John L. Morrison

Real time estimation of battery impedance

Electrochemical impedance measurement systems use the Bode analysis technique to characterize the impedance of an electrochemical process. It is a well established and proven technique. The battery being evaluated is excited with a current that is single frequency and its response is measured. The process is repeated over a range of frequencies of interest until the spectrum of the impedance is obtained. The method is effective but time consuming, as the process is serial. A parallel approach using band width limited noise as an excitation current can obtain the same information in less time. The system response to the noise is processed via correlation and fast Fourier transform (FFT) algorithms and many such responses are averaged. The result is the spectrum of response over the desired frequency range. The averaging of many responses also makes this process somewhat serial. Another technique assembles the current noise waveform from a sum of sinusoids each at a different frequency. The system response as a time record is acquired and processed with the FFT algorithm. To reduce noise multiple time records of waveforms are processed and their resultant spectra averaged. This process is also serial. There is interest in real time acquisition of battery impedance for control and diagnostics over a limited frequency range. To support this need a true parallel approach is proposed that uses a single acquired time record of the battery response with duration compatible to a real time control process. The time record duration is the battery impedance sample period. If that sample period can be as short as 10s of seconds then, many control system algorithms can use battery impedance as a sensed variable

Development and test of a real time battery impedance estimation system

Electrochemical impedance measurement systems use the Bode analysis technique to characterize the impedance of an electrochemical process in a well-established and proven technique. The battery being evaluated is excited with a single frequency current and its response is measured. The process is repeated over a range of frequencies of interest until the spectrum of the impedance is obtained. The method is effective but time consuming, as the process is serial. A parallel approach using bandwidth limited noise as an excitation current can obtain the same information in less time. The system response to the noise is processed via correlation and fast Fourier Transform (FFT) algorithms and many such responses are averaged. The result is the spectrum of response over the desired frequency range. The averaging of many responses also makes this process somewhat serial. Another technique assembles the current noise waveform from a sum of sinusoids each at a different frequency. The system response as a time record is acquired and processed with the FFT algorithm. To reduce noise, multiple time records of waveforms are processed and their resultant spectra averaged. This process is also serial. There is interest in real-time acquisition of battery impedance for control and diagnostics over a limited frequency range. To support this need, a true parallel approach has been developed by Montana Tech of the University of Montana (Montana Tech) that uses a single acquired time record of the battery response with duration compatible to a real-time control process. The system uses custom-designed instrumentation integrated with a National Instruments Data Acquisition System. The system excites a test battery with current and acquires a time record of the voltage response. The time record of data is processed with a Montana Tech-developed algorithm to yield a frequency spectrum of the test batteries impedance

Universal auto-calibration for a rapid battery impedance spectrum measurement device

Electrochemical impedance spectroscopy has been shown to be a valuable tool for diagnostics and prognostics of energy storage devices such as batteries and ultra-capacitors. Although measurements have been typically confined to laboratory environments, rapid impedance spectrum measurement techniques have been developed for on-line, embedded applications as well. The prototype hardware for the rapid technique has been validated using lithium-ion batteries, but issues with calibration had also been identified. A new, universal automatic calibration technique was developed to address the identified issues while also enabling a more simplified approach. A single, broad-frequency range is used to calibrate the system and then scaled to the actual range and conditions used when measuring a device under test. The range used for calibration must be broad relative to the expected measurement conditions for the scaling to be successful. Validation studies were performed by comparing the universal calibration approach with data acquired from targeted calibration ranges based on the expected range of performance for the device under test. First, a mid-level shunt range was used for calibration and used to measure devices with lower and higher impedance. Next, a high-excitation current level was used for calibration, followed by measurements using lower currents. Finally, calibration was performed over a wide frequency range and used to measure test articles with a lower set of frequencies. In all cases, the universal calibration approach compared very well with results acquired following a targeted calibration. Additionally, the shunts used for the automated calibration technique were successfully characterized such that the rapid impedance measurements compare very well with laboratory-scale measurements. These data indicate that the universal approach can be successfully used for onboard rapid impedance spectra measurements for a broad set of test devices and range of measurement conditions.

Heat Transfer Model for an RF Cold Crucible Induction Heated Melter

A method to reduce radioactive waste volume that includes melting glass in a cold crucible radio frequency induction heated melter has been investigated numerically. The purpose of the study is to correlate the numerical investigation with an experimental apparatus that melts glass in the above mentioned melter. A model has been created that couples the magnetic vector potential (real and imaginary) to a transient startup of the melting process. This magnetic field is coupled to the mass, momentum, and energy equations that vary with time and position as the melt grows. The coupling occurs with the electrical conductivity of the glass as it rises above the melt temperature of the glass and heat is generated. Natural convection within the molten glass helps determine the shape of the melt as it progresses in time. An electromagnetic force is also implemented that is dependent on the electrical properties and frequency of the coil. This study shows the progression of the melt shape with time along with temperatures, power input, velocites, and magnetic vector potential. A power controller is implemented that controls the primary coil current so that the power induced in the melt does not exceed 60 kW. The coupling with the 60 kW generator occurs with the impedance of the melt as it progresses and changes with time. With a current source of 70 Amps (rms) in the primary coil and a frequency of 2.6 MHz, the time to melt the glass takes 0.8 hours for a crucible that is 10 inches in diameter and 10 inches high.Copyright