Showing papers by "Johann W. Kolar published in 2014"

Optimal ZVS Modulation of Single-Phase Single-Stage Bidirectional DAB AC–DC Converters

Abstract: A comprehensive procedure for the derivation of optimal, full-operating-range zero voltage switching (ZVS) modulation schemes for single-phase, single-stage, bidirectional and isolated dual active bridge (DAB) ac-dc converters is presented. The converter topology consists of a DAB dc-dc converter, receiving a rectified ac line voltage via a synchronous rectifier. The DAB comprises primary and secondary side full bridges, linked by a high-frequency isolation transformer and a series inductor. ZVS modulation schemes previously proposed in the literature are either based on current-based or energy-based ZVS analyses. The procedure outlined in this paper for the calculation of optimal DAB modulation schemes (i.e., combined phase-shift, duty-cycle, and switching frequency modulation) relies on a novel, more accurate, current-dependent charge-based ZVS analysis, taking into account the amount of charge that is required to charge the nonlinear parasitic output capacitances of the switches during commutation. Thereby, the concept of “commutation inductance(s)” is shown to be an essential element in achieving full-operating-range ZVS. The proposed methods are applied to a 3.7 kW, bidirectional, and unity power factor electric vehicle battery charger which interfaces a 400 V dc-bus with the 230 Vac, 50-Hz utility grid. Experimental results obtained from a high-power-density, high-efficiency converter prototype are given to validate the theoretical analysis and practical feasibility of the proposed strategy.

Classification and Comparative Evaluation of PV Panel-Integrated DC–DC Converter Concepts

Abstract: The strings of photovoltaic panels have a significantly reduced power output when mismatch between the panels occurs, as, e.g., caused by partial shading. With mismatch, either the panel-integrated diodes are bypassing the shaded panels if the string is operated at the current level of the unshaded panels, or some power of the unshaded panels is lost if the string current is reduced to the level of the shaded panels. With the implementation of dc-dc converters on panel level, the maximum available power can be extracted from each panel regardless of any mismatch. In this paper, different concepts of PV panel-integrated dc-dc converters are presented and their suitability for panel integration is evaluated. The buck-boost converter is identified as the most promising concept and an efficiency/power density ( η- ρ) Pareto optimization of this topology is shown. Based on the optimization results, two 275 W converter prototypes with either Silicon MOSFETs with a switching frequency of 100 kHz or gallium nitride FETs with a switching frequency of 400 kHz are designed for an input voltage range of 15 to 45 V and an output voltage range of 10 to 100 V. The theoretical considerations are verified by efficiency measurements which are compared to the characteristics of a commercial panel-integrated converter.

Ultraflat Interleaved Triangular Current Mode (TCM) Single-Phase PFC Rectifier

Abstract: This paper presents the analysis and realization of a topology suitable to realize a power factor correction (PFC) rectifier with a thickness of only a few millimeters. The low height of the converter requires all components to be integrated into the printed circuit board (PCB). Still reasonable dimensions of the converter PCB are feasible (221 mm × 157 mm for a 200 W PFC rectifier), since PCB-integrated inductors and capacitors allow for high energy densities due to their large surface area which facilitates a low thermal resistance to ambient. A multicell totem-pole PFC rectifier employing a soft-switching modulation scheme over the complete mains period is identified as an adequate topology. The mode of operation is entitled triangular current mode (TCM) due to the triangular-shaped inductor currents. The modulation technique requires a reliable description of the switching transition of a half-bridge in order to provide accurate timing parameters. For this purpose, a simplified model of the nonlinear MOSFETs' output capacitances facilitates closed-form analytical expressions for duty cycle and switching frequency. Furthermore, this paper details the control of three interleaved converter cells which yields a reduction of the input current ripple. A 200 W TCM PFC rectifier with a low height of 5 mm has been realized and measurement results are provided in order to validate the theoretical considerations. The presented TCM PFC rectifier achieves an efficiency of 94.6% and a power factor of 99.3% at nominal power.

Volume/weight/cost comparison of a 1MVA 10 kV/400 V solid-state against a conventional low-frequency distribution transformer

Abstract: Solid-State Transformers (SSTs) are an emergent topic in the context of the Smart Grid paradigm, where SSTs could replace conventional passive transformers to add flexibility and controllability, such as power routing capabilities or reactive power compensation, to the grid. This paper presents a com- parison of a 1000kVA three-phase, low-frequency distribution transformer (LFT) and an equally rated SST, with respect to volume, weight, losses, and material costs, where the correspond- ing data of the SST is partly based on a full-scale prototype design. It is found that the SST's costs are at least five times and its losses about three times higher, its weight similar but its volume reduced to less than 80%. In addition, an AC/DC application is also considered, where the comparison turns out in favor of the SST-based concept, since its losses are only about half compared to the LFT-based system, and the volume and the weight are reduced to about one third, whereas the material costs advantage of the LFT is much less pronounced. I. INTRODUCTION

Solid-State-Transformers: Key Components of Future Traction and Smart Grid Systems

Abstract: The efficient supply of electric power relies strongly on the selection of suitable voltage levels for different sections of the energy distribution system. When higher levels of power are required, a medium-voltage level in the tens of kilovolts range is typically selected. In accordance to current trends in energy conversion, the supply of power must fulfil several functionality requirements among which high power-quality and access to a low-voltage DC interface can be highlighted. Moreover, low energy losses, high power-density, low failure rate and low total cost of ownership remain as major research challenges. Solid-state-transformers (SSTs) comply with these functionality requirements as well as with the demanded high performance levels while directly connecting to medium-voltage. This paper reviews the implementation of SST technology for transportation and Smart-Grid applications. The envisioned architectures for locomotive systems, remotely-operated-vehicles and large scale ships, which benefit from the compactness and high performance of SST are shown. In addition, the possible arrangement of micro-grid systems comprising SST concepts for integration of renewable energy and implementation of DCmicrogrids is detailed. The different SST concepts proposed for these applications can be grouped into distinctive categories, leading to a comprehensive classification of, first, general isolated AC-AC conversion systems and later to a specific classification of SST concepts based on the different levels of modularity. Finally, a detailed review of the numerous previously reported and functional SST concepts is presented and a comparison to systems employing low-frequency transformers is given. Keywords—Converter Topology Classification, Multicell and Multilevel Converter Topologis, Medium-Frequency Isolation, Performance Evaluation.

X-treme Efficiency Power Electronics

Abstract: In this paper a generalized description and an overview of degrees of freedom and selected measures for efficiency improvement of power electronics converters is given. The background of all considerations is formed by single-phase PFC rectifier systems, but the concepts shown are fundamental and fully applicable for other converter systems. First, the influence of the main components of the losses of a converter on the efficiency characteristic over the output power is discussed. Subsequently, a detailed analysis of the possibilities, of minimizing the semiconductor losses, the losses of the passive components including the EMI filter, and the power requirements of auxiliary systems in the course of the design process are given. In this context also the technological boundaries that limit the maximum efficiency of a converter are clarified and the compromise that always has to be made between efficiency and power density is highlighted. Furthermore, a control procedure is discussed to maximize the efficiency in the partial load range and a resonant transition mode ZVS converter system is presented that allows to attain efficiencies significantly over 99% without the use of SiC semiconductors. In addition the accuracy of the input and output power measurements required for measuring highest efficiencies is clarified, whereby the advantage of a direct loss measurement by means of a calorimeter becomes immediately clear. Finally, results of measurements on a demonstrator of a CCM single-phase PFC rectifier system with 99.1% max. efficiency and η > 99% above half rated power, and on a resonant transition mode PFC rectifier system with ηmax = 99.3% and η > 99% above 15% rated power are presented.

3-D Electromagnetic Modeling of Parasitics and Mutual Coupling in EMI Filters

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.

4.7 A sub-ns response on-chip switched-capacitor DC-DC voltage regulator delivering 3.7W/mm 2 at 90% efficiency using deep-trench capacitors in 32nm SOI CMOS

Abstract: For an on-chip or fully integrated microprocessor power-delivery system, the on-chip power converter must 1) be designed using the same technology as the microprocessor, 2) deliver high power density to supply a microprocessor core with small area overhead, 3) achieve high efficiency, and 4) perform fast regulation over a wide voltage range for dynamic voltage and frequency scaling (DVFS). On-chip switched-capacitor (SC) converters have gained increasing popularity for this application due to their ease of integration using only transistors and capacitors readily available in the chosen technologies [1-6].

Flux Balancing of Isolation Transformers and Application of “The Magnetic Ear” for Closed-Loop Volt–Second Compensation

Abstract: Semiconductor switches possess nonideal behavior which, in case of isolated dc-dc converters, can generate dc-voltage components which are then applied to the isolation 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's dc magnetization level using this transducer is experimentally verified. Additionally, a classification of the previously reported magnetic flux measurement and balancing concepts is performed.

Modeling and Comparison of Machine and Converter Losses for PWM and PAM in High-Speed Drives

Abstract: For variable-speed drives, the interaction of the machine and the converter is becoming increasingly important, especially for high-speed applications, mainly due to the effect of the converter modulation on the machine losses. The allocation of the losses to different components of the drive system needs to be known in order to choose the ideal machine and modulation combination. In this paper, individual models are introduced for calculating the rotor, copper, and core losses of the machine as well as the inverter losses, taking the modulation type into account. These models are developed by considering two typical high-speed permanent-magnet synchronous motor topologies (slotted and slotless machines) driven by pulse-amplitude modulation (PAM) and pulsewidth modulation (PWM) converters. The models are applied to two off-the-shelf machines and a converter operating with either PAM or PWM. The test bench used to experimentally verify the models is also described, and the model results are compared to the measurements. The results show that PAM produces a higher overall efficiency for the high-speed machines considered in this paper. However, PWM can be used to move the losses from the rotor to the converter at the expense of decreasing the overall drive efficiency. The possible benefits of these results are discussed.

Control method for Inductive Power Transfer with high partial-load efficiency and resonance tracking

Abstract: Frequency controlled Inductive Power Transfer (IPT) systems for Electric Vehicle (EV) battery charging applications often suffer from high power losses in partial-load, because the transmitter coil current is not significantly reduced at low output power. Therefore, in this paper a novel control method is presented that exhibits a substantially higher partial-load efficiency, while it also enables full control of the power semiconductor switching conditions. The power flow control is based on the dynamic regulation of the dc-link voltages on both sides of the resonant system with dc-dc-converters. Additionally, a tracking of the resonance with a current zero crossing detection circuit and a PLL makes the switched current an additional degree of freedom, that can be used, e.g., for the minimization of IGBT soft-switching losses due to stored-charge. All calculated results are supported by experimental measurements on an existing 5 kW/52mm air gap/210mm coil diameter prototype system with an efficiency of more than 96.5% at maximum power and above 96% down to 20% rated power.

Analysis and Design of a 300-W 500 000-r/min Slotless Self-Bearing Permanent-Magnet Motor

Abstract: Active magnetic bearings enable contactless operation and can therefore be used for supporting rotors spinning at high speeds. However, the rotational speed in conventional reluctance-force-based magnetic bearing topologies is limited, which is mainly due to high rotor losses and limited force control bandwidths. In this paper, a prototype of a self-bearing motor is presented, which overcomes several limitations of state-of-the-art high-speed magnetically levitated electric drive systems. Due to the employed magnetic bearing, the motor can be operated in high-purity or vacuum environments. An analytical mechanical and electrical bearing model is introduced and verified by measurements. Furthermore, a bearing inverter system is designed, and its controller performance is shown. Measurements of spinning levitated rotors up to speeds of 505 000 r/min verify the functionality of the overall system. To the authors' knowledge, this is the highest speed achieved by magnetically levitated electrical drive systems so far.

3-D Electromagnetic Modeling of EMI Input Filters

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.

Characterization of the Voltage and Electric Field Stresses in Multi-Cell Solid-State Transformers

Abstract: Solid-State Transformers (SSTs) are a promising technology since they enable a reduction in weight and volume of transformers while integrating new functionalities and services in the grid. However, a new kind of electric stress for the insulation occurs in this type of power converter, given that low-frequency medium-voltage stresses are mixed with high- frequency stresses generated by the converter's switching actions. This paper analyzes, in time and frequency domains, the voltage stresses appearing in cascaded converters, employing converter cells based on two-level or three-level bridge legs. The highest electric fields occur in the medium-frequency transformers of the converter cells' DC-DC converters, which provide galvanic isolation within the SST. Numerical simulations of the electric field distributions in these transformers are presented for the different frequency components and the impact of the converter topology on the insulation stress is highlighted. Furthermore, it is shown that the dielectric losses of the transformer can be ne- glected despite the presence of high-frequency harmonics. Finally, a transformer insulation concept based on semiconducting tape is proposed. Index Terms—Solid-State Transformers, Multi-cell converter, Medium-frequency transformer, Electric field, Insulation.

Inductive power transfer system and method for operating an inductive power transfer system

Abstract: An inductive power transfer system, in particular a battery charging system comprises: • a transmitter coil (3) and a receiver coil (4); • a transmitter-side power converter (8) comprising a mains rectifier stage (11) powering a transmitter-side dc-bus (10) and controlling a transmitter-side dc-bus voltage U 1,dc ; • a transmitter-side inverter stage (9) with switching frequency f sw supplying the transmitter (3) coil with an alternating current; • a receiver-side power converter (12) comprising a receiver-side rectifier stage (13) rectifying a voltage induced in the receiver coil (4) and powering a receiver-side dc-bus (14) and a receiver-side charging converter (15) controlling a receiver-side dc-bus voltage U 2,dc ; • power controllers (19, 18) determining, from a power transfer efficiency of the power transfer, reference values U 1,dc *, U 2,dc * for the transmitter and receiver side dc-bus voltages; • an inverter stage switching controller (20) controlling the switching frequency f sw to reduce losses in the transmitter-side inverter stage (9).

Scaling and balancing of multi-cell converters

Abstract: In this paper, the potential of the multi-cell approach for power electronic converters with efficiencies and power densities beyond the barriers of state-of-the-art systems is discussed. Based on fundamental scaling laws the benefits of splitting a system into multiple converter cells are derived in terms of lower volume and/or higher power density for a given cooling capacity. In addition, the conditions for equal current and/or balancing of multi­ cell systems is reviewed. The advantages of the mulit-cell systems are examined in more detail based on the example of a DC-DC boost converter realized with either parallel- or series-interleav ed boost cells. It is shown, that the multi-cell systems can offer lower switching and conduction losses and/or an improved voltage spectrum depending on the choice of the switching frequency relative to a single system. Furthermore, the effects of parasitic capacitances on

Performance comparison of a GaN GIT and a Si IGBT for high-speed drive applications

Abstract: GaN power switches enable better switching characteristics compared to state-of-the-art power transistors that are widely used today. Due to their lower switching losses, GaN switches may lead to new horizons in key application areas of power electronics such as photovoltaic converters, high-speed electrical drives and contactless power transfer. However, this technology has not yet diffused fully into the industry. Therefore, today only limited experimental data is available on those switches. In this paper, a synchronous buck converter is designed using two 600 V, 15 A GaN GIT switches developed by Panasonic. Guidelines for an optimum PCB layout are given. Both electrical and calorimetric power loss measurements are shown. Finally, a comparison is made between the GIT and a similarly rated Si IGBT for high-speed electrical drive applications where the higher switching frequencies enabled by the use of GaN is shown to reduce the rotor losses in two typical types (slotted and slotless stator) of high-speed permanent-magnet electric machines.

Slotless Bearingless Disk Drive for High-Speed and High-Purity Applications

Abstract: In this paper, a bearingless drive for high-speed applications with high purity and special chemical demands is introduced. To achieve high rotational speeds with low losses, a slotless bearingless disk drive with toroidal windings is used. We present the working principle of the bearingless drive as well as a model for calculating the achievable drive torque. An advantageous winding system for independent force and torque generation is proposed, which can be realized with standard inverter technology. Additionally, the winding inductances are examined to evaluate the dynamic properties of bearing and drive. The findings are verified with simulation results and the system performance is successfully demonstrated on an experimental prototype, which runs up to 20 000 rpm and is designed for an output power of 1 kW.

SiC-based unidirectional solid-state transformer concepts for directly interfacing 400V DC to Medium-Voltage AC distribution systems

Abstract: 400 V DC distribution networks present a promising solution for supplying high-power DC loads such as information processing systems, transportation battery charging facilities and DC micro grids, among others. For these applications, high transmission efficiency, reliability and controllability are mandatory. With the current technology, these loads are fed from PWM rectifiers which are connected to the three-phase Low-Voltage (LV) distribution grid (400 V AC in Europe). The LV grid itself is supplied via Low-Frequency Transformers (LFT) from the Medium-Voltage (MV) grid, providing galvanic isolation and the required voltage step down. This paper presents three unidirectional AC/DC SiC-based Solid-State Transformer (SST) topologies with direct connection to the MV grid, which avoid the utilization of the aforementioned LFT by integrating a Medium-Frequency (MF) conversion stage, thus increasing the efficiency and power density of this supply system. The SST topologies are compared by means of a chip area-based comparative evaluation. Finally, the most suited among the presented topologies is Pareto-optimized, achieving a total MV AC to 400 V DC efficiency of 98.3 %. It is shown that the optimized SST features 40 % less overall losses compared to state-of-the-art solutions.

Bidirectional isolated non-resonant DAB DC-DC converter for ultra-wide input voltage range applications

Abstract: This paper details efficiency optimized operation and design of a bi-directional and isolated five-level Dual Active Bridge (5LDAB) converter for an application that requires ultra-wide voltage and power ranges. The rated power of the considered converter is 7.5kW, the specified input voltage range is 150V ≤ V dc1 ≤ 800V and the output voltage is constant, V dc2 = 700V. In order to achieve high efficiency levels in a wide operating range, a modulation scheme is proposed to minimize the transformer rms current. Results of transformer rms currents and of efficiencies are presented for the 5LDAB and compared with the results obtained for an efficiency optimized conventional Dual Active Bridge (DAB) converter. Compared with the DAB topology, the 5LDAB converter can achieve an overall reduction of transformer rms currents and of conduction losses in the higher voltage regime of the operating range.

Accurate finite-element modeling and experimental verification of inductive power transfer coil design

Abstract: Inductive Power Transfer (IPT) is a promising technology for the charging of the traction batteries of electric and hybrid electric vehicles due to the significant simplification of the charging process implied by the contactless transmission of the charging energy. Typically, Finite-Element (FE) methods are used to predict the power loss in the IPT coils, to calculate equivalent circuit parameters, and to estimate the magnetic stray field of IPT coils. This paper gives insight into the FE modeling of the IPT coils of a 5kW prototype IPT system with a dc-to-dc efficiency of more than 96% (52mm air gap, coil diameter 210 mm). In the paper, modeling of IPT coils in the frequency domain using the FE tools FEMM and Ansys Maxwell is discussed and the calculation methods to predict power loss, equivalent circuit values, and stray fields are presented. The main part of the paper is a comprehensive experimental verification of the obtained FE results, which includes dc-to-dc conversion power loss, circuit parameter measurements, and measurements of the stray field. For the verification of the calculated stray fields the design of a highly compact, high-bandwidth, low-cost magnetic field probe is presented. Experimental data obtained from the designed field probe shows that the FE tools used in the design of the IPT coils deliver field data with a calculation error of less than 5%.

Multi-cell power conversion method and multi-cell power converter

Abstract: A method includes converting power by a power converter comprising a plurality of converter cells, and selectively operating at least one converter cell of the plurality of converter cells in one of an active and an inactive mode based on a level of a power reference signal.

Optimal Inductor Design for 3-Phase Voltage-Source PWM Converters Considering Different Magnetic Materials and a Wide Switching Frequency Range

Abstract: In this paper, an optimization regarding volume, efficiency and costs of AC boost inductors in 3-phase PWM converters based on detailed multi-domain models is presented. The optimization is performed for a wide switching frequency range of 5-80 kHz and a wide current ripple range of 5-100 %, considering ferrite, amorphous and powder core materials in combination with round, litz, foil and flat wire windings. The shown analysis and optimization identifies the best core material/winding type combinations for both thermally and efficiency-constrained inductor designs. Furthermore, the investigations reveal that simplified scaling assumptions, e.g. a proportional relationship between the inductor volume and the inverse of the frequency or the stored energy, are only accurate in special cases.

An Active Magnetic Damper Concept for Stabilization of Gas Bearings in High-Speed Permanent-Magnet Machines

Abstract: The successful application of ultrahigh-speed electrical-drive systems in industrial products is currently limited by lacking high-speed bearing technologies permitting high reliability and long lifetime. Promising bearing technologies for high rotational speeds are contactless bearing concepts such as active magnetic bearings or gas bearings. While magnetic bearings usually are major electromechanical systems with substantial complexity, gas bearings allow compact realizations with high load capacity and stiffness; however, poor dynamic stability has been limiting their use at high rotational speeds. Following a hybrid bearing approach with an aerodynamic gas bearing for load support, a small-sized active magnetic damper concept is proposed to enable the stable high-speed operation of the gas bearing with a minimum of additional complexity and costs. As for the effective stabilization of the gas bearing, a high-quality displacement measurement is essential, and a new eddy-current-based rotor-displacement self-sensing concept employing an auxiliary signal injection and rotor displacement measurement circuit is presented. A hardware implementation of the proposed concept is shown providing high-resolution measurement signals.

A Novel Motor Topology for High-Speed Micro-Machining Applications

Abstract: In this paper, a novel motor topology (lateral stator machine) is proposed for various drilling applications where the space in the tool head is limited. The stator of the motor grows in one lateral direction, allowing for a compact direct drive design. Finite-element analysis (FEA) is carried out and the machine design is optimized for the specifications of a high-speed micro-machining spindle which is given as an example. The design procedure for those specifications is described in detail, where the torque is maximized while considering the space limitations and the loss constraints at the critical operating points. The construction of a lateral stator machine merged into a test bench is also described. The test bench is used for measuring the standstill torque of the machine in a configuration without bearings, such that only the electromagnetic torque is measured without any friction effects from the bearings. Moreover, the test bench can be modified to measure the no-load losses and separate the mechanical and electromagnetic components of it. Although described on a lateral stator machine, the measurement methodology of this paper can be applied to any electrical machine. Finally, measurement results are given and the design procedure is verified.

Common-mode currents in multi-cell Solid-State Transformers

Abstract: Solid-State Transformers (SSTs) are considered important building blocks of a future Smart Grid, where they will replace conventional transformers and provide enhanced functionality and controllability. To deal with the medium-voltage levels at the input of an SST for distribution applications, commonly cascaded cells converter topologies are proposed. This paper presents a detailed analysis of the common-mode currents appearing in cascaded cells converter systems as a consequence of steep changes of the cells' potentials caused by the individual cells' switching actions. Common-mode chokes placed at the AC terminals of each individual cell are identified as the most feasible way of mitigating these common-mode current disturbances. Detailed, analytic design guidelines are provided and applied to a 1MVA, 10 kV/400V SST.

Optimization of Transcutaneous Energy Transfer coils for high power medical applications

Abstract: Inductive Power Transfer (IPT) technology is a promising solution for powering medical implants with a continuous high power consumption, due to the elimination of the percutaneous driveline, which is still the major cause of severe infections. However, at the present time, no Transcutaneous Energy Transfer (TET) system is commercially available and ready for long-term use. Specifically the heating of the tissue due to power losses in the TET coils is a major problem. The focus of this paper therefore is on the minimization of the power losses in the energy transmission and receiver coils of a TET system. Extensive parameter sweeps were performed in order to find the optimal winding configuration with minimized parasitic resistances and optimal inductance value. A thermal model of the human skin is developed to estimate the thermal limits. Based on the results, a prototype TET system is built to validate the optimization process. The prototype system is capable of transmitting 30W of power with an efficiency greater than 93 %, even at a coil separation distance of 20mm (0.79 in) and 70mm (2.76 in) coil diameter.

η-ρ Pareto optimization of 3-phase 3-level T-type AC-DC-AC converter comprising Si and SiC hybrid power stage

Abstract: In this paper, the η-ρ (efficiency - power density) Pareto front of a 20 kVA Uninterruptible Power Supply (UPS), comprising a Si and SiC hybrid 3-level T-type rectifier and inverter stage, and input / output side filters, is determined. A multi-objective optimization procedure is detailed, which employs an electrical converter model and coupled electro-thermal component models. Each component model determines the corresponding losses, volumes, and temperature rises. A detailed description of the inductor model is given which considers high frequency winding losses as well as core losses, and calculates the temperature rises inside the inductor, e.g. the hot-spot winding temperature. Based on the determined η-ρ Pareto front, the most suitable realization of the proposed UPS system is determined, which is based on the resulting sensitivities of the design parameters (switching frequency, current ripples, magnetic materials, etc.) on the performance of power converter system (efficiency and power density). As a result, a switching frequency of 16 kHz, maximum relative input and output side current ripples of 20%, amorphous core materials for DM inductors, and nanocrystalline core materials for CM inductors are selected in order to achieve a converter efficiency of 96.6% at a power density of 2.3 kVA/dm 3 .

High-speed magnetically levitated reaction wheel demonstrator

Abstract: Reaction wheels (RWs) for small satellites with active magnetic bearings allowing for ultra-high-speed operation show advantages in angular momentum density over ball bearing RWs with limited speed according to scaling laws developed in this paper. A reaction wheel demonstrator design based on a novel dual hetero­ Ihomoploar, slotless, self-bearing, permanent-magnet synchronous motor concept with a rotational speed of 250000 rpm is investigated. The design includes the rotor dynamics, mechanical stress analysis, electromagnetics , power electronics and control, and the sensor concept. The experimental setup ready for experimental verification is presented.

Successful online education - GeckoCIRCUITS as open-source simulation platform

Abstract: Modern lectures in power electronics should be complemented by interactive content, e.g. computer assisted learning via web-based applets or exercises employing a circuit simulator. The online e-learning system “iPES” was established in 2001; since then the iPES Java applets are frequently used in academia and industry to teach the basics of power electronics. This paper introduces new features of the open-source power electronics circuit simulator GeckoCIRCUITS, which enable a more flexible way to generate online content in comparison to iPES. In particular, the animation of current paths in a circuit model as well as a new language translation and internationalization scheme will be presented in detail. Finally, the popular iPES platform will be enhanced or replaced with Java applets based on GeckoCIRCUITS.