Method for determining the minimum number of power-on units at the transmitting end of UHVDC considering transient over-voltage

When UHVDC is used for long-distance, large-capacity transmission of renewable energy power, the transient overvoltage problem at the transmitting end caused by UHVDC power disturbance becomes the main factor that restricts the DC transmission capability. This problem can be effectively alleviated by constructing thermal power units at the UHVDC transmission end. However, for the calculation of transient over-voltage of the transmitting end caused by the large-capacity UHVDC power disturbance, the simulation analysis method is mainly used, and there is no effective theoretical calculation method; for the determination of the minimum number of power-on units for the nearby thermal power units, the simulation analysis combined with the trial-and-test method is mainly used, and the workload is huge. Based on the single-branch voltage drop formula, this paper derives the formula of the transient voltage rise caused by the change of the node load, which is used to effectively evaluate the risk of the transient over-voltage at the transmitting end during the DC disturbance and determine the minimum number of power-on units for the nearby thermal power units. This method can significantly reduce the amount of work involved.