design and evaluation of modular resonant switched capacitors
TRANSCRIPT
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Ben-Gurion University of the Negev β Power Electronics Laboratory
DESIGN AND EVALUATION
OF A MODULAR RESONANT
SWITCHED CAPACITORS EQUALIZER
FOR PV PANELS
Shmuel (Sam) Ben-Yaakov, Alon Blumenfeld, Alon Cervera, and Michael Evzelman
Power Electronics Laboratory
Department of Electrical and Computer Engineering
Ben-Gurion University of the Negev
September 20, 2012 1
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Ben-Gurion University of the Negev β Power Electronics Laboratory
The Shading Problem in Serially Connected Arrays
β’ Shading strongly affects the MPP current
β’ Panels with different light exposures connected in series canβt all be in MPP 0
50100150200250
300350400
450
0 20 40 60 80
3 Serial Connected PVs With Bypass Diodes
ππΏ [π]
ππΏ [w]
A PV Panelβs I-V characteristics for various Insolation levels
September 20, 2012 2
150W
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Existing Solutions
September 20, 2012 3
Local Modules Central Current Compensation Local MPPT Implemented by DC-DC converters or part-time bypass circuitry
Local MPPT Creates a parallel power source, fed from the main BUS
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Current Bypassβ Overview
September 20, 2012 4
Using
1 β π· β πππ£1 = π· β πππ£2
π = 1
Bypass route can only be an energy source!
π β πΌ > 0
π1ππ£ = π π2ππ£
Local Current Transfer Current Distribution
πππ£2πΌππ£2
=πΌ 00 πΌ
πππ£1πΌππ£1
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Voltage Equalizing β The Concept
MPP for different shadings share approximately the same voltage
September 20, 2012 5
A PV panelβs I-V and P-V characteristics for various Insolation levels
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Objective
β’ Evaluate a cost-effective shading problem solution
β’ Use a simple implement SCC modules
β’ Achieve high efficiency with voltage equalization
β’ Provide design guidelines
September 20, 2012 6
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Basic Implementation
Equalizing SCC modules Average model for the EQSCC
September 20, 2012 7
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Hard Switched Capacitor Average Model
π π =1
2πππΆ1β coth
π½12
π π1
+ 1
2πππΆ2β coth
π½22
π π2
, π½π =π‘ππ ππΆπ
β1
2ππ π ππΆππ = 1,2
β’ A good π½ is around 1
September 20, 2012 8 September 20, 2012 8
1 102
4
6
8
10
fs
tti
ti i
0.1
eRi
*
*
P.C
π ππβ β 2
N.C
C.C
π‘π β« RiCi π‘π β RiCi π‘π βͺ RiCi
π ππβ =
π πππ π
ππ β = ππ π ππΆπ
π π β charge/discharge Ohmic loop resistance πΆπ β charge/discharge loop capacitance
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Ben-Gurion University of the Negev β Power Electronics Laboratory
π0π =1
πΏππΆπ; πΈπ =
ππππ³π
πΉπ=
1
π π
πΏππΆπ
ππ =π
2 β 4ππ2 β 1
; π = 1,2
September 20, 2012 9
Q i
0 5 102
2.5
3
3.5
1 3
*eR i
Soft Switched Capacitor Average Model
A good Q factor is around 1
π ππβ =
π πππ π
π π β charge/discharge Ohmic loop resistance πΆπ β charge/discharge loop capacitance πΏπ β charge/discharge loop inductance π π = 4π1
2π 1 β π1 β tanh π1π π1
+ 4π22π 2 β π2 β tanh π2
π π2
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Peristaltic Relations
September 20, 2012 10
(3)
(2)
(1)
Current is delivered from adjacent panel and from neighbouring EQSCC
The peristaltic process is then formed from the whole chain
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Peristaltic Relations
Assuming panelsβ voltages is approximately equal:
β’ πΌπ· π=
πΌπβπΌπ
ππ , π < π
πΌπβπΌπ
ππ β π , π β₯ π
β’ πΌπΏ =πβ1 πΌπ+πΌπ
π
September 20, 2012 11
-2.00 -1.00 0.00 1.00 2.00
I(D1)
I(D2)
I(D3)
I(D4)
I(D5)
I(D6)
I(D7)
50% shaded
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Power losses and Efficiency
September 20, 2012 12
Power extraction efficiency for a chain of length with one shaded PV in the center
With EQSCC
Shaded PV is in short-
circuit
Insolation ratio
π =πππ’π‘
ππππ π + πππ’π‘ ππππ π = πΌπ·π
2 π πππ
Is/IO=0.625
90
92
94
96
98
100
2 5 8 11 14
Ξ· [%]
n
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Power losses and Efficiency
September 20, 2012 13
Power extraction efficiency for a chain of length with one shaded PV in the center
With EQSCC
Shaded PV is in short-
circuit
Insolation ratio
π =πππ’π‘
ππππ π + πππ’π‘ ππππ π = πΌπ·π
2 π πππ
Is/IO=0.125
90
92
94
96
98
100
2 5 8 11 14
Ξ· [%]
n
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Prototype Power Stage Diagram
September 20, 2012 14
DC Restorers
Drivers SCC
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Design Considerations β Resonant SCC
Rtotal - Designed according to maximum allowable power loss:
Rtotal β€ππππ π πππ₯
5 πΌπ·2πππ₯
L β Chosen or estimated according to switching frequency, providing π β 1:
πΏ =π
2πππ or ππ =
π
2ππΏ
C β Was chosen providing desired resonant frequency:
πΆ β1
4π2ππ 2πΏ
CBulk β Was chosen according to maximum allowable voltage ripple:
πΆπ΅ βπΌπ·πππ₯
2ππππππ
September 20, 2012 15
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Ben-Gurion University of the Negev β Power Electronics Laboratory September 20, 2012 16
Experimental Results β Differential Current
September 20, 2012 16
1st Generation EQSCC
2nd Generation EQSCC
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Experimental Results β Differential Current
September 20, 2012 17
Discharging
Charging
ID
Charging and Discharging Current to Average Differential Current
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Simulation β Power Improvment
Using only bypass diodes: β Complicate MPPT implementation (Multiple Power Points) β Lower Maximum Power Point
Using the EQSCC: β The Multiple Power Point problem is solved, with a higher MPP
September 20, 2012 18
0
100
0 25 50
150 W
105 W
105 W
Po [W]
Vo [V] Theoretical and experimental Pout curves for 2 panels, one with about 50% shade
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Experimental Results β Power Improvment
Using only bypass diodes: β Complicate MPPT implementation (Multiple Power Points) β Lower Maximum Power Point
Using the EQSCC: β The Multiple Power Point problem is solved, with a higher MPP
September 20, 2012 19
0
100
0 25 50
150 W
105 W
105 W
Po [W]
Vo [V] Theoretical and experimental Pout curves for 2 panels, one with about 50% shade
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Simulation β Efficiency
The EQSCC increases efficiency Up to 50% September 20, 2012 20
60%
80%
100%
0 0.25 0.5 0.75 1
95%
With EQSCC
Ξ·
Irradiance Ratio
ππ =ππππ ππππ
ππππ ππ£1 + ππππ ππ£2β 100%
Theoretical and experimental efficiency curves for 2 panels, one with irradiation swept from 0% to 100%
66%
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Experimental Results β Efficiency
The EQSCC increases efficiency Up to 50% September 20, 2012 21
60%
80%
100%
0 0.25 0.5 0.75 1
95%
66%
97%
With EQSCC
Ξ·
Irradiance Ratio 65%
78%
ππ =ππππ ππππ
ππππ ππ£1 + ππππ ππ£2β 100%
Theoretical and experimental efficiency curves for 2 panels, one with irradiation swept from 0% to 100%
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Conclusions
The EQSCC processes only the differential power
Voltage equalization implies low voltage stress on switches
Power losses match the theoretical analysis
Smaller loop resistance will lead to higher efficiency
System can be embedded in to PV Panel
September 20, 2012 22
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Thank You for Your Attention!
September 20, 2012 23
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Driver Design Approach
β’ R-C considerations for the DC Restorer:
β πΆππ’ππ β« πΆπππ‘π
β πΆππ’ππ β π πππππ β«1
ππ
β’ An added loop capacitor minimizes the ground loop impedance.
September 20, 2012 24
N-type circuit
P-type circuit
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Ben-Gurion University of the Negev β Power Electronics Laboratory
IMPP as a Function of VMPP
V.V.R. Scarpa, G. Spiazzi, and S. Buso, "Low complexity MPPT technique exploiting the effect of the PV cell series resistance," Twenty-Third Annual IEEE Applied Power Electronics Conference and Exposition, (APEC 2008), pp. 1958-1964, 24-28 Feb. 2008.
September 20, 2012 25
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Central Current Feedback
Y. Nimni and D. Shmilovitz, "A returned energy architecture for improved photovoltaic systems efficiency," Proceedings of 2010 IEEE International Symposium on Circuits and Systems (ISCAS 2010), pp. 2191-2194, May 30 2010-June 2 2010.
September 20, 2012 26
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Central Current Feedback
T. Shimizu, M. Hirakata, T. Kamezawa, and H. Watanabe, "Generation control circuit for photovoltaic modules," IEEE Transactions on Power Electronics, vol. 16, no. 3, pp. 293-300, May 2001.
September 20, 2012 27
Circuit configuration of GCC based on a dc/dc converter.
Circuit configuration of GCC based on a multistage chopper.
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Ben-Gurion University of the Negev β Power Electronics Laboratory
Buck-Boost Implementation Example
P.S. Shenoy, B. Johnson, and P.T. Krein, "Differential power processing architecture for increased energy production and reliability of photovoltaic systems," Twenty-Seventh Annual IEEE Applied Power Electronics Conference and Exposition, (APEC 2012), pp. 1987-1994, 5-9 Feb. 2012.
September 20, 2012 28
Differential power converters using a buck-boost topology connected to neighboring nodes. Differential power processing architecture.