Earth Fault Detection Circuit Using Capacitive Filtering
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Solution Overview
Problem
Existing earth fault detection circuits in high-voltage power source devices, such as those in electric cars, face difficulties in accurately judging earth faults due to noise interference from inverters, particularly when using filter circuits with resistors and capacitors, which are not safe and inefficient in terms of power consumption.
Innovation Solution
An earth fault detection circuit that generates an A.C. signal and uses capacitive elements to input the A.C. component of the voltage division signal to an earth fault detection portion, allowing for noise level determination and accurate fault detection between a high-voltage battery and a motor, even under inverter noise influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter circuit with resistor and capacitor is used to remove high-frequency noise, then noise removal function is improved, but safety and power consumption are worsened
Solution Approach 1:
The patent extracts only the necessary capacitive filtering function from the traditional RC filter circuit, removing the resistive component. The coupling capacitor C1 and detection capacitor C2 provide noise filtering while maintaining safety and reducing power consumption by eliminating the continuous power dissipation associated with resistors.
Solution Approach 2:
The patent uses capacitors instead of resistors, where the capacitor can be charged and discharged without continuous power consumption. The capacitor temporarily stores energy during charging and releases it during discharging, providing noise filtering without the continuous power loss characteristic of resistive circuits.
2Object-affected harmful factors
If a filter circuit with resistor and capacitor is used to remove high-frequency noise, then noise removal function is improved, but power consumption is worsened
Solution Approach 1:
The patent extracts only the necessary capacitive filtering function from the traditional RC filter circuit, removing the resistive component. The coupling capacitor C1 and detection capacitor C2 provide noise filtering while maintaining safety and reducing power consumption by eliminating the continuous power dissipation associated with resistors.
Solution Approach 2:
The patent uses capacitors instead of resistors, where the capacitor can be charged and discharged without continuous power consumption. The capacitor temporarily stores energy during charging and releases it during discharging, providing noise filtering without the continuous power loss characteristic of resistive circuits.
3Measurement precision
If noise removing circuit is turned ON to judge earth fault, then detection accuracy is improved, but noise is treated as earth fault causing false positives
Solution Approach 1:
The patent dynamically adjusts the noise filtering based on the detection mode. During AC signal-based earth fault detection, the capacitive coupling naturally filters high-frequency inverter noise while allowing the lower frequency detection signals to pass through, eliminating the need for active noise removal that could cause false positives.
Solution Approach 2:
The patent changes the frequency domain characteristics of the detection system by using AC signal injection and capacitive coupling. This frequency-based separation allows the system to distinguish between high-frequency inverter noise and lower frequency earth fault indicators, improving detection accuracy without treating noise as faults.
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 reliable earth fault judgment by suppressing inverter noise within the input voltage range of the microprocessor's AD converter, ensuring safe and efficient operation by minimizing power consumption and improving detection precision.
Implementation Method 1
a first capacitive element provided between the A.C. signal generation portion and one end side of the high-voltage battery; a second capacitive element provided between the voltage dividing circuit and the earth fault detection portion
Implementation Method 2
a voltage dividing circuit for dividing a voltage on the one end side of the high-voltage battery
Data Source
AI summary
An earth fault detection circuit for detecting an earth fault between a high-voltage battery and a motor includes: an A.C. signal generation portion generating an A.C. signal; a first capacitive element between the A.C. signal generation portion and one end side of the high-voltage battery; a voltage dividing circuit dividing a voltage on the one end side of the high-voltage battery; an earth fault detection portion detecting the earth fault between the high-voltage battery and the motor based on an earth fault detection signal inputted thereto; and a second capacitive element inputting an A.C. component of the voltage, on the one end side of the high-voltage battery, which is obtained by the voltage division in the voltage dividing circuit as the earth fault detection signal to the earth fault detection portion.