Post on 16-Mar-2018
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HVDC grids & its components - Torbjörn Thiringer, CTH - EERA Deep wind 2015 1(30)
Research challenges for offshore HVDC gridsand its components
Torbjörn ThiringerDep. of Energy and EnvironmentChalmers University of technologyGöteborg, Sweden
Chalmers, Göteborg
NTNU, SINTEF, Trondheim
HVDC grids & its components - Torbjörn Thiringer, CTH - EERA Deep wind 2015 2(30)
Why offshore HVDC grid ( in the North Sea ) ?
Economical benefit to make power transfer and to balance power variations in different parts of Europe with the Baltic and North Sea in-between
To long distances for AC ( could perhaps work with 15 Hz AC )
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Why offshore HVDC grid with wind turbines ?
• Interest for installing wind energy in Sea areas – space and wind speed issues
• 20-20-20
• Kyoto protocol
• Peak Oil
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SW corner of North Sea
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The supergrid
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HVDC system with offshore wind farm
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Research challengesSystem: overall operation – stability - connection to external ac-grids - cable and grid component dimensioning - grid code – insulation level –protection – current interuption – meshed vs non-meshed – sequential building strategy – dc switchgear station
DC-transformer – design – operation – extra functionality
WEC system – high efficiency – robust – direct drive? –converter-voltage levels- HVDC out
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Some thoughts/ideas/aspects
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Step-wise building
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Converter topologies2-level
3-level
n-level
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Series connected dc wind farm
dc
ac
PCC
Istack,1
Idc
Vdc
+
-
WT1,1 VWT,1,1
+
-
WT2,1 VWT,2,1
+
-
WTn,1 VWT,n,1
+
-
WT1,2 VWT,1,2
+
-
WT2,2 VWT,2,2
+
-
WTn,2 VWT,n,2
+
-
Istack,2
WT1,m VWT,1,m
+
-
WT2,m VWT,2,m
+
-
WTn,m VWT,n,m
+
-
Istack,m
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No 50 Hz transformers
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Grid Code
Required additional reactive current
-100%
-50%
Voltage drop
N
B
II
NUU
m=2
reactive currentrated current
Time in msFault occured
Line-to-line
voltageNU
U
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DC breaking
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DC breaker current
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Some research examples
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Example of system study
• Geographical locations
For hourly average wind speed data in the North Sea region
Vector ARIMA(6,0,0)
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Real exchange power
0 20 40 60 80 100-1000
-500
0
500
1000
Duration [%]Ex
chan
ge P
ower
[MW
]
NL=>NO
System dimensions
Existing HVDC transmission
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Branch power• WF 1 capacity=1700 MW
0 10 20 30 40 50-3
-2
-1
0
1
2
3
Time [hour]
Unc
ontro
lled
Bra
nch
Pow
er [p
u]
NO->WF 1NL->WF 1
0 20 40 60 80 100-3
-2
-1
0
1
2
3
Duration [%]
Unc
ontro
lled
Bra
nch
Pow
er [p
u]
NO->WF 1NL->WF 1
(84%,1)
Over loaded for about
15% of the year
Adding a wind farm of 1700 MW
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Exchange power• [WF1 WF2] capacity=[1700 2700] MW
0 20 40 60 80 100-4
-3
-2
-1
0
1
2
3
Duration [%]U
ncon
trolle
d B
ranc
h Po
wer
[pu]
NO->WF 1NL->WF 1DE->WF 2DK->WF 2WF 1->WF 2
1117MW
>30%
Peak >3pu
Multiterminal with added wind farms
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0 20 40 60 80 100-3
-2
-1
0
1
2
3
Duration [%]
Con
trolle
d B
ranc
h Po
wer
[pu]
NO->WF 1NL->WF 1DE->WF 2DK->WF 2WF 1->WF 2
Multiterminal with added wind farms
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0 0.34 0.68 1.02 1.36 1.7-600
-400
-200
0
200
400
600
WPP capacity [GW]N
PV o
f sys
tem
add
ed c
ost [
M€]
Ttariff=10 €/MWhTtariff=13 €/MWhTtariff=18 €/MWh
Reinforcing the system
0 0.34 0.68 1.02 1.36 1.7-100
0
100
200
300
400
WPP capacity [GW]
Add
ed c
ost [
M€]
Base caseReinforce-NO->WF1Reinforce-NL->WF1
0 0.34 0.68 1.02 1.36 1.7-100
0
100
200
300
WPP capacity [GW]
Add
ed c
ost [
M€]
Base caseReinforce with 216MWReinforce with 317MWReinforce with 490MW
Added cost and reinforcement
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Collection grid of offshore wind farmTypical offshore HVAC collection grid Existing VSC-HVDC collection grid
Future HVDC collection grid
Bulky 50 Hz transformers
AC Cables
Bulky 50 Hz transformers
High power density converters using HF High Power transformers
DC medium voltage cables
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The dc-transformer
Modular structure (PISO) :
Future HVDC collection grid with HF / MF transformers :
One module with HFT :
HF high power transformer + inductor
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Design and Optimization (Case Study)Optimization results
600’000 combinations of free parameters
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HF Resistance measurement
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DC-link voltage selection
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DC-link voltage and losses
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Other generators - SynRG
• 74 % of power given the same volyme
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Questions ?