Real-Time Measurement of Li-Ion Battery Cells Using Power Converter Pulse-Signal Injection and Fusion Methods

This article proposes a method to estimate the impedance of lithium-ion cells by using an excitation signal. The injection signal is intended to be delivered to the battery module by the power converter used for the interface of the energy storage and using the current and voltage measurements provided by the module battery management system (BMS). The estimation method is conducted in two steps. During the system commissioning, the impedance is estimated by using a frequency-domain method known as vector fitting. Despite its high accuracy, it has an important computational burden that makes it difficult to use in real-time applications running on the embedded systems often used for battery and converter control. For that reason, during the regular operation, a recursive least squares algorithm is proposed, being the initial estimation given by the frequency-domain method employed during the commissioning process. The discussion includes not only the description and testing of the method but also the effects due to the reduced digital-domain resolution of the acquired data used for the estimation (terminal current and cell voltage), as well as the discretization method used for the digital implementation. The proposal is validated by simulation and by experimental results using the cell measurements provided by a BMS of a commercial module.