ABSTRACT:
The paper proposes the
application of a Dynamic Voltage Restorer (DVR) to enhance the power quality
and improve the low voltage ride through (LVRT) capability of a three-phase
medium-voltage network connected to a hybrid distribution generation (DG)
system. In this system, the photovoltaic (PV) plant and the wind turbine
generator (WTG) are connected to the same point of common coupling (PCC) with a
sensitive load. The WTG consists of a DFIG generator connected to the network via a step-up
transformer. The PV system is connected to the PCC via a two-stage energy conversion
(DC-DC converter and DC-AC inverter). This topology allows, first, the extraction
of maximum power based on the incremental inductance technique. Second, it
allows the connection of the PV system to the public grid through a step-up transformer.
In addition, the DVR based on Fuzzy Logic Controller (FLC) is connected to the
same PCC. Different fault condition scenarios are tested for improving the
efficiency and the quality of the power supply and compliance with the requirements
of the LVRT grid code. The results of the LVRT capability, voltage stability,
active power, reactive power, injected current, and DC link voltage, speed of
turbine and power factor at the PCC are presented with and without the contribution
of the DVR system.
KEYWORDS:
1. Active power
2. DC-link voltage DFIG
3. Dynamic Voltage Restorer
4. LVRT
5. Power Factor
6. Photovoltaic
7. Voltage Stability
8. Reactive Power
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Figure 1: PV-WTG Hybrid System With
Dvr And A Load
Connected To Grid.
Figure 2: Voltage Phase Magnitude At Pcc During Faults With Typical Lvrt And Hvrt Characteristics Requirements Of Distributed Generation Code Of Germany As An Example.
Figure 3: Voltage Phase Magnitude At Pcc During Sag Fault.
Figure 4: Voltage Phase Magnitude At Pcc During Short Circuit Fault.
Figure 5: Phase Voltage At Pcc During Sag Fault.
Figure 6: Dvr Voltage Contribution At Pcc During Sag Fault.
Figure 7: Phase Voltage At Pcc During Short Circuit Fault.
Figure 8: Total Active Power Of Hybrid System At Pcc Injected To Grid.
Figure 9: Pv Active Power At Pcc Injected To Grid.
Figure 10: Wind Active Power At Pcc Injected To Grid.
Figure 11: Total Reactive Power Of Hybrid System At Pcc Injected
To Grid.
Figure 12: Pv Reactive Power At Pcc Injected To Grid.
Figure 13: Wind Reactive Power At Pcc Injected To Grid.
Figure 14: Total Pv-Wt Current Injected To Grid At Pcc.
Figure 15: Pv Current Injected At Pcc.
Figure 16: Wt Current Injected At Pcc To Grid.
Figure 17: Power Factor At Pcc.
Figure 18: Turbine Rotor Speed.
Figure 19: Vdc Link At Wtg Inverter.
Figure 20: Vdc Link Voltage At Pv Inverter.
CONCLUSION:
The simulation study was carried out
using MATLAB to demonstrate the effectiveness of the proposed DVR control system to improve the power quality and LVRT
capability of the hybrid PV-WT power system. The system has been tested under
different fault condition scenarios. The results have shown that the DVR connected
to the PV-Wind hybrid system at the medium voltage grid is very effective and
is able to mitigate voltage outages and short circuit failure with improved voltage regulation capabilities
and flexibility in the correction of the power factor.
The results of the
simulation also prove that the system designed is secure since the required
voltage ranges are respected correctly and the DG generators operate reliably. The
main advantage of the proposed design is the rapid recovery of voltage; the
power oscillations overshoot reduction, control of rotor speed and preventing
the system from having a DC link overvoltage and thus increasing the stability
of the power system in accordance with LVRT requirements.
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