Abstract
This article presents an accurate and robust method to calculate the phase offset of a reference waveform, usually produced by a digital-to-analog converter (DAC) in IEC Std 61850-9-2 calibration systems. The phase offset is defined with respect to the rising edge of a reference clock signal, locked to the Global Positioning System (GPS). The proposed method relies on the synchronous acquisition of the DAC output and the clock signal. In the complex plane, where the discrete Fourier transform (DFT) is defined, the acquired signals are processed to compensate the nonideal sampling rate and windowing. The method performance and its dependence from noise and parameters are thoroughly characterized by means of extensive numerical simulations. Two validation approaches, experimental and software-based, confirm the proposed method as a valuable and robust solution for calibration purposes.
Highlights
I N MODERN power systems, the ever-increasing integration of renewable energy sources and distributed generation is pushing for the development of enhanced measurement techniques capable of coping with faster dynamics and higher distortion rates [1]–[3]
The role of National Metrology Institutes (NMIs) consists in providing calibration systems characterized by accuracy and stability levels significantly higher than the devices under test (DUTs) [7], [8]
In most phasor measurement units (PMUs) and stand-alone merging units (SAMUs) calibrators [9]–[12], the test signal is synthetized by a digital-to-analog converter (DAC), supplied to the DUT and synchronously reacquired by an analogto-digital converter (ADC)
Summary
I N MODERN power systems, the ever-increasing integration of renewable energy sources and distributed generation is pushing for the development of enhanced measurement techniques capable of coping with faster dynamics and higher distortion rates [1]–[3]. The PRS that triggers ao0 and ai is acquired by ai0 In this way, the measurement setup gets a synchronous acquisition of both WRS and PRS, which can be further processed to determine the respective phase offset introduced by generation and acquisition stages (see Section III). The measurement setup gets a synchronous acquisition of both WRS and PRS, which can be further processed to determine the respective phase offset introduced by generation and acquisition stages (see Section III) Both PRS and WRS are generated and reacquired with 50- coaxial cables of the same length, and the delay due to the signal propagation through the wire is the same and is automatically eliminated in the postprocessing calculation. The PPS provides the trigger and accounts for the traceability to the common time reference, whereas the comparison between the rising edges of PRS and WRS is used to infer the DAC phase offset
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