Two-Wire Load Control Power Estimation Using Complementary 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 estimate 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 without a neutral connection, then the device complexity is reduced and ease of installation is improved, but the measurement precision of power consumption is deteriorated due to inability to directly measure voltage across the load
Solution Approach 1:
The system performs preliminary actions by measuring the AC source voltage before the controllable device switches, and uses this pre-measured voltage information to calculate power consumption during the on-state. This preliminary measurement approach enables accurate power measurement without requiring direct voltage measurement across the load during conduction, resolving the contradiction between simplified wiring and measurement accuracy.
Solution Approach 2:
The invention introduces an intermediary calculation method that uses the measured AC source voltage (obtained through the two-wire connection) as a proxy for the load voltage. By using this intermediary voltage measurement combined with current measurement and duty cycle information, the system calculates power consumption indirectly, achieving accurate measurement without the third wire that would provide direct load voltage access.
2Device complexity
If voltage is measured across the two-wire device during the off-state, then the measurement circuit complexity is reduced, but the power consumption calculation accuracy deteriorates due to inability to directly measure load voltage
Solution Approach 1:
The voltage measurement is performed preliminarily during the off-state when the controllable device is non-conductive, allowing the measurement circuit to capture the AC source voltage without needing to be complex. This pre-measured voltage serves as the basis for subsequent power calculations, simplifying the measurement circuit while maintaining calculation accuracy through proper timing and computation.
Solution Approach 2:
Instead of measuring voltage across the load directly during the on-state (which would require complex circuitry in a two-wire system), the invention inverts the approach by measuring the AC source voltage during the off-state and using this information to infer the load voltage characteristics. This inverted measurement strategy simplifies the circuit while preserving the ability to calculate power consumption accurately.
3Adaptability or versatility
If real-time power consumption data is provided through smart grid applications, then the energy management capability is improved, but the device complexity increases due to additional measurement and communication requirements
Solution Approach 1:
The load control device is designed with multi-functionality, serving both as a power control device and as a power measurement device. By integrating the power consumption calculation capability into the existing control circuitry that already measures current and controls switching, the system provides energy management data without requiring separate dedicated measurement circuits, thus improving versatility while limiting complexity growth.
Solution Approach 2:
The device performs self-service by using its own control signals and existing measurements to calculate and provide power consumption data. The controller that already generates switching signals also performs the power calculations using measurements it already takes for control purposes, eliminating the need for additional dedicated power measurement hardware and reducing overall device complexity while enhancing energy management capability.
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.