Roberto Candela

A Dynamic Electrical Scheme for the Optimal Reconfiguration of PV Modules under Non-Homogeneous Solar Irradiation

This paper presents a strategy for the maximization of the output power of photovoltaic (PV) systems under non homogeneous solar irradiation by means of automatic reconfiguration of the PV arrays layout. The innovation of the proposed approach is the employment of a simple Dynamic Electrical Scheme (DES), allowing a large number of possible modules interconnection, to be installed between the PV generator and the inverter. The models of the PV generator and of the DES have been realized and simulated with Simulink (Dynamic System Simulation for MATLAB). The attained experimental results appear to be quite interesting in terms of the attainable benefit in power and thus energy terms. The limited calculation times of the reconfiguration algorithm allows the application of the DES for the real time adaptation of the configuration to the changing weather conditions or other causes of non-uniform solar irradiation. Moreover, the results confirm that, in case of non uniform solar irradiation, this approach allows to attain considerably much better results than those attainable with a static configuration.

Composite laminates buckling optimization through Lévy based ant colony optimization

In this paper, the authors propose the use of the Levy probability distribution as leading mechanism for solutions differentiation in an efficient and bio-inspired optimization algorithm, ant colony optimization in continuous domains, ACOR. In the classical ACOR, new solutions are constructed starting from one solution, selected from an archive, where Gaussian distribution is used for parameter diversification. In the proposed approach, the Levy probability distributions are properly introduced in the solution construction step, in order to couple the ACOR algorithm with the exploration properties of the Levy distribution. The proposed approach has been tested on mathematical test functions and on a real world problem of structural engineering, the composite laminates buckling load maximization. In the latter case, as in many other cases in real world problems, the function to be optimized is multi-modal, and thus the exploration ability of the Levy perturbation operator allow the attainment of better results.

A portable instrument for the location and identification of defects generating PD

A portable instrument based on an antenna probe and suitable for partial discharge detection, have been characterized through both laboratory and on-site experiments carried out on coils and stator windings of ac rotating machines. The antenna probe allows the capture of electromagnetic waves in a bandwidth of 0.1–100 MHz. Pulse signals and ac supply voltage reference are obtained by means of high-pass and low-pass filters, respectively, so avoiding the need of a direct connection with the objects under test. By this way, real-time phase resolved partial discharge patterns can be derived. Results of a comparison of the diagnostic information provided by PD patterns due to conducted and irradiated PD signals, are reported in the paper. It is shown that the diagnostic information remains the same when the sensor is moved along the tested object thus allowing the defect location and its identification.

A novel partial discharge detection system based on wireless technology

A novel Partial Discharge detection system is here described. The system employs a special wideband antenna as a sensor, allowing to sense either Partial Discharges pulses either the AC supply voltage at a distance from the component under test, so avoiding the need of direct connection or component shutdown. Thanks to its wireless nature and small physical dimensions, the system enables to perform accurate on-line Partial Discharge diagnosis even in circumstances where conventional instrumentation would be impractical to use, so greatly extending the applicability of this diagnostic method.

An improved MSD-based method for PD defects classification

The new proposed method of pattern recognition is based on the application of multi-resolution signal decomposition (MSB) technique of wavelet transform. This technique has showed off interesting properties in capturing the embedded horizontal, vertical and diagonal variations within an image obtained from the PD pattern in a separable form. This feature was exploited to identify in the PD patterns MSD, relative at various family of partial discharge sources, some detail images typical of a single discharge phenomenon. The classification of a generic PD phenomenon is feasible through a comparison between its detail images and the detail images typical of a single discharge phenomenon. Tests have been performed on specimens having single defects. The obtained results prove that the proposed improved classification method is quite efficient and accurate

Overcoming synchronization issues in wireless technology Partial Discharge measurement

In this paper, several aspects of the fundamentals of wireless Partial Discharge (PD) measurements are first discussed. Then, the relevance of the problem of voltage synchronization in PD wireless diagnosis is outlined. When portable instruments are used for PD detection, the main issue is the voltage measurement at the site where the PD detection is carried out. When such analysis is carried out over shielded cables, the AC (50/60 Hz) voltage reference signal is not easily detectable, while one of the basic parameters for PD diagnosis, the displacement of the inception voltage of the PD as compared to the reference voltage, is not available. Even if high-performance sensors are readily available on the market, the authors are investigating the possibility to use remotely measured reference voltage at the closest accessible substation to create a reliable reference, thus reducing the time and associated costs required for performing field wireless measurements.

Remote voltage synchronization for wireless Partial Discharge diagnostics

The main objective of this paper is the assessment of the exact phase angle displacement of each Partial Discharge, PD, pulse with respect to the voltage reference waveform. Such problem also referred to as `synchronization is relevant when the cable is not accessible and the PD measure is carried out in wireless mode. It is well known, that the angle phase shift, due to the propagation phenomenon on the transmission line, can be calculated knowing the line type and length and typical operating conditions of the transmission line. The setup comprises a customized electronic device, the “Phase check”, a server to collect remote measurements and a Look up table to provide corrections to the measured phase shift values. To evaluate the voltage phase shift introduced by a transmission line, different simulations have been carried out in PSCAD. Then, to prove the correctness of simulated results and verify the “Phase check” precision, experimental measurements have been carries out on three transmission lines in Sicily, Italy. The experimental measurements prove that the proposed setup is effective and quite useful to provide precise assessment of voltage phase shift for PD wireless diagnosis.

A new technique for partial discharges measurement under DC periodic stress

The aim of the present work is to recognize the type of defect in insulating materials employed in DC electrical systems. This analysis, under AC stress, is carried out by using the Phase Resolved method (PRPD). While, under constant voltage stress this method cannot be performed and measurements show complexities. In order to overcome these problems, a new technique is proposed, based on the application of a periodic continuous waveform. Simulation results, carried out by using a model based on a time-variable conductance of an air void defect, showed the PRPD pattern that can be obtain. Furthermore, compared to the constant DC stress, the measurement duration became lower and the discharges repetition rate greater. Finally, experimental tests have been made in order to validate simulation results.

Partial Discharges analysis and parameters identification by continuous Ant Colony Optimization

The technique of ant colony optimization has been employed in this paper to efficiently deal with the problem of parameters identification in partial discharge, PD, analysis. The latter is a continuous optimization problem. From the technical point of view the identification of these parameters allows the modeling of the phenomenon of Partial Discharges in dielectrics. In this way it is possible the early diagnosis of defects in Medium Voltage cable lines and components and thus it is possible to prevent possible outages and service interruptions. Analytically, the problem consists of finding the Weibull parameters of the Pulse Amplitude Distribution (PAD) distributions allowing the identification and classification of the defects in dielectrics. The accuracy in this identification is crucial for correct classification of defects. The proposed algorithm, called DACS, Dynamic Ant Colony Search, allows the easy investigation of complex problems both in discrete and continuous search spaces. It dynamically redefines the search tree through which the ants (agents) move using an adaptive parameter in order to increase exploration or exploitation. In order to check the efficiency of the proposed algorithm in solving continuous optimization problems, many Partial Discharges, PD, experimental tests at various temperatures have been performed on some lumped capacity specimens. In this way, the experimental cumulative probability of amplitude histograms has been compared with those attained using the Weibull analysis. All the applications show that the error is quite limited and that the calculation times are considerably low compared to other techniques employed for the same purpose.