An Optimal Reactive Power Control Strategy for UHVAC/DC Hybrid System in East China Grid

During the holidays, the power load of the East China Grid dropped significantly, resulting in excess capacitive reactive power, which makes the grid voltage increase significantly. For ultra-high voltage alternating current/direct current (UHVAC/DC) hybrid system, restricted by the minimum input number of the alternating current filter (ACF) in the dc converter stations, multiple dc stations that operate at a low-power transmission mode will inject a large capacitive reactive power to 500 kV ac grid, leading to a dramatic voltage rise. In addition, the 1000 kV UHVAC system may also transport a large capacitive reactive power to 500 kV ac grid during the holidays. In this paper, an optimal reactive power control strategy based on multi-dc power modulation has been proposed. It includes two steps. First, the minimized reactive power interchange control strategy which minimizes the reactive power interchange (RPI) between the UHVAC grid and the 500 kV ac grid has been executed. After that, if the grid voltage still exceeds the upper limit, the multi-dc power modulation is used to minimize the RPI between the dc converter stations and the 500 kV ac grid. The example analysis shows that the proposed optimal reactive power control strategy can effectively optimize the reactive power distribution in the UHVAC/DC hybrid system, thus reasonably controling the grid voltage.