AC differential protection method for AC-DC interconnection system based on abc-αβ variation

Abstract

The invention relates to an alternating current and direct current interconnection system alternating current differential protection method based on abc-alphabeta change. The method comprises the following steps that inverter side direct current system equivalent injection current when a system runs normally and inverter side direct current system equivalent injection current after the system breaks down are collected and calculated to obtain resultant current magnitude ImN and Im during normal running and resultant current magnitude ImN and Im after a breakdown; whether or not the resultantcurrent magnitude Im after the breakdown is lower than an auxiliary criterion starting threshold is judged, and if the resultant current magnitude Im after the breakdown is lower than a threshold value, the fact that a rectifier side direct current control strategy is switched to voltage-dependent current-limit control is proven; whether or not delta Idiff and delta Ires meet a traditional criterion is judged, if the delta Idiff and the delta Ires meet the traditional criterion, the facts that an inverter side alternating current circuit generation zone breaks down, and the traditional protection criterion can accurately identify the breakdown are proven, and protection action is supposed to be exported immediately; if the traditional criterion fails to export protection action, if a ratiois large and meets the auxiliary criterion conditions at the same time, the fact that the inverter side alternating current circuit generation zone breaks down is proven, and equivalent injection current is under limiting action of a voltage-dependent current-limit link, so that the traditional criterion refuses to move, and meanwhile, the auxiliary criterion exports fault phase protection action.

Description

technical field [0001] The invention relates to the field of control and protection of AC and DC interconnected power grids in electric power systems, in particular to an AC system current differential protection method based on abc-αβ changes. Background technique [0002] my country's electric energy presents the characteristics of reverse distribution in terms of supply and demand, so my country has a great demand for cross-regional, long-distance and large-scale power transmission. The power pattern of AC and DC interconnection has been basically formed in our country. High voltage direct current (HVDC) lines have gradually become an important backbone of my country's inter-interval power grid due to its advantages of large transmission capacity, long distance, and less land occupation of line corridors. The split-phase optical fiber ratio braking current differential protection based on fault components is widely used as the main protection of AC lines with voltage lev...

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Problems solved by technology

"The Research on the Affection of the Qinghai-Tibet HVDC Transmission System upon Operating Characteristic of the Line Protection in Qinghai ACE Electrical Power System" combines engineering examples to conduct corresponding research on the actual operation of current differential protection after AC system faults, pointing out that DC The rapid adjustment of the system will lead to the decrease of the quick action of the current differential protection of the AC system

"Application Research of Pilot Protection Based on Parameter Identification in AC-DC Hybrid Power Grid" points out based on simulation that the connection of DC system will reduce the sensitivity of current differential protection in the event of high-resistance grounding faults in the AC system, and the Based on this, a longitudinal protection principle based on shunt reactors is proposed, but this principle is limited by the length of the AC line, and the protection action speed for shorter AC lines is relatively slow

"HVDC Commutation Failure Transient Characteristics and Its Impact on Differential Protection Analysis and Countermeasures" proposes a protection criterion method based on the current amplitude ratio at both ends of the AC line. To a certain extent, the sensitivity of the protection action has been improved, but it is still insufficient in terms of selectivity and reliability. The overall action performance of the protection is subject to the selection of criterion parameters.

The protection adaptability analysis and corresponding methods proposed by the above scholars provide ideas for further in-depth research, but the overall lack of systematic theoretical support and low feasibility in practical engineering

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