Energy-Balancing Control of a Delta-Configured Modular Multilevel Cascade Inverter for Utility-Scale Photovoltaic Systems

This paper provides a theoretical discussion on energy-balancing control and capability of a modular multilevel cascade inverter (MMCI) based on single-delta bridge cells (SDBC). The SDBC inverter is intended for applications to utility scale grid-tied photovoltaic (PV) systems involving asymmetric power generation. The distributed nature of electric power generated from individual power sources requires the inverter to be capable of operating under imbalanced conditions. As compared to a star-configured MMCI based on single-star bridge cells (SSBC), the SDBC inverter features a superior energy balancing capability making it more suitable for these kinds of applications. This paper discusses the control, operational behavior, and limitations of a phase-shifted carrier pulsewidth modulated (PWM) SDBC inverter under imbalanced conditions among both bridge cells and clusters.