Power Measurement Using Asynchronous Timing Synchronization
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Solution Overview
Problem
Measuring real power accurately when voltage and current are measured at separate locations on an AC power line is challenging due to the need for high galvanic isolation and the difficulty in tracking relative phase information, which is costly and complex, especially when multiple branch circuits need to be monitored.
Innovation Solution
An asynchronous data network is used to synchronize voltage and current measurements by sending a timing message from the voltage sensing device to the current sensing device at a predetermined point in the voltage cycle, allowing the current sensing device to establish a cycle reference time and calculate the actual power drawn based on the measured current and synchronized model of the voltage cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage and current are measured at the same location to ensure accurate power measurement, then measurement precision is improved, but device complexity and cost increase due to requirements for high galvanic isolation
Solution Approach 1:
The measurement system is divided into two separate locations: voltage measurement at the service entrance and current measurement at the load center. This segmentation allows each measurement to be optimized independently, with voltage measured using expensive isolated equipment only where necessary, and current measured using simpler, less expensive equipment at a different location.
Solution Approach 2:
A timing message is used as an intermediary to transfer phase information from the voltage measurement location to the current measurement location. This timing message contains the phase reference information needed to accurately calculate power without requiring direct galvanic isolation between the measurement points.
2Measurement precision
If voltage measurement equipment is used at multiple branch circuit locations to monitor power, then measurement precision is improved, but cost increases significantly
Solution Approach 1:
The timing message mechanism serves multiple functions: it provides phase reference information for power calculation, enables synchronization between different measurement locations, and works across all branch circuits using a single voltage measurement at the service entrance. This eliminates the need for separate voltage measurement equipment at each branch circuit location.
Solution Approach 2:
Instead of duplicating expensive voltage measurement equipment at each branch circuit, the system creates a timing message that copies the phase reference information from the single voltage measurement location and transmits it to the load center where current measurements are taken.
3Device complexity
If voltage and current measurements are separated to simplify current measurement circuits and reduce cost, then device complexity is reduced, but tracking relative phase information becomes difficult
Solution Approach 1:
The timing message provides feedback about the phase reference from the voltage measurement location to the current measurement location. This feedback mechanism ensures that the phase relationship between voltage and current is maintained and can be used to accurately calculate power despite the physical separation of measurement locations.
Data Source
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AI summary
Power measurement by tracking of a voltage cycle when voltage and current measurements are taken at different locations on an AC power line, with the devices taking the measurements interconnected by an asynchronous data network. In general, a synchronization/timing message is sent from the voltage sensing side to the current sensing side, with the synchronization/timing message being transmitted at a predetermined point in the periodic voltage cycle. The receipt of the synchronization/timing message by the current sensing side may be used to re-synchronize an internal model of the voltage cycle maintained by the current sensing side to the measured voltage cycle. The predetermined point in the voltage cycle may be the zero-crossing point, or other point, of the voltage cycle.