SLA management and service composition of virtualized applications in mobile networking environments
Winding losses in transformers dramatically increase with high frequency due to eddy current effects. SLA management and service composition of virtualized applications in mobile networking environments For design and optimization of transformers, there is a need for an accurate prediction of the winding losses over a wide frequency range and for various winding arrangements. Eddy current losses including skin effect and proximity effect losses, seriously impair the performance of transformers in high-frequency power conversion applications. For ac current flowing in a conductor, the alternating field inside this conductor induces eddy currents in the conductor, which produce a field that tends to cancel the field produced by the original current.
The tendency of the alternating current distributes itself within the conductor, so that the current density near the surface of the conductor is greater than that at its center. This is called skin effect, which causes the effective resistance of the conductor to increase with the frequency of the current. The proximity effect is similar, but it is caused by the current carried by an adjacent conductor. The current in the adjacent conductor causes a time-varying field and induces a circulating current inside the conductor. SLA management and service composition of virtualized applications in mobile networking environments Both the skin effect and the proximity effect cause the current density to be nonuniform inascddjkbff the cross section of the conductor and thus cause a higher winding resistance at higher frequency.
SLA management and service composition of virtualized applications in mobile networking environment
The skin effect of an infinite foil conductor with sinusoidal excitation can be represented by the ratio of ac resistance to dc resistance as in which describes the skin effect. In addition, the second term represents the proximity effect factor. The proximity effect loss, in a multilayer winding, may strongly dominate over the skin effect loss, depending on the value of m, which is related to the winding arrangement. Interleaving transformer windings can significantly reduce the proximity loss when the primary and secondary currents are in phase. shows the MMF distributions along the vertical direction for noninterleaving arrangement and fully interleaving arrangement, respectively. The value of m can be calculated according to and quite different results are also shown in In order to further illustrate the eddy current effect in different arrangements, a finite-element analysis FEA tool is used to analyze current distribution inside the conductors.and individually represent current distributions for interleaving windings and noninterleaving windings when the excitation frequency is PT model with cylindrical symmetry about the Z-axis has been built, and all of the conditions are the same in both figures, except the winding arrangement.
It can be seen from the two figures that current density is higher toward the symmetrical Z-axis due to the dc spirality effect. The skin and the proximity effects can further increase the nonuniform distribution of current density when the frequency goes high. In other words, the color division of current distribution is caused not only by the dc spirality effect but also by the skin and the proximity effects. It is noteworthy that ac resistance will not be contributed by the dc spirality effect. For the noninterleaving arrangement in, the tendency of current density toward conductor surface is enhanced due to higher proximity effect. SLA management and service composition of virtualized applications in mobile networking environments The strongest tendency toward conductor surface appears in the layer close to the interface between the primary and the secondary, and thus, the area of color division becomes smaller, which means that a higher ac resistance will be produced.