高串聯鋰鐵電池芯之平衡電路研究

Cell Balance Circuit Investigation for Lithium Iron Modules with High Numbers of Cells in Serials

鋰鐵電池芯間的不一致性會導致鋰鐵電池芯串聯之後電芯提早過充或過放的現象發生，進而導致電池芯使用壽命大幅降低，電芯電壓平衡電路是主要解決電芯不一致性的方法。本文深入探討常見之電芯電壓平衡電路，研究各平衡電路的特性與適用性，進而提出一新型的全域型主動式互補平衡電路。本研究所設計的平衡電路使用特殊的光繼電器開關元件及電路邏輯，以內部整組串聯電池組經由隔離型DC-DC 電源轉換器轉換成適合單電芯之電壓與電流做為單電芯平衡充電電源，並以此平衡充電電源對串聯電池組內部各電芯來做全域型互補電路，因隔離型DC-DC 電源轉換器擁有80%以上的效率，使用光繼電器開關元件的切換電路導通阻抗小於0.3 Ù並且耐流可達3 A，使得本文所選用之互補電路能做到高效率及高互補平衡電流，突破以往串聯電池組在串聯電芯電壓平衡上使用被動電阻式放電效率低的困境。本研究將所開發出之平衡電路應用在4串到24串的鋰鐵電池組上，並詳細評估新平衡電路的性能。

Variations among lithium iron cells could lead to earlier cell overchargingor overdischarging in a lithium iron battery module in a highnumber of cells in serials. Overcharging or overdischarging will inevitablyshorten the life cycle of any cell. Cell balance is the main approachto counteract cell inconsistencies. This paper investigated some of thesuitable cell balance circuits. Evaluation of the performance and suitabilityof the selected circuits are thoroughly conducted. To improvesome of the shortcomings of the selected balance circuits, we propose anew active and global type balance circuit. This new active balance circuit is basically based on DMOS switching components and speciallydesigned control logics. The single cell with the lowest voltage is compensatedby the whole module in series via an isolated buck converter,which converts the module voltage into a suitably low voltage to moveelectrons from the module to a single cell in a global fashion. Due to thehigh conversion efficiency of the DC-DC converter and high allowableconduction currents of the switching component DMOSs, the new cellbalance circuit show high balance efficiency and high balance current at thesame time. The new cell balance system therefore outperforms the passivedissipation balance system. This study conducts experiments onvarious battery modules with serial numbers from 4 to 24. Performanceof the current DMOS based cell balance system is evaluated in details inthe current paper.