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

Abstract

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.

Switched-Resistor Passive Balancing of Li-Ion Battery Pack and Estimation of Power Limits for Battery Management System

“…Passive and active balancing strategies can be distinguished. If a battery cell is replaced but does not have the same charge as the others, the battery will not be destroyed, but it will take more time to equalize, as stated by the authors in [45]. To finish out the monitoring infrastructure, a new Bluetooth-based smart-monitoring system and a mobile application built with "MIT app inventor 2" track the voltage levels of individual cells.…”

Simulation of Factor on SOC Inconsistency within a Series‐Connected Lithium‐Ion Battery Pack

“…Leakage current is mainly caused by the electronic equipment of the battery monitoring system, which requires a permanent connection to the battery and contributes significantly to the discharge losses. [ 21,22 ] Considering that the individual cells in the battery pack have different leakage current levels, the leakage current of every single cell is set to be randomly and evenly distributed between 10 and 12 mA, as shown in Figure 5d. The current flowing through the battery cell can be calculated by the equation $${I}_c = I + {I}_{leak}$$, where $${I}_{leak}$$ is the leakage current of the single cell.…”

Low-Cost/High-Precision Smart Power Supply for Data Loggers

“…They can be integrated into an electronic device, such as a microwave, which has all the components of the power supply inside the unit, or can be external, such as for notebooks and smartphones [2]. They can be part of external units for electric vehicles (EVs), or EV chargers [3,4], an they can be modulated, e.g., in a desktop computer power supply [5]. This type of power supply has a wide range of voltage outputs, can be remotely controlled, and its form factor allows it to be easily replaced [6,7].…”