Abstract
The widespread diffusion of Phasor Measurement Units (PMUs) is a becoming a need for the development of the “smartness” of power systems. However, PMU with accuracy compliant to the standard Institute of Electrical and Electronics Engineers (IEEE) C37.118.1-2011 and its amendment IEEE Std C37.118.1a-2014 have typically costs that constitute a brake for their diffusion. Therefore, in this paper, the design of a low-cost implementation of a PMU is presented. The low cost approach is followed in the design of all the building blocks of the PMU. A key feature of the presented approach is that the data acquisition, data processing and data communication are integrated in a single low cost microcontroller. The synchronization is obtained using a simple external Global Positioning System receiver, which does not provide a disciplined clock. The synchronization of sampling frequency, and thus of the measurement, to the Universal Time Coordinated, is obtained by means of a suitable signal processing technique. For this implementation, the Interpolated Discrete Fourier Transform has been used as the synchrophasor estimation algorithm. A thorough metrological characterization of the realized prototype in different test conditions proposed by the standards, using a high performance PMU calibrator, is also shown.
Highlights
The need for the best estimate of the power system’s state is recognized to be a crucial element in improving its performance and its resilience to face catastrophic failures
The realized Phasor Measurement Units (PMUs) prototype has been tested with a high performance PMU calibrator, the Fluke
10% of the fundamental; Amplitude Modulated (AM) sinewaves affected by a 2 Hz and 5 Hz modulating tone of amplitude equal to 10% of the fundamental; Phase Modulated (PM) sinewaves affected by a 2 Hz and 5 Hz modulating tone of amplitude equal to 0.1 rad; 50 Hz sinewaves corrupted by a single out-of-band inter-harmonic of amplitude equal to 10% of the fundamental at 24.9 Hz; Chirp waveforms with the fundamental frequency increasing linearly from about 48 Hz to 52 Hz and from 45 Hz to 55 Hz, and vice versa, at a rate of ±1 Hz/s
Summary
The need for the best estimate of the power system’s state is recognized to be a crucial element in improving its performance and its resilience to face catastrophic failures. A PMU measures the instantaneous voltage, current, frequency and the Rate Of Change Of Frequency (ROCOF) at specific locations in an electric power transmission system; it converts the measured parameters into phasor values, typically with a rate of 25 or more, per second It adds a precise time stamp to these phasor values, turning them into synchrophasors. In [26], a development of an analog-to-digital converter (ADC) for PMU applications, with GPS synchronization, based on an open hardware development platform, is discussed It makes use of external devices, such as a GPS receiver, a Phase Locked Loop (PLL) circuit and an ADC, managed by the powerful.
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