Control Strategy for Three Phase Grid Connected PV Inverters Enabling Current Limitation under Unbalanced Faults

S. Appalaraju, R. Indhu, A.Chandra Babu


Power quality and voltage control are among the most important aspects of the grid-connected power converter operation under faults. Non-sinusoidal current is injected during unbalanced voltage sag and active or/and reactive power includes double frequency content. This paper introduces a new Fuzzy Logic Controller based control approach to mitigate the double grid frequency oscillations in the active power and dc-link voltage of the two-stage three-phase grid-connected Photovoltaic (PV) inverters during unbalanced faults. With the Fuzzy Controller control method, PV inverter injects sinusoidal currents under unbalanced grid faults. In addition, an efficient and easy-to-implement current limitation method is introduced, which can effectively limit the injected currents to the rated value during faults. In this case, the fault-ride-through operation is ensured and it will not trigger the over current protection. A Non-MPPT operation mode is proposed for the dc-dc converter. The mode is enabled under severe faults, when the converter cannot handle the maximum PV power. Finally simulated validation is provided by implementing method at Matlab/Simulink environment and analyses the performance of the complete system with including PV inverter.

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