Analysis and Comparison of Medium Voltage High Power DC/DC Converters for Offshore Wind Energy Systems

ABSTRACT:

Offshore wind farm with an internal medium-voltage dc (MVDC)-grid collection connected HVDC transmission may be an option to harvest offshore wind energy. High-power MV dc/dc converters with high-step-up conversion ratios are the key components for the internal MVDC grid. In this paper, a high efficiency step-up resonant switched-capacitor converter for offshore wind energy system is studied, which is characterized by the soft-switching condition for all switches and diodes. This significantly reduces switching losses and higher switching frequency

is feasible to reduce the overall system volume and weight. The comparisons with other two kinds of topologies are also presented; moreover, the possible specification requirements of high power MV dc/dc converters are analyzed and set. The operation principle of the proposed converter has been successfully verified by simulation and experiment results.

KEYWORDS:

1.      High power

2.      Medium-voltage dc (MVDC) converter

3.      MVDC grid

4.      Offshore wind farm

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAMS:

 Fig.1. Layouts of three kinds of electrical systems for offshore wind farms. (a) AC system. (b) AC/DC system. (c) DC system.

CIRCUIT DIAGRAM:

Fig. 2. Configuration of the proposed ZCS RSC converter.

EXPECTED SIMULATION RESULTS:

 

Fig. 3. Idealized waveforms of Fig. 2.

 

Fig. 4. Simulation waveforms of an 8-level SCR converter.

Fig. 5. Experimental waveforms under full-load condition. (a) V_gs and V_ds of Q₁ , currents of L_p1 and L_{n 1} . (b) V_gs and V_ds of Q₁ , currents of L_p5 and L_p2 . (c) V_gs and V_ds of Q₁ , currents of D_p12 and D_p11 . (d) V_gs and V_ds of Q₁ , currents of D_p52 and D_p51 .

CONCLUSION:

High-power MV dc/dc converters with high-step-up conversion ratios are the key components in MVDC-grid collection systems for offshore wind farms. This paper has studied the possible specification requirements of high power MV dc/dc converters. A high efficiency step-up resonant switched-capacitor converter for offshore wind energy system has been proposed, which significantly reduces switching losses, increases switching frequency and minimizes the overall system volume. The operation principle and detailed design of the main circuit are presented. The experimental results from the prototype have confirmed the feasibility of the proposed converter.

REFERENCES:

[1] P. K. Steimer and O. Apeldoorn, “Medium voltage power conversion technology for efficient windpark power collection grids,” in Proc. IEEE Int. Symp. Power Electron. Distrib. Gener. Syst., Jun. 2010, pp. 12–18.

[2] S. M. Muyeen, R. Takahashi, and J. Tamura, “Operation and control of HVDC-connected offshore wind farm,” IEEE Trans. Sustainable Energy, vol. 1, no. 1, pp. 30–37, Apr. 2010.

[3] O.Martander, “DC grid for wind farms,” Licentiate of Engineering Thesis, Dept. of EPE, Chalmers University of Technology, Landala, Sweden, 2002.

[4] C. Meyer, M. H¨oing, A. Peterson, and R. W. De Doncker, “Control and design of DC grid for offshore wind farms,” IEEE Trans. Ind. Appli., vol. 43, no. 6, pp. 1474–1482, Nov./Dec. 2007.

[5] J. Robinson, D. Jovcic, and G. Jo´os, “Analysis and design of an offshore wind farm using a MV DC grid,” IEEE Trans. Power Deliv., vol. 25, no. 4, pp. 2164–2173, Oct. 2010.