PLL Frequency Detector With Phase-Jump Prediction Switching
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Solution Overview
Problem
Existing system frequency detectors face challenges in quickly tracking changes in system frequency and suppressing erroneous detections, especially during system disturbances and phase jumps in power systems.
Innovation Solution
A system frequency detector that includes an orthogonal coordinate signal generator and a frequency calculator with a rate limiter, prediction calculator, and switching circuit, which generates orthogonal two-phase voltage signals, calculates angular frequency using PLL, and limits frequency changes, predicts future angular frequency, and switches between actual and predicted values based on phase jump detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filter with a long time constant (not less than 200 msec) is used to acquire resistance to system disturbances, then reliability is improved, but the speed of tracking system frequency changes deteriorates
Solution Approach 1:
The patent applies dynamics by making the filter time constant adjustable rather than fixed. The control unit dynamically changes the time constant of the low-pass filter based on system conditions: using a longer time constant (e.g., 200 msec or more) during normal operation to suppress disturbances, and switching to a shorter time constant when frequency changes are detected to improve tracking speed. This dynamic adaptation resolves the contradiction between reliability and tracking speed.
2Speed
If PLL with DQ transformation is used to track system frequency quickly, then tracking speed is improved, but measurement precision deteriorates when phase jump occurs
Solution Approach 1:
The patent uses feedback by continuously monitoring the output of the inverse transformation and detecting phase jumps. When a phase jump is detected (indicated by abnormal values in the inverse transformation output), the control unit adjusts the filter time constant to suppress the erroneous frequency detection. This feedback mechanism allows the system to maintain fast tracking during normal operation while automatically correcting for measurement precision issues during phase jumps.
Solution Approach 2:
The system dynamically adjusts the low-pass filter time constant based on detected phase jump conditions. During normal operation, a shorter time constant enables fast tracking. When a phase jump is detected through the inverse transformation output, the system switches to a longer time constant to filter out the transient disturbance, thereby maintaining measurement precision during abnormal conditions.
3Device complexity
If the system uses a fixed filter time constant for frequency calculation, then device complexity is reduced, but adaptability to different system conditions deteriorates
Solution Approach 1:
The patent implements dynamics by introducing a control unit that dynamically adjusts the filter time constant based on system conditions. The control unit monitors the inverse transformation output and automatically changes the time constant setting: using longer time constants during disturbances and shorter time constants during normal operation. This dynamic adjustment provides adaptability to different system conditions while maintaining relatively simple system architecture.
Solution Approach 2:
The system changes the parameter (filter time constant) based on system conditions. The control unit modifies the time constant value dynamically: increasing it during phase jumps or disturbances to suppress erroneous detections, and decreasing it during normal operation to enable fast tracking. This parameter change approach provides adaptability without requiring completely different system configurations for different operating conditions.
Data Source
AI summary
A system includes an orthogonal coordinate signal generator that generates an orthogonal two-phase voltage signal from a three-phase voltage signal of three-phase alternating current power of a power system; and a frequency calculator including an angular frequency calculator calculating an angular frequency of the power system based on the two-phase voltage signal, and an arithmetic unit calculating a system frequency of the power system from the angular frequency. A prediction calculator calculates a predicted value of the angular frequency after a time has elapsed based on the angular frequency and a differential of the angular frequency. In a state in which the phase jump of the power system is not detected, the frequency calculator calculates the system frequency based on the angular frequency. When the phase jump of the power system is detected, the frequency calculator calculates the system frequency based on predicted value for a constant amount of time.