Energy storage is one of the biggest problems of nowadays engineering. Its great problem lies in the energy density that the systems are able to storing, that is, how much energy they are able to store. If there is a large amount of energy to be stored, it is best to use a pack of several batteries connected to each other. However, not all batteries are created equal. Even though models are the same, not all batteries have the exactly same characteristics and some are "stronger" than others. Putting several batteries together in a pack without proper equalization ends up drastically reducing their life span.The present paper covers the design and simulation of an equalization system for a battery pack. The main problems to be solved are the choice of the equalizer topology and the design of the control system. In addition, battery protections are designed and implemented. Simulations are done in the PSIM software.The results of this project can be applied to the design of a battery management system (BMS) and its assembly in a Formula Student electric vehicle.
The emerging nickel-rich/silicon-graphite lithium-ion technology is showing a notable increase in the specific energy, a main requirement for portable devices and electric vehicles. These applications also demand short charging times, while actual charging methods for this technology imply long time or a significant reduction in cycling life. This study analyses the factors that affect the charge behavior for 18,650 commercial nickel-rich/silicon-graphite batteries. For that, long-term cycling tests have been carried out, including electric vehicle standard tests. It can be concluded that this technology has two key issues to develop an efficient charge method: high charge rates should be avoided, mainly below 15% state of charge, and the charge should be finished at 95% of actual cell capacity. This allows that, regardless of application and cell degradation level, cells can be recharged in 2 h without a negative impact on cycling life. For faster charge applications, a new method has been developed to minimize charging time without compromising the cycle life as much as the high current manufacturer method. The proposed fast charge method has proven to be notably faster, recharging in an average 1.3 h (48% less than the high current method and 68% less than the standard method).
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