Decentralized stability rules for microgrids

Stability certification of microgrids can be challenging due to the lack of information on exact values of system parameters. Moreover, full-scale direct stability analysis for every system configuration can be economically and technically unjustified. There exist a demand for simple conditions imposed on system components that guarantee the whole system stability under arbitrary interconnections. Most of existing methods are relying on the so-called passivity property which can be difficult to realize by all the system components simultaneously. In the present manuscript we develop an approach for certifying the system stability by separately considering its properties in different regions of frequency domain. We illustrate our method on the case of droop-controlled inverters and show that while these inverters can never be made passive, reasonable stability certificates can be formulated by careful consideration of their input admittance for different frequency regions. We discuss the generalization of the method for different types of microgrid components.