Battery Impedance Measurement Using Sinusoidal Ripple Current Emulator

Battery impedance measurements are directly correlated with the internal thermal rise and lifetime of rechargeable Li-ion batteries. The ac impedance measurement is not only reflects the battery state of health, but also a crucial parameter for a charging control strategy to reduce the internal thermal rise. The battery ac impedance is achieved with a battery charger by injecting ac ripple current and measuring the ac voltage response with the sinusoidal ripple current (SRC) charging technique. The digital signal processor is used to extract the battery ac ripple content and calculate the impedance magnitude and phase angle. However, it has computational burden due to many signal transformation steps, extracting the ac ripple content, creating the virtual α-β frame for separating the impedance phase angle, and computational complexity with limited ADC sensing range between 0 to 3 V at 12-bit resolution. The battery online impedance measurement using SRC emulator is describes in this thesis. To perform the battery impedance measurement, the hardware implementation of a 16-channel filter sensing board (FSB) is proposed for extracting the battery ac ripple current and voltage response. In addition, impedance calculation algorithm is also developed by dSPACE1104 for calculating the battery impedance magnitude and phase angle. The experiment was performed by charging a 12.8 V, 40 Ah Li-ion battery at C/8 rate in CC mode with perturb ± 1 Aac ripple current, and the battery ac impedance was measured by sweeping the ripple frequency from 20 Hz to 2 kHz.