A five bus AC–DC hybrid nanogrid system for PV based modern buildings

Abstract

A five bus AC–DC hybrid transformerless nanogrid system for modern buildings, and its associated control strategy that can operate all the buses simultaneously, is proposed in this paper. The nanogrid has five buses that can exchange power among themselves. This feature improves the reliability of power availability in the system. Two DC buses and one AC bus can be operated in standalone mode as well as in grid connected mode which enables the scheme to operate with available DC microgrids and the AC utility grid. The PV array and the battery bank are interfaced with the remaining two buses which are PV bus, and the battery bus, respectively. In order to reduce the number of serially connected battery units, the voltage rating of the battery bus is kept low. Similarly, the voltage rating of the PV bus is maintained at a medium level to decrease the number of serially connected modules. Hence the effect of shading is minimized. The control strategy of the system is developed to judiciously operate all the buses. In order to validate the viability of the system, exhaustive experimental studies are carried out utilising a laboratory scale 1.2 kW nanogrid system developed for the purpose.