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Research On System Design And Energy Management Of Composite Energy Storage System For Electric Vehicles

Posted on:2016-10-06Degree:MasterType:Thesis
Country:ChinaCandidate:C XuFull Text:PDF
GTID:2272330467489044Subject:Power electronics and electric drive
Abstract/Summary:PDF Full Text Request
Many countries have put forward energy conservation and emission reduction policy due to the increasing seriousness of environmental pollution and engery crisis. As one of the new energy vehicles, electric vehicles (EVs) are drawing people’s extentive attention. However, the batteries, like lithium batteries, in electric vehicles suffer low power density and short life cycle so the frequent large current charging and discharing operation in start up, accerleration and braking can hardly be achieved, which weaken the dynamic performance of electric vehicles. Fortunately, the supercapactior features high power density and long life cycle. Hence, the composite energy storage system, which combines the battery and the supercapacitor, can greatly enhance the overall performance of electric vehicles. The study of this paper is mainly carried out on the following aspects:1. The composite energy storage system is analysed from three apects:system structure, building block and system control, from which different ways of the connection between energy storage and DC bus are listed and compared, the topologies and control strategies of bi-directional DC-DC converter are summarized and the pros and cons of differecnt system control methods are analysed. After that, an overall design concept, namely the hierarchical controlled modularized composite energy sotarge system is introduced.2. The generation mechanism of the surge current, which happens during the start-up of bi-directional DC-DC converter, is analyzed, upon which two soft start-up control strategies, duty cycle and phase shift control start-up schemes, are proposed. Without an auxiliary start-up circuit, the converter can safely start up with controllable peak current value under these two methods. Detailed formula derivation and comparison analysis of operating principle of each metheods are investigated. Finally, the simulation and experimental results are exhibited to verify the effectiveness of these two methods.3. A dual droop-frequency diving coordinated control strategy is proposed for the energy management of composite energy storage system. On one hand, the dynamic power allocation between the supercapacitor and batteries are obtained through the voltage cascaded control, upon which the high and low frequency power fluctuation are absorbed by the supercapacitor and batteries respectively. Hence the advantages of the supercapacitors and battery can be fully exploited. On the other hand, by adding SOC feedback into the traditional droop control, the dual droop coordinated control, including the output current and SOC as variables, are formed. Through this control strategy, current sharing performance is ensured and each blocks can make self-adaptive adjustment according to their SOC so that the load power can be shared effectively which can avoid the over-charge/over-discharge operation and contribute to the life cycles of energy storage system...
Keywords/Search Tags:electric vehicle, composite energy storage, soft start up, energy management
PDF Full Text Request
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