Analysis of current control interaction of multiple parallel grid connected inverters

The parallel connection of multiple electronic power converters is typically used to connect renewable power sources to the electricity grid, like often done, for example, in photovoltaic farms. This interconnection of systems can be affected by instability issues above the fundamental grid frequency, which has detrimental effects on power quality, protection effectiveness, and reliability. This paper proposes an accurate multi-input multi-output methodology to stability analysis that allows to highlight and analyze all the relevant stability contributions linked to converters as well as grid dynamics. The analytical study of a generic system representation is firstly discussed to introduce the approach. Then, the impedance multiplication effect, commonly applied when all the parallel connected inverters are equal, is herein extended to the case of converters with different parameters. The outcome of the study is an approach featuring both accurate stability analysis, as in multi-input multi-output based approaches, and modularity, as in impedance-based approaches. The results of the study are validated by means of extensive simulation and experimental tests on an experimental setup composed of three 5kVA parallel inverters.