In a proposed method of determining the resistances of individual DC electrical devices (e.g., batteries or fuel-cell stacks containing multiple electrochemical cells) connected in a series or parallel string, no attempt would be made to perform direct measurements on individual devices. Instead, (1) the devices would be instrumented by connecting reactive circuit components in parallel and/or in series with the devices, as appropriate; (2) a pulse or AC voltage excitation would be applied at a single point on the string; and (3) the transient or AC steady-state current response of the string would be measured at that point only. Each reactive component(s) associated with each device would be distinct in order to associate a unique time-dependent response with that device.
Using the known time-varying voltage excitation, the known values of inductance and/or capacitance, and the standard equation predicting the response for the known circuit configuration, the time-varying current response would be subjected to nonlinear regression analysis. In essence, this analysis would yield individual device resistances that result in a best fit between the predicted and actual time-varying current responses.
This work was done by Dan Hall of Lockheed Martin Corp. and Frank Davies of Hernandez Engineering, Inc. for 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-23623-1.