Battery BMS Open Cell Detection via Capacitor Voltage Switching
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Solution Overview
Problem
The existing battery management systems face inaccuracies in cell voltage measurement due to open cell failures, leading to missed or incorrect over/under-voltage protection operations, necessitating an improved method for detecting and recovering from open cell failures.
Innovation Solution
The proposed solution involves a battery management system with monitoring resistors, capacitors, balance switches, and balance resistors, where a control unit generates signals to turn on and off balance switches, measuring voltage values on capacitors to determine open cell failures and recoveries, using specific time periods and thresholds to accurately detect and correct open cell issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional voltage measurement methods are used in battery management systems, then the system structure remains simple, but open cell failures cause inaccurate voltage measurements leading to missed or incorrect protection operations
Solution Approach 1:
The patent applies preliminary action by performing open cell detection before protection operations are triggered. The control unit continuously monitors capacitor voltages and detects open cell conditions in advance, allowing the system to identify potential measurement errors before they lead to incorrect protection decisions. This proactive detection approach improves measurement reliability without requiring complex real-time correction mechanisms during critical protection events.
Solution Approach 2:
The patent introduces capacitors as intermediary elements between the cell voltage measurement circuit and the control unit. These capacitors serve as detection targets that reveal open cell conditions through their voltage characteristics. By measuring capacitor voltages rather than directly measuring cell voltages during detection phases, the system gains an indirect but more reliable indication of cell status, improving measurement accuracy while maintaining relatively simple circuit architecture.
2Reliability
If the BMS continuously monitors all cells for open cell failures, then detection reliability improves, but system complexity and energy consumption increase
Solution Approach 1:
The patent implements periodic action by having the control unit cyclically control balance switches to connect and disconnect capacitors from cells at specific time intervals. During each cycle, the system measures capacitor voltages to detect open cell conditions. This periodic monitoring approach ensures reliable detection of open cell failures while avoiding continuous monitoring of all cells simultaneously, thereby reducing system complexity and energy consumption compared to constant comprehensive monitoring.
Solution Approach 2:
The patent applies segmentation by dividing the monitoring process into distinct phases: a first time period where balance switches are turned on to charge capacitors, and a second time period where switches are turned off to measure capacitor voltages. This temporal segmentation allows the system to use the same hardware resources for different functions at different times, improving detection reliability while maintaining simple system architecture.
3Stability of the object's composition
If balance switches are kept on continuously to maintain cell voltage balance, then cell voltage uniformity improves, but energy consumption increases due to continuous discharge current
Solution Approach 1:
The patent implements periodic action by controlling balance switches to operate in cyclic periods rather than continuously. During each period, the switches are turned on only during the first time period to charge capacitors and maintain voltage balance, then turned off during the second time period for measurement. This periodic operation maintains cell voltage uniformity when needed while significantly reducing energy consumption compared to continuous balance operation.
Solution Approach 2:
The patent applies dynamics by making the balance switch states changeable over time rather than fixed. The control unit dynamically adjusts balance switch positions based on detected cell conditions and measurement requirements. This dynamic control allows the system to optimize the balance between maintaining voltage uniformity and minimizing energy consumption, turning switches on only when necessary for balance or measurement purposes.
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 method enables quick detection and recovery from open cell failures, preventing missed or incorrect identifications, ensuring timely and accurate battery management functions.
Implementation Method 1
a first cell of the cells corresponds to a first monitoring resistor, a second monitoring resistor, a first capacitor, a first balance switch, and a first balance resistor
Implementation Method 2
measuring a voltage value on the first capacitor, with a measure unit coupled to the control unit; if the voltage value on the first capacitor is less than an open cell threshold, then determining with the control unit that the first cell has an open cell failure
Data Source
AI summary
An open cell detection method includes: (a) generating a control signal by a control unit, to turn on a first balance switch for a first time period; (b) generating the control signal with the control unit, to turn off the first balance switch for a second time period; (c) measuring a voltage value on a first capacitor, with a measure unit; (d) if the voltage value on the first capacitor is less than an open cell threshold, then determining with the control unit that the first cell has an open cell failure; (e) for each cell of the cells, repeating steps (a)-(d); and (f) if at least one cell of the cells has an open cell failure, then determining with the control unit that the battery management system has an open cell failure.