Special Circuit :: ECE 445 - Senior Design Laboratory

Special Circuit

A student whose Senior Thesis Project (ECE 499) does not involve the design and construction or testing of electronic devices or hardware is required to complete a Special Circuit Project in the ECE 445 lab during the semester they take ECE 499. In addition, students enrolled in ECE 445 who are not undertaking a hardware dominant project are required to complete the special circuit (although this is strongly discouraged and the course staff will work with your team to make sure you have enough hardware in your project to avoid having to complete the special circuit.)

The special circuit is typically posted in the middle of the semester. Once you sign up for the special circuit (see below), you will be assigned a TA, a locker, and a special circuit which generally takes about 12-15 hours to complete. When you have it designed and built, you will give a functional demonstration to your TA, who will then inform the professor who will inform undergraduate advising that your task is complete. You are NOT required to attend any of the classes, reviews, demos, or presentations associate with the ECE 445 class.

Sign up for Spring 2020 is now open

Sign up for the Special Circuit assignment on the Lab Access page. Instructions for completing the special circuit will then be provided in the near future. Please check this page for updates.

Link to all Special Circuit design problems. 

Active Cell Balancing for Solar Vehicle Battery Pack

Tara D'Souza, John Han, Rohan Kamatar

Featured Project

# Problem

Illini Solar Car (ISC) utilizes lithium ion battery packs with 28 series modules of 15 parallel cells each. In order to ensure safe operation, each battery cell must remain in its safe voltage operating range (2.5 - 4.2 V). Currently, all modules charge and discharge simultaneously. If any single module reaches 4.2V while charging, or 2.5V while discharging, the car must stop charging or discharging, respectively. During normal use, it is natural for the modules to become unbalanced. As the pack grows more unbalanced, the capacity of the entire battery pack decreases as it can only charge and discharge to the range of the lowest capacity module. An actively balanced battery box would ensure that we utilize all possible charge during the race, up to 5% more charge based on previous calculations.

# Solution Overview

We will implement active balancing which will redistribute charge in order to fully utilize the capacity of every module. This system will be verified within a test battery box so that it can be incorporated into future solar vehicles.

Solution Components:

- Test Battery Box (Hardware): The test battery box provides an interface to test new battery management circuitry and active balancing.

- Battery Sensors (Hardware): The current battery sensors for ISC do not include hardware necessary for active balancing. The revised PCB will include the active balancing components proposed below while also including voltage and temperature sensing for each cell.

- Active Balancing Circuit (Hardware): The active balancing circuit includes a switching regulator IC, transformers, and the cell voltage monitors.

- BMS Test firmware (Software): The Battery Management System requires new firmware to control and test active balancing.

# Criterion for Success

- Charge can be redistributed from one module to another during discharge and charge, to be demonstrated by collected data of cell voltages over time.

- BMS can control balancing.

- The battery pack should always be kept within safe operating conditions.

- Test battery box provides a safe and usable platform for future tests.