MPPT Technique for Partially Shade Photovoltaic Module: Graph Laplacian Approach

Abstract

One of the topology that comes under distributed control rchitecture in pho-tovoltaic application is di erential power processing. This topology is basically a minimal power processing technique as the di erential convertors used here pro-vide mismatch current to the series connected PV module string. Series connected PV module su ers from mismatch problem due to di erent level of insolation,shading, or manufacturing variation of di erent sub-module as the current in se-ries connection is same thus the eciency of the PV system is compromised even when a single sub-module is amaged or solar irradiation is not uniform. This dis-tributed architecture uses bidirectional buck-boost convertor to enable the powerow from one module to another in either direction depending on the opening and closing of Mosfet switch which drive the convertor in buck or boost mode. The control algorithm used to achieve true MPPT is an iterative process which uses local voltage measured and neighbor to neighbor communication to update the algorithm and thus ecient tracking. This architecture overcomes the problem of the conventional power electronics solution for series connected PV module with mismatch, where there is a compromise between system eciency and total power production. Since the di erential convertor deals only with the mismatched power which is just a small fraction of total power and all convertors having same e-ciency the overall eciency can be improved signi cantly. If there is no mismatch between the modules then ideally no power loss will occur in DPP convertor and the eciency of system is limited by central invertor. This algorithm uses graph Laplacian approach where Laplacian matrix is used to obtain information from neighboring PV module. This approach reduces the number of iterations at each step thus improving the tracking speed with no added hardware making it more suitable for long series string PV module. Algorithm along with simulation and its properties are presented in this paper.