Pseudo Random Binary Sequence Technique for Li-ion Cell Parameter Extraction /

Abstract

This Thesis deals with impedance measurement of Li-ion Batteries using White noise like Pseudo Random Binary Sequence (PRBS), Battery Parameters like State of Charge, State of Health and Remaining useful life can be calculated using battery impedance, but it is quite difficult to extract on-board, it is possible to extract impedance of battery using Excitation signal like PRBS, using this PRBS method simulations and experiments are performed with different set of batteries and using different set of PRBS signals, A different set of approach is used in this experiment this technique uses Randles’ equivalent battery model in Simscape MATLAB, Battery parameters including series resistance, charge transfer resistance and double layer capacitance are found through Electrochemical Impedance spectroscopy. Input current is fed as square charging and discharging pulses. Battery has dynamic behavior in which all parameters in a battery tends to change with temperature and its operating conditions, that change in parameters predict a battery’s life and other characteristics. Hardware is also built to perform the experiment using different sets of battery with predefined impedance to verify our results in simulations using excitation signal. It is calculated that using excitation signal like PRBS can generate a electrochemical impedance spectrum in limited frequency range like any high quality laboratory impedance analyzer. This method of calculating Impedance is suitable for many applications with different temperature and charge. Impedance calculations are performed in low frequency signal to obtain best results, usage of high frequency PRBS signals is found to be difficult to obtain impedance in this experiment. Hardware combination comprises of PCB, a FPGA, and a battery cell. Hardware is capable of estimating battery impedance using Pseudo Random Bit Sequence PRBS signals and monitor State of charge of a battery without disconnecting it form its circuit. PRBS signal is fed to battery and monitor its voltage curve which on further processing gives its internal impedance. This impedance plays a crucial role in estimating battery state of health and its remaining useful life.