An Empiric Approach to State of Charge Assessment and Range Estimation of an Electric Vehicle

The diffusion of electric vehicles depends on a multiplicity of reasons, technical, economic, and at the end, there is also the driver's range anxiety, the fear don't reaching the recharging plug. An aid to overtaking this fear can be done by knowing the battery state of charge; the driver needs an electrochemical gauge indicating, in real time, the remaining fraction of vehicle range. The electrochemical behavior of large capacity Li-ion cell has been studied during the operation on an electric car, recording intensiodynamic polarization curves at different points of the run test. Some characteristic features in the curves of the cell tested, have been found and related to the run distance. The series of polarization curves related to a discharge cycle characterize the behavior of a cell, with respect to the power deliverable and the effective voltage plateau in the experimented dynamic regime. The plot of cell voltage interpolated at zero current (ZCV) vs. distance also characterizes a cell in order to accomplish a gauge of state of charge; the attempts have done better results than the open circuit voltage (OCV) method. The "electrochemical gauge" warns in real time how long range is remaining.