Battery Cell Balancing Circuit with Dynamic Pre-Balance Timing
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Solution Overview
Problem
Lithium-Ion battery packs with cells connected in series often experience voltage imbalances during charging, leading to some cells not being fully charged due to differing charging rates, and conventional balancing circuits either stop charging prematurely or increase costs by using multiple chargers.
Innovation Solution
A balancing circuit with a shunt path, controller, timer, and storage unit that pre-balances and balances cells by enabling a shunt current for specific times based on previous balancing cycles, ensuring all cells reach similar voltages when the charger switches from constant current to constant voltage mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single charger is used to charge multiple cells in series, then the charging cost is reduced, but voltage imbalances occur among cells causing some cells to not be fully charged
Solution Approach 1:
The patent applies preliminary action by implementing a pre-balancing phase before the main charging process. During this pre-balancing phase, the controller activates shunt paths for all cells simultaneously for a predetermined time period, allowing cells with higher voltage to discharge slightly before the main charging begins. This preliminary action ensures that when charging starts, all cells are at comparable voltage levels, preventing the voltage imbalance problem that would otherwise cause charging to stop prematurely due to the highest voltage cell reaching its threshold first.
2Reliability
If multiple chargers are used to charge multiple cells, then each cell can be fully charged, but the charging circuit cost increases
Solution Approach 1:
The patent merges the functions of multiple chargers into a single charger system. Instead of using separate chargers for each cell, the invention uses one charger with multiple controllable shunt paths that can independently control current flow to each cell. The controller manages the charging process by selectively activating shunt paths based on real-time voltage measurements, achieving the cell-by-cell charging control that would otherwise require multiple independent chargers, thereby reducing cost while maintaining charging completeness.
3Productivity
If cells are charged without pre-balancing, then the charging process is faster, but voltage imbalances cause some cells to be undercharged
Solution Approach 1:
The patent implements periodic action through its two-phase charging approach: a pre-balancing phase followed by a main charging phase. The pre-balancing phase operates periodically at the beginning of each charging cycle, activating shunt paths for a predetermined time to equalize cell voltages. After this periodic pre-balancing action, the main charging phase proceeds at full speed. This periodic intervention ensures voltage balance is maintained without continuously slowing down the overall charging process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution ensures all cells in the battery pack achieve similar voltages at the desired time, preventing overcharging and reducing heat generation, while dynamically adjusting pre-balancing times for optimal balance and efficiency.
Implementation Method 1
a first shunt path connected in parallel to a first cell... The controller pre-balances the first cell by enabling the first shunt path
Data Source
AI summary
A balancing circuit for balancing multiple cells in a battery. The cell balancing circuit includes a first shunt path connected in parallel to a first cell, a controller coupled to the first shunt path, a timer and a storage unit. The controller balances the cells and detects balance conditions of each cell. The timer measures pre-balance times and balance times for each cell. The storage unit stores the pre-balance times and balance times. The controller pre-balances the first cell by enabling the first shunt path for a first pre-balance time and balances the first cell by enabling the first shunt path for a first balance time if an unbalance condition of the first cell is detected by the controller, and updates the first pre-balance time for each balancing cycle based on the first pre-balance time and the first balance time from a previous balancing cycle.