A platform for real-time fault-tolerant distributed control of replica-determinate inverters

This paper presents the results of a proof-of-concept implementation of a platform for distributed, real-time fault-tolerant control of parallel single-phase inverters, integrated in modular uninterruptible power supplies (UPS) or Battery Energy Storage Systems (BESS). Each inverter controller runs a basic clock which schedules all the real-time control tasks, according to the time-triggered paradigm. The clocks in the different inverters are kept in synchronism with each other, by applying a distributed clock synchronization algorithm. The inverter controllers are connected through two serial buses. The first bus is a TDMA serial bus exclusively dedicated to the interchange of the short and frequent control variables needed to enforce load sharing between inverters. Each inverter applies to these variables a fault-tolerant variant of the averaging load sharing control method. The second bus is a CAN bus, with time stamping of messages, used to interchange the clock synchronization messages and the low bandwidth supervision and control variables.