ABSTRACT:
This paper presents a
voltage-controlled DSTATCOM-based voltage regulator for low voltage
distribution grids. The voltage regulator is designed to temporarily meet the
grid code, postponing unplanned investments while a definitive solution could
be planned to solve regulation issues. The power stage is composed of a
three-phase four-wire Voltage Source Inverter (VSI) and a second order low-pass
filter. The control strategy has three output voltage loops with active damping
and two dc bus voltage loops. In addition, two loops are included to the
proposed control strategy: the concept of Minimum Power Point Tracking (mPPT)
and the frequency loop. The mPPT allows the voltage regulator to operate at the
Minimum Power Point (mPP), avoiding the circulation of unnecessary reactive
compensation. The frequency loop allows the voltage regulator to be independent
of the grid voltage information, especially the grid angle, using only the
information available at the Point of Common Coupling (PCC). Experimental
results show the regulation capacity, the features of the mPPT algorithm for
linear and nonlinear loads and the frequency stability.
KEYWORDS:
1. DSTATCOM
2. Frequency
Compensation
3. Minimum Power
Point Tracker
4. Power Quality
5. Static VAR
Compensators
6. Voltage Control
7. Voltage Regulation
SOFTWARE:
MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig. 1. Low voltage
distribution grid under analysis with the voltage regulator
EXPECTED SIMULATION RESULTS:
Fig.
2. Dc bus voltages during the DSTATCOM initialization
Fig.
3. PCC voltages without compensation for linear loads
Fig.
4. PCC voltages with compensation for linear loads
Fig.
5. Voltage regulator currents for linear loads
Fig.
6. Grid, load and voltage regulator currents for linear loads
Fig.
7. PCC voltages without compensation for nonlinear loads
Fig.
8. PCC voltages with compensation for nonlinear loads
Fig.
9. Voltage regulator currents for nonlinear loads
Fig.
10. Grid, load and voltage regulator currents for nonlinear loads
Fig.
11. PCC rms value with linear loads
Fig.
12. Processed apparent power with linear loads
Fig.
13. Voltage regulator currents with mPPT enabled for linear loads
Fig.
14. PCC rms value with nonlinear loads
Fig.
15. Processed apparent power with nonlinear loads
Fig.
16. Voltage regulator currents with mPPT enabled for nonlinear loads
Fig.
17. Total dc bus voltage, PCC voltage, grid voltage and voltage regulator
current waveforms of a-phase with mPPT enabled with grid swell
Fig.
18. (a) Total dc bus voltage, PCC voltage, grid voltage and voltage regulator
current waveforms of a-phase and (b) detail of total dc bus voltage
performance with mPPT enabled with grid sag
CONCLUSION:
This paper presents a three
phase DSTATCOM as a voltage regulator and its control strategy, composed of the
conventional loops, output voltage and dc bus regulation loops, including the
voltage amplitude and the frequency loops.
Experimental results
demonstrate the voltage regulation capability, supplying three balanced
voltages at the PCC, even under nonlinear loads.
The proposed amplitude loop
was able to reduce the voltage regulator processed apparent power about 51 %
with nonlinear load and even more with linear load (80%). The mPPT algorithm
tracked the minimum power point within the allowable voltage range when
reactive power compensation is not necessary. With grid voltage sag and swell,
the amplitude loop meets the grid code. The mPPT can also be implemented in
current-controlled DSTATCOMs, achieving similar results.
The frequency loop kept the
compensation angle within the analog limits, increasing the autonomy of the
voltage regulator, and the dc bus voltage regulated at nominal value, thus
minimizing the dc bus voltage steady state error. Simultaneous operation of the
mPPT and the frequency loop was verified.
The proposed voltage
regulator is a shunt connected solution, which is tied to low voltage
distribution grids without any power interruption to the loads, without any
grid voltage and impedance information, and provides balanced and low-THD
voltages to the customers.
REFERENCES:
[1] ANEEL National Electric Power Distribution System Procedures –
PRODIST, Module 8: Energy Quality. Revision 07, 2014.
[2] M. Mishra, A. Ghosh and A. Joshi, “Operation of a DSTATCOM in
voltage control mode,” IEEE Trans. Power Del., vol. 18, no. 1, pp. 258-264,
Jan. 2003.
[3] G. Ledwich and A. Ghosh, “A flexible DSTATCOM operating in
voltage or current control mode,” IEE Proc.-Gener., Transmiss. Distrib., vol.
149, n. 2, pp. 215-224, Mar. 2002.
[4] T. P. Enderle, G. da Silva, C. Fischer, R. C. Beltrame, L.
Schuch, V. F. Montagner and C. Rech, “D-STATCOM applied to single-phase
distribution networks: Modeling and control,” in Proc. IEEE Ind. Electron. Soc.
Annu. Conf., Oct. 2012, pp. 321 - 326.
[5] C. Kumar and M. Mishra,
“Energy conservation and power quality improvement with voltage controlled
DSTATCOM,” in Proc. Annu. IEEE India Conf., Dec. 2013 pp. 1-6.
