Inácio, S., D. Inácio, J. M. Pina, S. Valtchev, M. V. Neves, and A. L. Rodrigues,
"An electrical gearbox by means of pole variation for induction and superconducting disc motor",
Journal of Physics: Conference Series, vol. 97, pp. 012221, 2008.
AbstractIn this paper, a poly-phase disc motor innovative feeding and control strategy, based on a variable poles approach, and its application to a HTS disc motor, are presented. The stator windings may be electronically commutated to implement a 2, 4, 6 or 8 poles winding, thus changing the motor's torque?speed characteristics. The motor may be a conventional induction motor with a conductive disc rotor, or a new HTS disc motor, with conventional copper windings at its two iron semi-stators, and a HTS disc as a rotor. The conventional induction motor's operation principle is related with the induced electromotive forces in the conductive rotor. Its behaviour, characteristics (namely their torque?speed characteristics for different number of pole pairs) and modelling through Steinmetz and others theories are well known. The operation principle of the motor with HTS rotor, however, is rather different and is related with vortices' dynamics and pinning characteristics; this is a much more complex process than induction, and its modelling is quite complicated. In this paper, the operation was simulated through finite-elements commercial software, whereas superconductivity was simulated by the E-J power law. The Electromechanical performances of both motors where computed and are presented and compared. Considerations about the systems overall efficiency, including cryogenics, are also discussed.
Baikova, {E. N. }, L. Romba, {S. S. } Valtchev, R. Melicio, V. {Fernão Pires}, A. Krusteva, and G. Gigov,
"Electromagnetic field generated by a wireless energy transfer system: comparison of simulation to measurement",
Journal of Electromagnetic Waves and Applications, vol. 32, no. 5: Taylor & Francis, pp. 554–571, 3, 2018.
AbstractThis paper presents a wireless energy transfer system operating at the frequency values of kHz order: modeling, simulation, and comparison with prototype measurement results. Wireless energy transfer system model using finite element method was carried out to simulate the electric field and the magnetic flux density for different air gap sizes between the transmitter and the receiver coils. Results are presented and compared with the electromagnetic emission measurements radiated by the wireless energy transfer system prototype. The electric field comparison between the simulated and the prototype measurement values shows an error of roughly 8.7{%}. In the recent years, the interest in the wireless energy transfer technology, especially for electric vehicles batteries charging, is rapidly increasing. As a result of the increasing application of this technology in the industrial and consumer electronic products, more concerns are raised about the electromagnetic compatibility, since the wireless energy transfer systems produce electromagnetic emissions in the surrounding environment.
Pereira, P., S. Valtchev, J. Pina, A. Gonçalves, V. M. Neves, and A. L. Rodrigues,
"Power electronics performance in cryogenic environment: evaluation for use in HTS power devices",
Journal of Physics: Conference Series, vol. 97: iopscience, pp. 012219, 2008.
AbstractPower electronics (PE) plays a major role in electrical devices and systems, namely in electromechanical drives, in motor and generator controllers, and in power grids, including high-voltage DC (HVDC) power transmission. PE is also used in devices for the protection against grid disturbances, like voltage sags or power breakdowns. To cope with these disturbances, back-up energy storage devices are used, like uninterruptible power supplies (UPS) and flywheels. Some of these devices may use superconductivity. Commercial PE semiconductor devices (power diodes, power MOSFETs, IGBTs, power Darlington transistors and others) are rarely (or never) experimented for cryogenic temperatures, even when designed for military applications. This means that its integration with HTS power devices is usually done in the hot environment, raising several implementation restrictions. These reasons led to the natural desire of characterising PE under extreme conditions, e. g. at liquid nitrogen temperatures, for use in HTS devices. Some researchers expect that cryogenic temperatures may increase power electronics' performance when compared with room-temperature operation, namely reducing conduction losses and switching time. Also the overall system efficiency may increase due to improved properties of semiconductor materials at low temperatures, reduced losses, and removal of dissipation elements. In this work, steady state operation of commercial PE semiconductors and devices were investigated at liquid nitrogen and room temperatures. Performances in cryogenic and room temperatures are compared. Results help to decide which environment is to be used for different power HTS applications.
Pina, J., P. Pereira, S. Valtchev, A. Gonçalves, V. M. Neves, A. Alvarez, and L. Rodrigues,
"A test rig for thrust force measurements of an all HTS linear synchronous motor",
Journal of Physics: Conference Series, vol. 97: IOPScience, pp. 012220, 2008.
AbstractThis paper presents the design of a test rig for an all HTS linear synchronous motor. Although this motor showed to have several unattractive characteristics, its design raised a number of problems which must be considered in future HTS machines design. HTS electromagnetic properties led to the development of new paradigms in electrical machines and power systems, as e. g. in some cases iron removal and consequent assembly of lighter devices. This is due to superconductor's ability to carry high currents with minimum losses and consequent generation in the surrounding air of flux densities much higher than the allowed by ferromagnetic saturation. However, severe restrictions in HTS power devices design that goes further beyond cryogenic considerations must be accounted in. This is usually the case when BSCCO tapes are used as conductors. Its bending limitations and the presence of flux components perpendicular to tape surface, due to the absence of iron, have to be considered for it may turn some possible applications not so attractive or even practically unfeasible. An all HTS linear synchronous motor built by BSCCO tapes as armature conductors and two trapped-flux YBCO bulks in the mover was constructed and thrust force measurements are starting to be performed. Although the device presents severe restrictions due to the exposed and other reasons, it allowed systematising its design. A pulsed-field magnetiser to generate opposite fluxes for both YBCO bulks is also detailed. Thrust force numerical predictions were already derived and presented.
Romba, L., {S. S. } Valtchev, and R. Melício,
"Three-phase magnetic field tested in wireless power transfer system",
International Review of Electrical Engineering, vol. 11, no. 6: Praise Worthy Prize, pp. 586–597, 1, 2016.
AbstractThis paper presents a magnetic field three dimensional mapping produced by a threephase prototype for wireless power transfer. The presented magnetic field mapping is a contribution to improve the design of electric vehicles battery chargers using the wireless power transfer. To collect the magnetic field data, a prototype was built, in order to support the tests. The prototype primary is an electrical three-phase system that allows to be connected electrically and geometrically in star or delta. The losses due to the magnetic field dispersion and the generated interferences in the surrounding equipment or in human body are discussed. The different standards organizations related to electric vehicles battery chargers are presented. Finally the magnetic field influence on the human body is addressed.