5th Connection of offshore wind farms · • Focuses on large offshore wind farms. • Objectives are to develop tools for techno-economical comparison and optimization of the OWPP

DTU Wind Energy5 February 2019

Connection of offshore wind farms

Nicolaos A. Cutululis15th International ACDC 2019 tutorial5th February 2019 – Coventry, UK

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Innovative Tools for Offshore Wind & DC grids

Marie Sklodowska-Curie funding European Union Horizon 2020 research & innovationThis project has received funding from the European Union's Horizon 2020 research andinnovation programme under the Marie Sklodowska-Curie grant agreement no. 765585

This presentation reflects only the author’s view. The Research Executive Agency and European Commission are not responsible for any use that may be made of the information it contains.


6 x countries - 14 x PartnersUniversity Beneficiaries:Cardiff University Universitat

Politècnica de Catalunya

Universidad Do Porto

DanmarksTekniskeUniversitet

KatholiekeUniversiteitLeuven

Non-academic Beneficiaries:CINERGIA, Spain EFACEC, Portugal CG Holdings Belgium ELIA, Belgium

Partner organisations (training & secondments):Vattenfall Toshiba Friends of the

SupergridChina ElectricPower Research Institute

Red Eléctrica de España


InnoDC Work package 2• Focuses on large offshore wind farms. • Objectives are to develop tools for techno-economical comparison and optimization

of the OWPP collector system and to develop novel control solutions for cluster supervisory control of large OWPP

• Contributions from Early Stage Researchers: – ESR-2: 'DC collection systems for offshore wind farms' (Cardiff – Gayan Abeynayake)– ESR-7: 'Development of tools for the analysis of the stability of offshore AC grids and

grids rich in power electronic converters' (UPC – Luis Orellana)– ESR-9: 'Tools for analysis of novel concepts of transmission systems for offshore wind

power plants (UPC – Jovana Dakic)– ESR-10: 'Cluster supervisory control of large offshore wind power plants’ (DTU – Anup

Kavimandan)– ESR-15: 'Black start and islanding operation capabilities of offshore wind power plants’

(DTU – Anubhav Jain)

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Agenda

• Collector systems– AC– DC

• Transmission technology–HVAC

• 50 Hz & LFAC–HVDC

• VSC & DRU HVDC• Control challenges in large OWPPs

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Wind farm (park) definition

• A wind farm is a collection of wind turbines connected to the public gridthrough the same point of connection (POC)

• The wind turbines in a wind farm are controlled in a coordinated manner, generally using a centralized controller, a.k.a wind farm control

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Wind farm layouts

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Horns Rev 2

91 WT x 2.3 MW=209 MW

Operational 2009

Horns Rev 1

80 WT x 2.0 MW=160 MW

Operational 2003

Horns Rev 3

49 WT x 8.3 MW=406.7 MW

Operational 2020


Collection system

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Radial Star Ring

Source: Hertem, Gomis-Bellmunt, Liang, HVDC grids, Wiley, ISBN: 978-1-118-85915-5

ESR-9: ' Tools for analysis of novel concepts of transmission systems for offshore wind power plants (UPC –

Jovana Dakic)


Collection systems

Radial Star RingMost used Highest cost High cost

Cost effective Reduced cable ratings Oversizing of (some) cablesLimited reliability Increased reliability Best reliability

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DC offshore wind power plants – shunt topology

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ESR-2: 'DC collection systems for offshore wind farms' (Cardiff – Gayan

Abeynayake)



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DC offshore wind power plants – series topology

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DC offshore wind power plants – hybrid topology

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DC Collection systems

Shunt Series HybridMost similar to AC Modified control Modified control

Cost effective Oversizing of components (Less) oversizing of components

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Technology developments:

- DC/DC converters

- MVDC breakers

- Protection and earthing

- Insulation


Offshore transmission systems

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AC vs DC

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Source figure: ABB, online

https://new.abb.com/systems/hvdc/why-hvdc/economic-and-environmental-advantages


HVAC Grid connection system

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Source: ABB


Main elements of a typical wind farm grid connection

G G G

Other radials

WTG generator

WTG transformer

WTG switchgear

Internal radial

MV switchgear Main transformer

HV switchgear

Wind power plant substation

HV line to POC

Metering

Low voltage <700V

High voltage 150/220 kV

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HVAC transmission

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WPP1 400MW

BKT1

Off-shore Comp. Reactor

BKst1

BKst2

BKst3

BKst4

BKst6

66/220 kV

Off-shoreTransformer

BKT2

PcableQcable

75 km

On-shoreTransformer VSG

ZS

On-shoreNetwork

ISVS

ωS

Vo

220/400 kV

BKst5

BKT3

On-shore Comp. Reactor

BKT3

PT1QT1

VT1IT1

PT2QT2

VT2IT2

PT3QT3

VT3IT3


Hornsea Project one – Offshore reactivecompensation

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120 km Source: Ørsted


Low Frequency AC (LFAC)

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J. Ruddy, R. Meere, and T. O’Donnell, “Low Frequency AC transmission for offshore wind power: A review”, Renewable and Sustainable Energy Reviews, Volume 56, April 2016, Pages 75‐86,


LFAC principles

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ESR-9: ' Tools for analysis of novel concepts of transmission systems for offshore wind power plants (UPC –

Jovana Dakic)


LFAC – Onshore converter

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Cycloconverter

Matrix

B2B



LFAC – Onshore converter

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LFAC – Offshore infrastructure• Offshore platforms:

– Smaller than HVDC, only AC tranformer and AC switchgears– However, size of AC transformers is larger: 3-times increase in core cross-sectional

area is expected (but not necessarily meaning 3 times transformer volume!)– AC swithgear size is also increasing

• Wind turbines– Larger transformers could also imply necessary modifications in the WT electrical

design– Would probably not work with Type 3 wind turbines

• Grid code compliance not straightforwards with cycloconverters or matrix converters

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HVAC Transmission systems

50 Hz LFACLimited range Potential for increase range of AC

transmissionMature technology Very early stage of development

Good reliability Larger WT components

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HVDC Grid connection system

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Source: ABB


VSC HVDC transmission

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PROMOTioN Deliverable 3.2: Specifications of the control strategies and the simulation test cases


DRU HVDC transmission

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currentVSC

solution

WPP transformers

HVDC offshore terminal

VSC-MMC

HVDC link

VSC-MMConshore

HVDC link

VSC-MMConshore

Diode-Rectifier Units (DRUs)

new DRU solution


DRU HVDC transmission

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DRU HVDC transmission – control paradigm

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GearBox

Generator

WT transformer

WPP transformer

WT transformer

ACDC AC

DC

HVDC transformer

VSC - HVDC Offshore HVDC

Onshore

Onshore AC Grid

WT Control

Offshore Voltage & Frequency

ACDC

ACDC

GearBox

Generator

ACDC

ACDC

WT Control

Active & Reactive Power

Active & Reactive Power

Grid following wind turbines

GearBox

Generator

WT transformer

WT transformer

ACDC AC

DC

Diode Rectifier Unit HVDC Onshore

Onshore AC Grid

WT Control

ACDC

ACDC

GearBox

Generator

ACDC

ACDC

WT Control

Active & Reactive PowerVoltage & Frequency Control

Grid forming wind turbines

Active & Reactive PowerVoltage & Frequency Control

Grid forming wind turbines control- dq current control based

- VSM control- GPS synchronization based

- master/slave based



Offshore AC Grid Start-up Options

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VSC-MMC

VSC-MMConshore

HVDC link

VSC-MMConshore

DRUs

Onshore AC Grid

Umbilical AC Cable Nearby VSC-HVDC (or AC)

HVDC link

VSC-MMConshore

DRUs

Energy Storage

Local Energy Storage (e.g. battery, diesel)

HVDC link

VSC-MMConshore

DRUs

es

es

es

Black-startable wind turbines


HVDC Transmission systems

VSC DRUOperational experience Early stage of developmentVery good controllability Potential for cost reduction

Potential for meshed grids Radical change in WT controlGood reliability Improved realibility

High costs Limited potential in meshed grids

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Offshore electrical resonance instability • Harmonic oscillatory instabilities

– High harmonics are caused by unstable or marginally stable controllers– Instabilities occur when harmonic frequency close to resonance points

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ESR-7: 'Development of tools for the analysis of the stability of offshore AC grids and grids rich in power electronic

converters' (UPC – Luis Orellana)

Source: InnoDC D2.1 Progress report, 2018

Figures: C. Buchhagen, M. Greve, A. Menze, and J. Jung, “Harmonic Stability – Practical Experience of a TSO,” in 15th Wind Integration Workshop, 2016.


Control Architectures for large OWPP clusters

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ESR-10: 'Cluster supervisory control of large offshore wind power plants’ (DTU –

Anup Kavimandan)

Source: A Kavimandan, K Das, A D Hansen and N A Cutululis, Hierarchy and complexity in control of large offshore wind power plant clusters, DeepWind Conference, Trondheim, 2019

Centralized

Decentralized Distributed


Black Start by Wind Turbines

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Step 1Self-start of

Wind Turbine

Step 2Self-Energization of Wind Power Plant

Step 3Contribution to Grid

Restoration

Objective: To avoid issues of non-operating wind turbines; - Moisture- Icing- Vibrations- Deformation

Objective:To energize WPP and substations (AC and/or HVDC) auxilary w/o any external supply

Objective:To provide/help black start for the power system

- Wind turbines start w/o grid voltage

- Wind turbines supply themselves using wind power(houseload operation)

WPP operates similar to the conventional black start units

WPP energize itself up to the PoC


Energization sequence for blackstart using OWPPsSplit into target states:

• Self- start • Self-sustain

• Parallel operation

• Offshore grid forming• Controlled islanded operation

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ESR-15: 'Black start and islanding operation capabilities of offshore wind power plants’ (DTU – Anubhav Jain)

Source: A. Jain, K. Das, Ö. Göksu, N. A. Cutululis, Control Solutions for Blackstart Capability and Islanding Operation of Offshore Wind Power Plants, Wind Integration Workshop, 2018, Stockholm


Summary and conclusions• Wind power is today based on AC technology, both for the collection and transmission

systems

• DC technology has potential for offshore wind:– Already a number of transmissions based on VSC-HVDC– Research towards DC collection systems– Proposals for DRU based tranmission

• The choice of technology is mainly based on economics (and less technical)!

• Tools for comparing the different technical options are needed

• Technology choices do have an impact on the control requirements!

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Course on “HVDC grids and offshore wind”Course description

In the past years, development of DC transmission has gained significant momentum as aresult of two key drivers. Firstly, the development of modern conversion technology(voltage source converter) and secondly, the need for transmission of offshore windpower. Plans for the interconnection of multiple renewable power sources, loads and ACgrids through DC technologies are leading to an exciting transmission concept: HVDC grids

The course covers the overall spectrum regarding HVDC technologies, including: (1) the advantages of HVDC compared to AC technologies for power transmission; (2) the key technologies and challenges for developing an HVDC grid; (3) Design, operation, control and protection of HVDC grids; (4) Offshore wind.

The course is based on the book “HVDC Grids: For Offshore and Supergrid of the Future”, edited by the course coordinators.

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Course on “HVDC grids and offshore wind”• Organizers

- Dr. Nicolaos A. Cutululis, Technical University of Denmark, Denmark

- Dr Dirk Van Hertem , University of Leuven, Belgium- Dr Oriol Gomis-Bellmunt, Technical University of Catalonia, Barcelona, Spain- Dr Jun Liang, Cardiff University, UK

Dates: 1-4 July 2019.

Venue: DTU Campus, Copenhagen (or Roskilde), Denmark

More info: Nicolaos A. Cutululis, [email protected],

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mailto:[email protected]

Documents

5th Connection of offshore wind farms · • Focuses on large offshore wind farms. • Objectives are to develop tools for techno-economical comparison and optimization of the OWPP