Virtual Capacity of Hybrid Energy Storage Systems Using Adaptive State of Charge Range Control for Smoothing Renewable Intermittency

This paper presents a method for improving capability of a Hybrid Energy Storage System (HESS) comprised of a battery and supercapacitor (SC), for smoothing power fluctuations of renewable energy sources by adaptively controlling the state of charge (SOC) allocation range using automatic SOC management. The proposed method secures the preset SOC range of both battery and SC for power smoothing applications of renewables and also has the ability to significantly smooth power fluctuations using the virtual capacity concept of an energy storage system (ESS) by extending the SOC usage range. The bode plots of the proposed method are analyzed to observe the coverage of the power spectrum in the frequency domain in each storage based on the case studies. A criterion of HESS sizing, both battery and SC, is also developed based on the SOC range, smoothing time constant, and the power rating of renewables. The proposed method for the integration of HESS on renewable energy sources is verified with simulation results and characteristic analysis using PSCAD/EMTDC and MATLAB software.