Load Control Device Power Measurement Without Current Transformers
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Solution Overview
Problem
Existing load control devices struggle to accurately measure operating characteristics like input power without using current transformers, which are large and expensive.
Innovation Solution
A load control device with a power converter having an inductor and a power switching device, coupled with a control circuit that calculates average input power using the on time, instantaneous AC line voltage, and inductance to control power delivery to electrical loads, and an electronic ballast with a boost converter that calculates cumulative output power to detect fault conditions in gas discharge lamps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current transformer is used to measure input current, then measurement accuracy is improved, but device size and cost increase
Solution Approach 1:
The patent extracts the measurement function from a separate current transformer component and integrates it into the existing power converter circuitry. The power converter's inductor and switching device are repurposed to provide measurement signals, eliminating the need for a dedicated current transformer while maintaining measurement accuracy.
Solution Approach 2:
The power converter components (inductor and switching device) perform dual functions: they convert power as originally designed, and simultaneously provide measurement signals for input current monitoring. This multi-functionality eliminates the need for separate measurement hardware, reducing device size and cost.
2Measurement precision
If a current transformer is used to measure input current, then measurement accuracy is improved, but device cost increases
Solution Approach 1:
The measurement function is extracted from a expensive current transformer and implemented using existing power converter components. This eliminates the need to purchase and install separate measurement hardware, significantly reducing device cost while maintaining measurement accuracy.
Solution Approach 2:
Existing power converter components are made multi-functional to perform both power conversion and measurement tasks. This eliminates the need for additional expensive measurement components, reducing overall device cost while maintaining manufacturing simplicity.
3Device complexity
If power measurement is implemented using existing power converter components, then device complexity is reduced, but measurement accuracy may deteriorate
Solution Approach 1:
The control circuit continuously monitors the switching device's on-time and uses this feedback information to calculate input power. By establishing a mathematical relationship between the measurable on-time parameter and the desired power measurement, the system achieves accurate power measurement without complex measurement circuits.
Solution Approach 2:
The patent changes the measurement approach from directly measuring current (which requires complex hardware) to measuring the switching device's on-time duration (which is simpler to implement). By establishing a mathematical relationship between these parameters, accurate power measurement is achieved through parameter transformation.
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
Enables accurate measurement and control of power delivery to electrical loads without the need for current transformers, effectively detecting fault conditions in gas discharge lamps.
Implementation Method 1
an inductor of the power converter charges when the power switching device is conductive and to discharges when the power switching device is non-conductive
Data Source
AI summary
A load control device, such as an electronic ballast, for controlling the power delivered from an AC power source to an electrical load, such as one or more fluorescent lamps, comprises a power converter having an inductor and a power switching device coupled to the inductor, a load control circuit adapted to be coupled to the electrical load, and a control circuit operable to calculate an average input power of the load control device. The control circuit may be operable to calculate a cumulative output power of the power converter while the ballast is preheating filaments of the lamps, and to subsequently determine a fault condition in the lamps in response to the calculated cumulative output power of the power converter. Further, the control circuit may be operable to transmit a digital message including the calculated average input power of the load control device.