Comparison of passive damping solutions of LCL-filter based grid connected inverter

In order to interface with the power grid a filter is required for grid connected inverter. Usually L or LC filter are used. LCL-filter is a third order passive filter which is having more interest to use for grid connected inverter. Compared to L, LC filters, LCL-filter has high attenuation ability even with the lower values of L and C. As it is a third order filter, this filter suffers from stability problems around the resonant frequency. LCL-filter resonance causes a sharp phase step down of -180 with a high resonant peak which should be damped. In order to ensure system stability different passive damping solutions based on the location of the resistor are analyzed in this paper. Mathematical model and design of LCL-filter for different passive damping solutions are presented. Simulation results are provided for each damping solution.