Generic Stability Impedance Criterion for the Parallel Inverters System

Parallel inverters are always utilized in renewable energy systems to transfer the power from different renewable resources to the grid. However, the parallel inverters may suffer instability problem, i.e., even though each inverter is stable individually, the paralleled inverters may be unstable due to the interaction among these inverters or cables. Though a lot of existing stability impedance criteria have already been proposed to assess the stability of the paralleled inverters, they are all targeting specific systems with special assumptions, such as supposing all the inverter parameters are the same, ignore the cable's impedance or treat all the cables as short cables, etc. In this paper, a generic stability impedance criterion has been proposed without any assumptions. Hence, this proposed criterion can evaluate the stability of any types of parallel inverters with different inverter parameters and long/short cables. The detailed derivation of the proposed criterion has also been presented. Finally, the effectiveness of this criterion has been validated by a 5 kW parallel inverters system including three totally different inverters cables.