A Hybrid Modular Multilevel Converter for Solar Power Integration

A hybrid modular multilevel converter (H-MMC) for grid-connected photovoltaic (PV) system is presented in this paper. The array of PV panels is connected in each submodule of the converter. The submodules are connected in series to form the dc link for each phase. The dc-link voltage is unipolar and multilevel in nature, which is converted to ac voltage by a low frequency converter. This topology can be applicable at high power by increasing number of submodules per phase. The H-MMC has many advantages compared to conventional MMC, e.g., more voltage levels, less capacitor count, no circulating current, higher efficiency, and less foot print. A global maximum power point tracking (MPPT) algorithm is proposed for this converter, which requires the voltage and current signals of only one submodule. The limitations of global MPPT under partial shading are overcome through distributed MPPT. A least-MPPT algorithm is presented to make the three phase powers balanced under nonuniform partial shading among the phases. The usefulness of this converter configuration with two different MPPT algorithms (global and distributed) is investigated through PSCAD/EMTDC simulation. A single-phase version of the converter with global and distributed MPPT is experimentally validated considering partial shading condition. The results show the usefulness of H-MMC and associated control for PV integration.