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THE IMPACT OF BoBC IN OFF-SHORE
WIND ENERGY CONVERSION SYSTEM
PRESENTED BY
E. SHEEBA PERCIS
Dr.M.G.R University
Abstract
Offshore windfarms is an emerging technology in the wind energy conversion
system. For onshore wind farms high voltage overhead lines are used for
transmitting power from the wind farm to the grid. However this option is not
possible in the case of an offshore windfarm as large part of the distance to
connection point must be covered by submarine cables. The application of
high voltage dc (HVDC) transmission for integrating large scale and/or offshore wind generation systems with the electric grid is attractive in comparison
to extra high voltage (EHV) ac transmission due to a variety of reasons like
efficiency, economics etc. In the case of HVDC transmission a converter is
connected between the wind farm and the utility grid. Even though CSC’s and
VSC’s are widely used for the realization of large HVDC systems, as an
alternative approach Bridge of Bridge converter (BoBC) is introduced recently.
In this work the performance of the VSC and BoBC are compared and
analyzed. The simulation is done using PSCAD/EMTDC software. Compared
with the onshore wind farms, the offshore wind farms have access to
significantly better wind energy resources and hence offer larger energy
generating capability. Therefore offshore wind farms are gaining importance
and the BoBC proves to be better than the VSC for similar applications.
Paper Publication
1. Sheeba Percis, L. Ramesh, Dr. S. P. Chowdhury, Dr. S. P. Chowdhury.
“The Technical Impacts prediction of Small Scale DG in Low Voltage
Distribution Networks” International Conference on Renewable Energy
, Anna University Chennai ,India ,August 2010 , Page 20-25.
2. Sheeba Percis, L. Ramesh, “ Impact of BoBC in Off-shore Wind Energy
Conversion System” , IEEE and IET International Conference on
Computer Communication (ICCCET 2011) ,National College of
Engineering , Tirunelveli, India ,March 2011,Page 50-56.
3. Sheeba Percis,“Detection of flaws in rolling of steel sheets using Image
processing”, National Conference on Future challenges and Budding
Intelligent Techniques in Electrical & Electronics Engineering (NCEEE
2010), Sathyabama University,Chennai ,India , April 2010, Page 78-81.
OUTLINE OF PRESENTATION
•Introduction
•Literature review
•Methodology
•Results and Discussion
•Conclusion
INTRODUCTION
• Wind - Promising renewable energy
resource.
• Wind energy conversion systems –
sustainable energy.
• Off-shore WECS are better than onshore WECS.
• Long distance transmission – HVDC
stands ahead of HVAC.
LITERATURE REVIEW
•Limited availability of onshore sites and better off-shore
wind conditions are the driving force for off –shore WECS.
•With a HVDC system power flow can be controlled rapidly.
•Development & availability of power electronic devices is
the underpinning technology for integration of large wind
farms with electricity grid.
•VSC based HVDC transmission is a good solution for
connection of large off-shore sites over long distances.
•The BoBC has proved to be advantageous than CSC’s &
VSC’s in terms of efficiency and economics.
METHODOLOGY
System Design
STAGE I: Design of VSC
STAGE II: Design of BoBC
STAGE III: Realization of HVDC system
SOFTWARE USED: PSCAD/EMTDC
Voltage Source Converter
Ea
A
A
I
D
I
D
I
D
I
D
I
D
I
D
I
D
I
D
I
D
I
D
I
D
I
D
A
100.0 [MVA]
Ea
Q
0.1 [H]
#1
#2
B
0.1 [H]
C .44 [kV]
C
0.1 [H]
C
.44 [kV]
R=0
B
1.0 [uF]
B
1.0 [uF]
1.0 [uF]
1.0 [uF]
Features Of VSC
•Consists of six arms with series connected submodules.
•Fully controlled switches accompanied with
anti-parallel diodes are used.
•Bi-directional current flow is obtained.
•Operated in four quadrants.
•Control of real and reactive power is possible.
•A dc bus capacitor is used to provide stiff dc.
•PWM is used.
Bridge Of Bridge Converter
Features of BOBC
•Has six arms with sub-modules connected in
series.
•Sub-modules are stand alone power converters.
•Any number of sub-modules can be connected
and desired voltage rating is obtained.
•Instead of PWM if discrete voltage steps are
used low harmonics and switching losses are
achieved.
TESTED RESULTS
0.350
Ea
1.00
0.300
Ea
0.80
0.250
0.60
0.200
y
y
0.40
0.150
0.20
0.100
0.050
0.00
0.000
-0.20
Output voltage of VSC
Output voltage of BoBC
• For an input of 0.44kV, the VSC gives an output of
0.3369kV.
• Q=15.799 kVAR
• For an input of 0.44kV, the BoBC gives an output of
0.432kV.
AC Side Reactive Component - VSC
Main : Graphs
16.0
Q
14.0
12.0
10.0
y
8.0
6.0
4.0
2.0
0.0
-2.0
0.00
0.10
0.20
0.30
Q=15.799KVAR
0.40
0.50
...
...
...
Realization OF HVDC System
C1
Cable2
Edc1
Pulse
I
A
A
Pulse
A Pulse
D
C2
I
D
Pulse
T
D
A2
Pulse
B
#1
T
B2
T
C2
Edc1
Cable2 C1
0.1 [H]
B
Edc2
C
Cable2
Pulse
I
D
I
D
Pulse
I
100.0 [MVA]
I
D
#2
B
Q
0.1 [H]
C .44 [kV]
C
C2
C
Pulse
theta
th
VCO
sin(th)
*
150.0
V
Alpha1OFF
T
T
Edc2
T
Eout
B2
C2
A2
D
Pulse
theta
H
OFF
L
theta
150.0
Alpha2OFF
theta
H
OFF
L
theta
150.0
Alpha3OFF
H
OFF
L
theta
H
ON
Alpha1ON
L
H
ON
Alpha2ON
L
H
ON
Alpha3ON
L
A
B
C
Alpha1ON
Alpha2ON
Alpha3ON
Alpha1OFF
Alpha2OFF
Alpha3OFF
theta
A
B
*
Sqrt (2)
theta
V
I
D
Pulse
cos(th)
D
Pulse
I
D
I
D
Pulse
Pulse
Vc
I
D
1.6 [uF]
V
1.0 [uF]
1.0 [uF]
1.0 [uF]
I
I
60.0
Eout
.44 [kV]
0.1 [H]
440.0
RMS Voltage
HVDC SYSTEM USING VSC
C
Edc1
D
D
D
D
D
D
HVDC System Using BoBC
I
I
I
I
I
I
0.1 [H]
Pulse
D
D
Pulse
Pulse
Pulse
Pulse
Pulse
Pulse
D
D
D
D
Pulse
V
*
theta
150.0
Cable2 C1
1.0 [uF]
T
A2
T
T
B2
Sqrt (2)
H
OFF
Alpha1OFF
L
*
theta
C2
H
ON
Alpha1ON
L
240.0
RMS Voltage
B
Edc2
C
.44 [kV]
0.1 [H]
Eout
A
Eout
theta
V
T
B
D
D
0.1 [H]
D
D
D
D
0.1 [H]
Edc1
2
T
C
P+jQ
T
2
A
2
150.0
H
OFF
Alpha2OFF
L
theta
Pulse
D
D
D
1.0 [uF]
D
D
theta
Alpha1ON
Alpha2ON
Alpha3ON
Alpha1OFF
Alpha2OFF
Alpha3OFF
0.1 [H]
1.0[uF]
D
Pulse
Pulse
Pulse
Pulse
Pulse
0.1 [H]
1.0 [uF]
H
ON
Alpha2ON
L
I
I
I
I
I
I
0.1 [H]
150.0
H
OFF
Alpha3OFF
L
theta
Pulse
Pulse
Pulse
Pulse
Pulse
1.0 [uF]
theta
A
I
1.0 [uF]
I
I
1.0 [uF]
I
I
I
Pulse
C .44 [kV]
theta
Edc2
0.1 [H]
1.0 [uF]
sin(th)
C2
#2
th
VCO
C
Cable2
0.233 [ohm]
V
C
#1
Vc
60.0
C2
I
B
I
I
I
I
I
B
C1 Cable2
1.0 [uF]
0.1 [H]
1.0 [uF]
A
100.0 [MVA]
0.1 [H]
1.0[uF]
0.1 [H]
A
Pulse
0.1 [H]
1.0 [uF]
A
Pulse
Pulse
Pulse
Pulse
cos(th)
H
ON
Alpha3ON
L
B
C
C
B
Output With HVDC System
Output of HVDC-VSC
Output of HVDC-BoBC
The efficiency of the HVDC-BOBC is 87 percent and hence the HVDC
system using BOBC is more efficient than the system using VSC.
Comparison
•In VSC, RC networks are needed for voltage
sharing. BoBC does not demand this.
•In VSC, the number of series connections are
restricted due to the RC networks. BoBC is not
affected in this manner.
•AC side reactive components.
•Fault tolerance.
•During fault, energy stored in dc bus capacitance of
VSC feeds the fault.
•BoBC is comparatively less costly and more
efficient.
CONCLUSION
•Off-shore WECS is an emerging solution for
green energy.
•As distance becomes longer, AC has technical
limitations.
•Based on PSCAD/EMTDC simulation results
BoBC is found to be better than VSC in
performance.
•BoBC based HVDC off-shore WECS is highly
efficient and cost effective.
REFERENCES
Daniel Ludois and Giri Venkataramanan, “An examination of AC/HVDC Power Circuits for
Interconnecting Bulk Wind Generation with the Electric grid”,energies 2010,vol 3,1263-1289,ISSN
1996-1073.
2. Sheng Jie Shao and Vassilios G. Agelidis, “Review of DC system Technologies for Large Scale
Integration of Wind Energy Systems with Electricity Grids”,Energies 2010,3,1303-1319,ISSN 19961073.
3. Juiping pan, Reynaldo Nuqui, Le Tang and Per Holmberg, “VSC-HVDC Control and Application in
Meshed AC Networks”
4. S. K. Chaudhary, R. Teodorescu and R. Rodriguez, “Wind Farm Grid Integration Using VSC Based
HVDC Transmission – An Overview”
5. Prasai,A, Yim.J, Divan.D, Bendre.A, Sul.s “A new architecture for offshore wind farms”, IEEE
Trans. Power Electr. 2008,23, 1198-1204.
6. S. M. Muyeen, R. Takahashi, T. Murata, and J. Tamura, “Control Strategy for HVDC interconnected
DC based offshore wind farm.
7. S. M. Muyeen, Member, IEEE, Rion Takahashi, Member, IEEE, and Junji Tamura, Senior Member,
IEEE,
“Operation and Control of HVDC connected Off-shore wind farm”, IEEE Transactions on
Sustainable Energy, Vol. 1, No. 1, April 2010.
8. Christian Feltes, Holger Wrede, Friedrich W. Koch andIstván Erlich, and Istvan Erlich, “Enhanced
Fault Ride Through Method for Wind Farms Connected to the Grid through VSC based HVDC
Transmission”, IEEE Transactions on Power Systems, Vol. 24, No. 3, Aug. 2009.
9. Hermann Koch and Deitmar Retzman, ‘Connecting Large Off Shore Wind Farms to the Transmission
Network”, 2010 T&D Conference, New Orleans.
10. Nikolas Flourentzou, Vassilios G. Agelidis and Georgios D. Cementriades, “VSC based HVDC
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1.
18 & 19 March 2011
ICCCET 2011 - National College of Engineering
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