Relay Contact Welding Detection Using Voltage Measurement
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Solution Overview
Problem
Current systems lack a cost-effective method to independently detect welding of relay contacts in DC power supply systems, particularly in hybrid electric and electric automobiles, without requiring additional detection circuits or special relay mechanisms.
Innovation Solution
A method and apparatus that utilize a sequence control of the main relays and precharge relay, measuring voltage across the load circuit to detect welding by shifting from a normal operation state to a suspension state, allowing independent detection of welding on either the positive or negative side without additional circuits or special relays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a precharge relay and resistor are added to prevent welding, then relay contact welding is prevented, but device complexity and cost increase
Solution Approach 1:
The system uses its own existing voltage measurement capability to detect relay contact welding without requiring external detection circuits. The control unit leverages the voltage measurement already performed for other control purposes, making the detection function self-service and avoiding additional hardware complexity.
Solution Approach 2:
The voltage measurement unit serves multiple functions: it measures voltage for normal operation control and simultaneously detects relay contact welding. This multi-functionality eliminates the need for separate detection circuits, resolving the contradiction between reliability improvement and device complexity.
2Difficulty of detecting and measuring
If additional detection circuits are added to detect welding, then welding detection capability is improved, but device complexity and cost increase
Solution Approach 1:
The control unit uses its existing voltage measurement capability to detect welding, making the detection function self-service. No external detection circuits are needed because the system leverages measurements already being performed for other control purposes.
Solution Approach 2:
The voltage measurement unit performs dual functions: normal operation voltage measurement and welding detection. This multi-functionality provides welding detection capability without adding separate detection circuits, resolving the contradiction between detection capability and device complexity.
3Difficulty of detecting and measuring
If special relay mechanisms are added to detect welding, then welding detection is enabled, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical relay-based detection mechanisms with an electronic voltage measurement approach. Instead of using special relay mechanisms with moving parts, the system uses electronic voltage sensing and control unit logic to detect welding, reducing mechanical complexity.
Solution Approach 2:
The control unit performs multiple functions including normal control and welding detection using the same voltage measurement hardware. This eliminates the need for special relay mechanisms and provides welding detection capability through software/logic in the existing control unit.
Data Source
AI summary
A method for detecting a welding of a relay contact in a circuit having a DC power supply; a load circuit; a first main relay and a second main relay respectively inserted in a pair of power supply lines disposed between the DC power supply and the load circuit; and a precharge relay which is provided in parallel to the contact of the first main relay has the step of carrying out a sequence control to each of the relays (11, 12, 13) while measuring voltage across both ends of the load circuit (16) when shifting from a normal operation state in which a first main relay (11) and a second main relay (12) are controlled to be on and the precharge relay (13) is controlled to be off to a suspension state in which each of the relays (11, 12, 13) are controlled to be off. The welding of the relay contact of the first main relay (11) and the second main relay (12) is determined independently and separately from a correspondence between the proceeding of the sequence and the measured voltage.