Parallel Battery Pack Impedance Control for Balanced Current Sharing
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Solution Overview
Problem
Current modular battery pack designs face challenges in current sharing due to small differences in impedance, leading to uneven stress and reduced battery pack lifetime, as well as frequent overcurrent protection triggers.
Innovation Solution
Incorporating a controlled impedance system within each battery pack, coupled with a control circuit that adjusts impedance to balance current sharing among parallel packs by exchanging data via a communication bus, ensuring equal current distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If battery packs are connected in parallel to increase capacity, then the total capacity and power output are improved, but small differences in impedance cause large differences in current sharing, leading to uneven stress and reduced lifetime
Solution Approach 1:
The patent implements a feedback control system where each battery pack's control circuit continuously monitors its own current output and the outputs of other parallel battery packs. Based on this feedback, the control circuit dynamically adjusts the controllable impedance element to balance current distribution. This closed-loop feedback mechanism ensures that even with manufacturing variations in passive impedance, the system maintains equitable current sharing and extends battery pack lifetime.
2Reliability
If manual cable balancing is performed during installation to minimize impedance effect, then current sharing may be improved, but the process is time consuming and unpredictable due to varying factors such as internal cable resistance, temperature, and cell resistance
Solution Approach 1:
The patent enables each battery pack to autonomously monitor and adjust its own impedance without requiring manual intervention. The control circuit within each pack independently measures current distribution and automatically modifies the controllable impedance element to achieve balanced current sharing. This self-service capability eliminates time-consuming manual cable balancing while providing predictable and reliable current distribution despite environmental variations.
3Device complexity
If passive impedance elements are used in battery packs, then the circuit simplicity is maintained, but the impedance unbalance effect cannot be minimized as internal factors cause varying input impedance
Solution Approach 1:
The patent replaces static passive impedance elements with dynamic controllable impedance elements that can actively adapt to changing conditions. The controllable impedance element, controlled by a feedback algorithm, dynamically adjusts its resistance value in real-time to compensate for variations in internal cable resistance, temperature, and cell resistance. This dynamic approach maintains circuit simplicity while achieving reliable impedance balance that passive elements cannot provide.
4Reliability
If controllable impedance is added to each battery pack to enable active impedance balancing, then current sharing balance is improved, but the device complexity increases
Solution Approach 1:
The patent changes the key parameter of impedance from a fixed physical property to a controllable electrical parameter. By using controllable impedance elements (such as MOSFETs or IGBTs operating in linear region) that can be electronically adjusted, the system achieves precise impedance matching without complex mechanical adjustments. The control circuits use straightforward feedback algorithms that monitor current differences and adjust impedance parameters, providing reliable current sharing with minimal added complexity.
Data Source
AI summary
Disclosed herein are battery packs, modular battery systems, and improved methods of impedance balancing for current sharing among parallel battery packs. Each parallel battery pack's impedance can be controlled by adding a controlled impedance and a control circuit. The controlled impedance is an impedance that can be varied, and/or controlled, using different impedance values. The control circuit communicates with other battery packs to determine impedance values (or an average impedance) for the other battery packs in a battery system. The controlled impedance can then increase the total impedance for the more highly used batteries (i.e., batteries delivering more current) to balance it with other less used batteries. By balancing impedance between parallel battery packs in a modular battery system, the current will be equally shared between the battery packs, thus ensuring all the battery packs in parallel have similar usage and similar operating lifetimes.