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Internal Model-Based Active Damping Strategy for a Back-to-Back Modular Multilevel Converter System for Advanced Grid Support

The proposed work focuses on the possibility of achieving the reduction in the size of the interfacing filter for the grid connection for a back-to-back modular multilevel converter system with the use of third order LCL filters. To achieve the same attenuation, it is possible to reduce the size of the interfacing filters by the usage of third-order filters; however, this kind of filtering comes with the limitation of having sustained oscillations caused by lack of damping especially during transient changes. Therefore, this work proposes, a methodology based on the principle of internal model to nullify these unwanted oscillations. The third-order system is modeled inside the microcontroller with the damping enabled. The error between the output from the model and the actual output are compared and the error is used to accomplish the active damping strategy. The proposed architecture is verified via computer simulations based on the MATLAB/Simulink domain. Various case study results and discussions are presented in this paper.