Development of equivalent circuit models for batteries and electrochemical capacitors

Portable electronic equipment has become prevalent. Operating time for such equipment is important and depends on battery and load characteristics. Electrochemical capacitors, sometimes referred to as supercapacitors or ultracapacitors, have been shown to "level" the discharge rate of the battery in some applications and thereby increase system run times. Therefore accurate equivalent circuit models are needed for the battery and the capacitor to effectively mate these two technologies. This paper describes approaches for developing battery and capacitor equivalent circuit models. They are based on impedance and discharge measurements and can be used to examine equipment operating performance using SPICE-based circuit analysis simulations. Optimization of the energy storage system can be performed with this approach.