Dr. Johan H. Enslin, FIEEE, FSAIEE, PrEng

Director, Energy Production and Infrastructure Center (EPIC)

Duke Energy Distinguished Chaired Professor

UNC Charlotte, NC, USA

JEnslin@uncc.edu EPIC.UNCC.EDU

Mitigating system impacts

of offshore wind farms

using onshore STATCOMs

Outline

Development of Off-shore Windfarms (OWF)

Interconnection Options for OWFs

AC Grid Impacts of OWFs

Characteristics of STATCOMs

Case Studies

Conclusions

Development of Off-shore Wind Energy

Image Source: Global Wind Energy Council (GWEC-2016) [1]

Energy form Wind

3)(2

1: wpRwt v C A = PPower

w

T

w

p

v

.R =

v

v =

RatiospeedTip

:

TURBINE POWER COEFFICIENT

2 4 6 8 10 12 14 16 18

0,1

0,2

0,3

0,4

0,5 C p

Annual wind production

0 5 10 15 20

wind speed [m/s]

Po

we

r, p

rob

ab

ilit

y &

po

we

r d

en

sit

yavailable wind turbine power

wind speed distribution

power density

λ

Trends in Offshore wind turbine technology

Increasing rotor diameter and power ratings:

Most common: 65 - 80 m and 1,5 - 2,5 MW

Installing: D = 120 m 5 MW,

Developing = 146 m 10 MW

Higher tip speeds 80 m/s for offshore

Lower Hub Heights

Variable Speed Generation

VSC-HVDC and HVAC cables

Offshore collection platform

Offshore Wind Collector Platforms

Image Source:- NREL-2016

AC Generator Options

Synchronous and Induction machines

Direct drive v/s gearbox options.

Low voltage v/s high voltage machines

Network Interface Issues

VSG:- Turbine - Generator – Converter - PCC

FSG:- Turbine – Generator - PCC

= ~

= ~ Gear

box

DC

Link

AC Machine

PCC

Kinetic energy Mechanical energy Electrical energy

Rectifier Inverter

Power Collector Network

Off-shore Windparks DC Connections

Off-shore Windpark AC Connections

string cluster

shore c b

G G G

b G G G

b turbine grid

platform

star cluster shore

a

a b c

G G

G G platform

grid

a.

b. platform

Grid Interface Issues for HVAC Connections Reactive Power Requirements due to HVAC Cable Capacitance

System Resonances due to Long HVAC Offshore Cables

Protection and Transformer Energization

HVAC Transmission Integration Issues

Steady-State Voltage / Reactive Power Control

Voltage Step Transients, especially with energization

Low-Voltage Ride Through during faults

Harmonics and Flicker

Wind power curtailment

HVDC Link Impacts – commutation failures etc.

Remedial Mitigation Measures

Shunt Reactive Power Compensation

Harmonic and Damping Filters

STATCOMs with Energy Storage

Special Protection Schemes

Point of Wave Switching

Converter / control options

System Resonances with HVAC Connections

Voltage Amplification Factor < 1.3

Inrush Current during cable energization

Inrush Current during cable transformer switching

Cable - Series Resonance

Transformer – Parallel / Series Resonance

Source TenneT [3]

Example of an Integrated AC OWF System

= ~

• Peak load shaving and ramp control

• Reactive power mitigation

• Voltage ride-through

• Harmonic filtering

• Voltage Amplification damping

STATCOM & APF with ESS

< 200 MW

± 50 MVA

300 MWP

1-2 hour ESS

Offshore Wind Farm with HVAC cable

STATCOM General Information

XT

UComp

UT

UGrid

IGrid

AC AC

Capacitive operation mode UC > UGrid

Injection of reactive current into the grid

Inductive operation mode

UC < UGrid

Absorption of reactive current from the Grid

UComp

UT

UGrid

IGrid

UT

UGrid

UComp

IGrid

Topologies Voltage Source Converters

Diode Clamped Multilevel-Converter (MLC)

Chain-Link Multilevel Converter

Case Studies - London Array Wind Farm [4]

Source N-Grid [4] 2013 Installed Capacity: 630 MW

175 Siemens 3.6 MW turbines

4x 150 kV 50 km HVAC cables

150 kV Harmonic Filters

(3rd, 5th and 7th harmonic)

± 50 MVAr STATCOM at Cleve Hill

Voltage and reactive power support

Source: http://www.londonarray.com/onshore-substation/

Westermost Rough Wind Farm (ABB) [9]

Installed Capacity: 210 MW

Site: 8 km offshore - 32 km2

35 Siemens 6 MW turbines

Commission date: May 2015

2x 25MVAr STATCOM in

50 MVAr MSR

For UK Grid Code compliance

Voltage stabilization

FRT

Harmonics

Power factor correction

HVAC connected OWFs in North-East Europe

The Netherlands (TenneT) - Commissioning

GEMINI 600 MW OWF 380 kV at Eemshaven.

Two HVAC cables at 220 kV for 100 km length.

Borssele 380 MW OWF 380 kV Alpha

Two HVAC cables at 220 kV for 51 km length

Germany - North Sea (TenneT)

Total of 4,300 MW

Germany / Denmark - Baltic Sea (50Hz Transmission):

Combined 150 kVac grid with B-t-B HVDC – 700 MW

Planned up to 5,000 MW – Wikinger & Arkona-Becken – 220 kVac

Source: http://www.4coffshore.com/ ; www.tennet.eu; http://www.50hertz.com/

Conclusions Large 300 – 800 MW European wind energy projects are currently developed - mostly Offshore

Wind generator ratings are increasing to 5 MW now and 10 MW in the future for offshore applications

Long (50 – 100 km) HVAC cable interconnections are preferred over HVDC due to cost.

Network Interface Issues, including Energization, System Resonances, Power Quality, Reactive Power and Voltage fluctuations are real concern.

Onshore STATCOM and Filter solutions are possible mitigation solution for grid integration.

Future wind farm concepts may include integrated STATCOM and Energy Storage options.

References 1. Global Wind Energy Council (GWEC-2016)

2. Enslin, JHR; Knijp, J; Jansen, CPJ; Schuld, JH: “Impact of Reactive Power Compensation Equipment on the Harmonic Impedance of High Voltage Networks”, IEEE PowerTech-2003, Bologna, Italy, 23-26 June 2003.

3. Jansen; K; Van Hulst, B; Engelbrecht, C; Hesen, P; Velitsikakis, K; Lakenbrink, C: “Resonances due to Long HVAC Offshore Cable Connections: Studies to verify the Immunity of Dutch Transmission network”, in 2015 IEEE PowerTech, Eindhoven, NL 29 June 29 – 2 July 2015.

4. Glasdam, J. B.; Kocewiak, L.; Hjerrild, J.; Bak, C. L.; Zeni, L: “Comparison of Field Measurements and EMT Simulation Results on a Multi-Level STATCOM for Grid Integration of London Array Wind Farm”, Proceedings of the 45th 2014 CIGRE Session, 2014

5. Laouera, M; Mekkaouia, A; Younesb, M: “STATCOM and Capacitor Banks in a fixed-speed wind farm”, TMREES, 2014

6. Saad-Saoud, Z; Lisboa, M; Ekanayake, Jenkins, N; Strbac, G: “Application of STATCOMs to wind farms”, Proc. IEE, Gener. Transm. Distrib., Vol. 145, No. 5, 1998, pp. 511-516

7. Ronner, B; Maibach, P; Thurnherr, T: “Operational experiences of STATCOMs for wind parks” , IET Renew. Power Gener., 2009, Vol. 3, Iss. 3, pp. 349–357

8. http://www.4coffshore.com/

9. http://new.abb.com/docs/librariesprovider78/chile-documentos/jornadas-tecnicas-2013---presentaciones/7-michael-neutz---power-quality.pdf, reviewed: 4/22/2016

10. http://www.energy.siemens.com/us/pool/hq/power-transmission/FACTS/SVC_PLUS_The%20efficient%20Way.pdf, reviewed: 4/22/2016