EPQU Journal Volume 13 Issue 1

EPQU Volume 13 Issue 1 is now available.

Willems  Jacques L.

 

Summary: The relations between the basic laws of circuit theory (Kirchhoff's laws and the conservation of generalized power) are discussed with respect to the active and reactive current components. It is shown that the active and reactive currents do not satisfy Kirchoff’s current law. It is proved that this is not in contradiction with the property that the active and reactive powers satisfy the conservation property.

By Paolo Tenti, Jacques L Willems, Paolo Mattavelli and Elisabetta Tedeschi

This paper deals with the generalization of the symmetrical components technique to periodic non-sinusoidal three-phase currents and voltages. The generalization of the concept of symmetrical components is discussed together with their derivation in both time and frequency domain.

The main conclusion of the paper is that an orthogonal decomposition of periodic nonsinusoidal three-phase signals into positive sequence, negative sequence and zero-sequence components is not possible, but that an additional current and voltage component should be introduced, which is called the residual component.

Paolo Tenti, Paolo Mattavelli and Elisabetta Tedeschi

 

Summary: The paper introduces two definitions of instantaneous reactive power terms, which are conservative in every network and apply even under non-sinusoidal conditions. Both quantities coincide with usual reactive power for sinusoidal operation, however they assume a different meaning for distorted behaviour. The first one is an energy-related term, and its unbiased integral accounts for the average energy stored in the network. The second has a differential nature and is suitable for dynamic analysis and control of harmonic and reactive power sources acting in the network. The combined use of both approaches allows cooperative operation of static and dynamic reactive and harmonic compensators, like STATCOMs and Active Power Filters.

Roberto Langella and Alfredo Testa

 

Summary: The amplitude and phase modulation effects of waveform distortion in power systems are analyzed. Recalls on Amplitude Modulation (AM) and Phase Modulation (PM) are given with particular reference to spectral components. Then, simple inverse formulas are obtained to demonstrate that summations of one or more small tones frequencies to a given tone of interest can always be interpreted in terms of AM and PM. The usefulness of AM and PM representation, in particular in the presence of interharmonic tones, is demonstrated with reference to simple case-studies and practical applications.

Alberto Borghetti, Mauro Bosetti, Mauro Di Silvestro, Carlo Alberto Nucci, Mario Paolone,
Lorenzo Peretto, Elisa Scala, Roberto Tinarelli

 

Summary: Methods aimed at locating the position where a fault is occurred can be seen as part of a complex measurement system oriented at more general power quality purposes. This paper faces the comparison between two methods recently proposed in literature for fault-location in distribution networks, based on a distributed and on a single-ended measurement system, respectively. By assuming a common distribution system topology, the two methods are applied in order to compare their performances as well as the obtained results. On the basis of the different drawbacks and advantages shown by the two methods, potential improvements are eventually taken into account, and a possible integration of the two approaches is investigated and discussed.

Emanuel Alexander E.

 

Summary: This article is a response to a paper presented at the sixth International Workshop on Power Definitions, a report that rejected the fact that the Poynting vector (PV) provides useful information “for academic interpretation of power properties and for practical applications of power theory”. This study explains how the PV reveals the existance of power oscillations unexplained by simple mathematical models used in the basic circuit theory. It sheds light on the puzzling situation where the  PV exists but does not  transfer energy and also presents some examples that reinforce the usefulness of PV as a fine tool in understanding the flow and the components of electromagnetic energy.

Herbert L. Ginn III

 

Summary: A new reference generation technique for active compensators based on the use of CPC theory along with the instantaneous reactive power (p-q) theory is presented here. Modifications to reference signal generation techniques based on instantaneous reactive power as well as to the synchronous reference frame (d-q) method are proposed. The proposed strategy utilizes the CPC theory instead of the filters typically used to extract the desired components of the current.  A simulation-based example is provided that shows this new approach retains the “instantaeous” property provided by the p-q or d-q methods under certain conditions without the negative effects found using the traditional method.

Andrzej Firlit

Summary: This paper presents the comparison among the control algorithms of a three phase, three wire shunt active power filter. The control algorithms are based on:
1) the current’s physical components theory,

2) the p-q power theory. The active power filter operation under the distorted supply voltage at the point of common coupling condition is considered. The comparison concerns the aspects of: filtering current harmonics, reactive power compensation (defined in the fundamental harmonic domain), supply current balancing and dynamic performance. The results of the laboratory investigation, using the fast prototyping system dSPACE, are given in the paper.
This paper confirms that the current’s physical components theory allows developing the control algorithm of shunt active power filter and its practical implementation. The investigation allows the conclusion that this control algorithm enables achieving the supply system current shape close to the sinusoidal, despite shunt active power filter operation under the distorted supply voltage. A sinusoidal supply current cannot be attained by the control algorithm based on the p-q power theory without some additional control elements, such as: PLL, signal filters, etc. The experiment also has shown that the control algorithm based on the p-q power theory is easier to implement and less demanding in terms of hardware than the control algorithm based on the current’s physical components theory.

Gaetano Pasini, Lorenzo Peretto, Elisa Pivello, Roberto Tinarelli

 

Summary: Low-cost handheld instruments performing a large variety of electrical measurements are recently appeared on the market. Their diffusion is mainly due to the availability of integrated circuits that carry out many measurement functions, thus simplifying the instrument implementation and reducing the costs. In this paper, the accuracy performances of an integrated circuit featuring rms and power measurements are evaluated under both sinusoidal and non-sinusoidal conditions. The implemented measurement bench and the obtained results are presented. The results show that the accuracy of the device under test is satisfactory for active power and current rms values, instead of the voltage channel accuracy is significantly worst.

Carlo Muscas, Fabrizio Pilo, Giuditta Pisano, Sara Sulis

Summary: The recent studies about the attribution of the responsibilities for harmonic distortion in electric distribution systems show that the most promising approaches are based on measurement data acquired simultaneously in different nodes of the network. Therefore, distributed measurement systems are needed. For economic reasons, only a small part of network nodes can be equipped with measurement instruments, whereas the information about the overall status of the electric system has to be evaluated by means of suitable Harmonic State Estimation (HSE) techniques.
This paper deals with the problem of choosing the optimal number and position of measurement devices, in order to ensure that the HSE algorithms can provide, at the lowest possible cost, results having a prefixed level of accuracy.
An optimization algorithm based on the techniques of the dynamic programming is proposed and the way to take into account the uncertainty introduced by all the elements of the measurement system is discussed.
Simulation results on a benchmark distribution network show the validity of the proposed approach.

By Alexander E. Emanuel

This paper deals with the subject of intrinsic power. This form of nonactive power is always present when active power is present. The intrinsic power does not cause power loss in conductors or ferromagnetic components. The paper describes different kinds of intrinsic power and shows how it originates.

Czarnecki Leszek S.

 

Summary: Discussion on the physical interpretation of the reactive power Q is the subject of the paper. This power in common physical interpretation used to be associated with energy oscillation between the load and the supply source. The paper demonstrates that such interpretation is not correct. Just the opposite, the interpretation of the reactive power Q as an effect of energy oscillation is one of the major misinterpretations of power phenomena in electrical circuits. The Currents’ Physical Components (CPC) power theory is the main theoretical tool used in the discussion presented in this paper.

Czarnecki Leszek S.

 

Summary: Power related phenomena in three-phase, three-wire circuits with linear time-invariant (LTI) loads supplied with asymmetrical sinusoidal voltage are investigated in this paper. The study is based on the concept of the Currents’ Physical Component (CPC) power theory. It is shown that the supply current of LTI loads with sinusoidal asymmetrical voltage, as in the case of symmetrical voltage, is composed of only three physical components, the active, reactive and unbalanced currents. Consequently, loads in such conditions can be characterized by the active, reactive and unbalanced powers. The equivalent and unbalanced admittances of three-phase loads at symmetrical supply voltage are constant, independent on the supply voltage, parameters. The paper shows that these parameters at asymmetrical supply depend on the voltage asymmetry.

Ferdinanda Ponci, Antonello Monti, Loredana Cristaldi

 

Summary: This paper presents an analysis of the introduction of power quality assessment through power quality indexes within the framework of an agent-based power system control. The objective is to account for power quality in the power management of systems where the total power of the loads significantly exceeds the power available from generation. This is typically the case of next generation all-electric warships

Lorenzo Peretto, Jacques L. Willems and Alexander E. Emanuel

 

Summary: In this paper the possibility of errors in the measurement of average values (in particular rms values or active powers) in power systems under nonsinusoidal conditions are discussed. The errors considered are either due to the fact that the measurement time interval is not an exact multiple of the fundamental period of the voltage and current signals, or due to the presence of interharmonics or subharmonics. The errors are calculated and the results are illustrated by means of simple examples.

Antonello Monti, Ferdinanda Ponci, Stefano Pelizzari, Loredana Cristaldi

The paper presents an implementation of a virtual instrument to perform wavelet analysis on the Park Power components. The main purpose of the analysis is an automatic detection of load in a power system applying load signature analysis. A justification for the approach is presented, followed by the details about the specific implementation performed in the laboratory. Finally a preliminary testing activity based on the use of Hardware in the Loop approach is also presented.

Grazia Todeschini and Alexander E. Emanuel

 

Summary: This work deals with the flow of the electromagnetic energy through an idealized single-phase transformer supplied with nonsinusoidal voltage and supplying a nonlinear load. The electromagnetic flux components of the energy that flows from primary to secondary as well as the flux of energy stored in and ejected from the dielectric space surrounding the windings are identified and quantified. The electromagnetic flux components are correlated to well known instantaneous powers. These powers are not clever mathematic expedients but correct expressions that mirror the actual physical phenomena and lead to a more realistic interpretation of apparent power and its resolution.