Battery Pack State-of-Charge Detection via Block Segmentation
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Solution Overview
Problem
Existing methods for detecting the state of charge (SOC) in battery packs, particularly those with lithium ion batteries, face challenges due to the uniform change in voltage with SOC, making it difficult to apply techniques that rely on abrupt voltage changes, such as those used for nickel-hydrogen batteries.
Innovation Solution
A charge state detecting device and method that divide battery cells into blocks, calculate individual SOC estimates, and set a total SOC based on these estimates to ensure the battery pack operates within defined limits, preventing overcharging or overdischarging by adjusting the total SOC based on the distribution of SOC values among the blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If battery cells are connected in series to form a battery pack, then the output voltage increases, but temperature becomes non-uniform among cells leading to SOC variation
Solution Approach 1:
The battery pack is divided into multiple battery blocks, each comprising one or more battery cells. This segmentation allows independent monitoring and management of each block's charge state, enabling precise detection of SOC variations among blocks while maintaining the high voltage output of the series-connected battery pack.
2Measurement precision
If SOC detection is based on abrupt voltage changes, then detection precision improves for nickel-hydrogen batteries, but this method cannot be applied to lithium ion batteries with uniform voltage change
Solution Approach 1:
The invention transitions from detecting abrupt voltage changes to monitoring the cumulative charge and discharge amounts (current integration) over time. This parameter change enables accurate SOC detection for lithium ion batteries with uniform voltage characteristics while maintaining adaptability to other battery types by adjusting the detection parameters.
3Productivity
If the battery pack operates at maximum capacity, then energy utilization increases, but risk of overcharging or overdischarging increases due to SOC variation among blocks
Solution Approach 1:
The control device continuously monitors the charge and discharge amounts of each battery block and provides feedback to adjust the overall battery pack's charge state. This feedback mechanism enables the system to operate at maximum capacity while preventing overcharging or overdischarging by identifying and limiting charge based on the most constrained block.
4Reliability
If the movable range for charge amounts is strictly limited, then safety against overcharging improves, but the operational range of the battery pack is excessively narrowed
Solution Approach 1:
The movable range for charge amounts is dynamically adjusted based on the detected SOC variation among battery blocks. When SOC variation is small, the operational range is expanded to maximize energy utilization. When SOC variation increases, the range is dynamically contracted to prevent overcharging, thus balancing safety and productivity.
Data Source
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AI summary
A total SOC of a battery pack including a collection of a plurality of battery blocks is calculated based on a plurality of block SOCs representing respective stored charge amounts in the plurality of battery blocks. In the case (401) where a block SOC maximum value (BSmax) is higher than a control upper limit value (SOCu), the total SOC is calculated to be higher than the control upper limit value. On the other hand, in the case (402) where a block SOC minimum value (BSmin) is lower than a control lower limit value (SOCl), the total SOC is calculated to be lower than the control upper limit value. Further, in the case (403) where each of the block SOCs is in a range of not less than the control lower limit value and not more than the control upper limit value, the total SOC is determined to fall within the range of not less than the control lower limit value and not more than the control upper limit value.