An Electrochemical Impedance Spectroscopy Technique for Battery Packs with Modular Dual Active Bridge Converter Based Active Balancers

In this paper, an electrochemical impedance spectroscopy technique is presented for series connected batteries with modular bidirectional dual-active-bridge converter based active balancers. Each battery is connected to a modular bidirectional dual-active-bridge converter to transfer charge to other batteries in the series connected string. The dual-active-bridge converters are coupled together through a common dc bus link enabling non-neighbour charge transfer. The electrochemical impedance spectroscopy capability is integrated in the active balancer by introducing a sinusoidal perturbation in the dc bus reference signal of one of the dual-active-bridge converters in the string. A PI controller is used to regulate the sinusoidal voltage perturbation to 10 mVpp in the battery voltage and the corresponding sinusoidal perturbation in the battery current is measured. The voltage and current perturbation signals are then used to calculate the impedance of the battery at desired frequencies and to draw a Nyquist plot. The simulation results presented in this paper for electrochemical impedance spectroscopy and active balancing are promising, and establish the effectiveness of the proposed technique.