  The open circuit voltage to the state of charge (OCVSOC) characteristic is
crucial for battery management systems. Using the OCV-SOC curve, the SOC and
the battery capacity can be estimated in real-time. Accurate SOC and capacity
information are important to carry out the majority of battery management
functionalities that ensure a safe, efficient, and reliable battery pack power
system. Numerous approaches have been reported in the literature for improved
SOC estimation and battery capacity estimation. These approaches focus on
various estimation and filtering techniques to reduce the effect of measurement
noise and uncertainties due to hysteresis and relaxation effects. Even though
all the existing approaches to SOC estimation rely on the OCV-SOC
characterization, little attention was paid to investigating the possibility of
errors in the OCV-SOC characterization and the effect of uncertainty in the
OCV-SOC curve on SOC and capacity estimates. In this paper, which is the first
part of a series of three papers, the effect of OCV-SOC modeling error in the
overall battery management system is discussed. The different sources of
uncertainties in the OCV-SOC curve include cell-to-cell variation, temperature
variation, aging drift, cycle rate effect, curve-fitting error, and
measurement/estimation error. The proposed uncertainty models can be
incorporated into battery management systems to improve their safety,
performance, and reliability.
