Application of an LLCL filter on three-phase three-wire shunt active power filter

This paper concentrates on a new high-order output filter, named LLCL filter, and its application issues on the three-phase three-wire shunt active power filter (SAPF). The LLCL topology is constructed by replacing the capacitor of the traditional LCL filter with an LC branch that resonant at the switching frequency. The SAPF with an LLCL filter exhibits excellent switching frequency harmonic attenuation capability, which is beneficial to the harmonic compensation for nonlinear load. System stability problems aroused by resonance are investigated, and a passive damping method by adding a real resistor in the LC branch is adopted for simplicity. The selection of the damping resistor is based on the criteria of minimization of power loss as well as maintaining good harmonic compensation performance. Simulation and experimental results have been presented to verify the theoretical analysis.