Battery Pack Isolation Fault Location Using Switched Resistances
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Solution Overview
Problem
Conventional battery management systems (BMS) are ineffective in accurately monitoring and characterizing isolation faults in high voltage battery packs, particularly in harsh conditions, leading to increased shock hazards due to reduced isolation resistance and capacitor discharge, and fail to provide precise fault location information, complicating repairs and increasing safety risks.
Innovation Solution
The battery management system (BMS) employs a switchable resistance ladder with electronically-controlled switches to measure current flow through resistors, determining the location and magnitude of isolation faults by comparing currents through different paths, and includes a mechanism to detect and characterize Y capacitance to mitigate shock hazards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage measurements are performed at multiple locations within a battery cell to improve fault detection accuracy, then measurement precision improves, but device complexity increases due to additional voltage taps and measurement circuits
Solution Approach 1:
The battery cell is divided into multiple measurement zones along its length, with voltage taps placed at strategic locations (e.g., at intervals along the wound structure). This segmentation allows localized fault detection without requiring continuous measurement, balancing precision with complexity. Each segment provides information about specific regions of the cell.
Solution Approach 2:
The patent uses the battery's existing current collectors and tab structure as intermediary elements for voltage measurement. Instead of adding completely independent measurement circuits, the system leverages the current collectors that already exist in the battery structure to carry measurement signals, reducing the need for additional complex circuitry.
2Measurement precision
If temperature sensors are distributed throughout the battery cell to improve thermal monitoring, then measurement precision improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent combines temperature sensing functionality with existing battery structural components. Temperature sensors are integrated into the battery housing or packaging structure, and in some embodiments, the current collectors themselves serve as thermal conduction paths that distribute temperature information to fewer measurement points. This merging reduces the number of discrete sensor components needed.
Solution Approach 2:
Existing battery components such as current collectors and housing structures are designed to serve multiple functions: structural support, electrical conduction, and thermal management. These same components also serve as the medium for temperature sensing, eliminating the need for separate dedicated sensor mounting structures and reducing overall system complexity.
3Measurement precision
If impedance spectroscopy is performed frequently to improve state of charge accuracy, then measurement precision improves, but energy consumption increases
Solution Approach 1:
Impedance spectroscopy measurements are performed periodically at strategically selected time points during battery operation, such as at the end of charge or discharge cycles, or at rest periods. This periodic measurement approach maintains state of charge accuracy while minimizing the frequency of high-energy measurements compared to continuous monitoring.
Solution Approach 2:
The system performs preliminary low-energy voltage and temperature measurements continuously, and only triggers full impedance spectroscopy measurements when specific conditions are met (e.g., when state of charge estimation uncertainty exceeds a threshold, or at predetermined cycle points). This preliminary screening reduces the number of high-energy impedance measurements needed.
Data Source
Figure 1
Figure 2A
Figure 2B~2C
AI summary
Battery management systems and methods for operation of same are provided. A first switchable resistance (110) may be connected between a cell stack positive end (101A) and ground. A second switchable resistance (114) may be connected between a cell stack negative end (101B) and ground. The switches (111, 115) for each resistance may be alternately opened and closed, with comparison of the resulting currents through each resistance (110, 114) being indicative of a location of isolation leakage current within a battery system cell stack (100), and/or the magnitude of isolation leakage current. Currents through the first and/or second switchable resistances (110, 114) may also be indicative of Y capacitance (130). The first and second switchable resistances (110, 114) may further be used to reduce energy stored by Y capacitance (130).