BS in Electrical Engineering
Electrical Engineering Department
There have been recent reports of multi-million dollar companies having to recall entire projects due to their BMS’s malfunctioning or operating incorrectly. The purpose of this project is to analyze the future of batteries, the Lithium-Ion cell, and to exercise a BMS to better understand its capabilities and possible cases for errors. Lithium ion batteries are intolerant of overcharge and overdischarge. Abuse of this kind can result in high temperatures, venting of gases, fire, or explosion. Therefore battery management systems have been devised to prevent such abuse. Recent events such as fires on the Boeing Dreamliner and the Tesla Model S have shown that these dangers are real. These products do have highly developed battery management systems, and the incidents were caused in spite of these systems. This study was undertaken to illustrate how one system from Texas Instruments, functions to monitor and control a simple battery pack.
Part I: Battery Data Acquisition
Preliminary battery tests were conducted to fully understand the operations of charging and discharging the battery. These tests were essential to gain a better understanding of typical battery behavior and to be able to perform calculations necessary in analyzing the characteristics of the batteries. Also, these tests were ran to ensure that the Lithium-Ion batteries being used correctly corresponded to the graphs and values provided by the datasheet. The knowledge gained from Part I was vital for a better comprehension of the functions needed to balance the cells for Part II as well as the importance of safety precautions necessary when dealing with multiple batteries.
Part II: Exercising the BQ76PL536 & GUI
The BQ76PL536 Evaluation Module (EVM) was tested using the BQ7PL536 BMS chips. An Aardvark adapter acts as a link between the EVM and PC allowing the user to read data from the BMS chips on a GUI. The BMS chips are validated by reading voltages of individual battery cells, pack voltage, and pack temperature. The GUI allows for enabling cell balancing between the cells but this feature is not automatic and must be engaged by the user.
Part III: BMS Application
A MSP430fr5969 microcontroller was implemented to create a BMS system that can read data from the BMS chips such as cell voltage, pack voltage, pack temperature, fault statuses, alert statuses, and a variety of other useful cell parameters. This data is displayed on a LCD screen through different menu options. The user scrolls through the menus using a capacitive touch slider on the microcontroller and selections a given option using the option select button. There is also a cell balance mode that will check the cells to see if they are out of balance and then enable cell balancing if the cells are unbalanced. This section is designed to remove the Aardvark adaptor and the GUI from the system.