Apparatuses and methods for testing electrochemical cells by measuring frequency response
First Claim
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1. A method of estimating an impedance of a device to be measured, comprising:
- generating a stimulus signal comprising a summation of two or more sinusoidal signals at different frequencies with a frequency step factor therebetween;
advancing the stimulus signal by one sample-time step;
applying the advanced stimulus signal to the device to be measured with an impedance measurement device;
detecting a response signal with the impedance measurement device, the response signal comprising a response of the device to be measured to the advanced stimulus signal; and
estimating the impedance of the device to be measured using a sum-of-sines analysis of the response signal; and
calibrating the impedance measurement device before applying the advanced stimulus signal by;
pre-emphasizing a magnitude and phase of each of the two or more sinusoidal signals;
applying the advanced and pre-emphasized stimulus signal to one or more shunt impedances at a known Root Mean Square (RMS) current;
detecting a current calibration response signal of the one or more shunt impedances with the impedance measurement device;
determining calibration coefficients from the current calibration response signal;
scaling the magnitude of calibration coefficients to each of the two or more sinusoidal signals to an RMS value less than or equal to the known RMS current; and
applying the calibration coefficients to each of the two or more sinusoidal signals.
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Abstract
Real-time battery impedance spectra are acquired by stimulating a battery or battery system with a signal generated as a sum of sine signals at related frequencies. An impedance measurement device can be used to interface between the battery system and a host computer for generating the signals. The impedance measurement device may be calibrated to adapt the response signal to more closely match other impedance measurement techniques. The impedance measurement device may be adapted to operate at mid-range voltages of about 50 volts and high-range voltages up to about 300 volts.
146 Citations
25 Claims
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1. A method of estimating an impedance of a device to be measured, comprising:
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generating a stimulus signal comprising a summation of two or more sinusoidal signals at different frequencies with a frequency step factor therebetween; advancing the stimulus signal by one sample-time step; applying the advanced stimulus signal to the device to be measured with an impedance measurement device; detecting a response signal with the impedance measurement device, the response signal comprising a response of the device to be measured to the advanced stimulus signal; and estimating the impedance of the device to be measured using a sum-of-sines analysis of the response signal; and calibrating the impedance measurement device before applying the advanced stimulus signal by; pre-emphasizing a magnitude and phase of each of the two or more sinusoidal signals; applying the advanced and pre-emphasized stimulus signal to one or more shunt impedances at a known Root Mean Square (RMS) current; detecting a current calibration response signal of the one or more shunt impedances with the impedance measurement device; determining calibration coefficients from the current calibration response signal; scaling the magnitude of calibration coefficients to each of the two or more sinusoidal signals to an RMS value less than or equal to the known RMS current; and applying the calibration coefficients to each of the two or more sinusoidal signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of estimating an impedance of a device to be measured, comprising:
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generating a stimulus signal comprising two or more sinusoidal signals at different frequencies with a frequency step factor therebetween; determining a final buck voltage by; comparing a buck voltage to a bias voltage comprising a voltage of the device to be measured; modifying the buck voltage; continuously repeating the comparing and modifying of the buck voltage until the comparison is within an error tolerance; and once within the error tolerance, maintaining the buck voltage as the final buck voltage; and after determining the final buck voltage; applying the stimulus signal to the device to be measured to develop a response signal, the response signal comprising a response of the device to be measured to the stimulus signal and including the bias voltage; continuously comparing the final buck voltage to the response signal to develop a bias-removed response signal comprising the response signal with the final buck voltage subtracted out; and estimating the impedance of the device to be measured responsive to the bias-removed response signal using the impedance measurement device. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. An impedance measurement device, comprising:
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a processor; a data acquisition system; a sum-of-sines generator for generating a stimulus signal to be applied to a device to be measured, the stimulus signal including a summation of two or more sinusoidal signals at different frequencies with a frequency step factor therebetween; and a preamplifier for; detecting a bias voltage comprising a voltage of the device to be measured; receiving a buck voltage; applying the stimulus signal to the device to be measured; and detecting a response signal comprising a response of the device to be measured to the stimulus signal and including the bias voltage; and wherein one or more of the processor and the data acquisition system are configured to; perform the functions of the sum-of-sines generator; determine a final buck voltage by; comparing the buck voltage to the bias voltage; modifying the buck voltage; continuously repeating the comparing and modifying of the buck voltage until the comparison is within an error tolerance; and once within the error tolerance, maintaining the buck voltage as the final buck voltage; continuously apply the final buck voltage to the preamplifier to subtract the final buck voltage from the response signal to generate a bias-removed response signal; and estimate the impedance of the device to be measured responsive to the bias-removed response signal. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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25. An impedance measurement device comprising:
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a processor; a data acquisition system; a sum-of-sines generator for generating a stimulus signal to be applied to a device to be measured, the stimulus signal including a summation of two or more sinusoidal signals at different frequencies with a frequency step factor therebetween; a preamplifier configured to interface to the device to be measured with the stimulus signal, a response of the device to be measured, and a final buck voltage as high-range voltages and for; detecting a bias voltage comprising a voltage of the device to be measured; supplying the final buck voltage matching the bias voltage; applying the stimulus signal to the device to be measured; and detecting a response signal comprising a response of the device to be measured to the stimulus signal and including the bias voltage; and a circuit combination including a coupling capacitor, and two or more relays configured for interfacing to the high-range voltages such that; one or more first relays close to charge the coupling capacitor to the high-range voltage of the device to be measured while a second relay isolates the impedance measurement device from the coupling capacitor; after the coupling capacitor is charged, the second relay closes to couple the impedance measurement device to the coupling capacitor to apply the stimulus signal; and after the sampling of the response signal, the one or more first relays open to decouple the device to be measured from the coupling capacitor; wherein one or more of the processor and the data acquisition system are configured to; perform the functions of the sum-of-sines generator; continuously apply the final buck voltage to the preamplifier to subtract the final buck voltage from the response signal to generate a bias-removed response signal; and estimate the impedance of the device to be measured responsive to the bias-removed response signal.
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Specification