Sizing a Hybrid Energy Storage System for Maintaining Power Balance of an Isolated System with High Penetration of Wind Generation

A frequency-based approach is proposed in this paper to size a battery-supercapacitor energy storage system for maintaining power balance of an isolated system with high penetration of wind generation, thus to maintain the grid frequency stability with the stochastic wind power fluctuations being considered. The sizing method proposed makes full use of the combined technical merits of two types of energy storage systems, battery and supercapacitor, as their specific power/energy densities and the corresponding expected life cycle cost/year are different. The power imbalance between hourly dispatched wind power and the corresponding actual real-time wind power output is decomposed into different time-varying periodic components by use of the Fourier transformation. Then two different types of energy storage systems are applied to balance the low-frequency and intermediate-frequency component respectively. A computational procedure is developed in the paper for choosing the optimal cut-off frequencies in determining the range of low and intermediate frequency for sizing the hybrid energy storage system. Comparative studies of a real isolated system in China are presented in the paper to demonstrate the effectiveness of the proposed method.