Adaptive Phase Compensation for Low-Pass Zero-Crossing Filters
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Solution Overview
Problem
Existing power quality measurement systems face challenges in accurately detecting zero crossing (ZC) events due to phase shifts introduced by low-pass filters and the impact of harmonics on signal precision.
Innovation Solution
A circuit and method that utilize a low-pass filter followed by a fixed all-pass filter and an adaptive all-pass filter to adjust phase and DC offset, ensuring a constant total phase shift and aligned zero crossings, thereby enhancing the accuracy of ZC detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-pass filter is used to remove noise and harmonics, then measurement precision is improved, but phase shift variability worsens
Solution Approach 1:
The patent employs a feedback mechanism where the system continuously monitors the phase shift introduced by the low-pass filter and dynamically adjusts the all-pass filter parameters to compensate. The control circuitry compares the original signal phase with the filtered signal phase and generates correction signals to maintain constant phase relationship, thereby resolving the contradiction between noise filtering and phase stability.
Solution Approach 2:
The patent changes the parameters of the all-pass filter dynamically based on the operating conditions. By adjusting the all-pass filter's phase characteristics in response to frequency variations and low-pass filter phase shifts, the system maintains constant overall phase shift while preserving the noise filtering benefits, thus resolving the contradiction between measurement precision and adaptability.
2Measurement precision
If a low-pass filter is used to reduce harmonics, then measurement precision is improved, but device complexity worsens
Solution Approach 1:
The patent merges the low-pass filter and all-pass filter into a single integrated filter circuit block. By combining these two filtering functions in one unified circuit architecture with shared control mechanisms, the system achieves the desired noise and harmonic reduction while minimizing the increase in device complexity that would result from completely separate filter circuits.
Solution Approach 2:
The filter circuit is designed with multi-functionality, where the same circuit architecture performs both low-pass filtering for noise reduction and all-pass filtering for phase compensation. This universal filter design achieves multiple objectives simultaneously, reducing the need for separate dedicated circuits and thereby limiting the increase in device complexity while maintaining measurement precision.
3Adaptability or versatility
If phase correction is applied dynamically, then adaptability is improved, but device complexity worsens
Solution Approach 1:
The patent implements dynamic phase correction where the all-pass filter parameters are adjusted in real-time based on operating conditions. The control circuitry continuously monitors signal characteristics and modifies the all-pass filter's phase response accordingly, enabling the system to adapt to frequency variations and maintain constant phase shift dynamically, thus improving adaptability while managing control circuit complexity through efficient algorithms.
Data Source
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AI summary
A circuit (10) detects zero crosses in an input-signal (IN) and includes a low-pass-filter, LPF (11) receiving the input-signal (IN) and introducing a phase-shift dependent on the frequency thereof. Filter circuitry (12, 13) receives the output of the LPF (11), applies a fixed phase-shift thereto, and adjusts phase and DC-offset thereof based on control signals to produce a filtered output-signal (YOUT). Control circuitry (14) has a zero-crossing detector (20) receiving the input-signal (IN) and the filtered output-signal (YOUT), detecting zero-crossings of the input-signal and the filtered output-signal, asserting a digital zero cross signal (DZC) at each zero crossing, and determining a phase-shift and DC-offset between the input-signal (IN) and filtered output-signal (YOUT). The control circuitry (14) has a controller (24) generating the control signals, based upon the phase-shift and DC-offset, so a total phase-shift between the input-signal (IN) and the filtered output-signal (YOUT) is constant and there is a same duty-cycle between the input-signal and the filtered output-signal, providing for accurate zero-crossing detection.