Offshore Wind Turbine Low-Frequency Transmission System
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Solution Overview
Problem
Existing offshore wind turbine systems require large equipment for low-frequency AC transmission, which is inefficient and costly due to the need for additional frequency conversion equipment at onshore grid connection points.
Innovation Solution
The system employs a gearbox and generator with a rated electrical frequency range of 50 Hz to 150 Hz, converting variable rotational speeds into electricity at a fixed low frequency (16-20 Hz) using an AC-to-AC converter, with an optional step-up transformer to increase voltage, allowing for efficient low-frequency transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If low-frequency AC transmission is used in offshore wind farms, then the economic distance of HVAC connections is extended, but undesirably large equipment is required
Solution Approach 1:
The patent changes the operating frequency parameter from standard grid frequency (50/60 Hz) to low frequency (16.7 Hz or 20 Hz). This parameter change allows the use of smaller transformers and frequency conversion equipment, as the lower frequency reduces the size requirements for magnetic components while still enabling extended transmission distances for HVAC connections.
Solution Approach 2:
The system dynamically adjusts between different frequency regimes by using frequency conversion equipment that can operate at both low frequency (for efficient transmission over distance) and grid frequency (for onshore connection). This dynamic flexibility resolves the contradiction by allowing the system to operate at optimal frequency for each transmission segment.
2Speed
If low-speed generators producing 16.7Hz or 20Hz AC output are used, then low-frequency transmission is achieved, but additional frequency conversion equipment at onshore grid connection point is required
Solution Approach 1:
The patent introduces an intermediary frequency conversion system that acts as a mediator between the low-speed generator output and the onshore grid. This intermediary equipment converts the low-frequency AC output (16.7Hz or 20Hz) to standard grid frequency, enabling compatibility with existing onshore infrastructure while maintaining the benefits of low-speed generation.
Solution Approach 2:
The frequency conversion equipment is designed to handle multiple functions: it accepts variable frequency input from the generator, converts to fixed low frequency for offshore transmission, and can also convert to grid frequency for onshore connection. This multi-functionality reduces overall system complexity by using a single versatile piece of equipment rather than multiple specialized devices.
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 configuration reduces equipment size and cost by enabling efficient conversion and transmission of electricity at a fixed low frequency, extending the economic distance of HVAC connections and optimizing wind power conversion.
Implementation Method 1
a gearbox configured to mechanically convert a first variable rotational speed of a wind turbine into a corresponding higher second variable rotational speed
Implementation Method 2
a generator having a rated electrical frequency for full-power output in a range from about 50 Hz to about 150 Hz, and configured to be driven at the variable second rotational speed by an output of the gearbox. The generator thereby generates electricity at a correspondingly variable first frequency
Implementation Method 3
an AC-to-AC converter configured to convert the electricity from the generator into electricity output from the AC-to-AC converter at a fixed low frequency for off-shore collection at the fixed low frequency
Implementation Method 4
a step-up transformer connected between the generator and the AC-to-AC converter. The step-up transformer has a rated frequency corresponding to the rated electrical frequency of the generator and is configured to step up a voltage of the electricity output from the generator
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
According to one aspect of the teachings herein, various feeder connection arrangements and architectures are disclosed, for collecting electricity from wind turbines in an offshore collection grid that operates at a fixed low frequency, e.g., at one third of the targeted utility grid frequency. Embodiments herein detail various feeder arrangements, such as the use of parallel feeder connections and cluster-based feeder arrangements where a centralized substation includes a common step-up transformer for outputting electricity at a stepped-up voltage, for low-frequency transmission to onshore equipment. Further aspects relate to advantageous generation arrangements, e.g., tower-based arrangements, for converting wind power into electrical power using, for example, medium-speed or high-speed gearboxes driving generators having a rated electrical frequency for full-power output in a range from about 50 Hz to about 150 Hz, with subsequent conversion to the fixed low frequency for off-shore collection.