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Indirect Sliding Mode Power Control associated to Virtual Resistor based Active Damping Method for LLCL-Filter-based Grid-Connected Converters

LLCL filters are becoming an attractive solution for Grid connected Converters (GcCs) due to their ability to reduce the filter cost and size while meeting new grid codes and power quality requirements. Compared to the conventional LCL filter, the LLCL filter inserts a small inductor in the capacitor branch to compose a series LC circuit that resonates at the GcC switching frequency. The LC branch has a very low impedance at the switching frequency, which can strongly suppress the harmonic current around switching frequency and therefore reduce the filter grid side inductor. However, the LLCL filter resonance phenomenon and the large changes in the grid inductance (typically under weak grid conditions and in rural areas) may compromise the system stability. In order to address these concerns, this paper proposes an Indirect Sliding Mode Power Control associated to Virtual Resistor based Active Damping method (ISMPC-VRAD) for LLCL -filter-based Grid-connected Converters ( LLCL-GcCs ) . The LLCL filter design parameters as well as the ISMPC-VRAD gains are carefully tuned in order to ensure stable operation under severe grid inductance variations while taking into account the influence of LLCL filter parameters changes on the system stability. Simulation results are presented and discussed in order to prove the efficiency and the reliability of the proposed ISMPC-VRAD for LLCL-GcCs as well as the high filtering performances of the designed LLCL-GcCs .