Variable Frequency AC Subsea Power Transmission
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Solution Overview
Problem
Conventional AC power cable transmission is limited in distance, requiring DC to AC conversion for subsea power transmission, which increases complexity and reduces reliability due to the need for large and heavy equipment, especially in long-distance subsea power transmission beyond 200 km.
Innovation Solution
A method that generates AC power and adjusts its frequency and voltage based on load consumption to avoid resonances and maintain stable voltage transfer, using a converter to change frequency and voltage in response to changing power demands, thereby improving reliability and reducing equipment size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If DC transmission is used for long-distance subsea power, then transmission distance is improved, but equipment complexity and size increase due to required DC to AC conversion
Solution Approach 1:
The patent extracts the frequency conversion function from the subsea location and places it at the onshore terminal. By using a variable frequency drive system onshore, the AC power can be transmitted directly through the cable without requiring DC to AC conversion equipment subsea, thus reducing subsea equipment complexity while enabling long-distance transmission
Solution Approach 2:
The patent changes the frequency parameter of the AC power transmission system. By using variable frequency AC transmission instead of fixed frequency, the system can optimize transmission characteristics for different distances and load conditions, eliminating the need for DC conversion equipment while achieving long-distance transmission
2Adaptability or versatility
If DC to AC conversion is implemented subsea, then AC power can be provided to subsea consumers, but system reliability decreases due to increased components
Solution Approach 1:
The patent removes the frequency conversion equipment from the subsea environment and relocates it to the onshore terminal. This eliminates numerous conversion components from the subsea system, reducing failure points and improving reliability while still providing AC power to subsea consumers through variable frequency AC transmission
Solution Approach 2:
The onshore variable frequency drive system serves multiple functions: it provides long-distance transmission capability, enables AC power delivery to subsea loads, and allows dynamic adjustment of transmission parameters. This multi-functionality eliminates the need for separate DC conversion equipment subsea, improving reliability
3Device complexity
If fixed frequency AC transmission is used, then transmission distance is limited, but equipment size and complexity are reduced
Solution Approach 1:
The patent introduces dynamic frequency adjustment capability to the AC transmission system. By making the transmission frequency variable rather than fixed, the system can adapt to different transmission distances and load conditions, significantly extending transmission distance while keeping equipment relatively simple
Solution Approach 2:
The patent changes the frequency parameter from fixed to variable. This parameter change allows the system to optimize transmission characteristics for different distances, enabling long-distance transmission without requiring complex DC conversion equipment, thus achieving both extended range and simplified design
Data Source
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AI summary
It is described a method and arrangement for transferring electrical power (103) in the sea, the method comprising: generating AC power (103); guiding, at least partially underwater, the AC power (103) through a cable (111) from a first end (113) of the cable to a second end (117) of the cable; and changing a frequency of the AC power (103) guided through the cable (111) in dependence of a value of power consumption (126) of a load (127) connected to the second end (117) of the cable (111).