Optimal zero sequence injection in multilevel cascaded H-bridge converter under unbalanced photovoltaic power generation

The multilevel cascaded H-bridge converter is a favorable candidate to directly connect large-scale photovoltaic power plants to the medium voltage electricity network. Nevertheless, due to the lack of a common dc link, the unequal power generation among the three phases, primarily caused by non-uniform solar irradiance, affects its operation. The existing power balancing control methods, however, fail to achieve optimal results due to their limitations. This paper proposes an optimal zero sequence injection method to maximize the converter power balancing capability. The feasibility and superiority of the new method are confirmed by simulation results.