Minimizing The State Of Health Degradation Of Li-Ion Battery For Low Earth Orbit Satellites

Abstract

Satellites have a tangible impact on our daily lives; they provide us with many services like communication, global positioning etc. Satellites may be sent to space for prolonged periods of time. There are several mission profiles for satellites i.e. low earth orbit (LEO), middle earth orbit (MEO) or geosynchronous orbit (GEO) missions. Batteries on board satellites are expected to deliver the power demand at any time during the period of an eclipse, or when the power received from the solar panel is not sufficient. The focus of this thesis is to develop a mixed integer nonlinear scheduling model that reduces the state of health (SOH) degradation of a battery in a LEO satellite. This will improve the battery lifetime, thus increasing the length of time a LEO satellite can stay in service. The developed model for a LEO satellite is solved separately for meeting three different objectives, which are minimizing the number of battery switches between charging and discharging, minimizing the sum of products of the battery state switches and battery current, and minimizing the total depth of discharge (DOD). In addition to the model, a heuristic approach is developed and compared with the mathematical model. In this endeavor, data are collected for an existing LEO satellite, Nayif-1, in order to analyze the current battery behavior in space and compare it with the developed model and heuristics. Sensitivity analysis is conducted to observe the effects of altering different parameters of the model. The results presented in this thesis show that minimizing the sum of products of the battery state switches and the battery current, yields the best results by enhancing the lifetime of the battery by 8 days and providing 122 more cycles than that observed in the data from Nayif-1, assuming that the DOD of the battery remains constant throughout all orbits. Therefore, based on the main results comparison and sensitivity analysis, it is concluded that the second objective function provides the best enhancement of the battery lifetime for LEO satellites.