Sensorless Temperature Measurements for Advanced Battery Management Systems

Abstract

Li-ion batteries have drawn considerable attention in the last decades due to the fact that these devices have a relative high energy density, long cycle life and low self-discharge rate. However, challenges are met in monitoring and controlling the states of a Li-ion battery, such as State of Charge, State of Health and temperature. In this thesis a new method is proposed in order to measure the (internal) battery temperature of Li-ion batteries through the so-called intercept frequency. The intercept frequency can be determined by measuring the battery impedance. After determining the intercept frequency, it can be related to the (internal) temperature. However, it turns out that some measurement issues arise when this new method is applied in, for example, electric vehicles. Impedance measurements in these typical applications are heavily disturbed by electric components and crosstalk, resulting in inaccurate temperature indications. In this thesis these disturbances are comprehensively described and solved in order to accurately measure the battery temperature. Furthermore, the impedance of both battery electrodes has been measured by the application of reference electrodes. The application of reference electrodes makes it possible to measure the intercept frequency of both electrodes and, subsequently, to determine which electrode is responsible for the intercept frequency behaviour of the total battery.