Hybrid Vehicle Battery SOC Estimation via Temperature and Current Integration
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Solution Overview
Problem
Existing methods for estimating the state of charge of batteries in hybrid-electric vehicles are inaccurate due to temperature variations and the reduction in battery capacity from repeated charging and discharging cycles, especially when considering driving conditions.
Innovation Solution
A method and apparatus that measure temperature and open circuit voltage to estimate the initial state of charge, and integrate electric current to account for capacity decrements over cycles, using a controller, temperature sensor, voltage meter, and current meter to calculate the state of charge accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the state of charge is estimated using open circuit voltage before the vehicle is driven, then the estimation is simple and quick, but the accuracy deteriorates because open circuit voltage changes according to temperature
Solution Approach 1:
The patent applies parameter changes by introducing temperature as a variable parameter that modifies the open circuit voltage characteristics. Different temperature conditions have corresponding different open circuit voltage parameters stored in memory, allowing the system to select the appropriate parameters based on measured temperature, thus maintaining accuracy while using the simple open circuit voltage method
Solution Approach 2:
The patent uses preliminary action by pre-storing multiple sets of open circuit voltage parameters corresponding to different temperatures in memory before actual use. When temperature is measured, the system quickly retrieves the appropriate parameters without real-time calculation, achieving both speed and accuracy
2Speed
If the state of charge is estimated using voltage during vehicle operation, then real-time monitoring is possible, but accuracy deteriorates because voltage instantaneously lowers during rapid acceleration regardless of state of charge
Solution Approach 1:
The patent applies dynamics by transitioning from a static voltage-based estimation method to a dynamic method that integrates current over time. The system continuously monitors current and accumulates it to calculate state of charge changes, adapting to varying operating conditions including rapid acceleration without being affected by instantaneous voltage drops
3Measurement precision
If the state of charge is estimated using discharging capability, then accurate state of charge can be obtained, but device complexity increases due to complicated algorithms required for different loading conditions
Solution Approach 1:
The patent extracts the essential factor for state of charge estimation - the integrated current - from the complicated discharging capability test. By removing the need for complex loading condition algorithms and focusing only on current integration, the system achieves accurate state of charge estimation with minimal complexity
Solution Approach 2:
The patent changes the estimation approach from measuring discharging capability under various loading conditions to simply integrating current over time. This parameter change from complex multi-condition testing to simple time-integrated current measurement reduces algorithm complexity while maintaining accuracy
4Device complexity
If battery capacity is not considered in state of charge estimation, then the calculation is simple, but accuracy deteriorates because output and total capacity decrease according to charging and discharging cycles
Solution Approach 1:
The patent uses preliminary action by pre-determining the relationship between charging/discharging cycles and capacity reduction. The system calculates cumulative charged and discharged current to estimate cycle number, then applies the corresponding capacity reduction factor from pre-established data, achieving accurate state of charge estimation without complex real-time capacity monitoring
Data Source
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AI summary
Disclosed are an apparatus and a method for accurately estimating a state of charge of a battery, which can measure a change of temperature and an open circuit voltage so as to estimate the state of charge at an initial time when a vehicle is not driven, and while measuring a decrement in a capacity of a battery according to charging and discharging of the battery when the vehicle is driven. The method includes the steps of: measuring a temperature in an initial estimation of the state of charge; measuring an open circuit voltage; obtaining parameters indicating a change of the open circuit voltage according to a change of temperature; and calculating the state of charge using the parameters and the open circuit voltage which is measured depending on the obtained parameters. The method further includes the steps of: measuring electric current in order to integrate the electric current during an estimation of the state of charge after initial time; calculating a decrement in capacity of the battery according to cycles; and estimating the state of charge by dividing a value, which is obtained by integrating electric current, by the decrement in the capacity of the battery according to the cycles.