AG3 battery.A brief analysis of the active charging balancing method of lithium-ion battery packs

　　The Automotive Systems Engineering Department of Infineon Technologies AG in Munich recently received a task to develop E-Cart. The E-Cart is a drivable vehicle primarily used to demonstrate the electrical performance of hybrid vehicles. The car would be powered by a massive lithium-ion battery pack, and developers realized at the time that battery management with charge balancing was an absolute necessity. In this case, active energy transfer between cells must be used instead of the traditional simple charge balancing scheme. The active charge balancing system they developed can provide better performance at the same material cost as passive solutions (see Figure 1).

　　Battery system architecture

　　Nickel-cadmium batteries, and later nickel-metal hydride batteries, dominated the battery market for many years. Lithium-ion batteries have only recently entered the market, but their market share is growing very rapidly due to their vastly improved performance. The energy storage capacity of lithium-ion batteries is amazing, but even so, the capacity of a single battery cell is still too low in terms of voltage and current to meet the needs of a hybrid engine. Connecting multiple battery cells in parallel can increase the current provided by the battery, and connecting multiple battery cells in series can increase the voltage provided by the battery.

　　Battery assemblers often use abbreviations to describe their battery products, such as "3P50S" means that the battery pack has 3 parallel battery cells and 50 series battery cells.

　　Modular structures are ideal when managing batteries containing multiple cells connected in series. For example, in a 3P12S battery array, every 12 battery cells form a module (block) after being connected in series. These battery cells are then managed and balanced by an electronic circuit with a microcontroller at its core.

　　The output voltage of such a battery module depends on the number of battery cells connected in series and the voltage of each battery cell. The voltage of a lithium-ion battery cell is usually between 3.3V and 3.6V, so the voltage of a battery module is approximately between 30V and 45V.

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