Charles R. Sullivan

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An improved calculation of ferrite core loss for nonsinusoidal waveforms separates a flux trajectory into major and minor loops via a new recursive algorithm. It is highly accurate and outperforms two previous methods for our measured data. The only characteristics of the material required are the standard Steinmetz-equation parameters.
Multiphase voltage regulator modules (VRMs) for microprocessor power delivery with coupled output inductors are discussed. Strong coupling is shown to be feasible and effective at reducing ripple if the correct magnetic topology is used. For more than two phases, this can be a “ladder” core with windings around each rung. Typical ripple reduction is better(More)
This paper investigates the loss characteristics of several commercial rf magnetic materials for power conversion applications in the 10 MHz to 100 MHz range. A measurement method is proposed that provides a direct measurement of inductor quality factor QL as a function of inductor current at rf frequencies, and enables indirect calculation of core loss as(More)
The design and fabrication of high-Q air-core toroidal inductors are described. Designs are optimized for maximum Q for a given size and inductance, independent any particular fabrication process. A fabrication process using a combination of thin-film processes and conventional machining has been used to make prototypes. Measurements performed on the first(More)
Current oscillations at about 24 MHz were observed during electrotransformation (ET) of the thermophilic anaerobes Clostridium thermocellum ATCC 27405, C. thermocellum DSM 1313, and Thermoanaerobacterium saccharolyticum YS 485, using a pulse gated by a square signal generated by a custom generator. In experiments in which only the field strength was varied,(More)
T paper explores opportunities and challenges in power conversion in the VHF frequency range of 30-300 MHz. The scaling of magnetic component size with frequency is investigated, and it is shown that substantial miniaturization is possible with increased frequencies even considering material and heat transfer limitations. Likewise, dramatic frequency(More)
The two best-known methods for calculating highfrequency winding loss in round-wire windings—the Dowell method and the Ferreira method—give significantly different results at high frequency. We apply 2-D finite-element method (FEM) simulations to evaluate the accuracy of each method for predicting proximity-effect losses. We find that both methods can have(More)
In many variable-torque applications of induction machines, it is desirable to operate the machine at high flux levels, thus allowing the machine to produce higher torques. This can lead to saturation of the main flux path, introducing crosscoupling effects which can severely disrupt the performance of controllers dependent on knowledge of the machine’s(More)
The squared-field-derivative method for calculating eddy-current (proximity-effect) losses in round-wire or litz-wire transformer and inductor windings is derived. The method is capable of analyzing losses due to two-dimensional and three-dimensional field effects in multiple windings with arbitrary waveforms in each winding. It uses a simple set of(More)
A set of four coupled inductors is applied to a four-phase interleaved 1 kW bi-directional 14 V to 42 V dc/dc converter for automotive applications. The coupled-inductor structure is optimized, and the performance is examined through simulations and experimental measurements. Although coupled inductors offer bigger advantages in applications that require(More)