Abstract
Cell voltage equalization is mandatory to eliminate voltage imbalance of series-connected energy storage cells, such as lithium-ion batteries (LIBs) and electric double-layer capacitors (EDLCs), to ensure years of safe operations. Although a variety of cell equalizers using selection switches have been proposed, conventional techniques require numerous switches in proportion to the cell count and are prone to complexity. This paper proposes a novel cell voltage equalizer using a selective voltage multiplier. By embedding selection switches into the voltage multiplier-based cell voltage equalizer, the number of selection switches can be reduced in comparison with that in conventional topologies, realizing the simplified circuit. A prototype for twelve cells was built, and an equalization test using LIBs was performed. The voltage imbalance decreased down to approximately 20 mV by the proposed equalizer, and the standard deviation of cell voltages at the end of the equalization test was as low as 10 mV, demonstrating its equalization performance.
Highlights
Voltages of series-connected energy storage cells, such as lithium-ion batteries (LIBs) and electric double-layer capacitors (EDLCs), gradually become imbalanced due to nonuniform individual cell characteristics in capacitance, internal impedance, coulombic efficiency, and self-discharge rate.Temperature mismatch in a battery pack or module leads to the occurrence of voltage imbalance because the self-discharge rate is dependent on temperature—the higher the temperature, the faster the self-discharge will be [1]
This paper proposes a novel pack-to-cell equalizer using a selective voltage multiplier
Topology cell selection switches into a voltage multiplier-based cell voltage equalizer, the numbers embedding of selection switches can equalizer be reduced to n, simplified circuit
Summary
Voltages of series-connected energy storage cells, such as lithium-ion batteries (LIBs) and electric double-layer capacitors (EDLCs), gradually become imbalanced due to nonuniform individual cell characteristics in capacitance, internal impedance, coulombic efficiency, and self-discharge rate. A conventional conventional pack-to-cell equalizer based on a voltage multiplier is shown in Figure as an example. This pack-to-cell equalizer based on a voltage multiplier is shown in Figure 1 as an example This topology topology requires requires only only two two switches, switches, regardless regardless of of cell cellcount, count,achieving achievingaasimplified simplifiedcircuit. This equalizer equalizer automatically anan equalization current toward the least cell having lowestthe voltage in automaticallysupplies supplies equalization current toward thecharged least charged cellthe having lowest the pack,in realizing therealizing automatic equalization without even feedback control.
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