GFCI Offset Correction Circuit for Ground Fault Detection
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Solution Overview
Problem
Existing measurement systems for electrical signals and parameters face challenges such as reduced input voltage range, high semiconductor material consumption, frequency limitations, and accuracy issues due to temperature and manufacturing shifts, particularly in detecting ground fault conditions.
Innovation Solution
A Ground Fault Circuit Interrupter (GFCI) system utilizing an Operational Transconductance Amplifier (OTA) to generate output signals, which are modulated and filtered to determine impedance levels, combined with a randomization mechanism for ground-to-neutral measurements and an offset correction circuit to enhance accuracy and reduce semiconductor material usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resonance is established in an inductor-resistor-capacitor network to detect ground fault conditions, then detection capability is achieved, but accuracy is reduced due to temperature and manufacturing shifts
Solution Approach 1:
The patent changes the operating parameters by using a current transformer with a current source to generate a magnetic field, rather than relying on resonance in an LRC network. This parameter change makes the detection system less sensitive to temperature and manufacturing variations, thereby improving measurement precision while maintaining ground fault detection capability
Solution Approach 2:
The patent replaces the electrical resonance-based detection system with a magnetic field-based detection system using a current transformer. This substitution eliminates the temperature and manufacturing sensitivity inherent in resonant circuits, improving detection accuracy
2Measurement precision
If a resistor is placed in series with a load to measure current, then current measurement is achieved, but input voltage range is reduced and semiconductor material area increases
Solution Approach 1:
The patent replaces the physical resistor-based current measurement method with a magnetic field-based measurement using a current transformer. This substitution eliminates the need for large semiconductor resistor areas while maintaining current measurement capability and expanding the input voltage range
3Measurement precision
If a resistor is placed in series with a load to measure current, then current measurement is achieved, but input voltage range is reduced
Solution Approach 1:
The patent replaces the resistor-based current measurement with a current transformer that uses magnetic field coupling. This substitution removes the voltage drop across the resistor, thereby expanding the input voltage range and improving the adaptability of the measurement system to different voltage levels
4Reliability
If steady state stimulus is delivered to monitor waveform changes for ground fault detection, then detection is achieved, but accuracy is reduced due to temperature and manufacturing shifts
Solution Approach 1:
The patent uses periodic pulse signals to stimulate the circuit and monitor transient responses, rather than using steady-state stimuli. This periodic action, combined with current transformer-based measurement, reduces sensitivity to temperature and manufacturing variations, thereby improving detection accuracy while maintaining ground fault detection capability
Data Source
AI summary
A method and circuit for dynamically correcting offsets associated with an AC power system. In an embodiment, a first offset current generated in response to a ground to neutral fault stimulus is decreased and a second offset current generated in response to a differential fault stimulus is decreased. In another embodiment, the circuit includes an offset correction circuit that has one of a chopper circuit or an auto-zeroing circuit. An amplifier is connected to the offset correction circuit and an output connected to the offset correction circuit. A signal generator is switchably coupled to a first input of the offset correction circuit and a bias generator is switchably coupled to the first input of the offset correction circuit.