A monitoring network has been created that can be added to a battery consisting of many parallel cells. This network allows the health of individual cells, as measured by the current that they produce under load, to be monitored. If one or more cells are producing less current than the others, the network allows the discrepant cell(s) to be sensed and located.
The sense network consists of individual saturating transformers connected in series with the individual cells of a bank of many parallel cells. The transformers share common excitation and sense windings. When a current waveform is applied to the excitation winding, while a test load is placed on the whole battery, the waveform that appears on the sense winding allows poorly performing cells to be detected (see figure).
Each transformer has three windings: (1) a battery winding consisting of a single turn in series with the monitored cell, (2) an excitation winding consisting of a single turn in series with the excitation windings of all the other transformers, and (3) a sense winding consisting of one or more turns in series with the sense windings of the other transformers. The number of turns will be different for each transformer so that each has a unique number of turns. The excitation and sense windings may be combined into a single winding if fault localization is unnecessary.
When the total current of a transformer passes through zero, the transformer will momentarily become unsaturated, and will induce a voltage pulse on each of the windings. Because the excitation winding passes through all the transformers with the same number of turns, they will each have the same excitation current waveform. If each battery cell current is the same, then all the transformers will pulse at the same time. If any battery cell current is different, then the transformer for that cell will pulse at a different time than the others. So, a healthy battery will show a single large pulse on the sense winding. This pulse will be composed of simultaneous pulses from each transformer added together. A battery with a poorly performing cell (one that is providing significantly less current than the other cells) will show two pulses, one corresponding to the poorly performing cell, and the other corresponding to the good cells. The deviant cell will be identifiable by the amplitude of the pulse. If a particular cell produces less current, the amplitude of its pulse will correspond to the number of turns on the sense winding of its transformer.
This innovation is intended to be operated during test and verification operations of the battery, and not during normal load operations. It may be operated during load checks of the battery, or during operating phases when the current consumption is well characterized.
This work was done by Francis J. Davies and Jason R. Graika of Johnson Space Center.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Johnson Space Center, (281) 483-1003. Refer to MSC-24509-1.