Battery Cell Charge Balancing Using Coulomb Counting
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Solution Overview
Problem
Existing battery balancing methods are inefficient and unreliable, particularly for Lithium-ion and other batteries where cell voltage is not an accurate indicator of State of Charge (SoC) or Depth of Discharge (DoD), leading to imbalanced charging and discharging, heat generation, and reduced battery availability for use.
Innovation Solution
A method using Coulomb counters to determine when cells reach specific charge states, allowing for accurate imbalance detection and transfer of charge between cells, enabling balancing during charging or discharging without relying on cell voltage, thus maintaining battery performance and availability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cell voltage is used to determine State of Charge for balancing, then the balancing process can be initiated, but the balancing accuracy is poor for batteries with flat EMF curves (e.g., LFP) where voltage does not accurately indicate SoC
Solution Approach 1:
The patent changes the measurement parameter from cell voltage to Coulomb counting (integration of current over time). This allows accurate SoC determination independent of the EMF curve shape, resolving the issue where voltage-based measurement fails for batteries with flat discharge curves like LFP.
2Reliability
If balancing is performed using top balancing (charging until full) or bottom balancing (discharging until empty), then charge balancing can be achieved, but battery availability is reduced as balancing cannot occur during normal use
Solution Approach 1:
The patent enables continuous Coulomb counting during normal battery operation (charging, discharging, or idle). This allows the system to accumulate accurate SoC data continuously without interrupting battery usage, and perform balancing adjustments at optimal moments, thereby maintaining both balancing effectiveness and high battery availability.
3Measurement precision
If balancing is performed after bulk charging when the battery is nearly full, then accurate SoC determination is possible, but the balancing time is delayed and battery availability is reduced
Solution Approach 1:
The patent performs preliminary Coulomb counting during the bulk charging phase to predict which cells will reach full charge first. This allows the system to prepare balancing strategies in advance and transition smoothly to absorption charging with precise cell-level control, eliminating delays associated with post-charging balancing.
4Device complexity
If cell voltage measurement is used for balancing, then the balancing process can be simple to implement, but it generates heat and reduces balancing efficiency for batteries where voltage is not correlated with SoC
Solution Approach 1:
The patent replaces voltage-based balancing control with Coulomb counting-based control. This substitution allows precise tracking of charge transfer without relying on voltage-SoC correlation, reducing unnecessary charging/discharging cycles and associated heat generation while maintaining implementation feasibility through standard current sensing.
Data Source
AI summary
A method for balancing charge over a plurality of cells connected in series in a battery, the method comprising: during the charging/discharging of the battery: determining when a characteristic parameter of a cell of the plurality of cells reaches a characteristic value associated with a first state of charge, counting the number of Coulombs exchanged with the cell by means of a respective Coulomb counter of a plurality of Coulomb counters connected to the plurality of cells, and repeating said acts until a predetermined charging or discharging criteria is fulfilled; determining a charge imbalance based on the counted number of Coulombs for each of the plurality of cells; and transferring charge to or away from at least one cell of the plurality of cells based on the determined charge imbalance to reduce the charge imbalance. A system for balancing charge over the plurality of battery cells.