Abstract
In the future, phasor measurement units are expected to be applied in distribution networks (DNs) for their control and monitoring. Because of the widely used power electronic devices in DNs, harmonics are widely present in a voltage/current signal. Particularly, second harmonics have the most significant uncertainty contributions to synchrophasor estimation, which is especially true when a short cycle observation window is used for a fast response. Based on the interpolated dynamic discrete Fourier transform (IpDFT), this paper introduces an enhanced IpDFT (e-IpDFT) synchrophasor estimator that considers second harmonic interferences. First, the adaptive equivalent filters of the IpDFT are given. Based on these, the optimal frequencies where the IpDFT has the least second harmonic interferences are then searched using an enumeration method, and the e-IpDFT synchrophasor estimator is accordingly proposed. Instantaneous frequency responses and several simulation tests show that the e-IpDFT performs much better than the IpDFT in second harmonic suppression, and can meet the P-class response time requirements and most of the M-class accuracy requirements of the IEEE standard C37.118.1 only over a three-cycle window.
Highlights
Nowadays, the power flows in distribution networks (DNs) become bidirectional due to the increasing penetrations of distributed energy resources (DERs) in power systems
According to the IEEE standard C37.118.1-2011 and its amendment standard C37.118.1a-2014 [1,2], phasor measurement units (PMUs) are divided into two classes for transmission networks (TNs): (1) P-class for fast response applications; and (2) M-class for high accuracy applications
We can see that the optimal discrete-time Fourier transform (DTFT) frequencies for two-cycle windows are very small. This is because the DTFT values at small frequencies will have small interferences from second harmonics
Summary
The power flows in distribution networks (DNs) become bidirectional due to the increasing penetrations of distributed energy resources (DERs) (e.g., photovoltaic power generation systems and energy storage systems) in power systems. The IpD2 FT is one of the most accurate synchrophasor estimators under oscillation and large frequency deviation conditions [3]. An enhanced IpD2 FT (e-IpD2 FT) synchrophasor estimator is proposed considering second harmonic interferences. It only uses a two- or three-cycle data window, and its response time is extremely short. It can sufficiently suppress second harmonic interferences, even when large frequency deviations and oscillations are present. The implementation steps of the e-IpD2 FT are summarized
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