A Zero-Voltage-Switching, Physically Flexible Multilevel GaN DC-DC Converter
Derek Chou, Yutian Lei, and Robert Pilawa-Podgurski
University of Illinois at Urbana-ChampaignPresented by: Derek Chou
Outline
Motivation Hardware Design Zero-Voltage Switching Experimental Results Future Work
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Motivation – Lightweight, flexible power converter
Wind turbine tip de-icing Deliver high power de-icing capabilities
while conforming to aerodynamic constraints
Electric machine exterior Deliver high power in a small and
conformal package 3D cooling structures Aerospace applications Resistant to thermal cycling Lightweight, high specific and
volumetric power density Research goals High power density High efficiency, electrical & thermal Lightweight
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Source: http://www.plainswindeis.anl.gov/
Source: Pilawa Group
Goal
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High power density power converter
Flexible PCB substrate
Images: Pilawa Research Group (left) http://www.directindustry.com/industrial-manufacturer/printed-circuit-board-flexible-90300.html (right)
Goal
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High power density power converter
Flexible PCB substrate
Images: Pilawa Research Group (left, bottom) http://www.directindustry.com/industrial-manufacturer/printed-circuit-board-flexible-90300.html (right)
Lightweight, flexible high power density power converter
Flexible PCBs
Polyimide substrate – flexible, high-voltage resistantMultiple copper layers possible Conform to 3D structures Thermal cycling resistant Soldered components not restricted by rigid substrate Need small passive components to leverage flexibility
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7-level FCML design Phase-shifted PWM
signals Natural capacitor
balancing Lower switch stress Smaller passive
components
Hardware Design – Flying Capacitor Multilevel Converter
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Vsw = Vin – VC3 + VC1= Vin – 3Vin/6 + Vin/6 = 4Vin/6
Vsw = Vin – VC5 + VC3= Vin – 5Vin/6 + 3Vin/6 = 4Vin/6
finductor = (N – 1) * fswitch
Hardware Design – Flying Capacitor Multilevel Converter
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Vin 5Vin / 6 4Vin / 6 3Vin / 6 2Vin / 6 Vin / 6
Zero-Voltage Switching
Turn on switches when VDS = 0 V Benefits Large reduction of switching losses Further reduce passive component size Very low switch stress
Challenges Higher-frequency switching Larger inductor ripple Full ZVS operation is dependent on load
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Zero-Voltage Switching
Turn on switches when VDS = 0 V Benefits Large reduction of switching losses Further reduce passive component size Very low switch stress
Challenges Higher-frequency switching Larger inductor ripple Full ZVS operation is dependent on load
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Zero-Voltage Switching
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t = ti1 to t = ti2
Both switches off (td,f); CS1B discharges through the inductor
Zero-Voltage Switching
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t = ti2
S1B turns on (ZVS)
Zero-Voltage Switching
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t = ti2 to t = ti3
(other switch pairs commutate)
Zero-Voltage Switching
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t = ti2 to t = ti3
(other switch pairs commutate)
Zero-Voltage Switching
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t = ti2 to t = ti3
(other switch pairs commutate) Inductor current is negative when t = ti3
Zero-Voltage Switching
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t = ti3
S1B turns off (ZVS), inductor current is negative
Zero-Voltage Switching
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t = ti3 to t = ti4
Both switches off (td,r); CS1B charges through the inductor
Zero-Voltage Switching
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t = ti4
S1A turns on (ZVS), inductor current is still negative
Zero-Voltage Switching
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t = ti4 to t = T Inductor current ramps up to positive value Cycle repeats after t = T
Zero-Voltage Switching
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Arbitrary switch pairs behave similarly ZVS achieved on all switch pairs
Zero-Voltage Switching
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Arbitrary switch pairs behave similarly ZVS achieved on all switch pairs
Zero-Voltage Switching
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Arbitrary switch pairs behave similarly ZVS achieved on all switch pairs
Zero-Voltage Switching
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Arbitrary switch pairs behave similarly ZVS achieved on all switch pairs
Hardware – Flexible PCB
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Side View
ZVS Control
Automatic ZVS control, as a function of output load Switching frequency controls ZVS operation Duty cycle controls output voltage
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Δippiout
ZVS Implementation
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Inductor current ripple maximized at certain duty ratios For a fixed switching frequency and input voltage, overall
current ripple decreases as number of levels, N, increases
Experimental Results – FCML ZVS
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Switching frequency 200-500 kHz at each switch Ripple frequency 1.2-3.0 MHz at the inductor D = 0.58, D = 0.25 Inductor ripple current maximized
Current Ripple Characteristics for 7-level FCML
Experimental Results
Automatic ZVS control, D = 0.58 vs D = 0.25
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Vin = 200 V, Vout = 116 V, D = 0.58 or D = 0.25, fsw = 200-500 kHz
Experimental Results
Variable frequency – high efficiency over wide load range Fixed frequency only achieves ZVS in a narrow range
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Vin = 200 V, Vout = 116 V, D = 0.58, fsw = 200-500 kHz
Experimental Results
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Parameter Notes Value
Output Power Tested 250 W
Switching Frequency Per Switch 200–500 kHz
Effective Frequency At Inductor 1.2–3.0 MHz
Weight Excl. controller 17.5 g
Volumetric Power Density Bounded by prism 109 W/in3 (6.65 W/cm3)
Volumetric Power Density Excl. empty space 902 W/in3 (6.65 W/cm3)
Specific Power Density Excl. controller 14 kW/kg
Conclusions
ZVS possible for FCML converters Thermal management of high power density
converters Flexible PCB allows for mechanical compliance and
routing of electrical signals in the 3D space 3D electro-mechanical integration for heatsinking Further layout development for optimization of FCML
operations
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Choice of Passive Components
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70 mJ of capacitor energy storage
70 mJ of inductor energy storage
Experimental Results – Loss Distribution
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Pout = 150 W, D = 0.58 ZVS – heat concentrated in inductor Hard switching – heat concentrated in switches
ZVS Hard switching