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
[1]
S. 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.
[2]
M. 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.
[3]
H. 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.
[4]
Y. 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.
[5]
S. 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.
