Performance evaluation of LLCL filter for active power filter

Active Power Filter (APF) is an inverter based device that compensates the harmonic currents generated by nonlinear loads. Inverters release high frequency switching ripple harmonics. In early studies, APFs have been generally interfaced to the grid via a single L filter to reduce these harmonics. However, high order filters like LCL and LLCL filters have been recently used with APFs instead of L filter due to insufficient mitigation of L filter. LCL and LLCL filters have better attenuation of switching ripple harmonics at high frequencies. Attenuation performance of LLCL filter at switching frequency is superior to LCL filter. Since LLCL filter has resonance problem, a simple resistor is connected in series with parallel LC branch. The purpose of this paper is to evaluate the performance of LLCL filter for different damping resistor values when used with APF. In order to examine the performance of the LLCL filter, a simulation model is developed in Simulink/MATLAB.