A Modular Cell Balancer Based on Multi-Winding Transformer and Switched-Capacitor Circuits for a Series-Connected Battery String in Electric Vehicles

Abstract

Abstract:In this paper, a cell balancing topology for a series-connected Lithium-Ion battery string (SCBS) in electric vehicles is proposed and experimentally verified. In particular, this balancing topology based on the modular balancer consists of an intra-module balancer based on a multi-winding transformer circuit and an outer-module balancer based on a switched capacitor converter, both offering the potential advantages and over conventional balancing methods, including short equalization time, simple control scheme, elimination of voltage sensors. In addition, a number of cells in the SCBS can be easily extended in this circuit. Furthermore, a system structure and an operating principle of the proposed topology are analyzed and experimentally verified for three different cases. The voltages of all cells in the SCBS reached the balanced state regardless of the various arrangement of the initial voltage, where the energy efficiency of the circuit reached 83.31%. Our experimental realization of the proposed balancing topology shows that such a technique could be employed in electric vehicles.

Lithium Battery Model and Its Application to Parallel Charging

“…The multi-winding flyback topology [3] for battery-charger applications which require a total output power level of approximately 200 W is shown in Figure 2. The design is specified for 12 V output voltage as required for a 3-cell Li-ion battery charger.…”

“…Current differences in parallel connecting can cause differences in the state of charge, temperature, and degradation rate of each cell. Several existing battery-charging [3,4] and cell-balancing [5,6] techniques with flybackbased converters are well presented. The flyback converter has been widely adopted for lithium-based batteries in electrical vehicles because of its simple structure and high conversion efficiency [3][4][5][6].…”

Cell equalisation circuits: A review

“…Therefore scalability is an issue when considering 96 cells within a series string. This circuit again benefits from a modular design to reduce the cost of the transformer [41,42].…”

Improved Control of Forest Microgrids with Hybrid Complementary Energy Storage

“…However, their charge-discharge efficiency is low, which is not recommended for frequent action to suppress power fluctuations. Contrarily, supercapacitors have the merits of high power density and long cycle life, as well as high charge and discharge efficiency [26]. Therefore, they are appropriate for suppressing the power fluctuations with high frequency and small amplitude that are typical in free mode and emergency mode, to assist the biomass unit in power regulation.…”