A System-Level Suppression Method for DC Bias Based on Reverse Unbalanced Currents in the Same Transmission Section

Conventional dc bias suppression strategies mainly rely on a single type of device, such as blocking capacitor or blocking resistance. However, these methods are passive palliatives and cannot restrain dc bias currents from the sources. In the light of this, a system-level suppression method for dc bias is proposed in this paper. The average value of currents flowing through the earth is offset by actively generating unbalanced current through other dc projects in the same transmission section, which will reduce the currents flowing into the neutral transformers and alleviate the negative impacts of dc bias. First, the feasibility of the same section dc continuous power support is analyzed. Then the dc bias suppression strategy based on reverse unbalanced currents is elaborated. By scanning all the theoretical operable solutions of unbalanced current generation modes and the possible switching combinations of blocking capacitors, the optimal dc bias suppression solution is output considering the number of adjusted dc projects, the overload margin of dc projects and neutral dc currents of transformers. The effectiveness and superiority of the proposed method are verified by comparative case studies of the East China power grid.