Optimal steady state design and feedback control in a Modular Multilevel Converter

The energy transition leads to an increasing importance of transfering large amounts of electric energy over long distances, which can be met by a Modular Multilevel Converter (MMC), ensuring high quality and an universal application due to its scalability. This paper introduces a method for analytically solving a minimization task, utilizing all degrees of freedom, for minimizing energy oscillations in the steady state, resulting in a 75% reduction in oscillation strength of the energy amplitudes compared to freezing the internal degrees of freedom to zero. Furthermore, a feedback control for compensating arbitrary deviations from a given trajectory is explained and its robustness is demonstrated. Therefore deviations are imposed, occurring due to the limited number of MMC submodules leading to an imprecisely design of the input variables. These deviations are even increased by unforeseen fluctuations in the external DC and AC voltages, along with an additional applied DC voltage drop.