MLS TESTING OF VRLA BATTERIES USING PSEUDO RANDOM BINARY SEQUENCES (PRBS)

Non-intrusive methods of establishing battery state offer distinct advantages to systems where complex charge and discharge profiles make implementation of conventional battery state reporting difficult. Furthermore, examination of equivalent circuit parameters for batteries and cells offers potential opportunities for State-of-Charge (SoC) and State-of-Health (SoH) reporting, irrespective of historic charge and discharge events. This paper expands the use of maximum length sequences as tools for parameter estimation within electrochemical cells, to seek to identify performance indicators within batteries. In order to facilitate this identification, Randles' model is used with Pseudo Random Binary Sequences (PRBS) as the excitation signal within the test system for the batteries being examined. Design of these sequences for experimental analysis is discussed, leading to application in the described test system, employing a monopolar current signal in order to apply the perturbation to the subject battery. Battery impedance is investigated using a frequency domain approach, leading to characteristic impedance spectra being produced for the test batteries. The experimental results obtained allow parameters to be established, and verification against conventional battery test methods, and a sampled data model, is carried out.
This analysis is used to present characteristics which can be subsequently used to inform the design of SoC and SoH algorithms, in order to develop online systems for evaluating these batteries.