Battery SOC Correction via Cell Balancing Circuits
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Solution Overview
Problem
Conventional battery management systems for hybrid electric vehicles face limitations in accurately estimating state of charge (SOC) in vehicles without an engine-driven generator, leading to reduced efficiency and limited applicability, especially when the SOC change in OCV is small in one range and large in another.
Innovation Solution
A battery management device with cell balancing circuits, an SOC calculation unit, and an SOC correction unit that adjusts the SOC of target battery cells within specific ranges to improve estimation accuracy without relying on engine-driven generators, reducing energy loss and increasing applicability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the power consumption of the motor and the power generation of the generator are changed to forcibly change the SOC from the second region to the first region, then the SOC estimation accuracy is improved, but the overall efficiency of the vehicle is reduced
Solution Approach 1:
The system uses the battery cells themselves to perform the SOC correction by selectively discharging higher-SOC cells through the equalization circuit, rather than relying on external energy input from the engine-driven generator. This self-service approach corrects SOC estimation without requiring additional energy conversion cycles that would reduce overall vehicle efficiency.
2Measurement precision
If the conventional control device is used to change the SOC to the first region for estimation, then the SOC estimation accuracy is improved, but the applicability is limited to hybrid electric vehicles with engine-driven generators
Solution Approach 1:
The equalization circuit, originally designed for cell balancing, is repurposed to perform dual functions: (1) traditional cell equalization by discharging higher-SOC cells, and (2) SOC correction by inducing controlled discharge in cells with SOC in the second region. This multi-functionality enables the system to operate in both HEVs and BEVs without requiring engine-driven generators, thereby achieving universality across different vehicle architectures.
3Measurement precision
If the SOC of battery cells is monitored continuously to detect when it stays in the first SOC range for a predetermined period, then the SOC estimation accuracy is improved, but the device complexity increases
Solution Approach 1:
The control device continuously monitors SOC values and uses feedback control to detect when SOC remains in the first region for a predetermined period. Based on this feedback, the system automatically activates the equalization circuit to discharge the target cell, thereby correcting the SOC estimation. This feedback mechanism achieves accurate SOC correction through simple conditional logic rather than complex control algorithms.
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
The solution enhances SOC estimation accuracy while minimizing efficiency decreases and expanding the system's applicability to battery electric vehicles without engine-driven generators, effectively managing batteries with varying OCV-SOC characteristics.
Implementation Method 1
a plurality of cell balancing circuits configured to charge, with power discharged from at least one of the battery cells, at least another one of the battery cells
Data Source
AI summary
A battery management device manages a battery including a plurality of battery cells in which a change in OCV relative to a change in SOC is smaller in a first SOC range than in a second SOC range. The battery management device is configured to: accumulate a current flowing in each battery cell to calculate the SOC of the battery cell; when the calculated SOC has stayed in the first SOC range for a predetermined period or more, control the cell balancing circuits in such a way that the SOC of a target battery cell selected from the battery cell s falls within the second SOC range; and calculate the SOC of the target battery cell based on the relationship between the SOC and the OCV in the second SOC range and correct the SOC of each battery cell by the amount of correction obtained based on the calculated SOC.