Parallel Battery Current Limit Control Using Current Ratios
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Solution Overview
Problem
In battery systems with multiple batteries connected in parallel, differences in production and aging lead to varying electrical properties, causing uneven current distribution, and existing methods fail to reliably determine the maximum current limit to prevent overloading.
Innovation Solution
A method and control device that detect individual and total currents, calculate current ratios, and determine maximum individual current limits for each battery, selecting the smallest limit as the system's maximum current limit, while optionally using resistance ratios and weighted mean values to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If batteries are connected in parallel to increase system capacity, then the total current capability is improved, but the current distribution becomes uneven due to production and aging differences, leading to unreliable maximum current limit determination
Solution Approach 1:
The patent segments the battery system into individual battery units, each with its own current detection and evaluation. By dividing the system into separate measurable units, the method can identify and account for individual variations in current characteristics, enabling reliable determination of the system's maximum current limit despite differences between batteries.
Solution Approach 2:
The patent implements a feedback mechanism where actual individual currents are continuously detected and used to calculate current ratios. These ratios provide feedback about the distribution state, which is then used to dynamically determine the maximum current limit. This closed-loop approach ensures the system adapts to changing conditions and maintains reliable limit determination.
2Reliability
If individual current limits are enforced for each battery, then battery safety is improved, but the system's total current capability is reduced due to the weakest battery limiting the overall current
Solution Approach 1:
The patent changes the parameter used for current limit determination from fixed nominal values to dynamic values based on actual measured currents and calculated current ratios. By using real-time current distribution data, the system can more accurately reflect the true capabilities of each battery, allowing safer operation without unnecessarily limiting total system capability.
Solution Approach 2:
The patent introduces dynamics into the current limit determination by continuously monitoring individual currents and adjusting the maximum current limit based on actual operating conditions. This dynamic approach allows the system to optimize current capability while maintaining safety, rather than relying on static conservative limits.
3Measurement precision
If current ratios are calculated based on detected currents, then the maximum current limit determination accuracy is improved, but the system complexity increases due to additional detection and calculation requirements
Solution Approach 1:
The patent makes the control device multi-functional by combining current detection, ratio calculation, and maximum current limit determination in a single integrated system. This universal approach allows the same device to perform multiple functions without proportionally increasing complexity, as the components serve multiple purposes within the overall control strategy.
Data Source
AI summary
Technologies and techniques for determining a maximum current limit of a battery system having at least two batteries. A separate current is measured at each of the at least two batteries, and a total current is measured of the battery system. For each of the measured separate currents, a current ratio is determined between the measured separate current in question and the measured total current. A maximum individual current limit of the battery system is determined for each of the at least two batteries on the basis of the determined current ratio in question and a nominal maximum current limit of the battery in question. The smallest determined maximum individual current limit is selected as a maximum current limit of the battery system and the determined maximum current limit is provided as a maximum current limit signal. Alternatively, or additionally, the measurements can also be carried out using resistances.