Offshore Wind Farms – VSC-based HVDC Connection

 

ABSTRACT:

Due to significantly higher and more constant wind speeds and the shortage of suitable sites for wind turbines on the land, offshore wind farms are becoming very attractive. The connection of the large offshore wind farms is possible with HVAC, classical HVDC and Voltage Source Converter (VSC based) HVDC technology. In this paper their main features will be given. From the economical and technical viewpoint, the type of connection depends on the size of the wind farm and on the distance to the connection point of the system.

As very promising technology, especially from the technical viewpoint, the focus of this paper will be put on the VSC-based HVDC technology. Its main technical features as well as its model will be detailed. At the end, obtained simulation results for different faults and disturbances for one offshore wind farm connected with VSC-based HVDC technology will be presented.

KEYWORDS:

  1. HVDC
  2. IGBT
  3. Offshore wind farm connection
  4. PWM
  5. Requirements
  6. Stability
  7. VSC

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 

Fig. 1. Principal scheme of VCS-based HVDC connection

EXPECTED SIMULATION RESULTS:

 

 Fig. 2. Active and reactive power at the connection point during reactive power control

Fig. 3. Active and reactive power at the wind farm side during reactive power control

Fig. 4. Active power, reactive power and voltage at system and wind farm side in case of single phase short circuit near to the connection point – 100ms

Fig. 5. Active power, reactive power and voltage at system and wind farm side in case of single phase short circuit at the wind farm side – 100ms

 CONCLUSION:

The connection of an offshore wind farm depends primarily on the amount of power that has to be transmitted and the distance to the connection point.

Primarily due to comparatively small size and short distance to the connection point as well as due to its lower costs and experience, all actual offshore wind farms and those planned to be installed are still using/plan to use HVAC connection.

The advantages of using a HVDC solution are more significant with increase of the distance and power.

The VSC-based HVDC technology is due to its technical advantages like: active and, especially, reactive power control (voltage control), isolated operation, no need for an active commutation voltage etc. very good solution for an offshore wind farm connection. Performed simulation and their results of simulated faults and disturbances show that the technical requirements can be fulfilled.

REFERENCES:

[1] European Wind Energy Association. (2004). Wind Energy – The Facts. [Online]. Available: http://www.ewea.org

[2] Global Wind Energy Council. (2004). [Online]. Available: http://www.gwec.net

[3] F.W. Koch, I. Erlich, F. Shewarega, and U. Bachmann, “Dynamic interaction of large offshore wind farms with the electric power system”, in Proc. 2003 IEEE Power Tech Conf., Bologna, Italy, vol. 3, pp. 632-638.

[4] J.G. Slootweg and W.L. Kling, “Is the Answer Blowing in the Wind?”, IEEE Power and Energy Magazine, vol. 1, pp. 26-33, Nov./Dec. 2003.

[5] Wind Energy Study 2004. [Online]. Available: http://www.ewea.org

Inertial Response of an Offshore Wind Power Plant with HVDC-VSC

 

ABSTRACT:

This paper analyzes the inertial response of an offshore wind power plant (WPP) to provide ancillary services to the power system grid. The WPP is connected to a high-voltage direct-current voltage source converter HVDC-VSC to deliver the power to the onshore substation. The wind turbine generator (WTG) used is a doubly-fed induction generator (Type 3 WTG). In this paper we analyze a control method for the WTGs in an offshore WPP to support the grid and contribute ancillary services to the power system network. Detailed time domain simulations will be conducted to show the transient behavior of the inertial response of an offshore WPP.

 KEYWORDS:

  1. HVDC
  2. Inertial response
  3. Offshore wind turbine

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Test system schematic

EXPECTED SIMULATION RESULTS:

 

Fig. 2. ΔT order applied to the controller of the DFIG

Fig. 3. DFIG rotating speed, 150 MW

Fig. 4. DFIG electromagnetic torque, 150 MW

Fig. 5. HVDC link voltage , 150 MW

Fig. 6. HVDC link current, 150 MW

Fig. 7. Real and reactive power (rectifier side), 150 MW

Fig. 8. Real and reactive power (inverter side), 150 MW

Fig. 9. DFIG rotating speed, 180 MW

Fig. 10. DFIG electromagnetic torque, 180 MW

Fig. 11. HVDC link voltage , 180 MW

 

Fig. 12. HVDC link current, 180 MW

Fig. 13. Real and reactive power (rectifier side), 180 MW

Fig. 14. Real and reactive power (inverter side), 180 MW

Fig. 15. DFIG rotating speed, 200 MW, 12 m/s

Fig. 16. DFIG electromagnetic torque, 200 MW, 12 m/s

Fig. 17. HVDC link voltage , 200 MW, 12 m/s

Fig. 18. HVDC link current, 200 MW, 12 m/s

 CONCLUSION:

Detailed time domain simulations were conducted in order to analyze the transients present on the inertial response of an offshore WPP delivering power through an HVDC-VSC link. Several results from transient behavior are presented, these results show that an offshore WPP connected to the grid via an HVDC-VSC link is able to deliver inertial response if it is requested.

These results are important as the WPP importance for the power system is growing and its performance during contingencies must be asured.

REFERENCES:

[1] A. Bodin, “HVDC Light—A Preferable Power Transmission System for Renewable Energies.” Proceedings of the 2011 Third International Youth Conference on Energetics; July 7–9, 2011, Leiria, Portugal

[2] M. de Prada Gil, O. Gomis-Bellmunt, A. Sumper, and J. Bergas-Jané, “Analysis of a Multi-Turbine Offshore Wind Farm Connected to a Single Large Power Converter Operated with Variable Frequency.” Energy (36: 5), May 2011; pp. 3272–3281

[3] Feltes, C., and Erlich, I. “Variable Frequency Operation of DFIG-Based Wind Farms Connected to the Grid Through VSC-HVDC Link.” IEEE Power Engineering Society General Meeting, June 24–28, 2007, Tampa, Florida.

[4] N. Miller, K. Clark, M. Cardinal, and R. Delmerico, “Grid-friendly wind plants controls: GE Wind CONTROL—Functionality and field tests,” presented at European Wind Energy Conf., Brussels, Belgium, 2008.

[5] N. W. Miller, K. Clark, and M. Shao, “Impact of frequency responsive wind plant controls on grid performance,” presented at 9th International Workshop on Large-Scale Integration of Wind Power, Quebec, Canada, Oct. 18–19, 2010.

A New Control Strategy for Active and Reactive Power Control of Three-Level VSC Based HVDC System

ABSTRACT

This paper presents a new control strategy for real and reactive power control of three-level multipulse voltage source converter based High Voltage DC (HVDC) transmission system operating at Fundamental Frequency Switching (FFS). A three-level voltage source converter replaces the conventional two-level VSC and it is designed for the real and reactive power control is all four quadrants operation. A new control method is developed for achieving the reactive power control by varying the pulse width and by keeping the dc link voltage constant. The steady state and dynamic performances of HVDC system interconnecting two different frequencies network are demonstrated for active and reactive powers control. Total numbers of transformers used in the system are reduced in comparison to two level VSCs. The performance of the HVDC system is also improved in terms of reduced harmonics level even at fundamental frequency switching.

 KEYWORDS 

  1. HVDC
  2. Voltage Source Converter
  3. Multilevel
  4. Multipulse
  5. Dead Angle (β)

 SOFTWARE:  MATLAB/SIMULINK

BLOCK DIAGRAM: 1

Fig. 1 A three-level 24-Pulse voltage source converter based HVDC system

 

CONTROL SCHEME

2

Fig. 2 Control scheme of three-level VSC based HVDC system using dynamic dead angle (β) Control

EXPECTED SIMULATION RESULTS

3

Fig. 3 Performance of rectifier station during simultaneous real and reactive power control of three-level 24-pulse VSC based HVDC system

4

Fig. 4 Performance of inverter station during simultaneous real and reactive power control of three-level 24-pulse VSC based HVDC system

5

Fig. 5 Variation of angles (δ) and (β) values of three-level 24-pulse VSC based HVDC system during simultaneous real and reactive power control

CONCLUSION

A new control method for three-level 24-pulse voltage source converter configuration has been designed for HVDC system. The performance of this 24-pulse VSC based HVDC system using the control method has been demonstrated in active power control in bidirectional, independent control of the reactive power and power quality improvement. A new dynamic dead angle (β) control has been introduced for three-level voltage source converter operating at fundamental frequency switching. In this control the HVDC system operation is successfully demonstrated and also an analysis of (β) value for various reactive power requirement and harmonic performance has been carried out in detail. Therefore, the selection of converter operation region is more flexible according to the requirement of the reactive power and power quality.

REFERENCES

[1] Gunnar Asplund, Kjell Eriksson and kjell Svensson, “DC Transmission based on Voltage Source Converters,” in Proc. Of CIGRE SC14 Colloquium in South Africa 1997, pp.1-7.

[2] “HVDC Light DC Transmission based on Voltage Source Converter,” ABB Review Manual 1998, pp. 4-9.

[3] Xiao Wang and Boon-Tech Ooi, “High Voltage Direct Current Transmission System Based on Voltage Source Converter,” in IEEEPESC’ 90 Record, vol.1, pp.325-332.

[4] Michael P. Bahrman, Jan G. Johansson and Bo A. Nilsson, “Voltage Source Converter Transmission Technologies-The Right Fit for the Applications,” in Proc. of IEEE-PES General Meeting, Toronto, Canada, July-2003, pp.1840-1847.

[5] Y. H. Liu R. H. Zhang, J. Arrillaga and N. R. Watson, “An Overview of Self-Commutating Converters and their Application in Transmission and Distribution,” in Conf. Proc of IEEE/PES T & DConf. & Exhibition, Asia and Pacific Dalian, China 2005, pp.1-7.