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
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[2]
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[3]
S. H. Song, S. Kang, and N. K. Hahm, “Implementation and control of grid
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system,” Appl. Power Electron. Conf. Expo., vol. 1, pp. 154–158, 2003.
[4]
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[5]
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