A Zero-Voltage-Switching, Physically Flexible Multilevel

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