Flexible DC power transmission system fault ride-through method and control system

Abstract

The invention discloses a flexible DC power transmission system fault ride-through method and a control system, and the system mostly employs a method for delaying a 1 / 4 fundamental frequency period to obtain positive and negative sequence voltage and current components, and then suppresses the negative sequence current at a fault moment through a negative sequence current inner loop control method. Due to the inherent characteristics of a 1 / 4 fundamental frequency period delay positive and negative sequence decomposition method, the periodic fluctuation of the impedance of the flexible direct current power transmission system is caused, especially at the high frequency, the risk that the impedance of the flexible direct current power transmission system exceeds 90 degrees is increased, and the possibility of instability exists when the flexible direct current power transmission system is connected with other systems. According to the method, the inner-loop total-sequence current control is adopted, periodic fluctuation of the flexible direct-current power transmission system is avoided in a steady state, the risk that flexible direct-current impedance exceeds 90 degrees is reduced, meanwhile, negative-sequence current control is overlaid in a fault period, and alternating-current fault ride-through of the flexible direct-current power transmission system is achieved.

Description

technical field [0001] The invention belongs to the field of flexible direct current transmission and distribution, and in particular relates to a method and a control system for fault ride-through of a flexible direct current transmission system. Background technique [0002] The flexible DC transmission and distribution system uses a voltage source converter, which can independently and quickly control the active power and reactive power of the system, thereby improving the stability of the system, suppressing the fluctuation of system frequency and voltage, and improving the steady-state performance of the AC system . [0003] With the development of flexible DC transmission technology, more and more flexible DC transmission projects have been built and put into operation at home and abroad. As of July 2020, the domestic flexible DC transmission projects that have been put into operation include: Nanhui Flexible DC Transmission Project, Nanao Three-Terminal Flexible DC T...

AI Technical Summary

Problems solved by technology

[0005] At the same time, in order to realize the ride-through of the flexible DC transmission system when the AC system fails, the flexible DC transmission system mostly uses negative sequence current loop control to suppress the negative sequence current of the fault, and the commonly used positive and negative sequence current with a delay of 1 / 4 cycle The decomposition link introduces the periodic fluctuation of the flexible straight impedance, so that the phase of the flexible straight system is more likely to exceed 90° in the middle and high frequency impedance characteristics, showing inductive negative resistance, which in turn causes differences between the flexible straight system and the AC system or new energy equipment. stable phenomenon

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