i-IpDFT Synchrophasor Estimation for Interharmonic Rejection
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Solution Overview
Problem
Current synchrophasor estimation methods in Phasor Measurement Units (PMUs) face challenges in accurately estimating signals corrupted by interharmonics close to the fundamental tone, lacking a single design that balances static and dynamic performance requirements, and fails to effectively compensate for spectral interference from both harmonic and interharmonic tones.
Innovation Solution
The iterative Interpolated Discrete Fourier Transform (i-IpDFT) method iteratively estimates and compensates for the effects of spectral interference from both interfering tones and the negative image of the fundamental tone, using a windowed discrete Fourier transform to enhance accuracy and response time, applicable for various window functions, interpolation points, and sampling frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single synchrophasor estimation algorithm is used to satisfy both high accuracy and fast response time requirements, then device complexity is reduced and cost is lowered, but the algorithm must simultaneously handle both static and dynamic performance requirements which are conflicting
Solution Approach 1:
The patent applies dynamics by making the filter characteristics adjustable rather than fixed. The synchrophasor estimation algorithm dynamically adapts its filtering behavior based on signal conditions, allowing it to switch between high accuracy mode for steady-state signals and fast response mode for transient signals, thereby resolving the contradiction between static accuracy requirements and dynamic response requirements in a single algorithm.
Solution Approach 2:
The patent changes the parameters of the filtering algorithm based on operating conditions. By adjusting filter coefficients and characteristics according to whether the system is in steady-state or transient condition, the single algorithm can achieve both high accuracy for static measurements and fast response for dynamic events, eliminating the need for multiple separate algorithms.
2Measurement precision
If interharmonic rejection is improved by using advanced filtering techniques, then measurement precision increases, but response time increases and fast transient detection capability deteriorates
Solution Approach 1:
The patent uses dynamic filtering where the filter characteristics are adjusted based on the signal state. During steady-state conditions, the filter operates in high accuracy mode to reject interharmonics. When transients are detected, the filter dynamically switches to a faster response mode, maintaining both high measurement precision for normal operation and fast response time for transient events.
Solution Approach 2:
The algorithm incorporates feedback mechanisms that monitor signal characteristics and adjust filtering parameters accordingly. By continuously assessing whether the system is in steady-state or transient condition, the feedback loop enables the filter to adapt its behavior, rejecting interharmonics during normal operation while maintaining fast response capability when needed.
3Measurement precision
If the filtering window length is increased to improve accuracy, then measurement precision increases, but the response time to transient events increases
Solution Approach 1:
The patent implements dynamic window length adjustment where the filtering window adapts its size based on system conditions. During steady-state operation, a longer window is used to maximize accuracy and reject interharmonics. When transients are detected, the window length is dynamically reduced to decrease the response time, allowing the system to maintain both high measurement precision and fast transient detection capability.
Data Source
AI summary
A method for performing synchrophasor estimation of an input signal, whereby the input signal is a sinusoidal power system voltage or current signal, comprising: a. Periodic sampling of a continuous time-domain waveform, consisting of a power system voltage or current signal, to obtain a discrete time-domain function; b. Transforming a discrete time-domain function to a discrete frequency-domain function; c. Estimating from the discrete frequency-domain function the instantaneous parameters of a synchrophasor of the sampled continuous time-domain waveform, the instantaneous parameters comprising a frequency, an amplitude and a phase angle. The method is directed to an improvement of the enhanced IpDFT-based synchrophasor estimation which takes into account interharmonic tones.