Oscillation frequency prediction and control method of flexible HVDC transmission in non-islanding control mode

Abstract

The invention discloses a flexible DC power transmission oscillation frequency prediction and control method under a non-island control mode. The prediction method comprises the following steps: unlocking a convertor station of a flexible DC power transmission system, and running the flexible DC power transmission system in the non-island control mode; extracting corresponding parameters of the flexible DC power transmission system, wherein the corresponding parameters comprise an AC system voltage effective value UtO, a gain kp of the phase-locked loop PLL and the proportion integral time constant ki; taking the AC system voltage as a reference value, computing the prediction oscillation frequency; and checking whether the prediction oscillation frequency is a non-zero real number; if theprediction oscillation parameter is the non-zero real number, regarding that the flexible DC power transmission system is unstable, the flexible DC power transmission system has the oscillation at the frequency band and cannot be put into the flexile DC power transmission; if the virtual number is equal to zero, regarding that the flexible DC power transmission system is stable, the frequency band oscillation mode is inexistent, and the system can be put into the flexible DC power transmission. The corresponding oscillation frequency can be computed through simple parameter, the prediction issimple and practicable, and in favor of engineering practice.

Description

technical field [0001] The invention relates to the technical field of control of a flexible direct current transmission system, in particular to a method for predicting and controlling oscillation frequency of a flexible direct current transmission under a non-islanding control mode. Background technique [0002] Compared with traditional LCC-HVDC, flexible direct current transmission VSC-HVDC can provide reactive power support for AC system without commutation failure, so it has wider application prospects in weak connection scenarios. In particular, in the island control mode (constant AC voltage, constant AC frequency), it can realize new functions that conventional transmission methods do not have, such as flexible grid connection of new energy, power transmission to passive systems, and auxiliary grid black start. [0003] When the VSC-HVDC is connected in parallel with the AC system, the system frequency is determined by the AC main network. At this time, the VSC must...

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Problems solved by technology

[0008] 2) Through the impedance modeling of the system, whether the input impedance characteristic of the system is negative is used to judge whether the system is stable. First, the overall modeling is required; : Wu Wenhua, Chen Yandong, Luo An, Zhou Leming, Zhou Xiaoping, Yang Ling, Huang Xucheng. DC Impedance Modeling, Oscillation Analysis and Suppression Methods of Island VSC-HVDC Transmission System. Proceedings of the Chinese Society for Electrical Engineering, 2018, 38(15):4359-4368+ 4636. "A Virtual Resistor Current Limit Control Method for Suppressing Continuous Commutation Failure in Traditional DC Transmission")

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