UCF Regional Campuses and UCF Continuing Education Fall 2013 Newsletter
Research Activities in Power Electronics at UCF
description
Transcript of Research Activities in Power Electronics at UCF
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Research Activities in Power Electronics at UCF Florida Power Electronics CenterOrlando, Florida [email protected] atPrincess Sumaya University forTechnology
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Outline of topics About Florida Power Electronics Center Single-Stage PFC Converters Low Voltage DC-DC converters Inverters Generalized Analysis of DC-DC Converters
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WELCOME TO FLORIDAOrlandoArea
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Florida Power Electronics CenterPower Factor Correction (PFC) Circuits - NASASoft-Switching DC-DC Converters - I-4 Florida InitiativeLow voltage AC-DC and DC-DC Converters - NSFDynamic Modeling and Control - NSFElectromagnetic Interference and Compatibility - NSF Inverter Application / Photovoltaic Cell Industry & I-4 Dr.Issa Batarseh DirectorDr.Wenkai Wu Asst DirectorHigh Frequency AC DPS NSF & I-4 Smart Electronic Load Maximum Power Point Tracking System
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Topologies and Converter System Dr. Issa Batarseh Magnetics Dr. Thomas Wu Power Devices Dr.J J Liou Modeling and Control Dr.Zhihua Qu Packaging Dr.Louis ChowMultidisciplinary Research Group
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FloridaPEC - Team Christopher IannelloJaber A.Abu QahouqWei GuWenkai WuWei HongKhalid RustomJoy MazumdarShailesh AnthonyDuy BuiAbdelhalim M AlsharqawiShiguo LuoJia LuoSongqrian DengPeter KornetzkyJay VaidyaShilba ReedyFloridaPEC.engr.ucf.edu
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AC/DC converter power supplyTelecommunication device, and other industrial equipmentComputerTV setsMedical equipment~ConverterAC SourceDC LoadPower Conversion
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Single-Stage PFC Converters
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For linear load:For nonlinear load :Definition of Power Factor
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--Distortion factor, where--Displacement factor
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Typical Line Current Waveform Without PFCLine current is zero when vl(t) < vc(t). PF 0.67 THD >110%
Chart1
100
81
60.6
37
15.7
2.4
6.3
7.9
Harmonic number
Current magnitue (%)
Sheet1
1100
381
560.6
737
915.7
112.4
136.3
157.9
Sheet1
Harmonic number
Current magnitue (%)
Sheet2
Sheet3
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PFC Approaches i) Passive PFC converter ii) Active two-stage PFC converter iii) Active single-stage PFC converter
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Three Basic PFC Approaches Active two stage PFC converterActive single stage PFC converterPassive PFC converter
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Special Family--Single-stage PFC AC/DC ConverterPFC stage and DC/DC stage share the same switchSingle Loop
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Prior Art(b) Boost/forward combination DCM+DCM (Russian circuit, 1992)(a) Boost/flyback combination DCM+DCM (Redl, 1994)Advantage SimpleLeast component count DisadvantageInherent Low efficiencyHigh DC Bus Voltage StressTurn off spike
Advantage No turn off spikeLow voltage rated capacitor DisadvantageInherent Low efficiencyHigh DC Bus Voltage Stress
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Conventional Energy transfer concept
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New energy transfer conceptk12+(1-k) 1> 12
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Flyboost PFC cell + Flyback DC/DC cellSingle active switch + single controllerNew Concept
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Operation modeFlyback mode:|Vin| < Vcs n1 * VoBoost mode: |Vin| > Vcs n1 * Vo
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Simulation resultsTrace 1 Current through flyback windingTrace 2 Rectified input currentTrace 3 DC/DC stage currentOperation waveform in one line cycle
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Apply to other topologies
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Measured Power Factor vs. line voltageMeasured Efficiency vs. line voltageMeasured storage capacitor voltage (Vs) vs. line voltage Line voltage and line current at line voltage=110V AC. Trace A: Line voltage (100V/div, 5ms/div); Trace B: Line current (measured after auxiliary line filter;1A/div; 5ms/div). The measured Power Factor is 99.4% Experimental Results
Chart1
97.3
98
98.9
99.3
99.3
99.3
99.5
99.2
99.1
99.3
98.8
98.7
98.7
98.7
97.8
97.7
97.5
97.3
97.2
97.2
PF/%
Line Voltage/V
PF/%
Sheet1
Measured Data of Single Switch Converter with Fly Back Loop
Load resistor: 5.2Ohm (Electronic Load Agilent N3305A)
AC Source:HP 6841ADate: 04/23/01
Vline/VPF/%Pline/WPout/WVout/VVs/Veff/%
8597.3183.3150.427.97104.682.05
9098.0182.3150.327.96108.782.45
10098.9181.2150.227.95118.182.89
11099.3180.3150.027.93127.983.19
12099.3180.0149.927.92137.683.28
13099.3179.8149.727.90147.683.26
14099.5179.5149.527.88156.083.29
15099.2179.4149.427.87163.483.28
16099.1179.7149.127.85171.982.97
17099.3179.8149.027.83182.282.87
18098.8179.6148.927.82188.182.91
19098.7180.0148.527.80197.082.50
20098.7180.4148.427.79206.582.26
21098.7180.6148.327.77216.082.12
22097.8180.6148.127.76219.082.00
23097.7180.8148.027.74224.981.86
24097.5181.0147.527.71232.581.49
25097.3181.5147.327.68241.081.16
26097.2182.1146.827.66251.580.62
27097.2182.5146.827.63261.180.44
Sheet1
PF/%
Line Voltage/V
PF/%
Sheet2
PF/%
Line Voltage/V
eff/%
Efficiency vs. Line Voltage
Sheet3
Vout/V
Line Voltage/V
Vout/V
Output Voltage vs. Line Voltage
Vs/V
Line Voltage/V
Vs/V
Storage Capacitor Voltage vs. Line Voltage
Chart2
82.0512820513
82.4465167307
82.8918322296
83.1946755408
83.2777777778
83.2591768632
83.286908078
83.2775919732
82.9716193656
82.8698553949
82.9064587973
82.5
82.2616407982
82.1151716501
82.0044296788
81.8584070796
81.4917127072
81.1570247934
80.6150466776
80.4383561644
PF/%
Line Voltage/V
eff/%
Sheet1
Measured Data of Single Switch Converter with Fly Back Loop
Load resistor: 5.2Ohm (Electronic Load Agilent N3305A)
AC Source:HP 6841ADate: 04/23/01
Vline/VPF/%Pline/WPout/WVout/VVs/Veff/%
8597.3183.3150.427.97104.682.05
9098.0182.3150.327.96108.782.45
10098.9181.2150.227.95118.182.89
11099.3180.3150.027.93127.983.19
12099.3180.0149.927.92137.683.28
13099.3179.8149.727.90147.683.26
14099.5179.5149.527.88156.083.29
15099.2179.4149.427.87163.483.28
16099.1179.7149.127.85171.982.97
17099.3179.8149.027.83182.282.87
18098.8179.6148.927.82188.182.91
19098.7180.0148.527.80197.082.50
20098.7180.4148.427.79206.582.26
21098.7180.6148.327.77216.082.12
22097.8180.6148.127.76219.082.00
23097.7180.8148.027.74224.981.86
24097.5181.0147.527.71232.581.49
25097.3181.5147.327.68241.081.16
26097.2182.1146.827.66251.580.62
27097.2182.5146.827.63261.180.44
Sheet1
PF/%
Line Voltage/V
PF/%
Sheet2
PF/%
Line Voltage/V
eff/%
Sheet3
Vout/V
Line Voltage/V
Vout/V
Output Voltage vs. Line Voltage
Vs/V
Line Voltage/V
Vs/V
Storage Capacitor Voltage vs. Line Voltage
Chart3
104.6
108.7
118.1
127.9
137.6
147.6
156
163.4
171.9
182.2
188.1
197
206.5
216
219
224.9
232.5
241
251.5
261.1
Vs/V
Line Voltage/V
Vs/V
Sheet1
Measured Data of Single Switch Converter with Fly Back Loop
Load resistor: 5.2Ohm (Electronic Load Agilent N3305A)
AC Source:HP 6841ADate: 04/23/01
Vline/VPF/%Pline/WPout/WVout/VVs/Veff/%
8597.3183.3150.427.97104.682.05
9098.0182.3150.327.96108.782.45
10098.9181.2150.227.95118.182.89
11099.3180.3150.027.93127.983.19
12099.3180.0149.927.92137.683.28
13099.3179.8149.727.90147.683.26
14099.5179.5149.527.88156.083.29
15099.2179.4149.427.87163.483.28
16099.1179.7149.127.85171.982.97
17099.3179.8149.027.83182.282.87
18098.8179.6148.927.82188.182.91
19098.7180.0148.527.80197.082.50
20098.7180.4148.427.79206.582.26
21098.7180.6148.327.77216.082.12
22097.8180.6148.127.76219.082.00
23097.7180.8148.027.74224.981.86
24097.5181.0147.527.71232.581.49
25097.3181.5147.327.68241.081.16
26097.2182.1146.827.66251.580.62
27097.2182.5146.827.63261.180.44
Sheet1
PF/%
Line Voltage/V
PF/%
Sheet2
PF/%
Line Voltage/V
eff/%
Sheet3
Vout/V
Line Voltage/V
Vout/V
Output Voltage vs. Line Voltage
Vs/V
Line Voltage/V
Vs/V
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Special application Bi-Flyback ConverterInegrate Bifred and Flyboost topologiesTwo flyback transformers, single switchSingle DC bus capacitor
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Soft switching application
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Developed prototype
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Input voltage: 220VOutput watts 150WInput voltage: 110VOutput watts 150WLine VoltageLine CurrentLine VoltageLine CurrentWaveforms
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Waveforms for the main switchVdsId
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Efficiency and Power Factor200KHz/[email protected]
Chart1
0.957
0.963
0.978
0.988
0.985
0.984
0.983
0.98
0.976
0.973
0.971
0.971
0.969
0.965
0.963
0.961
0.956
0.953
0.951
0.95
Input Voltage (V)
Power Factor
Sheet1
850.957183.8149.920.81566
900.963182.7149.920.8205801861
1000.978181.4149.950.8266262404
1100.988180.61500.8305647841
1200.985180.7150.10.8306585501
1300.984180.5150.10.8315789474
1400.983180.1150.120.8335369239
1500.98180150.20.8344444444
1600.976180.3150.30.8336106489
1700.973180.5150.30.8326869806
1800.971181.2150.30.8294701987
1900.971181.5150.30.8280991736
2000.969181.8150.30.8267326733
2100.965182.6150.50.8242059146
2200.963183.1150.40.8214090661
2300.961183.9150.470.818216422
2400.956184.6150.50.815276273
2500.953184.8150.60.8149350649
2600.951185.3150.60.8127361036
2650.95185.5150.60.8118598383
Sheet1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Input Voltage (V)
Power Factor
Sheet2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
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0
Input Voltage (V)
Power Factor
Sheet3
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Improved Results
Chart6
76.9
79.5570698467
82.3591923486
83.1282952548
83.6940836941
83.984375
84.1306884481
84.3971631206
84.6897253306
84.3580914904
84.2830009497
84.1335162323
84.2151675485
83.6846543002
83.927822073
Output power (W)
Efficiency (%)
Sheet1
23.331.6850.95731.624.376.9166
46.758.7900.96358.746.779.5570698467176.8
77.594.11000.97894.177.582.3591923486190.7
94.6113.81100.988113.894.683.1282952548202.8
116138.61200.985138.611683.6940836941215.3
129153.61300.984153.612983.984375227.1
144.2171.41400.983171.4144.284.1306884481239.2
154.7183.31500.98183.3154.784.3971631206251.9
166.5196.61600.976196.6166.584.6897253306264.1
171.5203.31700.973203.3171.584.3580914904277.2
177.5210.61800.971210.6177.584.2830009497290.2
184218.71900.971218.718484.1335162323302.9
191226.82000.969226.819184.2151675485319.4
198.5237.22100.965237.2198.583.6846543002332.4
200238.32200.963238.320083.927822073345.2
Sheet1
0
0
0
0
0
0
0
0
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0
0
0
0
0
0
Output power (W)
Efficiency (%)
Sheet2
Sheet3
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Key Features Higher efficiency due to soft switching operation of the main switch.
Low DC bus voltage make commercially available capacitor can be used as the energy storage part
Higher efficiency due to direct energy transfer in Flyback mode
Higher power density due to high frequency operation, which also benefit from soft switching
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Powering Future Generation of Microprocessors and ICsLow-Voltage High-Current Fast-Transient On-Board Voltage Regulator Modules(VRMs)
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Structure
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The Main Power Supply Requirements(Challenges)1. High output current slew rate (> 50A/s).
2. Low output voltage ripple and overshoot during transient (< 2% of the nominal output voltage).
3. High efficiency
4. High power density.
5. High VRM input current slew rate (
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Pentium 4 Voltage and Current Specs
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Current and Voltage RoadmapYear1999200020012002200320042005Vmax1.81.81.51.51.51.21.2Vmin1.51.51.21.21.20.90.9W90100115130140150160Imin(A)5056778793125133Imax(A)606796108117167178
Lately, there are news about even lower voltages and higher currents expectations in the future (APEC2001, March 2001)
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Interleaving Technique for Multi-phase Converters
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The Voltage-Mode Hysteretic Control
Tracks the output voltage (ripple) and keeps it within the required limits.
Near instantaneous response to load transients.
No feedback loop compensation is needed.
No limitations on the switches conduction time
Circuit simplicityThe Interleave Technique
High frequency output voltage ripple with lower switching frequency
Ripple cancellation
Current division between the phases
Fast transient response which is limited by the feedback control loop
Why Voltage-Mode Hysteretic Control and Interleave Technique?Effective &simple to apply+
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Initial Experimental PrototypeWaveformsPreliminary ResultsPhase 1 Drive SignalPhase 2 Drive SignalPhase 1 Inductor CurrentPhase 2 Inductor CurrentTotal CurrentOutput VoltageInput Voltage =12VOutput Voltage =1.5VOutput Current=30ASwitching Frequency/Phase=400KHzOutput Ripple Frequency=800KHz
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Initial Experimental ResultsTwo-Phase VRM ControlThree-Phase VRM ControlFour-Phase VRM Control
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Transient Cancellation Control Method for Future Generation of MicroprocessorsThe idea of the transient cancellation control scheme is to create a deliberate undershoot before an expected overshoot and vice versa to cancel the expected large overshoot to keep the output voltage within the allowable output voltage deviation limit. Ideal Output-Voltage Waveforms at High-to-Low Load Transient with the Transient Cancellation ControllerIdeal Output-Voltage Waveforms at High-to-Low Load Transient without the Transient Cancellation Controller
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Future Look on VRMs and their Control Methods
To satisfy future strict powering requirements of microprocessors especially the tight allowable voltage deviation (20mV), may have to be one or more of the following:
1) Proactive instead of reactive, i.e, to be able to take a response action before the load transients occur instead of after.
2) Future VRM controllers may need to be able to learn the load behavior and/or apply advanced response techniques to reduce the VRM output voltage overshoots/undershoots and to have fast transient response.
3) Methods such as fuzzy logic and neural networks may be applied to make the VRM controller smart.
4) Advanced Topology techniques that have naturally the voltage deviation reduction (cancellation)
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Generalized Analysis of Soft-Switching DC-DC Converters
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Conventional DC-DC Converters(Hard-Switching)BuckBoostBuck-BoostCukZetaSepic
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Switching-Cell Sharing
All the Conventional DC-DC Converters shares the same switching-cell With different orientation of the cell in a specific converterThe Conventional DC-DC Switching-Cell
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Analyzed Soft-Switching Cells
(a)
(b)
(c)
(d)
(e)
(f)
(g)
EMBED Visio.Drawing.5
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EMBED Visio.Drawing.5
_1013983271.vsd
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_1014915441.vsd
_1014915261.vsd
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_1013983389.vsd
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(a) Conventional Cell, (b) ZVS-QRC Cell, (c) ZCS-QRC Cell, (d) ZVS-QSW CV Cell, (e) ZCS-QSW CC Cell, (f) ZVT-PWM Cell, and (g) ZCT-PWM Cell
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Zero-Voltage-Switching Quasi-ResonantZVS-QRC Switching-CellZVS-QRC Cell Basic Switching-Waveforms
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Zero-Voltage-Transition PWMZVT-PWM Switching-CellZCT-PWM Cell Basic Switching-Waveforms
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ZVT-PWM FamilyZVT-PWM BuckZVT-PWM BoostZCT-PWM Buck-BoostZCT-PWM CukZVT-PWM ZetaZVT-PWM Sepic
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The Generalized Transformation Table
Single Generalized Transformation Table is complete and applies to all cells
,
,
,
Buck
1
1-M
-M
Boost
M
1
1-M
Buck-Boost, Cuk, Zeta, and Sepic
1+M
1
-M
_1012178854.unknown
_1012179084.unknown
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_1012178797.unknown
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Generalized Gain EquationGeneralized gain ( ):By using the normalized parameters:
_1014143808.unknown
_1015368991.unknown
_1006892111.unknown
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Summary of the Generalized Analysis(Basic Equations Intervals and Gain)
Chapter 8
Summary and Conclusion
CELL
(
(
(
(
(
(
(
Gain Equation
Quasi Resonant
Converters
ZVS
N/A
N/A
N/A
ZCS
N/A
N/A
N/A
Quasi
Square
Wave
ZVS CV
N/A
N/A
N/A
ZCS CC
N/A
N/A
N/A
Transition
PWM
ZVS
ZCS
N/A
N/A
Where:
The time delay between turning OFF
and
.
1
1
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_1014683542.unknown
_1014683539.unknown
_1014683461.unknown
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_1014679313.unknown
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Voltage Gain versus Duty Ratio
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Final RemarksA generalized analysis method for well known families of soft-switching dc-dc converters was proposed.It was shown that a single Generalized Transformation Table for all the converter families exists.
The simulation results verified the theoretical results.
The analysis generalization leads to several advantages such as:(1) Gives more insight into the converter-cell operation.(2) Improves the computer-aided analysis and design.(3) Simplifies mathematical modeling.(4) The cell-to-cell comparison becomes easier.(5) Improvement is made easier by deriving a new generalized cell.
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FUELCELLDC-DC STAGELCFILTERSPWMCONTROLPWMCONTROLFunctional Block DiagramPROTECTION
DC-AC STAGEREADYSIGNAL
VDC linkPHASE APHASE BEARTHVref
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Block Diagram of the power stage
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Design Specifications for 1.5kW prototypeOutput power rating 1.5 kW continuous, Split single-phase Output voltage 120 V/240 V nominalFrequency 60 Hz 0.1 Hz. Design input source type Fuel cell, photovoltaic or other qualified renewable energy sources. Nominal rating of 48 V dc.Overall efficiency Higher than 90% for resistive load.Total harmonic distortion Output voltage THD: less than 5% when supplying a standard nonlinear test loadVoltage Regulation +/- 6% from NL to FL. Frequency +/- 0.1 Hz
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Troubleshooting!!!!!
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Experimental Result (Output Voltage)
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2001 Future Energy ChallengeTM :Competition funded by the U.S. Department of Energy and the Department of Defense to design and build, at one half or less of the cost of todays equipment, a key low cost fuel cell component for converting direct current into alternating current in ten kilowatt or smaller fuel cells.Texas A&M UniversityVirginia Polytechnic Institute and State UniversityUniversity of Central FloridaUniversity of Wisconsin - MadisonDrexel UniversityUniversity of Illinois, ChicagoUS DoE and DoDFinalist
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Improved sinusoidal output inverter topology solution:Complex Structure. High cost.Low Efficiency.Disadvantages
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Characteristics of the High Frequency Link InverterNo low frequency component exists in the waveform transmitted by transformer. A compact high frequency transformer is allowed for the transmission.The operation frequency of the two switches in the secondary side of the transformer is low. Thus leads to low switching loss and high efficiency.Low distortion of the output waveform.Simple structure, lower loss and higher efficiency can be obtained.
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Configuration of the proposed topology:No low frequency component exists in the waveform transmitted by transformer. A compact high frequency transformer is allowed for the transmission.The operation frequency of the two switches in the secondary side of the transformer is line frequency which leads to low switching loss and high efficiency.Low distortion of the output waveform.Features
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Simulation Circuit: We used half bridge in the primary side to illustrate the principle in the simulation. The whole system consists of power stage and control circuit.
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Simulation ResultThe Generation of the Modulating Signal: The modulating signal is generated by the comparison between the sampled signal and the reference wave.
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Comparison of the Two Inverter TopologiesComplex system structure DC-AC-DC-Sinusoidal ACHigh voltage stress across the switches. All switches are operated at high frequency. High switching loss and low efficiency.Large size, high cost and difficult to design. Simple system structure DC-Sinusoidal ACLow voltage stress across the switches.Switches in the secondary side is operated at line frequency, switching loss drops greatly.Small size, low cost and easy to design.Low THD distortion at the output side.Inverter with Push-pull StructureNovel High Frequency Link Inverter
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Dynamic Modeling of DC-DC Converters
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Dynamic Modeling(a) Detailed circuit model; predicting device behavior, time consuming , convergence.(b) Switched circuit model; Predicting roughly system large signal behavior, steady- state waveform and transient, details lost, time consuming convergence problems.(c) Equivalent PWM switch model; Determination of steady-state operation pointOptimization of the control loopInvestigation of stability problemsPrediction of large signal transient behaviorEfficient computer simulation(1) Average switch model (Middlebrook)(2) Discrete time domain model(3) Three terminal PWM switch model (Vorperian)
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Special Problems to Model PFC CircuitsSwitching power stageDigital modulatorError compensatorOutput Ac line input Control, dFeedback loopNo standard three-terminal network is available to single stage AC/DC converters, In most of cases, three terminals PWM model can not be used directly
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DerivationUsing Circuit Analysis Technique while keeping Same functionality of each branch
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Verification of the new model (DC)Output voltage vs. input voltageStorage capacitor voltage vs. input voltage
Chart2
38.3938.15
42.6542.55
46.9246.96
51.1951.37
55.4555.46
59.7259.66
D=0.35
state-space averaging
large-signal model
Input voltage (V)
Output voltage (V)
Sheet1
9038.3938.15
10042.6542.55
11046.9246.96
12051.1951.37
13055.4555.46
14059.7259.66
Sheet1
00
00
00
00
00
00
D=0.35
state-space averaging
large-signal model
Input voltage (V)
Output voltage (V)
Sheet2
Sheet3
Chart3
149148
166165
182182
199199
215215
232231
D=0.35
state-space averaging
large-signal model
Input voltage (V)
Storage capacitor voltage (V)
Sheet1
90149148
100166165
110182182
120199199
130215215
140232231
Sheet1
00
00
00
00
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D=0.35
state-space averaging
large-signal model
Input voltage (V)
Storage capacitor voltage (V)
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Verification of the new model (small-signal)frequency response between line to outputfrequency response between control to outputState-space averaging model vs. the new model (Vin: 110V, V0: 50V)
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PWM and Average techniques to derive closed looptransfer functions Study decoupling circuit approach in non-three terminal converters Explore New averaging method to equivalent average circuitDynamic Modeling of DC/DC and PFC-AC/DC Converters
Along with the development of power electronics, the harmonics problems become more and more noticeable and troublesome. So power factor correction has been a hot topic in power electronic community, at same time its important to practical industry application.. From these five aspects, I will present some new points, give a review to the current PFC approaches, introduce our work on this subject. And then summary the issue and possible solutions. Finally, we will discuss application feasibility.
Totally, I need about 50 minutes to finish this presentation!
First of all, I would like to introduce some basic concepts and terms. As you know, For linear load, power factor is defined as real power over apparent power. For nonlinear load, the definition is modified like this, because current waveform is distorted, so a additional factor has to be considered in this formula.
That is, power factor is equal to distortion factor times displacement factor. The distortion factor kd and THD are defined by these equations. This equation shows the relationship between THD and Kd. Actually, most of power converters belong to a special case, that is, cos ZITA is nearly one, so we can simply calculate PF by THD like this.
Here is a typical example for traditional AC/DC power supply. Generally speaking, the power factor is lower than o.67, and THD is higher than 110%. This means serious harmonic problem exist in converter system. In next following, we will review the current PFC approaches on these items
As for as converters, we have three basic PFC approaches,one is second is . The last one is******
In single stage schemes, a special family is single stage single switch PFC converter its feature is>>>>>>>>>>
Let us take look some example circuits of S4 PFC converters. I think these topologies are preferable collection for practical application in the future. The first four guys look similar, but in fact, they are very different in operation and performance. This (fifth) one is also my favor, because it has low and narrow capacitor voltage. The last one is simple, but its inherent advantages are anti-inrush and overcurrent protection.
As for as converters, we have three basic PFC approaches,one is second is . The last one is******
As for as converters, we have three basic PFC approaches,one is second is . The last one is******
As for as converters, we have three basic PFC approaches,one is second is . The last one is******In conventional AC/DC PFC converters, power is processed serially by PFC and DC/DC two power stages. So the overall efficiency is given by the product of two-stage efficiencies, i.e., Where and are the efficiencies of two stages respectively.In fact, for the purpose of achieving PFC and DC/DC voltage regulation, it is no necessary to process all the input power by both stages. Intuitively, partial input power can be forward directly to the load through one converter stage. Suppose is the ratio at which power is transferred to the output just through PFC stage. Then, the efficiency of the proposed structure can be expressed as: Obviously the overall efficiency can be improved effectively by minimizing the power fraction that been processed twice.
As for as converters, we have three basic PFC approaches,one is second is . The last one is******
As for as converters, we have three basic PFC approaches,one is second is . The last one is******