Impact of Periodic Current Pulses on Li-Ion Battery Performance

International audiencePulse charging and pulse discharging have been reported by many authors in the literature to improve the performance of various secondary electrochemical cells. Only a few authors mentioned the effects of such charge and discharge method on lithium-ion batteries. The overall objective of this work is to experimentally investigate the impact of certain current pulse profiles on the electrical performance of Li-ion batteries. The results highlight a detrimental impact of periodic pulses on the cell performance compared to profiles with constant current

Multistage CC-CV Charge Method for Li-Ion Battery

Charging the Li-ion battery with constant current and constant voltage (CC-CV) strategy at −10°C can only reach 48.47% of the normal capacity. To improve the poor charging characteristic at low temperature, the working principle of charging battery at low temperature is analyzed using electrochemical model and first-order RC equivalent circuit model; moreover, the multistage CC-CV strategy is proposed. In the proposed multistage CC-CV strategy, the charging current is decreased to extend the charging process when terminal voltage reaches the charging cut-off voltage. The charging results of multistage CC-CV strategy are obtained at 25°C, 0°C, and −10°C, compared with the results of CC-CV and two-stage CC-CC strategies. The comparison results show that, at the target temperatures, the charging capacities are increased with multistage CC-CV strategy and it is notable that the charging capacity can reach 85.32% of the nominal capacity at −10°C; also, the charging time is decreased

Electric Vehicles Charging Technology Review and Optimal Size Estimation

AbstractMany different types of electric vehicle (EV) charging technologies are described in literature and implemented in practical applications. This paper presents an overview of the existing and proposed EV charging technologies in terms of converter topologies, power levels, power flow directions and charging control strategies. An overview of the main charging methods is presented as well, particularly the goal is to highlight an effective and fast charging technique for lithium ions batteries concerning prolonging cell cycle life and retaining high charging efficiency. Once presented the main important aspects of charging technologies and strategies, in the last part of this paper, through the use of genetic algorithm, the optimal size of the charging systems is estimated and, on the base of a sensitive analysis, the possible future trends in this field are finally valued

Design of duty-varied voltage pulse charger for improving Li-ion battery charging response

[[abstract]]In this paper, a duty-varied voltage pulse-charge strategy (DVVPCS), that can detect and dynamically track the suitable duty of the charge pulse, is proposed to improve the battery-charge performance. To assess the system performance, a prototype of the duty-varied voltage pulse charger (DVVPC) is designed and implemented. Comparing with the standard constant- current and constant-voltage (CC–CV) charge strategy, the charge speed of the proposed DVVPCS is improved by about 14%, while the proposed DVVPCS is improved by about 5% in comparison with the conventional duty-fixed voltage pulse-charge strategy (DFVPCS). The charge efficiency of the proposed DVVPC has been improved by about 3.4% as compared with that of the general CC–CV. In comparison with conventional DFVPCS with D=50%, the charge efficiency of the proposed DVVPCS is improved by about 1.5%. The results indicate that the DVVPCS can actually provide pulse with suitable duty to charge the battery, and the charge performance is improved

Desenvolvimento de Métodos Inteligentes de Carregamento e Balanceamento para Sistemas de Armazenamento

Entre a grande diversidade de baterias existentes tecnologicamente maduras, as baterias de Iões de Lítio (Li-ion) tornaram-se populares devido à sua longevidade, alta densidade de energia, alta eficiência e não sofrerem de efeito de memória. Este trabalho tem como objetivo desenvolver novos métodos de carregamento que incluam balanceamento para sistemas de baterias de Iões de Lítio. Este pode ser dividido em duas fases distintas: a primeira fase tem que ver com o desenvolvimento de toda a plataforma, a segunda fase refere-se ao desenvolvimento de novos algoritmos. De forma resumida a primeira fase teve como objetivo desenvolver todo o hardware e software necessários para a criação de uma plataforma versátil e intuitiva onde fosse possível criar algoritmos de carregamento e balanceamento de forma eficiente. O sistema principal do hardware implementado trata-se do Battery Management System (BMS), responsável por toda a monitorização do pack de baterias utilizado. A segunda fase do trabalho focou-se no desenvolvimento de novos algoritmos inteligentes de carregamento que incluam o balanceamento. A opção por esta abordagem refere-se ao facto de ser essencial controlar os desequilíbrios entre células durante o carregamento, resultando numa maior eficiência do sistema de armazenamento. Os resultados obtidos são comparados com os algoritmos tradicionais existentes na literatura.Among the wide diversity of existing technologically mature batteries, lithium-ion (Li-ion) batteries have become popular because of their longevity, high energy density, high efficiency and lack of memory effect. This work aims to develop new charging methods that include balancing for lithium-ion battery systems. This can be divided into two distinct phases: the first phase has to do with the development of the entire platform; the second phase refers to the development of new algorithms. Briefly in the first phase was developed all the hardware and software required to create a versatile and intuitive platform where it was possible to create charging and balancing algorithms. The main hardware implemented system is the Battery Management System (BMS), responsible for all the monitoring of the battery pack used. The second phase of the work focused on developing new intelligent charging algorithms that include balancing. The option for this approach has to do with the fact that it is essential to control the imbalances between cells during charging, resulting in greater efficiency of the storage system. The obtained results are compared with the traditional algorithms present in the literature

Conversor DC-DC em tecnologia CMOS para energy harvesting

Dissertação de mestrado integrado em Engenharia BiomédicaAs energias renováveis estão a ser cada vez mais utilizadas porque, para além de serem não poluentes, tentando compensar o consumo energético mundial excessivo, permitem o desenvolvimento de novas tecnologias, como por exemplo os sistemas sem fios. É o caso da energia fotovoltaica, na qual é produzida energia elétrica a partir da irradiação solar. No entanto, a corrente e potência produzidas pelas células fotovoltaicas depende muito do valor de irradiação que incide no painel, dessa forma a obtenção de um sistema eficiente de produção de energia elétrica, ainda é muito difícil. Por outro lado, nos sistemas de alimentação autónomos é utilizada uma bateria para armazenamento de energia, que normalmente fornece energia consoante a carga que possui, sendo que a tensão fornecida diminui à medida que a bateria descarrega. Para tentar combater a dependência destes sistemas dos valores da irradiação solar, são utilizados conversores MPPT (Maximum Power Point Tracker ), que são dispositivos que forçam os equipamentos a trabalhar no ponto de potência máxima. A presente dissertação tem como principal objetivo o desenho e simulação de um conversor DC-DC integrado com um MPPT em tecnologia CMOS, de dimensões reduzidas e capaz de carregar uma bateria através da energia de um painel fotovoltaico, sempre no seu ponto máximo. A ferramenta utilizada para construir o projeto foi o S-Edit™, um ambiente de programação gráfica para design de circuitos, integrado no Tanner EDA’s T-Spice™. O circuito a apresenta quatro partes, a célula fotovoltaica, o conversor DC-DC, a bateria, e o circuito de controlo. O conversor DC-DC desenhado é um step-up, ou seja um elevador de tensão, regulado através da onda de PWM (Pulse width modulation) que é, por sua vez, controlada pelo circuito de controlo. O circuito de controlo, compara a corrente fornecida pelo painel à carga, em momentos de tempo diferentes, e incrementa ou decrementa o PWM, se a última corrente medida for menor ou maior que a anterior, respetivamente.Renewable energies are being used more and more because, besides being non-polluting, trying to compensate the world's excessive energy consumption, they allow the development of new technologies like the wireless systems. Photovoltaic energy is a type of renewable energy, producing electric energy from solar irradiation. However the electric current and power produced by photovoltaic cells is too dependent of the irradiation's value that is absorbed by the panel, making it very difficult to attain an efficient energy production system. On the other hand, in autonomous systems, a battery is used for storing energy, which usually provides energy depending on how much energy it possesses. The voltage decreases as the battery discharges. To counter the system's dependence on solar irradiation values, MPPT converters are used. These converters are devices that force the equipments to work on full power. The main goal of this thesis is to design and simulate and DC-DC converter integrated with a MPPT in CMOS technology, with reduced dimensions and able to charge a battery through a photovoltaic panel always at its maximum point. The tool used for the project's development was S-Edit™, which is a graphic programming environment for circuit designing, integrated in Tanner EDA’s T-Spice™. The circuit consists of four parts, the photovoltaic cell, the DC-DC converter, the battery and control circuit. The designed DC-DC converter is a step-up, regulated by PWM wave which is controlled by the control circuit. The control circuit compares the current provided by the panel to the charge, in different moments in time, and increments or decrements the PWM, if the last measured current is smaller or bigger than the previous, respectively.Projeto PTDC/EEAELC/114713/200

Gestão da eficiência energética e análise da qualidade de energia em postos de carregamento de bicicletas elétricas

A crescente mobilidade levou diretamente à deterioração das condições de tráfego, ao consumo extra de combustível, ao aumento das emissões de gases de escape dos automóveis, à poluição do ar e à redução da qualidade de vida. Além de ser um modo de transporte limpo, barato e ótimo para viagens de curta distância, o ciclismo pode oferecer soluções para o problema da mobilidade urbana. O sistema de partilha de bicicletas elétricas é considerado como uma implementação de tecnologia limpa, uma vez que tem a possibilidade de utilizar a energia solar fotovoltaica, sendo esta, a chave de desenvolvimento deste sistema. Com a introdução das bicicletas elétricas na mobilidade nacional e, consequentemente, a necessidade de carregamento da bateria regularmente, é de esperar que estas possam estimular algum impacto nas redes elétricas. Por esta razão, o presente trabalho visa analisar o possível impacto que este meio de transporte pode causar na qualidade de energia elétrica distribuída. O estudo foi conduzido por meio de método analítico, que inclui a análise dos ensaios de carregamento. Para tal, recorreu-se aos ensaios feitos no posto de carregamento rápido de veículo elétrico localizado na FCS, de forma a obter uma análise do impacto desta tecnologia na rede de distribuição elétrica. Para os dados recolhidos (tensão, corrente, potência ativa, potência reativa, conteúdo harmónico e equilíbrio de fases), foram apenas analisados os valores médios de cada grandeza, com exceção do conteúdo harmónico em cada ordem, para os quais foram analisados os valores máximos. O registo dos dados foi feito de forma contínua durante todo o intervalo de carregamento, com períodos de amostragem de 1 segundo.The increased mobility has led directly to deteriorating traffic conditions, extra fuel consumption, increased exhaust emissions from cars, air pollution and reduced quality of life. In addition to being a clean, cheap and great mode of transport for short trips, cycling can offer solutions to the problem of urban mobility. The system of sharing electric bicycles is considered as an implementation of clean technology, since it has the possibility of using photovoltaic solar energy, which is the key to the development of this system. With the introduction of electric bicycles into national mobility and, consequently, the need to charge the battery regularly, it is to be expected that they may stimulate some impact in the electric networks. For this reason, the present work aims to analyze the possible impact that this means of transport can cause in the quality of distributed electric energy. The study was conducted using an analytical method, which included analysis of the loading assays. For this, we used the tests carried out at the electric vehicle rapid charging station located at FCS, in order to obtain an analysis of the impact of this technology on the electric distribution network. For the collected data (voltage, current, active power, reactive power, harmonic content and phase equilibrium), only the average values of each magnitude were analyzed, except for the harmonic content in each order, for which the maximum values were analyzed. The data was recorded continuously throughout the loading interval, with a sampling periods of 1 second