Abstract
Due to variations among the cells, large lithium ion batteries (LIB) such as those in battery energy storage stations (BESS) and electric vehicles (EVs) must have an equalizer (EQU) circuit to balance the cell voltages. In spite of their significant losses and other limitations, passive equalizers (PEQ) are used in most applications because they are relatively simple and low cost. Active equalizers (AEQ) reduce these PEQ problems, but are not as widely used due to their much higher cost and complexity. A new hybrid circuit called the Bilevel EQU (BEQ) combines the PEQ and AEQ to provide much higher performance than a pure PEQ but at a much lower cost than a pure AEQ.
Highlights
Large lithium ion batteries (LIB) are used in a wide variety of applications including electricLarge lithium ion batteries are storage used in a wide variety applications including electric vehicles, aerospace, and battery(LIB)energy stations for of electric utilities.For safety and vehicles, aerospace, and battery energy storage stations for electric utilities.For safety and maximum performance, all of these large packs of series connected cells require a battery management maximum performance, all ofseveral these functions large packs of most seriesbasic connected cells require the a voltage battery system (BMS)that must provide [1]
The efficiency increases with the number of cells because the losses become a lower percentage as the output power increases, and these results indicate this athnadn laopwurceoAstE. QA.ctive equalizers (AEQ) is not a very good choice for single cells
PEQs have serious limitations which can be alleviated with AEQs, but at a cost that is usually considered excessive
Summary
Large lithium ion batteries (LIB) are used in a wide variety of applications including electric. It is simple and relatively cheap, but it can dissipate a Batteries significant amount of heat and energy loss. 2017, 3, PEQs have another serious limitation since they cannot add charge to lower capacity cells, which is necessary to maximize the discharge capacity of thecapacity battery. PEQs AEQ still greater when higher equalization currents are needed since these this requires higherbut power dominate most markets due to their simplicity and much lower cost. This cost difference is even greater components. −t1 is less losses, than t1,core andloss thusinthe currentlosses from B1 is less
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