Series Voltage Injection for Multi-Terminal HVDC Networks
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Solution Overview
Problem
Multi-terminal HVDC networks face significant voltage drop issues due to long transmission line lengths, which cannot be effectively compensated by existing two-terminal HVDC link countermeasures, especially when using Voltage Source Converters (VSCs), leading to reduced power transfer capabilities and increased costs for designing converter stations to handle voltage variations.
Innovation Solution
An active voltage source device is introduced in series with one transmission line to inject additional DC voltage, controlled by a central unit to maintain voltage levels within a predefined range, allowing all converter stations to have standardized voltage ratings and reducing the risk of earth faults by minimizing DC current levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the length of transmission lines is increased to expand the network coverage and power transfer distance, then the network's power transfer capability and coverage area are improved, but the voltage drop along the lines increases significantly, leading to reduced power transfer capabilities and requiring higher converter station voltage ratings
Solution Approach 1:
An intermediary device (voltage source converter or series compensation device) is introduced into the transmission line to actively compensate for the voltage drop. This mediator injects or absorbs voltage to counteract the resistive and reactive losses in the long transmission line, thereby maintaining the voltage level without requiring higher converter station ratings.
Solution Approach 2:
The voltage compensation mechanism dynamically changes the voltage parameter along the transmission line by adjusting the compensation level based on the actual voltage drop. This allows the system to adapt to varying load conditions and line lengths, maintaining optimal voltage levels throughout the network.
2Adaptability or versatility
If converter stations are designed to handle larger voltage variations to accommodate long transmission lines, then the network's adaptability to different line lengths is improved, but the cost and complexity of converter station design increases
Solution Approach 1:
Instead of designing converter stations to handle the full range of voltage variations that would occur over very long distances, the invention applies partial compensation through intermediary devices. The converter stations only need to handle moderate voltage variations, while the series compensation or VSC devices provide the additional voltage support, avoiding the need for excessively rated converter stations.
3Device complexity
If existing two-terminal HVDC link countermeasures are applied to multi-terminal networks, then the implementation complexity is reduced, but the voltage drop compensation effectiveness is insufficient for multi-terminal network configurations
Solution Approach 1:
The voltage compensation mechanism is designed to be universal and applicable to multi-terminal HVDC networks, where a single compensation device can serve multiple converter stations and transmission lines. The system can dynamically adjust which lines or terminals receive compensation based on real-time network conditions, providing flexible and effective voltage support across the entire multi-terminal network.
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
This solution ensures stable power transfer across multi-terminal HVDC networks of any size by maintaining voltage levels, reducing heat generation, and minimizing the risk of earth faults, while standardizing converter station design and reducing operational costs.
Implementation Method 1
an active voltage source device is introduced in series with one transmission line to inject additional DC voltage
Data Source
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AI summary
In a multi-terminal HVDC power transmission network (10) comprising at least three HVDC converter stations (1 to 6) interconnected by at least two transmission lines (12, 14, 16, 18, 20), where at least one of the transmission lines is a long line, an active voltage source device (30) is series connected to one of the transmission lines (20), which maintains the DC voltage of the transmission lines of the network to be within a predefined voltage range by injecting an additional DC voltage in series with the one transmission line (20).