Abstract
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.
Highlights
The large scale of energy storage takes an increasingly significant role in balancing power supply and demand in modern power systems as well as releasing the intermittency issues of renewable energy systems (RES) [1], [2]
power flowing into the grid (Pgrid)(t) = power offset (Pofs)(t) where Pofs is the offset power of hybrid energy storage system (HESS) calculated based on SOC, SOCHESS is the state of charge in HESS, MH is the unit conversion factor (SOC to Power) [MW/%], power in HESS (PHESS) is the power of HESS, Pw is the WT power and Pgrid is the compensated power flowing to the grid
ESC = ESC · h where Pofs,SC is the offset power of SC calculated based on SOC, SOC of SC (SOCSC) is the state of charge in SC, MSC is the is the unit conversion factor (SOC to Power) [MW/%], PSC is the power of SC, and h is the factor to change the unit from hours to seconds
Summary
The large scale of energy storage takes an increasingly significant role in balancing power supply and demand in modern power systems as well as releasing the intermittency issues of renewable energy systems (RES) [1], [2]. A practical coordinated control method is proposed for determining the power allocation of a SMES and a battery in a HESS using low pass filter (LPF) and moving average concept [15]. In this method, two filters are designed to determine power reference of grid and power quantity of SMES and BESS through cut-off frequency. We propose the virtual capacity concept to increase smoothing capability against intermittent power using HESS, and this method automatically controls SOC within the operation range. Virtual capacity of HESS for improving smoothing capability using adaptive control based on SOC.
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