Relay Insulation Resistance Measurement Using Pre-Charge Relay
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Solution Overview
Problem
Existing methods for obtaining insulation resistance values of main relays in electric vehicle battery systems cannot measure external side insulation resistance when the relay is switched off, leading to safety risks due to potential high-voltage ground contact.
Innovation Solution
A method and device that utilize a low-frequency AC signal to measure both internal and external side insulation resistances of a main relay by switching the pre-charge relay on and off, allowing for safe determination of insulation conditions without direct switch-on of the main relay, using a circuit with sampling points and filters to collect and analyze electrical signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the main relay is switched on to obtain external side insulation resistance, then the external side insulation resistance can be measured, but high voltage ground contact safety risks occur due to potential insulation faults
Solution Approach 1:
The pre-charge relay is switched on in advance before the main relay to pre-charge the load and establish the external circuit connection. This preliminary action enables external side insulation resistance measurement while keeping the main relay off, thus avoiding safety risks from potential insulation faults
Solution Approach 2:
The pre-charge relay acts as an intermediary device that establishes the external circuit connection without requiring the main relay to be on. By using this intermediate component, the system can measure external side insulation resistance while maintaining safety isolation through the main relay being off
2Object-affected harmful factors
If the main relay is kept off to avoid safety risks, then safety is maintained, but external side insulation resistance cannot be obtained
Solution Approach 1:
The pre-charge relay serves as a mediator that provides the necessary circuit path for measuring external side insulation resistance without requiring the main relay to be on. This allows the system to obtain external side insulation information while maintaining safety by keeping the main relay off
Solution Approach 2:
The system performs preliminary circuit setup by switching on the pre-charge relay before measurement, which establishes the external circuit path needed for measuring external side insulation resistance while keeping the main relay off to maintain safety
3Ease of operation
If existing methods are used to obtain insulation resistance, then the process is simple, but only internal side insulation resistance can be obtained while external side insulation resistance remains unmeasurable when relay is off
Solution Approach 1:
The method adds a preliminary step of switching on the pre-charge relay before measurement, which enables external side insulation resistance measurement. Although this adds a step, it maintains overall simplicity by using existing relay control mechanisms and measurement circuits
Solution Approach 2:
The measurement system is designed to perform both internal side and external side insulation resistance measurements using the same basic measurement circuitry. By controlling different relay states (main relay off with pre-charge relay on for external side), the system achieves multi-functional measurement capability
Data Source
AI summary
Provided is a method and device for obtaining internal side and external side insulation resistances of a relay. The method includes: controlling an insulation resistance obtaining circuit to output an AC signal; when both a main relay and a pre-charge relay are switched off, obtaining a first phase shift of the AC signal between two sampling points according to first collected electrical signals; obtaining an internal side insulation resistance of the main relay according to the first collected electrical signals and the first phase shift; controlling the pre-charge relay to be switched on; when the main relay is switched off and the pre-charge relay is switched on, obtaining a second phase shift of the AC signal between the two sampling points according to second collected electrical signals; and obtaining an external side insulation resistance of the main relay according to the second collected electrical signals and the second phase shift.