Method for online battery AC impedance spectrum measurement using dc-dc power converter duty-cycle control

An online method of measuring battery AC impedance spectrum is presented in this paper. By adding a square wave perturbation to the steady-state value of the duty cycle of a boost power converter, AC impendence values can be devised from the responses of the battery voltage and current at the odd harmonics of the perturbation frequency. FFT analysis is applied to battery voltage and current to obtain the harmonic components, then the harmonic components of battery voltage and current can be used to calculate the battery AC impedance at these odd harmonics of perturbation frequency. The battery AC impedance measurement method of this paper allows for the measurement of battery impedance at several different frequencies in one single perturbation period. An experimental laboratory prototype is constructed to verify and validate the proposed online battery AC impedance spectrum measurement method.