THE IMPACT OF BoBC IN OFF-SHORE WIND ENERGY CONVERSION SYSTEM

AbstractAbstractOffshore 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 off-shore 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 PublicationPaper Publication1.1. Sheeba Percis, L. Ramesh, Dr. S. P. Chowdhury, Dr. S. P. Sheeba Percis, L. Ramesh, Dr. S. P. Chowdhury, Dr. S. P.

Chowdhury. “The Technical Impacts prediction of Small Chowdhury. “The Technical Impacts prediction of Small Scale DG in Low Voltage Distribution Networks” Scale DG in Low Voltage Distribution Networks” International Conference on Renewable Energy , Anna International Conference on Renewable Energy , Anna University Chennai ,India ,August 2010 , Page 20-25.University Chennai ,India ,August 2010 , Page 20-25.

2.2. Sheeba Percis, L. Ramesh, “ Impact of BoBC in Off-shore Sheeba Percis, L. Ramesh, “ Impact of BoBC in Off-shore Wind Energy Conversion System” , IEEE and IET Wind Energy Conversion System” , IEEE and IET International Conference on Computer Communication International Conference on Computer Communication (ICCCET 2011) ,National College of Engineering , (ICCCET 2011) ,National College of Engineering , Tirunelveli, India ,March 2011,Page 50-56.Tirunelveli, India ,March 2011,Page 50-56.

3.3.   Sheeba Percis,“Detection of flaws in rolling of steel Sheeba Percis,“Detection of flaws in rolling of steel sheets using Image processing”, National Conference on sheets using Image processing”, National Conference on Future challenges and Budding Intelligent Techniques in Future challenges and Budding Intelligent Techniques in Electrical & Electronics Engineering (NCEEE 2010), Electrical & Electronics Engineering (NCEEE 2010), Sathyabama University,Chennai ,India , April 2010, Page Sathyabama University,Chennai ,India , April 2010, Page 78-81.78-81.

  

OUTLINE OF PRESENTATIONOUTLINE OF PRESENTATION

•Introduction •Literature review •Methodology•Results and Discussion•Conclusion

INTRODUCTIONINTRODUCTION

• Wind - Promising renewable energy resource.• Wind energy conversion systems – sustainable energy.• Off-shore WECS are better than on- shore WECS.• Long distance transmission – HVDC stands ahead of HVAC.

LITERATURE REVIEWLITERATURE 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.

METHODOLOGYMETHODOLOGY

System DesignSystem Design

STAGE I: Design of VSC STAGE II: Design of BoBC

STAGE III: Realization of HVDC systemSOFTWARE USED: PSCAD/EMTDC

Voltage Source ConverterVoltage Source Converter

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Features Of VSC•Consists of six arms with series connected sub-modules.•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

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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 RESULTSTESTED RESULTS

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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

0.00 0.10 0.20 0.30 0.40 0.50 ... ... ...

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Realization OF HVDC System

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440.0RMS Voltage

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HVDC SYSTEM USING VSC

HVDC System Using BoBC

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lse

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Output With HVDC SystemOutput 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.

ComparisonComparison•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.

CONCLUSIONCONCLUSION•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.

REFERENCESREFERENCES1. 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 1996-1073.

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 Power Transmission Systems: An Overview”, IEEE Transactions on Power Electronics, Vol. 24, No. 3, March 2009.

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