Implementation Techniques for Online Impedance Measurement of Li-Ion Batteries

Li-ion batteries have become dominant energy storage technologies in various industrial and consumer products in recent years. Onboard monitoring of state parameters is an important task in order to ensure a safe and optimal operation of Li-ion battery applications. The battery internal impedance have been shown to give useful information about the states of the battery. Recent studies have demonstrated broadband methods such as the pseudo-random binary sequence (PRBS) to rapidly and accurately measure the battery internal impedance. In the method, a charging and discharging excitation is applied to the battery and Fourier methods are applied to compute the spectral information of the impedance. The excitation injection process plays an important role in the performance of the method. This paper presents three methods of injecting the excitation into the Li-ion battery for online impedance measurement. Experimental results based on a commercial Li-ion battery cell are presented to demonstrate the advantages and disadvantages of each method.