Battery Management System Overvoltage Detection via Current Sensing
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Solution Overview
Problem
Voltage imbalance between secondary cells in battery packs can lead to erroneous overvoltage determinations due to contact failures in wire connectors, causing malfunctions in devices powered by these packs, such as electric bicycles, due to changes in contact resistance from vibrations or adhesive application.
Innovation Solution
A battery management system with a controller that detects cell voltages and charging currents to determine overvoltage states based on the presence of charging current, using a current sensing resistor and voltage detection circuit, and turns off charge and discharge control switches when maximum cell voltage exceeds threshold values, preventing erroneous overvoltage determinations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wire connector is used to connect cell balancing circuit to each cell, then voltage monitoring function is achieved, but contact resistance changes due to vibration or adhesive application causing measurement errors
Solution Approach 1:
The patent introduces a current sensing resistor as an intermediary element in the high current path. By detecting voltage drops across this resistor, the system indirectly monitors charging current, serving as a mediator between the charging system and the controller to determine overvoltage states without relying on unstable wire connector connections to individual cells.
Solution Approach 2:
The patent replaces the mechanical wire connector system (which physically connects to each cell) with an electrical measurement approach using a current sensing resistor in the high current path. This substitution eliminates the mechanical contact reliability issues while achieving the same monitoring objective through electrical parameter detection.
2Reliability
If cell voltage is monitored through wire connector to determine overvoltage state, then overvoltage protection is achieved, but contact failure is erroneously detected as overvoltage state
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors both cell voltage and charging current status. By cross-referencing these two parameters, the system can distinguish between genuine overvoltage conditions (high voltage with charging current) and contact failures (high voltage without charging current), providing accurate feedback for proper control actions.
Solution Approach 2:
The patent performs preliminary detection of charging current status before making overvoltage determination. By checking whether charging current is flowing first, the system prepares the correct interpretation framework for subsequent voltage measurements, preventing erroneous conclusions before they occur.
3Reliability
If charge control switch is turned off based on voltage threshold alone, then overvoltage protection is provided, but false switching occurs due to connector contact failure
Solution Approach 1:
The patent introduces dynamic decision-making where the overvoltage protection action (turning off charge control switch) is not triggered by voltage threshold alone, but by the combination of voltage threshold and charging current status. This dynamic approach adapts the protection response based on real-time operational context, preventing false switching while maintaining genuine protection.
Solution Approach 2:
The patent changes the decision parameters from a single voltage threshold to a composite criterion involving both voltage threshold and charging current presence. This parameter change transforms the control logic from simple voltage-based switching to a more nuanced state-based control, eliminating false operations.
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
Prevents malfunctions by accurately determining overvoltage states and controlling switches to prevent power interruptions, ensuring reliable operation of battery-powered devices.
Implementation Method 1
a current sensing resistor connected in series to the high current path, and the controller may include a current detection circuit connected to opposite ends of the current sensing resistor to detect the charging current through the current detection circuit
Implementation Method 2
a voltage detection circuit connected to each of the cells through a balancing connector
Data Source
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AI summary
A battery management system may include: a charge control switch disposed in a high current path between a plurality of pack terminals and a battery module; and a controller configured to detect a cell voltage of each of a plurality of cells included in the battery module and a charging current flowing through a high current path, to determine an overvoltage state of the battery module based on presence or absence of the charging current and the cell voltage of each of the cells, and to turn off the charge control switch when the battery module is determined to be in an overvoltage state.