Transformer types

Abstract: Isolated high-output current DC/DC converters are critical for future data center power architecture. LLC converters with matrix transformer are suitable for these applications due to its high efficiency and high power density. Different matrix transformer structures are investigated in this paper. To improve the current design practice, a high-frequency transformer loss model is developed and a detailed design methodology is proposed. Moreover, a novel matrix transformer structure is proposed to integrate four elemental transformers into one magnetic core with simple four-layer print circuit board windings implementation and further reduced core loss. By pushing switching frequency up to megahertz with GaN devices, the proposed matrix transformer can achieve high efficiency, high power density, and automatic manufacturing for magnetic components. A 1-MHz 380 V/12 V 800-W LLC converter with GaN devices is demonstrated. The prototype achieves a peak efficiency of 97.6% and a power density of 900 W/in3.

Abstract: Switching circuits, operating at high frequencies, have led to considerable reductions in the size of magnetic components and power supplies. Nonsinusoidal voltage and current waveforms and high-frequency skin and proximity effects contribute to power transformer losses. Traditionally, power transformer design has been based on sinusoidal voltage and current waveforms operating at low frequencies. The physical and electrical properties of the transformer form the basis of a new design methodology while taking full account of the current and voltage waveforms and high-frequency effects. Core selection is based on the optimum throughput of energy with minimum losses. The optimum core is found directly from the following transformer specifications: frequency; power output; and temperature rise. The design methodology is illustrated with a detailed design of a push-pull power converter.

Abstract: A procedure for optimum design of a high-power, high-frequency transformer is presented. The procedure is based on both electrical and thermal processes in the power transformer and identifies: (a) the VA-rating of ferrite cores in relation to the operating frequency; (b) the optimum flux density in the core; and (c) the optimum current densities of the windings providing maximum transformer efficiency. Since the transformer is the major contributor to the volume and weight of the power supply, the results of transformer analysis can be used for entire power supply optimization as well. Two high-power, high-frequency transformers are optimally designed, built, and tested. Practical results show good agreement with the theory.

Abstract: The emergence of high power converters makes the modern power grid more active than it was before. One of the research directions in this area is the solid state transformer, which aims at replacing the traditional 50/60 Hz power transformer by means of high frequency isolated AC/AC solid state conversion techniques. This paper presents a systematical technology review essential for the development of solid state transformer in the distribution system, especially focusing on the following four areas: high voltage and high frequency power devices, high power and high frequency transformers, AC/AC converter topologies, and applications of solid state transformer in the distribution system. For each category, the state-of-art technologies are reviewed and possible research directions are presented. It is concluded that the solid state transformer is an emerging technology for the modernization of the future smart grid.