Transcript Multi-Cell Lithium-Ion Battery Management System

Abstract/Problem Statement
The goal of this project is to develop an efficient, safe and scalable
system for charging and monitoring a multi-cell battery pack for
electric vehicles. The system will use a switching mode power supply
and a battery management system. The initial scope of this project
was to charge the bank of lithium-ion batteries to 324 VDC supplied
from a 120 VAC wall outlet. In order to focus on battery management
and safe charging, this project was scaling down to developing a
battery management system for 18 series cells that can later be
scaled to 90 series cells.
Functional Decomposition
The system consists of two main components: the battery management
hardware and the power supply. Both of these components are controlled by an
MSP430 microcontroller, and output data for every cell is available with a
personal computer.
Solution Approach
The first objective of this project is to develop the battery
management system for a small scale battery pack (18 series cells).
Several integrated circuits are offered from Texas Instruments to
provide battery monitoring for battery packs with a large number of
cells. The bq76pl536 is used specifically to monitor the state of
charge and battery status of packs with many series cells. The
information obtained from the bq76pl536 integrated circuits is then
used to control a switching mode power supply that follows the
charging algorithm necessary for safe and efficient lithium ion battery
charging.
Design Requirements
Functional Requirements
 Li-Ion Battery Management
• Constant-Current Constant-Voltage
charging procedure
• Battery Gauging
• Temperature Monitoring
• Overcharge Protection
Implementation & Testing
Boost Converter
Usable by our client during the development of the full scale
version.
 Reliable operation, even in the condition of a fault.
 Low price to ensure the product is a competitive market
alternative.
 Robust and long-lasting.
 High efficiency for maximum power usage.
 Protect the user from unsafe conditions.
Intended Users and Uses
Intended Users
 Simulations are run to ensure the boost can
output from 28.8V to 64.8V
 The maximum current from the boost circuit
will be 3A at all output voltages
 Average efficiency in operating region is 87%
 Efficiency ranges from 78%-99%
80
Output Voltage [V]
Non-Functional Requirements
SMPS Output Voltage
70
60
50
40
Output V[23 Ohm]
30
Output V [50 Ohm]
20
10
0
1
5
10
15
20
25
30
35
40
45
50
55
60
65
PWM duty cycle [%]
Microcontroller
 The MSP430 is a low power microcontroller used to gather and organize the data from the bq76pl53
integrated circuits. MSP430 testing was done by hooking it up to test circuit where known voltage
and current information is present. Then the output PWM signal is observed.
Battery Management System
 Uses bq76PL536-EVM3 and Aardvark USB-SPI adaptor when displaying on a PC, as well
as an MSP430 for control. The EVMs allow SPI communication of the battery information
and the MSP430. Multiple EVMs can be connected in series to monitor up to 192 series cells
(18 shown). EVMs were tested with DC power supplies to model battery voltage information.
The users of the final design will be the vehicle owners, family
members, friends, etc. They could range anywhere between 14 to 100
years old and as long as they can pick up an extension cord and plug
it in, they could use this project. However, since this project is only a
scaled down version of the prototype, the intended user is the client
(Element 1 Systems).
Intended Uses
The intended use of the project is to charge a bank of lithium ion
batteries and manage their charge and discharge cycles. The high
voltage supply is designed to operate as a constant-current constantvoltage lithium ion battery supply, and only for the specified A123
battery chemistry.
Final Testing
Battery Management System
(Power Supply not shown)
bq76PL536-EVM3 battery information display GUI
Uncharged batteries are connected to the circuit to ensure they charge correctly
Summary
With global demand for oil increasing and supplies more difficult to obtain, the price of oil based fuels for
transportation is expected to rise. The need to find a viable alternative to oil necessitates researching in electric
alternatives. The long wait time to charge Electric Vehicle batteries makes transitioning from internal
combustion engines to battery electric vehicles inconvenient for a society dependent on traveling large
distances. Electric vehicles have to be convenient, safe, and affordable to meet the needs of consumers without
major sacrifices in perceived quality of life. Lithium ion batteries support a high energy density and are the
preferred source of mobile electric power. This project implements a solution for a battery management system
for a large number of lithium ion cells.
Team-id- sdmay11-04
Team Members
• Pramit Tamrakar – EE
•Jimmy Skadal - EE
•Matthew Schulte - EE
•Hao Wang - EE
•William Zimmerman - EE
Advisor
Ayman Fayed
Client
Adan Cervantes
Budget
Parts
Cost
bq76PL536EVM-3
$400
MSP430
$75
Various Discrete components
$50
Labor
Pramit Tamrakar
$4000
Matt Schulte
$4000
Jimmy Skadal
$4000
Hao Wang
$4000
William Zimmerman
$4000
Total cost
$20,779