Improved Impedance Measurements for Electric Vehicles with Reconfigurable Battery Systems

Embedding impedance spectroscopy into onboard applications such as electric vehicles increases the diagnostic capabilities of battery management systems largely. A novel approach is presented and experimentally investigated throughout this work, whereby the load current excitation injected by the electric powertrain is pulsed by transistors. With a reconfigurable battery system, this form of active impedance spectroscopy can be used without further hardware. To obtain high-quality impedance data, a broadband data processing algorithm in the frequency domain is employed that deals inherently with both pulsing and non-pulsing data. An experimental setup is constructed to evaluate the proposed methods under real world conditions and the measurement results are in great accordance with laboratory reference measurements. Finally, a linear regression model acts as filter to suppress outliers, smooth the impedance spectra and thus describe the time-varying impedance of each cell.