In converters, the passive components (mainly inductors) impact heavily in terms of weight, volume and cost. In detail, the most expensive part is the LCL filter stage hardware. Furthermore, while all power electronics components are becoming smaller and smaller, inductors remain heavy and bulky, making PCB design chal- lenging. The aim of this thesis is to reduce the total inductance required for the differential filter for the grid and thus reduce its total costs and volumes. This thesis analyzes the LCL filter theory applied in a grid filter for a three-level T-type AFE with a fourth neutral leg. PLECS simulations are used to quantify the stresses on the LCL filter inductors, find the worst operating conditions and choose the optimal values of neutral inductance.