Battery Management System Single Data Line Cell Monitoring
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Solution Overview
Problem
Existing battery management systems for lithium batteries require complex wiring due to the need for individual communication lines for each battery cell, making it difficult to manage cell voltage and prevent overcharging or over-discharging effectively.
Innovation Solution
A battery management system that uses a single data transceiver line to monitor and control multiple battery cells in series, employing sense boards with voltage dividers to identify cell positions and transmit data, and a constant current sink to balance cell charges, allowing for precise state of charge monitoring and control without separate grounds for each cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individual communication lines are used for each battery cell, then cell voltage monitoring precision is improved, but wiring complexity increases
Solution Approach 1:
Multiple individual communication lines for each battery cell are merged into a single shared communication bus. The system combines multiple data transmission channels into one common line, allowing all sense boards to communicate with the control device through this single bus, thereby reducing wiring complexity while maintaining monitoring capabilities
Solution Approach 2:
The system implements periodic time-division multiplexing where each sense board transmits data at specific time intervals along the shared communication bus. The control device polls each cell in sequence, with each sense board activated at predetermined time slots to transmit its voltage and temperature data, enabling multiple cells to share a single communication line through time-based separation
2Device complexity
If a single data transceiver line is used for multiple battery cells, then wiring complexity is reduced, but cell identification difficulty increases
Solution Approach 1:
Each sense board is pre-configured with a unique identification code during system setup or manufacturing. These identification codes are stored in the sense boards before operation, allowing the control device to automatically recognize and address each specific sense board along the communication bus without requiring real-time identification procedures
Solution Approach 2:
The system implements dynamic address assignment where the control device can dynamically poll and activate specific sense boards based on their identification codes. The communication protocol dynamically routes data requests to the appropriate sense board by matching the requested cell position with the pre-configured identification codes, enabling flexible cell identification through a single communication line
3Measurement precision
If voltage dividers with multiple resistor combinations are used, then cell position identification precision is improved, but device complexity increases
Solution Approach 1:
Each sense board is equipped with a unique voltage divider configuration tailored to its specific cell position. The resistor values in each voltage divider are locally optimized to create distinct voltage levels corresponding to each cell's position in the series string, allowing the control device to identify cell positions based on the voltage level received from each sense board
Solution Approach 2:
The system uses voltage level encoding where each cell position is represented by a specific voltage level generated by its corresponding voltage divider. By changing the voltage parameter (through different resistor combinations) for each cell position, the system encodes position information in the voltage signal itself, allowing the control device to decode cell positions by measuring the incoming voltage levels
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 wiring and effectively prevents overcharging and over-discharging by allowing for precise monitoring and balancing of battery cell states, ensuring the longevity of lithium batteries while reducing the complexity of the system.
Implementation Method 1
the delay times are set by two quaternary bits formed by a pair of voltage dividers configured between the plurality of battery cells and the data transceiver port. Each of the voltage dividers comprises a resistor affixed to a printed circuit board and a resistor located in a jumper block
Implementation Method 2
In the sense board, a PNP transistor connects the battery cell positive terminal to the single data line and serial data is sent in digital form with an amplitude proportional to the position of the battery cell in series
Implementation Method 3
The battery management system may drain some charge from one or more of the battery cells if they are above an upper threshold limit. A drain voltage regulator may be configured with a resistor that is coupled to a ground to drain charge from a battery cell
Implementation Method 4
Therefore, a voltage regulator may be configured to reduce the voltage of the battery pack to an appropriate voltage for these components of the system, such as down to 2V
Data Source
AI summary
A battery management system monitors and controls the state of charge of a plurality of battery cells with a single data transceiver line. A sense board coupled to each cell monitors the battery cell voltage and temperature and reports the cell voltage in series, according to the location in series. A data request signal is sent by the control device of the battery management system through the single data transceiver line to initiate battery cell data transmission. The first battery cell in the series sends the first battery data upon receiving the data request signal and each subsequent battery cell in the series sends their respective battery data after a predetermined delay time set by two quaternary bits formed by a pair of voltage dividers. The state of charge may be displayed in real time on a graphical or numerical display.