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Compensation of Current Transformers by means of Field Programmable Gate Array

Gallo D., Landi C., Luiso M.

Metrology and Measurement Systems

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2009

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Vol. 16, nr 2

279-288

EN

With the diffusion of non-linear and unbalanced loads, which often cause unacceptable quality level of energy, energy quality monitoring represents an increasing need. Analyzing conducted disturbances requires measuring instrumentation, and thus voltage and current transducers, with large bandwidth. Voltage and current transformers (CT) are the most often installed transducers in electrical power system and typically they are constructed to operate at industrial frequency 50/60 Hz, but it is clear that their substitution would require an unsustainable cost. Therefore in this paper a digital technique for the compensation of CT, based on field programmable gate array, is presented: it implements a digital filter with a frequency response equal to the inverse one of the CT. The compensated CT continues to be an analog device since the FPGA board is opportunely equipped with analog-to-digital and digital-to-analog converters.

2

A study on the feasibility and effectiveness of digital filter application for harmonic and interharmonic measurement in compliance with IEC 61000-4-7

Ferrigno L., Landi C., Laracca M., Luongo C.

Metrology and Measurement Systems

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2007

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Vol. 14, nr 4

577-593

EN

Large scale monitoring of power quality in electrical power plants is nowadays a pressing need due to the liberalization of the electrical market in many countries and the deeper interconnections of electrical networks. Many instruments are today available on the market. Even if they provide good accuracy and measurement capability, they are generally developed for single point measurements. Their use in large scale monitoring leads to high costs. In this framework research activity, the authors aim at the realization of a measurement instrument for power quality monitoring in compliance with IEC 61000-4-30 and 61000-4-7 standards capable of granting good accuracy, satisfying repeatability, and cost effectiveness since the use in large scale monitoring is allowed. In this paper the attention is paid to the measurement algorithm to be adopted. The use of an alternative measurement approach with respect to the FFT one is proposed. Digital filters shaped on the harmonic group are thoroughly optimized for grouping measurements required by the IEC EN 61000-4-7 standard both in simulation and emulation environments. The obtained results confirm the advantages of the proposal.

3

A multi-DSP based instrument for real-time energy and PQ measurements

D'Apice B., Landi C., Pelvio A., Rignano N.

Metrology and Measurement Systems

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2007

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Vol. 14, nr 4

495-506

EN

The evaluation of electrical energy flows is at the base of all operations connected to commercial transactions on the energy market. Typically, the measurement apparatuses are made and characterized to work in ideal sinusoidal conditions. But, with increasing diffusion of power electronic devices, the typical characteristics of a power network are far from sinusoidal ones. With the aim to link the cost of energy to the level of power quality, it is necessary to determine the energy but also the indexes which characterize the power quality. In this paper the design and implementation of a multi-processor measuring instrument based on multiple digital signal processors (DSPs) is discussed. This system can embody a number of special signal processors and analog I/O modules, specifically designed to obtain the flexibility and scaling ability to meet the needs of real-time measurement applications and low cost. After a prototype description, part of the analysis algorithm is reported. The paper is completed by preliminary results of metrological characterization.