MOSFET Synchronous Rectification for Self-Powered Leakage Current Measurement
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Solution Overview
Problem
Existing methods for measuring leakage current through conductors, such as those used in surge arresters, are costly, complex, and require external power sources due to the use of active electronics or complex assembly processes, and face issues with spark gap control and environmental fluctuations.
Innovation Solution
A device utilizing a magnetic core and synchronous rectification circuit with MOSFETs to convert and measure AC leakage current, eliminating the need for external power and reducing rectification losses, and incorporating overvoltage protection to isolate the measurement circuit during surge events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional diodes are used to rectify the secondary current signal in a toroidal core conversion circuit, then the leakage current can be measured, but very small secondary currents are generated so passive electronics and cost-effective analog meters cannot be used and active electronics with digital displays must be used which require external power sources
Solution Approach 1:
The patent transforms the secondary current from AC to DC using synchronous rectification with MOSFETs, fundamentally changing the electrical parameter. This DC conversion enables the use of simple, passive analog meters instead of complex active electronics with digital displays, eliminating the need for external power sources while maintaining measurement precision
Solution Approach 2:
The patent replaces the electronic rectification system (conventional diodes requiring active electronics) with a synchronous rectification system using MOSFETs controlled by optical isolation. This substitution eliminates the need for external power sources and complex digital displays, allowing the use of simple analog meters
2Measurement precision
If a metal oxide (MO) block is used to divert the leakage current to a measurement circuit, then the leakage current can be measured, but the MO block must be selected to match the characteristics of the surge arrester and the assembly process is complex
Solution Approach 1:
The patent extracts the measurement function from the surge arrester itself by using a separate toroidal core conversion circuit that magnetically couples to the ground conductor. This separation eliminates the need to select and assemble MO blocks that match the surge arrester characteristics, simplifying the manufacturing process while maintaining measurement accuracy
Solution Approach 2:
The patent introduces a toroidal core conversion circuit as an intermediary between the ground conductor and the measurement circuit. This magnetic coupling intermediary transfers the leakage current signal without direct electrical contact, eliminating the need for matched MO blocks and complex assembly procedures
3Measurement precision
If a spark gap is used to divert the leakage current to a measurement circuit, then the leakage current can be measured, but difficulties are involved in providing a specific gap distance and ensuring a safe failure mode requiring a very rigid housing
Solution Approach 1:
The patent replaces the mechanical spark gap system with a magnetic field-based toroidal core conversion circuit. This substitution eliminates the need for precise mechanical gap spacing and rigid housing structures, as the magnetic coupling occurs through the core material itself. The system inherently provides safe failure modes without requiring complex structural constraints
Solution Approach 2:
The toroidal core acts as a magnetic intermediary that couples the ground conductor to the measurement circuit without requiring direct electrical contact or precise mechanical spacing. This magnetic mediation eliminates the structural complexity and safety concerns associated with spark gap designs
4Measurement precision
If active electronics with digital displays are used to measure the leakage current, then small leakage currents can be measured, but external power sources such as solar cells, auxiliary power or batteries are required which need to be replaced periodically
Solution Approach 1:
The patent makes the measurement system self-powered by using the leakage current itself to drive the synchronous rectification circuit and analog meter. The MOSFETs are controlled by the signal being measured, and the entire system operates without external power sources, eliminating maintenance requirements for battery replacement while maintaining the ability to detect small leakage currents
Solution Approach 2:
The patent changes the electrical parameter from AC secondary current to DC current through synchronous rectification. This parameter transformation enables the use of passive analog meters that can be directly driven by the rectified current without requiring external power sources, making the system self-sufficient
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 efficient, cost-effective measurement of low leakage currents without active electronics, using the measured current to power the system and providing protection against surges, thereby reducing maintenance costs and improving reliability.
Implementation Method 1
a conversion circuit (14) comprising a magnetic core (20), wherein the conductor (12) is arranged to pass through, or wind around, the magnetic core (20) in one or more turns
Implementation Method 2
a synchronous rectification circuit (16) that comprises a plurality of metal oxide semiconductor field effect transistors (MOSFETs) (24), wherein the synchronous rectification circuit (16) is configured to rectify an alternating current (AC) to a direct current (DC)
Data Source
Figure 1
Figure 2
AI summary
Device (10) for measuring an alternating (AC) leakage current though a conductor (12), whereby the device (10) comprises: a conversion circuit (14) comprising a magnetic core (20) and a leakage current measurement circuit (18). The device (10) comprises a synchronous rectification circuit (16) that comprises a plurality of metal oxide semiconductor field effect transistors (MOSFETs) (24). The conversion circuit (14) is configured so that the conductor (12) is arranged to pass through, or wind around the magnetic core (20), and the conversion circuit (14) comprises a plurality of pairs of secondary windings (26, 28) or a single secondary winding with a plurality of taps, whereby the plurality of pairs of secondary windings (26,28) or the single secondary winding is wound around the magnetic core (20). The conversion circuit (14) is configured to convert a primary AC current in the conductor (12) to a secondary AC current in the plurality of pairs of secondary windings (26, 28) or the single secondary winding, whereby at least one first pair of secondary windings (26) or at least one first pair of taps is configured to apply a voltage to the plurality of MOSFETs, and at least one second pair of secondary windings (28) or at least one second pair of taps is connected to the synchronous rectification circuit (16). The synchronous rectification circuit (16) is configured to rectify the secondary AC current in the at least one second pair of secondary windings (28) or in the at least one second pair of taps to a direct current (DC) and supply the DC current to the leakage current measurement circuit (18).