Daisy Chain Bus Protocol for Battery Cell Supervision
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Solution Overview
Problem
Existing battery management systems face challenges in efficiently communicating with lithium-ion battery cells in electric vehicles, particularly due to high voltage levels and latency issues in data transmission, which affect real-time parameter control and measurement accuracy.
Innovation Solution
A daisy-chain communication bus and protocol are developed, enabling real-time parameter control and observation using lithium-ion in-cell supervisor (LIICS) circuits, which monitor and preprocess data, and support features like impedance measurements and passive charge balancing, using a single-wire interface that operates at moderate voltage levels, reducing the need for galvanic isolation and minimizing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional high-voltage communication buses are used to communicate with battery cells, then communication can be established, but galvanic isolation and high-voltage components are required, increasing device complexity and cost
Solution Approach 1:
A communication bus interface circuit is introduced as an intermediary between the high-voltage battery cell environment and the low-voltage control system. This interface circuit enables electrical connection without galvanic isolation by translating signals and adapting voltage levels, thereby eliminating the need for complex isolation components while maintaining communication reliability
Solution Approach 2:
The communication system changes voltage level parameters to operate at moderate levels compatible with standard digital logic. By transforming the high-voltage battery domain signals into low-voltage digital signals, the system avoids the need for high-voltage components and galvanic isolation, reducing device complexity while maintaining reliable communication
2Productivity
If traditional multi-wire communication interfaces are used, then data transfer can occur, but mechanical complexity and wiring requirements increase
Solution Approach 1:
Multiple communication functions (data transmission, acknowledgment, error detection) are merged into a single-wire interface. The interface uses bidirectional communication over one wire, combining multiple signal paths into a single physical connection, thereby reducing mechanical complexity and wiring requirements while maintaining data transfer efficiency
Solution Approach 2:
The patent extracts the essential communication function from complex multi-wire interfaces, retaining only the critical data exchange capability. By removing unnecessary wires and protocols, the system achieves efficient data transfer with minimal wiring, reducing mechanical complexity without sacrificing productivity
3Reliability
If high-voltage components and galvanic isolation are used, then safety is improved, but cost and device complexity increase
Solution Approach 1:
The communication bus interface circuit serves as a safe intermediary that enables controlled electrical connection between high-voltage and low-voltage domains. It provides inherent protection through voltage translation and signal conditioning, maintaining safety without requiring additional isolation components, thereby reducing complexity while preserving safety
4Productivity
If real-time parameter control is implemented, then battery performance is improved, but communication latency must be minimized
Solution Approach 1:
Command and acknowledgment signals are merged into the same single-wire communication channel, transmitted in alternating directions. This eliminates the need for separate dedicated signal paths, reducing communication overhead and latency while enabling real-time parameter control through efficient bidirectional communication
Data Source
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Figure 3A
AI summary
A battery pack has first and second battery terminals, plural battery cells each with a battery element, a cell supervisor electrically connected to the battery element, and a communication section to communicate with the cell supervisor. The battery elements are connected serially between the first and second battery terminals. Bus interfaces are arranged in alternating fashion with the battery cells to define a daisy chain bus, each such bus interface being configured for signal communication, the interfaces respectively connecting the communication sections of two adjacent battery cells. A battery manager communicates with the battery cells via the daisy chain bus. The battery manager sends a command message to the battery cells using a through mode protocol, and each battery cell sends at least one of a confirmation message and a service request to the battery manager using a shift mode protocol.