LCC-HVDC Line Protection Using Virtual Grounding Resistance
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Solution Overview
Problem
Existing DC line protection methods fail to consider the influence of the AC system, leading to poor immunity to fault resistance, maloperation in external faults, and inaccurate fault location determination due to reliance on DC system parameters alone.
Innovation Solution
A method and system for pilot directional protection of LCC-HVDC lines based on virtual grounding resistance, which involves obtaining conduction state information and characteristic parameters of the converter circuit, determining characteristic frequencies, and calculating virtual grounding resistance to differentiate between internal and external faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing protection methods (traveling wave, differential under-voltage, or pilot current differential protection) are used, then the protection system can operate with simple parameter monitoring, but the immunity to fault resistance is poor and maloperation occurs in external fault cases
Solution Approach 1:
The patent changes the parameter basis from simple DC system parameters to comprehensive parameters including AC system parameters, converter conduction states, and virtual grounding resistance. This allows the protection system to distinguish internal from external faults by analyzing the virtual grounding resistance characteristics, thereby improving reliability without excessive complexity increase
Solution Approach 2:
The patent introduces virtual grounding resistance as an intermediary parameter that bridges the AC and DC systems. This intermediary enables fault discrimination by providing a measurable quantity that reflects the combined influence of both systems, resolving the contradiction between simple operation and reliable fault judgment
2Reliability
If existing protection methods are used without considering AC system influence, then the system operates with simplified monitoring, but the protection easily mal-operates in external fault cases and is affected by converter and AC system operating conditions
Solution Approach 1:
The patent segments the fault analysis into distinct components: converter conduction state identification, AC system parameter monitoring, and virtual grounding resistance calculation. This segmentation allows systematic consideration of AC system influence while maintaining structured analysis, improving fault resistance immunity without overwhelming complexity
Solution Approach 2:
The patent replaces direct mechanical/electrical parameter monitoring with a virtual parameter (virtual grounding resistance) that mathematically represents the combined system state. This substitution enables comprehensive AC-DC system analysis while simplifying the actual measurement and comparison operations
3Measurement precision
If existing protection methods rely only on DC system parameters, then the system operates with simple parameter acquisition, but the fault location determination is inaccurate due to lack of AC system influence consideration
Solution Approach 1:
The patent merges AC system parameters and DC system parameters into a unified analysis framework through the virtual grounding resistance calculation. This combination enables accurate fault location determination by considering the coupled AC-DC system behavior, achieving high measurement precision while managing complexity through integrated parameter acquisition
Data Source
AI summary
The application relates to a method and system for a pilot directional protection of LCC-HVDC lines based on virtual grounding resistance. The method comprises: Obtaining a conduction state information of a converter and characteristic parameters of a converter circuit within one commutation period after a fault occurs; according to the conduction state information and characteristic parameters, determining characteristic frequency of the circuit; according to the characteristic frequency and characteristic parameters, determining a virtual grounding resistance; according to the virtual grounding resistance, determining fault areas.