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Resonant electromagnetic vibration harvesters: determination of the equivalent electric circuit parameters and simplified closed-form analysis for the identification of the optimal bridge rectifier DC load
No full textIn this paper, the guidelines leading to the identification of the values of the parameters of the equivalent
electric circuit of vibration electromagnetic harvesters are identified and discussed. A simplified closed
form analysis of the non-linear system composed by a vibration electromagnetic harvester which supplies
a DC load by means of a diode bridge rectifier is also presented. Such an analysis clearly puts in evidence
that the maximum power which can be extracted by a given vibration harvester (when it supplies
the optimal load impedance) is higher than the maximum power which can be extracted by such an harvester
when it is cascaded with a diode bridge rectifier which supplies the optimal DC load. The term ‘‘optimal
load” identifies in both cases the load in correspondence of which the electric power which is
extracted from vibrations attains its maximum value
DMPPT experimental demonstration unit based on buck converter
Full text linkDistributed Maximum Power Point Tracking (DMPPT) technique represents the most promising solution to enhance the lackluster energetic performance of the mismatched PhotoVoltaic (PV) systems. Despite that, there are several factors which restrict its performance some of which are still to be explored. To fully understand the advantages offered by the DMPPT solution, the implementation of a DMPPT emulator is necessary. Based on the above needs, this paper describes the realization and use of a DMPPT experimental demonstration unit based on the Buck DC/DC converter. The above device is capable to emulate the output current vs. voltage (I-V) characteristics of many commercial PV modules with a dedicated Buck DC/DC converter not only in controlled atmospheric conditions but also with different currents rating of the switching devices. The system implementation is based on a commercial power supply controlled by a low-cost Arduino board. Data acquisition is performed through a low-cost current and voltage sensor by using a multichannel board by National Instruments. Experimental results confirm the validity and potential of the proposed DMPPT emulator
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Computation of Electric and Magnetic Fields Generated by Cloud-to-Cloud Lightning Channels
No full textThe paper presents analytical formulas for computation in the time domain of electromagnetic (EM) fields generated by tortuous cloud-to-cloud (CC) lightning channels over a perfectly conducting ground. For the first time, the study was not limited to a horizontal lightning path but was extended to take into account the natural, tortuous geometry of the lightning channel. After the calculation of the step response, a convolution integration was applied for the computation of the fields generated by an arbitrary current source. The produced electric and magnetic fields were then compared with the fields generated by a horizontal channel. The method can be of primary importance to evaluating the hazards for electric and electronic systems of flying aircraft, estimating the voltages induced on overhead transmission lines by CC lightning, and, in general, evaluating the induced effects on sensitive electric and electronic components. Moreover, it may represent a simple, robust, and time-saving tool for estimating important physical parameters that characterize lightning phenomena
Piecewise Linear Modeling for Inrush Safety Regions Detection and Its Validation Through a Preisach Model and Experimental Data
No full textA simple scheme for the inversion of a Preisach like hysteresis operator in saturation conditions
Full text linkA class of operators based on a Prandtl-Ishilinskii operator with inverse in a closed form is presented. Conversely to those considered in the past, they describe the B - H constitutive equation and not the usual J - H link. This allows its application in numerical schemes for the description of nonlinear dynamic circuits in transient conditions, with low formulation effort and computational weight, with respect to the standard inversion of the operator. The model has been implemented into a numerical scheme describing a RL nonlinear and hysteretic circuit, outlining the effects of residual magnetization and coercive field on the global current dynamics. The model performances are preliminary compared to numerical model based on the standard numerical inversion of the operator, along with the experimental results of transient current analysis
MULTI-OBJECTIVE OPTIMIZATION OF PV ARRAYS PERFORMANCES BY MEANS OF THE DYNAMICAL RECONFIGURATION OF PV MODULES CONNECTIONS
No full textLora-based Smart Sensor for PD Detection in Underground Electrical Substations
Full text linkThe paper deals with the development of an IoT smart sensor for the monitoring of Partial Discharges (PD) in underground substations. The sensor consists of (i) an ultrasonic receiver for the detection of discharges, (ii) a programmable conditioning circuit that adapts the output of the ultrasonic receiver to the noise floor of the environment, and (iii) a digital section of processing and transmission of eventual warning message if the presence of discharges is detected. Given the challenge of transmitting messages from underground substations, LoRaWAN has been adopted as transmission technology. In the paper, several tests for the sensor assessment have been reported. In particular, the analog section has been assessed through tests in high voltage laboratory; it was so possible to tailor the conditioning circuit to the ultrasonic signal and to establish the alarm thresholds, comparing the sensor signal with a reference instrument for PD detection based on the electrical method. The performance of the transmission module has been evaluated through on field tests, placing the transmission module in a manhole. Finally the entire smart sensor has been assessed through tests in a real electrical substation. All tests have shown that the developed sensor is capable of detecting discharges with a reliability comparable to reference systems currently used by electrical energy distributors, and that LoRaWAN transmission has remarkable reliability also in underground environments characterized by thick concrete walls and high electromagnetic interference
Identification of the parameters of the equivalent electric circuit of electromagnetic harvesters
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