Application of real-time fault-tolerant distributed control in parallel operation of inverters

Abstract

This article presents a study on the application of distributed fault-tolerant real-time control for the parallel operation of single-phase inverters integrated in modular uninterruptible power supplies (UPS) or Battery Energy Storage Systems (BESS). The inverter controllers run the fundamental control tasks in synchronization with each other to create a replica determinate set. Control of the parallel inverters follows an active load sharing scheme supported over a digital real-time fault-tolerant control layer. Each inverter applies a Smith predictor for delay compensation and a Kalman observer to estimate output current. Thus the set of parallel inverters behaves as an AC source with low output impedance, whereas the output current is shared equally between the inverters, avoiding circulating currents. Variants and extensions of the method are also proposed. The paper concludes by discussing grounds for standardizing a distributed real-time control layer for modular converter systems.