Algorithms

There are a number of fundamental functions that the BMS needs to control and report with the help of algorithms. These include:

  • State of Charge (SoC)
  • State of Health (SoH)
  • State of Function (SoF)
  • State of Power (SoP)
  • Cell Temperature
  • HV Isolation
  • Control contactors
  • Cell Balancing
  • Protection

Therefore there are a number of algorithms required to estimate, compare, publish and control.

State of Charge

Abbreviated as SoC and defined as the amount of charge in the cell as a percentage compared to the nominal capacity of the cell in Ah.

SoC from OCV lookup

SoC Estimation Techniques

A look at the estimation of State of Charge (SoC) using voltage profiling and coulomb counting. These two methods give a good overview of the difficulty and errors associated in estimating this critical battery parameter.

State of Health

The SoH of the cell is the total available charge capacity of the cell as a percentage compared to the nominal capacity in Ah when the cell was new.

Mileage equals Wear

Mileage equals Wear – a discussion around the spread in SoH data from real users and some of the factors that impact it.

Fast Charging

There are a number of parameters around fast charging from the atomic to the system scale, including algorithm / approaches:

  • Constant Current – Constant Voltage (CC-CV)
  • Constant Power – Constant Voltage (CP-CV)
  • Multistage Constant Current – Constant Voltage (MCC-CV)
  • Pulse charging
  • Boost charging with a CC-CV-CC-CV scheme
  • Variable Current Profile (VCP)
  • Stepped Constant Current – Constant Voltage (SCC-CV)

Cell Temperature

Very rarely do you measure the temperature of every cell in a battery pack, however, you do need to operate the pack within the limits and apply these limits to every cell. This means you need good estimation techniques that take into account:

This is just a starter, you also need to understand how the system will age and how the measurement system works. Algorithms are key are factor of BMS.