Design of Critical Passive Damping Parameters for LCL-Type Grid-Connected Inverter

LCL filter is widely used in grid-connected inverter system for its advanced filtering performance. However, the inherent resonance characteristic of LCL filter and digital control delay will seriously endanger system stability. To increase the system robustness, passive damping method is usually applied to suppress the filter resonance in engineering. Since the filter resonance problem is affected by many factors, the selection standard of damping resistor is unclear. In order to design the damping resistor accurately and efficiently, this paper introduces the index of “ critical damping factor” and analyzes two typical passive damping methods: damping resistor in series with filter capacitor or in parallel with filter capacitor. When system damping factor is larger than the critical damping factor, the resonant peak of the amplitude frequency characteristic curve can be completely suppressed and the stability of grid-connected inverter system is fully guaranteed with the minimum cost of passive damping losses. Moreover, the simulation of three-phase grid-connected inverter is carried out in PLECS and the simulation results verify the effectiveness and correctness of the theoretical analysis. This work is supported by National Natural Science Foundation of China (No. 51807152, No. 52177193).