ABSTRACT:
This paper presents a new control strategy
for low-voltage ride-through for 3-phase grid-connected photovoltaic systems.
The proposed fault ride through control algorithm, which is designed based on
mixed potential function, can protect the inverter from over current failure
under both symmetric and asymmetric faults, reduce the double frequency
oscillation and provides reactive power support by applying a voltage
compensation unit. With the proposed method, the inverter can also inject
sinusoidal current during asymmetric faults. The method does not require a hard
switch to switch from the Maximum Power Point Tracking (MPPT) to a non-MPPT
algorithm, which ensures a smooth transition.
KEYWORDS:
1. Current control
2. Fault-ride-through
3. Photovoltaic
4. Micro-grids
5. Large-signal analysis
SOFTWARE:
MATLAB/SIMULINK
CONCLUSION:
This paper proposes a LVRT control strategy
for low voltage distribution networks with PV system directly connected to the
grid. The method is based on the classic cascaded voltage and current loops in
dqframe, while the positive and negative sequence components are used to modify
the reference DC-link voltage to limit the inverter current during the grid
faults. The mixed-potential function is used to regulate the compensation term
of the DC-link voltage. Through applying this regulation, the double grid
frequency oscillation, which is appeared in inverter active power and DC-link
voltage following an asymmetric fault, can be reduced. The method also
generates sinusoidal inverter current during faults. The reactive power
injection is used to supply the required reactive power to restore the voltage.
In choosing the DC-link capacitor this should be taken into account that the
proposed method increases the DC-link voltage during faults. However, since the
protection systems must operate within a fracture of a second, this should not
be a huge burden on an appropriate power capacitor. The proposed method is
validated in MATLAB/SIMULINK. Simulation results show the proposed LVRT control
strategy can be used for both symmetric and asymmetric faults. The simulation
results also demonstrate that the proposed voltage compensation unit, derived
from the mixed potential function, reduces the double grid frequency
oscillation. The presented results show that for a severe voltage sag (3-phase fault),
the proposed method could reduce the fault current to 1.5 pu to protect the
inverter from overcurrent failure. For asymmetric voltage sags, the proposed
method could limit the fault current to almost rated value. In addition, this
method does not require a hard switch to switch from the MPPT to a non-MPPT
algorithm, which ensures a smooth transition. It is noted that the proposed
method does not affect the
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