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 This paper proposes a design method of LCL-filter for a grid-connected three-phase inverter using a discontinuous PWM (DPWM) method. When using a DPWM method, many harmonic voltages are generated in the inverter output compared to a continuous PWM (CPWM) method. Therefor, an optimized grid-connected filter design is required for a DPWM method. The proposed design method provides generalized formula to design accurate LCL-filter without trial and error procedures. An inverter side inductance is designed by analyzing the current ripple injected to the grid. The optimized parameters of CLC-filter can be designed by analyzing the total harmonic distortion (THD) and the ripple attenuation factor of the output current. The proposed LCL filter design method is demonstrated by simulation and experimental results.