Alternating Contactor Weld Check for EV Safety
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Solution Overview
Problem
In electrified vehicles, contactors can become welded closed due to high voltage stress, leading to improper isolation and potential safety issues, as existing weld check strategies are ineffective in detecting single or double welded contactor conditions, particularly when only one contactor is affected.
Innovation Solution
A controller is programmed to alternate the closing order of charger contactors during charge events and perform a weld check by opening the last closed contactor after each event, comparing charger and battery voltages to inhibit subsequent operations if a welded contactor condition is detected, and display indicators for operators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If contactors are used to selectively isolate high-voltage components, then safety and operational control are improved, but contactors may become welded closed under abnormal conditions, leading to improper isolation and safety issues
Solution Approach 1:
The system performs a weld check by attempting to open the contactor and verifying the expected voltage change before allowing normal operation to proceed. This preliminary detection action identifies welded contactors before they can cause safety issues or improper isolation.
Solution Approach 2:
The system continuously monitors voltage across the contactor and compares it against expected values to detect welded conditions. This feedback mechanism allows the system to identify when a contactor has become welded closed and take appropriate corrective actions.
2Reliability
If weld check strategies are implemented to detect welded contactors, then safety is improved, but existing strategies are ineffective in detecting single or double welded contactor conditions
Solution Approach 1:
The system segments the weld detection process into distinct phases: attempting to open the contactor, measuring voltage during the transition, and comparing against expected values. This segmented approach allows detection of single welded contactors by isolating the detection of each contactor's status.
Solution Approach 2:
The system uses voltage as a key parameter to detect welded contactors. By monitoring voltage across the contactor terminals and comparing it against expected voltage changes that should occur when a contactor opens, the system can detect welded conditions even when only one contactor is affected.
3Productivity
If contactors operate under high voltage stress, then charging functionality is maintained, but contactor life is reduced due to welding risk
Solution Approach 1:
The system performs weld checks after charge events by attempting to open contactors and verifying their status before allowing subsequent charging operations. This preliminary detection prevents continued operation of welded contactors, extending their effective life by identifying failures early.
Solution Approach 2:
The system uses its own operational cycles (charge events) to perform self-diagnosis of contactor health. During and after charging operations, the system automatically checks contactor status, allowing the system to monitor its own component health without external intervention.
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 approach effectively identifies and prevents vehicle operation when a welded contactor is detected, ensuring safety and extending contactor life by distributing stress evenly and guaranteeing detection of both single and double weld conditions.
Implementation Method 1
comparing charger and battery voltages to inhibit subsequent operations if a welded contactor condition is detected
Data Source
AI summary
A power distribution system for a vehicle includes contactors that selectively electrically couple a charger to a high-voltage bus. The contactors are closed at the start of a charge event in an order that alternates for successive charge events. Upon completion of the charge event, the last closed contactor at the start of the charge event is opened first and a weld check is performed. If the weld check is indicative of a welded contactor, then the weld check is performed on the other contactor.