Standby VRLA battery behavioural prediction.
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis describes VRLA battery behavioural prediction models for extracting reserve time, state of health (SOH) and reserve life knowledge. A model for simulating battery discharge behaviour is also described. The research is focussed primarily on the standby VRLA battery such as that commonly employed by the telecommunications industry. Two approaches have been developed for extracting reserve time knowledge. The first utilises a discharge voltage versus reserve charge characteristic. This characteristic robust against modest variations in operating conditions and is reasonably robust against deterioration in battery SOH. To cater for different battery types an adaptive approach has been developed which also allows more accurate reserve time estimations for batteries with deteriorated SOH. It has been determined that reserve charge and therefore reserve time can be estimated to an accuracy of within ±10% after approximately 10% into a discharge. The second approach utilises a unified characteristic, which enables the direct estimation of reserve time. It has the advantage over the approach based on the voltage versus reserve charge characteristic that it is not battery type specific. It is also more tolerant to changes in battery SOH. This comes at the disadvantage of greater initial estimation error, although the error reduces significantly throughout the discharge. This approach is less capable of dealing with stepped discharge rates or the discharging of partially charged batteries compared to the model based on the voltage versus SOC characteristic. Both approaches can also be used to obtain estimates of capacity, the primary battery SOH indicator. In addition battery SOH knowledge can be obtained from the coup de fouet region. This region is influenced by battery operating conditions as well as battery SOH. Various techniques for extracting SOH knowledge from the coup de fouet region are described. By incorporating the coup de fouet SOH estimation approach with the previous approaches, along with circumstantial knowledge obtained by monitoring (voltage, current and temperature) base parameters, reserve operational life can be estimated, The combination of approaches also enables the construction of a battery discharge simulation model.