ABSTRACT
The
unified power quality conditioner (UPQC) is a custom power device, which
mitigates voltage and current-related PQ issues in the power distribution
systems. In this paper, a UPQC topology for applications with non-stiff source
is proposed. The proposed topology enables UPQC to have a reduced dc-link voltage
without compromising its compensation capability. This proposed topology also
helps to match the dc-link voltage requirement of the shunt and series active
filters of the UPQC. The topology uses a capacitor in series with the
interfacing inductor of the shunt active filter, and the system neutral is
connected to the negative terminal of the dc-link voltage to avoid the
requirement of the fourth leg in the voltage source inverter (VSI) of the shunt
active filter. The average switching frequency of the switches in the VSI also
reduces, consequently the switching losses in the inverters reduce. Detailed
design aspects of the series capacitor and VSI parameters have been discussed
in the paper. A simulation study of the proposed topology has been carried out
using PSCAD simulator, and the results are presented. Experimental studies are carried
out on three-phase UPQC prototype to verify the proposed topology.
KEYWORDS
1.
Average
switching frequency
2.
Dc-link
voltage
3.
Hybrid
topology
4.
Non-stiff
source
5.
Unified power
quality conditioner (UPQC)
SOFTWARE:
MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. Equivalent circuit of proposed VSI topology for UPQC compensated system
(modified topology).
EXPECTED SIMULATION RESULTS
Fig.
2. Simulation results before compensation (a) load currents (b) terminal voltages.
Fig.
3. Simulation results using conventional topology. (a) DC capacitor voltages
(top and bottom). (b) Source currents after compensation. (c) Voltage across
the interfacing inductor in phase-a of the shunt active filter. (d)
Shunt active filter currents. (e) Terminal voltages with sag, DVR-injected
voltages,
and
load voltages after compensation.
Fig.
4. Simulation results with modified topology. (a) Voltage across series capacitor
and load voltage in phase-a. (b) Inverter output voltage in leg-a of
shunt active filter. (c) DC and fundamental values of voltage across series capacitor
and inverter output voltage.
Fig.
5. Simulation results using modified topology. (a) DC capacitor voltages. (b)
Source currents after compensation. (c) Voltage across the interfacing inductor
in phase-a of the shunt active filter. (d) Shunt active filter currents.
(e) Terminal voltages with sag, DVR injected voltages, and load voltages after compensation.
CONCLUSION
A
modified UPQC topology for three-phase four-wire system has been proposed in
this paper, which has the capability to compensate the load at a lower dc-link
voltage under nonstiff source. Design of the filter parameters for the series
and shunt active filters is explained in detail. The proposed method is
validated through simulation and experimental studies in a three-phase
distribution system with neutral-clamped UPQC topology (conventional). The
proposed modified topology gives the advantages of both the conventional
neutral-clamped topology and the four-leg topology. Detailed comparative
studies are made for the conventional and modified topologies. From the study,
it is found that the modified topology has less average switching frequency,
less THDs in the source currents, and load voltages with reduced dc-link
voltage as compared to the conventional UPQC topology.
REFERENCES
[1]
M. Bollen, Understanding Power Quality Problems: Voltage Sags and Interruptions.
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[2]
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[3]
B. T. Ooi, J. C. Salmon, J. W. Dixon, and A. B. Kulkarni, “A three phase controlled-current
PWM converter with leading power factor,” IEEE Trans. Ind. Appl., vol.
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[4]
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[5]
R. Gupta, A. Ghosh, and A. Joshi, “Multiband hysteresis modulation and switching
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