High-Frequency Rectifier HVDC for Lower-Cost Offshore Wind Transmission
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Solution Overview
Problem
Current offshore wind power transmission systems face high construction costs and power losses due to the use of alternating current (AC) systems, particularly for long-distance transmission, and existing low-cost converter solutions are bulky and inefficient, lacking a comprehensive replacement for conventional VSC-HVDC systems.
Innovation Solution
A high-frequency uncontrolled rectifier-based DC transmission system is introduced, increasing the rated frequency of the offshore AC system to reduce the size and weight of transformers and reactive power components, utilizing a symmetrical monopolar DC structure with adaptive transformer parameters and modular multilevel converters, and incorporating three-phase six-pulse uncontrolled rectifier bridges and AC filters to minimize costs and enhance engineering feasibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional VSC-HVDC systems are used for offshore wind power transmission, then transmission reliability is improved, but construction costs and system complexity increase
Solution Approach 1:
The patent replaces expensive and complex VSC-HVDC converter systems with simpler, more economical uncontrolled rectifier bridges. The invention uses conventional AC/DC rectifier technology that is proven, reliable, and significantly cheaper than voltage-source converter systems, while maintaining adequate transmission reliability for offshore wind farms.
Solution Approach 2:
The patent changes the operating frequency parameter from standard 50Hz to high frequency (200-400Hz) to enable the use of smaller transformers and reactive power compensators. This parameter change allows the system to achieve the same power transmission capability with reduced component sizes and lower costs while maintaining system reliability.
2Ease of manufacture
If low-cost converters such as diode rectifier bridges are used, then construction costs are reduced, but transformer size and weight increase
Solution Approach 1:
The patent increases the operating frequency from 50Hz to 200-400Hz, which allows transformers and reactive power compensators to be designed with smaller cores and windings. This frequency parameter change directly reduces the weight and volume of stationary components while maintaining the cost-effectiveness of uncontrolled rectifier technology.
3Reliability
If additional reactive power compensators and AC filters are installed, then power quality is improved, but device complexity and construction costs increase
Solution Approach 1:
By operating at high frequency (200-400Hz), the system reduces the size and reactive power requirements of filters and compensators. The higher frequency allows for more compact filter designs with fewer components, improving power quality while reducing overall device complexity and construction costs.
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 solution significantly reduces construction costs and enhances the reliability of offshore wind power transmission by simplifying the system structure, reducing the size and weight of transformers and reactive power components, and providing a more efficient means of transmitting wind power far from the shore.
Implementation Method 1
a four-arm uncontrolled rectifier bridge comprising four bridge arms H1-H4 respectively, each bridge arm comprising a plurality of diodes connected in series and parallel
Implementation Method 2
parameters of a step-up transformer in the offshore step-up station are adaptive to the rated frequency of the offshore AC system
Data Source
AI summary
The present disclosure provides a high-frequency uncontrolled rectifier-based DC transmission system for an offshore wind farm, including a DC system and an offshore AC system. The offshore AC system mainly includes wind turbines based on permanent magnet synchronous generators with full-scale power converters, AC submarine cables, and offshore step-up stations. The DC system includes an offshore station and an onshore station that are connected by DC submarine cables, where a converter of the offshore is a three-phase six-pulse uncontrolled rectifier bridge, while a converter of the onshore station is MMC. Each of the offshore AC system and the offshore station has a rated frequency far above 50 Hz, which can usually be chosen to be in a range of about 100 Hz to 400 Hz. The disclosed transmission system allows for a great reduction in construction costs and demonstrating great application potentials in actual engineering.