Impact of Submodule Energy Balancing on Grid Emulation Performance of Modular Multilevel Converters

Modular multilevel converters can be used to emulate the electrical ac grid to test devices with expanded power ranges due to their versatility and adaptability. The performance of the voltages at the point of common coupling can be impacted by ac voltage controllers. The assumption of decoupled voltage and energy balancing control in the modular multilevel converter suggests that the influence of submodule energy balancing on the ac output waveform performance should be negligible. However, contrary to expectations, this paper demonstrates that the influence is not negligible, particularly in the dc-ac energy decoupled mode. This study investigates the influence of sorting algorithms and internal energy balancing control strategies on the steady-state performance and transient response of the voltages at the point of common coupling for the grid emulator in both ac-dc energy-coupled and decoupled mode. The study is validated by simulations of a 400 V dc-link modular multilevel converter consisting of 32 submodules.