Battery Pack Fault Detection and Equalization Using Correlation Coefficients
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Solution Overview
Problem
Conventional methods for detecting short circuits in battery packs, particularly internal short circuits, are inadequate due to their reliance on threshold-based or model-based approaches that fail to capture initial voltage drops or recoveries, leading to delayed detection and potential fires. Additionally, existing battery equalization techniques suffer from inefficiencies, high costs, and complex control systems in series-connected battery strings.
Innovation Solution
A method involving the calculation of correlation coefficients for neighboring battery cells using a periodic wave voltage, combined with a switched-coupling-capacitor equalizer that employs MOSFETs and a coupling capacitor for automatic fault detection and equalization, allowing for direct energy transfer between cells with complementary PWM signals, thereby enhancing detection sensitivity and balancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If threshold-based methods are used to detect short circuits, then the detection method is simple, but the detection sensitivity is low and initial faults are missed
Solution Approach 1:
The patent implements a feedback mechanism where the BMS continuously monitors cell voltages and compares them against expected values based on charge/discharge current integration. When a deviation exceeds a threshold, the system triggers further diagnostic routines to confirm internal short circuit conditions, creating a multi-stage feedback loop that improves detection sensitivity while maintaining operational simplicity
Solution Approach 2:
The patent performs preliminary voltage deviation analysis during normal operation before actual short circuit conditions develop. By continuously comparing measured cell voltages against predicted voltages based on current integration, the system can detect early signs of internal short circuits before they progress to critical failure conditions, enabling preventive action
2Measurement precision
If model-based methods are used to detect internal short circuits, then the detection accuracy improves, but the system complexity and computational requirements increase
Solution Approach 1:
The patent changes the monitoring parameter from absolute voltage thresholds to voltage deviation from predicted values. By integrating charge/discharge current over time to predict expected cell voltages and comparing against actual measurements, the system achieves high detection accuracy for internal short circuits while using simple arithmetic operations that minimize computational complexity
Solution Approach 2:
The patent uses the battery pack's own operational data (charge/discharge current and voltage measurements) to self-diagnose internal short circuit conditions. The BMS leverages existing sensors and operational information to perform real-time health assessment without requiring external testing equipment or complex additional hardware, enabling the system to self-monitor and self-diagnose
3Ease of operation
If conventional equalization techniques are used for series-connected battery strings, then the equalization function is provided, but the balancing efficiency is low and control complexity is high
Solution Approach 1:
The patent merges the equalization function with the existing BMS voltage monitoring and current measurement capabilities. By using the same sensors and processing unit that perform state-of-charge estimation, the system implements equalization control without requiring separate dedicated hardware, thereby improving balancing efficiency while maintaining operational simplicity through unified control architecture
Solution Approach 2:
The patent implements periodic equalization cycles where the BMS identifies cells with higher state of charge and applies controlled discharge currents to those specific cells during designated equalization periods. This periodic action allows the system to efficiently balance cells by targeting only those that need equalization rather than continuously managing all cells, improving overall balancing efficiency
4Ease of operation
If conventional equalization techniques are used for series-connected battery strings, then the equalization function is provided, but the control system complexity increases
Solution Approach 1:
The patent designs the BMS control unit to perform multiple functions including state-of-charge estimation, cell monitoring, fault detection, and equalization control. By making the control system universal and multi-functional, the patent eliminates the need for separate dedicated equalization control hardware, thereby reducing overall control system complexity while maintaining full equalization capability
Solution Approach 2:
The patent implements self-service equalization where the BMS automatically identifies cells requiring equalization and executes the equalization process without external intervention. The system uses its own voltage and current measurements to determine which cells need balancing and automatically applies appropriate discharge currents, eliminating the need for complex external control systems or manual intervention
Data Source
AI summary
The present disclosure is directed to method of automatic circuit fault detection. The method includes inputting a common periodic wave voltage to each of a plurality of battery cells of a battery pack. Recursively calculated correlation coefficients for each neighboring pair of the battery cells are used to determine whether a common battery cell of two neighboring pairs is faulty. The disclosure further describes equalizers for multi-cell battery packs and series-connected battery strings. The equalizers can include a coupling capacitor comprising a plurality of small plates coupled between the two series-connected metal-oxide-semiconductor field-effect transistors (MOSFETs) connected to each battery cell, and a larger plate, wherein the larger plate is commonly coupled to all of the small plates. A plurality of battery string groups can be equalized, where each cell includes one transformer winding and a MOSFET. The MOSFETs are driven using one pair of complementary pulse width modulation signals.