Design and Optimization of Hybrid Energy Storage for Photovoltaic Power Fluctuation Smoothing Based on Frequency Analysis

Abstract

A proper design of energy storage system (ESS) can effectively smooth the photovoltaic (PV) output power fluctuation, lower the cost, and improve the power quality and stability. According to the response characteristics of different energy storage equipment, an optimal hybrid EES sizing method is proposed based on frequency analysis. A hybrid ESS including lead-acid battery, lithium battery and electric double-layer capacitor (EDLC) is selected to smooth out PV power fluctuation and meet both power and energy requirement of the power grid. Fast Fourier Transform (FFT) method is applied for analyzing the spectrum of unwanted PV fluctuation. From the FFT analysis, different frequencies combinations can be determined to meet both the power and energy requirements of the potential hybrid ESS solution. An optimization technique is conducted to find the best frequency combination, hence the best hybrid ESS solution. The goal of the optimization is to minimum total hybrid ESS cost by taking selected ESS cycle life and charge/discharge loss into consideration. The proposed method is based on the worst case scenario of PV fluctuation. Through the proposed method, the least cost ESS solution will be determined to meet both the power and energy requirements as well as smooth out the PV output fluctuation under the worst case scenario.