EE 442 642 Diode Rectifiers
-
Upload
nithin-dev-guttikonda -
Category
Documents
-
view
15 -
download
0
description
Transcript of EE 442 642 Diode Rectifiers
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.