Electrical component model for a nickel-cadmium electric vehicle traction battery

Abstract

Saft STM 5.140 nickel cadmium batteries were evaluated at the UMASS Lowell Battery Evaluation Laboratory. An electrical component model was developed based on the test data. Step responses of the battery from seconds to days were considered. Faster time constants than this were not considered because they are presumed to be attenuated within the input filter of the traction motor drive controller. An impedance element model was developed with components associated with the current collection grid, the active plate materials, the electrolyte, and the self discharge. Model elements may be approximated as resistors and capacitors, however some of the values of capacitor and resistor elements vary as a function of load current or state of charge. Constant current charge and discharge tests provided baseline characteristics. Element values were determined using data from self discharge and pulse test cycles. The model was validated using a realistic electric vehicle test in which the response of the battery model to an actual electric vehicle load profile was compared to that of the actual battery