Low-frequency Selection Switch based Cell-to-Cell Battery Voltage Equalizer with Reduced Switch Count

TL;DR

This paper introduces a low-frequency cell-to-cell voltage equalizer using a capacitively level-shifted Cuk converter and fewer switches, achieving high efficiency and reduced switching operations for battery management.

Contribution

It proposes a novel low-frequency selection switch network and a voltage recovery compensation method, significantly reducing switch count and equalization time in battery balancing systems.

Findings

Efficiency over 90% achieved in prototype

Approximately tenfold reduction in relay switchings

Effective voltage balancing during various load conditions

Abstract

A selection switch based cell-to-cell voltage equalizer requires only one dual-port dc-dc converter shared by all the cells. A cell-to-cell voltage equalizer is proposed that utilizes a capacitively level-shifted Cuk converter and low-frequency cell selection switches. The absence of isolation transformer and diodes in the equalizer leads to high efficiency, and the use of low-frequency selection switches significantly reduces the cost of the drive circuits. A low-frequency cell selection network is proposed using bipolar voltage buses, where the switch count is almost half, compared to the existing low-frequency cell-to-cell equalizers for the case of a large number of cells. A novel approach for cell voltage recovery compensation is proposed, which reduces the number of operations of the selection switches and the equalization time. The proposed equalizer is implemented with relays and verified with an 8-cell Li-ion stack. The developed prototype shows the efficiency of over 90\% and good voltage balancing performance during charging, discharging, and varying load conditions. Experimental results also show about one order of magnitude reduction in the number of relay switchings and a significant reduction in equalization time using the proposed voltage compensation.