Connecting Wind Farms to Grid: Technical Challenges and Opportunities Bikash Pal Control and Power Group Electrical and Electronic Engineering

 Chairman, Ladies and Gentleman – a very good morning  This is my honour to be your guest  I cannot speak fluent Farsi so will cover the technical part of the presentation in English

Overview  Introduction  Wind farm and grid integration problem  Offshore wind farm experience  Possible explanations  Research issues  Conclusions  Questions  Acknowledgements

Imperial College London Objectives –World-class scholarship, education & research in science, technology & medicine –Interdisciplinary collaboration –Communication & sharing of knowledge Academic Faculties –Engineering –Natural Sciences –Medicine –Business School

Imperial College London World-class scholarship, education and research in science, technology, medicine and business Number 2 in QS Word Ranking ,400 students 8,500 undergraduates 2,400 taught postgraduates 2,500 research postgraduates from 123 countries 3,300 academic & research staff 3,100 support staff

Energy research themes Sustainable Power: includes research on marine energy; bioenergy; solar thermal and PV fuel cells; nuclear fission & fusion; wind turbine structures and interfaces Policy and Innovation: includes research on energy policy impacts; inventive mechanisms; energy service innovation; energy resource mix assessment Low Carbon Transport: includes research on electric and hybrid vehicles; transport use modelling; future fuels; more electric ships and aircraft. Energy Infrastructure: includes research on smart grids; energy storage; multiple energy vectors; energy efficiency Clean Fossil Fuels: includes research on carbon capture and storage; down-well processing; sustainable gas

Electric power grid as of now

Electric power grid in future

European supergrid in 2050

Grid integration challenges  Capacity ?  Curtailment ?  Technology ?  Economics ?  Let’s look at what is happening around the world

China  China (115 GW) produced TWh from wind and curtailed 16.2 (7%) TWh energy from wind  Grid remains the bottleneck  There is no established market/policy reform to remove these barriers

USA  PTC helped to have a cumulative capacity of 65GW  The issue is transmission network capacity  Continuation of longer term renewable energy development policy

India  Has 22 GW capacity installed  Project financing (high interest rate)  Turbine development issues to cater to low wind speed  Weak grid: Farm of 50 MW capacity or beyond need to be connected at transmission voltage level ( >220 kV ) adding to the total project cost

Germany  At 40 GW, grid expansion and system optimization remains the bottleneck  Issues with radar and rare species extinction needing longer project clearing time

UK  Has the best wind resource in Europe  13 GW capacity (5 GW offshore)  Slow and unpredictable planning process marred by local political interference  Lack of long term market to sustain the growth  Inadequate transmission capacity

 68 GW over 118 wind farm ( MW) in North Sea  Off-shore EHV AC cables have reactive power and voltage problem  VSC-MTDC technology Future Offshore AC-DC network around the UK

Some serious problems so far

What could be the reasons?  Harmonics?  Phase lock loop instability?  HVDC converter control and WF control interaction?  Resonance in the AC-DC offshore network?

Layout of a typical (500 MW) wind farm

A typical wind turbine generator Rotor side converter Grid side converter DFIG WTG High frequency filter WTG transformer Collector netowrk cable

WTG model

Resonances in wind farm

Effect of wind farm operating conditions

Effect of AC-DC converter control on network resonance

A typical frequency response Transfer function input : VSC voltage reference Transfer function output : Magnitude of voltage at wind turbine bus (stator)

Summary of the case study  Very high frequency modes (>2kHz) Electrical dynamics of AC cables  High frequency modes (500Hz-2kHz) WTG TF and cables  Medium frequency modes (50 Hz-500 Hz Close to 2nd, 5th and 7th Harmonics HVDC control, AC voltage, WF-TF currents  Low frequency modes (< 50 Hz) Within WTG Interaction between WTGs

Insights  No interaction is observed between WTG mechanical side and collector system  WTG electric circuit is found to have poor damping and frequency close to synchronous frequency –needing proper converter control

Insights  AC system of wind farm shows poorly damped modes close to harmonic frequency, 2nd, 5th and 7th  Damping of these modes are dependent on the operating conditions of wind farm and VSC control settings  Robust control will play a significant role

Conclusions  It is very important to design control for a successful offshore grid operation  Power Electronics+ Power Systems+ System Theory experts = Solution 30

Estimation MonitoringControl Modelling My research group George Linash AntonioYashodhanOdilonElizete Ankur Ariff Sara Abhinav Steffi Emilio

20 Greatest engineering achievements of the 20 th century Source: NAE, USA

IEEE Power & Energy Society (PES)

Questions?

Acknowledgements  I always had admiration for very rich Persian history and culture  I have several research students from Iran who are extremely polite, intelligent and humble and that has attracted me to explore the Iranian people and culture more

Acknowledgements  This is the civilisation where first the concept of truth and justice were born  This is the civilisation that has evolved and excelled because it was driven by minds not by muscles

Acknowledgements  This is the land where some of the great minds of the human civilisation like Omar Khyaam, Ferdowse, Saadi, Hafez, Rumi were born and Farsi is the language through which they expressed their great literary and scientific thoughts

Acknowledgments  But Long before Ferdowse wrote his Sahehnamah, the Persian built windmill in Sistan in 700 AD

Acknowledgements  This is also a country where beautiful films like Bachhe yeh Ashman and Separation are made  This is the country where 66% of university students are female

Acknowledgements  This is the country where the family of the chief architect of the most admired Indian mausoleum, The Taj Mahal, the finest display of eternal love in the world came from

Acknowledgments  I had a very enjoyable trip to the two world’s great historically and culturally rich cities Isfahan and Shiraz earlier this week  I was looking forward to this visit for long

Acknowledgments  I thank the conference organiser very much for giving me this rare opportunity  God bless you all

Connecting Wind Farms to Grid: Technical Challenges and Opportunities Bikash Pal Control and Power Group Electrical and Electronic Engineering