Ground Fault Detection via Inverted Flying Capacitor Voltage
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Solution Overview
Problem
Existing ground fault detection devices using flying capacitors face challenges in measuring insulation resistance when the capacitor is charged with reverse polarity, leading to complications in configuration and control, and potential exposure of control devices to high voltage, resulting in incomplete charging and inability to calculate insulation resistance.
Innovation Solution
A ground fault detection device with a capacitor and switching units connected via resistances, incorporating an offset voltage divider circuit to manage voltage measurements and ensure accurate calculation of insulation resistance regardless of charging direction, and including port failure judgment to detect abnormalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional flying capacitor ground fault detection device is used, then the insulation resistance can be measured under normal charging conditions, but the measurement fails when the capacitor is charged with reverse polarity and the configuration becomes complicated
Solution Approach 1:
The patent applies inversion by detecting ground faults through the secondary side of the booster instead of the conventional primary side (battery side) approach. By measuring insulation resistance from the output side where the flying capacitor is located, the system can detect ground faults even when the capacitor charges with reverse polarity, avoiding the need for complex polarity detection and switch control mechanisms required in conventional primary-side detection methods
2Measurement precision
If the control device directly measures the charging voltage of the flying capacitor, then the measurement can be performed, but the control device is exposed to high voltage which is unsafe
Solution Approach 1:
The patent introduces an intermediary voltage division circuit between the flying capacitor and the control device. This circuit divides the high charging voltage into a lower, safe voltage level that can be measured by the control device's A/D converter, eliminating direct high voltage exposure while preserving measurement accuracy through proper calibration of the division ratio
3Reliability
If diodes are added to prevent reverse polarity charging issues, then the measurement can be performed, but the charging becomes incomplete and insulation resistance cannot be calculated
Solution Approach 1:
The patent changes the detection parameter from direct voltage measurement to a ratio-based measurement using two different voltage division ratios. By measuring voltages through two different paths with different division ratios and calculating the insulation resistance from the ratio of these measurements, the system can accurately determine insulation resistance regardless of the charging polarity, eliminating the need for diodes that would prevent complete charging
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 easy measurement of charging voltage in both polarities, preventing control device exposure to high voltage and allowing for reliable calculation of insulation resistance, thus effectively detecting ground faults.
Implementation Method 1
a capacitor C1 functioning as a flying capacitor is charged in a path formed by turning on/off the switches S1 to S4, and the charging voltage is measured by the control device 510
Implementation Method 2
The positive electrode side insulation resistance RLp is a combined resistance of RLp1 and RLp2, and the negative electrode side insulation resistance RLn is a combined resistance of RLn1 and RLn2
Data Source
AI summary
A ground fault detection device includes: a capacitor operating as a flying capacitor; a first switching unit for switching between a state in which a positive electrode side of a battery and a first electrode plate of the capacitor are connected via a resistance, and a state in which the first electrode plate of the capacitor is connected to the ground via a measurement resistance; a second switching unit for switching between a state in which a negative electrode side of a high-voltage battery and a second electrode plate of a detection capacitor are connected with a resistance, and a state in which the second electrode plate of the detection capacitor is connected to the ground via the resistance; a control unit for controlling the first switching unit and the second switching unit; and an offset voltage divider circuit that divides and offsets the voltage generated in the measurement resistance.