Voltage Source Converter Fault Positioning via Zero Sequence Voltage
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Solution Overview
Problem
In transformerless voltage source converter systems, accurately positioning faults caused by zero sequence voltages is challenging, leading to unbalanced AC voltages across multiple stations, which affects the normal operation of non-faulty stations and hinders the adoption of transformerless connections due to increased space, loss, and cost requirements.
Innovation Solution
A method and system for fault positioning and recovery that locks converter stations when zero sequence voltages are detected, allowing for the identification of faulty stations by monitoring AC and DC voltages, and enables rapid recovery by isolating the faulty station from non-faulty ones, ensuring continuous operation and reducing the impact of faulty stations on the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If transformerless connection is used to reduce space, loss, and cost, then manufacturing cost and occupied space are reduced, but fault positioning accuracy deteriorates due to zero sequence voltage transmission
Solution Approach 1:
The patent introduces an intermediary mechanism by detecting zero sequence voltage at both terminals of the DC transmission line. This intermediary detection method allows indirect identification of the faulty station through voltage comparison, resolving the fault positioning accuracy issue while maintaining the transformerless connection structure.
Solution Approach 2:
The patent changes the detection parameter from phase voltage to zero sequence voltage. By monitoring the zero sequence voltage component (U0) at both terminals and comparing its magnitude, the system can accurately identify the faulty station. This parameter change enables fault positioning without requiring transformers, thus reducing cost and space while maintaining accuracy.
2Area of stationary object
If transformerless connection is used to reduce occupied space, then space requirement is reduced, but system reliability deteriorates due to unbalanced voltage propagation
Solution Approach 1:
The patent segments the DC transmission system into two independent terminals (sending end and receiving end) with independent zero sequence voltage detection capabilities. This segmentation allows each terminal to independently identify faults, preventing unbalanced voltage propagation and maintaining system reliability while using transformerless connection.
Solution Approach 2:
The patent implements a feedback mechanism where zero sequence voltage detection results from both terminals are continuously monitored and compared. When a fault is detected at one terminal, the system provides feedback to lock that terminal and prevent further propagation, thereby maintaining system reliability without requiring transformers.
3Device complexity
If conventional detection method is used to simplify the system, then device complexity is reduced, but fault detection capability deteriorates due to inability to detect zero sequence voltage
Solution Approach 1:
The patent introduces dynamic control by implementing a locking mechanism on the DC side. When zero sequence voltage is detected, the system dynamically locks the converter at the faulty terminal, preventing further propagation of unbalanced voltage. This dynamic response enhances fault detection capability while maintaining relatively simple device structure.
Solution Approach 2:
The patent performs preliminary action by detecting zero sequence voltage before significant unbalanced voltage propagation occurs. The system continuously monitors zero sequence voltage components and takes preventive action by locking the faulty terminal early in the fault process, thereby improving detection capability without adding complex equipment.
Data Source
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AI summary
The present invention relates to a method and system for fault positioning and recovery of a voltage source converter. The method comprises: locking a converter station when it is detected that an alternating-current voltage contains a zero sequence voltage or a direct-current voltage contains an unbalanced voltage; positioning a fault by continuing to detect the zero sequence voltage of an alternating-current side of the converter; and recovering the operation of each station after the fault is positioned. The method for fault positioning and recovery is simple and practical, has high reliability and can effectively detect the problems that each station contains a zero sequence voltage of an alternating-current side and cannot easily position a fault caused due to the fact that the zero sequence voltage of the alternating-current side is transmitted by a voltage source converter to an opposite-side alternating-current system; meanwhile, by means of the recovery method, a non-faulty converter station can get rid of the influences of a faulty converter station for rapid recovery, rapid recovery based on a voltage source converter station system is implemented, and the application of a transformerless wiring method in the voltage source converter can be promoted, thereby finally achieving that the occupied space of a converter station is reduced, losses are reduced, and manufacture costs are reduced.