Feature: Batteries
Successful battery monitoring of
stacked-cell systems By Rolf Horn, Applications Engineer, Digi-Key Electronics
R
echargeable batteries are increasingly being used to deliver higher voltages and more power in applications such as electric vehicles (EVs)
and hybrid-electric vehicles (HEVs), power tools, lawn equipment and uninterruptible power supplies (UPSs). Whilst their various chemistries require careful monitoring and management to ensure their cells’ effective, reliable and safe operation, the series-connected stacks of many tens of cells call for careful consideration, particularly when dealing with a large number of cells. Te challenge is taking measurements in the presence of hazardous or high common-mode voltages, single-cell failures, multiplexing across a large number of cells, cell mismatch and balancing, and battery-stack temperature differentials, to cite just a few. Tese require advanced battery management ICs (BMICs) and systems (BMS) to perform parametric measurement and control, and a good degree of engineering know-how to use them correctly.
22 June 2022
www.electronicsworld.co.uk
The measurement performance needed for modern battery packs is fairly high: each cell must be measured to within a few mV and mA, and to about a degree centigrade
Unique challenges Typical battery monitoring involves measuring current flow into and out of the battery (fuel gauging), monitoring terminal voltages and cell temperatures, assessing battery capacity, and managing charge/discharge cycles, to optimise energy storage and maximise them over the battery’s lifetime. Widely-used BMICs or BMSs offer these functions for small battery packs with only one or two cells that handle single-digit voltages. Te BMIC and BMS act as a data acquisition front-end, with the data fed to a cell management controller (CMC). In more complex systems, the CMC connects to a higher-order function called a “battery management controller”, or BMC.
Here we will refer to a “cell” as an
individual energy storage unit, and a “battery” as the entire power pack, comprising multiple cells in series and parallel combinations. Whilst an individual cell produces only a few volts, a battery pack can be made of dozens of cells and deliver tens of volts, or higher. For effective management, the critical
cell parameters to be measured are terminal voltage, charge/discharge current and temperature. Te measurement performance needed for modern battery packs is fairly high: each cell must be measured to within a few mV and mA, and to about a degree centigrade. Te reasons for such close cell monitoring include:
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