Modular AC-DC Converter Series for Offshore Wind Transmission
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Solution Overview
Problem
Conventional AC power transmission over long distances faces inefficiencies due to capacitance-related charging currents, which reduce the cable's source carrying capability, especially in bulk power transmission from remote sources like offshore wind farms, leading to increased costs and complexity.
Innovation Solution
A DC power transmission system with AC-to-DC power converter modules coupled in series to a DC link, allowing for efficient power transmission from offshore sources to the grid, reducing the need for transformers and circuit breakers, and incorporating modular redundancy and phase shifting features to enhance reliability and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If AC power transmission is used over long distances, then power can be transmitted from remote sources, but capacitance causes charging current to flow which reduces the cable's source carrying capability
Solution Approach 1:
The patent changes the fundamental parameter of power transmission from AC to DC. By converting AC to DC at the source end and back to AC at the receiving end, the system eliminates the capacitance-related charging current problem that plagues long-distance AC transmission, thereby restoring full source carrying capability to the cable.
Solution Approach 2:
The patent introduces AC-DC power converter modules as intermediary devices at both ends of the transmission line. These converters act as mediators that transform the power form to enable efficient long-distance transmission without the harmful effects of AC capacitance, allowing the cable to transmit only useful source current.
2Loss of energy
If AC transmission voltage is increased to minimize line losses and voltage drop, then transmission efficiency improves, but charging current also increases
Solution Approach 1:
The patent changes the power transmission parameter from AC to DC, fundamentally eliminating the charging current phenomenon. In DC transmission, there is no capacitive charging current regardless of voltage level, allowing the system to operate at high voltages to minimize line losses without the penalty of increased charging current.
3Ease of manufacture
If conventional AC transmission systems are used, then power transmission is straightforward, but transformers and switchgears are required which increase cost and complexity
Solution Approach 1:
The patent replaces the traditional AC transmission mechanism with a DC transmission mechanism using power electronic converters. This substitution eliminates the need for bulky transformers and switchgears along the transmission line, reducing both cost and complexity while maintaining the ability to transmit power over long distances.
4Power
If series connection of semiconductor devices is used to handle high voltages, then converter capability is achieved, but reliability decreases due to multiple failure points
Solution Approach 1:
The patent segments the high voltage converter into multiple independent modular units, each handling a portion of the total voltage. These modular converters are connected in series on the DC side, allowing the system to achieve high voltage capability while maintaining reliability through redundancy and independent operation of each module.
Solution Approach 2:
The patent implements redundancy by having multiple modular converters that can compensate for individual failures. If one module fails, the others can continue operating, providing beforehand cushioning against complete system failure and thereby improving overall reliability.
Data Source
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AI summary
A collection and transmission system (10) includes: a system direct current (DC) link (12) configured for carrying power from a source (13) to a grid (16); and alternating current (AC) to DC power converter modules (19, 119, 219, 319) coupled in series to the system DC link on a source side of the system DC link, each power converter module configured for being coupled to one or more sources (114, 214, 314, 414) on the source side, wherein each power converter module is configured to short circuit the DC terminals of the power converter module upon receipt of a respective command signal.