This paper deals with the design and optimization of a 1.2 MVA medium-voltage (MV) power electronic traction transformer (PETT) for an AC 15 kV/16.7 Hz railway grid, in which a simple two-stage multi-cell PETT topology consisting of a bidirectional 170 kW, 2.5 kV AC rms to 6 kV DC power factor corrected (PFC) converter stage followed by a bidirectional isolated 46 kHz, 6 kV to 1.5 kV series resonant DC/DC converter for each cell is presented. This paper presents a methodology that maximizes the converter"s efficiency and minimizes the converter"s size and weight. Accordingly, the first stage employs 10 kV SiC MOSFETs based on the integrated Triangular Current Mode (iTCM). The second stage uses 10 kV SiC MOSFETs on the MV-side, 3.3 kV SiC MOSFETs on the LV-side, and a medium frequency (MF) MV transformer operating at 46 kHz. MF transformers offer a way to reduce weight and improve energy efficiency, particularly in electric multiple-unit applications. The MF MV transformer requires power electronic converters, which invert and rectify the voltages and currents at the desired operating frequency. The development of high voltage SiC MOSFETs, which can be used instead of Si IGBTs in PETT topologies, increases the operating frequency without reducing the converter"s efficiency. The designed MV PETT achieves 98.95% efficiency and 0.76 kVA/kg power density.

This paper deals with the design and optimization of a 1.2 MVA medium-voltage (MV) power electronic traction transformer (PETT) for an AC 15 kV/16.7 Hz railway grid, in which a simple two-stage multi-cell PETT topology consisting of a bidirectional 170 kW, 2.5 kV AC rms to 6 kV DC power factor corrected (PFC) converter stage followed by a bidirectional isolated 46 kHz, 6 kV to 1.5 kV series resonant DC/DC converter for each cell is presented. This paper presents a methodology that maximizes the converter"s efficiency and minimizes the converter"s size and weight. Accordingly, the first stage employs 10 kV SiC MOSFETs based on the integrated Triangular Current Mode (iTCM). The second stage uses 10 kV SiC MOSFETs on the MV-side, 3.3 kV SiC MOSFETs on the LV-side, and a medium frequency (MF) MV transformer operating at 46 kHz. MF transformers offer a way to reduce weight and improve energy efficiency, particularly in electric multiple-unit applications. The MF MV transformer requires power electronic converters, which invert and rectify the voltages and currents at the desired operating frequency. The development of high voltage SiC MOSFETs, which can be used instead of Si IGBTs in PETT topologies, increases the operating frequency without reducing the converter"s efficiency. The designed MV PETT achieves 98.95% efficiency and 0.76 kVA/kg power density.

This paper presents the development of a multi-coil eddy current (EC) sensor that uses an axial rotating magnetic field for the measurement of electrical resistance to determine the electrical conductivity tensor of stratified carbon fiber reinforced polymer (CFRP) materials. The sensor consists of an identical planar racetrack multi-coil, excited by two-phase sinusoidal current sources that are 90° apart in phase to generate an axial rotating magnetic field and eliminate the need for mechanical rotation. Each sensor's coil's resistance variation is measured using a developed experimental prototype unit and computed using a 3D finite element method (FEM) based on the (A, V–A) formulation. The inverse problem technique that minimizes the difference between the calculated and measured resistances is then used to identify the electrical conductivity tensor components using the particle swarm optimization (PSO) algorithm. The comparison between the computed resistances and the measured ones shows an excellent concordance.

In this paper, we have carried out an experimental study of the detection of top rail surface cracks. Firstly, we have highlighted the inability to inspect the entire rail head surface by a single sensor with a single scan. To overcome this inspection inability, we have proposed a multisensor system composed of three differential probes arranged within a specific configuration. The yielded results showed the efficiency and the robustness of the proposed configuration in the detection of cracks regardless its size, orientation and location.

In this paper, an iterative technique, employing the T formulation associated with the finite element method, based on Maxwell’s equations and the Biot-savart law, is used for analyzing the density of eddy currents in composite carbon fiber reinforced polymer (CFRP) materials. For this purpose, a code has been developed for solving an electromagnetic 3D non-destructive evaluation problem. This latter permits the characterization of this CFRP and determinate of fibers orientation using the impedance variation which is implanted in polar diagram. Firstly, the obtained results are compared with those of the analytical model. This comparison reveals a high concordance which proves the validity of the proposed method. Secondly, three different applications are shown for illustrating the characterization of unidirectional, bidirectional and multidirectional piece using a rectangular coil plotted in normalized impedance diagram.

This article presents a study of a Multi-coils circular eddy current non-destructive testing sensor for determining the fibers orientation as well as the detection of defect in multidirectional carbon fibers reinforced polymer (CFRP). The developed sensor contains 16 rectangular coils connected in series and supplied by a single-phase sinusoidal source. This sensor allows the annulations of the mechanical rotation of the conventional sensors and it permits to reduce the inspection procedure duration. The electromagnetic phenomena are calculated by using 3D finite element method (FEM) based on the electromagnetic AV-A formulation. Finally, the Multi-coils circular sensor responses are analyzed through polar diagrams of the impedance variation, where the defect is taken into consideration. A great concordance between the obtained results and those of literatures has been noticed. The provided results show that the proposed sensor allows an efficient characterization of multidirectional CFRP and detection of defects in different layers.

This paper presents a new modeling approach of eddy current nondestructive evaluation systems containing magnetic materials. Originally, the proposed model is based on coupled circuits principle and the notion of equivalent current density. In order to make the model homogenous, we consider the current density as a state variable since this density is compatible with the representation of the magnetisation by equivalent currents. By introducing the fictitious electric conductivity approach, the sensor impedance is expressed according to magnetic tube or plate characteristics such as electric conductivity and magnetic permeability. An excellent concordance is achieved by comparing the calculated results to those of analytical ones. Regarding the mesh simplicity and the fast calculation, this method is very adapted for the resolution of the inverse problems for real time evaluation of the properties of magnetic materials.

It is a challenging task to detect the hidden cracks in multilayer riveted structures in a nondestructive manner. This paper puts forward an eddy current nondestructive method for crack detection in such structures based on the electric conductivity of the rivets. Specifically, an eddy current sensor was designed with a ferrite core coil to evaluate the surface and inner defects of different layers. The magnetic phenomena during the detection process was simulated based on the magnetic potential and the scalar electrical potential, and the magnetic potential vector was solved by finite-element method. The proposed method was compared with the eddy current detection method without considering rivet conductivity through an experiment on a three-layer riveted aluminum structure. The length and position of each defect on each layer were changed in the experiment. The results show that the proposed method achieved better accuracy than the contrastive method, and its sensitivity depends on two issues: the position of the defect relative to the separation of the layers and the length of the defect relative to the length of the rivet head. The research results are of great significance for nondestructive testing of multilayer riveted structures in many fields.

Eddy Current Nondestructive Testing Calibration for Cracks Detection in Aircraft Based Riveted Multilayer Structures