Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
Ben-Gurion University of the Negev – 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
Ben-Gurion University of the Negev – Power Electronics Laboratory
The Shading Problem in Serially Connected Arrays
• Shading strongly affects the MPP current
• Panels with different light exposures connected in series can’t all be in MPP 0
50100150200250
300350400
450
0 20 40 60 80
3 Serial Connected PVs With Bypass Diodes
𝑉𝐿 [𝑉]
𝑃𝐿 [w]
A PV Panel’s I-V characteristics for various Insolation levels
September 20, 2012 2
150W
Ben-Gurion University of the Negev – 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
Ben-Gurion University of the Negev – Power Electronics Laboratory
Current Bypass– Overview
September 20, 2012 4
Using
1 − 𝐷 ⋅ 𝑉𝑎𝑣1 = 𝐷 ⋅ 𝑉𝑎𝑣2
𝑛 = 1
Bypass route can only be an energy source!
𝑉 ⋅ 𝐼 > 0
𝑉1𝑎𝑣 = 𝑛 𝑉2𝑎𝑣
Local Current Transfer Current Distribution
𝑉𝑎𝑣2𝐼𝑎𝑣2
=𝛼 00 𝛼
𝑉𝑎𝑣1𝐼𝑎𝑣1
Ben-Gurion University of the Negev – Power Electronics Laboratory
Voltage Equalizing – The Concept
MPP for different shadings share approximately the same voltage
September 20, 2012 5
A PV panel’s I-V and P-V characteristics for various Insolation levels
Ben-Gurion University of the Negev – Power Electronics Laboratory
Objective
• Evaluate a cost-effective shading problem solution
• Use a simple implement SCC modules
• Achieve high efficiency with voltage equalization
• Provide design guidelines
September 20, 2012 6
Ben-Gurion University of the Negev – Power Electronics Laboratory
Basic Implementation
Equalizing SCC modules Average model for the EQSCC
September 20, 2012 7
Ben-Gurion University of the Negev – Power Electronics Laboratory
Hard Switched Capacitor Average Model
𝑅𝑒 =1
2𝑓𝑆𝐶1⋅ coth
𝛽12
𝑅𝑒1
+ 1
2𝑓𝑆𝐶2⋅ coth
𝛽22
𝑅𝑒2
, 𝛽𝑖 =𝑡𝑖𝑅𝑖𝐶𝑖
≈1
2𝑓𝑠𝑅𝑖𝐶𝑖𝑖 = 1,2
• A good 𝛽 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
𝑅𝑒𝑖∗ → 2
N.C
C.C
𝑡𝑖 ≫ RiCi 𝑡𝑖 ≈ RiCi 𝑡𝑖 ≪ RiCi
𝑅𝑒𝑖∗ =
𝑅𝑒𝑖𝑅𝑖
𝑓𝑠∗ = 𝑓𝑠𝑅𝑖𝐶𝑖
𝑅𝑖 − charge/discharge Ohmic loop resistance 𝐶𝑖 − charge/discharge loop capacitance
Ben-Gurion University of the Negev – Power Electronics Laboratory
𝜔0𝑖 =1
𝐿𝑖𝐶𝑖; 𝑸𝒊 =
𝝎𝟎𝒊𝑳𝒊
𝑹𝒊=
1
𝑅𝑖
𝐿𝑖𝐶𝑖
𝜙𝑖 =𝜋
2 ∙ 4𝑄𝑖2 − 1
; 𝑖 = 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
𝑅𝑒𝑖∗ =
𝑅𝑒𝑖𝑅𝑖
𝑅𝑖 − charge/discharge Ohmic loop resistance 𝐶𝑖 − charge/discharge loop capacitance 𝐿𝑖 − charge/discharge loop inductance 𝑅𝑒 = 4𝑄1
2𝑅1 ⋅ 𝜙1 ⋅ tanh 𝜙1𝑅𝑒1
+ 4𝑄22𝑅2 ⋅ 𝜙2 ⋅ tanh 𝜙2
𝑅𝑒2
Ben-Gurion University of the Negev – 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
Ben-Gurion University of the Negev – Power Electronics Laboratory
Peristaltic Relations
Assuming panels’ voltages is approximately equal:
• 𝐼𝐷 𝑘=
𝐼𝑂−𝐼𝑆
𝑁𝑘 , 𝑘 < 𝑆
𝐼𝑂−𝐼𝑆
𝑁𝑁 − 𝑘 , 𝑘 ≥ 𝑆
• 𝐼𝐿 =𝑁−1 𝐼𝑂+𝐼𝑆
𝑁
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
Ben-Gurion University of the Negev – 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
𝜂 =𝑃𝑜𝑢𝑡
𝑃𝑙𝑜𝑠𝑠 + 𝑃𝑜𝑢𝑡 𝑃𝑙𝑜𝑠𝑠 = 𝐼𝐷𝑖
2 𝑅𝑒𝑖𝑖
Is/IO=0.625
90
92
94
96
98
100
2 5 8 11 14
η [%]
n
Ben-Gurion University of the Negev – 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
𝜂 =𝑃𝑜𝑢𝑡
𝑃𝑙𝑜𝑠𝑠 + 𝑃𝑜𝑢𝑡 𝑃𝑙𝑜𝑠𝑠 = 𝐼𝐷𝑖
2 𝑅𝑒𝑖𝑖
Is/IO=0.125
90
92
94
96
98
100
2 5 8 11 14
η [%]
n
Ben-Gurion University of the Negev – Power Electronics Laboratory
Prototype Power Stage Diagram
September 20, 2012 14
DC Restorers
Drivers SCC
Ben-Gurion University of the Negev – Power Electronics Laboratory
Design Considerations – Resonant SCC
Rtotal - Designed according to maximum allowable power loss:
Rtotal ≤𝑃𝑙𝑜𝑠𝑠𝑚𝑎𝑥
5 𝐼𝐷2𝑚𝑎𝑥
L – Chosen or estimated according to switching frequency, providing 𝑄 ≈ 1:
𝐿 =𝑅
2𝜋𝑓𝑠 or 𝑓𝑠 =
𝑅
2𝜋𝐿
C – Was chosen providing desired resonant frequency:
𝐶 ≈1
4𝜋2𝑓𝑠2𝐿
CBulk – Was chosen according to maximum allowable voltage ripple:
𝐶𝐵 ≈𝐼𝐷𝑚𝑎𝑥
2𝑓𝑆𝑉𝑟𝑝𝑝
September 20, 2012 15
Ben-Gurion University of the Negev – Power Electronics Laboratory September 20, 2012 16
Experimental Results – Differential Current
September 20, 2012 16
1st Generation EQSCC
2nd Generation EQSCC
Ben-Gurion University of the Negev – Power Electronics Laboratory
Experimental Results – Differential Current
September 20, 2012 17
Discharging
Charging
ID
Charging and Discharging Current to Average Differential Current
Ben-Gurion University of the Negev – Power Electronics Laboratory
Simulation – Power Improvment
Using only bypass diodes: – Complicate MPPT implementation (Multiple Power Points) – Lower Maximum Power Point
Using the EQSCC: – 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
Ben-Gurion University of the Negev – Power Electronics Laboratory
Experimental Results – Power Improvment
Using only bypass diodes: – Complicate MPPT implementation (Multiple Power Points) – Lower Maximum Power Point
Using the EQSCC: – 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
Ben-Gurion University of the Negev – Power Electronics Laboratory
Simulation – 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
η
Irradiance Ratio
𝜂𝑟 =𝑃𝑚𝑝𝑝 𝑙𝑜𝑎𝑑
𝑃𝑚𝑝𝑝 𝑝𝑣1 + 𝑃𝑚𝑝𝑝 𝑝𝑣2⋅ 100%
Theoretical and experimental efficiency curves for 2 panels, one with irradiation swept from 0% to 100%
66%
Ben-Gurion University of the Negev – Power Electronics Laboratory
Experimental Results – 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
η
Irradiance Ratio 65%
78%
𝜂𝑟 =𝑃𝑚𝑝𝑝 𝑙𝑜𝑎𝑑
𝑃𝑚𝑝𝑝 𝑝𝑣1 + 𝑃𝑚𝑝𝑝 𝑝𝑣2⋅ 100%
Theoretical and experimental efficiency curves for 2 panels, one with irradiation swept from 0% to 100%
Ben-Gurion University of the Negev – 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
Ben-Gurion University of the Negev – Power Electronics Laboratory
Thank You for Your Attention!
September 20, 2012 23
Ben-Gurion University of the Negev – Power Electronics Laboratory
Driver Design Approach
• R-C considerations for the DC Restorer:
– 𝐶𝑏𝑢𝑓𝑓 ≫ 𝐶𝑔𝑎𝑡𝑒
– 𝐶𝑏𝑢𝑓𝑓 ⋅ 𝑅𝑏𝑙𝑒𝑒𝑑 ≫1
𝑓𝑆
• An added loop capacitor minimizes the ground loop impedance.
September 20, 2012 24
N-type circuit
P-type circuit
Ben-Gurion University of the Negev – 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
Ben-Gurion University of the Negev – 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
Ben-Gurion University of the Negev – 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.
Ben-Gurion University of the Negev – 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.