Detection of cell-level fault conditions within a photovoltaic array system

Characteristics of photovoltaic (PV) modules are quite different from traditional power generation sources. For traditional generation sources, such as the fossil fuel generators, the current magnitude increases drastically when short circuited. This drastic current magnitude increase is not the case with PV modules. The short circuit current of the PV module could be as low as 105 to 110% of its maximum power point current. Furthermore, most PV systems have a blocking diode which prevents the back-feed of current from the power grid to the PV array system. Therefore, if a fault occurs within the PV array, the series fuse, a common protective device in the PV industry, may not operate. The fuse may not operate because the current through the fuse is limited by the blocking diode. This low current magnitude makes the identification of fault conditions in the PV array even more challenging. To further complicate the challenge, the current generated by the PV array is solar irradiance dependent. Therefore, on a very cloudy day, the fault current magnitude will be a lot less compared to a non-cloudy day, with all other conditions being the same. Also, it is possible that the current magnitude at one operating condition be the same magnitude as a short circuit condition at another operating condition. In this paper, a dynamic state estimation-based algorithm for detecting various fault conditions within the PV array is presented. It is demonstrated that various fault conditions within the PV array system are reliably identified using the proposed algorithm.

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