Optimal design of LCL filter in grid‐connected inverters

As an essential part in technologies for energy storage systems (ESSs) or renewable energy systems (RESs), grid‐connected inverters need power passive filters to meet grid regulations. As typical passive filters, L filter and LCL filter are employed. Although LCL filter is more cost‐effective than L filter, a design of LCL filter is more complicated than L filter. LCL filter has three filter elements: inverter‐side inductor, grid‐side inductor, and filter capacitor. To design the three elements for LCL filter, three or more simultaneous equations should be required, which means that three or more design target should exist. Since conventional design methods for LCL filter do not suggest clear targets and do follow try & error method which cannot be matched exactly with design targets, the conventional methods cannot be optimal design. In this study, a filter inductance ratio to minimise total filter inductance, a filter admittance to meet grid regulation and characteristic impedance for low current stress of switch stack are suggested as design goals. Optimal design equation is proposed to meet the three design goals. The proposed method can solve unique filter elements for LCL filter without iterative try & error. The design method is evaluated through simulation and experiment.