Modeling the Control of Islanded Networks Supplied by Inverters: the Case of MV and LV Systems

The increasing number of inverter-based Distributed Generator (DG) units connected to both MV and LV distribution networks can be used as a resource in order to overcome some emergency conditions. The presence of different inverter-based DG units could introduce issues regarding the management of intentional islanded networks, therefore reliable inverter control strategies for islanded operation assume an essential role. In this paper an inverter operating scheme has been implemented suitable in presence of networks supplied by a single DG or multiple DGs and for both grid tie and grid off operation. This inverter control scheme has been modeled and tested through detailed dynamic simulations in LV and MV islanded networks. Moreover the dynamic behavior of the proposed inverter control strategy has been studied and analyzed in light of the recently issued Italian connection grid codes for active users. The results show that the control scheme allows operation of intentional islanded networks supplied by single or multiple DG units. In case of multiple DG units, simulations show that, grid connection rules influence the dynamic of islanding operations depending on the power balance existing before the islanding forming.