Lithium Iron Phosphate Cell Open Circuit Voltage Equilibrium Mapping
Lithium iron phosphate open circuit voltage equilibrium maps two-phase hysteresis using multi-hour relaxation testing for state of charge estimation
Coulomb Counting Drift
Meaning
Continuous integration of current measurement noise over time causes progressive deviation in state of charge calculations. This systematic divergence is known as coulomb counting drift. It occurs because any offset in the current sensor is integrated continuously.
Error Accumulation
The integration of a small, constant bias in current sensor readings creates a linear deviation in the calculated remaining capacity. When a vehicle or storage system operates for long periods without resting, this offset goes uncorrected. The estimation discrepancy grows larger with each duty cycle, and the battery management system eventually loses track of the actual available energy.
This drift can result in unexpected power limitations or premature shutdown of the system.
Sensor Limitation
Electronic analogue-to-digital converters in current sensors possess inherent resolution limits and temperature-dependent offsets. Even high-precision shunt resistors or Hall-effect sensors suffer from thermal variance and electronic noise. These small errors are invisible in instantaneous readings but become significant when integrated over hours of continuous battery operation.
Correction Strategy
Periodic calibration resets the accumulated variance using stable open-circuit voltage measurements. When the battery rests for a sufficient duration, the system maps the measured voltage to a known state of charge. This reset operation eliminates the integrated current error and restores estimation accuracy.