Chain-Link Module Topology for Low-Loss DC Fault Clearing
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Solution Overview
Problem
Voltage source converters in HVDC power transmission networks face challenges in efficiently managing voltage levels and fault currents, leading to high conduction losses and the need for expensive DC circuit breakers.
Innovation Solution
A chain-link module with a unique configuration of series-connected switching elements and energy storage devices, allowing for selective voltage generation and fault current management, reducing conduction losses and eliminating the need for DC circuit breakers by enabling full DC fault clearing functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional voltage source converters are used in HVDC power transmission networks, then voltage conversion between AC and DC networks can be achieved, but high conduction losses occur and expensive DC circuit breakers are required for fault current management
Solution Approach 1:
The converter is divided into multiple chain-link modules, each containing series-connected switching elements and energy storage devices. This segmentation allows independent control of each module, reducing overall conduction losses while maintaining voltage conversion capability without requiring expensive DC circuit breakers
Solution Approach 2:
The patent employs dynamically controllable switching elements that can rapidly change state to manage fault currents. This dynamic control enables the converter to respond to fault conditions without requiring mechanical DC circuit breakers, reducing both losses and device complexity
2Power
If multiple chain-link modules are connected in series to build up combined voltage, then higher voltage output is achieved, but the converter requires expensive DC circuit breakers for fault current clearing
Solution Approach 1:
Each chain-link module contains energy storage devices (capacitors) that can rapidly discharge to clear fault currents. This self-service capability eliminates the need for external DC circuit breakers, allowing high voltage output through series connection of multiple modules while simplifying fault current management
Solution Approach 2:
Energy storage devices are pre-charged within each chain-link module during normal operation. When a fault occurs, these pre-charged capacitors immediately discharge to clear the fault current, providing rapid protection without requiring expensive DC circuit breakers
3Ease of manufacture
If conventional converter design is used, then basic voltage conversion is achieved, but conduction losses remain high and cost is increased
Solution Approach 1:
The patent changes the operational parameters by using series-connected switching elements within chain-link modules, allowing for optimized current paths and reduced conduction losses. This approach maintains ease of manufacture through modular design while significantly reducing energy losses
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
The chain-link module achieves lower conduction losses and simplified converter design by providing efficient voltage management and rapid DC fault clearing, reducing costs and enhancing power transmission reliability.
Implementation Method 1
each chain-link module includes a number of switching elements which are connected in parallel with an energy storage device, usually in the form of a capacitor
Implementation Method 2
Each chain-link module includes a first pair of series-connected switching elements, which are separated by a first connection terminal and which are also connected in parallel with first and second series-connected energy storage devices
Data Source
Figure 1
Figure 2(a)~2(d)
Figure 2(b)~2(c)
AI summary
In the field of chain-link modules for voltage source converters, there is a need for an improved chain-link module. A chain-link module (10), for connection in series with other chain-link modules to form a chain-link converter selectively operable to provide a stepped variable voltage source within a voltage source converter, comprises a first pair (12) of series-connected switching elements (14A, 14B) which are separated by a first connection terminal (16) and are connected in parallel with first and second series-connected energy storage devices (18, 20). The chain-link module (10) also includes a second pair (22) of series-connected switching elements (14C, 14D) that are separated by a second connection terminal (24), and which are connected in parallel with one or other of the first and second energy storage devices (18, 20). Switching of the switching elements (14A, 14B, 14C, 14D), in use, selectively: (i) directs current (I) through the first and second energy storage devices (18, 20), whereby the chain-link module (10) provides a positive voltage across the first and second connection terminals (16, 24); (ii) causes current (I) to bypass the first and second energy storage devices (18, 20) whereby the chain-link module (10) provides zero voltage; and (iii) directs current (I) through the one of the first and second energy storage devices (18, 20) with which the second pair (22) of switching elements (14C, 14D) is connected in parallel, whereby the chain-link module (10) provides a negative voltage across the first and second connection terminals (14, 24).