T. Friedli

ETH Zurich, Zürich, ZH, Switzerland

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Publications (45)64.29 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The second part of the essence of three-phase PFC Rectifier Systems is dedicated to a comparative evaluation of four active three-phase PFC rectifiers that are of interest for industrial application: the active six-switch boost-type PFC rectifier, the Vienna Rectifier (VR), the active six-switch buck-type PFC rectifier, and the Swiss Rectifier. Typical dynamic feed-back control structures of the considered topologies are shown, and analytical equations for calculating the current stresses of the power semiconductors are provided. In addition, EMI filtering is discussed. The rectifier systems are assessed and compared based on simple and demonstrative performance indices such as the semiconductor stresses, the required semiconductor chip area, the volume of the main passive components, the DM and CM conducted EMI noise levels, and the efficiency. Two implementation variants, a more advanced one using SiC JFETs and SiC Schottky diodes and one using Si IGBTs and SiC Schottky diodes, are considered. The comparison is extended with selected examples of hardware demonstrators of VR systems that are optimized for efficiency and/or power density. This allows to determine the tradeoff between efficiency and power density and to quantify a typical efficiency versus power density limit (Pareto-Front) for practical three-phase PFC rectifier systems using standard printed circuit board interconnection technology.
    IEEE Transactions on Power Electronics 02/2014; 29(2). · 4.08 Impact Factor
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    ABSTRACT: In this paper, a novel 3-D electromagnetic modeling approach which enables electromagnetic compatibility (EMC) analysis of power converter systems in an accurate and computationally efficient way is presented. The 3-D electromagnetic modeling approach, implemented in the EMC simulation tool GeckoEMC, is based on two numerical techniques, the partial element equivalent circuit method and the boundary integral method (PEEC-BIM). The developed PEEC-BIM coupled method enables comprehensive EMC analysis taking into account different effects of the PCB layout, self-parasitics, mutual coupling, shielding, etc., which in turn provides a detailed insight into the electromagnetic behavior of power electronic systems in advance to the implementation of hardware prototypes. The modeling features of the GeckoEMC simulation tool for virtual design of electromagnetic interference (EMI) filters and power converters is demonstrated on the examples of a single-phase two-stage EMI filter and a practical EMI filter for a single-phase PFC input stage. Good agreement between the PEEC-BIM simulation and the small signal transfer function measurement results is achieved over a wide frequency range, from dc up to 30 MHz. The EMC simulation environment enables a step-by-step EMC analysis distinguishing the impact of various electromagnetic effects on the EMI filter performance and allowing an optimal EMI filter design.
    IEEE Transactions on Industrial Electronics 01/2014; 61(1):231-242. · 6.50 Impact Factor
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    ABSTRACT: The electromagnetic compatibility (EMC) analysis of electromagnetic interference (EMI) filter circuits using 3-D numerical modeling by the partial element equivalent circuit (PEEC) method represents the central topic of this paper. The PEEC-based modeling method is introduced as a useful tool for the prediction of the high frequency performance of EMI input filters, which is affected by PCB component placement and self- and mutual-parasitic effects. Since the measuring of all these effects is rather difficult and time consuming, the modeling and simulation approach represents a valuable design aid before building the final hardware prototypes. The parasitic cancellation techniques proposed in the literature are modeled by the developed PEEC-boundary integral method (PEEC-BIM) and then verified by the transfer function and impedance measurements of the L-C and C-L-C filter circuits. Good agreement between the PEEC-BIM simulation and the measurements is achieved in a wide frequency range. The PEEC-BIM method is implemented in an EMC simulation tool GeckoEMC. The main task of the presented research is the exploration of building an EMC modeling environment for virtual prototyping of EMI input filters and power converter systems.
    IEEE Transactions on Power Electronics 01/2014; 29(1):135-149. · 4.08 Impact Factor
  • Schweizer M., Friedli T., Kolar J. W.
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    ABSTRACT: Efficient energy conversion in low-voltage applications has gained more attention due to increasing energy costs and environmental issues. Accordingly, three-level converters have been discussed as an alternative to the standard two-level voltage-source converter because they offer an increased efficiency at higher switching frequencies. From a system perspective, the benefits of using three-level converters are not only limited to the converter itself, but there are additional positive impacts on the surrounding such as on the load machine losses or on the electromagnetic interference input filter volume. In this paper, a holistic comparison of advanced three-level topologies against the two-level topology is given. Simple analytical calculations and measurements show the benefits and the optimization potential concerning several aspects, such as the necessary semiconductor chip area, the harmonic losses in the load machine and in filter components, and the volume of passive components.
    IEEE Transactions on Industrial Electronics 12/2013; 60(12):5515-5527. · 6.50 Impact Factor
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    ABSTRACT: Airborne wind turbines (AWTs) represent a radically new and fascinating concept for future harnessing of wind power. This concept consists of realizing only the blades of a conventional wind turbine (CWT) in the form of a power kite flying at high speed perpendicular to the wind. On the kite are mounted a turbine, an electrical generator, and a power electronics converter. The electric power generated is transmitted via a medium voltage cable to the ground. Because of the high flight speed of the power kite, several times the actual wind speed, only a very small swept area of the turbine is required according to Betz's Law and/or a turbine of low weight for the generation of a given electric power. Moreover, because of the high turbine rotational speed, no gear transmission is necessary and the size of the generator is also reduced. For takeoff and landing of the power kite, the turbines act as propellers and the generators as motors, i.e., electric power is supplied so that the system can be maneuvered like a helicopter. In the present work, the configuration of power electronics converters for the implementation of a 100 kW AWT is considered. The major aspect here is the trade-off between power-to-weight ratio (W/kg) and efficiency. The dependence of cable weight and cable losses on the voltage level of power transmission is investigated, and a comparison is made between low voltage (LV) and medium voltage (MV) versions of generators. Furthermore, the interdependence of the weight and efficiency of a bidirectional dual active bridge dc-dc converter for coupling the rectified output voltage of a LV generator to the MV cable is discussed. On the basis of this discussion, the concept offering the best possible compromise of weight and efficiency in the power electronics system is selected and a model of the control behavior is derived for both the power flow directions. A control structure is then proposed and dimensioned. Furthermore, questions of electromagnetic - ompatibility and electrical safety are treated. In conclusion, the essential results of this paper are summarized, and an outlook on future research is given. To enable the reader to make simplified calculations and a comparison of a CWT with an AWT, the aerodynamic fundamentals of both the systems are summarized in highly simplified form in an Appendix, and numerical values are given for the 100 kW system discussed in this paper.
    IEEE Journal of Emerging and Selected Topics in Power Electronics. 06/2013; 1(2):73-103.
  • Soeiro T., Friedli T., Kolar J. W.
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    ABSTRACT: In this paper, a three-phase buck-type unity power factor rectifier is designed for high-power electric vehicle battery charging mains interfaces. The characteristics of the converter, named the Swiss Rectifier (SR), including the principle of operation, modulation strategy, suitable control structure, and dimensioning equations are described in detail. Exemplarily, a 7.5 kW hardware prototype is then designed based on the derived analytical expressions and the feasibility of the SR concept is demonstrated by the means of experimental measurements. Finally, the SR is compared with a conventional six-switch buck-type ac–dc power conversion. According to the results, the SR is the topology of choice for a buck-type PFC.
    IEEE Transactions on Power Electronics 04/2013; 28(4):1608-1621. · 4.08 Impact Factor
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    ABSTRACT: In this paper, the performance of a new method based on the coupling of the partial element equivalent circuit method and boundary integral method (the PEEC-BIM method) for 3D modeling of toroidal inductors, which are typically used in electromagnetic interference (EMI) filter applications, is presented. The presence of magnetic materials is modeled by replacing the surface of magnetic regions with an equivalent distribution of fictitious current loops. It is shown that the influence of the magnetic core on the impedance and the stray field of EMI filter inductors can be modeled and explained in detail by PEEC-BIM simulation results. The developed PEEC-BIM approach is verified by both 3D finite-element method (FEM) simulations and near-field measurements for different winding configurations and magnetic cores. Regarding computational complexity, the developed PEEC-BIM method applied to toroidal inductors performs extremely well. The PEEC-BIM simulation is at least twice faster than the corresponding FEM-based analysis. The PEEC-BIM method has been implemented in a PEEC-based simulation tool, which facilitates the simulation of entire EMI filter structures.
    IEEE Transactions on Magnetics 01/2013; 49(10):5248-5256. · 1.42 Impact Factor
  • Johann Walter Kolar, Friedli T.
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    ABSTRACT: In the first part of this paper, three-phase power factor correction (PFC) rectifier topologies with sinusoidal input currents and controlled output voltage are derived from known single-phase PFC rectifier systems and/or passive three-phase diode rectifiers. The systems are classified into hybrid and fully active pulsewidth modulation boost-type or buck-type rectifiers, and their functionality and basic control concepts are briefly described. This facilitates the understanding of the operating principle of three-phase PFC rectifiers starting from single-phase systems, and organizes and completes the knowledge base with a new hybrid three-phase buck-type PFC rectifier topology denominated as Swiss Rectifier. Finally, core topics of future research on three-phase PFC rectifier systems are discussed, such as the analysis of novel hybrid buck-type PFC rectifier topologies, the direct input current control of buck-type systems, and the multi-objective optimization of PFC rectifier systems. The second part of this paper is dedicated to a comparative evaluation of four rectifier systems offering a high potential for industrial applications based on simple and demonstrative performance metrics concerning the semiconductor stresses, the loading and volume of the main passive components, the differential mode and common mode electromagnetic interference noise level, and ultimately the achievable converter efficiency and power density. The results are substantiated with selected examples of hardware prototypes that are optimized for efficiency and/or power density.
    IEEE Transactions on Power Electronics 01/2013; 28(1):176-198. · 4.08 Impact Factor
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    ABSTRACT: This paper introduces the methodology and the results of a comprehensive comparison of a direct matrix converter (MC), an indirect MC, and a voltage dc-link back-to-back converter for a 15-kW permanent magnet synchronous motor drive. The comparison involves the investigation of the passive components, including the EMI input filter, the required silicon chip area for a defined maximum admissible thermal loading of the power semiconductors, the total losses and/or achievable efficiency, a prediction of the resulting volume and weight of the passive components, and, finally, a tradeoff study between the efficiency, volume, and weight of the converters. Different performance indicators that ultimately allow a systematic determination of the application area of each converter topology are provided with this comparative evaluation.
    IEEE Transactions on Industrial Electronics 12/2012; 59(12):4487-4510. · 6.50 Impact Factor
  • Friedli T., Kolar J. W.
    IEEJ Transactions on Industry Applications 07/2012; 1(1):2-14.
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    ABSTRACT: In telecom applications, the vision for a total power conversion efficiency from the mains to the output of point-of-load (PoL) converters of 95% demands optimization of every conversion step, i.e., the power factor correction (PFC) rectifier front-end should show an outstanding efficiency in the range of 99%. For recently discussed 400-V dc distribution bus voltages, a buck-type PFC rectifier is a logical solution. In this paper, an efficiency-optimized, 98.8% efficient, 5-kW three-phase buck-type PFC rectifier with 400-V output is presented. Methods for calculating losses of all components are described and are used to optimize the converter design for efficiency at full load. Special attention is paid to semiconductor losses, which are shown to be dominant, with the parasitic device capacitance losses being a significant component. The calculation of these parasitic capacitance losses is treated in detail, and the charge-balance approach used is verified. A prototype of the proposed rectifier is constructed which verifies the accuracy of the models used for loss calculation and optimization.
    IEEE Transactions on Power Electronics 04/2012; 27(4):1732-1744. · 4.08 Impact Factor
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    ABSTRACT: A new strategy for indirect matrix converters which allows an optimal control of source and load currents is presented in this paper. This method uses the commutation state of the converter in the subsequent sampling time according to an optimization algorithm given by a simple cost functional and the discrete system model. The control goals are regulation of output current according to an arbitrary reference and also a good tracking of the source current to its reference which is imposed to have a sinusoidal waveform with low distortion. Experimental results support the theoretical development.
    IEEE Transactions on Industrial Electronics 01/2012; 59(9):3427-3435. · 6.50 Impact Factor
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    ABSTRACT: Photovoltaic systems (PV) of higher power are connected to the grid through three-phase inverters via output filters which are designed to limit Electromagnetic Interference (EMI), in order to comply with international standards. With the purpose of reducing the volume of this converter, this paper evaluates 3 configurations of bridge legs and output magnetic components and identifies the most compact options for a system of 10kVA. A single bridge leg and two interleaved bridge legs with coupled or uncoupled inductors are considered in the comparison. Switching frequency and total silicon area are fixed and the volume of the passive components and the heatsink are evaluated as well as the system efficiency. The analysis developed in this paper show that the configuration with interleaved bridge legs and coupled inductors has a total volume close to 70% when compared to the configuration with interleaved bridge legs and uncoupled inductors, but it has a similar total volume when compared to the configuration with a single bridge leg. Although it is reported in the literature that systems with coupled inductors usually have a lower volume, the case at hand has the output filters designed to comply with EMI standards and it will be shown that, like this, the volume reduction of magnetic components provided by coupled inductors is compensated by the increase on the volume of capacitors.
    Integrated Power Electronics Systems (CIPS), 2012 7th International Conference on; 01/2012
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    ABSTRACT: This paper proposes a systematic approach to design the output filter of a 10 kW, low-voltage 400 Vll,rms, fouroutput phase, hard-switched AC source based on the Three-Level Neutral Point Clamped Voltage Source Converter topology. Given specifications of the AC source, such as the voltage quality, the control performance or the conducted EMI at the output of the source, are translated into corresponding families of curves in the parameter space of the output filter. The area/volume enclosed by these curves represents the design space of the output filter in which all tuples (Lf, Cf), e.g. for a single-stage LC-filter, fulfill every single AC source specification. From all possible filter parameters in the design space, the set of parameters resulting in the smallest filter volume, the lowest filter weight, the highest filter efficiency and/or the lowest filter costs can be selected.
    01/2012;
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    ABSTRACT: The paper summarizes a new modeling procedure for 3D virtual design of EMI filter circuits. The proposed method, based on the coupling of the Partial Element Equivalent Circuit (PEEC) and Boundary Integral Method (BIM) methods, extends the standard PEEC approach for modeling in the presence of magnetic materials, hence allowing the PEEC-based modeling of toroidal EMI filter inductors. The PEEC-BIM coupled method is implemented into a 3D CAD PEEC-based virtual prototyping platform (GeckoEMC). The developed EM simulation tool can give a comprehensive understanding of EM behaviour of EMI filter inductors and capacitors, taking their geometrical and material properties into account. Furthermore, it enables the modeling of optimal EMI filter structures including both parasitics and the effects originating from the mutual coupling and the interconnection of filter elements. The approach is verified by impedance and transfer function measurements of different single phase single-/two-stage EMI filter structures. Good agreement between the measurement and the PEEC-based simulation results was achieved for the frequency range from DC up to 30 MHz.
    01/2012;
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    T. Soeiro, T. Friedli, J. W. Kolar
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    ABSTRACT: This paper discusses novel three-phase high power factor mains interfaces appropriate for Electric Vehicle (EV) battery charging systems. Initially, a highly efficient two-stage ac-dc system, consisting of a three-phase line-commuted rectifier combined with a three-phase shunt connected Active Power Filter (APF) and a group of interleaved dc-dc buck converters operating in Triangular Current Mode (TCM), is presented. In order to replace the costly APF circuit of the front-end converter, while maintaining PFC capability at the input and allowing similar operating conditions for the back-end dc-dc converter, a rectifier topology employing an active third harmonic current injection circuit is proposed. In addition, a novel three-phase buck-type PFC rectifier is introduced for EV charging systems. The characteristics of the presented EV systems, including the principle of operation, modulation strategy, suitable control structures, and dimensioning equations, are described in detail. Finally, a comprehensive comparison of the studied converters rated to 12kW is shown.
    01/2012;
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    T. B. Soeiro, T. Friedli, J. W. Kolar
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    ABSTRACT: This paper introduces a novel three-phase buck-type unity power factor rectifier appropriate for high power Electric Vehicle battery charging mains interfaces. The characteristics of the converter, named the Swiss Rectifier, including the principle of operation, modulation strategy, suitable control structure, and dimensioning equations are described in detail. Additionally, the proposed rectifier is compared to a conventional 6-switch buck-type ac-dc power conversion. According to the results, the Swiss Rectifier is the topology of choice for a buck-type PFC. Finally, the feasibility of the Swiss Rectifier concept for buck-type rectifier applications is demonstrated by means of a hardware prototype.
    01/2012;
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    ABSTRACT: This paper presents first an overview of the well-known voltage and current dc-link converter topologies used to implement a three-phase PWM ac-ac converter system. Starting from the voltage source inverter and the current source rectifier, the basics of space vector modulation are summarized. Based on that, the topology of the indirect matrix converter (IMC) and its modulation are gradually developed from a voltage dc-link back-to-back converter by omitting the dc-link capacitor. In the next step, the topology of the conventional (direct) matrix converter (CMC) is introduced, and the relationship between the IMC and the CMCs is discussed in a figurative manner by investigating the switching states. Subsequently, three-phase ac-ac buck-type chopper circuits are considered as a special case of matrix converters (MCs), and a summary of extended MC topologies is provided, including three-level and hybrid MCs. Therewith, a common knowledge basis of the individual converter topologies is established.
    IEEE Transactions on Industrial Electronics 12/2011; · 6.50 Impact Factor
  • IEEE Transactions on Industrial Electronics 11/2011; 58(11):4988-5006. · 6.50 Impact Factor
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    ABSTRACT: The paper summarizes a step by step Partial Element Equivalent Circuit (PEEC) modeling approach for Electromagnetic Interference (EMI) filter components (e.g. foil capacitors, common mode and differential mode inductors) and PCB tracks, to design complete EMI input filters with an optimal selection and placement of the individual components. The presence of magnetic cores is modeled with the proposed PEEC-Boundary Integral Coupled Method (PEEC-BIM) by means of fictitious magnetic surface currents, using the core geometry and permeability as inputs. The developed PEEC based models are verified by transfer function measurements of several single-phase single/two-stage filter circuits. The resulting PEEC simulation time is determined by the time required to perform the surface mesh of the magnetic volume and is in the order of several minutes. The good results of the presented PEEC modeling approach enable a fast virtual design of EMI filters and help to accelerate the design process of power converter systems.
    Energy Conversion Congress and Exposition (ECCE), 2011 IEEE; 10/2011