Control of Bidirectional Grid-Forming Inverter for Nearly Zero Energy Buildings

Abstract

A conventional nearly zero energy building (NZEB) is a grid connected system that cannot operate off-grid. By adding a special power electronic interface (PEI) to the point of common coupling, the conventional NZEB could be transformed into a hybrid nanogrid with a wider variety of functions, incl. off-grid operation and bidirectional energy flow control. However, most of the sources in the NZEB are grid followers and require a single grid-forming unit. Thus, typical decentralized control methods (e.g. droop control, virtual generator) cannot be implemented in such systems. This paper analyzes the bidirectional operation of the grid-forming inverter for the NZEB. The main focus is on the light or no load operation that corresponds to a mode when the PEI is naturally unable to control the voltage inside the building. Four control methods are proposed, analyzed and compared. The best method was determined and verified by the help of computer simulations.