A Modularized Equalization Method Based on Magnetizing Energy for a Series-Connected Lithium-Ion Battery String

Abstract

A single charge equalizer using the multi-winding transformer (SCEMT) is useful for the precise and fast equalization. Since this type of equalizer requires voltage sensing circuits for each battery cell, the size and cost of the overall equalizer system increase. In this paper, a novel switching method, which does not require voltage sensing circuits, is proposed for the SCEMT. However, due to the problems related to the implementation of multiwinding in a single transformer, the SCEMT is definitely difficult to apply to long series-connected lithium-ion battery string. In order to overcome these drawbacks, a novel module charge equalizer based on the configuration of the SCEMT is developed. Unlike the conventional module charge equalizer using additional components, the proposed novel module charge equalizer utilizes the magnetizing energy of the multiwinding transformer for the equalization among modules. Therefore, proposed module charge equalizer does not suffer from the size, cost, and loss related to the modularization. The validity of the proposed module charge equalizer is verified through experimental results.

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

“…The MWTFC-based balancer equalizes the voltage of cells in the SCBS by selectively turning the switches S k on or off according to the constant duty cycle (D) simultaneously. Figure 2 shows an active cell balancing circuit using the MWT with the forward converter structure and operating modes [17,18,21,25,28]. This circuit consists of N series-connected cells.…”

“…Therefore, this causes a charge imbalance problem by itself. In order to reduce this problem, the number of windings of the transformer needs to be reduced [28]. This requirement motivates our proposed cell balancing circuit to solve these issues.…”

A Novel Cell Balancing Circuit for Fast Charge Equalization

“…A simple voltage sensorless charge balancing circuit has been proposed in the past [1] . This cell balancing circuit automatically transfers energy from high-to low-voltage battery cells.…”

“…능동형 셀 밸런싱 회로는 전하 전달 방식에 따라 간 접 전달 방식 [4]- [6] 과 직접 전달 방식 [1], [7]- [15] 으로 나눌 수 있다. 간접 전달 방식은 인접하지 않은 배터리 셀로 의 직접적인 전하 전달이 불가능하여 직렬 연결하는 배 터리 셀의 수에 비례하여 밸런싱을 위한 시간이 길어지 는 단점이 있다.…”

“…직접 전달방식은 인접하지 않은 배터리 셀로 직접적인 전하 전달이 가능하여 직렬 연결된 배터 리 셀의 수와 관계없이 빠른 균일화 속도를 낼 수 있다. 직접 전달 방식은 각 배터리 셀당 개별 컨버터를 연 결하여 사용하는 방법 [7]- [11] 과 다권선 변압기를 이용하여 하나의 코어를 여러 개의 배터리 셀이 공유하여 사용하 는 방법 [1], [12]- [15] 으로 나눌 수 있다. 개별 컨버터를 이용 하는 방식은 배터리 셀의 충방전 속도는 매우 빠르지만, 배터리 수와 비례하여 시스템의 크기 및 구현 비용이 증가한다.…”