AC Coupling Contactor Detection for EV Battery Isolation
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Solution Overview
Problem
Existing methods for detecting defective contactors in high-voltage battery systems of electric vehicles compromise DC isolation and may lead to safety hazards due to failure in opening or closing properly, causing potential energy loss and hazardous conditions.
Innovation Solution
A system and method using an AC test signal and AC coupling circuit to detect defective contactors by analyzing AC return signals, maintaining DC isolation and enabling safe disconnection of faulty battery strings from the DC bus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC current or voltage is measured directly in the high-voltage DC circuit to detect defective contactor, then detection capability is improved, but DC isolation between contactor and chassis ground is compromised
Solution Approach 1:
The patent introduces an AC coupling circuit as an intermediary component between the detection circuit and the high-voltage DC circuit. This AC coupling circuit allows AC test signals to pass through for contactor detection while blocking DC current, thereby maintaining DC isolation between the contactor and chassis ground. The intermediary AC coupling circuit resolves the contradiction by enabling detection functionality without compromising the critical DC isolation safety requirement.
2Device complexity
If contactor degradation is not detected, then system simplicity is maintained, but safety hazards and energy loss occur due to failure to open or close properly
Solution Approach 1:
The patent implements preliminary detection action by continuously monitoring contactor status through AC coupling before actual failure occurs. The detection circuit proactively identifies contactor degradation, welding, or failure conditions by analyzing AC test signal responses, enabling early warning and preventive maintenance. This preliminary detection prevents safety hazards and energy loss by alerting the system to contactor issues before they cause catastrophic failure.
3Reliability
If AC coupling circuit is used for contactor detection, then DC isolation is maintained, but device complexity increases
Solution Approach 1:
The AC coupling circuit serves multiple functions simultaneously: it acts as a DC block to maintain isolation, serves as a signal path for AC test signals, and provides impedance transformation for the detection circuit. By making the AC coupling circuit multi-functional, the patent reduces the need for additional separate components, thereby limiting the increase in overall device complexity while achieving the critical DC isolation requirement.
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
Effectively detects defective contactors without compromising DC isolation, preventing energy loss and safety hazards by enabling timely disconnection and providing warning signals or inhibiting vehicle functions.
Implementation Method 1
an AC coupling circuit having a primary side and a secondary side. The primary side of the AC coupling circuit may be connected to the AC test signal source, and the secondary side may be connected to the contactor
Data Source
AI summary
A system for detecting a condition of a contactor configured to connect a battery string to a direct-current bus in a vehicle may include a controller configured to open or close the contactor. The system may also include an alternating-current (AC) signal source configured to provide an AC test signal when the controller opens the contactor. The system may further include an AC coupling circuit. The AC coupling circuit may include a primary side of the AC coupling circuit connected to the AC test signal source, and a secondary side connected to the contactor. The system may also include a detection circuit configured to receive an AC return signal corresponding to the AC test signal, and determine a defective condition of the contactor based on the AC return signal.