Fault Diagnosis Strategy For Solar Cells Based On Reverse Derivation of I-V Curve
Fault Diagnosis Strategy For Solar Cells Based On Reverse Derivation of I-V Curve
Abstract: This paper proposes a fault diagnosis strategy for solar cells based on the reverse
derivation of the I-V curve. This strategy does not require real-time monitoring of the surface
irradiance and average temperature of the solar cell during operation. It only needs to
calculate(establish) the I-V curve library under different irradiance and solar cell temperature
in advance, then measure the open circuit voltage and short circuit current of the photovoltaic
module during operation. And the measured voltage and current at the maximum power point
can determine whether the solar cell is faulty. The possible faults of various solar cells are
simulated by setting up experimental equipment, and the method is used for fault diagnosis.
Experimental results show that the proposed method can effectively monitor various faults of
solar cells. The method improves the accuracy of fault detection of the solar cell, enhances the
reliability and economical benefits of the photovoltaic power station, and realizes online fault
detection of the solar cell.
1. Introduction
With the looming global fossil energy shortage and environmental pollution, the demand for
renewable energy is very urgent [1]. As an important form of renewable energy power generation,
solar power generation has developed rapidly in recent years. In a solar generation station, there are
a large number of solar cells, and the failure characteristics are not obvious. If the failure cannot be
inspected and predicted, it will cause the degradation of the performance of the photovoltaic module,
which may also shorten the service life of the module, or even lead to the early scrapping of the
photovoltaic module and then result in a large economic loss [2]. Therefore, it is of great importance
to study the fault detection method of solar cells.
At present, online fault diagnosis methods for solar modules are mainly based on a feature
comparison. That is, comparing the measured values of the components with the calculated values of
the model. If there is a large deviation between the two results, it can be judged that the component
is faulty. There are two main types of component models—numerical models and artificial
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2023 2nd International Conference on Power System and Power Engineering IOP Publishing
Journal of Physics: Conference Series 2564 (2023) 012018 doi:10.1088/1742-6596/2564/1/012018
intelligence models.
The numerical model refers to the model established based on the physical laws of photovoltaic
modules, such as the classic single (double) diode model. The diagnosis method based on the
numerical model mainly measures the real-time temperature and irradiance and substitutes them into
the numerical model formula to obtain the I-V curve of the photovoltaic cell and the corresponding
working maximum power point. The fault can be detected by the difference between the data of the
maximum power point and the measured power. For example, in [8], researchers proposed a method
of simulating solar system power based on the measured temperature and irradiance and used power
loss to analyze faults. In [9], a method for analyzing solar power generation systems based on
measured temperature and irradiance was proposed. The method of fault diagnosis is based on
power loss. In [10], scholars simulate the solar power generation system in real time through the
environmental irradiance and component temperature changes and automatically monitor the faults
of the solar cell array by defining four electrical indicators.
The artificial intelligence model mainly uses intelligent algorithms to model solar modules, and
the subsequent diagnosis process is basically consistent with the algorithm of the numerical model.
In [3] and [4], corresponding photovoltaic array fault diagnosis methods based on different neural
network algorithms were proposed. In [5], the firefly disturbance sparrow search algorithm-extreme
learning machine was used to realize the diagnosis of solar module faults. In [6], scholars proposed
a photovoltaic array intelligent fault diagnosis method based on an optimized nuclear extreme
learning machine and IV characteristic curve. In [7], a solar photovoltaic power plant fault feature
classification method based on RGB image recognition and convolutional neural network was
proposed. Although there are many theoretical studies on the detection method of artificial
intelligence models, it still faces great challenges in large-scale promotion because it requires a large
amount of data for training, and the training data needs to be updated regularly.
However, the theoretical value in the operating state which is calculated based on the battery
numerical model or the artificial intelligence model, both of them depend on the accurate
measurement of the battery operating environment parameters. Photovoltaic power plants cover a
large area and are widely distributed. The components in the same power plant may have large
differences in operating status, while the temperature and irradiance sensors can only monitor data at
a certain location, and cannot cover all components in the station, so they cannot accurately obtain
the operating parameters of each component, eventually resulting in large errors in diagnostic
results.
This paper proposes a fault diagnosis strategy for solar cells based on the inverse I-V curves. It
does not need to measure the temperature and irradiance of the power station, but to test the
short-circuit current and open circuit voltage of the components, and inversely find them in the
preset I-V curve library and matched I-V curves. By comparing the MPPT point on the curve with
the MPPT point measured by the component, it can be judged whether there is a fault.
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2023 2nd International Conference on Power System and Power Engineering IOP Publishing
Journal of Physics: Conference Series 2564 (2023) 012018 doi:10.1088/1742-6596/2564/1/012018
Power
Supply
Circuit
micro Switch
Energy controller circuit
storage
Circuit
PV- PV-OUT-
Current
detection
circuit
Figure 1. Monitoring circuit
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2023 2nd International Conference on Power System and Power Engineering IOP Publishing
Journal of Physics: Conference Series 2564 (2023) 012018 doi:10.1088/1742-6596/2564/1/012018
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2023 2nd International Conference on Power System and Power Engineering IOP Publishing
Journal of Physics: Conference Series 2564 (2023) 012018 doi:10.1088/1742-6596/2564/1/012018
Start
Rs=0
Calculate Rp=Rp, min by formula
(10)
Calculate I0 through formula(3)
Solving Pmax by perturbation
observation method
ΔP=|Pmax-Pmax.e |
ΔP>threshold
Yes
No
Quantitative increase of Rs
Calculate Ipv, n by formula (11)
Calculate Rp, n by formula (8)
Solving Pmax by perturbation
observation method
ΔP=|Pmax -Pmax.e|
End
4
Current (A)
0
0 5 10 15 20 25 30 35 40 45
Voltage (V)
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2023 2nd International Conference on Power System and Power Engineering IOP Publishing
Journal of Physics: Conference Series 2564 (2023) 012018 doi:10.1088/1742-6596/2564/1/012018
parameters of solar cells, the IV curves under different temperatures and different irradiances can be
obtained by calculation, and then a series of [ Voc , I sc , Vmppt , I mppt ] can be obtained to form an IV
curve library. Through the photovoltaic cell online monitoring module shown above, you can
' ' '
measure V oc , I 'sc , V mppt , find the I mppt same data pair I sc in the IV curve library Voc , and
'
locate the corresponding IV curve Through the actual measurement of V mppt and the curve I mppt ,
'
the corresponding measured maximum power P mppt and theoretical maximum power Pmppt are
obtained and compared. If the difference between the two exceeds the preset threshold value, it can
be determined that the fault exists.
i=1
ΔI=|Isci-I sc|
ΔU=|Uoci-U oc|
calculationΔ
X
P mppt=Vmppt*I mppt
P ,mppt=V ,mppt*I ,mpp
calculationΔP
ΔP>threshold No
Yes
normal
fault
operation
End
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2023 2nd International Conference on Power System and Power Engineering IOP Publishing
Journal of Physics: Conference Series 2564 (2023) 012018 doi:10.1088/1742-6596/2564/1/012018
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2023 2nd International Conference on Power System and Power Engineering IOP Publishing
Journal of Physics: Conference Series 2564 (2023) 012018 doi:10.1088/1742-6596/2564/1/012018
In order to determine the error range set by the threshold method, the operating data of the solar
cell during the normal operation was collected under different temperatures and irradiances, the
corresponding IV curve was located and the power error was calculated. Some results are shown in
Table 3 and Table 4:
Table 3 Measured data during normal operation
measured
V mppt (V) Im ppt (A) V OC (V) I sc (A) P max (W)
value
1 38.78 6.71 48.13 7.29 260.21
2 38.72 6.83 48.14 7.33 264.46
3 38.76 6.77 48.04 7.31 262.41
4 39.07 6.94 48.09 7.51 271.15
When a shadow occlusion fault occurs, the power error between the measured data and the
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2023 2nd International Conference on Power System and Power Engineering IOP Publishing
Journal of Physics: Conference Series 2564 (2023) 012018 doi:10.1088/1742-6596/2564/1/012018
corresponding I V curve data is extremely large, both greater than 75 %, far exceeding the set
threshold of 3.5%, which can accurately determine the existence of a fault. This result fully
demonstrates the correctness of the method.
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2023 2nd International Conference on Power System and Power Engineering IOP Publishing
Journal of Physics: Conference Series 2564 (2023) 012018 doi:10.1088/1742-6596/2564/1/012018
6. Conclusions
This paper proposes a method for online monitoring of solar module failures and proposes a method
based on an iterative method to calculate IV curves under different working conditions and form a
library of IV curves. By comparing the open-circuit voltage and short-circuit current of the
measured data with the open-circuit voltage and short-circuit current in the I V curve library, the
corresponding I V curve is located. Finally, the threshold method is used to monitor the fault, and
the measured maximum power is compared with the maximum power corresponding to the IV curve.
And if the threshold is exceeded, it is judged that there is a fault. The research method in this paper
is verified by the actual 3200 Wp solar power generation system. Compared with the 5% threshold
of power error used in [15], the power error is reduced and the range of faults that can be identified
is expanded. Compared with the method proposed by predecessors to calculate the theoretical value
by online monitoring of the operating environment of solar modules, this method eliminates the
error caused by monitoring the operating environment and improves the accuracy of fault
monitoring.
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