Battery SOC Initialization Using Internal Temperature and OCV
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Solution Overview
Problem
Conventional methods for setting the initial State Of Charge (SOC) of a battery in electric vehicles fail to accurately consider both internal and external temperature changes, leading to errors in SOC estimation, especially when the battery has not reached the Open Circuit Voltage (OCV) state.
Innovation Solution
A method that measures internal temperature changes over time after the battery transitions from a loaded to an unloaded state, constructing an SOC estimation table based on these measurements, and using this table to determine the initial SOC value, taking into account both internal and external temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the initial SOC value is set based on OCV assuming it is an absolute reference value, then the setting method is simple, but the SOC estimation accuracy deteriorates due to OCV changes according to temperature and aging
Solution Approach 1:
The patent changes the parameters used for SOC initialization from a single OCV-based approach to a multi-parameter approach including OCV, temperature (internal and external), and time. By considering how OCV varies with temperature and time, the system achieves more accurate SOC estimation without excessive complexity
Solution Approach 2:
The patent performs preliminary measurements of internal temperature, external temperature, and OCV immediately after load interruption, and uses these preliminary values along with time information to initialize SOC. This preliminary action captures the battery state before it fully stabilizes, enabling accurate SOC estimation without requiring long waiting periods
2Loss of time
If the SOC is initialized using OCV measured immediately after load interruption, then the initialization can be performed quickly, but errors occur because the voltage has not reached the stable OCV state
Solution Approach 1:
The system performs preliminary measurements of OCV, internal temperature, and external temperature immediately after load interruption. Instead of waiting for voltage stabilization, it uses these preliminary measurements combined with time information and thermal models to estimate SOC accurately within seconds
Solution Approach 2:
The patent introduces temperature measurements (both internal and external) and time as intermediary parameters that mediate between the immediate post-load state and the stable OCV state. These intermediaries allow the system to bridge the gap and estimate SOC accurately without waiting for full voltage stabilization
3Measurement precision
If the battery is allowed to reach stable OCV state before SOC initialization, then the SOC value is accurate, but the process requires waiting more than one hour which is impractical for hybrid vehicles
Solution Approach 1:
The system performs all necessary measurements (OCV, internal temperature, external temperature) as preliminary actions immediately after load interruption. Using these preliminary data points with time-based thermal models, it calculates SOC within seconds rather than requiring hours of waiting for voltage stabilization
Solution Approach 2:
The patent transitions from a static approach (waiting for voltage to stabilize) to a dynamic approach where SOC is estimated in real-time based on the rate of voltage change, temperature changes, and time. This dynamic estimation allows accurate SOC determination during the transient period without requiring the system to reach steady state
4Device complexity
If only external temperature is considered for SOC initialization, then the method is simpler, but the accuracy deteriorates because internal temperature changes are not accounted for
Solution Approach 1:
The patent uses external temperature as an intermediary to estimate internal temperature through thermal models. The external temperature sensor acts as an accessible mediator that provides information about the battery's thermal state, which is then used to infer the internal temperature and its effects on OCV and SOC
Solution Approach 2:
The patent replaces the need for direct internal temperature sensing (which would require complex mechanical/physical access to battery internals) with a thermal modeling approach. Using external temperature measurements and heat transfer models, it substitutes the mechanical complexity of internal sensing with computational thermal analysis
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
This approach enhances the accuracy of initial SOC value setup by considering the battery's internal and external temperature changes, preventing errors associated with disregarding these factors and ensuring a more precise SOC estimation.
Implementation Method 1
the voltage converges to the a stable unloaded voltage or the OCV after passage of predetermined time, usually more than one hour
Implementation Method 2
chemical reaction occurs in the battery when the battery is in a loaded state
Data Source
AI summary
Disclosed is a method for setting an initial SOC value, which initializes the SOC in consideration of not only the temperature change of the external environment of the battery but also the internal temperature change of the battery before the battery reaches a stable unloaded state, thereby enhancing the accuracy in the setup of the initial SOC value. The method includes: measuring internal temperatures of the battery and SOCs corresponding to voltages of the battery, which change according to the time passage after a loaded state is converted into an unloaded state, and constructing an SOC estimation table by using measured values, and storing the SOC estimation table; measuring the internal temperature and the voltage of the battery when estimation of an initial SOC value of the battery is required; and reading an SOC corresponding to the measured internal temperature and the voltage of the battery from the SOC estimation table.