High Power Capacitive Power Transfer for Electric...
Transcript of High Power Capacitive Power Transfer for Electric...
Chris Mi, Ph.D, Fellow IEEEProfessor and Chair, Dept. Electrical and Computer Engineering
Director, DOE GATE Center for Electric Drive TransportationSan Diego State University, (619)594-3741; [email protected]
High Power Capacitive Power Transfer for Electric Vehicle
Charging Applications
1
Contents
1.Motivation
2.Double-sided LCLC Compensation Topology
3.Capacitive Coupler Structure
4.Prototypes and Experimental Results
5.System Improvements
6.Conclusion and Future Work2
San Diego State University (SDSU)
• Located in San Diego, California• Ranked the best city in the world in terms of
climate• Full time equivalent students ~30,000, head
count over 50,000• Joint Ph.D program with UC San Diego• Ranked 149 in the US News Report for all US
Universities• Some programs ranked top 20 in the US• ECE department has 4 IEEE Fellows
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GATE Center for Electric Drive Transportation
• US Department funded Graduate Automotive Technology Education Center of Excellence
• There are total 7 centers in the US• Funds of DOE is supplemented by industrial
support• Produce the best automotive graduates by
offering fellowship and research opportunities
Sustainable Power and Energy Research Center (SPARC)
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Capacitive vs. Inductive Power Transfer CPT System Structure
IPT System Structure
Electric field is not sensitive to metal material nearby Electric field does not generate eddy-current loss in the metal Capacitive coupler uses metal plates, instead of Litz-wire, to reduce system c6
Limitations of Recent CPT Systems Low Power Capacity (Desk Lamp[1] and Soccer Robot[2])
Short Distance (Vehicle Charging[3] and Motor Excitation[4])
[1] C. Liu, A.P. Hu, N.C. Nair, “Coupling Study of a Rotary Capacitive Power Transfer System,” 2009 IEEE ICIT, 1-6.[2] A.P. Hu, C. Liu, H. Li, “A Novel Contactless Battery Charging System for Soccer Playing Robot,” 2008 IEEE M2VIP, 646-650.[3] J. Dai, D.C. Ludios, “Wireless Electric Vehicle Charging via Capacitive Power Transfer through a Conformal Bumper,” 2015 IEEEAPEC, 3307-3313.[4] D.C. Ludois, M.J. Erickson, J.K. Reed, “Aerodynamic Fluid Bearing for Translational and Rotating Capacitors in NoncontactCapacitive Power Transfer Systems,” IEEE Transactions on Industrial Electronics, Vol 50, 2014, 1025-1033.
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Reason of Limitations Series Compensation[5]
Class-E Compensation[6]
PWM Converter[7]
Pros: simplicity Cons: capacitance is limited by fsw
Pros: frequency can be 10’s MHz Cons: power level is limited
Pros: power can be kW level Cons: capacitance is limited by fsw
[5] C. Liu, A.P. Hu, G.A. Covic, N.C. Nair, “ComparativeStudy of CCPT Systems with Two Different Inductor TuningPositions,” IEEE Transactions on Power Electronics, Vol 27,2012, 294-306.
[6] H. Liang, A.P. Hu, A. Swain, X. Dai, “Comparison of TwoHigh Frequency Converters for Capacitive Power Transfer,”2014 IEEE ECCE, 5437-5443.
[7] J. Dai, D.C. Ludios, “Single Active Switch PowerElectronics for KiloWatt Scale Capacitive Power Transfer,”IEEE Journal of Emerging and Selected Topics in PowerElectronics, Vol 3, 2015, 315-323. 8
Challenges of CPT for EV Charging Small Coupling Capacitance
20.891 1
1[1 2.343 ( / ) ] 36.7pFsl
C d ld
An Example: Plates Size l1=610mm (24in) Distance d=150mm Coupling capacitance of parallel plates is[8]:
[8] H. Nishiyama, M. Nakamura, “Form and Capacitance of Parallel Plate Capacitor,” IEEE Transactions on Components, Packing, andManufacturing Tech-Part A, Vol 17, 1994, 477-484.
The former compensation topologies are not suitable to transfer HIGH power with so SMALL coupling capacitance Series topology: requires too large inductance or too high switching frequency Class-E topology: cannot provide enough output power PWM topology: cannot provide high enough switching frequency
NEW Compensation Topology is Required! 9
Double-sided LCLC Circuit Topology
Full-bridge inverter provides square-wave excitation
Full-bridge rectifier feeds dc current to battery load
Two inductors are two capacitors are used at each side
P1 and P2 are at the primary side, P3 and P4 are at the secondary side
P1 and P3 form a coupling capacitor, P2 and P4 form the other capacitor11
Fundamental Harmonics Approximation
Square-wave input and output contains fundamental and high-order
harmonics
Lf1-Cf1, Lf2-Cf2 work as low pass filters
Input and output are represented by sinusoidal waveforms
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Superposition Theorem Excited Only by Primary (Contains Two Parallel Resonances)
1 2 1 2
1 1 2 2
1 11 2
1 1 0
2 2 20
0
/ ( )/ ( )
1
1
2
s s s s s
p s s
f p
f p
f f
sw
C C C C CC C C C C C
C CL
C C
L C
f
L1, Cf1, Cp1 form one parallel resonance
Lf2, Cf2 form the other parallel resonance
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Superposition Theorem Excited Only by Primary (Contains Two Parallel Resonances)
Output Current I2 only depends on Input Voltage V1
12121
11
1
1
2
21
2
22
11
11
1
11
11
11
11
/1/1/1
/1/1/1
)/(1)/(1
)/(1)/(1
VCCCCCC
CCV
CC
CCCV
CCCV
VCC
VCj
CjV
CjLjCj
V
VV
ss
fs
p
f
sC
sC
p
f
f
p
p
pC
Cf
Output Current 121212
1
2
22 )(
VCCCCCCLj
CCLj
VI
ssf
fs
f
Cf
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Superposition Theorem Excited Only by Secondary (Contains Two Parallel Resonances)
1 2 1 2
2 2 1 1
2 22 2
2 2 0
1 1 20
0
/ ( )/ ( )
1
1
2
s s s s s
p s s
f p
f p
f f
sw
C C C C CC C C C C C
C CL
C C
L C
f
L2, Cf2, Cp2 form one parallel resonance
Lf1, Cf1 form the other parallel resonance
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Superposition Theorem Excited Only by Secondary (Contains Two Parallel Resonances)
Input Current I1 only depends on Output Voltage V2
22121
22
2
2
1
12
1
11
22
21
2
22
22
22
22
/1/1/1
/1/1/1
)/(1)/(1
)/(1)/(1
VCCCCCC
CCV
CC
CCCV
CCCV
VCC
VCj
CjV
CjLjCj
V
VV
ss
fs
p
f
sC
sC
p
f
f
p
p
pC
Cf
Input Current 221211
2
1
12 )(
VCCCCCCLj
CCLj
VI
ssf
fs
f
Cf
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System Power of FHA Analysis
At input inverter side, V1 and I1 are in phase At output rectifier side, V2 and (–I2) are in phase Neglect passive components losses, the system power is expressed as:
0 1 2 0 1 21 2
1 2 1 2 1 2 1 2
2 2 2 2s f f s f fin out in out
s s s s
C C C C C CP P V V V V
C C C C C C C C C C C C
If there exists C1,2>>Cs1 2
01 2
2 2 2 2f fin out s in out
C CP P C V V
C C
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3D Dimensions of the Plates
An Example: Square plates are used and the size l1=610mm The plates distance d=150mm The thickness of the plate is 2mm The separation between two pairs dc=500mm to reduce the cross-coupling19
X-Y Direction Misalignment Each pair of plates are modeled by a
coupling capacitor
The cross-couplings of P1-P4, P2-P3
are small and neglected
The variation of Cs1,2 with the X
direction misalignment:
Coupling capacitor is not sensitive to misalignment
0 50 100 150 200 250 30030
32
34
36
38
Misalignment(mm)
Capa
cita
nce(
pF)
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Distance Variation at Z Direction All the cross-couplings are neglected
The distance d increase to 300mm,
double the original distance
Coupling capacitance decrease to 67% of the original value,
when distance is doubled
150 200 250 30020
25
30
35
40
Distance(mm)
Capa
cita
nce(
pF)
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0 0.5 1 1.5 2-300-150
0150300
V 1(V)
Time(s)
0 0.5 1 1.5 2-300-150
0150300
V 2(V)
Time(s)
0 0.5 1 1.5 2
-10
0
10
I 1(A)
V1
I1
0 0.5 1 1.5 2
-10
0
10
I 2(A)
V2
I2
Parameter Design and Simulation A 2.4kW CPT system is designed with parameters in the following table.
Vin Vout fsw Lf1 (Lf2) Cf1 (Cf2) C1 (C2) Cs1(Cs2) L1 L2
265V 280V 1MHz 11.6μH 2.18nF 100pF 36.7pF 231μH 242μH
Circuit simulation is shown below
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Voltage and Current Stress Voltage are current stress are calculated by the previous FHA analysis
Components Lf1 (Lf2) Cf1 (Cf2) C1 (C2) L1(L2) Plates
Voltage 1.0 kV 1.0 kV 7.2 kV 7.2 kV 3.2 kV
Current 15.5 A 15.0 A 4.8 A 5.2 A 0.7 A
Inductors are wound with multiple turns to reduce voltage stress
between turns
Multiple capacitors are connected in series to form C1 and C2
Multiple capacitors are connected in parallel to form Cf1 and Cf2
The electric field in this system is 3.2kV/150mm, and the breakdown
field of air is about 3.0kV/mm. Therefore, there is no concern of arcing24
Leakage Field Strength
At 1MHz, the human exposure to electric field should be lower than
614V/m for safety concern[9]
The safe area for this system is about 0.6m away from the plates
Future study will reduce the radiation of electric field to the environment[9] IEEE Stand for safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3kHz to 300GHz, C95.1, 2005.
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Prototype Design
Plates are made by aluminum sheets
Inductors are wound by AWG46 Litz-wire without magnetic core
High-power-frequency thin film capacitors resonate with the inductors
Silicon Carbide (SiC) MOSFETs C2M0025120D are used in the inverter
SiC diodes IDW30G65C5 are used in the rectifier 26
Experimental Results Pout=2.4kW at designed input/output
The experimental waveform is the
same with the simulations
Soft-switching is achieved
There is high frequency noise on the
driver signal
Most of the power losses distribute on
the capacitors and plates
If the inductors are wound on magnetic
core, the system efficiency will drop
1%-3%.
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Tolerance to Misalignment and Distance Output Power maintains 2.1 kW at 300 mm X axis misalignment
0 0.5 1 1.5 2 2.586
87
88
89
90
91
Pout (kW)
Effic
ienc
y (%
)
No Mis100mm200mm300mm
Output Power maintains 1.7 kW at 300 mm Z axis distance
0 0.5 1 1.5 2 2.586
87
88
89
90
91
Pout (W)
Effic
ienc
y (%
)
150mm200mm250mm300mm
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Vertical Plate Structure
A compact plate structure
includes four plates that are
vertically arranged
This structure is robust to the
rotation misalignment
The distance d=150mm
The plate distance dc is much
smaller than d
The cross-couplings between
the plates should be considered
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LCL Compensation Topology
Compensation topology is simplified
The LCL compensation circuit is used to resonate with the
plates, instead of the LCLC topology31
IPT+CPT Combined System
The two inductors L1 are L2 are inductively coupled
The system utilized both electric and magnetic fields to transfer power
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Experiments of IPT+CPT Combined System
Coil size: 320×320mm
Plate size: 610×610mm
Only LC compensation
network is required at each
side
At nominal input and
output condition,
PIPT=2000W, and
PCPT=800W
The system also has good
misalignment ability 0 500 1000 1500 2000 2500 3000
90
92
94
Output Power (W)
Effic
ienc
y (%
)
No Mis10cm Mis15cm Mis20cm Mis
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Conclusion and Future Work
1. Capacitive power transfer has become practical for
electric vehicle charging application
2. The double-sided LCLC compensation circuit topology
is suitable to increase the power level of CPT system
3. The plate structure can be improve to enhance the
misalignment ability of CPT system
4. Future work will study the radiation of the CPT system
and come up with effective shielding method,
integrated IPT+CPT, etc.34