Design and Analysis of Different Passive Damping for Grid-Connected LCL filters to Achieve Desirable System Performance

The LCL filter has excellent high-frequency harmonics attenuation capability, However, due to the inherent resonance of LCL filter, it is necessary to add damping strategy. Although there are many passive damping schemes, such as series R, series RL, shunt RC and shunt RLC, there are few studies on the performance comparisons of these passive damping schemes. Besides, it is hard to know which one is cost-effective, given that higher-order damping methods complicate the power circuit and require more components. Therefore, this paper aims to study the performances, merits and applicable occasions of various types of passive damping schemes. At first, based on the traditional LCL filter parameter design method, combined with the design criteria derived from the view of improving the system dynamic, the unified design flowchart of the LCL filter with various passive damping is proposed. Then, for a 5kW single-phase grid-connected inverter, the parameters of LCL filter with above four passive damping schemes are selected. Their performances are evaluated from the aspects of damping loss, volume and weight. Finally, comparative results have shown the applicable occasions of different passive damping schemes.