Line Frequency Detector Using Dual Band Pass Filters
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Solution Overview
Problem
Dimmable solid-state lighting devices are sensitive to changes in line frequency, leading to malfunctions if the controller cannot detect frequency changes and adjust accordingly.
Innovation Solution
A line frequency detector using two band pass filters arranged in parallel, with pass bands centered at the high and low ends of the expected frequency range, attenuating higher order harmonics, and generating sinusoidal signals that are then rectified and filtered to calculate a characteristic ratio representing the line frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single band pass filter is used to detect line frequency, then the detection circuit is simple, but it cannot accurately distinguish between different frequencies within the expected range
Solution Approach 1:
The frequency detection range is segmented into multiple sub-ranges, each handled by a dedicated band pass filter. The first filter handles the lower frequency portion (e.g., 45-55 Hz) while the second filter handles the upper frequency portion (e.g., 55-65 Hz). This segmentation allows each filter to be optimized for its specific range, improving overall detection accuracy without requiring an overly complex single-filter design.
Solution Approach 2:
Instead of using a single filter with a wide bandwidth that would compromise selectivity, the invention uses multiple filters with narrower, overlapping bandwidths. This partial action approach ensures that each filter provides sufficient frequency discrimination for its designated range while maintaining adequate signal strength through the overlap regions.
2Object-affected harmful factors
If wide bandwidth filters are used to cover the entire frequency range, then the filter circuit is simple, but higher order harmonics cannot be attenuated effectively
Solution Approach 1:
By segmenting the frequency detection into multiple narrow-band filters, each filter naturally provides better harmonic attenuation for its specific frequency range. The narrow bandwidth of each filter inherently rejects higher order harmonics that fall outside its pass band, eliminating the need for additional harmonic filtering stages.
Solution Approach 2:
Each band pass filter is designed with specific local characteristics optimized for its frequency range, including appropriate Q-factors and cutoff frequencies. This local optimization ensures that each filter provides maximum harmonic rejection for its designated range while maintaining the fundamental frequency signal.
3Reliability
If the controller does not detect line frequency changes, then the control circuit is simple, but the lighting device malfunctions when line frequency varies
Solution Approach 1:
The line frequency detection circuit provides continuous feedback to the controller about the actual line frequency. Based on this feedback, the controller dynamically adjusts the dimming control parameters to compensate for frequency variations. This closed-loop feedback mechanism ensures reliable operation across different line frequencies without requiring an overly complex control algorithm.
Solution Approach 2:
The system performs self-adjustment by automatically detecting line frequency changes and correcting its operation accordingly. The controller uses the detected frequency information to self-correct timing and control parameters, eliminating the need for external calibration or manual adjustment mechanisms.
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
The line frequency detector reliably determines the line frequency, enabling the controller to generate appropriate control signals for the solid-state light source, even with distorted input signals or varying line voltages, thus preventing malfunctions and ensuring consistent performance.
Implementation Method 1
The input signal is sent through two band pass filters arranged in parallel. The pass band of the first filter is centered approximately at the high end of an expected range for the frequency of the input signal. The pass band of the second filter is centered approximately at the low end of the expected frequency range. In addition, both pass bands are narrow enough that any higher order harmonics of the input signal are substantially attenuated.
Implementation Method 2
The filtered signals are rectified and sent through low-pass filters to create two characteristic signals that both have substantially constant values.
Implementation Method 3
The filtered signals are rectified and sent through low-pass filters to create two characteristic signals that both have substantially constant values.
Data Source
Figure 1
Figure 2A
Figure 2B~2D
AI summary
A line frequency detector (100) receives an input signal (102) representing a power source and detects a line frequency of the power source based on the input signal. The line frequency detector includes a first band pass filter (112A) having a pass band centered at an upper end of an expected frequency range of the power source and a second band pass filter (112B) having a pass band centered at a lower end of the expected frequency range. The input signal is filtered by the first and second band pass filters, generating a first characteristic signal and a second characteristic signal (122A, 122B). The line frequency detector determines a characteristic ratio (126) between the first characteristic signal and the second characteristic signal, and maps the characteristic ratio to the line frequency (130) of the power source.