Battery Core Temperature Estimation Using Ohmic Resistance and Thermal Transfer
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Solution Overview
Problem
Accurately estimating the core temperature of battery cells in hybrid or electric vehicles is challenging due to the discrepancy between surface and core temperatures, making existing methods unreliable and expensive.
Innovation Solution
A method that independently estimates core temperature using parameters such as terminal current, terminal voltage, ohmic resistance, and state of charge, with a weighting factor applied to combine fast and slow estimations based on thermal energy transfer, allowing for real-time dynamic core temperature determination without relying on surface temperature measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensor is placed in the core of the cell to measure core temperature, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses surface temperature measurements as an intermediary to indirectly estimate core temperature. Instead of placing sensors directly in the cell core, the system measures surface temperature and uses thermal diffusion models to calculate the core temperature, thereby avoiding the complexity of core sensor placement while still achieving accurate core temperature estimation.
Solution Approach 2:
The patent replaces the mechanical/physical approach of direct core temperature sensing with a computational approach. By using thermal diffusion equations and surface temperature measurements, the system substitutes physical sensor placement with mathematical modeling to achieve core temperature estimation.
2Device complexity
If surface temperature is measured to estimate core temperature, then device complexity is reduced, but measurement precision deteriorates due to temperature gradient between surface and core
Solution Approach 1:
The patent implements a feedback mechanism where surface temperature measurements continuously inform the core temperature estimation model. The system uses the measured surface temperature as input to the thermal diffusion model, which then provides corrected core temperature estimates that account for the temperature gradient, effectively using feedback to maintain precision despite the indirect measurement approach.
Solution Approach 2:
The patent transforms the measurement parameter from direct core temperature to surface temperature, and then uses mathematical transformation (thermal diffusion modeling) to convert this parameter change back into accurate core temperature information. This parameter transformation approach allows the system to measure what is easily accessible (surface temperature) while obtaining what is needed (core temperature).
3Reliability
If thermal conduction-based estimation is used to determine core temperature, then reliability is improved by accounting for heat transfer, but response time increases due to thermal inertia
Solution Approach 1:
The patent applies dynamic weighting to the estimation process, where the contribution of thermal conduction-based estimation varies over time. During transient conditions, the system reduces the weight of thermal conduction estimation to respond faster, while during steady-state conditions, it increases the weight to improve reliability. This dynamic adjustment resolves the contradiction between response time and reliability.
4Measurement precision
If weighting factors are applied to combine multiple estimations, then measurement precision is improved, but device complexity increases due to additional calculations
Solution Approach 1:
The patent changes the parameters used for weighting from complex multi-variable functions to simpler parameters such as ambient temperature variation and air flow rate. This parameter simplification maintains the ability to adjust estimation precision while reducing the computational complexity of determining the weighting factors.
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 provides a reliable and cost-effective means to accurately estimate core temperatures in real-time, enhancing battery performance, fuel economy, and longevity by correcting for thermal energy transfer and ambient conditions.
Implementation Method 1
The increasing demand to improve vehicular fuel economy and reduce vehicular emissions has led to the development of both hybrid vehicles and pure electric vehicles. Pure electric vehicles may be powered by a battery pack
Implementation Method 2
performing a second estimation of the core temperature as a function of thermal energy transfer through the battery
Implementation Method 3
the weighting factor is determined as a function of ambient temperature variation and air flow rate
Data Source
AI summary
Methods and systems for dynamically estimating the core temperature of at least one cell in a battery. In one aspect, the method includes using a combination of estimations including one based on ohmic resistance and another based on a function of thermal energy transfer through the battery. A weighting factor may be used for each of the estimations as a way to calculating a core temperature. The estimation based on ohmic resistance may be made determined independently of a measured surface temperature of the battery or any of the cells in the battery.