Performance Improvement of PV-Fed Hybrid Modular Multilevel Converter Under Partial Shading Condition

Abstract

This article presents a hybrid modular multilevel converter (HMMC) for large-scale photo voltaic (PV) integration to grid. PV panels are directly connected to each submodule of the converter without using any dc–dc converter. A distributed maximum power point tracking (D-MPPT) method is used to extract maximum power from each PV-string under normal, as well as, shading (uniform/nonuniform) condition. Power unbalance among the phases during partial shading is a major issue of such type of converter, which needs to be properly handled for satisfactory operation. To address this issue in a cascaded H-bridge converter, zero sequence voltage (ZSV) injection based methods have been utilized. In this work, ZSV injection is integrated with D-MPPT and the combined method is applied on HMMC to address both interphase and intraphase partial shading satisfying MPPT operation in each submodule. The feasibility of the proposed control method is first verified through PSCAD/EMTDC simulation. Thereafter, a dSPACE Micro-Lab-Box-based experimental prototype is developed to check the performance at 10 kW power level under the presence of real PV panels. A comparative assessment of the proposed system with available topologies has been performed to highlight the notable features. The capability of ZSV controlled HMMC is evaluated under various shading conditions to explore its usefulness to deal with power unbalance conditions. It may be predicted that an HMMC-based PV system with the aforesaid control methods has sufficient merits to become a potential candidate for high power PV integration.