Fuzzy logic-based state-of-health determination of lead acid batteries

Determining the state-of-health (SOH) of uninterruptible power supply (UPS) batteries using impedance measurements has been demonstrated by several researchers. One such approach uses single frequency impedance measurements, which may not be reliable under all circumstances. Another approach employs measurements over a wide frequency range and uses extracted equivalent circuit parameters to correlate with battery SOH. This is a computationally extensive approach and not easily incorporated into a low cost system. Over the last five years, Villanova University and US Nanocorp. have been jointly developing a patented fuzzy logic method for estimating the state-of-charge (SOC) and SOH of batteries. This methodology has proven to be both a simple and powerful means to model battery characteristics accurately and robustly. In this paper we describe how impedance measurements, combined with fuzzy logic data analysis have been used to estimate the SOH of lead acid batteries used in portable defibrillators. We also propose ways in which this approach may be extended to estimating the SOH of UPS batteries.