The introduction of battery-super capacitor hybrid energy storage into the microgrid can better regulate the tie-line power between the microgrid and the distribution network. This paper proposes a capacity optimization method of hybrid energy storage system for optimizing the microgrid tie-line power. Firstly

the capacity optimization method for hybrid energy storage is modeled. The whole life cycle net present value which takes the energy storage life and replacement into account is chosen as the objective function. The boundary frequency between different compensation frequency bands of hybrid energy storage is the optimization variable. In the constraints

the charging and discharging efficiency of non-ideal energy storage system and the state of charge (SOC) are considered as well. A genetic algorithm based approach to solve the model is then given. The key steps involved in the genetic algorithm are: calculation of the time constant of filter through boundary frequency to achieve power allocation of hybrid energy storage

capacity calculation and economic evaluation. Finally

a case of a microgrid system in Tianjin Eco-friendly City is used for verification

and the comparisons with the energy storage actually installed and the method of mainstream papers are made. The results show that the proposed method delivers better economy while achieving the same compensation effect.