LAUSR

A large scale energy storage system has become increasingly attractive and has been applied to various ancillary services. To serve energy for a longer time and to increase the profit of a multiple energy storages system, it should be operated considering each available energy source and the different efficiencies of the subordinate storages. This paper proposes a hierarchical control structure and three types of the power sharing methods for a multiple battery energy storages system. A maximum efficiency optimization method based on a piecewise linearized Lagrangian equation is suggested. In addition, a usable energy sharing algorithm is proposed to distribute the output power evenly according to the available energy of each battery. To improve the system availability, a combination algorithm that selects the appropriate control according to the situation is also proposed. The improvement in energy efficiency of the proposed methods is verified with a duty cycle test of Pacific Northwest National Laboratory by PSCAD/EMTDC.