development of a solar panels curve characterizer – hardware
TRANSCRIPT
GESEP – Ger cia de Especialistas e Siste as El tricos de Pot cia
Título:DEVELOPMENT OF A SOLAR PANELS CURVE CHARACTERIZER - HARDWARE AND SOFTWAREAutores:CAMPOS, E. L. F. ; Adria o da Silva A to io ; OLIVEIRA, L. O. M. ; SANTOS, G. V. ; PEREIRA, H. A.Pu li ado em:Si pósio Brasileiro e Siste as Elétricos - SBSEData da pu li ação:
4Citação para a versão pu li ada:CAMPOS, E. L. F. ; Adria o da Silva A to io ; OLIVEIRA, L. O. M. ; SANTOS, G. V. ; PEREIRA, H. A. .DEVELOPMENT OF A SOLAR PANELS CURVE CHARACTERIZER - HARDWARE AND SOFTWARE. I :Si pósio Brasileiro e Siste as Elétricos - SBSE, 4, Foz do Iguaçu. A ais do SBSE 4, 4.
Development of a Solar Panels Curve Characterizer –
Hardware and Software
Eduardo Luiz Ferreira Campos1, Adriano da Silva Antônio1, Luís Otávio Maciel de Oliveira1, Guilherme Vianna Santos1
and Heverton Augusto Pereira1,2
1 Gerência de Especialistas em Sistemas Elétricos de Potência
Universidade Federal de Viçosa
Av. P. H. Rolfs s/nº, 36570-000
Viçosa, MG, Brazil
[email protected], [email protected],
[email protected], [email protected]
2 Graduate Program in Electrical Engineering
Federal University of Minas Gerais
Av. Antônio Carlos 6627, 31270-901
Belo Horizonte, MG, Brazil
Abstract— This work aims assembly a solar panel curve characterizer using a boost converter which works as an electronically controlled load. This device provides information that allows the user to increase the efficiency of power
generation in photovoltaic systems. The detection of operation issues or abnormal conditions such as partial shadowing caused by dirt or objects can affect adversely the maximum power point. Simulations were performed in three different software:
PSIM, Matlab/Simulink and Proteus. The results of these simulations showed the expected behavior of the model and allowed the development of the device. Tests were realized with the solar characterizer in a 48 W panel manufactured by Kyocera. The tests were realized in the city of Viçosa, Brazil. The results presented accordance with the behavior predicted in the simulations and, therefore validates the device.
Index Terms—DC-DC power converters, Graphical users interface, Photovoltaic systems, Solar energy.
I. INTRODUCTION
The researches for alternative power generation systems
have been strategically encouraging by many countries. The current world power generation through non-renewable sources has a lifetime and one day can be exhausted. Besides the electrical companies have to expand their power system due to consumption increase [1].
In this context the energy generated by the sun appears as an interesting alternative, clean and renewable solution [2]. The amounts of solar energy arriving at the earth’s surface every day are bigger than the global energy consumption, but their use is still limited, due to political and economic issues.
This scenario is changing, according to a study based on the collection of data in the photovoltaic sector industries, power utilities, agencies and national associations of energy, made by EPIA (European Photovoltaic Industry Association).
The installed global capacity of photovoltaic energy is growing fast between the years of 2000 and 2012 reaching 102 GW in global cumulative installed capacity. Some of the major reasons for this success are the reduction of the manufacturing cost, increasing in the number of projects, interest of stakeholders and policy developments incentives given by various countries around the world [3].
The energy production is further reduced on cloudy days or in shaded situations and it is even worse in the night time when there is no generation [4]. The shadow of a solar PV array can cause undesired effects such as decrease of real power generated by the solar PV array [5]. Considering that each PV cell is a current source connected in series with adjacent PV cells, a cell in a shadow region may be damaged due to its resistive aspect seen by the PV systems [6].
Furthermore, partially shaded cells can still generate a certain amount of energy, that energy cannot be collected in systems of the traditional configuration [7]. If bypass diodes are not used, any shaded cell inhibits power production from the entire series-connected string of cells. If bypass diodes are used, then the fraction of energy that could be generated by the partially shaded cells is still lost even if it does not impede collection of energy from the rest of the cells [8].
This work aims to develop a solar panel curve characterizer, using a boost converter operating as an electronically controlled load. The prototype will be able to connect in a computer, where through a graphical interface created using the Matlab/Guide software will build the characteristic curve of the panel and provides relevant information of the panel.
The authors would like to thank CNPq, FAPEMIG and CAPES by their
financial support.
II. METHODOLOGY
A. The Impedance Seen by the Panel Terminals
The aim of this section is compute an expression for the
impedance at the input terminals of the converter �� in function of the duty cycle � and the resistance of the load��.
Considering the continuous conduction operation mode, the voltage gain of the converter is given by:
V�V
1
�1 D� (1)
Where �� is the output voltage and �� is the input voltage of the converter.
Neglecting the losses of the boost converter, it is possible to obtain [7]:
�� ���
���� (2)
Where � is the duty cycle of the converter.
Using equations (1) and (2), it is possible to obtain:
Z V�R����V��
R�����1 D�² (3)
Analyzing (3) it can be seen that when � tends to 1, the input impedance, or the impedance seen by the panel terminal tends to zero, which represents the situation of short circuit. When � tends to 0, the input impedance tends to �����, which represents a condition to the open circuit. Therefore:
D → 1 ⇒ �� → 0 (4)
D → 0 ⇒ �� → ����� (5)
Figure 1 illustrates how the impedance seen by the terminals of the solar panel behaves in the characteristic curve.
Figure 1. Behavior of the Impedance Seen by the Panel Terminals.
B. Definition of the Project Parameters
The tests were realized using the photovoltaic solar panel
SM-48SKM from Kyocera manufacturer, whose main parameters on standard test conditions are shown in Table 1.
TABLE 1. MAIN PARAMETER OF THE SOLAR PANEL
Parameter Symbol Value
Maximum Power (W) ! 48
Maximum Power Voltage (V) �!" 18.6
Maximum Power Current (A) �!" 2.59
Open Circuit Voltage (V) ��# 22.1
Short Circuit Current (A) �$# 2.89
Temperature Coefficient of ��# (V/K) %& -0.070
Temperature Coefficient of �$# (mA/K) %� 1.66
This panel has a maximum power of 48 W for an incident solar radiation of 1000 W/m² and 25 °C. It weighs approximately 4.5 kg and it dimensions are 56 cm high, 68 cm wide and 3.8 cm thick.
The inductor design for the boost converter has 1 mH inductance and internal resistance of 1 Ω. The converter works in continuous mode driving, and a minimum inductance is calculated by [4]:
'#(�)�#�� �*+$2��-
��1 �� (6)
Where ��- is the current of the inductor in the limit boundary between the continuous conduction mode and the non-continuous conduction mode that is given by [7]:
��- 1
2��,"/�0 (7)
The capacitor chosen for the boost converter has a capacitance of 2.35 mF, achieved through parallel association of 5 capacitors of 470 μF each. For the choice of this element it was took into account the availability factor of the capacitor and the fact that this component should be large enough to hold the output voltage of the load.
The load resistor chosen for the boost converter has a resistance of 70 Ω. Boost converters can emulate a resistance that ranges from 0 to ����� and thus be able to achieve open circuit condition in the characteristic curve panel. Using this type of converter was simulated and plotted on the same graph the characteristic curve of the panel and some values of load resistance to make possible the choose of this parameter. Figure 2 shows the curves obtained for this simulation. It can be noted that the larger resistor improve the range of the converter to trace the characteristic curve.
Figure 2. Chosen of the Load Resistance.
Finally, the last parameter that was chosen was the switching frequency of the converter. It was used a PIC microcontroller, 18F4550, and was adopted a switching frequency of 20 kHz.
C. Simulations
After being defined the relevant parameters of the project, the system was initially simulated in the software PSIM, which already has a block of a photovoltaic solar panel, where is possible to change all parameters according to the manufacturer. This software includes a tool called solar module, where the user can enter with solar panel parameters and calculate the characteristic curve. Figure 3 illustrates the layout of the prototype designed on the software PSIM.
Figure 3. PSIM simulation.
Simulations were made in Matlab / Simulink, using a solar panel model developed in [4]. Figure 4 illustrates the layout of the prototype designed on Matlab / Simulink.
Figure 4. Matlab/ Simulink simulation.
Finally, simulations were made in the software Proteus. Figure 5 illustrates the layout of the prototype designed on Proteus that simulates virtually all electronic components that used in the project, including the PIC 18F4550 microcontroller. For this simulation, the equivalent circuit model was chosen to represent the solar panel due to its simplicity.
Figure 5. Proteus simulation.
D. Prototype Development
For the construction of the prototype some points had to be
observed. For example, the addition of an amplifier circuit at the output of PWM, because the microcontroller provides PWM signal from 0-5 V and the IGBT used requires a supply voltage at least 12 V. It was defined that the duty cycle sweep delay 0.5 seconds and a hundred of voltage and current points were collected to construct the characteristic curve.
III. RESULTS
The results of this project are divided into two categories, firstly it is shown the results obtained from the simulations and later appear the experimental results obtained by the prototype assembly. In addition, it was made a comparison between the simulated and experimental results to check the quality of the device constructed.
0 5 10 15 20 25 300
0.5
1
1.5
2
2.5
3
3.5Solar Panel Characteristic Curve
Voltage (V)
Curr
ent(
A)
Characteristic Curve
Rout = 50 ohms
Rout= 60 ohms
Rout = 70 ohms
Rout = 90 ohms
A. Simulation Results
The obtained results by simulating the system of Figure 3 in PSIM software may be seen in Figure 6, where the characteristic curve I-V is shown above and the P-V curve is shown below.
Figure 6. Characteristics curves obtained with PSIM software.
Figure 7 shows the interface of the solar module tool and the I-V and P-V curves for the tested solar panel.
Figure 7. Solar module tool from PSIM software.
Comparing results obtained from Figure 6 and Figure 7, it can be noted that the curves provided by the tested model are similar to the results obtained by the solar module tool, which demonstrates the efficiency of the method used to obtain the characteristic curve.
The obtained results by simulating the system of Figure 4 in Matlab / Simulink can be seen in Figure 8.
Figure 8. Characteristics curves obtained with Matlab/Simulink software.
The analyze of Figure 8 it is possible to see a similar result compared to the results obtained in PSIM software. It is noted that the curve obtained in the software Matlab/Simulink presents a small drop in current between 0-15 V. This result is more consistent with the actual result of the characteristic curve of a solar panel, and this difference should occur mainly due to the solar panel model used in Matlab/Simulink is more complete and therefore produces a closer result compared to a real system.
B. Experimental Results
Figure 9 represents the interface created to manage all the collected data. It allows to manipulated the information from
the panel like the characteristic curve I x V, P x V, �!", �!"
and !�1. In this interface, it is possible to save the collected data and to maintain a historic data from the panel that can be used to determine the lifetime panel.
Figure 9. Graphical Users Interface.
Tests were made with the panel in two different situations, normal condition and shadow conditions. In the first, shown in Figure 10, it can be observed that the V x I curve stooped before the open circuit voltage, limited by the resistance load.
In the second situation were analyzed shadows in three parts of the panel: two cells, central cells and line cells. Both tests show changing on V x I curve format and on power curve, these results are shown in Figure 11, Figure 12 and Figure 13. The partial shadowing and the place that this shadowing is on the solar panel produce different behaviors that can be identified by the test.
Figure 10. Solar panel in normal conditions.
Figure 11. Solar panel with two capped cells.
Figure 12. Solar panel with central cells covered.
Figure 13. Solar panel with bottom cells covered.
IV. CONCLUSIONS
This work designed and assembled a boost converter operating as a controlled electronic load. This device was used to develop a characterization system of solar panels curves at different radiation levels.
Some improvements like a wireless communication and a professional box structure are necessary, because the solar panels are installed distant of the computer and are exposed to weather conditions.
REFERENCES
[1] ANEEL, “Atlas de Energia Elétrica do Brasil,” Agência
Nacional de Energia Elétrica , 2008.
[2] H. Zheng, S. Li e J. Proano, “PV energy extraction
characteristic study under shading conditions for different
converter configurations,” em Power and Energy Society
General Meeting, 2012.
[3] EPIA, “Global Market Outlook For Photovoltaics,”
European Photovoltaic Industry Association, 2013-2017.
[4] A. Vilela, J. de Oliveira, G. Ribeiro, A. Brandao e H.
Pereira, “Switching reconfiguration of a solar
photavoltaic converter considering shadow conditions,”
em International Symposium on Industrial Electronics,
2011.
[5] L. Gao, R. Dougal, S. Liu e A.P.otova, “Parallel-
Connected Solar PV System to Address Partial and
Rapidly Fluctuating Shadow Conditions,” IEEE
Transactions on Industrial Electronics, vol. 56, nº 5, pp.
1548-1556, 2009.
[6] N. N. Lima, “Sistema de Caracterização de Painéis
Fotovoltaicos de baixo custo para detecção de falhas,”
CBA, 2012.
[7] N. Mohan, “First Course on Power Electronics and
Drives,” Minneapolis, 2003.
BIOGRAPHIES
Eduardo Luiz Ferreira Campos was born in the city
of Belo Horizonte - MG, 1989, he joined the Electrical
Engineering course at the Federal University of Viçosa in 2008. Currently developing projects in Electric
Power Systems with emphasis on Solar Energy.
Adriano da Silva Antônio was born in Viçosa, Brazil.
He joined the Electrical Engineering course at the
Federal University of Viçosa (UFV) in 2008.
Participant of the Project Interchange Brazil-France in
Institut National Polytechnique de Lorraine (Nancy -
France) 2011-2012 . He is integrant of GESEP, where
developed works about solar energy.
Luis Otávio Maciel de Oliveira was born in Sete
Lagoas/ MG, 1993. He joined the Electrical
Engineering course at the Federal University of Viçosa
in 2011. Worked in research groups GESEP and
UFVBaja acting in the area of electronics and
microcontrollers in 2013. Currently participating in an
exchange program in the Netherlands in Hanze Institute
of Technology in the course of Advanced Sensor
Applications.
Guilherme Vianna Santos was born in Vilha-
Velha/ES, 1989, participated as a finalist in the project
"From Garbage became Physics" in Brazilian Fair of Science and Engineering (FEBRACE) in 2006. He
joined the Electrical Engineering course at the Federal
University of Viçosa (UFV) in 2007. Currently,
performs work in the area of electronics, power
electronics, automation and control applied to
renewable energy.
Heverton Augusto Pereira received the B.S. degree in
electrical engineering from the Federal University of
Viçosa (UFV), Viçosa, Brazil, in 2007, the M.S. degree
in electrical engineering from the State University of
Campinas (UNICAMP), Campinas, Brazil, in 2009.
Currently he is Ph.D. student from the Federal
University of Minas Gerais (UFMG), Belo Horizonte,
Brazil. Since 2009 he has been with the Department of
Electric Engineering, UFV, Brazil. His research
interests are wind power and solar energy.