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.
EXPECTED SIMULATION RESULTS:
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 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.
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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