A New Variable-Speed Wind Energy Conversion System Using Permanent-Magnet Synchronous Generator and Z-Source Inverter

ABSTRACT:

With the growth of wind energy conversion systems (WECSs), various technologies are developed for them. Permanent-magnet synchronous generators (PMSGs) are used by these technologies due to special characteristics of PMSGs such as low weight and volume, high performance, and the elimination of the gearbox. In this paper, a new variable-speed WECS with a PMSG and Z-source inverter is proposed. Characteristics of Z-source inverter are used for maximum power tracking control and delivering power to the grid, simultaneously.  Two control methods are proposed for delivering power to the grid: Capacitor voltage control and dc-link voltage control. Operation of system with these methods is compared from the viewpoint of power quality and total switching device power (TSDP). In addition, TSDP, current ripple of inductor, performance, and total harmonic distortion of grid current of proposed system is compared with traditional wind energy system with a boost converter.

 KEYWORDS:

  1. Maximum power point tracking (MPPT) control
  2. Permanent-magnet synchronous generator (PMSG)
  3. Wind energy conversion system (WECS)
  4. Z-source inverter

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Proposed PMSG-based WECS with Z-source inverter.

EXPECTED SIMULATION RESULTS:

Fig. 2. DC voltage and optimum rotor speed relation: simulated and approximated and calculated (actual).

Fig. 3. Wind speed variation.

Fig. 4. PMSG rotor speed (capacitor voltage control).

Fig. 5. Maximum mechanical power of turbine and the extracted mechanical power from turbine (capacitor voltage control).

Fig. 6. Capacitor voltage (capacitor voltage control).

Fig. 7. Active and reactive powers (capacitor voltage control).

Fig. 8. Active power delivered to the grid and extracted mechanical power

(capacitor voltage control).

Fig. 9. Inductor current of Z-source inverter (capacitor voltage control).

Fig. 10. Input voltage of Inverter (Vi ) (capacitor voltage control).

Fig. 11. PMSG rotor speed (dc-link voltage control).

Fig. 12. The maximum mechanical power of turbine and the extracted mechanical  power from turbine (dc-link voltage control).

Fig. 13. Active power delivered to the grid and extracted mechanical power (dc-link voltage control).

Fig. 14. Capacitor voltage (dc-link voltage control).

Fig. 15. Input voltage of Inverter (Vi ) (dc-link voltage control).

Fig. 16. DC-link voltage across the rectifier.

 

Fig. 17. DC-link voltage across the Z-source inverter.

Fig. 18. Inductor current of Z-source inverter.

Fig. 19. Inductor current of Z-source inverter (zoomed).

Fig. 20. Grid current in proposed WECS.

Fig. 21. Spectra of grid current in proposed WECS.

 

Fig. 22. Inductor current of boost converter (zoomed).

Fig. 23. Inductor current of boost converter.

Fig. 24. Grid current in traditional WECS without dead time.

Fig. 25. Spectra of grid current in traditional WECS without dead time.

Fig. 26 Grid current in traditional WECS with dead time.

Fig. 27. Spectra of grid current in traditional WECS with dead time.

Fig. 28. Active power delivered to the grid in conventional and proposed WECSs.

Fig. 29. Efficiency of conventional and proposed WECSs.

CONCLUSION:

In this paper, a PMSG-based WECS with Z-source inverter is proposed. Z-source inverter is used for maximum power tracking control and delivering power to the grid, simultaneously. Compared to conventional WECS with boost converter, the number of switching semiconductors is reduced by one and reliability of system is improved, because there is no requirement for dead time in a Z-source inverter. For active power control, two control methods: capacitor voltage control and dc-link voltage control is proposed and compared. It is shown that with dc-link voltage control method, TSDP is increased only 6% compared to conventional system, but there is more power fluctuations compared to capacitor voltage control. With capacitor voltage control TSDP in increased 19% compared to conventional system. It was also shown that due to elimination of dead time, the THD of proposed system is reduced by 40% compared to conventional system by 5mS dead time. Finally, with same value of passive components, inductor current ripple is the same for both systems.

REFERENCES:

[1] E. Spooner and A. C. Williamson, “Direct coupled permanent magnet generators for wind turbine applications,” Inst. Elect. Eng. Proc., Elect. Power Appl., vol. 143, no. 1, pp. 1–8, 1996.

[2] N. Yamamura, M. Ishida, and T. Hori, “A simple wind power generating system with permanent magnet type synchronous generator,” in Proc. IEEE Int. Conf. Power Electron. Drive Syst., 1999, vol. 2, pp. 849–854.

[3] S. H. Song, S. Kang, and N. K. Hahm, “Implementation and control of grid connected AC–DC–AC power converter for variable speed wind energy conversion system,” Appl. Power Electron. Conf. Expo., vol. 1, pp. 154–158, 2003.

[4] A. M. Knight and G. E. Peters, “Simple wind energy controller for an expanded operating range,” IEEE Trans. Energy Convers., vol. 20, no. 2, pp. 459–466, Jun. 2005.

[5] T. Tafticht, K. Agbossou, A. Cheriti, and M. L. Doumbia, “Output power maximization of a permanent magnet synchronous generator based standalone wind turbine,” in Proc. IEEE ISIE 2006, Montreal, QC, Canada, pp. 2412–2416.

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