A straightforward method is proposed in this paper to optimally design the damping sections of the LCL or LCL plus trap filters. The proposed method simplifies the iterative design procedure of the overall filter while ensuring minimum resonance peaking and smaller capacitor than otherwise would be the case. The choice of the traps parameters in case of adopting multi-tuned traps is systematically described. By using the proposed method, the size of the damping elements and the quality factor of the filter are very easy to be calculated by the filter designer. Time-domain and frequency domain analysis and experimental tests show that the proposed method allows decreasing the size of the filter reactive elements, while still meeting present standard harmonic requirements, even in the case of drifts in the reactive element values or changes in the grid impedance.