An advanced control concept for modular multilevel converter using capacitor voltage estimation

An advanced control concept for a Modular Multilevel Converter (MMC) is presented in this paper. By using a Notch Filter and a Kalman Filter it is possible to reduce unwanted AC components within circulating currents in the MMC significantly. Subsequently the current stress and the conduction and switching losses in the semiconductors can be minimized. In the second part of this paper, approaches to estimate the capacitor voltages are presented. The observability is inverstigated theoretically and via simulations. A disadvantage of the MMC topology is the need of a complex and expensive communication system. While the submodule voltages are being estimated, the communication effort between the submodules and the main controller hardware is significantly reduced.