Development of hybrid super-capacitor and lead-acid battery energy storage systems

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Development of hybrid super-capacitor and lead-acid battery energy storage systems


Author: Gu, Guangyue
Title: Development of hybrid super-capacitor and lead-acid battery energy storage systems
Degree: M.Eng.
Year: 2015
Subject: Energy storage.
Lead-acid batteries.
Hong Kong Polytechnic University -- Dissertations
Department: Faculty of Construction and Environment
Pages: 63 pages : color illustrations
Language: English
Abstract: Due to intermittent features of the renewable energy (RE) power generation system, the energy storage system is usually required, to keep energy when there is excess and release it when there is high demand. Among the energy storage technologies, batteries, particularly the lead-acid batteries, are widely used for remote area RE power supply systems. However, the intermittent RE output makes it is difficult for batteries to recover from fast power fluctuations without dramatically reducing their lifetime. In addition, due to the low power density of battery, the charge and discharged rate is limited. It causes severe stress on the battery under quick supply/load fluctuations and result in extended periods of low state of charge and increase in the number of charge/discharge cycles. As a result, battery lifetime is significantly reduced and project cost will increase as well.In this study, the super-capacitor is introduced in the battery storage system to make a hybrid energy storage system (HESS). The super-capacitor has the benefits in higher power density, longer cycle life and higher charging-discharging efficiency, while its disadvantage is low energy density. The super-capacitor and battery can complement in technical characters, therefore it is reasonable to combine them to create a HESS where the battery absorb/supplies long term continuous energy and the super-capacitor responses speedily to dynamic and instantaneous power.This study has been divided into five chapters.In Chapter 1,some background information is introduced.In Chapter 2, a literature review on relevant studies on the HESS and their limitations are presented.In Chapter 3, the mathematical models of the HESS have been developed, and these models are further constructed in Matlab software to do simulation In Chapter 4, some experimental tests have been conducted to validate the simulation results and some hypothesis that put forward in the section of literature review.In Chapter 5,this dissertation is summarized and some suggestions for future study are presented.This study shows that the combination of battery and super-capacitor can achieve complementary performance in both charge and discharge processes. The theoretical analysis, simulation and experimental results demonstrate that the HESS leads to improved energy storage performance, particularly for the battery. The battery in the HESS performs as the primary energy source for longer periods and the super-capacitor as the auxiliary power source for peak power smoothing and emergency reserve. Therefore the combination can make energy storage possessing both high power and energy density, and finally extending battery life as well. In addition, the inductance, which has the filtering effects on the battery, is introduced to smooth the current curve of the battery. Beside it, a smaller inter-resistance of super-capacitor can effectively increase the battery life-time and discharge performance. In conclusion, the hybrid super-capacitor and battery energy storage system has dominant position than the traditional storage system.

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