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Publication
Rendimento de Ciclos de Carga e Descarga em Baterias de Armazenamento de Energia Elétrica Aplicadas em Veículos
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Advisor(s)
Abstract(s)
A eletrificação do setor automóvel torna as baterias recarregáveis centrais para o desempenho
e fiabilidade de veículos elétricos e híbridos, mas existe escassez de dados sobre o rendimento
energético real em uso quotidiano. Este trabalho avalia experimentalmente diferentes
tecnologias de baterias através de ensaios controlados, esclarecendo o seu desempenho real.
Inicialmente, é apresentado o estado da arte dos veículos eletrificados, das tecnologias existentes
e dos métodos de medição de eficiência em baterias, com destaque para as inovações
e limitações atuais no setor automóvel. Foram ensaiadas seis baterias de naturezas distintas
– iões de lítio (NCA, NCM+ (estado semi-sólido), LFP), polímero de lítio (Li − Po) e
chumbo-ácido do tipo AGM – de modo a representar o panorama atual da aplicação de
baterias em veículos. Os ensaios realizados envolveram ciclos de carga-descarga sob várias
condições de operação, medindo corrente, tensão e temperatura. A metodologia baseou-se
na utilização combinada de um carregador inteligente com uma fonte e multímetro, permitindo
registar, com elevada precisão, os perfis de tensão e corrente ao longo dos ciclos, com
posterior cálculo da potência e energia acumulada, compreendendo medições experimentais
detalhadas, definição das condições de teste e análise comparativa dos resultados obtidos
com dados de referência. Neste sentido foram definidos dois casos de estudo: (#1) determinação
do rendimento energético em diferentes condições de carga e descarga; e (#2)
avaliação da capacidade real comparada com os valores nominais indicados.
Nos resultados do Caso de Estudo #1, a eficiência das baterias revelou forte dependência
da tecnologia e da faixa de SoC. As baterias de NMC+ mostraram maior eficiência na
faixa parcial 20–80 %, enquanto as restantes baterias Li − ion foram mais eficientes em
ciclo completo devido à menor corrente aplicada (0.2 C). A bateria de Li −Po destacou-se
com eficiência significativamente maior em ciclo completo (95.2% vs. 81.6 %); a bateria
AGM manteve valores próximos do de referência mesmo em fim de vida. Globalmente, as
eficiências situaram-se entre 88% e 91.4 %.
No Caso de Estudo #2, com apenas um ensaio realizado por C-rate, os resultados mostraram
energia e capacidade geralmente ligeiramente superiores a 100% das especificações. Ensaios
adicionais seriam necessários para maior rigor e minimização de erros.
Os resultados reforçam que nenhum sistema atinge 100% de eficiência, sendo as perdas
internas um dos aspetos críticos, sobretudo a elevadas taxas de corrente e em ciclos completos.
Salienta-se ainda que a eficiência global calculada considera apenas perdas internas
da célula, não incluindo BMS, conversores e cablagem, pelo que a eficiência útil real tende
a ser inferior aos valores medidos.
Conclui-se que a caracterização experimental é essencial para validar informações técnicas e
apoiar o desenvolvimento de sistemas de mobilidade elétrica mais fiáveis. O estudo contribui
também para a definição de metodologias de ensaio aplicáveis em contextos académicos e
industriais, identificando limitações e sugerindo futuras linhas de investigação.
The electrification of the automotive sector makes rechargeable batteries central to the performance and reliability of electric and hybrid vehicles, but there is a lack of data on actual energy efficiency in everyday use. This work experimentally evaluates different battery technologies through controlled tests, clarifying their actual performance. First, the state of the art of electrified vehicles, existing technologies, and battery efficiency measurement methods are presented, highlighting current innovations and limitations in the automotive sector. Six different types of batteries were tested – lithium-ion (NCA, NCM+ (semi-solid state), LFP), lithium polymer (Li −Po) and AGM lead-acid – in order to represent the current landscape of battery application in vehicles. The tests involved charge-discharge cycles under various operating conditions, measuring current, voltage and temperature. The methodology was based on the combined use of a smart charger with a power supply and multimeter, allowing the voltage and current profiles to be recorded with high precision throughout the cycles, with subsequent calculation of the power and accumulated energy, comprising detailed experimental measurements, definition of test conditions and comparative analysis of the results obtained with reference data. In this regard, two case studies were defined: (#1) determination of energy yield under different charging and discharging conditions; and (#2) evaluation of actual capacity compared to the nominal values indicated. In the results of Case Study #1, battery efficiency showed a strong dependence on technology and SoC range. NMC+ batteries showed greater efficiency in the partial range 20–80 %, while the remaining Li − ion batteries were more efficient in a full cycle due to the lower applied current (0.2 C). The Li − Po battery stood out with significantly higher efficiency in full cycle (95.2% vs. 81.6 %); the AGM battery maintained values close to the reference even at the end of its life. Overall, efficiencies ranged between 88% and 91.4 %. In Case Study #2, with only one test performed by C-rate, the results showed energy and capacity generally slightly higher than 100% of the specifications. Additional tests would be necessary for greater accuracy and minimisation of errors. The results reinforce that no system achieves 100% efficiency, with internal losses being one of the critical aspects, especially at high current rates and in full cycles. It should also be noted that the calculated overall efficiency only considers internal cell losses, not including BMS, converters, and cabling, so the actual useful efficiency tends to be lower than the measured values. It is concluded that experimental characterisation is essential to validate technical information and support the development of more reliable electric mobility systems. The study also contributes to the definition of test methodologies applicable in academic and industrial contexts, identifying limitations and suggesting future lines of research.
The electrification of the automotive sector makes rechargeable batteries central to the performance and reliability of electric and hybrid vehicles, but there is a lack of data on actual energy efficiency in everyday use. This work experimentally evaluates different battery technologies through controlled tests, clarifying their actual performance. First, the state of the art of electrified vehicles, existing technologies, and battery efficiency measurement methods are presented, highlighting current innovations and limitations in the automotive sector. Six different types of batteries were tested – lithium-ion (NCA, NCM+ (semi-solid state), LFP), lithium polymer (Li −Po) and AGM lead-acid – in order to represent the current landscape of battery application in vehicles. The tests involved charge-discharge cycles under various operating conditions, measuring current, voltage and temperature. The methodology was based on the combined use of a smart charger with a power supply and multimeter, allowing the voltage and current profiles to be recorded with high precision throughout the cycles, with subsequent calculation of the power and accumulated energy, comprising detailed experimental measurements, definition of test conditions and comparative analysis of the results obtained with reference data. In this regard, two case studies were defined: (#1) determination of energy yield under different charging and discharging conditions; and (#2) evaluation of actual capacity compared to the nominal values indicated. In the results of Case Study #1, battery efficiency showed a strong dependence on technology and SoC range. NMC+ batteries showed greater efficiency in the partial range 20–80 %, while the remaining Li − ion batteries were more efficient in a full cycle due to the lower applied current (0.2 C). The Li − Po battery stood out with significantly higher efficiency in full cycle (95.2% vs. 81.6 %); the AGM battery maintained values close to the reference even at the end of its life. Overall, efficiencies ranged between 88% and 91.4 %. In Case Study #2, with only one test performed by C-rate, the results showed energy and capacity generally slightly higher than 100% of the specifications. Additional tests would be necessary for greater accuracy and minimisation of errors. The results reinforce that no system achieves 100% efficiency, with internal losses being one of the critical aspects, especially at high current rates and in full cycles. It should also be noted that the calculated overall efficiency only considers internal cell losses, not including BMS, converters, and cabling, so the actual useful efficiency tends to be lower than the measured values. It is concluded that experimental characterisation is essential to validate technical information and support the development of more reliable electric mobility systems. The study also contributes to the definition of test methodologies applicable in academic and industrial contexts, identifying limitations and suggesting future lines of research.
Description
Keywords
Batteries Charging and Discharging Energy Efficiency Baterias Carga e Descarga Rendimento e Eficiência Energética