Contactor Health Diagnosis via Voltage Decay Analysis
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Solution Overview
Problem
High-voltage electrical systems face challenges in diagnosing the health of contactors, which can lead to deep discharge and degradation of battery packs due to welded contactor conditions, resulting in either hard or soft weld states, and existing methods fail to differentiate between these conditions effectively.
Innovation Solution
A method using a controller with sensor input from current or voltage sensors to diagnose the state of health (SOH) of contactors by analyzing the decay rate of output voltage upon opening, differentiating between healthy, hard-welded, and soft-welded conditions, and executing control actions to manage the electrical system's functionality accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If contactor health diagnosis is not performed, then the electrical system operates without monitoring, but welded contactor conditions cause deep discharge and degradation of battery packs
Solution Approach 1:
The electrical system performs self-diagnosis by monitoring its own operational parameters (voltage decay rate, current flow) to detect contactor health status. The controller uses existing sensors and measurement capabilities to automatically identify welded contactor conditions without requiring external diagnostic equipment, thereby protecting the battery pack while maintaining system simplicity.
2Measurement precision
If existing diagnosis methods are used, then contactor health is monitored, but they fail to differentiate between hard weld and soft weld conditions
Solution Approach 1:
The system differentiates between hard weld and soft weld conditions by analyzing changes in voltage decay rate parameters. By measuring the rate at which voltage decreases after contactor opening and comparing it against threshold values, the system can precisely identify the specific weld condition type. This parameter-based approach enables accurate differentiation using standard measurement capabilities without requiring complex diagnostic equipment.
3Reliability
If the electrical system is disabled upon detecting unhealthy contactor conditions, then battery degradation is prevented, but system functionality is lost
Solution Approach 1:
Instead of completely disabling the electrical system upon detecting unhealthy contactor conditions, the system applies partial action by implementing controlled discharge protocols. The controller manages the discharge process to safely dissipate energy and protect the battery pack from degradation, while maintaining limited system functionality. This approach prevents total system shutdown while still providing adequate protection against battery damage.
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
Enables accurate diagnosis of contactor health, allowing for limited functionality or preventive measures without disabling the system, thereby preventing battery degradation and ensuring safe operation.
Implementation Method 1
a voltage sensor configured to measure an output voltage across the capacitor
Implementation Method 2
command a discharge of the link capacitor through the resistive paths of the electric machine
Implementation Method 3
discharge of the link capacitor through the resistive paths of the electric machine
Implementation Method 4
A contactor uses an electromagnet to open and close conductive mechanical contacts connected to the high-voltage bus
Data Source
AI summary
An electrical system includes a voltage bus, battery pack, power inverter module (PIM), electric machine, first contactor, and controller. The PIM is connected to the battery pack and has a capacitor, voltage sensor, and semiconductor switches. The electric machine having phase legs with a corresponding phase winding and resistive path. The first contactor connects the PIM to a positive rail of the bus. The controller opens the first contactor in response to a power-off event, commands a discharge of the capacitor through the resistive paths, diagnoses a state of health (SOH) of the first contactor using a first threshold decay rate of the capacitor output voltage upon opening the first contactor, and executes a control action with respect to the electrical system using the diagnosed SOH. The three possible SOH are unhealthy/hard-welded contactor, unhealthy/soft-welded contactor, and healthy/normally-functioning contactor condition. A vehicle and method are also disclosed.