Electric vehicles (EV) use battery banks containing series-parallel combinations of several small units to meet the high power demand of the drive system. In recent years, lithium-ion (Li-ion) batteries are being popularly used in EVs for energy storage instead of conventional lead acid batteries due to the advantages of higher cell voltage, no memory effect, low self-discharge, longer battery life and reduced size and weight. However, Li-ion battery packs require external power balancing circuits for its protection from getting damaged by overcharge and deep discharge. This work proposes an active circuit for charge balancing of Li-ion battery packs. The proposed charge balancing circuit uses a multi-winding flyback converter with n+1 number of active switches to protect a stack of n number of series connected cells. Performance of the proposed system has been verified through computer simulation in MATLAB with a 4 cell battery pack. Simulated results were found in close agreement with the predicted behaviour of the system.
{"title":"Active Cell Balancing of Li-Ion Batteries for Electric Vehicles","authors":"Debadyuti Banerjee, A. Giri, S. Saha","doi":"10.2139/ssrn.3495810","DOIUrl":"https://doi.org/10.2139/ssrn.3495810","url":null,"abstract":"Electric vehicles (EV) use battery banks containing series-parallel combinations of several small units to meet the high power demand of the drive system. In recent years, lithium-ion (Li-ion) batteries are being popularly used in EVs for energy storage instead of conventional lead acid batteries due to the advantages of higher cell voltage, no memory effect, low self-discharge, longer battery life and reduced size and weight. However, Li-ion battery packs require external power balancing circuits for its protection from getting damaged by overcharge and deep discharge. This work proposes an active circuit for charge balancing of Li-ion battery packs. The proposed charge balancing circuit uses a multi-winding flyback converter with n+1 number of active switches to protect a stack of n number of series connected cells. Performance of the proposed system has been verified through computer simulation in MATLAB with a 4 cell battery pack. Simulated results were found in close agreement with the predicted behaviour of the system.","PeriodicalId":391497,"journal":{"name":"ChemRN: Fuel Cells (Topic)","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130097917","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Numerous attempts have been made to improve the oxidation resistance and electrical conductivity of the interconnectors in solid oxide fuel cells. A Co-W alloy coating on ferritic stainless steel has attracted attention because the Co-W oxide layer formed by the oxidation treatment of the Co-W alloy coating has proven effective in reducing the outward diffusion of Cr and improving oxidation resistance. This study was designed to elucidate the formation kinetics and diffusion barrier mechanism of the Co-W coating. After oxidation in air at 750 °C, a dense, multilayered oxide formed, comprising (from the stainless steel substrate to the outer layer) Cr oxide, Cr-Fe-Co oxide, Co-W oxide, Co-Fe oxide, and Co oxide layers. The CoWO4 layer and neighboring oxide layers were carefully analyzed by scanning electron microscopy and transmission electron microscopy, which revealed that the innermost Cr2O3 layer grows via the reaction between Cr in the substrate and inward-diffusing oxygen, whereas outward diffusion of Fe and Co is involved in the formation and growth of (Co,Fe)3O4 and Co3O4. Analysis by electron energy-loss spectroscopy confirmed the absence of trivalent cations (Co3+, Fe3+, and Cr3+) and the presence of Fe2+ ions in the CoWO4 layer; thus, CoWO4 functions as a selective diffusion barrier to trivalent cations as hypothesized.
为了提高固体氧化物燃料电池中互连体的抗氧化性和导电性，人们进行了许多尝试。铁素体不锈钢上的Co-W合金涂层引起了人们的关注，因为Co-W合金涂层经过氧化处理后形成的Co-W氧化层可以有效地减少Cr的向外扩散，提高抗氧化性。本研究旨在阐明Co-W涂层的形成动力学和扩散屏障机理。在750°C的空气中氧化后，形成致密的多层氧化物，包括(从不锈钢衬底到外层)氧化Cr, Cr- fe -Co氧化物，Co- w氧化物，Co- fe氧化物和Co氧化物层。通过扫描电镜和透射电镜对CoWO4层和邻近的氧化层进行了仔细的分析，发现最内层的Cr2O3层是通过衬底中的Cr与向内扩散的氧反应生长的，而Fe和Co的向外扩散则参与了(Co,Fe)3O4和Co3O4的形成和生长。电子能谱分析证实CoWO4层中不存在Co3+、Fe3+和Cr3+三价阳离子，存在Fe2+离子;因此，CoWO4可以作为三价阳离子的选择性扩散屏障。
{"title":"Microstructure, Formation, and Diffusion Kinetics of Multilayered Oxides Formed on a Co-W Electroplated Ferritic Stainless Steel Followed by Oxidation Treatment","authors":"L. Gan, Tomoyuki Yamamoto, H. Murakami","doi":"10.2139/ssrn.3491242","DOIUrl":"https://doi.org/10.2139/ssrn.3491242","url":null,"abstract":"Numerous attempts have been made to improve the oxidation resistance and electrical conductivity of the interconnectors in solid oxide fuel cells. A Co-W alloy coating on ferritic stainless steel has attracted attention because the Co-W oxide layer formed by the oxidation treatment of the Co-W alloy coating has proven effective in reducing the outward diffusion of Cr and improving oxidation resistance. This study was designed to elucidate the formation kinetics and diffusion barrier mechanism of the Co-W coating. After oxidation in air at 750 °C, a dense, multilayered oxide formed, comprising (from the stainless steel substrate to the outer layer) Cr oxide, Cr-Fe-Co oxide, Co-W oxide, Co-Fe oxide, and Co oxide layers. The CoWO<sub>4</sub> layer and neighboring oxide layers were carefully analyzed by scanning electron microscopy and transmission electron microscopy, which revealed that the innermost Cr<sub>2</sub>O<sub>3</sub> layer grows via the reaction between Cr in the substrate and inward-diffusing oxygen, whereas outward diffusion of Fe and Co is involved in the formation and growth of (Co,Fe)<sub>3</sub>O<sub>4</sub> and Co<sub>3</sub>O<sub>4</sub>. Analysis by electron energy-loss spectroscopy confirmed the absence of trivalent cations (Co<sup>3+</sup>, Fe<sup>3+</sup>, and Cr<sup>3+</sup>) and the presence of Fe<sup>2+</sup> ions in the CoWO<sub>4</sub> layer; thus, CoWO<sub>4</sub> functions as a selective diffusion barrier to trivalent cations as hypothesized.","PeriodicalId":391497,"journal":{"name":"ChemRN: Fuel Cells (Topic)","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121679559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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