Dual DFT Frequency Measurement Device for Power Systems
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Solution Overview
Problem
Conventional frequency measurement technologies in power systems face inaccuracies due to transient processes, non-integral harmonic waves, and abrupt voltage and phase changes, leading to unreliable frequency measurements and potential false actions in automatic devices like under frequency load shedding devices.
Innovation Solution
A frequency measurement device and method that combines single-cycle and multi-cycle Discrete Fourier Transform (DFT) to compute angle shifts, selecting the smaller absolute value for improved accuracy, and adjusts sampling frequency using under-compensation to enhance measurement reliability and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If single-cycle DFT is used for frequency measurement, then the response speed is fast, but the measurement accuracy deteriorates under disturbance conditions
Solution Approach 1:
The patent combines single-cycle DFT and multi-cycle DFT computation units into one system. The selection unit chooses between their output angle shifts based on which absolute value is smaller, thereby merging the fast response of single-cycle DFT with the high accuracy of multi-cycle DFT under disturbance conditions.
2Measurement precision
If multi-cycle DFT is used for frequency measurement, then the measurement accuracy is improved, but the response time increases
Solution Approach 1:
The patent merges single-cycle and multi-cycle DFT approaches by providing both computation units simultaneously and selecting the better result based on disturbance detection, thus achieving high accuracy without excessive time loss.
Solution Approach 2:
The system dynamically switches between single-cycle and multi-cycle DFT results based on real-time disturbance detection. The selection unit adapts its choice according to the smaller absolute angle shift value, making the measurement process dynamic rather than static.
3Stability of the object's composition
If the control factor G is set to 1 for frequency stability, then the frequency stability error decreases, but the frequency response becomes dramatically changed
Solution Approach 1:
The patent applies dynamic under-compensation to the sampling frequency adjustment process. By using a control factor less than 1 (under-compensation), the system smoothly adjusts the sampling frequency in response to frequency changes, avoiding dramatic response while maintaining stability through the dual DFT approach.
4Speed
If the control factor G is reduced for smooth frequency response, then the frequency response smoothness is improved, but the frequency stability error increases
Solution Approach 1:
The patent combines under-compensated sampling frequency adjustment with dual DFT computation to achieve both smooth response and high stability. The selection unit ensures accuracy by choosing the smaller absolute angle shift, compensating for the conservative nature of under-compensation.
Data Source
AI summary
A frequency measurement device includes a sampling unit that outputs a voltage sampling value in accordance with a voltage to be sampled and a sampling frequency; an single-cycle DFT angle shift computation unit that computes and outputs a first angle shift in accordance with the voltage sampling value; an multi-cycle DFT angle shift computation unit that computes and outputs a second angle shift in accordance with the voltage sampling value; a selection unit that selects and outputs one of the first and second angle shifts as a selected angle offset; a sampling frequency computation and outputting unit that computes a sampling frequency in accordance with the selected angle offset and outputs the same to the sampling module unit as a new sampling frequency; and a frequency measurement value computation and outputting unit that computes and outputs a frequency measurement value in accordance with the selected angle offset.