METHOD FOR INITIATING FLEXIBLE DC TRANSMISSION SYSTEM UNDER ISOLATED ISLAND CONDITION

Disclosed in the present application is a method for initiating a flexible DC transmission system under 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 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 Uxand rapidly increases to UakV at a rate of a kV/s, so as to avoid the problem that when an output voltage reference wave is too small, the 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 UbkV at a rate of β kV/s, a third segment increases to UckV at a rate of γ kV/s, ..., and the Nthsegment increases to a rated voltage of UNkV at a rate of ε kV/s, thereby achieving non-disturbance and shockless initiation of a flexible DC transmission system under an isolated island condition.