Power Factor

955.0

3

1

%31]1)9/([100

,...7,5,3,/

78.0)/6(

816.03/2

2

1

1

PF

DPF

THD

hhII

III

III

ssh

dds

dds

5-14

3-Phase, Full-Bridge Rectifier with ac-side inductance

Commutation angle:

Average of DC-side voltage:

dsLLd

LL

ds

ILVV

V

IL

335.1

2

21cos

5-15

3-Phase Rectifier with DC Source

5-16

Three-Phase Rectifier with Capacitor Filter

• PSpice-based analysis

5-17

Inrush Current and Over-voltage at Turn ON

• Theroretical maximum voltage across the capacitor occurs

when the capacitor is initially discharged and the AC input

is switched at its peak:

– twice the peak phase voltage (in 1-phase ckts),

– twice the peak line voltage (in 3-phase ckts).

• Overvoltages and inrush currents that follow may be

damaging to capacitors and diodes.

• Possible solution: Use current limiting resistor on the DC

side between the rectifier output and filter capacitor. The

resistor should be shorted out after few cycles to limit

losses.