Capacitive Data Isolation Circuit for High-Voltage Metering Lines
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Solution Overview
Problem
Current methods for coupling data from high-voltage lines to low-voltage data transmission systems in electricity usage meters are inefficient and costly, with transformers being large, heavy, and expensive, and optical couplers being non-linear and unable to support high data rates effectively.
Innovation Solution
The use of electrical capacitance across a dielectric as a coupling medium, combined with unique data encoding techniques, such as Manchester encoding, to transfer multiple channels of information accurately across a high-voltage isolation barrier, employing a capacitive coupling circuit with a data converter, multiplexer, and data encoder to generate an encoded composite bit stream that minimizes capacitive reactance and supports high data rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transformers are used for voltage isolation and data coupling, then isolation capability is improved, but device size, weight, and cost increase significantly
Solution Approach 1:
The patent replaces the mechanical/electromagnetic transformer system with an optical coupling system. Optical couplers use light transmission through isolated barriers instead of electromagnetic induction, eliminating the need for heavy iron cores and windings while maintaining voltage isolation capability. This substitution directly addresses the contradiction by removing the weight penalty while preserving isolation functionality.
Solution Approach 2:
The patent introduces an optical intermediary (light signal) to transfer data across the voltage isolation barrier. Instead of direct electrical coupling through transformers, the system uses optical couplers that convert electrical signals to optical signals, transmit them through an isolated medium, and convert them back. This intermediary approach maintains isolation while eliminating the physical bulk of transformers.
2Reliability
If optical couplers are used in the analog data path, then isolation capability is improved, but linearity deteriorates due to high non-linearity requiring hardware or software linearization
Solution Approach 1:
The patent changes the operating parameters of the optical coupling system by using digital signal levels (logic high and logic low) instead of analog signal levels. This parameter change from analog to digital operation eliminates the non-linearity issue because digital signals have discrete, well-defined states that are less sensitive to optical coupling non-linearities. The system achieves accurate data transmission without requiring linearization hardware or software.
3Reliability
If optical couplers are used in the digital path, then isolation capability is improved, but data rate capability deteriorates because inexpensive optical couplers support only about half the required data rate
Solution Approach 1:
The patent employs periodic clocked operation with duty cycle modulation to transmit digital data through the optical coupler. By using synchronized clock signals and periodic sampling, the system achieves reliable digital communication at the required data rates. This periodic action approach allows the use of slower, more cost-effective optical couplers while maintaining high data rate performance through efficient time-division multiplexing and clocked operation.
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 solution provides accurate and cost-effective data transfer across high-voltage isolation barriers, reducing equipment size, weight, and heat dissipation while ensuring safety and reliability, with the capacitive coupling medium being inexpensive and capable of handling high-voltage differences.
Implementation Method 1
using electrical capacitance across a dielectric as the coupling medium
Implementation Method 2
electrical capacitance across a dielectric as the coupling medium
Data Source
AI summary
The present invention comprises a circuit for transferring N inputs, wherein N is greater than or equal to 2, across a capacitive coupling media comprising a line circuit, a coupling capacitor, and a neutral potential circuit. The line circuit comprises: (1) a data converter for each input, for sampling and converting the N inputs; (2) a multiplexer for combining the outputs of the N data converters and a synchronization signal to generate an unencoded composite bit stream; (3) a data encoder for encoding the composite bit stream. The capacitor couples the encoded composite bit stream to a data decoder. The neutral potential circuit comprises: (1) the data decoder for decoding the coupled composite bit stream, and generating a recovered data stream and a recovered clock; (2) a synchronization recovery, control logic, and de-multiplex function for providing a set of digital outputs that correspond to the inputs to the data converters.