Method for initiating flexible DC transmission system under isolated island condition

摘要

Disclosed in the present invention is a method for initiating a flexible DC transmission system in an isolated island condition. When no AC power supply is present in an AC grid region connected to a flexible DC converter station, the flexible DC converter station needs to initiate and operate in an isolated island mode. The isolated island mode uses dual closed-loop control, wherein an outer loop controls the amplitude and frequency of the output voltage and an inner loop controls the output current. During initiation under an isolated island condition, the amplitude size of a voltage reference wave output generated by a flexible DC transmission control and protection system is in a segmented mode, wherein a first segment of the reference wave amplitude begins at zero or a fixed value Ux and rapidly increases to Ua kV at a rate of α kV/s, so as to avoid the problem that when an output voltage reference wave is too small, error and harmonic content of a sampled voltage and current are too high, resulting in an adverse effect on the control system; and a second segment increases to Ub kV at a rate of β kV/s, a third segment increases to Uc kV at a rate of γ kV/s, …, and an N