Analysing dynamics and synthesising a robust vector control for the dc-voltage power port based on the modular multilevel converter in multi-infeed AC/DC smart grids

Among all converters, one of the most prominent technologies employed in multi-infeed ac/dc (MIACDC) smart grids is the modular multilevel converters (MMCs). The core part of the MIACDC grids is their dc-voltage power port. All MMC's components in a dc-voltage power port – which are capable of significantly impacting on the dynamics – are mathematically modelled in the space-phasor representation using the rotating dq-frame. Afterwards, the effects of each submodule capacitors and arm inductors on the dc-voltage power port's dynamics are investigated and analysed, separately. This paper mathematically shows that the former is affecting the low-frequency range of the bandwidth, and the latter is impacting on the high-frequency one. Moreover, this paper demonstrates that a robust, optimal controller synthesized by the µ-analysis is a good candidate to induce both robust stability and performance in an MMC-based dc-voltage power port. In order to illustrate the contributions of this article, detailed mathematical analyses; comparative results simulated by the switching model of MMC; and experimental results produced by a test rig, which is able to examine the transient performance of an MMC-based dc-voltage power port, are provided. For comparison, the results of the PI-Lead controller and those of another controller optimally synthesized have been provided.