Galvanically Isolated Differential Current Circuit With High-Resolution Timing
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Solution Overview
Problem
Existing methods for measuring differential current in electrical systems face limitations in resolution and require complex, costly circuit arrangements, especially when detecting small currents or current changes, and are not economically viable for certain applications.
Innovation Solution
An electrical circuit arrangement using a toroidal current transformer with separate driver and second oscillator circuits, enabling high-resolution differential current measurement by modulating the magnetization curve between saturation points and utilizing a high-frequency clock signal for precise dwell time determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If oscillator circuits with ASIC or integrated circuits are used for differential current measurement, then measurement sensitivity is improved, but device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent divides the measurement system into functionally independent modules: a current transformer for magnetic field detection, a first oscillator circuit for signal generation, a second oscillator circuit for time measurement, and an evaluation unit for processing. This segmentation allows each module to be optimized independently and simplifies the overall system architecture compared to monolithic ASIC designs.
Solution Approach 2:
The patent introduces a magnetic core as an intermediary element that couples the primary current to be measured with the secondary measurement circuitry. The magnetic core transforms electrical current into magnetic flux, which then modulates the oscillator circuits, providing galvanic isolation while enabling precise measurement.
2Measurement precision
If a second current-limited path to earth is connected to increase differential current for measurement, then measurement signal strength is improved, but system safety and regulatory compliance deteriorate
Solution Approach 1:
The patent uses oscillator circuits to generate periodic excitation signals that modulate the magnetic core's magnetization state. This oscillatory approach allows the system to detect very small differential currents by measuring changes in the oscillator's duty cycle, eliminating the need to create artificial current paths.
Solution Approach 2:
The patent changes the measurement parameter from direct current magnitude to time-modulated oscillator signal characteristics (duty cycle). By measuring the duty cycle of the first oscillator circuit, which is modulated by the differential current through the magnetic core, the system can detect currents below 10 μA without requiring additional current paths.
3Measurement precision
If high-resolution measurement of small differential currents is achieved, then measurement sensitivity is improved, but measurement resolution requirements increase system complexity
Solution Approach 1:
The patent replaces direct electrical measurement methods with a magnetic field-based measurement system. The current transformer and magnetic core convert electrical current into magnetic flux, which then modulates the oscillator circuits. This substitution enables high-resolution measurement of small currents while maintaining system simplicity.
Solution Approach 2:
The patent employs periodic oscillation of the magnetic core's magnetization state through the first oscillator circuit. By measuring the duty cycle of these periodic oscillations, which are modulated by the differential current, the system achieves high measurement resolution for small currents without complex measurement circuitry.
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
Achieves high-resolution detection of small differential currents and changes with economic efficiency, offering a large dynamic range and improved measurement sensitivity without increasing costs.
Implementation Method 1
the vector sum of the currents (primary current) on all active conductors of a supply line, for example, the line of a power supply system, is zero, and therefore no magnetic field exists in a magnetizable ring core of a current transformer surrounding the supply line
Implementation Method 2
The changing magnetic flux caused by this differential current within the ring core induces a voltage in a secondary coil of the current transformer
Implementation Method 3
These circuits sweep the magnetization curve of the current transformer's core between upper and lower saturation points by means of a controlled secondary-side current flow
Data Source
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AI summary
The invention relates to an electrical circuit arrangement (2) and a measuring method for galvanically isolated, all-current-sensitive differential current measurement with high resolution and comprises the following elements: a toroidal current transformer (4) with at least one secondary winding (6) for detecting a differential current (I d), a driver circuit (12) for energizing the secondary winding (6), a first oscillator circuit (22) for controlling the driver circuit (12) and for generating a time-modulated, binary oscillator signal (V) with dwell times (Th, Tl) in a state 1 (S1) and in a state 2 (S2), a second oscillator circuit (32) for high-resolution determination of the respective dwell time (Th, Tl) in states 1 and 2 by means of a clock signal (C) with a clock rate independent of the oscillator signal (V), an evaluation unit (42) for evaluating the dwell times (Th, Tl), and a data interface (52) for outputting a Differential current measurement (Im, I'm),wherein the driver circuit (12) and the second oscillator circuit (32) are each implemented as physically separate, integrated circuits.