Firstly

imbalance power in isolated microgrids has been analyzed. Based on discrete Fourier transform(DFT)

the imbalance power is decoupled into day and hour components

which can be balanced by compressed-air energy storage and sodium-sulfur cell

respectively. In order to obtain the optimal components

the DFT segmentation principle is studied. By considering investment and operating cost including energy storage

loss of load and wind abandoning penalty comprehensively

the capacity optimization model of hybrid storage systems for isolated microgrids is built. This model can simultaneously optimize the DFT segment point and the hybrid energy storage capacity. And its solving complexity has been greatly simplified as the model can thoroughly decouple the configuration optimization of compressed-air energy storage and sodium-sulfur cell. Finally

the correctness of the model and the method has been verified in a certain practical microgrid. This work is supported by National Natural Science Foundation of China(No. 51307185)

Fundamental Research Funds for the Central Universities(No. CDJPY12150002)and China Southern Power Grid Company Limited(No. K-GZ2013-468).