Research of Li-Ion Battery’s Equalizer Circuit Based on TL431

Abstract

Li-ion battery, as a new type of energy storage equipment, has small size, large power density, high individual voltage, low rate of self-discharging and small self-resistance etc. It substitutes the traditional power battery in AGV.In practical process, due to the difference of battery cells, after a period of charge-discharge time, the upper and lower voltage limits of every unit of batteries become various, seriously affecting the system performance. The idea of upper and lower equalizer is released for this case. Then, a further research is made on the equalizer circuit of li-ion battery. The experiment result proves the correctness of design on several types of lithium battery equalizer circuit.

A simple and effective capacitor‐based equalizer for cell‐to‐cell battery equalization

“…The energy transfer unit of the active equalization method may be based on the inductor, [7][8][9] the transformer, 10-12 the combination of inductor and capacitor (LC resonant circuit [13][14][15] and dc-dc converter [16][17][18][19] ), or the capacitor. [20][21][22][23][24][25] Note that voltage difference is small between cells and is large between cell and pack. So, the energy transfer unit commonly uses inductor, capacitor, or their combination for C2C topology and uses transformer for C2P, P2C, or C2P2C topology.…”

“…Traditional capacitor-based equalizers use the switched capacitor (SC) method 20,21 or the flying capacitor (FC) method. 22 The original SC method can only exchange energy between two adjacent cells. Several improvements have been made for this method, such as the starstructured SC, mesh-structured SC, and delta-structured SC [23][24][25] for the purpose of providing flexible energy exchange paths.…”

“…The energy transfer unit of the active equalization method may be based on the inductor, 7–9 the transformer, 10–12 the combination of inductor and capacitor (LC resonant circuit 13–15 and dc–dc converter 16–19 ), or the capacitor 20–25 . Note that voltage difference is small between cells and is large between cell and pack.…”

“…So, the capacitor‐based method is natively safer than the inductor‐based one. Traditional capacitor‐based equalizers use the switched capacitor (SC) method 20,21 or the flying capacitor (FC) method 22 . The original SC method can only exchange energy between two adjacent cells.…”

Research of Li-Ion Battery’s Upper Equalizer Circuit

“…However, if apply the power designed above in AGV system, after a period of time of discharge and charge with large current, it is found that the upper limit voltage of every cell is seriously differen.The reason is that the difference between every cell has been ignored in the initial design of li-ion battery protection. In this case, referring to the foreign design released, li-ion upper equalizer circuits are designed [4][5].…”