Complete Development of an Battery Charger System with State-of-charge Analysis

Battery charging and State-Of-Charge management is one of the main relevant issues for developing mobile autonomous robots. This paper presents a complete development of an battery charger for an autonomous mobile robot and a discussion of SOC estimation models. Initially a charger prototype, based on a HalfBridge DC-DC converter, was developed and tested. Furthermore, the MATLAB SimPowerSystems default battery model was analyzed and a limitation of the model concerning the effect of battery internal resistance is then discussed. Afterwards, a bench test was made by measuring charge voltage and current in a prototype board. After testing was through, it was observed that the battery model used in SimPowerSystems is not accurate due to the assumption of a constant battery internal resistance. Then, a variable resistance modification to this model was introduced and a new bench test showed satisfactory results. The variable resistance model provides a correction for both charge and discharge models for a lead acid battery, thus improving the accuracy of the autonomous robot autonomy, as well as avoiding excessive battery depth of charge, which is a limiting factor for their economic life and serviceability. Whereas such results are of limited reach in an applied research project, they mean economic scale gains for the widespread industrial lead-acid battery applications, hence a better battery model, shall allow more accurate battery serviceability, on time battery inspections and maintenance of their elements, and thus a lesser rate of disposal of lead sulphates and plastic casings into the environment, when disposing used lead-acid batteries.