Vehicle Battery Module SOC Bias Correction and Active Balancing
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Solution Overview
Problem
Existing state of charge (SOC) estimation methods for vehicle battery modules are computationally intensive and lack robustness, leading to inaccurate SOC estimation and imbalance among battery modules.
Innovation Solution
A method that utilizes a pack-level SOC estimator to estimate individual battery module SOC by applying a shifting bias value, reducing computational load and enhancing estimation robustness through real-time correction using a common battery model and low-pass filtering, followed by active balancing using distributed converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individual battery module SOC is estimated using existing methods, then SOC estimation is obtained, but computational load is high and estimation accuracy is poor
Solution Approach 1:
The battery pack is divided into multiple battery modules, each with its own SOC estimation. The system segments the estimation problem by applying a common battery model to each module while using pack-level SOC as a reference, reducing the computational complexity of individual module estimation without sacrificing accuracy
Solution Approach 2:
The system uses feedback by comparing the estimated individual module SOC with the pack-level SOC and applying a shifting bias value to correct deviations. This feedback mechanism improves estimation accuracy by continuously adjusting individual module estimates based on overall pack performance
2Reliability
If individual battery module SOC is estimated using existing methods, then SOC estimation is obtained, but robustness is poor leading to imbalance among battery modules
Solution Approach 1:
The system changes parameters by introducing a shifting bias value that adjusts individual module SOC estimates based on their deviation from the pack-level SOC. This parameter adjustment enhances robustness and ensures that individual module estimates remain consistent with overall pack state, preventing imbalance
Solution Approach 2:
The common battery model serves multiple functions by providing a standardized estimation framework for all battery modules simultaneously. This universal approach ensures consistent estimation robustness across all modules while maintaining their individual characteristics
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 reduces computational burden on the vehicle control module while improving SOC estimation accuracy and balancing across battery modules, ensuring efficient and reliable power management.
Implementation Method 1
estimating a state of charge of the vehicle battery pack based on the output current, using a coulomb counter
Implementation Method 2
measure an output voltage of the battery module, determine a state of charge shifting bias value for the battery module, based on the output voltage
Implementation Method 3
passively balance state of charge values of its corresponding multiple rechargeable battery cells by supplying current to a resistor from at least one of the multiple rechargeable battery cells having a highest state of charge value
Data Source
AI summary
An example vehicle battery control system includes an electric motor, a vehicle battery pack configured to supply power to the electric motor, the vehicle battery pack including multiple battery modules each including multiple rechargeable battery cells, and a vehicle control module configured to measure an output current of the vehicle battery pack, estimate a state of charge of the vehicle battery pack using a coulomb counter, and for each of the multiple battery modules, measure an output voltage of the battery module, determine a state of charge shifting bias value for the battery module, estimate an individual state of charge of the battery module by applying the state of charge shifting bias value to the state of charge of the vehicle battery pack, and control at least one of a charging current and a discharging current according to the individual state of charge of the battery module.