Coulomb Counting - MSXV

Current and Voltage Measurements

• Current and voltage measurements need to be performed precisely.

Possible Solution:

• Connect analog-to-digital converter like ADS1115 module to the battery. 

• The module measures the voltage across a sense resistor connected in series to the positive voltage of the battery, and the current is calculated using Ohm’s law.

What to do:

• Connect current/voltage measurement device to microcontroller and battery.

• Write software for MCU that takes in values from sensor(s) and calculate current.

Hardware/Software

Charging Module

• A charging module that charges battery with constant current and voltage.

• When the battery is at its full capacity, the charging process should be terminated.

  • The battery is determined to have reached its full capacity when the battery voltage is 4.2 V and the charging current falls below the threshold.

What to do:

• Manufacuture or purchase charging module for our battery box.

• Write software that evaluates whether the battery is fully charged/discharged.

Hardware/Software

Initial System Calibration

• During initial system calibration, the initial SOC, battery capacity and coulombic efficiency need to be evaluated.

  • During the system calibration, the battery is charged and discharged through one complete cycle.

    • During the cycle, the initial SOC is set to 0% at the fully discharged state and 100% at the fully charged state. At the end of the cycle, the battery capacity is evaluated as the net capacity discharged during the cycle, and the coulombic efficiency is evaluated as the ratio of the discharged capacity to the charged capacity during the cycle.

What to do:

• Develop system calibration program

Software

P.S. this needs to be done once

SOC Estimation

• A piece of code that actually estimates SOC of battery with the use of measured current is needed.

  • Receive the current value every arbitrary time step duration (e.g. 100 ms)

  • Calculate the current SOC of the battery with the use of SOC in the previous time step, measured current, the duration of each time step, coulombic efficiency (kept 1 during discharge), and rate capacity.

What to do:

• Make SOC estimation function.

Software

Error Evaluation

• Evaluate how accurate our coulomb counting model is. (Guess we can ask strategy team for help?)

System Integration

• Integrate features listed above.

• Connect battery box, MCU, voltage/current measurement, and display.

• Connect pieces of softwares and implement on microcontroller.

Display

• Display to show the SOC and other parameters.