AC Power Measurement Phase Drift Correction
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Solution Overview
Problem
Monitoring electrical parameters like voltage, current, and power from multiple AC power sources with different synchronization and phase issues is challenging, especially during outages, as existing solutions struggle to maintain continuous synchronization and accuracy.
Innovation Solution
A microprocessor with a crystal oscillator generating a frequency multiple of common power line frequencies, such as 60 Hz, is used to sample and convert electrical parameters, with internal clocks allowing operation across multiple sources, and phase drift correction is applied through Fourier analysis and calibration to ensure accurate monitoring and power factor determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the microprocessor synchronizes to one AC power source using zero-crossings, then accurate monitoring is achieved for that source, but continuous operation during outages is lost
Solution Approach 1:
The patent introduces an intermediary crystal oscillator that operates independently of the AC power sources. This oscillator serves as a mediator between the microprocessor and the power sources, providing a stable timing reference that allows the microprocessor to continue monitoring electrical parameters even when power sources are outaged or unsynchronized
Solution Approach 2:
The patent replaces the mechanical synchronization method (using AC zero-crossings to trigger microprocessor timing) with an electronic crystal oscillator-based timing system. This substitution allows the microprocessor to operate independently from the AC power source synchronization, enabling continuous monitoring during outages while maintaining measurement accuracy through software-based phase drift correction
2Adaptability or versatility
If the microprocessor uses AC zero-crossings for timing, then power source synchronization is achieved, but phase drift occurs due to frequency differences
Solution Approach 1:
The patent replaces the AC-synchronized timing mechanism with a crystal oscillator-based timing system. The crystal oscillator provides a stable, high-frequency reference that does not drift with AC frequency variations. Software then measures the phase difference between the crystal-based samples and the AC waveform, enabling accurate power factor calculation despite frequency differences between the microprocessor clock and power source
Solution Approach 2:
The patent changes the timing reference parameter from AC zero-crossings to crystal oscillator pulses. This parameter change fundamentally alters the synchronization approach, allowing the system to measure phase relationships through software rather than hardware synchronization, thereby eliminating phase drift caused by frequency mismatches
3Reliability
If separate monitoring devices are used for each power source, then continuous monitoring is maintained, but device complexity increases
Solution Approach 1:
The patent makes a single microprocessor universal by enabling it to monitor electrical parameters from multiple AC power sources using a single crystal oscillator timing reference. The microprocessor can track parameters from both sources simultaneously and determine which source is currently powering loads, eliminating the need for separate monitoring devices while maintaining continuous monitoring capability
Solution Approach 2:
The patent merges the functionality of multiple power source monitors into a single integrated system. By combining the crystal oscillator timing reference with software that can process waveforms from multiple sources and determine active source status, the system achieves continuous monitoring of multiple sources without requiring separate hardware monitors for each source
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 enables continuous and accurate monitoring of electrical parameters across multiple AC power sources, including during outages, by using internal clocks and phase drift correction, ensuring reliable power monitoring and energy consumption tracking.
Implementation Method 1
A microprocessor is provided with a crystal oscillator which is a large integer multiple of common power line frequencies, such as 50 and 60 Hz
Implementation Method 2
The power supply for the microprocessor is obtained by half-wave rectifying and diode-ORing every phase of every electrical source so that it continues to function even if all phase bar one have failed
Implementation Method 3
The power supply for the microprocessor is obtained by half-wave rectifying and diode-ORing every phase of every electrical source
Implementation Method 4
A set of numerical values for each voltage and current, approximately equally spaced in time over a cycle, are Fourier analyzed to determine the fundamental component of each for each complete cycle
Data Source
AI summary
An electrical measurement device for monitoring the current and power taken by a plurality of electrical loads that may be powered by a selected one of multiple AC power sources comprises sampling the voltage of said sources and the current taken by said loads at a integral number of samples per cycle at sample times determined by an independent processor clock. The integral number of samples of each measured parameter for each cycle are processed to determine a complex number for each parameter representative of the amplitude and the phase relative to the independent processor clock. The phase drift of the substantially constant source voltages may be determined as a measure of frequency of the sources, and may be used to cancel drift of the current measurement to enable averaging. When the source feeding a load is changed, the phase drift is removed from its current measurement by selecting the voltage samples of the source now feeding it to use for drift cancellation or for average power computation and cumulative energy computation.