Multi-Winding Equalization Technique for Lithium Ion Batteries for Electrical Vehicles

2019

Electronics

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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.

Section: Introductionmentioning

confidence: 99%

An Efficient Equalizing Method for Lithium-Ion Batteries Based on Coupled Inductor Balancing

2019

Electronics

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“…Several cell equalization techniques are introduced in the last decades. These balancing methods are principally separated into two categories, active and passive balancing methods [10][11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

“…The transformer balancing technique has a smaller equalizing time compared to other methods [12,15]. The multi winding transformer has a magnetic core with one primary and multiple secondaries for every cell, as shown in Figure 3.…”

Section: Introductionmentioning

confidence: 99%

A Ćuk Converter Cell Balancing Technique by Using Coupled Inductors for Lithium-Based Batteries

2019

Energies

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In this paper, a c ´ uk converter balancing method by using a coupled inductor for lithium based batteries is investigated. The proposed circuit is an active balancing circuit that will equalize eight battery cells in a series. In electrical vehicles (EV), a battery management system (BMS) is a vital task to achieve the best performance of the batteries and longer lifetime. The problem of voltage difference in a battery pack is an important issue to be improved. To overcome the voltage differences in battery string, an equalizing method is mandatory. The conventional c ´ uk converter requires 2(n − 1) switches to balance n cells, while the proposed circuit requires only n switches for n cells in series. In addition, the proposed developed topology uses coupled inductors instead of un-coupled inductors, unlike the traditional c ´ uk converter balancing method. Since the c ´ uk balancing transfers the energy among two adjacent cells, it requires a proportionately long equalization time particularly for long string battery packs, but the coupled inductor c ´ uk converter type overcomes this problem. The switches are N-channel metal-oxide field-effect transistor (MOSFET) to achieve lower drain-source on-resistance, R D S ( o n ) , and less voltage drop as compared to the P-channels. The switches are triggered by complementary signals. The coupled inductor is made in such a way to hold the same magnetizing inductance. It can be done by using five wires in one hand. The circuit contains five inductors, one magnetic core, with five winding for eight cells, and one capacitor for two cells. Therefore, the overall circuitry and complexity of the circuit are reduced, resulting in a more cost-effective and easy to implement circuit. The system also does not demand complicated control for battery equalizing. The experimental circuit was implemented and simulation results were obtained to confirm the validity of the proposed system.

“…For the battery to have a long life, it requires an appropriate battery management system (BMS) to equalize the cells in a battery string. Several cell-balancing strategies have been presented in the literature [8][9][10][11][12][13][14][15]. Slight differences between the series-connected cells in a lithium-ion (Li-ion) battery pack can produce imbalances in cell voltages, and this effect causes great reductions in the charge capacity [16,17].…”

Section: Introductionmentioning

confidence: 99%

“…The transformer/flyback balancing method is an active balancing method and removes energy from one cell to another cell [11][12][13]15,[26][27][28]. It may have a smaller balancing/executing time.…”

Section: Introductionmentioning

confidence: 99%

A Smart High-Voltage Cell Detecting and Equalizing Circuit for LiFePO4 Batteries in Electric Vehicles

2019

Applied Sciences

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A battery management system (BMS) plays an important role in electric vehicles (EVs) in order to achieve a reasonable-lasting lifetime. An equalizing method is essential in order to obtain the best performance. A monitoring system is required to check if any cell voltage is high or low. In this paper, an equalizing and monitoring system for an ultra-light electric vehicle is proposed. The monitoring system detects if one cell is fully charged or all cells are fully charged and the equalizing system tops each cell at the desired voltage. To solve this issue, a light-emitting diode (LED) band gap is used as a voltage reference to inform the user if any cell is at its high voltage. A smart monitoring displays on the liquid crystal display (LCD), if one cell is high or all cells are high. This detection also provides a signal to the microcontroller to turn on/off the charger if all cells are high. Also, a Bluetooth module was designed to command the microcontroller the charger to turn on/off via voice/text message by using a smartphone. Additionally, a new smart monitoring system based on the Bluetooth model (HC05) and mobile app has been made in order to monitor individual cell voltage. A major feature of the system is to draw a very-low current, so that the system does not contribute significantly to the self-discharge of the battery and the circuit does not need sophisticated control. Manufacturers of large electric vehicles may have more intelligent systems that may require a permanent connection to the grid and allow high standby losses, where more state of charge (SOC) may be lost per day. The paper is rather focused on reducing the standby losses, and to activate the equalizer only when charging and/or driving. The experimental results are performed in order to verify the feasibility of the proposed circuit.