AC Load Controller Pulse Timing for Zero-Crossing Misfire Recovery
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Solution Overview
Problem
Existing electrical load controllers face challenges in precisely controlling the switching points of AC power to electrical loads, leading to variations in brightness and flickering, especially with loads having inductive or nonlinear characteristics, due to misfiring and voltage sag issues.
Innovation Solution
An electrical load controller that determines a firing angle after zero-crossings of the AC waveform, selects a control signal pulse duration between fixed and variable times, and adjusts based on voltage sag detection to maintain stable power conduction, using a controller to manage the switching circuit's ON state effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed control signal pulse duration is used to latch the switching circuit, then the control signal is simple to generate, but the switching circuit may unlatch during the conduction cycle causing brightness variation and flickering
Solution Approach 1:
The patent implements dynamic adjustment of the control signal pulse duration based on the firing angle. When the firing angle is large (dimmer setting), a longer pulse duration is used to ensure reliable latching. When the firing angle is small (brighter setting), a shorter pulse duration suffices. This dynamic adaptation resolves the contradiction by optimizing the pulse duration for each operating condition rather than using a fixed value.
Solution Approach 2:
The patent changes the parameter of control signal pulse duration based on the firing angle detected from the AC waveform. The controller adjusts this parameter in real-time to match the load's latching requirements at different power levels, thereby maintaining reliable switching circuit operation across all dimming ranges while avoiding excessive pulse widths that would cause flickering.
2Reliability
If the control signal pulse duration is extended to ensure reliable latching, then switching circuit stability improves, but flickering and perceived brightness variation increase
Solution Approach 1:
The patent dynamically adjusts the control signal pulse duration to match the minimum required for reliable latching at each firing angle. By using the smallest effective pulse width rather than a consistently extended pulse, the switching circuit maintains stability without introducing excessive on-time that would cause visible flickering or brightness variation in the load.
3Measurement precision
If zero-crossing detection is used to determine firing points, then power control precision is improved, but voltage sag and misfiring occur with inductive or nonlinear loads
Solution Approach 1:
The patent employs feedback by monitoring the actual AC waveform and detecting zero-crossings in real-time. When voltage sag or distortion occurs with inductive or nonlinear loads, the system uses this feedback to adjust the firing angle and control signal parameters, ensuring reliable power conduction despite waveform variations caused by the load characteristics.
Solution Approach 2:
The patent performs preliminary detection of the AC waveform characteristics and voltage sag conditions before issuing the control signal. By anticipating potential misfiring situations with inductive loads, the system pre-adjusts the firing strategy and pulse duration to ensure reliable latching and conduction from the start of each half-cycle.
Data Source
AI summary
Operating an electrical load controller includes determining a firing angle at which to fire a switching circuit of the electrical load controller, the firing angle corresponding to a firing delay time. In some aspects, the operating includes selecting a control signal pulse duration between a fixed duration and a variable duration, and controlling the supply of AC power to the load based on the selected control signal pulse duration. In some aspects, the operating includes detecting whether a voltage sag is present in the AC waveform and the selecting is based on determining that voltage sag is present in the AC waveform.