Earth Leakage Detection Circuit With Coupling Capacitor Voltage Compression
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Solution Overview
Problem
In earth leakage detection devices for electric vehicles, sudden changes in the earth leakage state, such as the opening and closing of main relays, cause voltage deviations from the measurement range, leading to prolonged periods where the voltage at the measurement point is outside the acceptable range.
Innovation Solution
An earth leakage detection device with a coupling capacitor, a voltage output unit generating a periodically changing voltage, and resistors connected in series between the coupling capacitor and a fixed potential, allowing for voltage measurement and determination of earth leakage between the power storage unit and ground, effectively compressing the voltage range to shorten deviation periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pulse voltage is applied to detect earth leakage in an AC type earth leakage detection device, then the presence or absence of earth leakage can be detected, but the voltage at the measurement point may deviate from the measurement range during sudden changes in earth leakage state such as opening and closing of main relay
Solution Approach 1:
A coupling capacitor is introduced as an intermediary component between the pulse voltage application circuit and the measurement point. This capacitor blocks the direct coupling of large voltage transients caused by main relay switching, allowing the detection circuit to measure earth leakage accurately while preventing measurement range deviations. The capacitor acts as a mediator that separates the high-voltage switching domain from the low-voltage measurement domain.
Solution Approach 2:
The invention changes the electrical parameters at the measurement point by using the coupling capacitor to transform the voltage waveform. The capacitor filters out high-frequency transient components and scales the voltage amplitude, ensuring that even during sudden earth leakage changes, the measurement point voltage remains within the acceptable measurement range while still containing sufficient information for accurate earth leakage detection.
2Reliability
If additional filtering components are added to prevent voltage deviation from measurement range, then measurement reliability can be improved, but device complexity increases
Solution Approach 1:
The coupling capacitor serves multiple functions simultaneously: it acts as a transient filter to prevent voltage deviations, serves as a coupling element to transfer the detection signal, and provides impedance transformation. By making this single component multi-functional, the invention achieves measurement reliability improvement without adding multiple separate filtering components, thus avoiding increased device complexity.
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
This configuration significantly reduces the time the voltage at the measurement point deviates from the measurement range, enhancing safety and reducing the need for additional filtering components, thus improving detection accuracy and system reliability.
Implementation Method 1
a coupling capacitor having one end connected to a current path of a power storage unit connected to a load in a state of being insulated from a ground
Implementation Method 2
a second resistor and a third resistor connected in series between a node between the coupling capacitor and the first resistor and a predetermined fixed potential
Data Source
AI summary
In earth leakage detection device, one end of coupling capacitor is connected to a current path of power storage unit connected to load in a state of being insulated from the ground. Voltage output unit generates a periodically changing periodic voltage, and applies the periodic voltage to the other end of coupling capacitor via first resistor. Second resistor and third resistor are connected in series between a node between coupling capacitor and first resistor and a predetermined fixed potential. Voltage measurement unit measures a voltage at a voltage dividing point between second resistor and third resistor. Earth leakage determination unit determines presence or absence of an earth leakage between the current path of power storage unit and the ground based on the measured voltage.