EV Ground Fault Detection via Switch-Driven Capacitance Transients
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Solution Overview
Problem
Current fault detection systems for high voltage DC systems in electric vehicles are unreliable due to high parasitic and inherent capacitance, making capacitively coupled signals noisy and Wheatstone bridge shorts undetectable, necessitating a more reliable method for identifying ground faults.
Innovation Solution
A fault detection apparatus and method that utilizes a fault detection module connected between the chassis ground and switches in a high voltage DC system, with a switch driver to charge and discharge inherent capacitance, and a current sensor to measure currents, determining parasitic resistance and leakage current to detect ground faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitively coupled signal is used for fault detection in high voltage DC systems, then fault detection capability is provided, but the high parasitic and inherent capacitance makes the signal too noisy for reliable detection
Solution Approach 1:
The patent applies periodic action by sequentially and alternately closing switches S1 and S2 to charge and discharge the inherent capacitance C in predetermined intervals. This periodic charging/discharging generates measurable current transients that can be detected despite the presence of parasitic capacitance, transforming a continuous noisy signal problem into a periodic measurement problem with distinct detectable events.
Solution Approach 2:
The patent changes the measurement parameter from voltage-based capacitively coupled signals to current-based measurements. By measuring the current transients during charging and discharging phases through the sequential switch operation, the system achieves reliable fault detection by detecting changes in current parameters rather than relying on noisy voltage signals.
2Device complexity
If a Wheatstone bridge is used for fault detection, then a detection structure is provided, but shorts across the detection nodes become undetectable
Solution Approach 1:
The patent inverts the traditional Wheatstone bridge approach by using sequential switch closure to charge and discharge capacitance, then measuring the resulting current transients. Instead of measuring voltage dividers as in a traditional bridge, the system measures current flow during capacitive charging/discharging phases, which remains sensitive to shorts across detection nodes while providing detectable signals.
3Measurement precision
If sequential switch operation is used to charge and discharge inherent capacitance, then current measurement for fault detection is enabled, but additional switching components and control logic are required
Solution Approach 1:
The patent makes the switches S1 and S2 serve multiple functions: they act as isolation switches for the high voltage DC system, as charging/discharging switches for the inherent capacitance, and as measurement enablement switches. This multi-functionality reduces the need for separate dedicated measurement components, offsetting the added complexity with functional consolidation.
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
The solution effectively identifies ground faults by accurately measuring currents through the inherent capacitance, providing reliable fault detection even in electrically noisy environments, thereby ensuring safety by preventing dangerous voltage leakage.
Implementation Method 1
a device having inherent capacitance between the direct current system and a chassis ground
Data Source
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AI summary
A method of detecting a ground fault condition between a direct current power system and the chassis ground of an electric or hybrid-electric vehicle is provided. The method includes sequentially opening and closing a first switch connected between a positive node of the direct current power system and the chassis ground of the vehicle and a second switch connected between a negative node of direct current power system and the chassis ground. The sequential opening and closing of the first and second switches charges and discharges an inherent capacitance present between the metal components of the direct current power system and the chassis. First and second currents are created as the inherent capacitance is charged and discharged. Measurements of the created first and second currents are then used to determine whether a ground fault condition exists between the direct current power system and the vehicle chassis ground.