Two modified DFT‐based algorithms for fundamental phasor estimation

Abstract

The discrete Fourier transform (DFT) is a powerful phasor estimation algorithm conventionally used in digital relaying applications. The DFT-based phasor estimation is usually accompanied by oscillatory error due to the presence of the decaying DC (DDC) components in fault current signals. Accordingly, two modified DFT-based phasor estimation algorithms are proposed in this paper. The proposed algorithms accurately estimate the exact fundamental phasor by extracting the DDC components using successive outputs of the conventional DFT algorithm. The performance of the proposed algorithms is validated by the mathematically generated and PSCAD-simulated signals and is compared with previous algorithms. The results demonstrate that the proposed algorithms in this paper are more robust than other ones. Moreover, they are applicable in the DFT algorithm with different data windows. INTRODUCTIONThe fundamental phasor estimation plays an important role in detecting, locating, and discriminating faults in power systems. There are a number of conventional phasor estimation algorithms, that include: discrete Fourier transform (DFT), least-square error (LSE), discrete wavelet transform (DWT), Kalman filters, discrete Hartley transform (DHT), and artificial neural networks (ANNs) [1][2][3][4]. The discrete Fourier transform (DFT) is a powerful phasor estimation algorithm, widely used in digital relaying applications due to its simplicity, accuracy, and speed. The DFT algorithm has a high capability to estimate the fundamental phasor of periodic sinusoidal signals. However, its performance is extremely influenced by non-periodic signals such as decaying DC components (DDCs), which are created in the current and voltage signals during fault conditions. This issue causes an undesired oscillating error in the estimated phasor, especially phase angle. Although this error decays after a certain period of time (depending on the time constant of the DDC component), it extremely reduces the speed and accuracy of decision-making in relays. The DDC component has two parameters, the initial value and time constant, which depend on fault inception angle and the value of pathway X ∕R ratio, respectively. Because the source impedance and line X ∕R ratio are so close to each other, the initial value ofThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

A Wavelet Transform-Based Real-Time Filtering Algorithm for Fusion Magnet Power Signals and Its Implementation

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