AC Load Controller Zero-Crossing Recovery for Stable Dimming

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Solution Overview

Problem

Existing electrical load controllers face challenges in precisely controlling the switching points of AC power to minimize flickering and brightness variations in lighting loads, especially with loads having inductive or nonlinear characteristics, due to misfiring issues and voltage sags, which affect the reliability and stability of dimming systems.

Innovation Solution

The method involves predetermining a detection window for zero-crossing detection, selecting a control signal pulse duration based on the firing angle and presence of voltage sag, and selectively controlling AC power supply to the load to improve the accuracy of switching circuit firing, thereby reducing flickering and maintaining stable brightness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If zero-crossing detection is used to control switching points, then power control precision is improved, but detection accuracy deteriorates due to voltage sags and misfiring

Engineering Contradiction:

Improvepower control precisionVSAvoidzero-crossing detection accuracy

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by predicting the expected zero-crossing time based on AC waveform frequency before the actual zero-crossing occurs. A detection window is established around this predicted time, and if no zero-crossing is detected within the window (due to voltage sags or misfiring), the system recovers the expected zero-crossing time for use in control calculations, ensuring continuous accurate operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by continuously monitoring the zero-crossing signal within the detection window and comparing actual detections with expected values. When voltage sags or misfiring cause detection failures, the system uses the feedback from the detection window status to trigger recovery mechanisms that restore accurate zero-crossing timing information for subsequent control cycles.

Inventive Principle:

Principle #23Feedback

2Reliability

If control signal pulse duration is extended to ensure switching circuit latching, then switching reliability is improved, but power consumption increases

Engineering Contradiction:

Improveswitching circuit latching reliabilityVSAvoidcontrol signal power consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent applies dynamics by making the control signal pulse duration variable rather than fixed. The system adjusts the pulse duration dynamically based on detected conditions: extending the pulse when voltage sags or misfiring are detected to ensure reliable latching, and reducing or eliminating extended pulsing when conditions are normal, thereby optimizing both reliability and power consumption.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter of control signal pulse duration based on operating conditions. The system monitors for voltage sags and detection failures, then adjusts the pulse duration parameter accordingly - using longer pulses only when necessary to overcome latching failures, and using shorter or standard pulses during normal operation to minimize power consumption.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If detection window is widened to accommodate voltage sags, then zero-crossing detection robustness is improved, but timing precision deteriorates

Engineering Contradiction:

Improvezero-crossing detection robustnessVSAvoidswitching point timing precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent uses preliminary action by calculating the expected zero-crossing time based on AC waveform frequency before establishing the detection window. This expected time serves as a reference point that allows the system to use a wider detection window for robustness while still maintaining timing precision through the predicted reference value when actual detections fail.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces an intermediary element - the predicted expected zero-crossing time - that mediates between the wide detection window needed for robustness and the precise timing needed for accurate control. The predicted time acts as a fallback reference that preserves timing precision even when the wide window is necessary to accommodate voltage sags or misfiring events.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11903105B2Prediction and recovery of zero-crossing information and selective control signal pulse duration

Publication Date: 2024.02.13 LEVITON MFG CO INC

AI summary

Operation of an electrical load controller includes predetermining a duration of time based at least in part on a frequency of an alternating current (AC) waveform, the AC waveform oscillating though full cycles, selecting a detection window of time equal in duration to the predetermined duration of time, the selected detection window extending from a selected first time to a selected second time and straddling an expected time of a next zero-crossing of the AC waveform, monitoring a zero-crossing signal for a zero-crossing indication, of the next zero-crossing, occurring within the selected detection window, ascertaining a time of the next zero-crossing based on the monitoring, and selectively controlling a supply of AC power to a load, wherein the controlling uses the ascertained time of the next zero-crossing of the AC waveform to fire a switching circuit of the electrical load controller.