Minimum Cell Voltage Measurement via Series Resistor Current Comparison
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Solution Overview
Problem
Current methods for monitoring cell voltages in large series-connected battery systems, such as those used in hybrid and electric vehicles, are complex and expensive, as they require individual monitoring of each cell using integrated circuits with multiplexers and analog/digital converters, posing reliability and safety concerns due to potential battery failures.
Innovation Solution
A device utilizing a series of ohmic resistors, transistors, and diodes is connected to battery cells, where each resistor measures the smaller of the cell voltage and the preceding resistor's current, allowing for efficient determination of the minimum cell voltage, and can be integrated into a battery management unit to prevent deep discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individual monitoring of each battery cell is performed using integrated circuits with multiplexers and analog/digital converters, then measurement precision of cell voltages is improved, but device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent merges multiple individual cell monitoring circuits into a single integrated monitoring device that processes all cell voltages through a unified current comparison mechanism. Instead of having separate ADC and multiplexer circuits for each cell, the invention combines all measurements into one device that uses current mirrors and comparison circuits to identify the minimum voltage cell, thereby reducing overall system complexity while maintaining measurement precision.
Solution Approach 2:
The patent introduces current as an intermediary quantity to mediate between voltage measurement and digital processing. By converting cell voltages into proportional currents and using current mirrors to transfer these signals, the system avoids the need for multiple expensive ADC circuits. The current comparison mechanism serves as an efficient intermediary that enables precise voltage measurement without complex digital conversion hardware for each cell.
2Reliability
If individual monitoring of each battery cell is performed using integrated circuits with multiplexers and analog/digital converters, then reliability of battery protection is improved, but manufacturing cost increases
Solution Approach 1:
The patent combines multiple monitoring functions into a single integrated circuit device, reducing the total component count and assembly complexity. By merging the functions of multiple ADCs, multiplexers, and comparison circuits into one unified device, the invention lowers manufacturing costs while maintaining the reliability needed for battery protection through centralized monitoring and control.
Solution Approach 2:
The monitoring device automatically identifies the minimum voltage cell through internal current comparison mechanisms without requiring external control logic for each cell. The circuit self-regulates by using current mirrors to naturally compare voltages and generate appropriate protection signals, reducing the need for complex external control hardware and lowering overall system cost while ensuring reliable protection.
3Device complexity
If a simplified monitoring device using ohmic resistors and current comparison is used, then device complexity and cost are reduced, but measurement precision may be compromised
Solution Approach 1:
The patent uses current as an intermediary to maintain measurement precision in the simplified device. By converting voltages to currents through precision resistors and using current mirrors to transfer these signals without loss, the system achieves accurate minimum voltage detection. The current comparison mechanism serves as a precise intermediary that preserves voltage information while enabling simplified circuit implementation.
Solution Approach 2:
The patent changes the measurement parameter from direct voltage comparison to current comparison. By converting all cell voltages into proportional currents and comparing these currents, the system achieves precise minimum voltage detection using simpler circuitry. This parameter transformation enables the use of straightforward current mirror circuits and comparison logic while maintaining measurement accuracy.
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 solution simplifies and cost-reduces the monitoring of minimum cell voltage, enhancing system reliability and safety by effectively preventing deep discharge and ensuring efficient battery management in series-connected battery systems.
Implementation Method 1
a first ohmic resistor, which precedes all other ohmic resistors in the series circuit, is designed to carry a current corresponding to the cell voltage of the associated battery cell
Data Source
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AI summary
The invention relates to a device for measuring the minimum cell voltage among the cell voltages (U1, U2, U3) of a plurality of battery cells connected in series, wherein the device comprises a plurality of ohmic resistors (R1, R2, R3) connected in series, wherein the device can be connected to a plurality of battery cells connected in series in such a way that a respective battery cell is associated with each ohmic resistor (R1, R2, R3) according to the series connections, wherein each ohmic resistor (R1, R2, R3) with the exception of a first ohmic resistor (R3) is designed to conduct the smaller of a current that corresponds to the cell voltage (U1, U2) of the associated battery cell and the current that is conducted by the preceding ohmic resistor (R2, R3) in the series connection. The invention further relates to a corresponding method, to a corresponding battery management unit, to a corresponding battery, and to a motor vehicle having such a battery.