Method for connecting convertor station into multiport flexible direct current transmission system in a live manner

Abstract

The invention relates to a method for connecting a convertor station into a multiport flexible direct current transmission system in a live manner, and pertains to the technical field of power electronics. According to the method, with the help of the structure characteristics of the flexible direct current transmission system itself, and through the characteristic that a disconnecting switch can be used to open and close a small-load current or a capacitive current, by appropriately reducing the flexible direct current system direct-current voltage, positive and negative electrode direct-current disconnecting switches are closed successively to realize the multiport flexible direct current transmission system live connection function. According to the invention, through the structure of the flexible direct current transmission system itself and the simple successive operation of the disconnecting switches, the multiport flexible direct-current transmission system live connection problem in the condition that a direct-current circuit breaker cannot be popularize and applied can be solved, advantages of mature technology, reliable operation, easy implementation and excellent performance can be realized, and the method can be applied into actual multiport flexible direct-current transmission projects.

Description

technical field [0001] The invention relates to a method for connecting a converter station to a multi-terminal flexible direct current transmission system with electricity, and belongs to the technical field of power electronics. Background technique [0002] In China, the topological structure of the single station of the multi-terminal flexible direct current transmission system is as follows: figure 1 As shown, the DC side includes the isolation switch QS connected in series with the DC bus, and the AC side includes the AC incoming switch Q1 connected in series, the converter transformer, etc., and the converter transformer adopts the Δ / Yn type connection method, that is, the converter transformer The network side winding adopts delta connection, the valve side winding adopts star connection, and the neutral point of the valve side winding is grounded through a large resistance R. The main purpose of using the Δ / Yn type connection method is to make the DC line of the fl...

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Problems solved by technology

This method has the following disadvantages: it increases the outage probability of the multi-terminal flexible DC transmission system; if the operating system is connected with important loads, the entire system will be shut down in order to merge into the converter station, which will cause heavy losses; if the operating system is connected to the wind farm ( New energy) is connected, then in order to merge into the converter station outage of the whole system will lead to the withdrawal of new energy and re-investment, reducing the energy utilization rate; Merging into the converter station and shutting down the entire system will lead to internal power imbalance of the two asynchronous grids, grid stability control and protection actions, loss of part of the power supply or load, and even lead to cascading failures, resulting in the paralysis of the synchronous grid; Composed of AC and multi-terminal flexible DC transmission systems, the outage of the entire system in order to merge into the converter station may cause AC line overload, and even the line flow exceeds its temporary stability limit, resulting in grid stability control and protection actions; the integration takes a long time, and The operation is cumbersome, and the advantages of the flexible transportation system structure are not fully utilized

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