Parallel Battery Pack Current Control for Mixed-Health Charging
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Solution Overview
Problem
Battery packs with different impedances, ages, and temperatures, when charged or discharged in parallel, lead to uneven current distribution, reducing the lifetime of lower impedance packs and requiring complex charging strategies to prevent overcurrent and voltage imbalances.
Innovation Solution
Implementing a Battery Management System (BMS) that allows each battery pack to independently control its maximum charging and discharging currents based on State of Health (SoH), impedance, and temperature, enabling voltage equalization and extending the operational life of older batteries by limiting their cycles and automatically adjusting energy flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple battery packs with different impedances are connected in parallel, then the power supply capacity is increased, but the current distribution becomes uneven causing lower impedance packs to draw higher current and reduce their lifetime
Solution Approach 1:
The patent divides the battery system into independent battery packs, each with its own BMS that can independently control its charging and discharging current. This segmentation allows each pack to manage its own current contribution to the parallel system, preventing the lower impedance packs from drawing excessive current and extending their operational lifetime while maintaining the increased power capacity of the parallel configuration.
2Device complexity
If battery packs are charged in parallel without individual current control, then the charging process is simplified, but voltage imbalances and overcurrent conditions occur requiring complex protection circuits
Solution Approach 1:
The patent implements a self-service mechanism where each battery pack's BMS independently monitors its own voltage, current, and impedance characteristics, and automatically adjusts its charging and discharging current limits accordingly. This self-regulation eliminates the need for complex external control circuits to manage voltage imbalances and overcurrent protection, achieving both simplified charging process and high reliability simultaneously.
3Ease of manufacture
If older battery packs are used in parallel with newer packs, then system cost is reduced, but the older packs experience accelerated degradation from higher current cycles
Solution Approach 1:
The patent dynamically changes the operating parameters (current limits) of each battery pack based on its state of health, age, and impedance characteristics. Older battery packs are assigned lower current limits while newer packs can handle higher currents, allowing the system to maintain cost-effectiveness by using mixed-age packs while extending the lifetime of older packs through reduced current stress.
4Productivity
If hot swapping of battery packs is enabled, then system availability is improved, but inrush current during insertion can trip overcurrent protections
Solution Approach 1:
The patent implements preliminary action by having the BMS pre-configure current limiting parameters before the battery pack is fully connected to the parallel system. When a battery pack is inserted for hot swapping, the BMS immediately activates current limits that prevent inrush current from tripping overcurrent protections, allowing seamless hot swapping while maintaining system reliability.
Data Source
AI summary
Disclosed herein are different charging stations, systems, and methods for recharging swappable or non-swappable batteries having differing states of health, impedance, age, etc. Swappable and non-swappable battery packs may be charged in parallel, but the amount of charge current supplied to each parallel battery pack is determined individually by the battery pack itself. Each battery may have its own maximum charge and/or discharge current limits set individually to avoid using a battery pack over its rating, provide voltage equalization, and control energy flow among the plurality of rechargeable battery packs. This also extends the operating lifetime of older battery packs. In a charging mode, a battery charger may set a floating voltage and each battery pack may take its own current to provide voltage equalization. Additionally, a battery pack can boost its own voltage to maintain the required voltage level by a particular load/application.