Author: Shoko Koga
Koga, Shoko, 2023 Battery Management System with Individual Cell COntroller for a High-Power Battery, Flinders University, College of Science and Engineering
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The more popular the Lithium-ion battery is, the more need for a Battery Management System (BMS) for it is. This is because Lithium-ion batteries cannot manage itself. The general BMS for a single cell has a monitoring function and protection function. In addition, the BMS for cells in series connected has a cell balancing function to prevent over-charging and over-discharging, but the BMS for cells in parallel connected does not because the unbalance in parallel connection is not critical. However, it is not a small problem for high-power batteries. Therefore, the BMS with individual cell controller is proposed to isolate cells with problems. It can monitor and control all cells individually. An individual cell controller has similar functions as general BMS, but it is for a single cell, and it is communicated with a high-level controller through the I2C bus isolating each controller. The Cell Controller (CC) is proposed to consist of a Fuel Gauge IC and three MOSFETs. A Fuel Gauge IC can report cell status based on the Open-Circuit Voltage (OCV) model. Arduino, as the main controller, communicates with this IC and three MOSFETs. As a result, the cell controller can stop charging or discharging once the terminal voltage reaches its threshold. However, the accuracy of State of Charge (SoC) estimation is not enough. Two reasons for this problem can be considered. One is the common GND between Arduino and a CC. The other is the deterioration of cells. In addition, two cells in series or parallel could not be monitored and controlled because the reference point (GND) was common. Therefore, in the next step, each GND for an Arduino and CCs has to be isolated.
Keywords: cell balance, individual cells, Lithium-ion battery, Open-Circuit Voltage, State of Charge
Subject: Engineering thesis
Thesis type: Masters
Completed: 2023
School: College of Science and Engineering
Supervisor: Nasser Asgari