This paper proposes the self-reconfigurable batteries topology without DC-DC converter, which is similar to selfreconfigurable batteries, but it can guarantee that the voltage of the battery pack is within the set range when the SOC (state of charge) is from 0 to 100%, even if the voltage will drop with the SOC or some cells will be bypassed. Simply put, when the battery pack is discharged, the batteries whose SOC is high and their voltages satisfy the demand are discharged, and the cell with lower SOC is continuously replaced, and the consistency of the battery pack is ensured while stabilizing the voltage. The topological and control strategy are analyzed in detail. The proposed topology is verified by the battery pack composed of 9 cells in series, the experiment result shows that this topology not only retains the advantages of good equalization of self-reconfiguration batteries but also maintains low voltage fluctuations even without DC-DC converters, besides, without the DC-DC converter, the capacity utilization rate of the battery pack reaches 99.8%, demonstrating the superior performance of the proposed topology.

Introduction

Lithium-ion batteries are widely used in a variety of applications, including electric vehicles, energy storage systems, due to their high energy density, long cycle life and low self-discharge rate [1]. A number of battery cells are usually connected in series in order to supply higher voltage and higher power to the load in a wide range of applications, while significant efforts are made by designers to select the battery cells such that they are as identical/matched as possible, the battery cells will still have mismatches in practice due to manufacturing tolerances, different self-discharge rates, uneven operating temperature across the battery cells, and nonuniform aging process, among others [2]. Such inevitable differences within battery cells will drift apart through cycling and could potentially lead to overcharging or over discharging, it is clear that such non-uniformity limits the battery capacity and may even cause safety issues [3]. Therefore, to properly maintain all cells balanced is of significant importance for enhancing battery life [4–۶]. While the passive balancing dissipates the excess energy through resistors in the form of heat, the active balancing equalizes the battery cells by transferring the excess energy between battery cells [7].