Battery Pack Impedance Spectroscopy During Live Cell Operation
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Solution Overview
Problem
Conventional battery management systems (BMS) are unable to perform in-situ impedance spectroscopy of battery cells in multi-cell battery packs, leading to limited performance, power losses, and inability to identify unsafe cells or degradation modes, while also requiring disruptive offline testing for SOC balancing.
Innovation Solution
A novel architecture for battery packs with multiple nodes and node controllers allows for in-situ impedance spectroscopy by applying signals to cells while the pack operates, using power compensation by other cells to maintain voltage and power output, enabling real-time impedance feedback and cell-specific operating adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional BMS performs offline impedance testing for cell analysis, then cell impedance can be determined, but the pack operation is interrupted and requires disruptive testing procedures
Solution Approach 1:
The system performs impedance measurements in-situ during normal pack operation without requiring the pack to be taken offline. The measurement process is integrated into the operational workflow, allowing continuous monitoring of cell impedance while the battery pack remains in service, thus eliminating the need for disruptive offline testing procedures
Solution Approach 2:
The system introduces a current source as an intermediary component that can independently apply excitation signals to individual cells or cell groups during operation. This intermediary enables measurement functions without disrupting the main power flow through the battery pack, allowing simultaneous operation and measurement
2Ease of operation
If conventional BMS uses cell balancing circuits with resistors to equalize SOC, then cell charge/discharge rates can be adjusted, but power losses occur and functionality is limited
Solution Approach 1:
The system changes the control parameters from simple resistor-based current diversion to active control of cell voltage and current using power electronic converters. This allows precise adjustment of cell charge/discharge rates with minimal energy loss by dynamically controlling electrical parameters rather than using passive resistive elements
Solution Approach 2:
The system replaces the mechanical/passive resistor-based balancing circuit with an active electronic control system using power converters. This substitution enables more efficient current control with significantly reduced power losses compared to conventional resistive balancing methods
3Reliability
If conventional BMS limits pack performance to accommodate impedance variations, then cell safety can be maintained, but overall pack performance is reduced
Solution Approach 1:
The system applies individualized control strategies to each cell or cell group based on its specific impedance characteristics and state of health. Instead of uniformly limiting the entire pack's performance, the controller adjusts parameters locally for each cell, allowing high-performance cells to operate at full capacity while providing enhanced monitoring and protection for cells with degradation issues
Solution Approach 2:
The system dynamically adjusts cell operating parameters in real-time based on continuously monitored impedance data. The control strategy adapts to changing cell conditions, allowing the pack to operate at optimal performance levels when cells are healthy while automatically adjusting to maintain safety when degradation is detected, rather than using static performance limits
4Ease of operation
If conventional BMS requires SOC balancing to bring offline cells back online, then cell state can be equalized, but the process is complex and time-consuming
Solution Approach 1:
The system performs continuous impedance monitoring and early detection of cell degradation trends during normal operation. By identifying potential issues before they require cell shutdown, the system prevents the need for complex offline balancing procedures and enables proactive maintenance scheduling that minimizes operational disruption
Solution Approach 2:
The system uses real-time impedance measurement feedback to continuously assess cell health status and predict remaining useful life. This feedback mechanism enables the controller to automatically adjust operating parameters to extend cell life and schedule maintenance optimally, reducing the frequency and duration of offline balancing operations
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
Enables uninterrupted operation of battery packs during impedance testing, providing real-time impedance feedback for cell-specific adjustments, enhancing performance and safety by identifying degradation modes and maintaining overall pack efficiency.
Implementation Method 1
Cell impedance is determined based on the cell's response to the signal applied to the cell. For example, a current through the cell is charged while monitoring cells' voltage response.
Data Source
AI summary
Described methods and systems are used for in-situ impedance spectroscopy analysis of battery cells in multi-cell battery packs. Specifically, the cell impedances are determined while the pack continues to operate, such as being charged or discharged. For example, the pack voltage/power output remains unchanged while this analysis is initiated, performed, and ended. Cell impedance is determined based on the cell's response to the signal applied to the cell. For example, a current through the cell is charged while monitoring cells' voltage response. Although the power output of the changes during this testing, but the operation of the pack is not impacted due to the power compensation provided by one or more other cells in the pack thereby ensuring uninterrupted operation of the pack. This in situ testing is provided by the unique architecture of the pack, comprising multiple nodes and individual node controllers.