Sensitive Load Voltage Compensation Performed by a Suitable Control Method

IEEE Transactions on Industry Applications, 2016

ABSTRACT

This work proposes the usage of a repetitive-based control to dynamically restore the voltage applied to sensitive and critical loads of power system. The control intrinsically is able to wipe off harmonic distortion and relies on simple transfer function. As a consequence, there is no need to apply harmonic selective filters. Furthermore, the control system is able to work out on sinusoid references and, thus, avoids the need of employing the dq transform. A recursive least-squares is also included to the control system in order to assure the synchronization of the voltages to be restored. The design of the control parameters along with the system stability is discussed. The experimental results are produced with a setup of a three phase series compensator. The scenarios for emulating faulty voltages are the same for experimental and simulated results. The results corroborate the usage of the proposed method.

 

KEYWORDS

  1. Bode plot
  2. DVR-Dynamic voltage restorer
  3. Nyquist stability
  4. Repetitive control
  5. Sensitive load
  6. Series compensator
  7. Voltage quality
  8. Voltage sag.

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Fig. 1 Series compensation system. (a) Electrical grid with compensation to sensitive load. (b) Single-phase equivalent circuit for the feed of sensitive load.

 

EXPECTED SIMULATION RESULTS:

Fig. 2. Sagged grid scenario. (a) Sagged and controlled output voltages. (b) Detail of the correction instant.

 

Fig. 3 Sagged/distorted grid and controlled output voltages.

Fig. 4. Sagged grid and controlled output voltages with RLS algorithm included.

Fig. 5. Sagged/distorted grid scenario. (a) Sagged/distorted and controlled output voltages. (b) Detail of the correction instant.

 

CONCLUSION

This paper has proposed a repetitive control technique to be applied to a series compensator which protects critical loads against voltage distortions from the power grid. The system stability is assured by a low-pass filter which attenuates the resonant peaks from the repetitive controller above a frequency value. This value should be greater than the expected highest harmonic interference endured by the system. The low-pass filter is cascaded with the repetitive controller. The control system is implemented in the discrete domain, employing the trapezoidal integration. Three scenarios including harmonics and sag interferences have been used to test the proposed control system. The controller has proved to be effective to mitigate them. Furthermore, an experimental setup of the series compensator has been mounted to verify the simulations. The results corroborate the proposed controller.

 

REFERENCES

  • Jothibasu and M. Mishra, “An improved direct AC-AC converter for voltage sag mitigation,” IEEE Trans. Ind. Electron., vol. 62, no. 1, pp. 21–29, Jan. 2015.
  • R. Alam, K. M. Muttaqi, and A. Bouzerdoum, “Characterizing voltage sags and swells using three-phase voltage ellipse parameters,” IEEE Trans. Ind. Appl., vol. 51, no. 4, pp. 2780–2790, Apr. 2015.
  • Hao and X. Yonghai, “Control strategy of PV inverter under unbalanced grid voltage sag,” in IEEE Energy Conversion Congress and Exposition, ECCE, vol. 1, no. 1, Sept. 2014, pp. 1029–1034.
  • W. Li, D. M. Vilathgamuwa, F. Blaabjerg, and P. Loh, “A robust control scheme for medium-voltage-level DVR implementation,” IEEE Trans. Ind. Electron., vol. 54, no. 4, pp. 2249–2261, Aug. 2007.
  • Jothibasu and M. Mishra, “A control scheme for storageless DVR based on characterization of voltage sags,” IEEE Trans. Power Del., vol. 29, no. 5, pp. 2261–2269, Oct. 2014.

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