A method for the fast estimation of the maximum power points in mismatched PV strings

The power vs. voltage curve of a photovoltaic string operating under mismatched conditions can exhibit more than one maximum power point (MPP). In this paper, a direct method for the estimation of these points using explicit equations is introduced. The method employs a piecewise linear approximation of the current vs. voltage curve of each photovoltaic panel in the string and assumes that the open circuit voltage and the position of the maximum power points of each panel are known. Numerical results comparing the performances of the proposed approach with those offered by the adoption of the accurate single diode model show that the computational burden is reduced by almost four orders of magnitude. The approach is validated by experimental results exhibiting estimation errors lower than 5%. The satisfactory trade-off between accuracy and computation time provided by the proposed method is illustrated using two application examples: reconfiguration and long-term power production of PV strings. Moreover, an in-depth comparison of the existing simplified methods to estimate the MPPs has been performed.