Medium Voltage DC Collection System for Offshore Wind
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Solution Overview
Problem
Current offshore wind power plants face inefficiencies and complexity due to low voltage medium voltage AC collection systems, which result in high power losses and require large electrical equipment, while transitioning to medium voltage DC systems poses challenges in achieving high voltage levels without DC/DC conversion at wind turbines.
Innovation Solution
A power generation system utilizing multi-phase wind turbine generators with dual three-phase stator windings and power cell based modular converters to achieve a high range medium voltage DC system up to 50 kV, eliminating the need for wind turbine step-up transformers and incorporating DC/AC converters for efficient grid integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If medium voltage AC collection system (33 kV) is used, then system compatibility with existing wind turbine technologies is maintained, but power loss increases and system efficiency decreases
Solution Approach 1:
The patent changes the voltage level parameter from 33 kV AC to higher voltage DC (50-80 kV), and transforms the current type from AC to DC. This parameter change reduces power loss in cable transmissions and eliminates the need for step-up transformers, directly addressing the energy loss problem while maintaining adaptability through power electronic conversion interfaces.
Solution Approach 2:
The patent replaces mechanical/physical transformer systems with power electronic conversion systems. Instead of using traditional AC-AC transformer connections, the invention uses rectifier-converter systems to transform generator output to DC collection system voltage, eliminating bulky step-up transformers and reducing energy losses.
2Loss of energy
If collection system voltage is increased from 33 kV to 72 kV, then system efficiency improves, but electrical equipment dimensions increase
Solution Approach 1:
The patent replaces traditional AC collection system equipment (transformers, switchgear) with DC collection system equipment. DC circuit breakers and DC disconnectors have smaller dimensions compared to their AC counterparts at equivalent voltage levels, allowing high voltage operation without proportionally increasing equipment size.
Solution Approach 2:
The patent extracts and removes the step-up transformer component from the wind turbine system when using DC collection. By converting generator output directly to DC at the generator voltage level and collecting it on the DC network, the system eliminates the need for large transformer equipment, reducing overall electrical equipment dimensions.
3Loss of energy
If medium voltage DC collection system is adopted, then power loss is reduced and efficiency improves, but system complexity increases due to DC/DC conversion requirements
Solution Approach 1:
The patent extracts and removes the DC/DC conversion stage from the system architecture. By using power cell based modular converters that can directly convert generator output to the required DC collection voltage level, the system eliminates the need for intermediate DC/DC conversion equipment, thereby reducing system complexity while maintaining the benefits of DC collection.
Solution Approach 2:
The patent employs power cell based modular converters that perform multiple functions: rectification, voltage conversion, and DC collection interface. These multi-functional converters replace what would traditionally require separate rectifier and DC/DC converter stages, simplifying the overall system architecture while achieving reduced power loss.
4Power
If dual three-phase stator windings with power cell based modular converters are used, then high voltage DC (50-80 kV) is achieved without DC/DC conversion, but converter complexity increases
Solution Approach 1:
The patent segments the converter system into modular power cells, where each cell handles a portion of the total power conversion. This segmentation allows the system to achieve high voltage (50-80 kV) through series connection of multiple identical modular units, making the complex high voltage conversion manageable through standardized, repeatable modules rather than a single complex converter.
Solution Approach 2:
The patent utilizes the generator's dual three-phase stator windings to directly produce the voltage required for high voltage DC collection. By changing the electrical connection configuration and using power electronic switching, the system transforms the generator's natural output into the required DC voltage level, achieving high voltage without intermediate DC/DC conversion stages.
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 enables a high-efficiency, reliable medium voltage DC system with reduced equipment size and complexity, improving overall system performance and controllability by minimizing harmonic filters and allowing for advanced control strategies through coordinated DC/AC converter management.
Implementation Method 1
a rectifier for a wind generator has at least two sets of stator windings with power cell based modular converters associated with each set of stator windings wherein each winding is connected to an AC voltage side of the associated rectifier
Data Source
Figure 1
Figure 1A
Figure 2
AI summary
A power generation system includes at least one generator having at least two sets of stator windings, an active rectifier comprising power cell based modular converters associated with each set of generator windings. Each set of windings is connected to an AC voltage side of the associated active rectifier, with each active rectifier having a positive DC voltage output and a negative DC voltage output. The DC voltage outputs of active rectifiers are connected to each other in series. A medium voltage DC (MVDC) collection network comprises positive pole cables and negative pole cables, wherein each positive pole cable is connected to the positive DC voltage output of a first active rectifier and each negative pole cable is connected to the negative DC voltage output of a last active rectifier. A substation receives the negative and positive pole cables of the MVDC collection network for further transformation and transmission.