An improved additional frequency control method and system for a multi-terminal flexible direct current transmission system

Abstract

The invention discloses an improved additional frequency control method and system for a multi-terminal flexible DC power transmission system. The method comprises the steps of calculating the frequency deviation of an AC system, calculating a frequency droop coefficient actual value according to the AC system frequency deviation, calculating an error between the converter station active power actual value and a reference value according to the frequency droop coefficient actual value and the active power transmitted by the converter station, subtracting the DC side outlet voltage of the converter station from the DC voltage reference value of the converter station to obtain an error between the actual value of the DC side outlet voltage of the converter station and the reference value, calculating an actual value of a DC voltage droop coefficient according to the AC system frequency deviation, and calculating a converter station d-axis current reference value according to the error between the converter station active power actual value and the reference value, the error between the converter station DC side outlet voltage actual value and the reference value and the DC voltage droop coefficient actual value. By adopting the method and the system provided by the invention, the DC voltage can be prevented from being greatly reduced due to a large amount of unbalanced power, andthe frequency of a weak AC system can be prevented from greatly deviating.

Description

technical field [0001] The invention relates to the technical field of power system stability control, in particular to an improved additional frequency control method and system for a multi-terminal flexible direct current transmission system. Background technique [0002] Flexible HVDC technology represented by Voltage Sourced Converter (Voltage Sourced Converter, VSC) and Modular Multilevel Converter (Modular Multilevel Converter, MMC) has the advantages of no commutation failure, power decoupling control, etc. It has been widely used in engineering. The Multi-Terminal Flexible DC Transmission System (Voltage Sourced Converter Based Multi-Terminal High Voltage DirectCurrent, VSC-MTDC) based on VSC and MMC technology has flexible and diverse operation modes, and it can accommodate new energy generation and adapt to the imbalance between energy supply and power demand. Has great potential for development. [0003] Maintaining the energy balance of the multi-terminal flexi...

AI Technical Summary

Problems solved by technology

However, there are two problems in this traditional additional frequency control: 1) The unbalanced power delivered to the DC network by the faulty AC system increases proportionally with the increase of the frequency deviation of the faulty AC system, and too much unbalanced power is transmitted to the DC network It will threaten the stability of the DC voltage; 2) There is no coordination to consider the ability of the non-fault side AC system to bear unbalanced power, and the weak AC system can bear too much unbalanced power, which may cause frequency instability of the non-fault AC system

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