Wideband digital phase comparator for high current shunts

A wideband phase comparator for precise measurements of phase difference of high current shunts has been developed at INRIM. The two-input digital phase detector is realized with a precision wideband digitizer connected through a pair of symmetric active guarded transformers to the outputs of the shunts under comparison. Data are first acquired asynchronously, and then transferred from on-board memory to host memory. Because of the large amount of data collected the filtering process and the analysis algorithms are performed outside the acquisition routine. Most of the systematic errors can be compensated by a proper inversion procedure. The system is suitable for comparing shunts in a wide range of currents, from several hundred of milliampere up to 100 A, and frequencies ranging between 500 Hz and 100 kHz. Expanded uncertainty (k=2) less than 0.05 mrad, for frequency up to 100 kHz, is obtained in the measurement of the phase difference of a group of 10 A shunts, provided by some European NMIs, using a digitizer with sampling frequency up to 1 MHz. An enhanced version of the phase comparator employs a new digital phase detector with higher sampling frequency and vertical resolution. This permits to decrease the contribution to the uncertainty budget of the phase detector of a factor two from 20 kHz to 100 kHz. Theories and experiments show that the phase difference between two high precision wideband digitizers, coupled as phase detector, depends on multiple factors derived from both analog and digital imprint of each sampling system.Comment: 20 pages, 9 figure

Automation of capacitance measurements for power semiconductor modules

This paper presents an overview of questions related to the increase in accuracy of measurements of capacitance parameters of power semiconductor modules when developing a device for automated measurements. The paper addresses the matters of circuit engineering of primary components, technical characteristics and software of a meter designed to automate the process of testing of capacitance parameters of power modules based on insulated gatebipolar transistors and fast recovery diodes. Unit testing results that prove the efficiency ofthe proposed method of the technical implementation are provided. Software implementation is described; ways to improve software-hardware solution are proposed. The paper is of value for developers and users of equipment for automated testing of electric parameters of semiconductor devices.Keywords: automated test equipment (ATE), capacitance parameters, IGBT, FRD, power semiconductor modules, MATLAB

A South African review of harmonic emission level assessment as per IEC61000-3-6

Large-scale renewable power producing plants are being integrated into South African networks. Network operators need to ensure that Renewable Power Plants (RPP) do not negatively affect the power quality levels of their networks, as harmonics amongst others could become a concern. IEC 61000-3-6 details a method for allocating voltage harmonic emission limits for distorting loads. This method works well for the allocation of emission limits; however it does not address the management of harmonic emissions once a plant is connected to the network. The management of harmonic emissions requires that network operators measure or quantify the emissions from loads and generators to determine compliance. Post-connection quantification of harmonic levels and compliance is a challenge for network operators. The question asked is “How should a network operator measure/quantify the harmonic emissions of a load/generator to establish compliance with the calculated limits as per IEC 61000-3-6”. This paper reviews within a South African context methods of assessing harmonic emission levels and then evaluates these methods by means of field data. Opportunities for improvement are identified and operational requirements discussed

A Fast Digital Integrator for magnetic measurements

In this work, the Fast Digital Integrator (FDI), conceived for characterizing dynamic features of superconducting magnets and measuring fast transients of magnetic fields at the European Organization for Nuclear Research (CERN) and other high-energy physics research centres, is presented. FDI development was carried out inside a framework of cooperation between the group of Magnet Tests and Measurements of CERN and the Department of Engineering of the University of Sannio. Drawbacks related to measurement time decrease of main high-performance analog-to-digital architectures, such as Sigma-Delta and integrators, are overcome by founding the design on (i) a new generation of successive-approximation converters, for high resolution (18-bit) at high rate (500 kS/s), (ii) a digital signal processor, for on-line down-sampling by integrating the input signal, (iii) a custom time base, based on a Universal Time Counter, for reducing time-domain uncertainty, and (iv) a PXI board, for high bus transfer rate, as well as noise and heat immunity. A metrological analysis, aimed at verifying the effect of main uncertainty sources, systematic errors, and design parameters on the instrument performance is presented. In particular, results of an analytical study, a preliminary numerical analysis, and a comprehensive multi-factor analysis carried out to confirm the instrument design, are reported. Then, the selection of physical components and the FDI implementation on a PXI board according to the above described conceptual architecture are highlighted. The on-line integration algorithm, developed on the DSP in order to achieve a real-time Nyquist bandwidth of 125 kHz on the flux, is described. C++ classes for remote control of FDI, developed as a part of a new software framework, the Flexible Framework for Magnetic Measurements, conceived for managing a wide spectrum of magnetic measurements techniques, are described. Experimental results of metrological and throughput characterization of FDI are reported. In particular, in metrological characterization, FDI working as a digitizer and as an integrator, was assessed by means of static, dynamic, and time base tests. Typical values of static integral nonlinearity of ±7 ppm, ±3 ppm of 24-h stability, and 108 dB of signal-to-noise-anddistortion ratio at 10 Hz on Nyquist bandwidth of 125 kHz, were surveyed during the integrator working. The actual throughput rate was measured by a specific procedure of PXI bus analysis, by highlighting typical values of 1 MB/s. Finally, the experimental campaign, carried out at CERN facilities of superconducting magnet testing for on-field qualification of FDI, is illustrated. In particular, the FDI was included in a measurement station using also the new generation of fast transducers. The performance of such a station was compared with the one of the previous standard station used in series tests for qualifying LHC magnets. All the results highlight the FDI full capability of acting as the new de-facto standard for high-performance magnetic measurements at CERN and in other high-energy physics research centres

Microgrid Application in Algeria Saharian Remote Areas

This paper presents a model and simulation for the development of microgrids in remote areas of the Algerian Sahara, including micro power plants, photovoltaic panels, wind farms, diesel energy and storage facilities. The climate of the Algerian Sahara, located on both sides of a tropical region, is hot, sunny and arid. Daytime temperatures are very high and can exceed 50°C, while the thermal amplitude between day and night is often above 350 or 400°C. In addition, there are many microclimates that are characterised by very high wind speeds. This means that wind energy and photovoltaic energy are both widely appropriate in this field, especially if we assume that the distribution of the population is very dispersed. The creation of microgrids for consumption will be an interesting solution to provide energy to the local population. The microgrid is part of the electrical system and is very dynamic. Production and supply forecasts will lead to reshipment, demand and price effects on regional markets. These feedback effects must be modelled and understood to achieve a stable energy system based on renewable energy

Are inductive current transformers performance really affected by actual distorted network conditions? An experimental case study

The aim of this work is to assess whether actual distorted conditions of the network are really affecting the accuracy of inductive current transformers. The study started from the need to evaluate the accuracy performance of inductive current transformers in off-nominal conditions, and to improve the related standards. In fact, standards do not provide a uniform set of distorted waveforms to be applied on inductive or low-power instrument transformers. Moreover, there is no agreement yet, among the experts, about how to evaluate the uncertainty of the instrument transformer when the operating conditions are different from the rated ones. To this purpose, the authors collected currents from the power network and injected them into two off-the-shelf current transformers. Then, their accuracy performances have been evaluated by means of the well-known composite error index and an approximated version of it. The obtained results show that under realistic non-rated conditions of the network, the tested transformers show a very good behavior considering their nonlinear nature, arising the question in the title. A secondary result is that the use of the composite error should be more and more supported by the standards, considering its effectiveness in the accuracy evaluation of instrument transformers for measuring purposes

Synchrophasors Determination Based on Interpolated FFT Algorithm

Within the standard IEEE C37.118 applications and proposed hardware structure of a phasor measurement unit (PMU) are described. This paper presents the concept of the system for measuring and transferring synchrophasors from a theoretical aspect. Synchrophasor algorithms are developed in MATLAB/Simulink for the purpose of easier verification and hardware deployment on today’s market available and affordable real time development kits. Analysis of the synchrophasor measurement process is performed gradually. Firstly, by defining the synchrophasor based on three-phase to αβ-transformation and then introducing a discrete Fourier transform (DFT) based on synchrophasor estimation algorithm. Later, accompanying adverse effects resulting from its application are analyzed by means of simulation. To increase accuracy and improve estimation algorithm interpolated discrete Fourier transform (IpDFT) with and without windowing technique is used. To further optimize algorithm performance convolution sum in recursive form has been implemented instead of classical DFT approach. This study was carried out in order to validate described measurement system for the monitoring of transients during island operation of a local power electric system. Finally, simulation and experimental results including error analysis are also presented