Abstract
The assessment of an in-flight battery health status is of great interest. However, it is very difficult to perform with sufficient accuracy because the battery is constantly operated and no full discharge during a space mission can be done. Currently, a method for performing a health assessment is via the correlation of battery capacity with internal resistance, which can be more easily measured. Another method is to fit the on board battery voltage using the telemetry of current and temperature as inputs by advanced modelling techniques and to derive the ageing parameters of the battery. This is done by optimising the parameters so that the fitted voltage curve is as close as possible to the actual measured voltage telemetry curve. Then an assessment of the battery capacity and energy can be done by simulating a battery discharge at the desired conditions with the required voltage limits. However, these two methods often require extensive battery life tests on ground to estimate the ageing behaviour for a particular mission.In this paper a novel health assessment system is proposed by which a more straight forward and accurate assessment of the battery health in terms of capacity and energy can be performed. The proposed system consists to use one or some battery string(s), which can be safely disconnected via the PCDU (Power Conditioning and Distribution Unit) from the battery for a dedicated capacity measurement while the main part of the battery continues to operate normally. In this paper, the viability of the proposed system is demonstrated and the implications on the battery and the power system are discussed.
Highlights
It is difficult to assess the health status of a spacecraft battery in operation
Every time an increasing current step occurs on the battery bus, the voltage across the battery terminals drops
A prediction of the capacity fade of a spacecraft battery has to be based on the relationship between the internal resistance and remaining capacity, which is probably a complex one
Summary
It is difficult to assess the health status of a spacecraft battery in operation. Due to design, operational and safety constraints, it is essentially impossible to fully discharge the battery in order to accurately measure the currently available capacity. A prediction of the capacity fade of a spacecraft battery has to be based on the relationship between the internal resistance and remaining capacity, which is probably a complex one. The basis for this approach is the availability of experimental data for the cells in similar conditions to the ones encountered in the spacecraft of which the remaining battery capacity is to be determined. The derived values for capacity fade and resistance increase are validated towards other telemetry data before an assessment of capacity and energy are done Examples of this approach are given in references [1,2,3,4]. - get in-flight data about battery capacity fading in order to improve knowledge and optimise future space power systems
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