high step-up flying capacitor multilevel converters
TRANSCRIPT
Outlines
βͺMotivation
βͺ Comparison between boost and FCMLβͺ Switchesβͺ Inductors
βͺ Loss calculation and reduction
βͺ Conclusion and future works
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Motivation β Compact High Voltage DC Generation
βͺ Satellite Propulsion Systemβͺ Ion Thruster Unit
βͺ Pulse Electric Field (PEF)βͺ Food and beverage
preservation
βͺ Research Goalsβͺ 100βs V to 1 kV Output, 1 kW
power converterβͺ High power densityβͺ High efficiency
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Source: elea-technology.eu
Source: NASA
Boost converters- switches
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ILβπΌπΏ
π·ππ π€ ππ π€
VL
πΌππ
πππ
πππ β πππ’π‘
IL β
+ -
π·ππ π€ ππ π€
Vout
βͺ 1 kV, 10 A
βͺ High blocking voltage:βͺ Large Rds_on -> conduction lossβͺ Large Qg, Qoss-> switching loss
βͺ Thermal βͺ Hard to cool a single hot spot
βͺ Availability?
FCML Boost Converters- switches
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1
6πππ’π‘
2
6πππ’π‘
3
6πππ’π‘
4
6πππ’π‘
5
6πππ’π‘
βͺ Natural balancing of flying capacitors
βͺ S1 open: ππ π€ = ππ1 =1
6πππ’π‘
βͺ S2 open: ππ π€ = ππ2 β ππ1
=2
6πππ’π‘ β
1
6πππ’π‘
βͺ Switch Rating: 1
6πππ’π‘, 10 A
βͺ 7-level Flying Capacitor Multilevel Converter
βͺ 166 V, 10 A
βͺ Lower voltage rating:βͺ Lower Rds_onβͺ Lower Qg
βͺ Thermalβͺ Heat is distributed to more switches
βͺ Availabilityβͺ More likely to find in stockβ¦
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FCML Boost Converters- switches
FCML Boost Converters- switches
βͺ EPC 2034, GaN
βͺ 200 V, 48 A
βͺ Rds_on =7 mOhm
βͺ Qg = 8.8 nC
βͺ Size: 0.18 X 0.1 inch2
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βͺ IXYS, IXFR26N100P, MOSFET
βͺ 1 kV, 15 A
βͺ Rds_on = 430 mOhm
βͺ Qg = 197 nC
βͺ Size: 0.62 X 0.54 inch2
Boost Converters- sizing the inductor
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ILβπΌπΏ
π·ππ π€ ππ π€
πΌπππ₯
πΌπππ
β’ πΏ =π·πππ
βπΌπΏππ π€
β’ πΌπππ₯ = πΌππ +βπΌπΏ
2
β’ πΈππππ =1
2πΏπΌπππ₯
2
β’ πΈππππ β€ πΈπΏ, πππ₯ = ππΏππππΏ
Higher switching loss, gate driving loss etc.
Higher RMS conduction loss, core loss.
ππ π€β
β β
π β
β’ πΈππππ =π·πππ
2ππ π€π(πΌ)
β’ Where π πΌ =1
πΌ+
πΌ
4+ 1, (0 < πΌ β€ 2)
Inductor energy density: ππΏ=πΈπΏ, πππ₯
ππππΏ=
π΅π ππ‘2
2π
Current ripple ratio: πΌ =βπΌ
πΌππ
βπΌ β (π πΌ β)
βͺ πΈππππ β β ππππΏ ββπ β
βͺ For a given ππ π€, πΈππππ, πππ =π·πππ
ππ π€(πΌ = 2, largest current ripple).
Thinking process:
Conclusions:
FCML Boost Converter- sizing the inductor
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βͺ 7-level Flying Capacitor Multilevel Converter
βͺ πΈππππ, ππππ π‘ =π·πππ
2ππ π€π πΌ
0
0.2
0.4
0.6
0.8
1
2 3 4 5 6 7 8 9 10
Norm
aliz
ed I
nduct
or
Volu
me
FCML Level
Normalized Inductor Size v.s. FCML Level
(D=0.9)
13.5x reduction
Total Passive Component Volume
1
6πππ’π‘
2
6πππ’π‘
3
6πππ’π‘
4
6πππ’π‘
5
6πππ’π‘
β πΈππππ, ππππ =1 β 1 β π· π β 1 πππ
2ππ π€ π β 1π(πΌ)
Y. Lei, W-C Liu, R.C.N. Pilawa-Podgurski, βAn Analytical Method to Evaluate and Design Hybrid Switched-Capacitor and Multilevel Converters,β IEEE Transactions on Power Electronics, in press
βͺ Effective switching frequency βͺ D to (1-(1-D)(N-1))
βͺ Effective duty ratioβͺ fsw to (N-1)fsw
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βͺ πΈππππ, ππππ π‘ =π·πππ
2ππ π€π πΌ β πΈππππ, ππππ =
1 β 1 β π· π β 1 πππ2ππ π€ π β 1
π(πΌ)
FCML Boost Converter- sizing the inductor
Energy transfer and delivery (D=0.8)
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10 J 8 J
2 J
10 J
4 J
1 J
10 J
3 J
4 J
1 J
2 J
3 J
2 J
Source Load
Conventional Boost Converter
Conventional Boost Converter:Switch twice as fast
inductor source
3-level FCML
Hardware Prototype
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DiodesGaNSwitches
Isolated DC-DC for gate drivers
Flying capacitorsInductor Digital Isolators
Input
Input
Z. Liao, Y. Lei and R.C.N. Pilawa-Podgurski βA GaN-based Flying-Capacitor Multilevel Boost Converter for High Step-up Conversion,β IEEE Energy Conversion Congress and Exposition, Milwaukee, WI, 2016
Loss distribution
βͺ Conduction lossβͺ Rds_on ,diode Ron and inductor DCR
βͺ Switching lossβͺ Overlap loss and reverse recovery loss
βͺ Inductor core lossβͺ Current ripple and switching frequency
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p-n junction reverse recovery βͺ Parameters we care about:βͺ Peak reverse current : Irrm
βͺ Total reverse recovery charge : Qrr
βͺ Total reverse recovery time : trr
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Diodes in hard-switched boost converters
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Vsw
Ifet
t0 t2 t4
πππ = ππ π€ π‘πππΌππ + πππ ππ π€
πΈππ = ππ π€πΌπππ‘ππ + ππ π€πππ
βͺ Reverse recovery increases switching loss because:βͺ Longer switching transition: trr
βͺ Extra charge: Qrr
Iin
Qrr
Reduction of reverse recovery
βͺ Parallel diodes
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βͺ Both Qrr and trr increase with temperature
βͺ Temperature increases with input current
βͺ Wrrβ IinN
, (N>1). Paralleling diode should reduce Wrr .
βͺ I assumed linear relationship between πππ, π‘ππ and Iin, so N = 2
πππ = πππ’π‘ π‘πππΌππ + πππ ππ π€πππ, π‘ππ β πΌππ
Comparison
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[1] [2] [3] FCML Boost
Rated power 450 W 250 W 2 kW 820 W
Input voltage 25- 30 V 28- 38 V 275 V 100 V
Max outputvoltage
400 V300 β980 V
2 kV 1 kV
Switching Frequency
100 kHz 100 kHz 13.56 MHz 72 kHz
Peak efficiency
96% 97% 84% 94.1%
Overall powerdensity 38 W/in3 19 W/in3 250 W/in3
337 W/in3
19Power Density
Efficiency
[1] L. MΓΌller and J. W. Kimball, βHigh gain dcdc converter based on the cockcroftwalton multiplier,β IEEE Transactions on Power Electronics,vol. 31, pp. 6405β6415, Sept 2016.[2] M. Kim, D. Yang, and S. Choi, βA fully soft-switched single switch isolated dc-dc converter,β in 2014 IEEE Applied Power ElectronicsConference and Exposition - APEC 2014, pp. 1106β1111, March 2014.[3] L. Raymond, W. Liang, K. Surakitbovorn, and J. Davila, β27.12 mhz isolated high voltage gain multi-level resonant dc-dc converter,β inEnergy Conversion Congress and Exposition (ECCE), 2015 IEEE, pp. 5074β5080, Sept 2015.
Improvements- QSW-ZVS
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t1 t2 t4
βͺ ZVS turn-on of FET
βͺ Qrr and Qoss of FET are both discharged back to the input source
βͺ Trade-offs:βͺ High RMS conduction loss and peak current
βͺ High core loss
βͺ Variable frequency control
βͺ Operating at shallow DCM
βͺ For FCML Boost
πΏππΉπΆππΏ β€ 0.5 1 β π· 2 π· βπ β 2
π β 1π ππ’π‘ β¦(π· >
π β 2
π β 1)
QSW-ZVS
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Hard-Switching QSW-ZVS
Pin= 108.68 WPout= 101.99 WSwitching Frequency: 69 kHzInductor: 4 uH
Pin = 106 WPout = 100 WSwitching Frequency: 72 kHzInductor: 22 uH
βͺ Switches are cooler: switching loss β > conduction loss β
βͺ Need better inductor design for lower core loss
Conclusions
βͺ FCML:βͺ Lower rating deviceβͺ Smaller inductor
βͺ Improvements:βͺ Soft-switching techniquesβͺ Better inductor design
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