An online battery impedance spectrum measurement method with increased frequency resolution

This paper presents a perturbation method in order to increase the frequency resolution when measuring the online battery impedance spectrum based on a previously proposed method that utilizes closed-loop control of DC-DC power converter. By adding pulse waveform perturbation to the output voltage reference of power converter, the responses of battery voltage and current contain harmonic components at the odd and the even harmonics of perturbation frequency and not only the odd harmonic components. Discrete fast Fourier (DFT) or fast Fourier transform (FFT) analysis is applied to battery voltage and current to extract the harmonic components. Then based on Ohm's law, the harmonic components can be used to calculate battery impedance at different frequencies. The high frequency resolution of the battery impedance spectrum measurement of this paper enables to obtain impedance at frequencies of interest with shorter time and under the same conditions of operation. The presented method is verified using a proof-of-concept experimental prototype.