Trend Removal in Measurements of Best Linear Time-Varying Approximations—With Application to Operando Electrochemical Impedance Spectroscopy

Equilibria evolving over time, also called trends, are often present in ongoing measurements of real-life systems. These trends considered as disturbances when computing the best linear time-varying approximation (BLTVA) system. Current techniques for dealing with BLTVA consist modeling trend a finite number basis functions. However, dominant cannot always be captured well enough by this set functions, and hence, uncertainty on increases. As consequence, one loses low-frequency information. In article, state-of-the-art method estimating is extended removing differencing operator. It shown that novel technique, information becomes more visible. Moreover, decreases variance allows to measure fewer periods. Hence, technique improves route treating arbitrary out-of-equilibrium or operando, measurements. an illustration, it applied operando impedance three electrochemical processes: charging Li-ion battery cell, electrorefining copper, anodizing aluminum.