Abstract
In PV (Photovoltaic) systems, the PV array is a structure in which many PV strings are connected in parallel. The voltage mismatch between PV strings, in which PV modules are connected in a series, occurs due to a voltage decrease in some modules. In this paper, research on the electrical characteristics of PV arrays due to a voltage mismatch was conducted. Considering the voltage mismatch, experiments on partial shading, the non-uniformity of irradiance, and the failure of bypass diodes were conducted on the PV module level. It was confirmed that the open-circuit voltage greatly decreased due to the failure of bypass diodes, which is among the causes of voltage mismatch. From the simulation results at the PV array level, it can be seen that a reverse current flowed into the low-potential string, which includes PV modules, causing the failure of the bypass diodes. Measuring the reverse current at one low-potential string, it was found that, in four parallel circuits, the reverse current was 12 A. For this reason, in large PV plants, an overcurrent can flow into the fuse due to the potential difference between strings, causing an output decrease of PV plants and the burnout of fuses.
Highlights
PV (Photovoltaic) systems are largely divided into PV arrays that produce DC (Direct current) power and PV inverters that convert the generated DC power into AC (Alternating current) power.An PV array is a structure in which PV modules are connected in a series, and many such strings are connected in parallel
Research was conducted to confirm whether reverse current flows into a PV string
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
Summary
PV (Photovoltaic) systems are largely divided into PV arrays that produce DC (Direct current) power and PV inverters that convert the generated DC power into AC (Alternating current) power. According to the research results, the mismatch factors of PV arrays, such as PV module mismatching and partial shading, reduce the output of the PV system by about. According to IEC TS 62257-7-1: 2010, blocking diodes can be a source of the failure and power loss and are not recommended for use [10] In this connection, the revised combiner box standard (KS C 8567;2019). Research was conducted to analyze the current flow of PV arrays, considering the system configuration and failure condition under the voltage mismatch due to output mismatch. From the simulation and experiment, the current flow of PV arrays caused by various factors (voltage mismatch, blocking diodes, and inverter failure) was analyzed, and the resulting effect of the system was confirmed
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