Chain-Link Converter Current Direction from Module Energy Change
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Solution Overview
Problem
HVDC power transmission networks face issues with DCCT devices being a single point of failure, leading to potential shutdowns due to unreliable current flow direction measurements, especially when current flow is low or when experiencing high levels of harmonics, and DCCT devices can be inaccurate, causing incorrect balancing of chain-link module energy storage levels.
Innovation Solution
A controller for chain-link converters that determines the overall current flow direction by evaluating indications from multiple chain-link modules, using a voting methodology to eliminate faulty module influences and assess the health of each module, deriving flow directions from energy storage rate changes, and applying filtering and hysteresis to ensure accurate and reliable current flow direction determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DCCT devices are used to measure current flow direction, then current flow direction can be determined, but the system becomes vulnerable to single point of failure and shutdowns
Solution Approach 1:
The patent divides the current measurement function into multiple independent chain-link modules, each with its own current sensor. Instead of relying on a single DCCT device, the system segments the measurement across multiple sensors that independently monitor current flow direction in their respective modules, eliminating the single point of failure.
Solution Approach 2:
The patent combines the measurements from multiple chain-link modules to determine the overall current flow direction. By merging the data from multiple independent sensors and using a voting mechanism, the system achieves both measurement precision and reliability, as the combined result is more robust than any single measurement.
2Loss of information
If DCCT devices are used to determine current flow direction, then current direction information is available, but accuracy deteriorates under low current conditions and high harmonics
Solution Approach 1:
The patent combines current flow direction indications from multiple chain-link modules to determine the overall direction. This merging of multiple independent measurements improves accuracy under challenging conditions (low current, high harmonics) because the voting mechanism filters out erroneous indications from individual modules.
Solution Approach 2:
The system implements a voting mechanism that provides feedback validation for current flow direction determination. Each chain-link module's measurement is cross-checked against others, and the overall direction is established only when there is majority agreement, providing a feedback-based error correction mechanism that maintains accuracy under varying conditions.
3Power
If multiple chain-link modules are used to provide stepped variable voltage, then higher voltage capability is achieved, but the system complexity increases
Solution Approach 1:
The patent segments the voltage generation function into multiple identical chain-link modules connected in series. Each module contributes a discrete voltage step, and by combining multiple standardized modules, the system achieves high voltage capability while managing complexity through modular design and standardized interfaces.
Data Source
Figure 1
AI summary
In the field of controllers for chain-link converters that have a plurality of series-connected chain-link modules that are operable in combination to provide a stepped variable voltage source, there is a need for an improved controller. A controller (10), for a chain-link converter having a plurality of series-connected chain-link modules that are operable in combination to provide a stepped variable voltage source, is programmed to obtain for each chain-link module (12) an indication (22) of whether the current flow through the corresponding chain-link module (12) is in a first flow direction or a second flow direction. The controller (10) is additionally programmed to evaluate the number of indications (22) in the first flow direction and the number of indications (22) in the second flow direction, and thereafter to establish (36) an overall current flow direction (38) through the chain-link converter equal to the flow direction having the largest number of indications (22).