MVDC Collection Grid With Modular DC-DC Converters

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Solution Overview

Problem

Current DC connection systems for large-scale offshore wind farms face inefficiencies and high costs due to the need for two-stage DC-DC power conversions and practical limitations in achieving high voltage levels, particularly with conventional HVDC transmission systems.

Innovation Solution

A DC connection scheme featuring a high-range MVDC collection grid with modular DC-DC converters and a bipole HVDC transmission system, utilizing active rectifiers and energy storage circuits to achieve one-stage centralized DC-DC conversion, enabling efficient power transfer from the MVDC system to the HVDC transmission system.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If two-stage DC-DC power conversion is used at wind turbines and offshore platform, then voltage level matching is achieved, but system complexity and cost increase

Engineering Contradiction:

Improvevoltage level matchingVSAvoidsystem complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent extracts the DC-DC conversion function from the wind turbine level and concentrates it at the offshore platform level. By removing the need for DC-DC converters at each wind turbine and keeping only one stage at the platform, the system achieves voltage level matching while reducing overall system complexity and the number of power conversion devices required.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent merges the voltage transformation function into the HVDC transmission system itself, combining the collection grid operation with the voltage boosting function. This consolidation eliminates the need for separate two-stage conversion systems and reduces the total number of power electronic devices while maintaining adaptability to different voltage levels.

Inventive Principle:

Principle #5Merging (Combining)

2Adaptability or versatility

If series connection of wind turbines is used to reach HVDC voltage level, then voltage matching is achieved, but practical implementation becomes infeasible

Engineering Contradiction:

Improvevoltage level matchingVSAvoidpractical feasibility

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent introduces an intermediary MVDC collection grid at the offshore platform that serves as a buffer between the wind turbine AC outputs and the final DC transmission. This intermediate stage allows voltage transformation without requiring direct series connection of turbines, making the system practically feasible while still achieving the necessary voltage levels for HVDC transmission.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If MVAC collection grid with transformers is used, then power transfer is achieved, but system efficiency decreases

Engineering Contradiction:

Improvepower transfer capabilityVSAvoidsystem efficiency

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent replaces the mechanical transformer-based AC collection grid with an electronic DC collection and conversion system. By substituting electromagnetic transformers with power electronic DC-DC converters at the offshore platform, the system eliminates transformer losses and achieves higher overall efficiency while maintaining full power transfer capability from wind turbines to the HVDC transmission system.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enhances system efficiency and reduces costs by enabling balanced operation of the HVDC system, allowing for compact converter stations and flexible voltage control, suitable for large offshore wind farms and long-distance connections.

Implementation Method 1

a plurality of generator-rectifier subsystems, the subsystems having at least one generator with an active rectifier

Methodology Applied

Scientific EffectRectification: Diode

Implementation Method 2

utilizing active rectifiers and energy storage circuits to achieve one-stage centralized DC-DC conversion

Methodology Applied

Scientific EffectEnergy storage: Capacitance

Data Source

PatentEP2810353B1DC connection scheme for windfarm with internal MVDC collection grid

Publication Date: 2015.10.28 ABB RES LTD

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AI summary

Connection schemes for offshore power generation with an internal collection grid include a power generation system (22) which includes a plurality of generator-rectifier subsystems (23). The scheme further includes a medium voltage DC (MVDC) collection network with positive pole cables (42) and negative pole cables (44) connected to the DC outputs of the generator-rectifier subsystems (23). At least one offshore substation (50) includes a positive bus bar (54) and a negative bus bar (56) correspondingly connected to the positive pole cables (42) and negative pole cables (44) of the MVDC collection network and a plurality of main DC-DC converters (58). Each main DC-DC converter (58) includes modules connected to the MVDC bus bars (54, 56) and each module has a positive and a negative output with the modules' outputs serially connected to one another. The schemes may also include a high voltage DC transmission system connected to the modules' outputs and at least one DC/AC converter at a substation.