ABSTRACT
This
study analyzes various anti-islanding (AI) protection relays when the islanding
condition of Grid-Tied PV (photovoltaic) System appears at the Point of Common
Coupling (PCC) between the PV Solar Power System and the power grid. The main
purpose of the study is to determine the performance of several AI prevention
schemes in detecting the presence of an island, by monitoring the detection
time of the islanding condition through different methods. The devices used to implement
the methods include over-current and under-current (OI/UI) relays, over-voltage
and under-voltage (OV/UV) relays, over-frequency and under-frequency (OF/UF)
relays, rate of change of frequency (ROCOF) and Vector Shift relays. The protection
was tested in case of complete disconnection of the PV system from the electric
power grid and also in case of various grid faults.
SOFTWARE:
MATLAB/SIMULINK
CIRCUIT DIAGRAM:
EXPECTED SIMULATION RESULTS
Fig.2: Output results of boost
converter
Fig. 3. The output result of dc link voltage (V DC) in VSC
Fig. 4. Id and Iq currents (pu) of VSC Control
Fig. 5. The Voltage between phase A and phase B of VSC
Fig. 6. Simulation result in 20kV measurement point of utility grid.
Fig. 7. The RMS value of voltage in PCC.
Fig. 8. The RMS value of current in PCC.
Fig. 9. The output result of frequency in PCC.
CONCLUSION :
This
paper studies and compares different AI detection techniques such as passive AI
prevention by standard protection schemes: OI/UI, OV/UV, OF/UF, as well as ROCOF
and Vector Shift in case of a 100kW Grid-Connected PV Array. The PV System is
completely disconnected from EPS and continues to energize a 20kV
utility grid at 50Hz, and respectively various grid faults occurs at 5km away
from the PCC of the PV System. The effectiveness of different AI detection
algorithms is tested and the impact on network fault conditions and relays
behavior during islanding is studied. From the results provided by the
performed Matlab/Simulink simulations, it was observed that using traditional relays
for islanding detection such as the OC or UV resulted
in
significantly better performance in respect to detection time of islanding
conditions. The ROCOF and Vector Shift relays have a detection time comparable
with frequency relays. However, if the ROCOF threshold is exceeded, the
formation of an island is quickly detected. The terminal voltage of PV inverter
needs to exceed a certain threshold when the frequency is not stabilized by
VSC. The UC relay failed entirely to detect the islanding in both analyzed
cases. The effects of unintentional islanding were observed from simulation of
transient grid faults on a power distribution network. The protection equipment
needs to distinguish between islanding event and grid faults. The Grid-Tied PV System
protections should detect the fault and trip before islanding occurs as a result
of the opening of the circuit breaker in response to a downstream fault. In
order to minimize these effects and to perform according to the. international
standards, the AI relays have to be inserted at the points where islanding
conditions may occur. The theoretical simulation results are useful to select
these points and design the AI protection devices for Grid-Tied PV Systems.
REFERENCES
[1]
D. Rekioua and E. Matagne, Optimization of Photovoltaic Power Systems,
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[2]
IEEE Std 1547-2003, Standard for Interconnecting Distributed Resources with
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[3]
R. Teodorescu, M. Liserre and P. RodrÃguez, Grid Converters for Photovoltaic
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[4]
CIGRE Working Group B5.34, “The Impact of Renewable Energy Sources and
Distributed Generation on Substation Protection and Automation,” CIGRE, 2010.
[5]
IEEE Std 1547.2-2008, IEEE Application Guide for IEEE Std 1547™, IEEE
Standard for Interconnecting Distributed Resources with Electric Power Systems,
IEEE, 2008
