Capacity-based adaptive droop control for battery energy storage operation

With more renewable resources integrated to the grid, energy storage is expected to rise to the challenge of the grid caused by the characteristics of the intermittent renewable sources. This paper presents an innovative battery energy storage system (BESS) combined with the decoupled PQ control and adaptive capacity-based droop control for both grid-connected operation and stand-alone operation. When the system is islanded, such BESS synchronizes to form a reliable frequency source which does not collapse when member BESS fail. The flexibility of the proposed control method enables the BESS to adjust the power output according to its available capacity respectively so that the decentralized autonomous frequency control with load sharing is achieved without violating the stability limit. The paper also highlights the significant role of the Phase Lock Loop for the proposed control principles.