Realtime Internal-Impedance Measurement of Lithium-ion Battery Using Discrete-Interval-Binary-Sequence Injection

Internal impedance of a Lithium-ion (Li-ion) battery is an important parameter in evaluating the battery characteristics such as the state-of-charge (SOC) and state-of-health (SOH). Recent studies have shown broadband methods based on pseudo-random binary sequence (PRBS) and Fourier techniques with which the battery impedance can be accurately and rapidly measured in real time. Applying the conventional PRBS requires, however, a relatively high injection amplitude that may easily interfere with the normal battery operation and produce nonlinear distortions. This paper proposes the use of a discrete-interval-binary sequence (DIBS) for a battery impedance measurement. The DIBS is a computer-optimized binary sequence in which the energy is maximized at specified harmonic frequencies to minimize the required level of signal injection. Otherwise the DIBS has the same attractive characteristics as the conventional PRBS. Experimental results based on a commercial Li-ion battery are presented to demonstrate the effectiveness of the proposed method.