Switched Cell Strings for Fast EV Battery Charging
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Solution Overview
Problem
Current battery charging methods for electric vehicles are slow, with standard chargers taking around ten hours to fully charge and more powerful chargers taking 40 minutes to reach 80% capacity, necessitating the development of faster charging schemes without increasing peak current, which poses thermal and grid challenges.
Innovation Solution
A battery pack with N parallel-coupled switched cell strings and a control circuitry that steers charging current using predetermined duty cycles based on cell state of charge, terminal voltage, and accumulated charging time, allowing cells to receive full current for only part of the charging cycle with relaxation intervals, and optionally using a shunt path to manage charging current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If standard charging methods are used, then thermal management is simpler, but charging time is excessively long (10 hours for full charge)
Solution Approach 1:
The battery pack is divided into multiple parallel cell strings (N strings), each with independent switching capability. The control circuitry segments the charging current distribution, allowing selective activation of different cell strings based on charging phase and cell state, thereby reducing overall charging time while managing thermal loads across multiple independent pathways.
Solution Approach 2:
The charging system dynamically adjusts which cell strings are active during charging phases. The control circuitry switches between different cell string configurations based on real-time cell parameters (state of charge, temperature, voltage), enabling adaptive optimization of charging speed and thermal management throughout the charging process.
2Productivity
If higher peak current is used to reduce charging time, then charging speed increases, but thermal challenges and grid challenges worsen
Solution Approach 1:
By segmenting the battery into N parallel cell strings with independent switching, the system can distribute high charging current across multiple strings sequentially or in parallel combinations. This allows achieving high charging speeds without concentrating excessive current in a single cell string, thereby reducing peak thermal loads on individual cells.
Solution Approach 2:
The control circuitry implements periodic switching between different cell string configurations during charging. By cycling through different active cell string combinations, the system maintains high average charging power while providing periodic rest intervals for individual cell strings, allowing thermal dissipation and preventing overheating.
3Productivity
If cells are charged continuously without interruption, then charging efficiency is maximized, but metallic lithium formation occurs
Solution Approach 1:
The control circuitry implements periodic charging phases followed by relaxation intervals where no charging current is applied. During these relaxation intervals, cells are allowed to rest and equilibrate, preventing continuous charging conditions that lead to metallic lithium deposition. This periodic on-off charging pattern maintains high overall charging efficiency while ensuring cell safety.
Solution Approach 2:
Before applying charging current to a cell string, the control circuitry checks cell parameters (state of charge, temperature, voltage) to determine if the cell is ready for charging. This preliminary assessment prevents charging conditions that would lead to lithium formation, allowing the system to maintain high charging efficiency by only interrupting charging when necessary for safety.
Data Source
AI summary
A battery pack comprising: a set of N parallel-coupled switched cell strings, each switched cell string comprising a cell and a switch for selectively coupling a first terminal of the cell to a first terminal of the battery pack.