Research on Equalization Strategy Based on Credibility Factor Inference for Lithium-Ion Battery Packs

Abstract

In this paper, a two-stage equalization topology based on Zero-Voltage Switching Quasi-Resonant Converter (ZVS QRC) is proposed to solve the problems of long equalization time and low energy utilization of series lithium-ion battery packs. The equalization topology is divided into two forms: intra-group and inter-group, ZVS QRCs are adopted in both intra-group and inter-group, which can equalize any single cell within a group, and the equalization circuit within each pack can equalize simultaneously, which greatly reduces the equalization time, and reduces the switching loss during the equalization process by introducing quasi-resonant circuit to improve the energy utilization. Taking the State of Charge (SOC) as the equalization target, a group equalization strategy based on the Credibility Factor (C-F) inference model is proposed. The strategy defines the SOC unbalance degree of a single battery, gets the group unbalance degree according to the C-F inference model, and gets the group equalization state from the unbalance degree, to control the group for equalization. Matlab/Simulink software is used to build the model and simulate it. The experimental results demonstrate that the proposed topology saves approximately 25% of the equalization time compared to the traditional Buck-Boost group equalization topology. Under the same static and charge/discharge conditions, the equalization time is reduced by about 21% and the energy utilization is improved by about 6% after using the C-F inference model for equalization compared to the fixed-threshold method.

Switching Control for Voltage Balancing of Lithium Batteries

“…Figure 2.Flowchart of improved switching control algorithm. After calculating the switch closure time of the shunt branch circuit for each single cell, the switch closure with the longest closure time is controlled first in a cycle, and after the switch closure, the charging current of that single cell is slightly less than the charging current of the other single cell [13], and the above calculation step with the switch closure operation is repeated after the end of a very short cycle.…”

A Battery Cell Equalisation System Based on a Supercapacitors Tank and DC–DC Converters for Automotive Applications

“…As a primary benefit, the study reports an equalisation efficiency improvement of 4.89% and a time reduction of 37.4% based on an adaptive fuzzy neural network equalisation algorithm. Further efficiency and equalisation time improvements are found using zero voltage switching quasi-resonant converters [4], giving an efficiency improvement of 6%.…”

“…The battery cell equalisation techniques have been an object of research in numerous studies in recent years [1][2][3][4][5][6]. The review of the primary equalisation circuits in [1] presents and compares capacitive and inductive energy storage, single and multi-tube flyback, and different DC-DC converter topologies.…”

“…The required capacitors' energy W C is given with the integral of the power P C over the time t [3,4,6,7,12,19,20,29,30]:…”

“…The SCES charge and discharge basic equations [3,4,6,7,12,19,20,29,30] necessary for the simulation models are given in Table 2. The results of the simulations present the comparison between constant voltage (CV) and constant current (CC) illustrated, respectively, with block diagrams in Figures 3 and 4 Figure 5 shows the results for CV charging as follows: (A) the transi cess continues for 17.5 s, e.g., five times the time constant 𝑇 = 3.5 s wi voltage 𝑉 = 10 V ; (B) the peak current at the beginning of the tra 499.86 A, and the average current is 100.72 A, which are considered una selected battery cells; (C) the peak capacitor loss is 44.64 W, and the a loss is 17.61 W; (D) the peak power delivered to the energy storage is 12 average power is 493.13 W; (E) the peak energy is 8629.12 J, and the lated energy is 6124 J.…”