GFCI Current Measurement Using Electromagnetic Induction
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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 reduced accuracy 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 multiple output signals, which are modulated and filtered to determine impedance levels, and a single wound single current transformer circuit for cost-efficient implementation, along with a digital control circuit and randomization of ground-to-neutral measurements to minimize interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistor is placed in series with a load to determine current, then the current measurement is achieved, but the input voltage range is reduced
Solution Approach 1:
The patent replaces the traditional resistive current sensing method with a current transformer-based electromagnetic sensing system. The current transformer uses electromagnetic induction to sense current without introducing a series resistance, thereby preserving the full input voltage range while achieving accurate current measurement through magnetic field coupling rather than voltage drop.
Solution Approach 2:
The patent introduces a current transformer as an intermediary device between the load and the measurement circuit. This transformer acts as a mediator that couples the primary current to the secondary measurement circuit through electromagnetic induction, allowing current sensing without directly inserting a resistance into the power path.
2Measurement precision
If traditional measurement circuits are used, then current measurement is achieved, but large areas of semiconductor material are consumed
Solution Approach 1:
The patent replaces complex semiconductor-based measurement circuits with a current transformer implementation that can be realized using fewer semiconductor components. The current transformer approach shifts the measurement function to an electromagnetic domain, reducing the need for large-area semiconductor circuits for signal conditioning and measurement.
Solution Approach 2:
The current transformer serves multiple functions simultaneously: it provides current sensing, galvanic isolation, and signal transformation in a single component, eliminating the need for separate semiconductor circuits for each function and thereby reducing total semiconductor material area.
3Reliability
If resonance technique is used to detect ground fault, then ground fault detection is achieved, but temperature and manufacturing shifts reduce accuracy
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors the differential voltage and compares it against dynamically adjusted thresholds. The system uses feedback to compensate for temperature and manufacturing variations by adapting the detection criteria based on real-time operating conditions, thereby maintaining high detection accuracy despite environmental changes.
Solution Approach 2:
The patent transitions from a static resonance-based detection method to a dynamic differential voltage measurement approach. The system continuously adapts its measurement and comparison process based on real-time conditions, allowing it to compensate for temperature drift and manufacturing tolerances through dynamic threshold adjustment rather than relying on fixed resonant frequencies.
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 GFCI system provides accurate and cost-effective measurement of electrical signals and parameters, including impedance, while minimizing false trips and reducing the impact of temperature and manufacturing variations, thereby enhancing the reliability of ground fault detection.
Implementation Method 1
a current transformer 51 having a primary winding 52 and a secondary winding 53
Implementation Method 2
establish resonance in an inductor-resistor-capacitor network when it is exposed to a ground-to-neutral condition. Resonance may be established by delivering a pulse to a positive feedback system that includes an operational amplifier
Data Source
AI summary
A method for determining a circuit element parameter in a ground fault circuit interrupter circuit. An electrical signal provided to a first node is used to generate another electrical signal at a second node. The electrical signal at the second node is multiplexed with a modulation signal to generate a modulated signal that is then filtered and converted into a digital representation of a portion of the circuit element parameter. The electrical signal at the second node is multiplexed with the modulation signal after it has been phase shifted to produce a modulated signal that is filter and converted into a digital representation of another portion of the circuit element parameter. In another aspect, a slope based solenoid self-test method is used for self-testing in a GFCI circuit. Alternatively, a method for determining a wiring fault is provided using a digital filter.