RF Electrical Phase Computation Using Free-Run Timers
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Solution Overview
Problem
Existing communication methods in smart electrical grids, such as powerline communications and RF techniques, face challenges in accurately determining the electrical phase of smart metering devices due to clock variance and data transmission latency, leading to inaccurate phase identification.
Innovation Solution
The use of free-run timers to measure time differences between zero-crossing events at different metering devices, allowing for phase difference determination without relying on accurate clock synchronization, and the implementation of spread spectrum techniques to determine phase differences through time-slot based calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If clock synchronization methods are used to determine phase differences, then phase identification accuracy may be improved, but system complexity and overhead increase significantly
Solution Approach 1:
The patent extracts the clock synchronization requirement from the phase determination process entirely. Instead of using synchronized clocks to measure phase differences, the invention uses zero-crossing detection combined with time-stamping and interpolation methods that work with unsynchronized clocks, thereby eliminating the complex synchronization infrastructure while maintaining measurement capability
Solution Approach 2:
The patent replaces the mechanical clock synchronization system with an electrical signal-based measurement system. By using zero-crossing detection of the voltage waveform itself and comparing time-stamps from different meters, the system substitutes complex clock synchronization mechanics with simpler electrical measurement and mathematical interpolation
2Measurement precision
If zero-crossing time-stamping is used to determine phase differences, then measurement capability is provided, but clock variance among meters renders determination inaccurate
Solution Approach 1:
The patent applies feedback by using the known frequency of the power system as a reference. The interpolation algorithm uses the expected zero-crossing intervals based on system frequency to correct and refine the measured zero-crossing times, thereby compensating for clock variance through feedback from the known system characteristics
Solution Approach 2:
The patent changes the measurement parameter from direct clock time comparison to interpolated time estimation. By calculating expected zero-crossing times based on system frequency and interpolating between actual measurements, the system transforms the raw clock time data into corrected phase information that compensates for clock variance
3Measurement precision
If clock correction overhead is implemented, then phase determination accuracy may improve, but data transmission latency and overhead increase
Solution Approach 1:
The patent performs preliminary action by pre-calculating expected zero-crossing times based on the known system frequency before actual measurements are taken. This allows the system to immediately compare actual zero-crossing occurrences with expected times and perform interpolation without requiring real-time clock synchronization or correction overhead
Data Source
AI summary
A method includes computing electrical phase of electrical metering devices including obtaining data indicating zero-crossing times at first and second metering devices. A time difference between the zero-crossing times may be determined. In a first example, the time difference may be based at least in part on calculations involving a first value of a first free-run timer on a first metering device, a second value of a second free-run timer on a second metering device, the time of reception of a packet, and a latency defined by a time taken for the packet to propagate through at least one layer of at least one of the first metering device and the second metering device. A phase difference between the first zero-crossing and the second zero-crossing may be determined, based at least in part on the determined time difference.