Two-Wire Load Control Power Estimation From Half-Cycle Voltage
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Solution Overview
Problem
Two-wire load control devices lack the capability to accurately compute and report real-time power consumption due to the absence of a direct connection to the neutral side of the AC power source, preventing them from determining the actual voltage drop across the load.
Innovation Solution
A two-wire lighting control device is configured with a controllably conductive device and a control circuit that measures voltage across the device during a half-cycle, generates a complementary voltage waveform to approximate the voltage across the load, and computes power consumption based on this estimation and current measurement, allowing for accurate power delivery control and reporting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a two-wire load control device is used, then device complexity is reduced and ease of installation is improved, but the ability to accurately measure and report real-time power consumption deteriorates
Solution Approach 1:
The patent applies preliminary action by measuring the voltage across the load during the off-state (when the triac is non-conductive) before the actual power delivery occurs. This pre-measurement captures the line voltage information that would otherwise be unavailable during the on-state, enabling subsequent accurate power calculation without adding measurement complexity during power delivery.
Solution Approach 2:
The patent creates a copy of the voltage waveform information by measuring and storing the voltage across the load during the off-state. This copied voltage data is then used in conjunction with current measurements to reconstruct the power consumption information, effectively copying the essential measurement data needed for accurate power reporting without requiring direct simultaneous voltage-current measurement.
2Measurement precision
If a three-wire load control device is used, then accurate power consumption measurement is enabled, but device complexity increases and ease of installation deteriorates
Solution Approach 1:
The patent extracts the essential voltage measurement function from the traditional three-wire configuration by measuring voltage across the load terminals themselves during the off-state. This extraction eliminates the need for a separate neutral wire connection while preserving the ability to obtain accurate voltage information for power calculation.
Solution Approach 2:
The patent makes the two-wire load control device multi-functional by enabling it to perform both load control and accurate power measurement functions that were traditionally reserved for three-wire devices. The same control circuitry used for triac switching is also utilized for voltage measurement during the off-state, eliminating the need for separate measurement circuits.
3Loss of information
If voltage is measured across the load during the on-state, then real-time voltage data is available, but measurement accuracy deteriorates due to voltage drop across the control device
Solution Approach 1:
The patent applies periodic action by measuring the voltage across the load periodically during each off-state cycle. Instead of attempting continuous measurement during the on-state (which would be inaccurate), the system performs discrete measurements during the off-state intervals, capturing the voltage information at regular periodic opportunities when the control device is not interfering with the measurement.
Data Source
AI summary
A two-wire load control device may be configured to compute an accurate estimate of real-time power consumption by a load that is electrically connected to, and controlled by, the two-wire load control device. The load control device may be adapted to measure a voltage drop across the device during a first portion of a half-cycle of an AC waveform provided to the device. The device may be further configured to estimate a voltage drop across the load during the second portion of the half-cycle. The estimated voltage drop may be based on the measured voltage drop. The device may be further configured to measure a current supplied to the load during a second portion of the half-cycle. The device may be configured to estimate power consumed by the load based on the measured current and the estimated voltage drop.