Active Charge Equalizer of Li-Ion Battery Cells Using Double Energy Carriers

Sang-Won Lee,Yoon-Geol Choi,Bongkoo Kang

doi:10.3390/en12122290

Sang-Won Lee, Yoon-Geol Choi + Show 1 more

Open Access

https://doi.org/10.3390/en12122290

Copy DOI

Journal: Energies	Publication Date: Jun 15, 2019
Citations: 10	License type: CC BY 4.0

Affiliation: Pohang University of Science and Technology

Abstract

In this work, a new active balancing circuit is proposed. This circuit consists of a cell-access network and an energy-transfer network. The cell-access network requires 2n + 6 switches, where n is the number of cells, and creates an energy-transfer path between unbalanced cells and the energy-transfer network. The energy-transfer network has double energy carriers and simultaneously implements cell-to-pack and pack-to-cell balancing operations without overlapping. As a result, a high power rate and fast balancing operation can be achieved by using two energy carriers in a single balancing circuit. The prototype of a proposed balancing circuit was built for six cells and then tested under various conditions; all cells in the state of charge (SOC) region of 70% to 80% were equalized after 93 min, and one charging/discharging period in the SOC region of 10% to 90% was increased by 8.58% compared to the non-balancing operation. These results show that the proposed circuit is a good way to balance charges among batteries in a battery pack.

Highlights

Rechargeable batteries have been widely used in many applications, including energy storage systems (ESS), electric vehicles (EV), and photo voltaic (PV) systems
This variability means that all serially connected cells cannot be simultaneously charged or discharged within the safe operating area (SOA), which is the region between charging voltage limit (CVL) and discharging voltage limit (DVL) (Figure 1); the total capacity of the battery pack is determined by the strongest or weakest cell [5]
The circuit consists of a cell-access network and an energy-transfer network; these networks are composed of two transformers as energy carriers, two diodes, and 2n + 8 MOSFETs

Summary

Introduction

Rechargeable batteries have been widely used in many applications, including energy storage systems (ESS), electric vehicles (EV), and photo voltaic (PV) systems. Lithium-ion batteries (LIBs) in particular have high power density, high energy density, and a long life cycle [1,2], meaning they are widely used to store energy. Manufacturing is inconsistent and usage environments differ [3,4], causing voltage and capacity to differ among cells in a battery string. This variability means that all serially connected cells cannot be simultaneously charged or discharged within the safe operating area (SOA), which is the region between charging voltage limit (CVL) and discharging voltage limit (DVL) (Figure 1); the total capacity of the battery pack is determined by the strongest or weakest cell [5]. The battery pack requires a balancing circuit which evens the capacities of the batteries [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]

Results

Discussion

Conclusion