A new impedance-based approach is introduced<br/>in which the integral battery temperature is related to other<br/>frequencies than the recently developed zero-intercept frequen…
A new impedance-based approach is introduced<br/>in which the integral battery temperature is related to other<br/>frequencies than the recently developed zero-intercept frequency<br/>(ZIF). The advantage of the proposed non-zero-intercept frequency<br/>(NZIF) method is that measurement interferences,<br/>resulting from the current flowing through the battery (pack),<br/>can be avoided at these frequencies. This gives higher signal-to-noise<br/>ratios (SNR) and, consequently, more accurate temperature<br/>measurements. A theoretical analysis, using an equivalent circuit<br/>model of a Li-ion battery, shows that NZIFs are temperature<br/>dependent in a way similar to the ZIF and can therefore also<br/>be used as a battery temperature indicator. To validate the<br/>proposed method impedance measurements have been performed<br/>with individual LiFePO4 batteries and with large LiFePO4<br/>battery packs tested in a full electric vehicle under driving<br/>conditions. The measurement results show that the NZIF is<br/>clearly dependent on the integral battery temperature and reveals<br/>a similar behavior to that of the ZIF method. This makes it<br/>possible to optimally adjust the NZIF method to frequencies with<br/>the highest SNR.