HVDC Tapping Arrangement Using Voltage Source Converters
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Solution Overview
Problem
HVDC transmission systems face challenges in efficiently tapping electric power along the line due to the need for converter stations of equal capacity, which can lead to disturbances and interruptions in the AC network, making it costly and less reliable compared to AC transmission systems.
Innovation Solution
A tapping arrangement using Voltage Source Converters (VSC) with a switching mechanism to maintain continuous connection and polarity consistency, allowing for flexible power direction and minimizing disruptions, comprising mechanically operated switches, semiconductors, or diodes, and a configuration with multiple VSCs connected between HVDC transmission lines with a common grounding point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a converter station with full capacity is used for tapping power from HVDC line, then power tapping capability is achieved, but system complexity and cost increase significantly
Solution Approach 1:
The converter station is divided into two independent converters: a first converter connected in series with the HVDC line for maintaining line operation, and a second converter connected to the local AC network for power tapping. This segmentation allows each converter to operate independently at reduced capacity, eliminating the need for a full-capacity converter station and enabling flexible power tapping without compromising system complexity.
2Adaptability or versatility
If AC network connection is implemented at tap point, then local power distribution is enabled, but disturbances may temporarily interrupt main HVDC transmission
Solution Approach 1:
The first converter acts as an intermediary between the HVDC line and the second converter. It is connected in series with the HVDC line and can isolate disturbances from the local AC network, preventing them from propagating to the main transmission line. This intermediary structure enables local power distribution while maintaining HVDC transmission continuity by blocking disturbance propagation.
3Adaptability or versatility
If current source converters are used with polarity change capability, then transmission direction flexibility is improved, but tapping arrangement operation becomes complex
Solution Approach 1:
Instead of using current source converters that require polarity changes for bidirectional transmission, the invention uses voltage source converters that maintain constant polarity. This inversion of the converter type eliminates the need for polarity changes and associated complexity in the tapping arrangement, while still achieving transmission flexibility through the independent operation of the two converters.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient and continuous power tapping with reduced resource requirements, minimizing interference with the HVDC system, and maintaining stable AC voltage, even in remote areas with weak AC networks, thus improving the reliability and cost-effectiveness of HVDC transmission.
Implementation Method 1
a voltage source converter (VSC) differ from each other in that the polarity of the dc side of a CSC changes with the transmission direction, while the polarity on the dc side of a VSC is the same irrespective of the transmission direction
Implementation Method 2
a switching arrangement to disconnect the ac network in case of polarity change on the dc transmission line
Data Source
Figure 1~2
Figure 3~4
AI summary
An apparatus for tapping electric energy from an HVDC power transmission system comprises at least one voltage source converter. The apparatus contains an intermediate ac network containing the VSC, and a switching arrangement for disconnecting the intermediate ac network in dependence on the transmission direction of the HVDC power transmission system.