**Holistic Modeling and Performance Evaluation for Converged Network-Cloud Service Provisioning**

Combining with the analysis of winding loss, core loss, leakage inductance, and stray capacitance, some overlapping occur in affecting each other, as described here. Number of turns N. The lesser the N, the lesser the winding loss but the more the core loss that will be produced due to higher peak flux density; furthermore, a lower leakage inductance can also be obtained. The stray capacitance is also probably benefited, depending on the winding configuration. The choice of N will have to be a key in optimizing design.

Excitation frequency f. Although a higher frequency can cause a lower core loss as mentioned before, ac resistance will be increased due to eddy current effect. The leakage inductance slightly decreases with increased frequency because of a small change in the permeability of conductors. The designed frequency has to be considered the carrying capacity of the switching devices and the switching losses. Thickness of conductors h and insulator h. Holistic Modeling and Performance Evaluation for Converged Network-Cloud Service Provisioning The optimal thickness h for winding loss has been introduced in Section A larger h also causes a larger leakage inductance.

## Holistic Modeling and Performance Evaluation for Converged Network-Cloud Service Provisionings

There is a contradiction for hΔ between the leakage inductance and the stray capacitance. The larger the hΔ, the larger the leakage inductance and the smaller the capacitance. It is impossible to achieve both low values by optimizing the physical parameters. The only way to obtain optimal behaviors of both leakage inductance andstray capacitance is to change the winding configurations. Considering the loss in parasitic elements, a low leakage inductance has priority over a low stray capacitance in high-current low-voltage application. Reversely, Holistic Modeling and Performance Evaluation for Converged Network-Cloud Service Provisioning in lowcurrent high-voltage application, a low stray capacitance has to be required rather than a low leakage inductance. Core geometry. For a certain number of turns, a bigger cross section Ae of core can bring a lower core loss, but the length of windings will have to be sacrificed, which increases the winding loss.

In order to facilitate a clear understanding of tradeoffs in turn ratio transformer will be analyzed as an example of simplification. The assumed specification of a full-bridge buck dc–dc converter with primary excitation of duty cycle, and a switching frequency of is used. Full interleaving is employed to make the MMF ratios *m *in each layer equal to According to the analysis of winding loss and mm-thick conductors are chosen in this example. The authors write a small program in virtue of Matlab to figure out the tradeoffs. shows that the total loss, the winding loss, and the core loss vary as a function of different numbers of turns when the other parameters are fixed. The red curve and blue curve individually represent the total loss for the core. The core losses decrease with the increased number of turns; this is due to the fact that the flux density is reduced. The winding losses, however, increase, because higher dc resistances are achieved. Apparently, an optimal number of turns in this example can be found. In addition, reflects a relationship between losses and frequency. Holistic Modeling and Performance Evaluation for Converged Network-Cloud Service Provisioning An optimal frequency for the total loss can be found as well. Taken together as the intersection points between the red line and the blue line illuminate the tradeoff also caused by the core geometry. Holistic Modeling and Performance Evaluation for Converged Network-Cloud Service Provisioning Following the analysis of ac resistance and core loss, the relationship between the losses and the number of turns N can be written