State of Charge Tracking Corrections under Battery Open Circuit Hysteresis
Dynamic hysteresis state expansion in Kalman filters fixes open circuit voltage tracking errors, maintaining state of charge accuracy across flat plateau chemistries.
Temperature Dependent Hysteresis
Meaning
Phenomenon where the path dependent relationship between variables shifts in response to changes in thermal energy. Engineers account for temperature dependent hysteresis when modeling the voltage of lithium iron phosphate cells, which show different lag effects at freezing versus room temperatures. This behavior occurs because the speed of phase transitions and ion diffusion is thermally activated.
The presence of these shifts means that a single mathematical curve cannot accurately describe the battery at all operating points.
Kinetic Variation
Rate of chemical reactions within the electrode material increases as the environment warms. In systems with temperature dependent hysteresis, the width of the voltage loop typically narrows as the temperature rises. This change happens because the internal resistance drops and the ions move more freely through the lattice.
Accurate models must use coefficients that are functions of the measured temperature.
Estimation Error
Neglecting the thermal influence on the voltage lag leads to notable inaccuracies in fuel gauging. If the software assumes a fixed loop, the state of charge reading will drift as the battery heats up during use. This discrepancy is particularly problematic in outdoor applications like solar storage or electric bikes.
Calibration Process
Developing a resilient model requires extensive testing at multiple thermal setpoints in a laboratory. Data collected during these tests informs the lookup tables or equations used for temperature dependent hysteresis in the final product.