Practical PHM for Medium to Large Aerospace Grade Li-Ion Battery Systems

Mike Boost, Kyle Hamblin, John Jackson, Yair Korenblit, Ravi Rajamani, Thom Stevens, and Joe Stewart
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Full Paper
phmce_14_060.pdf343.17 KBJune 22, 2014 - 10:23am

In this brief paper we will discuss our experience with developing State of Charge (SoC) and State of Health (SoH) algorithms for rechargeable Li-Ion batteries for aerospace application. This early generation of battery systems is developed for commercial aviation applications and hence is necessarily conservative in its design. We will demonstrate how the Securaplane batteries are designed so as to enhance safety with analytical SoC and SoH algorithms coded into the embedded electronics and describe the operating envelop for these batteries which will determine the constraints for the algorithms. The SoC algorithm is basically a variant of coulomb counting with some enhancements built in to take care of extreme conditions. The SoH is more sophisticated, relying on calibrating the battery based on each new cell’s characteristics at the beginning of life and then deriving the lost life over time. The battery system has been designed with sufficient extra memory and compute power so that more powerful algorithms, which are currently being developed, can be applied into the system in the future. The paper will describe briefly the tests carried out to develop and validate these algorithms. An industry working group convened to help guide in the development and testing of Li-Ion battery systems for civil aerospace application exists to support the emergence of rechargeable lithium within aviation. We will describe how this guidance has been used in the design and testing of our battery systems. There are numerous considerations taken to effectively design a rechargeable lithium battery. These include the interaction of chemistry with charge algorithm, cell balancing with PHM capacity, environmental control and reaction to unexpected perturbations. In these batteries the chemistry used is iron based, i.e. Lithium Iron Phosphate, as opposed to the cobalt based systems which have more energy density but can more easily release its own oxygen. Securaplane battery systems use smaller, 18650 form-factor cells, not much bigger than standard C-type cells. Also, many safety features are built into the electronic design such as discharge cell balancing, temperature monitoring, emergency fuses, etc. Finally, the software aspects of the system are also designed to monitor the safety of the system. All of this will be described in the paper so that the reader can appreciate the subtleties of the design process. Testing is a critical part of the process. In this paper, we will show how the testing was carried out before the systems were deployed. Finally, if available, we will share data from the field on operational systems and demonstrate how the batteries are behaving compared to their design intent.

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Submission Topic Areas: 
Component-level PHM
Industrial applications
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