A Grid-Supporting Strategy for Cascaded H-Bridge PV Converter Using VSG Algorithm With Modular Active Power Reserve

The cascaded H-bridge (CHB) converter is a favorable candidate in the photovoltaic (PV) field due to its modular multilevel construction, which could pursue the maximum energy yield by adopting the maximum power point tracking (MPPT) strategy. However, with the increasing penetration of PV generation, challenges are arising for the grid stability due to the deficiency of converter inertia and damping. To improve the system inertia besides the energy efficiency, this article proposes a control strategy for the CHB converter with the combination of MPPT and virtual synchronous generator (VSG). Taking advantage of the modularity of CHB converter, a proportion of the total PV power is reserved by the selected reserved cells to provide the power buffer between the VSG and PV power for grid frequency supporting, and the nonreserved cells are utilizing the MPPT to ensure the energy efficiency. With the proposed control strategy, the CHB converter could be equipped with the frequency regulation capacity without any energy storage device and the full use of PV power is realized, which is verified by the simulation and experimental results.