SOC Estimation Using Segmented Charging and Discharging Curves
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Solution Overview
Problem
Secondary batteries with silicon-based negative-electrode active materials exhibit increased hysteresis on the SOC-OCV curve, leading to low SOC estimation accuracy when relying solely on open-circuit voltage (OCV) based methods, as charging and discharging curves diverge significantly.
Innovation Solution
A battery system and SOC estimation method that utilize both discharging and charging curve lines to set initial SOC values, considering the influence of hysteresis and polarization, by determining whether the SOC change is caused by hysteresis or polarization, and adjusting the initial SOC value accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is used as negative-electrode active material to increase energy density, then full-charge capacity is increased, but hysteresis on the SOC-OCV curve is increased
Solution Approach 1:
The SOC-OCV curve is segmented into two separate curves: a discharging curve line for discharge processes and a charging curve line for charge processes. This segmentation allows the system to select the appropriate curve based on the current operational state, thereby resolving the hysteresis issue caused by using a single curve for both charging and discharging.
Solution Approach 2:
The system dynamically determines whether the battery is in a charge or discharge state and switches between the discharging curve line and charging curve line accordingly. This dynamic adaptation enables accurate SOC estimation that accounts for the direction of current flow and the associated hysteresis effects.
2Device complexity
If SOC is estimated from OCV using a single SOC-OCV curve, then the estimation method is simple, but SOC estimation accuracy is low when hysteresis exists
Solution Approach 1:
The system dynamically determines whether the battery is in a charge or discharge state and switches between the discharging curve line and charging curve line accordingly. This dynamic adaptation enables accurate SOC estimation that accounts for the direction of current flow and the associated hysteresis effects.
Solution Approach 2:
The controller acts as an intermediary that determines the operational state (charge or discharge) and selects the appropriate curve line. This intermediary function resolves the contradiction by introducing a decision-making layer that chooses the most accurate curve based on current conditions, rather than using a single static curve.
3Ease of manufacture
If only OCV-based SOC estimation is used, then the estimation method is simple and inexpensive, but accuracy is insufficient for batteries with significant hysteresis
Solution Approach 1:
The SOC-OCV curve is segmented into two separate curves: a discharging curve line for discharge processes and a charging curve line for charge processes. This segmentation allows the system to select the appropriate curve based on the current operational state, thereby resolving the hysteresis issue caused by using a single curve for both charging and discharging.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Improves SOC estimation accuracy by accounting for hysteresis and polarization effects, enhancing the reliability of SOC estimation in secondary batteries with silicon-based materials.
Implementation Method 1
a discharging curve line (a discharging curve) representing a SOC-OCV characteristic when the secondary battery is discharged, and a charging curve line (a charging curve) representing a SOC-OCV characteristic when the secondary battery is charged
Data Source
AI summary
An ECU sets a SOC estimated from an OCV at the time of activating a system of a vehicle as an initial SOC value in the case where the SOC during a stop of the system is higher than a first SOC, which represents the SOC estimated from the OCV at the time of activating the system by using a discharging curve line, or the SOC during the stop of the system is lower than a second SOC, which represents the SOC estimated from the OCV at the time of activating the system by using a charging curve line. The ECU sets the SOC during the stop of the system as the initial SOC value in the case where the SOC during the stop of the system is equal to or lower than the first SOC and is equal to or higher than the second SOC.