Two-Wire Dimmer Zero-Cross Detection With Virtual AC Waveform
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Solution Overview
Problem
Two-wire lighting control systems face instability and errors in zero-crossing detection due to variations in phase delay through filters, especially at low power levels, caused by electrical noise and harmonics on the AC line, leading to flickering and intensity variations.
Innovation Solution
A two-wire lighting control device generates a non-zero-magnitude signal to mitigate filter delay variations by combining it with the dimmer-voltage waveform, ensuring consistent filter delay and stability, using a control circuit with a signal generator and filter circuit to produce a combined signal that complements the dimmer-voltage waveform, thereby reducing errors in zero-crossing detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If filtering is applied to detect zero-crossings in a two-wire dimming system, then noise and harmonic distortions are reduced, but phase delay variations occur due to changes in the conduction period of the controllably conductive device
Solution Approach 1:
A virtual AC line voltage waveform is introduced as an intermediary signal to represent the actual AC line voltage. This virtual waveform is generated by combining the dimmer-voltage waveform with a synthesized signal that fills in the portions where the controllably conductive device is non-conductive. By filtering this virtual waveform instead of the actual dimmer-voltage waveform, the system achieves consistent phase delay while accurately detecting zero-crossings, as the virtual waveform maintains a constant conduction period regardless of dimming level.
2Adaptability or versatility
If the conduction period of the controllably conductive device is varied to control power delivery, then dimming levels are adjusted, but phase delay through the filter varies causing intensity fluctuations and flickering
Solution Approach 1:
A virtual AC line voltage waveform is created as a copy that mimics the characteristics of the actual AC line voltage. This virtual waveform is constructed by taking the measured dimmer-voltage waveform and adding a synthesized signal that represents the voltage across the controllably conductive device when it is non-conductive. The virtual waveform maintains a constant conduction period equal to the full AC cycle, ensuring that phase delay through the filter remains consistent across all dimming levels, thereby eliminating intensity fluctuations and flickering.
3Measurement precision
If zero-crossing detection is performed on the dimmer-voltage waveform, then the control timing is synchronized with the AC line, but electrical noise and harmonics cause false zero-crossing detection
Solution Approach 1:
The harmful effects of electrical noise and harmonics are extracted and isolated from the zero-crossing detection process. Instead of directly detecting zero-crossings on the noisy dimmer-voltage waveform, the system first constructs a virtual AC line voltage waveform that separates the signal of interest (the actual AC line voltage characteristics) from the noise and harmonics introduced by the dimming operation. The virtual waveform is then filtered to remove remaining noise, and zero-crossings are detected on this cleaned signal, significantly reducing false detections while maintaining accurate timing synchronization.
Data Source
Figure 1A~1D
Figure 2A~2C
Figure 3A~3B
AI summary
A two-wire lighting control device, may include a controllably conductive device, a signal generation circuit, and a filter circuit. The controllably conductive device may apply an AC line voltage to a load, being conductive for a first duration of time and non-conductive for a second duration of time within a half-cycle of the AC line voltage. The signal generation circuit may generate a non-zero-magnitude signal. And, the filter circuit may receive a signal from the controllably conductive device during the first duration of time and the non-zero-magnitude signal from the signal generation circuit during the second duration of time. The non-zero-magnitude signal may, in effect, fill-in or complement the signal from the controllably conductive device, and any delay variation as a function of the firing angle of the controllably conductive device through the filter circuit may be mitigated by the presence of the non-zero-magnitude signal.