An Efficient Method of Multiple Storage Control in Microgrids

This paper proposes a control method to coordinate multiple energy storage systems (ESS) spread across an AC microgrid. Each storage unit controls its own local node voltage (i.e., where the storage is connected in the network) as well as a global node voltage (i.e., a remote location in the network) that is controlled by all ESSs together. The storage power output is controlled in a way that the node voltage is restored and maintained in case it drops or rises outside the predefined limits. This can occur due to disturbances, such as load changes, loss of distributed generators (DGs), or power limitations in the DGs. In order to determine the power reference for each storage unit, a state of charge (SoC) based adaptive deadband droop control is used. In this decentralized control, the storage power output is inversely proportional to its SoC. By using this approach, the ESS with higher SoC will inject more power whereas storage units with lower SoC will inject less power, leading to more balanced SoC levels among the ESSs. The controller is tested in a microgrid in both island- and grid-connected modes in different scenarios. The microgrid includes several DGs that operate in different control modes depending on the microgrid operation. The storage unit configurations differ in their response time and capacity. This has significant implication in dynamic response of the storage units which is scrutinized in this paper with time-domain simulation.