Maximum power point searching method for partial shaded PV strings

This paper presents two methods aimed to search the global maximum power point (MPP) in conditions of multiple local MPPs. These conditions arise in cases where different photovoltaic (PV) panels in a string may be subject to different conditions of irradiance and/or temperature. The methods are referred as voltage-based global maximum power point searching (G-MPPS) method and current-based G-MPPS method. The former uses the voltage as the variable of control, in the sense that a voltage reference is generated, while the latter generates a current reference. These methods are based on the geometrical characteristics of the iv-characteristic curve. The idea behind the methods is to enlarge the increments of the voltage (or current), by using a set of auxiliary curves. These last are defined as the rectangular hyperboles defining subspaces of constant power. The result is a considerably faster searching process compared to the conventional sweep method. Simulations and experimental results are presented to assess the performance of the proposed method.