hvdc grid connection - in japaninjapan.no/energy2015-day1/files/2015/06/darco-osw-may-27.pdf ·...

Technology for a better society

Tokyo, 27-05-2015

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Salvatore D'Arco Research Scientist [email protected]

HVDC grid connection

mailto:[email protected]


• Relevance of HVDC transmission research in Norway • Background for research on HVDC technologies • Examples of R&D focus areas and research projects at SINTEF

• R&D activities on HVDC technologies from a system perspective • R&D activities on HVDC technologies at a component level

• Joint laboratory facilities at NTNU/SINTEF

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Outline of presentation


• Geographical location on the North Sea • Electrification of oil and gas installations • Integration of offshore wind farms • Transnational export of hydropower and balancing reserve

• Present involvement of Norwegian industry in the development of offshore

wind farms in UK and future perspectives of developments of offshore wind in Norway

• Relevance of Norwegian industry as supplier of components as cables, subsea equipment, offshore platforms

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Relevance of HVDC technologies for Norway


• HVAC connection is the preferred option for connection of offshore wind farms relatively close to shore. Cable capacitance prevents its application for longer distances.

• Technology transition from point to point connections based on Line Commutated Converters to meshed grids (e.g. North Sea supergrid) based on Voltage Source Converters

• Recent advances in HVDC technologies • Cable technologies (higher voltage ratings) • Converter terminals (Modular Multilevel Converter) • DC breakers

• Pressure on costs due to expected lower price of energy and lower incentives

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Background for HVDC grid connection


• Reduction of installation and operation costs • Increase conversion efficiency, reduce platform space • Alternatives to HVDC (low frequency HVAC, capacitance compensation)

• Power system protection (fault detection, fault clearance) • Interoperability of converter technologies

• Integration of offshore wind farms • Challenges in power system dominated by power electronics • Load flow analysis and market assessments in future scenarios

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R&D on HVDC technologies from a system perspective


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Protection and Fault Handling in Offshore HVDC grids Objectives: Establish tools and guidelines to support the design of multi-terminal offshore HVDC grids in order to maximize system availability. Focus will be on limiting the effects of failures and the risks associated to unexpected interactions between components.

• Develop models of offshore grid components for electromagnetic transient studies.

• Define guidelines to reduce the risks of unexpected interactions between components during normal and fault conditions.

• Define strategies for protection and fault handling to improve the availability of the grid in case of failures.

• Demonstrate the effectiveness of these tools with numerical simulations, and experimental tests.

• Expand the knowledge base on offshore grids by completion of two PhD degrees and a PostDoc at NTNU and at RWTH.


• Project focus on decentralized architecture not relying on communication between terminals. • Identify fault detection markers to trigger protection devices • Mechanisms to ensure protection selectivity • Impact of Fault Current Limiters on protection schemes

• Verified in simulation a protection scheme based on current derivatives and threshold limits.

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Fault handling in MT HVDC systems

6 6.001 6.002 6.003 6.004 6.005

2

4

6

8

10

12

14

16

I dc2-

>1,P

[kA

]

Time [s]

6 6.0005 6.001 6.0015 6.002 6.0025 6.003 6.0035

-2

0

2

4

6

8

10

12

14

16

d(I dc

2->1

,P)/d

t [kA

/s]

Time [s]

9: 380km 2->18: 390km 2->17: 400km 2->11: 400km 1->32: 410km 1->3R

2 set-point

BestPaths Project

• Large energy project in FP7 (39 partners from 11 countries, 62 M€ budget)

• Objective is help to overcome the challenges of integrating renewable energies into Europe’s energy mix. It aims to develop novel network technologies to increase the pan-European transmission network capacity and electricity system flexibility.

• The project unites expert partners around five large-scale demonstrations to validate the technical feasibility, costs, impacts and benefits of the tested grid technologies.

• SINTEF Energy hosting demo 1

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BestPaths Project, Demo 1

• Main focus is on interoperability of HVDC technologies • To investigate the electrical interactions between the HVDC link

converters and the wind turbine converters in offshore windfarms. • To de-risk the multivendor and multiterminal schemes from the point of

view of resonances, power flow and control. • To demonstrate the results in a laboratory environment using scaled

models - 4-terminal DC grid with 50 kW MMC VSC prototypes and a Real Time Digital Simulator system to emulate the AC grid.

• To extrapolate the results to a real project (East Anglia Offshore Wind 7,2 GW in the UK Round 3)

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The Virtual Synchronous Machine (VSM) is a concept for controlling power electronic converters in order to reproduce the characteristics of traditional synchronous machines. • Introducing virtual inertia and damping to controlled power converters

Applicable in a wide range of relevant power system configurations: • Power systems with high penetration of renewables • Islanded power systems dominated by power converters • Offshore power systems (e.g. AC grids for HVDC connected offshore wind farms

and/or oil platforms) Compared to inertia emulation based on frequency derivative offers better performances since does not depend on dominant presence of physical inertia

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Application of the Virtual Synchronous Machine concept


Offshore wind farm with multi-infeed HVDC

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VSM-controlled


• Characterization and reliability of semiconductor devices for high power applications

• Wide band modelling of components for electromagnetic transient analysis • Subsea cable technologies for high power transmission

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R&D on HVDC technologies at a component level


Power Cycling Reliability of Power Electronics Devices

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Step#1: Temperature determination Step#3: Lifetime prediction according

Miner’s rule

Step#2: Cycle counting

Possibility 1calculation

Possibility 2measurement

Tvj(t)

Minima and Maxima extraction

Input data:e.g.: P(t), Q(t),

wind speed

Ciruit simulationLosses model

Thermal model Rainflow counting algorithm

Linear composition

Nf curves

Residual lifetimexy%

Wind profile

Lifetime characteristics


Power Cycling Tester with 4x modules + 4x press packs

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Technology for a better society 15

Wide band modeling of HVDC components

Volta

ge [p

.u.]

• Advanced techniques for modeling and simulation of linear devices via rational functions.

• Wide-band transformer modeling from measurements

• Non-linear transformer core modeling • Advanced numerical modeling and

simulation of power cables

Simulation of voltage transfer in distribution transformer, validation by measurements

Characterizing transformer via frequency sweep measurements, modeling via rational functions


Renewable energy / Smartgrids laboratory

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• 55kVA wind turbine emulator • 60 kVA 2L-VSC converters

(back-to-back or STATCOM configurations)

• in-house developed 20 kVA laboratory converters with FPGA-based control systems

• OPAL-RT multiprocessor platform • Rapid prototyping • Real-Time & Hardware-

In-the-Loop simulations


Laboratory Scale of a Multi Terminal DC Grid

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AC

DC

ACDC

AC

DC

AC

DC

60 kVA VSC

60 kVA VSC60 kVA VSC

60 kVA VSC

55 kVA Induction gen-set

IM IGAC

AC

17 kVA Synchronous Generator

Grid model with variable load

IM SGAC

AC


Future planned developments

• National Smart Grid Laboratory & Demonstration Platform – Infrastructure project financed by RCN – Physical extension and general upgrade – Grid emulator (200 kW, >5 kHz bandwidth) – Strengthening of real time simulation computational capabilities

• Bestpaths project – Development of 3 MMC units – Addition of DC breakers

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