High Voltage Resolution Auxiliary Power Converter for Online Battery Impedance Measurement

Battery impedance measurements can be used to monitor battery health. In impedance spectroscopy based health monitoring, battery impedance is measured over a frequency range and relevant battery parameters are estimated from the measured impedances. Power converter used for charging and discharging of the battery can be used for impedance measurement. However, the output voltage resolution of the power converter may not be sufficient to produce small amplitude sinusoidal perturbation required for impedance measurement. It is shown in this work that it is possible to use a small power rated auxiliary power converter along with the main charge/discharge converter to provide the desired voltage resolution for impedance measurement. The auxiliary converter is a plug-in module which uses an ultra-capacitor and does not require an external power source to supply the required energy during the impedance measurement. The proposed approach is experimentally verified with a prototype and it is shown to be capable of producing small voltage perturbation over a wide frequency range.