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In many applications, a current measurement that can measure ac currents with dc offset is required. This is not possible using conventional current transformers (CTs) due to the core saturation because of the dc offset. In this paper, a new sensor concept is presented, which consists of a wideband CT and a demagnetizing circuit. The sensor concept is capable of measuring ac currents with dc offset, which have periodic zero crossings, as given in power-factor-corrected (PFC) circuits. Using the demagnetization circuit, the core is actively reset during the zero crossing intervals. The operation principle and design equations are discussed in detail in this paper. For validating the presented concept, three sensors have been built using different core materials, and measurements of the transfer functions as well as operation in a PFC system are presented. A bandwidth from dc up to 20 MHz has been achieved. Index Terms--Current measurement, current transformer (CT), nanocrystalline material.

The demand for decreasing cost and volume and also for increasing efficiency leads to a constantly increasing power density of converter systems. For maximizing the power density of a 5 kW telecom supply, an optimization procedure that automatically balances the switching frequency, semiconductor and passive losses, and thermal performance has been developed. This procedure and the belonging analytical converter and transformer models are presented in this paper. Moreover, the resulting optimized design, which has a power density of 10 kW/[dm.sup.3] and an efficiency of 94.5% at a height of 1 U, is presented. Index Terms--DC--DC converter, optimization, resonant converter, telecom power supply.

Two new planar integrated electromagnetic interference (EMI) filter structures that reduce the filter volume and that are based on standard printed circuit board (PCB) process technology are presented in this paper. First, a passive integrated EMI filter is presented, which results in a volume reduction of 24% compared to the discrete solution. However, this filter requires a planar ferrite core for the common-mode inductor. In order to eliminate the ferrite core and reduce the filter volume further (-40% versus discrete filter), a passive integrated structure is combined with an active EMI filtering circuit. The transfer function, the volume, and the losses of the discrete and the two integrated filters, which are designed for a 600 W power-factor-corrected converter, are compared. Index Terms--Active filter, electromagnetic interference (EMI) filter, integrated passives, printed circuit board (PCB) inductor.

The demand for decreasing costs and volume leads to a constantly increasing power density of industrial converter systems. In order to improve the power density, further different aspects, like thermal management and electromagnetic effects, must be considered in conjunction with the electrical design. Therefore, a comprehensive optimization procedure based on analytical models for minimizing volume of dc-dc converter systems has been developed at the Power Electronic Systems Laboratory of the Swiss Federal Institute of Technology (ETH Zurich). Based on this procedure, three converter topologies--a phase-shift converter with current doubler and with capacitive output filter and a series-parallel resonant converter--are optimized with respect to power density for a telecom supply (400 V/48 V). There, the characteristic of the power density, the efficiency, and the volume distribution between the components as functions of frequency are discussed. For the operating points with maximal power density, the loss distribution is also presented. Furthermore, the sensitivity of the optimum with respect to junction temperature, cooling, and core material is investigated. The highest power density is achieved by the series-parallel resonant converter. For a 5-kW supply, a density of approximately 12 kW/L and a switching frequency of ca. 130 kHz are obtained. Index Terms--DC-DC power conversion, optimization, phase-shift converter, power density, resonant converter.

A three-phase Y-rectifier is formed by the star connection of single-phase unity-power-factor rectifier systems and represents a highly interesting concept for the realization of the input stage of high-power telecommunications power supply modules using established single-phase technology. However, for stable operation, control and balancing of the independent dc output voltages of the phase rectifier systems is required. A novel, easy-to-implement dc output voltage control concept is proposed in this paper. Here, the mean value of all three dc output voltages is controlled, and, in addition, always two out of the three dc voltages are compared and balanced. The basic operating principle of the control is described, the theoretical limit for the admissible asymmetric loading of the dc voltages is calculated, and numeric results for a 10-kW system are given. Finally, the theoretical considerations are verified by measurements on a 3 x 1 kW Y-rectifier prototype. Index Terms--AC-DC power conversion, asymmetrical load, output voltage balancing.