Multi-Timescale Stability of Modular Cascaded Power Electronic Systems

By connecting multiple power electronic converter modules in series, the modular cascaded power electronic systems, also known as Modular Multilevel Converters (MMCs), are emerging as a promising technology for high-power conversion at high-voltage levels, i.e. from tens to hundreds of kilovolts. The modularity of the MMC provides the obvious advantages of scalability, redundancy, and high reliability, but it tends also to bring in oscillations at multiple time scales, owing to the dynamic interactions among the internal converter modules and with the external electric network. The nonlinear switching behavior of converter modules also cause cross frequency couplings between the DC and AC terminals of MMCs, which tend to give rise to multi-time-scale transient responses. This project, in collaboration with Ørsted Offshore Wind and ABB Power Grids Sweden, aims at developing an efficient analytical tool to understand the fundamental mechanism underlying the multi-time-scale dynamics of MMCs, and to further cope with the instabilities or resonances by means of smart control and hardware solutions.