Abstract
This article developed a coupled inductor balancing method to overcome cell voltage variation among cells in series, for Lithium Ion (Li-ion) batteries in Electrical Vehicles (EV). For an "eight cells in series" example, the developed balance circuit has four inductors, one magnetic circuit with one winding per two cells, and one control switch per cell, as compared to the traditional inductor-based equalizer that needs N-1 inductors and magnetic circuits for N number of cells and more switches. Therefore, ultimately, a more efficient, cost-effective circuit and low bill of materials (BOM) will be built up. All switches are logic-level N-Channel metal-oxide-semiconductor field-effect transistors (MOSFETs) and they are controlled by a pair of complementary signals in a synchronous trigger pattern. In the proposed topology, less components and fast equalization are achieved compared to the conventional battery management system (BMS) technique for electrical vehicles based on the inductor balancing method. This scheme is suitable for fast equalization due to the inductor-based balancing method. The inductors are made with a well-chosen winding ratio and all are coupled with one magnetic core with an air gap. Theoretical derivation of the proposed circuit was well-presented, and numerical simulation relevant to the electrochemical storage devices was conducted to show the validity of the proposed balance circuit. A complete balance circuit was built to verify that the proposed circuit could resolve imbalance problems which existed inside battery modules.
Highlights
Electrical vehicles (EV) can achieve low pollution and low noise compared to gasoline-powered vehicles; the demand for electrical vehicles has increased during the last decade
Lithium Ion (Li-ion) batteries are widely used in many applications, such as electrical vehicles, electric bikes, and uninterruptible power supplies (UPS) due to their advantages, such as high energy density, low self-discharge rates, compact volume, lower weight, and higher discharge current without effects on memory and a long life cycle [1,2,3,4]
All the switches were logic-level N-Channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with body diodes, and were controlled by a pair of complementary signals in a synchronous trigger pattern generated by a microcontroller
Summary
Electrical vehicles (EV) can achieve low pollution and low noise compared to gasoline-powered vehicles; the demand for electrical vehicles has increased during the last decade. The passive balancing technique connects resistors and switches to each battery cell and dissipates energy using the resistor, while the active balancing technique is used to overcome the problem of energy loss and equalizes voltages of battery cells by transferring charge from high-voltage battery cells to low-voltage battery cells, and is divided into two categories, such as charging-pass type and multi-winding transformer type [4,13,14,15]. The control system senses the voltage of the cells and selects the two cells which will be used for energy transferring, while the multi-switched inductor balancing needs an N-1 inductor for balancing N cells They are featured by fast equalization time [26,32]
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