A Unified Nonlinear Controller Design for On-grid/Off-grid Wind Energy Battery-Storage System

 ABSTRACT:

The goal of this paper is to investigate the application of nonlinear control technique to a multi-input multi output (MIMO) nonlinear model of a wind energy battery storage system using a permanent magnet synchronous generator (PMSG). The challenge is that the system should operate in both grid-connected and standalone modes while ensuring a seamless transition between the two modes and an efficient power distribution between the load, the battery and the grid. Our approach is different from the conventional methods found in literature, which use a different controller for each of the modes. Instead, in this work, a single unified nonlinear controller is proposed. The proposed control system is evaluated in simulation. The results showed that the proposed control scheme gives high dynamic responses in response to grid power outage and load variation as well as zero steady-state error.

KEYWORDS:

1.      Battery storage

2.      Bi-directional buck-boost converter

3.      Feedback linearization

4.      Grid-connected

5.      Multi-input mutioutput

6.      Permanent magnet synchronous generator

7.      Stand-alone

8.      Wind turbine

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. WECS based permanent magnet synchronous generator.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Optimum Rotor Speed and Output Power.

Fig. 3. Voltage and current of the load.

Fig. 4. dc-link voltage.

Fig. 5. Wind Turbine Output Power (MW).

Fig. 6. Load Power (MW).

Fig. 7. Charge/discharge of Battery (%).

Fig. 8. Grid Power (MW).

CONCLUSION:

This paper has proposed a nonlinear MIMO controller based on the feedback linearization theory to regulate the load voltage in both grid-connected and stand-alone mode while ensuring a seamless transition between the two modes and an efficient power distribution between the load, the battery and the grid. Our approach is different from the conventional methods found in literature, which use a different controller, PID based, for each mode of operation. Instead, in this work, a single unified nonlinear controller is proposed. The performance of the proposed controller has been tested with different wind speeds as well as in the two modes of operation with dynamic load. The simulation results show that applying nonlinear feedback linearization based control strategy provides a good control performance. This performance is characterized by fast and smooth transient response as well as good steady state stability and reference tracking quality, even with variable wind speed and dynamic load operation. However, this study assume that the system parameters are fixed. A future work will be to test the system when parameters are unknown using adaptive control design theory.

REFERENCES:

[1] M. Fatu, F. Blaabjerg, and I. Boldea, “Grid to standalone transition motion-sensorless dual-inverter control of pmsg with asymmetrical grid voltage sags and harmonics filtering,” IEEE Transactions on Power Electronics, vol. 29, no. 7, pp. 3463–3472, Jul. 2014.

[2] M. Fatu, L. Tutelea, R. Teodorescu, F. Blaabjerg, and I. Boldea, “Motion sensorless bidirectional pwm converter control with seamless switching from power grid to stand alone and back,” in Power Electronics Specialists Conference, 2007. PESC 2007. IEEE. IEEE, 2007, pp. 1239–1244.

[3] R. Teodorescu and F. Blaabjerg, “Flexible control of small wind turbines with grid failure detection operating in stand-alone and grid-connected mode,” IEEE Transactions on Power Electronics, vol. 19, no. 5, pp. 1323–1332, Sept. 2004.

[4] T. Chaiyatham and I. Ngamroo, “Optimal fuzzy gain scheduling of pid controller of superconducting magnetic energy storage for power system stabilization,” International Journal of Innovative Computing, Information and Control, vol. 9, no. 2, pp. 651–666, 2013.

[5] N. Instruments, “Improving pid controller performance,” 2009.

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.