A Study on the Impact of AC Transformer due to Shared AC/DC Neutral Line

As the integration of renewable energy into the power grid continues, there is a growing need for transitioning to the next-generation power grid, namely the DC distribution system. Since the DC distribution system will be built upon the existing AC distribution system, this paper introduces and analyzes the impact of a structure where DC distribution systems share AC neutral lines. AC/DC hybrid distribution systems that share a neutral line can cause half-cycle saturation of the AC transformer under conditions of DC load imbalance. Although this can be prevented by existing DC bias suppression strategies, they have the drawback of adversely affecting protection coordination within the AC system. This paper presents a method that not only prevents DC bias but also does not impact protection coordination within the AC system. Additionally, this method is examined within the AC/DC hybrid distribution system using MATLAB Simulink.