Robust Decentralized Secondary Control Validation in Inverter-based Microgrid Testbed

Grid-forming inverter-based microgrids are increasingly becoming popular. They provide reliability and resilience, especially, when operating in islanded mode. Although microgrid operations rely on centralized controllers, communication failures due to cyber-physical attacks or natural disasters can make autonomous operation of islanded microgrids with multiple grid-forming inverters challenging. This paper examines a decentralized secondary control scheme that is robust to inverter clock synchronization errors and can be seamlessly applied to grid-forming control architectures. The proposed scheme over-comes the well-known stability problem that arises from parallel operation of local integral controllers and provides theoretical guarantees for stability. Moreover, valid conditions are provided for appropriately choosing the secondary control gains. The efficacy of our approach in restoring the frequency while ensuring fair power sharing is demonstrated in our microgrid hardware testbed comprising of six grid-forming inverters.