A charge equalization scheme for battery string with charging current allocation

Abstract

Summary This research proposes a charge equalization scheme based on a flyback converter with the polarity‐inverting folding switches together with a set of selection switches for series‐connected batteries. By the selection switches, the converter can provide an additional charging current to the battery with the lowest loaded voltage. In addition to intervening a low current charging to prolong the discrepant charging, a finalizing individual charging is performed to ensure charge equalization even under extremely unbalanced situation. Thus, all the batteries can be allocated with appropriate electric charge through the proposed charge‐balance strategy to make the voltage of all batteries be even after the charging process. Three sets of experiments with different initial conditions are performed. Experimental results show that the charge imbalance can be effectively reduced after the regular current charging for most practical cases. All batteries can be charged to their full capacities with individual charging, even under extremely unbalanced situation. Eventually, the voltage difference among batteries can be alleviated to about 50 mV.

A bidirectional converter with integrated voltage equalizer for series‐connected supercapacitors

“…However, the obvious disadvantage of using a converter as the EU is that a converter is required between every two adjacent cells connected in series, which leads to an increase in the complexity, cost, and size of the system. Using selective switching technology can greatly reduce the number of components but increase the complexity of the control algorithm 9–11 …”

“…Using selective switching technology can greatly reduce the number of components but increase the complexity of the control algorithm. [9][10][11] Since each active switch requires a gate driver IC and its related passive components and auxiliary power supplies, the complexity of the system is proportional to the number of active switches. Equalization methods based on multiple transformers [12][13][14] can reduce the number of active switches.…”

A Cost-Effective Passive/Active Hybrid Equalizer Circuit Design

“…The equalization unit is also called the cell balancing unit. The equalization unit is composed of two parts: an equalization control strategy [23][24][25][26][27][28][29] and an equalization circuit (EC) [28,29,[31][32][33][34]. Its purpose is to reduce the maximum and minimum cell voltage differences of the battery pack to avoid battery overcharge and overdischarge, which can improve the safety and lifespan.…”

“…Retired vehicle lithium battery packs with good cell balance can be reused in energy storage systems for secondary use to produce huge economic and environmental benefits. Various ECs have been proposed in the past, which can be divided into two types: (1) the passive equalizer circuit (PEC) [28], also called dissipative balance, discharges the energy with a power resistor to the series-connected cell with the highest voltage, and (2) the active equalizer circuit (AEC) [27][28][29][30][31][32][33][34][36][37][38], also called non-dissipative balance, charges the energy to the cell with the lowest voltage. Many review articles have provided a detailed summary or comparison for the equalization design [17,26,28,30,32,33,36].…”

“…Briefly, HIL is a good auxiliary tool in the development sta BMS, which can significantly reduce the development time and testing risk of the B many practical experiences, most battery pack failures are caused by the cell volta balance issue, which means the voltage difference is enormous, drastically reduci battery pack's available power, capacity, lifespan, and safety. Therefore, most BM signs have an equalization unit to solve the imbalance issue [22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”