Antonio Cataliotti

A Phase-Locked Loop for the Synchronization of Power Quality Instruments in the Presence of Stationary and Transient Disturbances

Power quality instrumentation requires accurate fundamental frequency estimation and signal synchronization, even in the presence of both stationary and transient disturbances. In this paper, the authors present a synchronization technique for power quality instruments based on a single-phase software phase-locked loop (PLL), which is able to perform the synchronization, even in the presence of such disturbances. Moreover, PLL is able to detect the occurrence of a transient disturbance. To evaluate if and how the synchronization technique is adversely affected by the application of stationary and transient disturbing influences, appropriate testing conditions have been developed, taking into account the requirements of the in-force standards and the presence of the voltage transducer.

Synchronization techniques for power quality instruments

The measurement of voltage characteristics in power systems requires the accurate estimation of the power supply frequency and signal synchronization, even in the presence of disturbances. The authors developed and tested two innovative techniques for instrument synchronization. The first is based on signal spectral analysis techniques performed by means of the Chirp- transform analysis. The second is a phase-locked loop (PLL) software based on a time-domain coordinate transformation and an innovative phase-detection technique. To evaluate how synchronization techniques are adversely affected by the application of a disturbing influence, experimental tests were carried out, taking into account the requirements of the standards. The proposed techniques were compared with a standard hardware solution. In this paper, the proposed techniques are described, the experimental results are presented, and the accuracy specifications are discussed.

Theoretical and experimental comparison of total harmonic distortion factors for the evaluation of harmonic and interharmonic pollution of grid-connected photovoltaic systems

Grid-connected photovoltaic systems are increasingly used in electrical distribution systems. However, they inject distorted currents. Therefore, special attention must be paid to harmonic and interharmonic measurements. The new edition of IEC 61000-4-7 introduces the concept of harmonic and interharmonic groups, which implies new expressions for total harmonic distortion (THD) factors. In this paper, a theoretical and experimental comparison is made between the different THD factors in order to show which of the currently defined distortion factors is best suited to detect harmonic and interharmonic pollution. Experimental tests were carried out first by means of a calibrator and subsequently in a single-phase grid-connected photovoltaic system. In both cases, measurements were carried out with a PC-based instrument developed by the authors and able to calculate the distortion factors according to IEC 61000-4-7.

Generalized PWM–VSI Control Algorithm Based on a Universal Duty-Cycle Expression: Theoretical Analysis, Simulation Results, and Experimental Validations

This paper presents a new approach in realizing various carrier-based pulsewidth-modulation techniques by a generalized control algorithm, which is referred to as the universal control algorithm and is obtained via unequal sharing of null states. The flexibility of such an approach allows one to easily and quickly control two-level inverters. Furthermore, this approach may be also extended with few changes to the control of multilevel inverters. The algorithm that is presented here for two-level voltage-source inverters (VSIs) also obtains efficient detection and management of both the linear and overmodulation ranges. In the overmodulation range, which is treated by using the alpha-beta components of the reference-voltage space vector, the algorithm shows the advantage of lower calculation time, thus allowing one, if required, to increase the switching frequency. Several simulation runs have been performed, aiming to test the proposed procedure for both two-level and multilevel VSIs. Finally, the new algorithm was experimentally validated in the case of two-level inverters by using it in a VSI workbench that can carry out several experimental tests

A Chirp Z transform based synchronizer for power system measurements

Power system analyzers are required for performing an accurate evaluation of harmonic pollution, voltage and current synchronous sampling in order to limit leakage error and to assure reproducible results. Moreover, the increased interest about power and voltage quality, forced international working groups to define new standards for testing and measurement techniques. In particular, harmonic and interharmonic measurement and instrumentation standards require the correct voltage or current signal synchronization and the recognition of the same condition. In this paper a new synchronizer algorithm is proposed, able to respect in force and draft standards for its accuracy and characteristics. Theoretical aspects are discussed and different experimental tests are reported, comparing the proposed method with a similar well-known one based on interpolated fast Fourier transform.

Power Line Communication in Medium Voltage Systems: Characterization of MV Cables

The aim of this paper is to illustrate the development of a theoretical and experimental study on the characterization of medium voltage (MV) cables in the frequency range 25-200 kHz. Two transmission line configurations, line-ground and line-line, were considered in order to evaluate the main parameters, such as the characteristic impedance and the attenuation constant alpha. A simplified model of the line-ground configuration is proposed which allows one to evaluate the characteristic impedance and the attenuation constant by means of geometrical dimensions. The model was verified by experimental measurements on commonly used MV cables, RG7H1R, with an aluminium core of different sections, 95 mm2 and 185 mm2. Moreover, the experimental tests were carried out for the line-line configuration.

An induction motor speed measurement method based on current harmonic analysis with the chirp-Z transform

This paper presents a new method to measure motor speed by means of frequency estimation of rotor slot spectral components in the supply current of squirrel single-cage induction motors. The novelty of the method consists in the harmonic analysis of the supply current by means of the chirp-Z transform (CZT). The advantages are improved accuracy due to better spectral resolution and resolvability. Moreover, a shorter observation window is required, thus reducing errors related to nonstationary current signals. The experimental results are presented to validate the proposed method and to make a comparison with a similar method based on the fast Fourier transform (FFT).

A virtual instrument for the measurement of IEEE Std 1459-2000 power quantities

In this paper, the authors present a PC-based instrument for the measurement of electrical-power quantities defined in IEEE Std. 1459. The instrument is based on a time-domain technique for the detection of the fundamental and harmonic components of voltages and currents. The time-domain strategy was originally developed by the authors for three-phase, three-wire systems. In that paper, the strategy had been extended to both three-phase, four-wire and single-phase systems. Simulation tests were carried out to assess the uncertainty contribution of the proposed strategy in the absence of the measurement transducers. Moreover, the accuracy of the PC-based instrument with its transducers was evaluated; the experimental tests were carried out by using a power calibrator.

A self-synchronizing instrument for harmonic sources detection in power systems

The energy markets deregulation holds a new contractual perspective between customers and utilities, in which energy price can depend on voltage quality and load characteristics, as well as on responsibility for disturbances caused on supply voltage in power systems. In this contest, harmonic sources detection is one of the most urgent problems, because of the proliferation of loads which draw nonsinusoidal currents. In this paper, the authors present a new instrument based on a time domain method for harmonic active power detection in three phase systems. Amplitude and sign of harmonic powers can be measured directly and no spectral analyses are required for the evaluation of amplitudes and phase angles of currents. Moreover, the instrument is able to synchronize itself to the input signal, to measure voltage and current total distortion factors and harmonic voltages amplitudes. Theoretical aspects are discussed, measurement accuracy is evaluated and experimental results are presented.

A Novel Approach to Current Transformer Characterization in the Presence of Harmonic Distortion

The current transformer (CT) performance under distorted waveform conditions is usually characterized by means of the frequency-response test. In this paper, a new way to characterize CTs, closer to real operation conditions, is proposed. The harmonic phase-angle and ratio errors are measured using a nonsinusoidal current composed of fundamental and one harmonic with adjustable phase shift. The new method was tested by determining the performance of two metering class CTs commonly used by the Italian power company. The errors measured using the proposed approach are larger than the ones obtained with the frequency response. This result suggests that the frequency-response approach for the evaluation of CT performance under distorted waveform conditions is not a reliable method.