## 5 Conclusions  
In this paper, research was conducted to confirm whether reverse current flows into a PV string due to a specific cause, especially the voltage mismatch between PV strings in PV arrays. The voltage mismatch between the PV strings was created by the operation of the bypass diode and the short-circuit failure of the bypass diode in the junction box. Experiments were conducted to analyze the electrical characteristics of each case of voltage mismatch. If there is a non-uniformity of irradiance between  
Figure 12: The current flow due to potential difference in a DC array circuit of a PV system.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**A Number of PV** & **Simulation** & **Measurement** \\ \hline
1 & \(-3.32\) & \(-3.76\) \\
2 & \(-6.43\) & \(-6.41\) \\
3 & \(-11.3\) & \(-12.03\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of simulated and measured reverse currents due to the failure of bypass diodes.  
PV strings or the operation of the bypass diode in PV modules, the voltage mismatch is less than 2 V. However, the bypass diode failure reduced the voltage to the open-circuit voltage of a PV module, resulting in a voltage mismatch above 30 V. The simulation and experiments were conducted at the PV array level to consider the difference in electrical characteristics. It was found that no reverse current flowed into the string due to the operation of the bypass diode. However, the failure of the bypass diode created a significant voltage mismatch between PV strings, so a reverse current of more than the short-circuit current (about 10 A) of the PV module flowed into the low-potential string. The conclusions that can be drawn from this study are as follows:  
1. When there is a non-uniformity of irradiance, and the bypass diode is in operation, the voltage mismatch value is less than 2 V. Simulations and experiments confirmed that the voltage mismatch of less than about 2 V for a PV array consisting of dozens of PV modules in a series is not a difference that can potentially cause a reverse current between PV strings. Thus, in this situation, the reverse current hardly flows to the PV string.
2. The voltage mismatch caused by the failure of the bypass diode was about 33 V (the case of the PV module with all fault bypass diodes). In a PV array of dozens of PV modules in a series, the simulation results show that the potential difference between PV strings is more than 30 V, and the reverse current flows into the low-potential string. When three modules consisted of a short circuit in one string of the PV array, the mismatching current from the other strings is more than about 12 A.
3. In general, PV plants consist of more than four parallel circuits (typically, 20-22 parallel circuits for 100 kW solar power plants). When the inverter stops for routine checking of the PV system with more than 22 parallel strings, and if one string has a short circuit PV module, a mismatching current of about 12 A will flow. Since the mismatching current of about 10 A or more is larger than the rated current of the fuse installed in the PV combiner box, the fuse may be burned out. The device for monitoring to fuse may be needed to prevent power loss and safety accidents in standalone PV plants.  
[PERSON] wrote the main part of the paper and analyzed and conducted the experiment. [PERSON] established the research direction of the paper and suggested a method for conducting the experiment. [PERSON] analyzed all of the data using the paper and provided important comments. [PERSON] and [PERSON] provided technical ideas and assistance in establishing an outdoor site for the experiment. [PERSON] reviewed and revised the overall contents of the paper.  
This research received no external funding.  
This work was supported by a grant from the Renewable Energy of Korea Institute of Energy Technology Evaluation and Planning (KETEP) funded by the Ministry of Trade, Industry and Energy, Republic of Korea (Project No. 20183020010990).  
The authors declare no conflict of interest.