Current-Limiting Circuit for Parallel Battery Pack Switching
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Solution Overview
Problem
Existing electricity storage systems using lithium ion secondary batteries face voltage imbalances and cross-currents when secondary battery packs with different states of deterioration are connected in parallel, limiting operational flexibility and preventing safe and efficient use of mixed batteries.
Innovation Solution
Incorporating a current-limiting circuit in conjunction with charging and discharging switches, allowing for controlled charging and discharging operations by limiting the charging current to a fixed value, thereby preventing cross-currents and enabling safe switching between secondary battery packs without halting the charging process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If secondary battery packs with different states of deterioration are connected in parallel, then the storage capacity and flexibility of the electricity storage system is improved, but voltage imbalances cause cross-currents that prevent normal operation
Solution Approach 1:
The patent divides the charging control into segmented stages based on voltage levels. The charging process is segmented into: (1) charging only the low-voltage pack when voltage difference exceeds threshold, (2) charging both packs when voltage difference is within threshold, and (3) charging only the high-voltage pack when voltage difference reverses. This segmentation prevents cross-currents while enabling flexible use of mixed battery packs with different states of deterioration.
Solution Approach 2:
The patent implements dynamic charging control where the charging configuration changes in real-time based on voltage measurements. The control device continuously monitors voltage across parallel-connected packs and dynamically adjusts which packs receive charging current, transitioning between different charging modes (single-pack charging, dual-pack charging) to maintain safe operation while maximizing utilization of all battery packs.
2Ease of operation
If switching between secondary battery packs is performed without current limiting, then the operational flexibility is improved, but cross-currents occur causing safety issues
Solution Approach 1:
The patent applies preliminary action by measuring the voltage across battery packs before switching charging targets and comparing it with the previously charged pack. This preliminary voltage comparison determines whether to charge the new pack, the old pack, or both packs simultaneously, ensuring that cross-currents are prevented before they can occur during the switching operation.
Solution Approach 2:
The control device continuously measures voltage across battery packs and uses this feedback to dynamically adjust charging decisions. When voltage difference exceeds the threshold, the system feedback-controls to charge only the low-voltage pack; when voltage difference is within threshold, both packs are charged; when voltage difference reverses, charging switches to the previously charged pack. This feedback mechanism enables safe switching while preventing cross-currents.
Data Source
AI summary
In an electricity storage system that has a plurality of secondary battery packs, at the time of switching the object that is to be charged from a first secondary battery pack to a second secondary battery pack that has voltage across terminals lower than that of the first secondary battery pack, by causing a current-limiting circuit of the second secondary battery pack to operate, forms a path for the flow of a charging current for charging secondary batteries that are provided in the second secondary battery pack, and starts charging of the second secondary battery pack while limiting the charging current to a fixed value or less by means of the current-limiting circuit.