An improved topology of Unified Power Flow Controller based on MMC with Fault Current Limiting

This paper proposes a new topology for Unified Power Flow Controller (UPFC), traditional UPFC based on Voltage Source Controller (VSC) has a higher switch frequency, an obvious voltage harmonic and a lower voltage level. In the new circuit, Modular Multilevel Converter (MMC) has replaced VSC. Moreover, UPFC has a big risk to suffer the short circuit fault, which can cause the damage to device, especially on the high voltage occasion. Thus, the paper has applied the Fault Current Limiting (FCL) to the UPFC, which won't increase any structure burden to UPFC. In all, this proposed system has such advantages: higher modularity level, smaller harmonic wave, more rapid current-limiting in the short circuit fault occasion and so on, as well increases the system's reliability, safety, economy. At last, the topology and control strategies of the proposed system are verified by the PSCAD/EMTDC simulations, the result is perfect.