Bi-directional DC-DC Converters for Scalable Energy Storage Packs
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Solution Overview
Problem
Conventional battery packs face performance degradation due to variations among individual cells, with the weakest cell limiting the overall pack performance, and existing battery management systems only provide partial solutions, potentially reducing the usable lifetime of cells.
Innovation Solution
A system and method that uses bi-directional DC-DC converters to buffer each cell independently, allowing for optimized charge and discharge management, accommodating cell-to-cell variability, and enabling high-voltage series strings with minimized energy losses, while using less expensive cells and extending pack lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional battery management systems use switched-resistor, switched-capacitor, or switched-inductor architectures to equalize cell voltages, then cell voltage variations are partially managed, but the usable lifetime of cells is reduced and the ability to accommodate cell capacity and lifetime variations is limited
Solution Approach 1:
The battery pack is divided into multiple independently managed modules, each with its own DC-DC converter. This segmentation allows each cell or cell group to be managed individually, accommodating variations in capacity and lifetime without forcing all cells to operate within the constraints of the weakest cell. The modular architecture enables flexible configuration and independent optimization of each segment.
Solution Approach 2:
DC-DC converters are introduced as intermediary devices between cells and the battery management system. These converters act as mediators that can independently control power flow to and from each cell, enabling precise voltage and current management. The intermediaries facilitate charge transfer between cells with different states of charge without requiring direct electrical connection, thereby extending usable lifetime while maintaining voltage equalization.
2Power
If multiple energy storage cells are connected in series to form a series string, then the overall voltage is increased, but the performance of the battery pack is degraded by the weakest cell in the string
Solution Approach 1:
The series string is segmented into multiple modules, each containing one or more cells with their own DC-DC converter. This allows the high voltage to be maintained through series connection while each segment can be independently managed. The segmentation enables the system to accommodate cell variations by allowing each module to operate at its optimal performance level rather than being constrained by the weakest cell.
Solution Approach 2:
The system dynamically adjusts the operation of each cell through independent DC-DC converter control. The converters can modify voltage and current levels in real-time based on individual cell conditions, enabling the series string to maintain high voltage while adapting to variations in cell performance. This dynamic control allows the weakest cell to be compensated without limiting the overall pack performance.
3Reliability
If conventional battery management systems use charge balancing circuitry at each cell or grouping of cells, then cell voltages are equalized, but the system complexity increases and the ability to accommodate cell capacity and lifetime variations remains limited
Solution Approach 1:
The DC-DC converters perform multiple functions simultaneously: voltage equalization, charge balancing, cell monitoring, and power management. By using a universal component that can handle all these tasks, the system avoids the need for separate dedicated circuits for each function, thereby managing complexity while achieving comprehensive cell management. The multi-functionality of the converters allows the system to accommodate cell variations effectively.
4Reliability
If battery cells are manufactured with tighter tolerances to reduce cell-to-cell variations, then pack performance is improved, but manufacturing costs increase
Solution Approach 1:
Instead of requiring all cells to have uniform high quality, the system applies local quality management through independent DC-DC converter control for each cell or cell group. Each converter can be tailored to the specific characteristics of its associated cell, allowing cells with varying quality levels to be effectively managed. This approach enables the use of less expensive cells with wider tolerances while maintaining overall pack performance through localized optimization.
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
The solution enhances battery pack performance by optimizing power flow, extending the lifetime of each cell, and allowing the use of less expensive cells, while maintaining high reliability and safety through cell-level monitoring and fault detection.
Implementation Method 1
The first converter circuit transforms a first voltage from the first energy storage cell to a desired first bus contribution voltage according to the first control signals
Data Source
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AI summary
A system and method for scalable configuration of intelligent energy storage packs are disclosed. According to one embodiment, a method comprises providing a first current measurement of a first energy storage cell electrically connected to a first converter circuit, and the first converter circuit controls the charge and discharge of the first energy storage cell. A first voltage measurement of the first energy storage cell is provided. First control signals are received and the first control signals are determined according to a load policy. The first converter circuit transforms a first voltage from the first energy storage cell to a desired first bus contribution voltage according to the first control signals.