Battery Equivalent Circuit Parameter Estimation Under Current Variation
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Solution Overview
Problem
Existing methods for estimating battery state of charge (SOC) and internal resistance are inaccurate due to variations in resistance with current magnitude, particularly at low temperatures, necessitating consideration of current information for improved accuracy.
Innovation Solution
A parameter estimation apparatus and method that includes an acquisition unit for acquiring battery information, a parameter estimation unit to estimate equivalent circuit model parameters using current, temperature, and SOC, and a correction unit to refine predetermined values based on measured resistance, estimating open circuit voltage (OCV), DC and AC component voltages, and terminal voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional EKF-based methods using equivalent circuit model are used for SOC estimation, then the estimation process can be implemented, but the accuracy deteriorates due to variations in internal resistance with current magnitude especially at low temperatures
Solution Approach 1:
The patent applies parameter changes by modifying the equivalent circuit model to include current-dependent resistance parameters. Specifically, the internal resistance is expressed as a function of current magnitude (R = R0 + R1*|I| + R2*|I|^2), allowing the model parameters to adapt dynamically based on operating conditions, thereby resolving the contradiction between implementation feasibility and estimation accuracy
Solution Approach 2:
The patent implements dynamics by transitioning from static resistance values to dynamic resistance calculations that continuously adapt to changing current conditions. The resistance parameters are updated in real-time based on the measured current magnitude, enabling the system to respond to varying operational states and maintain accuracy across different temperature and current conditions
2Device complexity
If battery parameters are estimated based only on temperature and SOC, then the estimation process is simplified, but the accuracy deteriorates due to ignoring current influence on internal resistance
Solution Approach 1:
The patent applies preliminary action by pre-defining the functional relationship between resistance and current magnitude in the equivalent circuit model. The resistance parameters (R0, R1, R2) are predetermined based on battery characteristics, allowing the system to quickly calculate accurate resistance values without complex real-time optimization, thus maintaining simplicity while improving accuracy
Solution Approach 2:
The patent implements feedback by using the measured current magnitude to continuously update the resistance parameters in the equivalent circuit model. The current information feeds back into the resistance calculation (R = R0 + R1*|I| + R2*|I|^2), creating a closed-loop system that automatically adjusts parameters based on actual operating conditions, thereby improving accuracy without significantly increasing system complexity
Data Source
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AI summary
The parameter estimation apparatus according to an embodiment disclosed in this document may include an acquisition unit configured to acquire battery information comprising current, temperature, and state of charge of a battery unit, and a parameter estimation unit configured to estimate parameters of an equivalent circuit model for the battery unit based on the battery information, wherein the equivalent circuit model may include a first resistor, a second resistor connected in series with the first resistor, and a capacitor connected in parallel with the second resistor, and the parameter estimation unit may estimate the resistance of the first resistor among the parameters by inputting the current of the battery unit into an equation comprising at least one predetermined value corresponding to the temperature and the state of charge, with the current as a variable.