Bidirectional Half-Forward Converter for Li-Ion Cell Balancing
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Solution Overview
Problem
Lithium-Ion batteries face inefficiencies in balancing cells during charging and discharging, leading to heat losses, reduced capacity, and premature degradation due to existing balancing methods, which are either inefficient or require complex and costly circuits.
Innovation Solution
A bidirectional half-forward converter circuit with synchronous rectifiers and a common power core allows for continuous, self-adjusting, and self-correcting balancing of cells, enabling energy transfer in both directions with high efficiency and minimizing heat losses, without the need for intelligent controls or precise state-of-charge measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dissipative balancing is used to balance Li-Ion cells, then the balancing function is achieved, but significant heat losses occur and energy efficiency deteriorates
Solution Approach 1:
A capacitor is introduced as an intermediary energy storage element between cells with different charge states. The capacitor temporarily stores excess energy from higher-voltage cells and transfers it to lower-voltage cells, enabling direct energy transfer without dissipative resistors and thereby reducing heat losses while maintaining the balancing function.
Solution Approach 2:
The patent changes the operating parameters by using variable switching control to dynamically adjust the charging and discharging rates of cells based on their individual states. This allows optimization of energy transfer efficiency and minimizes energy losses during the balancing process.
2Loss of energy
If chain balancing is used to transfer charge between cells, then energy transfer is achieved, but the efficiency deteriorates when cells are located far apart in the series-connected string
Solution Approach 1:
Multiple balancing operations are merged into a single parallel circuit architecture where all cells are connected to a common capacitor through individual switches. This allows simultaneous balancing of any number of cells regardless of their position in the series string, achieving high efficiency without the compounding losses inherent in sequential chain balancing.
Solution Approach 2:
The battery system is segmented into individually controllable cell units, each with its own switching element that can independently connect to the common capacitor. This segmentation allows selective balancing of specific cells without affecting others, optimizing energy transfer efficiency regardless of cell position.
3Reliability
If dissipative balancing is used, then cell balancing is achieved during charging, but the circuit cannot recover energy during discharging and becomes unusable when one cell reaches minimum voltage
Solution Approach 1:
The capacitor serves as a reversible intermediary that can both receive and release energy. During charging, it absorbs excess energy from overcharged cells; during discharging, it releases stored energy to undercharged cells, enabling continuous operation and full utilization of battery capacity without premature termination.
Solution Approach 2:
The balancing system operates continuously throughout both charging and discharging cycles rather than being limited to charging only. The capacitor maintains energy transfer capability across the entire operational range, allowing the battery to fully exploit the capacity of all cells including those previously considered unusable.
4Loss of energy
If active balancing circuits are implemented, then energy transfer between cells is achieved, but the device complexity and cost increase
Solution Approach 1:
A single common capacitor and control logic serve all cells in the battery pack, providing universal balancing capability. This multi-functional approach replaces the need for separate balancing circuits for each cell or cell pair, significantly reducing overall device complexity and cost while maintaining high energy transfer efficiency.
Solution Approach 2:
Multiple balancing functions are merged into a shared circuit architecture with a common capacitor and centralized control. This consolidation reduces the total number of active components compared to individual cell balancing circuits, achieving simplicity and cost-effectiveness without sacrificing efficiency.
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 achieves high efficiency in balancing cells throughout the battery's lifecycle, maximizing energy storage capacity and extending battery life by allowing continuous balancing during charging, discharging, and idle times, with minimal heat losses and reduced operational complexity.
Implementation Method 1
A bidirectional half-forward converter circuit with synchronous rectifiers and a common power core allows for continuous, self-adjusting, and self-correcting balancing of cells, enabling energy transfer in both directions with high efficiency
Implementation Method 2
A bidirectional half-forward converter circuit with synchronous rectifiers and a common power core allows for continuous, self-adjusting, and self-correcting balancing of cells
Data Source
AI summary
A method, circuit, and topology are provided for utilization of this circuit in Li-Ion or any other battery that benefits from balancing between individual cells. The whole system is characterized as having high efficiency (and thus low heat losses) compared to previous art implementations. The actions of the circuit are continuous and bi-directional in respect to each cell.