Cell Balancing Circuit and Control Method Thereof

Low-Peak Cell Balancing Circuit Combining Parallel Capacitors and Lowest SOC Cell Selection Control

This technology is a cell balancing method that adds a capacitor in parallel to both ends of the battery unit and allows the control unit to manage PWM and unidirectional switches, reducing the peak cell discharge current while maintaining energy transfer efficiency.

Conventional single-inductor cell balancing circuits suffer from high discharge current peaks, which can degrade battery State of Health (SOH). Increasing inductance to mitigate this leads to space constraints, while raising the switching frequency increases switching losses.

This technology configures the circuit by connecting a capacitor in parallel with the battery unit and inductor, and applies control logic to identify the cell with the lowest SOC, selectively transferring energy only to that cell. This reduces the peak discharge current at the same transfer efficiency. It can be applied to BMS for EV packs with many series cells, uninterruptible power supplies, and battery management boards for electric mobility, extending pack life by reducing cell-to-cell deviation without relying on large inductors or high-frequency switching.

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Key Features:

• An inductor connected in parallel to both ends of a battery unit comprising at least two battery cells connected in series
• A capacitor connected in parallel with the inductor at both ends of the battery unit to mitigate discharge current peaks
• First and second PWM switches connected between both ends of the battery unit and the inductor to open and close energy transfer to the inductor
• Unidirectional switches and diodes positioned between each battery cell and the inductor to select connections and restrict current direction

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