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8/6/2019 057 - Norpie 2004 Presentation
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All rectified ac sine wave voltages with capacitive
filtering draw high amplitude discontinuous current
pulses rich in harmonics , causing:
Low input power factor
High circulating currents
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There are many approaches to mitigate this
problem :
Passive and Active power factor correction
Passive and Active filtering of network
Accepting non-sinusoidal voltage / current in the
system.
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Passive Power Factor Correction
Simple inductive input filter
Inductor stores energy to maintainconduction throughout half cycle
Hence reduces harmonic distortation andimproves power factor
But size, weight and cost limits itsapplication upto 200W
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Active high frequency power factor correction
Makes load behave like a resistor
Near unity load power factor
Load generating negligible harmonics
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Types of active PFC circuits with Boost
converter topologies
Hard switched
Soft switched using ZVT
Discontinuous Conduction mode (DCM)
Critical Conduction mode (CRM)
Continuous Conduction mode (CCM)
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Block Diagram of an active PFC Circuit of
CCM Boost converter
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Mosfet & Diode switching waveforms showing switching losses
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Switching loss reduction strategies
RCD Snubber Circuits
Magnetic Snubber Circuits
Power Switch types - IGBT or MOSFET
Boost Diode Options
SiC Schottky Diodes
Single Package Series connected diodes
PFC specific single diodes
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Magnetic Snubber Circuit
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Comparison of recovery time of various diodes
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Comparision of RECOVERY TIME and COST of various diodes
Diode TypePart
NumberRating
TypicalRecovery
time
SupplierCost in
USD
Sic Schottky SDT12S60 12A, 600V Zero Infineon 7.69
Single package
seriesconnected
DSEE 808CC 10A, 600V 30ns IXY S 2.46
Single package
series
connected
STTH806TTI 8A, 600V 30ns ST Micro 1.82
PFC Specific 1SL9R1560P2 15A, 600V 25ns Fairchild 1.42
PFC Specific 15ETX06 15A, 600V 18ns IR 1.03
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Experimental Results
PFC Specific DiodeSingle Package
Series ConnectedDiode
SiC SchottkyDiodes
Input AC Voltage
(RMS)
85 264V 85 264V 85 264V
SwitchingFrequency
100kHz 100kHz 100kHz
Input Power (W) 652 1076 653 1078 642 1049
Output Power (W) 600 1006 598 998 597 1001
Efficiency 0.92 0.935 0.915 0.925 0.93 0.954
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Effect of Diode Recovery Current on the
Switching Current at turn-on
The switch turn-on peak current was the lowest
for the SiC Schottky Diode and highest for the
Single Package Series Diode
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Effect of Diode recovery current on Mosfet
drain current with a SiC Diode
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Effect of Diode recovery current on Mosfet
drain current with a PFC specific diode
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Effect of Diode recovery current on Mosfet
drain current with a single package series
connected diode
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Conducted EMI generated by the PFC board
was measured separately for each of the
three diode types:
Measurements were made at90V AC input, 600W output load witha 3mH common mode EMI filter connected at the input circuit
Low freq part of conducted emission spectrum ( 150kHz - 1
MHz) is almost unaffected by different diode types
High freq part of conducted emission spectrum ( 1 MHz -30MHz) is affected by diode behavior
SDT12S60 SiC Schottky diode generates lower noise
Increased EMI caused by STTH806TTI single package seriesconnected diodes is only about 4dBQV
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Low frequency conducted emission
SiC DiodeSiC Diode Single package series connected diodeSingle package series connected diode
PFC Specific DiodePFC Specific Diode
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High frequency conducted emission
Single package series connected diodeSingle package series connected diode
PFC Specific DiodePFC Specific Diode
SiC DiodeSiC Diode
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OPTIMIZING PERFORMANCE BY DESIGN -
A SUMMARY
Power levels < 200 - Criticalconduction mode PFC may beconsidered
Power levels > 200 - HardswitchedCCM PFCis preferred
Power levels < 1000 & sw. freqof 100kHz -PFCspecificisthe bestchoice
Power levels > 1000 & sw. freq> 100kHz -HigherinitialcostsofSiCSchottkydiodesare justified
Hi ereffi i encyor i er sw. freq-ZVTresonant mode boostconvertermay beconsidered
Power levels < 600 - OldergenerationMosfetslike IRF N(IR) couldreducecostsw/oaffecting performancesignificantly
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