Bernardo Tellini

Direct and inverse Preisach modeling of soft materials

A product-type Preisach model, called here the Modified Scalar Preisach Model (MSPM), is accounted for the modeling of the magnetic hysteresis in soft ferromagnetic materials. The hypothesis of stochastic independence of the switching field parameters leads to a formulation of the model that allows a relatively simple identification procedure, also from the viewpoint of the computational cost. The numerical efficiency of the procedure is shown in a series of proper applications.

Conducted and radiated interference measurements in the line-pantograph system

We present the results of a measurement campaign aimed at investigating electromagnetic interference (EMI) phenomena in the interaction between overhead railway power supply lines and pantograph. In order to obtain such data, an experimental setup was assembled in a shielded room, consisting in a short section of overhead line and a full scale pantograph. One of the most interesting results consists in the observation of a very significant (both from the qualitative and the quantitative point of view) difference between the EMI behavior in the switch-on (pantograph going up) and switch-off (pantograph going down) transients.

3-D field analysis in tubular induction launchers with armature transverse motion

In this paper the transition between the sections of a generator driven induction launcher is investigated. During the transition a possible mismatch of the currents in the sleeve with the driving coils currents can give rise to strong braking force. If the sleeve is not in coaxial position with the barrels, forces in the transverse direction of motion can produce contacts with the flyway tube. Transverse motion of the sleeve has to be considered. The equations of motion are derived assuming a rigid projectile and a flyway restoring force that is proportional to the local deformation. A full 3-D analysis, required because of the departure from the coaxial configuration, has been performed by means of a computer code based on an integral formulation of the Maxwell equations; the resulting equations are those of an electrical time-varying network. Simulations of the behaviour of the system have been performed to search for the optimal initial position of the sleeve in the second section. The results show that smooth transition between the sections is obtained if the energization of the coils of the second section is done in correspondence with the proper positions of the sleeve. Under these conditions the motion is characterized by the greater muzzle velocity.

Single PEM Fuel Cell Analysis for the Evaluation of Current Ripple Effects

In this paper, the results of an experimental analysis performed on a polymer electrolyte membrane fuel cell (FC) for the evaluation of the current ripple effects are reported. The polarization curve (PC) and the impedance spectrum measured for a single FC with a Nafion membrane are presented discussing some advantages and disadvantages of the two adopted techniques from the measurement point of view. The ohmic and activation resistance values provided by the PC are compared to the frequency limits of the equivalent resistance estimated by the spectroscopic analysis to evaluate the additional losses and the system efficiency reduction introduced by the current ripple. The presence of a voltage–current hysteretic behavior is discussed throughout the paper, and some comments on how such a relationship can impact on the identification of the indicated parameters are included.

Characterization of the Accommodation Effect in Soft Hysteretic Materials Via Sensorless Measurement Technique

The well-known voltamperometric method has only been used so far in the identification of symmetric hysteresis cycles for reasons that are explained in the main text. This paper extends the sensorless measurement method to the characterization of asymmetric loops, without losing the main advantage of this technique, i.e., the low-cost setup and the simplicity of the procedure. The current through-and the induced voltage on-the primary and secondary coils, which are wound around a magnetic core, are the measurands. Moreover, by carefully choosing the input signals, so that a series of major loops is defined along the whole B - H measured path, a way is suggested to avoid the problems caused by the dc offset of the instrumentation chain and to reduce the uncertainty in the determination of the initial state of magnetization. Both the offset and the initial magnetization state are necessary for a correct reconstruction of the induction field. A complete analysis of the capabilities and critical aspects of the proposed measurement procedure is carried out through a theoretical discussion supported by simulation and experimental results. The measurement of nonsymmetric cycles and their accommodation are shown and discussed as the final objective of the proposed approach.

Sensorless Measurement Technique for Characterization of Magnetic Material Under Nonperiodic Conditions

This paper deals with the sensorless characterization of magnetic materials under nonperiodic conditions. A volt-amperometric method based on general physical principles has been adopted to do the measurements. Starting from the concept of magnetic hysteresis as a multibranch nonlinearity with nonlocal memory, we provide a description of the proposed measurement procedure, focusing on two significant topic points: 1) the determination of a well-known (within a certain interval of confidence) initial state of magnetization and 2) the effect on the final experimental results of the offset introduced by the instrumentation. Finally, we present experimental results done on a sample of soft ferrite, showing how the method is capable of measuring phenomena like accommodation or noncongruency of minor loops.

A new method to characterize magnetic hysteresis in soft ferrites up to high frequencies

Characterization of magnetic cores is an indispensable task in order to securely accomplish the requirements of a power electronic design and prevent failures. The hysteresis cycle of the material is one of the more complex features to characterize due to the well-known nonlinear and memory effects; moreover, there is a less known but noticeable dependence of the B-H relationship with time. This curve is easily obtained at low frequencies (up to 10 kHz) by means of a well-known traditional method. However, there is a major obstacle when trying to operate at higher frequencies in this manner due to the cost and difficulty of operation of high-frequency-high-voltage generators. In this paper, a new method for measuring hysteresis based on a quasi-sinusoidal generator that allows us to reach much higher values in frequency with a simple setup is presented.

Identification of parameters in a Rogowski coil used for the measurement of partial discharges

The Rogowski coil is a simple and inexpensive device that can be adapted to measure high frequency currents such as those created by partial discharges in dielectrics. It has been demonstrated in previous works that the Rogowski coil can be self-integrating when used at high frequencies and can be tuned to measure partial discharges without the need of cumbersome electronic devices. The aim of this paper is to explore the possibilities of obtaining better measurements simply changing the electric parameters and hence, the geometry of the coil. In the process, the inductance, mutual inductance, resistance and capacitance are written in function of geometric variables. Then, a bode plot simulates the effect of changing some of these variables and the results are commented focused on the pursued objective.

A new analytic approach for dealing with hysteretic materials

We present analytic formulations for studying the energetic behavior of hysteretic magnetic materials. One formulation reduces the full nonlinear diffusion problem to a linear problem through an optimization procedure. A second formulation attempts to approximate the magnetic permeability tensor by a complete set of functions. By means of scalar product defined in the function space, we obtain a series of linear nonhomogeneous diffusion equations. We analyze for the vector case qualitatively and give solutions for a one-dimensional field configuration. For the scalar case, we investigate two different magnetic materials and, for simplicity, we approximate the relevant hysteresis cycles by a closed polygonal. A scalar Preisach model, numerically treated, is used as a benchmark.

Line-pantograph EMI in railway systems

At present, the EN50121 standards are the main reference for electromagnetic compatibility in European railway systems. These standards should improve as technology and testing develops. Therefore, major sources of EMI in a railway environment need to be better understood. This study is complex because many different railway power systems exist in Europe (1.5 kV DC, 3 kV DC, 15 kV 16.7 Hz, 25 kV 50 Hz). European railways are using new control and communication systems, and electromagnetic compatibility problems should be carefully studied and solved.