Contactor Weld Detection Circuit for Electric Vehicle Battery Packs
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Solution Overview
Problem
Welding of contactors in electric vehicles poses a hazard to passengers and repair technicians due to the risk of electrical shock, as existing methods lack high reliability and isolation fault tolerance for detecting contactor welds.
Innovation Solution
A method and apparatus for contactor weld detection in electric vehicles, utilizing a circuit with series-connected switches and resistors to measure current flow and determine the health status of contactors, including the ability to differentiate between partial and complete welds, and employing a tri-state switch to isolate the measurement from chassis-related faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional contactor weld detection methods are used, then the system structure is simple, but the detection reliability and isolation fault tolerance are insufficient
Solution Approach 1:
The detection circuit is segmented into multiple independent legs (first leg with first switch and first resistor, second leg with second switch and second resistor, third leg with third switch and third resistor, fourth leg with fourth switch and fourth resistor), allowing isolated testing of each contactor through separate electrical paths. This segmentation enables reliable detection while maintaining manageable circuit complexity through modular structure.
Solution Approach 2:
Resistors are introduced as intermediary elements in series with each switch and leg, enabling current measurement and weld detection without directly exposing the measurement circuit to high-voltage contactor terminals. The resistors act as protective intermediaries that facilitate safe and reliable detection.
2Measurement precision
If the detection circuit directly measures current through contactors, then the measurement is straightforward, but the system becomes vulnerable to chassis-related faults and isolation errors
Solution Approach 1:
Resistors serve as intermediary measurement elements that enable precise current measurement while electrically isolating the measurement circuit from direct contact with high-voltage contactor terminals and chassis ground. This intermediary approach maintains measurement precision while blocking harmful chassis-related faults and isolation errors from affecting the detection system.
Solution Approach 2:
The detection circuit uses itself to measure its own operating current through the series-connected resistors and switches. By measuring the current flowing through its own legs and switches, the circuit can determine contactor weld status without requiring external measurement equipment that would be vulnerable to chassis faults.
3Power
If high current is conducted through contactors for normal operation, then the vehicle can be powered effectively, but metallic parts may weld together due to heat or Lorentz force
Solution Approach 1:
The detection circuit performs preliminary weld detection by measuring current through the contactors before hazardous welding conditions develop. By continuously monitoring current flow through the legs and switches during normal high-power operation, the system can detect early signs of welding (such as abnormal current changes or voltage drops) and trigger safety responses before complete weld occurs, preventing the harmful effect while maintaining power delivery capability.
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
The solution provides high accuracy and isolation fault tolerance in contactor weld detection, ensuring safe operation by accurately identifying weld types and preventing electrical shocks during repairs.
Implementation Method 1
measuring a current that flows through the electrical path; and determining a health status of the contactor based at least on the measured current
Data Source
AI summary
The proposed mechanism for weld detection, uses isolation monitoring circuits (which is used for measurement of the leakage current between battery positive and negative to the chassis ground (on pack or link side) and checks the health status of the contactors. The mechanism connects isolation monitoring circuit between two points on the battery pack (between two sides of the high current contactors) and measures the resistance of two points, therefore checking the continuity of the contactors in the system. Since it can measure a range of resistance, it can also check if a contactor is completely welded or it has been partially welded. This would be important because in case of partial weld, the car can fix the problem and remove the partial weld by activating and deactivating the contactors for several time, with or without inserting high current in the coil of the contactors. Since the proposed mechanism is using available measurement circuits of the isolation monitoring unit and these circuits are designed with high reliability (which is required for the electrical vehicles), the proposed mechanism is going to lower the cost of the entire vehicle while keeping the passenger safe.