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
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& research in science, technology
& medicine
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knowledge
Academic Faculties
– Engineering
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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 134.9
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
Future Offshore AC-DC network
around the UK
 68 GW over 118
wind farm (6001000 MW) in North
Sea
 Off-shore EHV AC
cables have
reactive power and
voltage problem
 VSC-MTDC
technology
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
048
052
001
061
005
071
014
System 1
081
024
183
334.8 MW: 93x3.6 MW
034
System 7
173
137
162
151
145
143
127
116
105
099
128
117
106
100
129
118
107
130
119
108
131
120
109
097
090
006
015
025
007
016
026
035
043
System 2
002
138
083
System 8
008
017
027
036
044
101
33 kV bus
System 3
003
009
018
028
037
155-kV
System 9
010
019
029
038
011
020
030
039
021
031
040
022
032
041
139
155-kV
045
096
095
121
110
122
111
System 4
190
132
189
System 10
046
140
133
123
112
141
134
124
113
102
135
125
114
103
188
182
172
161
150 System 6
142
136
126
115
104
051
System 5
012
004
System 12
060
070
013
213
193
080
023
216
196
199
047
042
System L6
219
222
211
191
033
202
144
094
089
225
260
197
200
203
System L12
208
33 kV bus
System L8
194
165 MW: 33x5 MW
228
205
155-kV VSC
259
256
155-kV
33 kV bus
206
243
254
241
195
198
201
204
252
239
250
237
248
246
235
233
209
System L4
System L10
192
207
098
210
231
258
244
242
240
245
238
236
234
232
A typical wind turbine generator
DFIG WTG
Rotor side
converter
Grid side
converter
High
frequency
filter
WTG
transformer
Collector
netowrk cable
WTG model
Resonances in wind farm
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
My research group
Control
Monitoring
Abhinav
Ariff
Estimation
Modelling
Emilio
George
Linash
Sara
Steffi
Ankur
Antonio
Yashodhan
Odilon
Elizete
20 Greatest engineering achievements of
the 20th century
Source: NAE, USA
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