Online Impedance Measurement of Lithium-Ion Battery : Applying Broadband Injection with Specified Fourier Amplitude Spectrum

Abstract

State parameters such as the state-of-charge (SOC) and state-of-health (SOH) play important role in the operation of Li-ion batteries, and accurate estimate of the parameters is of prime importance in evaluating the battery condition and guaranteeing the safe use. While it is difficult to measure the SOC and SOH directly, the battery internal impedance can be used to obtain the parameters. Recent studies have shown methods based on pseudo-random binary sequence (PRBS) with which the battery impedance can be rapidly measured in real time. Using this method, the battery is charged and recharged according to the excitation waveform and Fourier methods are applied to obtain the impedance. The PRBS often produces accurate impedance measurements, but the method may require a high perturbation amplitude, which may easily interfere with the nominal battery operation and create nonlinear distortions. This paper proposes the use of discrete-interval-binary sequence (DIBS) for measuring the battery impedance. The DIBS is a computer-optimized binary sequence in which the power spectral densities are maximized at specified frequencies without increasing the signal time-domain amplitude. Experimental measurements of a commercial Li-ion battery are presented to demonstrate the effectiveness of the proposed method.