Impact of Power Density Maximization on Efficiency of DC-DC Converter Systems

J.W. Kolar,J. Biela,U. Badstubner 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

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 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 (400V/48V). There, the characteristic of the power density, the efficiency and the volume distribution between the components as function of frequency is discussed. For the operating points with maximal power density also the loss distribution is 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 ㎾ supply a density of approximately 12 ㎾/ltr. and a switching frequency of ca. 130 ㎑ results.

Loss Modeling of Inductive Components Employed in Power Electronic Systems

J. Muhlethaler,J. W. Kolar,A. Ecklebe 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

Loss models of inductive components are thoroughly investigated, thereby all different aspects of loss modeling are considered. The impact of peak-to-peak flux density ?B, frequency f, DC premagnetization HDC, temperature T, core shape, minor and major loops, flux waveform, and material on core loss calculation are considered. In order to calculate winding losses, formulas for round conductors and litz wires, each including skin- and proximity effects (including the influence of an airgap fringing field) are included. A high level of accuracy is achieved by combining the best state-of-the-art approaches and by embedding newly-developed approaches into a novel loss calculation framework. The loss models are verified by FEM simulations and experimental measurements.

A Novel Approach for 3D Air Gap Reluctance Calculations

J. Muhlethaler,J. W. Kolar,A. Ecklebe 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

An approach to accurately calculate the reluctance of an air gap is introduced. The approach is easy to handle as it is based on a modular concept where a simple basic geometry is used as a building block to describe different three dimensional air gap shapes. A high degree of accuracy is achieved as the approach is based on an analytical field solution.

“Magnetic Ear”-Based Balancing of Magnetic Flux in High Power Medium Frequency Dual Active Bridge Converter Transformer Cores

G. Ortiz,J. Muhlethaler,J. W. Kolar 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

Semiconductor switches posses non-ideal behavior which, in case of isolated DC-DC converters, can generate DC voltage components in the voltage applied to the transformer. This DC voltage component is translated into a DC flux density component in the transformer core, increasing the risk of driving the core into saturation. In this paper, a novel noninvasive flux density measurement principle, called the “Magnetic Ear”, based on sharing of magnetic path between the main and an auxiliary core is proposed. The active compensation of the transformer DC magnetization level using this transducer is experimentally verified. Additionally, a classification of the previously reported magnetic flux measurement and balancing concepts is performed.

Comparison of Winding Concepts for Bearingless Pumps

K. Raggl,J. W. Kolar,T. Nussbaumer 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

Bearingless slice motors as employed in semiconductor, pharmaceutical and medical industry perform magnetic levitation by radial bearing forces and rotation by tangential forces. This requires bearing and drive windings, which can be realized as separate bearing and drive coils or as identical, concentrated coils on the stator claws. In this paper, a detailed comparison between these two winding concepts is undertaken, where the coil losses, the coil volume, the power electronics requirements and the achievable rotation speed are evaluated. Furthermore, practical features such as control complexity, cabling effort and manufacturability are taken into account. Finally, the trade-off between losses, volume and realization effort will be discussed in order to give a guideline for the selection of the appropriate winding concept for a specific application of a bearingless pump.

A Novel Low-Loss Modulation Strategy for High-Power Bi-directional Buck+Boost Converters

S. Waffler,J. W. Kolar 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

A novel low-loss, constant-frequency, zerovoltage-switching (ZVS) modulation strategy for bi-directional, cascaded, buck-boost DC/DC converters, used in a hybrid electrical vehicle (HEV), is presented and its benefits over state-of-the-art converters and soft-switching solutions are discussed in a comparative evaluation. To obtain ZVS with the purposed modulation strategy, the buck+boost inductance is selected and the switches are gated in a way that the inductor current has a negative offset current at the beginning and the end of each pulse period. This allows the MOSFET switches to turn on when the anti-parallel body diode is conducting. As the novel modulation strategy is a software-only solution, there are no additional expenses for active or passive components compared to conventional modulation implementations. Furthermore, an analytical and simulation investigation predicts an excellent efficiency over the complete operating range and a higher power density for a multi-phase converter equipped with the low-loss modulation. Experimental measurements performed with a converter prototype verify the mode of operation and the ZVS principle.

Research Articles : Optimization of Wheat Harvest

(S. H. Kim),(W. J. Kolaric) 한국농업기계학회 2000 Agricultural Mechanization in Korea Vol.1 No.1

Novel Single-Phase Buck+Boost PFC Rectifier with Integrated Series Power Pulsation Buffer

M. Haider,D. Bortis,J. W. Kolar,Y. Ono 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

This paper introduces a novel integrated series power pulsation buffer (iSPPB) concept for a single-phase ACto-DC two-switch buck+boost PFC rectifier to compensate the fluctuating power mismatch between the AC input and the DC output. Accordingly, the DC-link capacitance can be drastically reduced and an electrolytic-capacitor-less PFC rectifier system featuring a higher power density and an increased lifetime is obtained. The proposed iSPPB concept consists of a simple full-bridge circuit with a buffer capacitor and is placed in series with the buck-boost inductor, thus no additional inductive component is required for the iSPPB realization. The basic operating principle of the buck+boost PFC rectifier with iSPPB is investigated and the characteristic waveforms are presented. As shown in the analysis, due to the employment of the iSPPB also the maximum buck+boost inductor current is reduced, which compared to the conventional rectifier system without iSPPB allows to further downsize the inductive component. Consequently, the major drawbacks of conventional single-phase PFC rectifiers are eliminated. Furthermore, the control structure is presented and the proper operation is verified based on a closed-loop circuit simulation. Finally, the proposed buck+boost PFC rectifier with iSPPB and a conventional two-switch implementation employing electrolytic capacitors are quantitatively compared by means of simple performance indices.

New Series-Resonant Solid-State DC Transformer Providing Three Self-Stabilized Isolated Medium-Voltage Input Ports

F. Krismer,J. Bohler,J. W. Kolar,G. Pammer 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

This work analyzes the properties of a new fourport, series-resonant, and bidirectional DC transformer topology in steady-state and transient conditions. The investigated topology evolves from the Integration of Three (3) Series-Resonant Converters (I3SRC), enables the realization of a converter with high efficiency (99.0%) and high power density (7.1kW/dm3), due to the utilization of a three-phase High Frequency (HF) transformer and reduced capacitor currents in the secondary-side DC link, and features the use of a six-pack power module on the secondary side. The analysis is based on the results of detailed circuit simulations of an I3SRC, which takes the couplings between the phases, introduced by the three-phase transformer, into account and considers a DC transformer, i.e., DC–DC converter, with a total rated power of 15kW, three primary-side DC voltages of 1.1kV, and a secondary-side DC voltage of 700V, which is a core part of a scaled demonstrator of a Solid-State Transformer (SST). The obtained findings clarify the self-stabilizing capabilities of the I3SRC for operation with Half-Cycle Discontinuous Conduction Mode (HC-DCM), even if the three isolated DC ports are subject to time-varying and substantially different power levels and different directions of energy transfer.

Control of the Input Characteristic and the Displacement Factor of Uni- and Bidirectional SWISS Rectifier for Symmetrical and Unsymmetrical Three-Phase Mains

L. Schrittwieser,M. F. Vancu,J. W. Kolar,T. B. Soeiro 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

This paper introduces a phase-oriented control strategy for the uni- and bidirectional three-phase, bucktype SWISS Rectifier. It allows phase shifted sinusoidal input currents which enable the generation of capacitive or inductive reactive power at the converter’s AC grid interface. Furthermore, the operation of the SWISS Rectifier with unsymmetrical AC mains voltages is analyzed. Modifications of the control structure, allowing constant AC input power or ohmic mains behavior even with unsymmetrical AC voltages are presented. Simulations and measurements taken on a 7:5 kW bidirectional SWISS Rectifier hardware prototype demonstrate the validity of the theoretical considerations.