A Demonstrator for Experimental Testing Integration of Offshore Wind Farms With HVDC Connection
S.D'Arco, A. Endegnanew, SINTEF Energi
BEST PATHS PROJECT
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• Validate the technical feasibility, impacts and benefits of novel grid technologies,
• Five large-scale demonstrations• Deliver solutions that allow for transition from High Voltage Direct Current (HVDC) lines to HVDC grids;
• Upgrade and repower existing Alternating Current (AC) parts of the network;
• Integrate superconducting high power DC links within AC meshed network
BEyond State-of-the-art Technologies for re-Powering AC corridors and multi-Terminal HVDC Systems
LARGE SCALE DEMONSTRATIONS
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1. HVDC in offshore wind farms and offshore interconnections
2. HVDC-VSC multivendor interoperability
3. Upgrading multiterminal HVDC links
4. Innovative repowering of AC corridors
5. DC Superconducting cable
From HVDC lines to HVDC grid
Upgrading ofexisting AC grids
DEMO 1 Objectives
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• To investigate the electrical interactions between HVDC link converters and wind turbine converters in offshore wind farms.
• To de-risk the multivendor and multiterminal schemes: resonances, power flow and control.
• To demonstrate the results in a laboratory environment using scaled models (4-terminal DC grid with MMC VSC prototypes and a Real Time Digital Simulator system to emulate the AC grid).
• To use the validated use the validated models to simulate a real grid with offshore wind farms connected in HVDC.
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Substation Wind farm
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8
Substation Wind farm
HVDCHVAC
Demonstrator overview
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• Three-terminal scheme MMC with • MMC with HB cells, 18 cells and 6 cells per arm,
• MMC with FB cells, 12 cells per arm
• Wind farm emulator
• National smart grid laboratory
Wind farm emulator
National Smart Grid Laboratory
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• Laboratory formally opened in September 2016 after a major upgrade
• Jointly operated by NTNU and SINTEF
• Reconfigurable layout with multiple ac and dc bus
• Power electronics converters• 2 level VSC 60 kVA, MMC 60 kVA
• Electrical machines• Synchronous generators, Induction
machines
• Real-time simulator
Real-time simulation and PHIL capabilities
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• OPAL-RT based real time simulator platform• 5 parallel cores,• 2 FPGAs for IO and small time step simulation,• Fiber optic communication
• Egston Compiso Grid emulator• 200 kVA rated power• 6 individual outputs• > 10 kHz bandwidth• Connected to the OPAL-RT system via fiber optics with 4 µs update rate for measurements and
references
Demonstration of HVDC transmission systems connected to offshore wind farms
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• Designed and built 3 MMC prototypes
• Tested the converters in point to point and multiterminal configurations
• Planned PHIL experiements with real time model of a wind farm
GSC
Pw1
Pg1,Qg1Onshore
AC Grid #1
DC CABLE
Vdc and Q Controller
AC VoltageControl
Vdc_g1
Vdc_g1*fw1*|Vac_w1*|
Vac_w1
Offshore Grid #1
WFC Offshore Onshore
Qg1*
θw1*
Pw1
DC NETWORK
AC VoltageControl
fw1*Vac_w1*
Vac_w1
Offshore Grid #1
WFC #1
Offshore Onshore
θw1*
GSC #1 Pg1,Qg1Onshore
AC Grid #1
(Vdc vs. P) and Q Controller
Vdc_g1* Qg1*
Vdc_g1
AC VoltageControl
fw12*Vac_w2*
Vac_w2
WFC #2
θw2*
Pw2
Offshore Grid #1
MMC Converters
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• Three MMC converters were designed from scratch• MMC with HB cells, 18 cells per arm• MMC with FB cells, 12 cells per arm• MMC with HB cells, 6 cells per arm
• Built and successfully tested at full rating• 42 modules• 144 power cell boards• 1764 capacitors
Power cell boards
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Assembling stages
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Converter performance test
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Conv12 700UDC, 100% active current Id (-81.2A) ● Phase C upper arm voltage, ● Phase C Lower arm voltage, ● Phase
C output voltage, ● Phase C arm current
Conv18 700UDC, 24.3kW,7.8kVar ● Phase C upper arm voltage, ● Phase C Lower arm voltage, ● Phase
C output voltage, ● Phase C arm current
Point-to-point and multiterminal configurations
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• Tests to evaluate the accuracy of the models to represent the demonstrator
28 29 30 31 32 33
-80
-60
-40
-20
0
20
40
60
80
Time (s)
Id (A
)
DemonstratorModel
4 4.01 4.02 4.03 4.04 4.05-20
-10
0
10
20
30
40
Time (s)
Arm
Cur
rent
(A)
ModelModelDemonstratorDemonstrator
4 4.01 4.02 4.03 4.04 4.05660
670
680
690
700
710
720
Time (s)
Cel
l Vol
tage
(V)
Wind farm emulator
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• Wind farm model is adapted to run in the 200 kVA high-bandwidth grid emulator
• PHIL implementation combining the real time simulator and the grid emulator• Flexibility in the model simulated
• Possibility to reproduce faster dynamics
IA
IB
IC
IA *
IB *
IC *
UA
UB
UC
Real Time Wind Farm Model UA*
UB*
UC*
Grid EmulatorReal Time Simulator
Current References
Voltage Measurements
Interaction of an offshore wind farm with an HVDC
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Low costModerate costHigh cost
• Complex issues • Noise, randomness of event timings, and
hardware design
• Numerical simulations are widely accepted and cost effective • Test a wide variety of different cases, however,
the fidelity of the results is difficult to assess.
• Hardware power-in-the-loop (HIL) simulation offers a good balance between test coverage and fidelity.
PHIL experiment: Wind farm connected to VSC-based HVDC
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Grid emulator
~=VSC
Transf. vabc
HWGE
Measurement points
vabc
iabc*
iabc*
VSC controller (Island mode)
HVDC dc voltage
refeence
Wind farm simulation
Real-time simulator
f 1s-2π
vd *=1 puvq*=0
abcdq
• Simulated wind farm• Input: Wind speed and measured voltage
• Output: Grid emulator reference current
• Hardware• Two-level VSC generates a three-phase ac
voltage with a fixed frequency
• The close-loop behaviour of the PHIL setup was stable
Simulation Hardware
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ResultsW
ind
spee
d (m
/s)
Angu
larv
el. (
rpm
)Po
wer
(pu)
Volta
ge(V
)Cu
rren
t(A)
Conclusions
• Power hardware-in-the-loop (PHIL) approach combines hardware devices with software simulation.
• The hardware part allows a high fidelity of the results whereas, the software simulation part allows an extensive study of different cases at a reasonable cost
• Grid integration of wind farm using VSC-based HVDC system was evaluated in PHIL experiment as a proof of concept.
• In the future work ,PHIL implementation using modular multilevel concepts will be studied
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