Device and Method for Estimating State of Charge Based on Battery Voltage in a Steady State

SoC Estimation Device Combining Voltage Gradient-Based Steady-State Determination and Current-Specific Reference Curve Matching

This technology determines the steady state of a battery by analyzing the stabilization of internal lithium-ion concentration, the elapsed time following current fluctuations, and the gradient of the measured voltage, subsequently estimating the State of Charge (SoC) using current and voltage data at that specific point.

Accurate SoC estimation typically requires Open Circuit Voltage (OCV) measurement. However, in real-world operating environments, it is difficult to secure sufficient rest periods, leading to estimation errors caused by the effects of overvoltage.

This technology establishes reference information under maximum and minimum current conditions in advance. It identifies the steady-state point after current changes—once lithium-ion diffusion has concluded—and calculates the SoC by comparing the measured values at that moment against the reference data. Applicable to EV BMS, ESS operation systems, and power tool battery pack indicators, it provides highly reliable remaining capacity information by filtering out overvoltage distortion, even during continuous operation without rest periods.

‍

‍

Key Features:

• A battery measurement unit that measures battery voltage and current, and a storage unit that stores reference information representing voltages for different states of charge.
• A steady-state determination unit that identifies a steady state when the measured gradient, based on the voltage difference between the measurement time and a subsequent interval, matches a reference gradient within a set range.
• An SoC determination unit that extracts the state of charge corresponding to the voltage closest to the measured voltage from the reference information matched to the measured current at the steady-state point.
• A reference information generation unit that creates multiple sets of reference information for arbitrary currents using reference information from maximum and minimum current conditions.

‍