A fuzzy logic based controller of DC-link voltage regulation of parallel inverters operation during unintended islanding mode

Abstract

This paper investigates the effects of unintended island operation mode on parallel inverters' performance for microgrid applications. In the grid-connected mode, each inverter has a different power set point. The power flows between the inverters and the grid. In the islanding mode, the power flows inherently from the inverter that has higher set point power to the inverter has lower one leading to a substantial and rapid increase in dc-link voltage. Consequently, a controller is needed to protect the inverters from highly dc link voltage (HDLV) that may lead to fatal damages of the capacitor and power switches. However, the use of a dc-link controller for the second inverter makes unstable the first inverter dc-link voltage regulation. This work proposes a fuzzy logic controller (FLC) designed to avoid any rising in DC link voltage DLV for the second inverter and make it more stable. The effectiveness and performance of the proposed control method are demonstrated with numerical simulations carried out for three operation scenarios. The first one deal with two inverters operating in islanding mode where each inverter has a different set point P∗ 1 = 20 kW, and P∗ 2 = 0 kW. The second scenario considers two inverters operating in grid connected mode before being switched to the unintended islanding mode at a specific time without using dc-link voltage controller. And finally the third scenario investigates the effect of adding a dc-link voltage controller (DLC) to the system.