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An advanced control concept for modular multilevel converter using capacitor voltage estimation
(2017)
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.
An approach to estimate the submodule capacitor voltages in a Modular Multilevel Converter (MMC) is presented and realized in a hardware test setup. One disadvantage of the MMC topology is the high communication and measurement effort. As the submodule voltages are being estimated, the measurement effort as well as the communication effort between the submodules and the main controller hardware is significantly reduced. Thereby, the reliability of the system also increases. In the hardware test setup, it is verified that using a notch filter in the feedback path of the energy control loop significantly decreases unwanted AC components of the circulating currents within the MMC. Subsequently the current stress as well as the conduction and switching losses in the semiconductors can be minimized. Furthermore, the dynamic performance of the capacitor voltage estimation and control scheme was analyzed via hardware tests.