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Wireless power converter topology with small size and high conversion efficiency has an increasing demand on small power applications. Some design techniques to transmit power by customized cores are already developed. However, when transferring energy by wide-gap transformers employing small size commercialized cores, the power losses on the winding greatly increase as the frequency increases. Then, the efficiency of the contactless power system decreases significantly due to the conduction loss and reactive components in the resonant circuit. Even though series parallel resonant converters (SPRC) are largely employed which can provide infinite shunt impedance regardless of the coupling coefficient, when a commercialized core is employed for loosely coupled contactless power transfer applications, the large leakage inductance of the transformer significantly influences on additional power dissipation on transformer windings. In this paper, an operating principle how the contactless transformer with commercialized core contributes to the low efficiency is discussed. Also, a new frequencydependent R-L ladder circuit model is introduced for the designoriented analysis of wide air-gap contactless power converters including the frequency dependent losses of the transformer. New design procedure with the proposed model is suitable for the contactless transformers employing commercialized cores. The proposed design approach is validated by 98.8W hardware experiments. Finally the simulation waveforms and the hardware results are compared to verify the accuracy of the frequency dependant-transformer model. 0278-0046 (c)

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-This paper proposes the modeling and control strategy to track the MPPs of hybrid PV and Wind power systems, using a new dual input boost converter. The dual input power conditioning system with an independent MPPT control scheme is introduced with minimum number of circuit elements in order to reduce the switching loss, size and cost of the system. Since the operating conditions for the PV and Wind power systems are very distinct from each other, an efficient and superior control system is required to track the MPPs of both renewable sources with the use of a simply-structured single-ended single-inductor converter. The design of Power-Conditioning System (PCS) and detail control strategy are presented in this paper. To provide independent tracking of MPPs, a variable duty-cycle control strategy is employed for the wind system and a variable frequency strategy is employed for the PV system. Finally, the proposed dual-input converter for hybrid power conditioning system is implemented and the hardware test results are presented. From the hardware experiment, it is concluded that the proposed system successfully tracks the MPPs of both of the renewable power systems independently.

In this paper, we propose a novel technique to build a charge-balancing circuit for series-connected battery strings using various kinds of disk-type ceramic Pb(Zr ∙ Ti)O3 piezoelectric resonators (PRs). The use of PRs replaces the whole external battery voltage-balancer circuit, which consists mainly of a bulky magnetic element. The proposed technique is validated using different ceramic PRs and the results are analyzed in terms of their physical properties. A series-connected battery string with a voltage rating of 61.5 V is set as a hardware prototype under test, then the power transfer efficiency of the system is measured at different imbalance voltages. The performance of the proposed battery voltage-balancer circuit employed with a PR is also validated through hardware implementation. Furthermore, the temperature distribution image of the PR is obtained to compare power transfer efficiency and thermal stress under different operating conditions. The test results show that the battery voltage-balancer circuit can be successfully implemented using PRs with the maximum power conversion efficiency of over 96% for energy storage systems.

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