Exact maximum power point tracking of partially shaded PV strings based on current equalization concept

Abstract

Under partially shaded conditions, series connection of PV modules results in the flow of lowest current in the PV string, thus reducing the power output. To maximize power output, it is necessary to ensure that maximum possible current flows in the string. This needs current equalization across the modules. To achieve this, a converter is connected in parallel with each PV module. This converter provides the extra (equalization) current in parallel with the shaded module to make the string current equal to the maximum string current, i.e. the current corresponding to the least shaded PV module. The equalization current supports the PV module to have its voltage regulated at a value that corresponds to its MPP (Maximum Power Point) voltage. However, the existing current equalization schemes use approximate maximum power point voltage and not an exact one. This paper proposes an improvement over the existing schemes by using synchronous fly-back converters to regulate the exact MPP voltage across PV modules in a partially shaded PV array. Unlike existing schemes that operate on similar principle, the proposed scheme makes no assumptions and ensures that each module is regulated at its exact MPP voltage i.e. exact MPP of individual PV module is tracked.