A Non-Invasive Procedure for Estimating the Exponential Model Parameters of Bypass Diodes in Photovoltaic Modules

Resumen

Bypass diodes (BDs) present in photovoltaic (PV) modules are represented by the exponential model, which requires two parameters: the inverse-saturation current ( $I_{sat,db}$ ) and the ideality factor ( ${?}_{db}$ ). However, it is difficult to estimate those parameters since the terminals of the BDs are not isolated, hence there is only access to the series connection of the module BDs. This problem must be addressed since inaccurate BDs parameters could produce errors in the reproduction of the current-voltage (I-V) curves of commercial PV modules, which lead to wrong predictions of the power production. This paper proposes a non-invasive procedure to estimate $I_{sat,db}$ and ${?}_{db}$ of the bypass diodes present in a PV module using two experimental I-V curves. One I-V curve is measured completely covering the submodule of the module whose BD will be parameterized; while the other I-V curve is measured without any shadow on the module. From those curves, the I-V curve of the BD is estimated and $I_{sat,db}$ and ${?}_{db}$ are calculated by solving a system of two nonlinear equations. The proposed procedure is validated through simulations and experimental results considering a commercial PV module formed by three submodules, where the estimation errors in the reproduction of the BD I-V curve are less than 1% in the simulations and less than 10% in the experiments.