Cascaded H-bridge multilevel converter for large-scale PV grid-integration with isolated DC-DC stage

The integration of large-scale PV systems to the grid is a growing trend in modern power systems. The cascaded H-bridge (CHB) converter is a suitable candidate for the grid interconnection due to its modular characteristics, high-quality output waveforms and capability of connecting to medium-voltage grids. However, the CHB converter requires isolated DC sources. In order to avoid the leakage currents caused by the high potential differences across the parasitic capacitance of the PV panels to ground, an isolated DC-DC conversion stage is required when the CHB topology is used. The objective of this paper is to compare two PV system configurations based on the CHB multilevel converter using two isolated DC-DC converter topologies, namely the boost-half-bridge (BHB) and the flyback, for their performance on providing isolation and achieving individual MPPT at the DC-DC power conversion stage of large-scale PV power systems. Simulation results from a 263 kW PV system based on a seven-level CHB converter with the two aforementioned isolated DC-DC converters are provided for comparison and evaluation with different input PV voltages.