A Novel Coordinated Control Strategy for Energy Storage System in DC Microgrid With Weak Communication

DC microgrid, consisting of renewable energy sources, energy storage systems, and new types of loads like electric vehicles, has gained more and more attention nowadays. Energy storage systems in dc microgrid are required to regulate dc bus voltage as a backup power source at the islanding state while getting charged or discharged corresponding to energy management command at the grid-connected state. However, the dc bus voltage overshoot would occur with weak communication such as low-speed wireless communication and non-real-time network communication because of the large communication delay during the sudden state switching from grid-connected to islanding state. In this article, a novel coordinated control strategy for energy storage systems independent of real-time communication is proposed. With a novel sliding surface as the outer loop and an auto-tuning dead-beat current control as the inner loop, a smooth mode transition can be achieved even with a large communication delay, which means, real-time communication is unnecessary for the mode transitions. Therefore, the high reliance on the real-time communication is overcome with the system reliability enhanced as well. The proposed control strategy is verified by simulation and experimental results on a 450 V-3.5 kW prototype.