Broadband Identification of Battery Electrical Impedance for Hev

Electrical impedance measurements provide useful information about the characteristics of a Li-ion battery. The classical method of measurement consists in performing an impedance spectroscopy relying on offline records of the response of the battery to a controlled current or voltage test signal. This method is robust but presents an important drawback: it is very time consuming, especially for low frequency measurements. In order to overcome this problem and to address embedded applications, we propose to apply broadband excitation signals to perform such impedance measurements. Spectral coherence is an advanced parameter estimated in order to define the frequency bands where the transfer function of a system is accurately identified. The calculation of this parameter can also assess the normalized random errors on both magnitude and phase of the identified impedance since they are related by an explicit mathematical expression. After a brief review of some signal processing tools for identification with broadband excitation signals, we apply this method to identify the impedance of a Liion battery and compare performances of various identification patterns on noisy simulated and experimental data. Keywords— battery impedance, spectroscopy, broadband signals, Li-ion battery, spectral coherence, confidence limits, identification.