Download - Morelia workshop presentation william ross
Provision of Ancillary Services from Offshore
Wind Farms
William RossUniversity of Strathclyde
SupervisorsDr Olimpo Anaya-LaraProf. Stephen Finney
Slide 2
Contents
William Ross
• Background
• Grid Codes
• Modelling of Wind Farm and HVDC link to shore
• Results
• Future Work
• Research Objective
Slide 3
Driving Factors
William Ross
• Wind power installations are increasing significantly worldwide - More recently offshore
• However, investment costs for offshore wind power are much higher than those for onshore installation
• Wind speed offshore is higher and more reliable than onshore
• Average distance of off-shore wind farms continues to increase
• 2011 - 23.4km, 2012 - 29km from shore
• Projects announced for installations up to 200km from shore
(EWEA 2011, 2012, Deep Waters Reports)
Slide 4
Issues with Wind
William Ross
• Grid codes requiring WPPs to behave more like conventional power plants in maintaining power system stability and reliability i.e. providing ancillary services
• As installation of WPPs rises, so does their impact on the characteristics of the utility gird
• If large amount of wind gen. disconnected during survivable fault on utility side
• Includes:• Power quality • Flicker• Reliability of connection
Further imbalance resulting in a drop in system frequency over a wider region
Larger voltage depression due to increased power imbalance Eventually can lead to collapse of voltage in affected region
Slide 5
Research Objectives
William Ross
The research aims to:• Appraise the state-of-the-art of offshore wind power technologies and identify
Grid Code specifications for connection of large offshore wind power plant
• Enhance the available InstEE modelling platform of multi-technology offshore wind power networks to study wind power plant capability and requirements to be able to provide ancillary services.
• Design improved control approaches to deliver ancillary services from HVDC-interfaced wind power plant.
• Conduct, in cooperation with DNV, a cost-benefit analysis to weigh the impact of shorter lifetime versus increased ROI from delivery of power ancillary services to the grid.
Slide 6 William Ross
Ancillary Services from Offshore Wind farms
Frequency Control Ancillary Services (FCAS)
Network Control Ancillary Services (NCAS)
System Restart Ancillary Services (SRAS)
• Used to maintain the frequency on the electrical system, at any point in time, within certain range of nominal frequency, as defined in grid codes
• Control voltage at different points of the electrical network to within grid code standards
• Control the power flow on network elements to within the physical limitations of those elements.
• Reserved for contingency situations in which there has been a whole or partial system blackout and the electrical system must be restarted
primarily used to:
Slide 7
Grid Codes
William Ross
In most countries, grid codes apply to the wind farm at point where connects to grid or Point of Common Coupling (PCC)
Normal operation:• Frequency & voltage within ranges• Active power (P) control• Reactive power (Q) control
• Continuous operation in a limited range below and above the nominal point
• Time limited operation with possible reduced output in extended ranges
• Immediate disconnection
Grid disturbances in the form of voltage sags or swells can lead to WPP disconnections and possible cascaded loss of generation – Critical to avoid!
3 main operating zonesCommon Requirements
Behaviour under grid disturbances• Voltage ride through (VRT)• Reactive current injection (RCI)
Slide 8
Grid Codes
William Ross
Typical shape of continuous & reduced output regions
(An Overview of the Present Grid Codes for Integration of Distributed Generation - Traian-Nicolae - NTNU – Norway)
(Review of grid connection requirements forwind farms in the UK -O. S. Adagha)
Typical FRT requirements
Slide 9
Grid Codes – Unifying a mixed bunch
William Ross
Most extreme requirements for Wind Farm operation at deviations from nominl voltage and freq.
Fault ride through profile to satisfy all grid codes.
“Grid Code Requirements for Wind Power Integration in Europe” C. Sourkounis, P. Tourou
Slide 10 William Ross
• For large offshore wind farms at distances greater than 80 km the preferable way of transferring power to onshore is HVDC.
Grid Codes – Unifying a mixed bunch
“Grid Code Requirements for Wind Power Integration in Europe” C. Sourkounis, P. Tourou
Slide 11
Why HVDC?
William Ross
[“Economic limitations of the HVAC transmission system when applied to offshore wind farms”J. Machado; M. V. Neves; P. J. Santos]
Slide 12
Why HVDC?
William Ross
• Large amounts of reactive power required in HVAC to feed the capacitive charging current of the cables.
• For wind farms capacity with capacity <500MW, point at which HVDC becomes more economic can be as low as 50km
Using Voltage Source Converter based HVDC• VSCs use self commutating devices such as IGBTs and GTOs
that have voltage ratings close to 6.5kV • Unlike LCCs , they provide rapid, independent control of active
and reactive power.• By using Pulse Width Modulation any phase angle or
magnitude can be constructed• Lower filtering requirements, thus improving the overall converter
footprint.• Black-start capability and no restriction on multiple infeeds
Slide 13
Variable Speed – PMSG FRC based
William Ross
• PMSG connected to grid through back-to-back frequency converter
• PMGs also have no slip rings or brushes, and so reduced maintenance and greater reliability
• PMGs almost or about as efficient at full-load generation as standard DFIGs, but more efficient at part-loads – the most common conditions that wind turbines operate in
• Large PMGs require expensive rare earth magnets
• Fully rated PEC is expensive
Slide 14
Converters
William Ross
As VSWT installation is ever increasing, PEC becoming ever more critical
Two-level PWM converterLower cost due to its maturity/simplicity
High frequency harmonics(additional cost in EMI-filters)
Lower total harmonic distortion
Multilevel Converters
Smaller switching losses
Back-to-back PWM converter NPC cell and ANPC cell
Complex control
May also use uncontrolled diode rectifier on wind farm end• Cheap, robust, lack of control
Slide 15
Wind Turbine Modelling
William Ross
Noise signal injected into
Reflect wind variability in the output power to illustrate mitigation effect of the VSC-HVDC transmission system.
is set to zero for unity power operation
Fully-rated converter decouples generator from collection network
Only grid-side converter modelled in detail
Further simplified by modelling wind farm as single very large wind turbine
Slide 16
Developing Link Control
William Ross
WG
WG
WG
WG
SEC REC
GSCMSC
LgLfVdc2
DC cable
GridVdc1
BGBWF
For initial investigation:Wind turbines modelled as DC source connected to Grid-Side Converter in order to simplify the model and reduce simulation time
For further simplicity, the entire offshore wind farm is represented by one equivalent unit.
VSC as two level converter
Slide 17
-+
-+
ωL
PI
-+
-+ ∑ PI
ωL
PI ∑ PI
dq
abc
Vdc2
V*dc2
vsd
vsd
isd
isq
|V*BG=1|
|VBG|
PWM
Md
Mq
i*sd
i*sq
ud
uq
-
+
+
-+
+
Outer Controllers Inner Controllers
Id max
Id min
Iq max
Iq min
Developing Link Control
William Ross
Outer loops provide reference values & for current controller on each end
For GS-VSC
Maintaining DC link voltage
Maintain AC voltage synchronised to onshore AC grid
Slide 18
Developing Link Control
William Ross
-+
-+
ωL
PI
-+
-+ ∑ PI
ωL
PI ∑ PI
dq
abc
vd
v*d = 1pu
vsd
vsd
isd
isqvq
PWM
Md
Mq
i*sd
i*sq
ud
uq
-
+
+
-+
+
Outer Controllers Inner Controllers
Id max
Id min
Iq max
Iq min
v*q = 0pu
For WF-VSC
Control offshore AC voltage and frequency through d and q components
Slide 19
Simulation with ramp up in power delivered from wind farm
William Ross
Slide 20
More results
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Slide 21
FRT on Point to Point VSC HVDC
William Ross
Slide 22
Low cost Diode/VSC Hybrid design
William Ross
• HVDC link using 12P-Rec and an VSC• 12PREC utilized to deliver
part of the wind farm power• Reduced power rating of the
VSC
• the SEMMC is used to control the offshore AC grid voltage at a constant magnitude and frequency
Slide 23
Previously…
William Ross
• Cost of power semiconductor devices and gate drivers ~ 75.2% and 45.6% compared with those of the NPC-based HVDC and MMC based HVDC transmission systems
• Power losses of the converters for NPC-based and MMC-based HVDC links are about 1.6% and 1.0%, respectively
• Average power loss of the converters then becomes 0.733%
(A Cost-Effective Converter System for HVDC Links Integrated with Offshore Wind Farms – T. H. Nguyen, D Lee, C. Kim)
Slide 24
Simulation Results
William Ross
DC link voltages at SEC and REC respectively
Slide 25
It is important that Vdc3 remains balanced with Vdc1 and Vdc2
This could be approached either by using measurements of Vdc3 directly or using control of real power injected through VSC
Both these approached will be tested and compared against benchmark model
Conclusions from simulations
William Ross
Slide 26
Future Work
William Ross
• Modelling of novel hybrid topology to achieve similar performance comparable to benchmark model. Then build on this to begin expanding modelling of wind turbines .
• Consolidate results from existing model, test limitations, and expand control to provide frequency support also
April - May
April
• Investigate addition of Novel Frequency measurement technique for provision of frequency support services
May-July
Slide 27
Presentations to date
• Deepwind conference (Trondheim, Norway) 2014 Oral presentation with my colleague Ioannis Antoniou
“The Future of HVDC” Ioannis Antoniou, Dr Olimpo Anaya-Lara, Prof. Stephen Finney
• Deepwind conference (Trondheim, Norway) 2016 Poster presentation
“Provision of Ancillary Services from Large Offshore Wind Farms” Dr Olimpo Anaya-Lara, Prof. Stephen Finney, Prof. Aurelio Medina-Rios
William Ross
• ETP annual conference 2014 – Dundee, Scotland Poster Presentation
• ETP annual conference 2015 – Glasgow, Scotland Oral Presentation
“Wind Farm Technologies towards Ancillary Services”
Slide 28
Others activities
William Ross
• Part of group funded by IET to organise, create and give presentation to groups of 100-300 high school kids (~14 years old) in 4 Scottish cities on importance of Power Engineering to promote interest for higher studies
• Member of newly formed IEEE IAS student chapter for Strathclyde & part of organising 2 day workshop with guests from Distinguished Lecturers program
• Also beginning to plan organisation of full conference in 2018
• Upcoming conference
Abstract submitted for UPEC 2016 conference in September“Providing Ancillary Services from Large HVDC-connected
Offshore Wind Farm Using Low Cost Hybrid Converter”Dr Olimpo Anaya-Lara, Prof. Stephen Finney, Prof. Aurelio Medina-Rios
Slide 29 William Ross
Thank you!