Showing papers by "Johann W. Kolar published in 2009"

Accurate Small-Signal Model for the Digital Control of an Automotive Bidirectional Dual Active Bridge

Abstract: The derivation of an accurate small-signal model for a galvanically isolated, bidirectional dc-dc converter and the implementation of a corresponding controller on a DSP as well as key methods and functions required for the digital implementation are detailed in this paper. The investigated dc-dc converter, an automotive dual active bridge (DAB) system, enables power transfer between a low-voltage port (ranging from 11 to 16 V) and an HV port (240 to 450 V). The nominal power rating is 2 kW. The developed small-signal model yields highly accurate results for the DAB system, but the proposed modeling procedure could also be applied to arbitrary resonant power converters with unidirectional or bidirectional power transfer.

Design Guidelines for Interleaved Single-Phase Boost PFC Circuits

Abstract: This paper provides a comprehensive guideline for the design of a single-phase PFC targeting for minimal volume, as it is highly relevant for ultracompact integrated systems. It is shown, how different operation modes (continuous, boundary, and discontinuous conduction mode) may influence the design and consequently the achieved power density. Furthermore, the effect of interleaving of several boost stages is analyzed as a measure for compactness increase. Finally, the selection of the appropriate switching frequency in order to achieve an overall optimized system is discussed. In this way, the design of the crucial components is carried out, namely, the boost inductor, including a volume optimization through a thermal connection to the heat sink; the output capacitor considering the rms current stress; and the input filter, which is designed for compliance with high-frequency electromagnetic compatibility standards, taking into account the quasi-peak detection measurement of the test receiver equipment.

A Novel Low-Loss Modulation Strategy for High-Power Bidirectional Buck ${\bm +}$ Boost Converters

Abstract: A novel, low-loss, constant-frequency, zero-voltage-switching (ZVS) modulation strategy for bidirectional, cascaded, buck-boost DC-DC converters, used in hybrid electrical vehicles or fuel cell vehicles (FCVs), 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 proposed 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 antiparallel body diode is conducting. As the novel modulation strategy is a software-only solution, there are no additional expenses for the 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 nonisolated multiphase converter equipped with the low-loss modulation. Experimental measurements performed with 12 kW, 17.4 kW/L prototypes in stand-alone and multiphase configuration verify the low-loss operation over a wide output power range and a maximum efficiency of 98.3% is achieved.

Megaspeed Drive Systems: Pushing Beyond 1 Million r/min

Abstract: The latest research in mesoscale drive systems is targeting rotational speeds toward 1 million r/min for a power range of 1-1 kW. Emerging applications for megaspeed drives (MegaNdrives) are to be found in future turbo compressor systems for fuel cells and heat pumps, generators/starters for portable nanoscale gas turbines, printed circuit board drilling and machining spindles, and electric power generation from pressurized gas flow. The selection of the machine type and the challenges involved in designing a machine for megaspeed operation such as the winding concepts, a mechanical rotor design capable of 1 000 000 r/min, the selection of magnetic materials for the stator, and the optimization concerning high-frequency losses and torque density are presented. Furthermore, a review of the advantageous inverter topologies, taking into account the extremely low stator inductance and possible high-speed bearing types such as ball bearings, air bearings, foil bearings, and magnetic bearings, are given. Finally, prototypes and experimental results originating from MegaNdrive research at Swiss Federal Institute of Technology Zurich are discussed and extreme temperature operation and power microelectricalmechanical system are identified as targets for future research.

Design and Performance of a 200-kHz All-SiC JFET Current DC-Link Back-to-Back Converter

Abstract: Silicon carbide (SiC) switching devices have been widely discussed in power electronics due to their desirable properties and are believed to set new standards in efficiency, switching behavior, and power density for state-of-the-art converter systems. In this paper, the design, construction, and performance of a 3-kVA All-SiC current-source converter (CSC), also known as current dc-link back-to-back converter (CLBBC), is presented. CSC topologies have been successfully used for many years for high-power applications. However, for low-power-range converter systems, they could not compete with voltage-source-converter topologies with capacitors in the dc-link, since the link inductor has always been a physically large and heavy component due to the comparatively low switching frequencies of conventional high-blocking-voltage silicon devices. New SiC switches such as the JFET, which are providing simultaneously high-voltage blocking, low switching losses, and low on-state resistance (three times lower compared with Si MOSFET with similar V- I rating), offer new possibilities and enable the implementation of a high switching frequency CLBBC and, thus, reducing size and weight of the dc-link inductor. The prototype CLBBC has been designed specifically for the latest generation 1200-V 6-A SiC JFETs and a target switching frequency of 200 kHz.

Exploring the pareto front of multi-objective single-phase PFC rectifier design optimization - 99.2% efficiency vs. 7kW/din 3 power density

Abstract: Up to now, in the development of power electronics systems, the reduction of the initial costs or the increase of the power density have been of primary concern. However, with increasing energy costs also the power conversion efficiency is gaining higher and higher importance. Accordingly, while maintaining high power density, an efficiency as high as possible must be obtained. In this paper the maximum attainable efficiency and the dependency of the efficiency limit on technological parameters is determined for single-phase PFC boost rectifiers. In a first step basic PFC boost rectifier topologies are briefly compared with regard to high efficiency and a dual-boost PFC rectifier with integral common-mode filtering is selected as basis for the investigations. Next, simple approximations of the technological limits of the system performance are calculated in the efficiencypower density plane. With this, the Feasible Performance Space and the reduction in power density which has to be accepted for increasing the efficiency are clarified, and the trade-off limit curve (Pareto Front) of a multi-objective, i.e. efficiency and power density design optimization is determined. Furthermore, a comprehensive numerical efficiency optimization is carried out which identifies an efficiency limit of 99.2% for a 3.2kW system. The theoretical considerations are verified by experimental results from a laboratory prototype of the ultra-high efficiency system achieving 99.1% efficiency at a power density of 1.1kW/din3, as well as those firom an ultra-compact dual-boost PFC rectifier (95.8%, 5.5kW/dn3) and a very low switching freluency (3kHz) conventional PFC boost rectifier (96.7%, 2kW/din3). Finally, the sensitivity of the efficiency optimum with regard to various technological parameters is analyzed and an outlook on the further course of the research is given.

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

Abstract: 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.

Comprehensive Design and Optimization of a High-Power-Density Single-Phase Boost PFC

Abstract: The design of a single-phase boost power-factor-correction (PFC) circuit is associated with a large variety of considerations, such as the following questions. Which operation mode should be selected (e.g., continuous or discontinuous operation)? How many interleaved boost cells are advantageous? Which switching frequency should be selected? What is the optimum number of EMI input filter stages? Which semiconductor technology should be chosen? All these issues have a significant influence on the converter efficiency and power density. In this paper, the aforementioned questions are addressed for exemplary specifications of the PFC (300-W output power, 400-V output voltage, and 230-V mains voltage), whereby the focus in the design is mainly put on very high power density. As a result, different design points are identified and comparatively evaluated. By considering different aspects such as volume, losses, capacitor lifetime, and also cost issues (e.g., by additional current sensors or expensive silicon carbide devices), a dual-interleaved PFC operated in discontinuous conduction mode at 200 kHz is selected. With an experimental prototype, a superior power density of 5.5 kW/L and a system efficiency of 96.4% are achieved, which is close to the values predicted by the design procedure. Furthermore, measurements verify a near-unity power factor (PF = 99.7%) and the compliance with electromagnetic compatibility conducted noise emission standards. Finally, it is investigated to which extent the power density could be further increased by an integration of the input filter in the PCB.

Passive and Active Hybrid Integrated EMI Filters

Abstract: 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.

Impact of EMC Filters on the Power Density of Modern Three-Phase PWM Converters

Abstract: Electromagnetic compatibility (EMC) filters are typically included in offline power converters, controlling electromagnetic emissions, but adding volume to power electronic systems. During the last decades, one of the main objectives of the power electronics industry has been the increase of the power density. Thus, it is reasonable to analyze how filters affect power density values, imposing limits or ldquobarriersrdquo to it. The impact of the EMC filters on the overall volume of three-phase pulsewidth modulation (PWM) converters is studied here for converters in the range of 5-10 kW. An analytical procedure based on the volume minimization of the EMC filters is proposed to estimate the total filter volume as function of the converters' rated power and switching frequency. With this, the minimum volume for EMC filters that allow the converters to comply with EMC standards regarding conducted emissions can be estimated and volume limitations identified. A discussion about the limits of power density for the considered three-phase PWM converters for state-of-the-art power semiconductors is performed, and optimum switching frequencies are identified. An experimental verification is carried out, which validates the achieved results.

Digital Current Controller for a 1 MHz, 10 kW Three-Phase VIENNA Rectifier

Abstract: Active three-phase rectifiers operated at switching frequencies of 500 kHz and above, in order to increase their power density, require high-speed current controllers. If these current controllers are implemented purely digitally, which is well established today for 20-200 kHz converter systems, then very high numerical data processing demands result. In this paper, two different types of field-programmable gate arrays (FPGAs) are evaluated for realizing high-speed converter current control. For the implementation of such controllers, not only the FPGA has to be considered but rather the entire signal chain. Two alternative A/D interfaces (including high-speed low-voltage differential signaling data transmission) that are able to handle data sampling rates up to 25 MSa/s are verified. Subsequently, a digital current controller is designed and it is shown how hardware multiplier blocks of modern FPGAs can be used advantageously. Furthermore, the FPGA implementation of high-resolution pulsewidth modulation providing symmetrical pulse patterns for high switching frequencies is described. Measurements taken from a 10 kW VIENNA rectifier laboratory prototype finally demonstrate the high performance of the proposed control concept and show that a low mains current total harmonic distortion of 1.4% can be achieved for such ultrahigh switching frequency converters.

Design of a 5-kW, 1-U, 10-kW/dm $^{\hbox{3}}$ Resonant DC–DC Converter for Telecom Applications

Abstract: 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 3 and an efficiency of 94.5% at a height of 1 U, is presented.

SiC power semiconductors in HEVs: Influence of junction temperature on power density, chip utilization and efficiency

Abstract: With SiC, junction temperatures of power semiconductors of more than 700 _C are theoretically possible due to the low intrinsic charge carrier concentration of SiC. Hence, a lot of research on package configurations for power semiconductor operation above 175 _C is currently carried out, especially within the automotive industry due to the possible high ambient temperatures occurring in hybrid electric vehicles (HEVs). This paper shows, that a higher junction temperature though does not necessarily guarantee a higher utilization of the SiC chips with respect to the current that the device can conduct without overheating. The reason is, that for most power devices the power losses start to increase very rapidly at high junction temperatures while the power that can be dissipated always increases linearly with the junction temperature. The junction temperature, where the device current starts to decrease at, is derived for different SiC chips using measured onstate conduction and switching losses in this paper. This paper furthermore analyzes in detail, how the junction temperature on the one hand is influenced by boundary conditions and on the other hand influences itself the core parameters of a converter such as efficiency, the required chip area (i. e. cost) as well as the volumetric power density and thus forms an additional degree of freedom in the design of a power electronic converter. While calculating the optimum junction temperature and analyzing its impact on the system performance, it is demonstrated, how these results can help to find the best suited power semiconductor device for the particular application. The performance of the calculations is shown on a design applied to a drive inverter for hybrid electric vehicles with normally-off SiC JFETs. Operated close to the optimum junction temperature of the SiC JFETs, it reaches a power density of 51 kW/l for the power modules and the air-cooling system, which is shown to be doubled by increasing chip size and using an advanced power semiconductor package with a lower thermal resistance from junction to ambient than the for this case assumed 1 K/W.

Comparative Evaluation of Polyphase Bearingless Slice Motors for Fluid-Handling Applications

Abstract: For the bearingless slice motor (BSM) concept, which has been successfully introduced in semiconductor fluid-handling and medical applications over the last years, different motor configurations in terms of stator construction, number of phases, and winding arrangement exist. This paper comparatively evaluates these topologies for their suitability in possible future industry applications, such as the food, biotechnology, and pharmaceutical industries. The comparison is carried out for two-, three-, and four-phase BSM concepts based on performance indexes such as motor losses, losses in the power electronics, and voltampere requirements depending on the required magnetic bearing force and the motor torque. Finally, the performance data are discussed, and also, practical aspects such as realization effort, copper and iron mass, control effort, and scalability of the concepts are taken into account.

Robust Angle-Sensorless Control of a PMSM Bearingless Pump

Abstract: In the semiconductor industry, where bearingless pump systems are employed as the state-of-the-art technology, the trend goes toward higher fluid temperatures (150degC and more) in order to further increase process efficiency. This fact translates into the requirement of a high-temperature bearingless pump system and/or the elimination of thermal-critical components such as Hall sensors. This paper introduces a new method for a hall-sensorless control of a permanent-magnet synchronous machine bearingless pump in its operating range from 0 to 8000 r/min and from zero load to full load. The sensorless operation is performed by the following three novel control functionalities: a controlled startup routine, enabling a sure levitation and zero-angle setting; an open-loop angle estimation based on stator voltage and stator current measurement and known machine parameters; and an angle synchronization establishing a robust operation of the pump in the whole operating range even for a large machine parameter drift. In particular, considering the temperature degrading of the permanent-magnet flux density, the novel robust control concept is of great benefit for bearingless pump systems employed in high-temperature applications.

Solid state modulator for plasma channel drilling

Abstract: In addition to conventional drilling and demolition techniques, drilling with pulsed electric power has been investigated intensively, and commercial applications have begun to emerge. The most efficient method, often called plasma channel drilling (PCD), uses electrical pulses to generate a plasma channel in the rock. The expansion of this channel within the rock performs the demolition. The technique relies on that fact that for fast pulse rise-times (50 ns - 500 ns) the breakdown field-strength of water is higher than that of rock, so that the discharge takes place in the rock. To date, in publications dealing with this topic, plasma dynamics, crack formation, and setup of the electrodes are the primary areas of investigation. In these investigations, the high voltage pulses have been generated using modulators based on spark gaps: either as single-switch or in a Marx-generator setup. These modulators are able to generate high voltages and high currents simultaneously, but the PCD method does not require high currents for igniting the discharge. Meanwhile, after ignition the voltage across the arc is relatively small. Thus these modulators are oversized. In this paper, a new concept, consisting of a solid state modulator which generates a high-voltage pulse for ignition, and a high output-current to expand the plasma, is presented. The solid state modulator consists of a single semiconductor switch, saturable inductors and a pulse transformer. In addition to being more compact, the solid state approach has improved lifetime and reliability compared to approaches using spark gap switches.

A Semiconductor Area Based Assessment of AC Motor Drive Converter Topologies

Abstract: In order to find the optimal converter topology for a given ac motor drive, as defined by its mission profile, suitable assessment criteria have to be applied. A new semiconductor chip area based approach is proposed to compare and assess different motor drive converter topologies. It determines the total semi-conductor chip area based on the drive's operating point and the optimal partitioning of the transistor and diode chip areas. This approach not only provides a distinct figure-of-merit for comparison but also enables the semiconductor costs of different converter topologies to be determined. The chip area based comparison has been successfully used to assess three 3-phase ac-dc-ac converter topologies for a 15 kW (20 HP) motor drive. It is shown that the Voltage DC-Link Back-to-Back Converter based drive provides the best overall performance in terms of chip area, cost, efficiency, and available nominal torque.

Magnetically levitated slice motors - an overview

Abstract: This publication gives a comprehensive overview over different concepts of magnetically levitated motors with slice-shaped rotors that differ in their construction and the way the bearing and drive forces are created After a description of the technical principle of the topologies the motor concepts are then compared by different criteria such as the acceleration behavior, the compactness and the complexity of the control The qualitative comparison is supported by performance measurements on the laboratory prototypes

Contactless energy transmission for an isolated 100W gate driver supply of a medium voltage converter

Abstract: In this paper, an innovative DC-DC converter is investigated which provides electrical power to the gate driver units of medium voltage level converters. For the discussed DC-DC converter, a galvanic isolation (isolation voltages of up to 35 kV) is required. This electrical isolation is achieved with a coreless transformer in order to obtain a cost-effective solution. Furthermore, the DC-DC converter contains a full-bridge converter being operated with low switching losses, a resonant compensation network to achieve a high overall efficiency and an output side rectifier. In this paper, the design of the coreless transformer, the appropriate compensation networks and the power electronics are discussed in detail. Moreover, measurement results obtained from a 100 W prototype, operated at a switching frequency of 410 kHz, are presented. With the proposed setup, a high overall efficiency of up to 80% and a transformer breakdown voltage of 55 kVrms is achieved. Thus, the proposed converter concept represents a very competitive solution with respect to the typically employed DC-DC converters with dry-type cast coil transformers.

Multi-objective optimization and comparative evaluation of Si soft-switched and SiC hard-switched automotive DC-DC converters

Abstract: The application of soft-switching concepts or Silicon Carbide (SiC) devices are two enabling technologies to further push the efficiency, power density or specific weight of power electronics converters. For an automotive application, such as a dc-dc converter that interconnects the high voltage battery or ultra-capacitor in a hybrid electrical vehicle (HEV) or a fuel cell vehicle (FCV) to the dc-link, costs and failure rate are likewise of importance. Due to increasing requirements on multiple of these converter characteristics the comprehensive multi-objective optimization of the entire converter system gains importance. Thereto, this paper proposes an optimization method to explore the limits of power density as a function of the switching frequency and the number of phases of non-isolated bi-directional multi-phase dc-dc converters operated with soft-switching and Silicon devices and hard-switched converters that take advantage of SiC devices. In addition, the optimization includes an algorithm to determine the chip size required for the semiconductor devices under consideration of the thermal characteristics and efficiency requirements. Based on detailed analytical volume, loss and cost models of the converter components as well as on measurements demonstrative results on the optimum converter designs are provided and evaluated comparatively for the different converter concepts.

An Optimized 5 kW, 147 W/in 3 Telecom Phase-Shift DC-DC Converter with Magnetically Integrated Current Doubler

Abstract: In the last decade there has been a tremendous growth in the number of data centers due to the increasing demand for internet services. At the same time, the cost for energy and materials have increased because of reducing resources and increased demand. That has caused a change in the driving forces for new power supply development, with more consideration on power density and efficiency. The commonly used DC-DC converter in the power supply unit (PSU) for data centers and telecom applications are full bridge phase-shift converters since they meet the demands of high power levels and concurrently efficient power conversion as well as a compact design. The constant operating frequency allows a simple control and EMI design. To develop a new converter with higher power density and/or high efficiency the designer has a lot of degrees of freedom. An optimization procedure, based on comprehensive analytical models, has been developed and leads to the optimal parameters (e.g. switching frequency or transformer design) to achieve the most compact and/or efficient design. In this paper an volume optimized 400V/48V phase-shift DC-DC converter with current doubler rectifier based on analytical models is constructed. The power density of the converter is increased by integrating the output inductors in the transformers core. The intrinsic voltage ringing of the rectifier diodes is damped by a lossless magnetic snubber, which feeds ringing energy to the output. Experimental results prove the theoretical analytical models and the design procedure.

Efficiency optimization of an automotive multi-phase bi-directional DC-DC converter

Abstract: The paper proposes methods to improve the efficiency of a bi-directional, multi-phase buck+boost DC-DC converter for application in Hybrid Electrical Vehicles (HEV) or Fuel Cell Vehicles (FCV) Thereto, the modulation strategy for a highly-compact, 30kW/Liter, constant-frequency soft-switching converter is optimized based on a converter loss model that includes the losses in the power semiconductors and the buck+boost inductor An algorithm for numerical calculation of the optimum switching times is given, whereas the values for the loss-optimized operation of the converter are stored in a lookup-table that is accessed by the digital controller In addition, a novel method and control concept to ensure a Zero Voltage Switching (ZVS) of all semiconductor switches by determination of a zero voltage across the MOSFET switches with analog comparators is proposed that results in the lowest inductor RMS currents for ZVS operation at the same time Furthermore, at low output power an absolute efficiency gain of over 28% is achieved by partial operation of the six interleaved converter phases A detailed description on the control concept that determines the optimum number of activated phases for the current operating point of the converter is given and verified by experimental results The measurements prove the capability to instantaneously switch the number of active phases during operation without a overshoot or drop in the converter output voltage

Efficient Calculation of Non-Orthogonal Partial Elements for the PEEC Method

Abstract: For various electrical interconnect and EMC problems, the partial element equivalent circuit (PEEC) method has proven to be a valid and fast solution method of the electrical field integral equation in the time as well as the frequency domain. Therefore, PEEC has become a multipurpose full-wave method, especially suited for the solution of combined circuit and EM problems, as found, for instance, on printed circuit board layouts, power electronics devices or EMC filters. Recent research introduced various extensions to the basic PEEC approach, for example a non-orthogonal cell geometry formulation. This paper presents a fast, flexible and accurate computational method for determining the matrix entries of partial inductances and the coefficients of potential for general non-orthogonal PEEC cell geometries. The presented computation method utilizes analytical filament formulas to reduce the integration order and therefore to reduce computation time. The validity, accuracy, and speed of the proposed method is compared with a standard integration routine on example cell geometries where the numeric results of the new method show improved accuracy, coming along with reduced computation time.

Output ripple reduction of an automotive multi-phase bi-directional dc-dc converter

Abstract: Bi-directional dc-dc converters for automotive applications typically are limited to generate only a small voltage ripple, especially when a ultra-capacitor with a limited ripple current capability is interfaced by the converter. Thus, to minimize the ripple quantities and the converter volume at the same time, interleaved multi-phase dc-dc converters are utilized. However, tolerances of the buck+boost inductors of the interleaved phases generate sub-harmonics in the ripple spectrum that are counterproductive to the advantage of ripple reduction. A method to cancel the fundamental frequency of the voltage ripple is proposed that is applicable to a converter consisting of three or more phases. It is shown that even for a low phase count the overall ripple amplitude is greatly reduced, only by adjustment of the phase shift angles. Experimental results carried out with a three-phase interleaved bi-directional dc-dc converter proof the concept functionality.

A Comparison of Separated and Combined Winding Concepts for Bearingless Centrifugal Pumps

Abstract: Bearingless centrifugal pump systems are employed in the semiconductor, pharmaceutical and medical industries due to their facility for pumping high purity fluids without particle contamination. Two types of forces have to be generated by the stator units, namely bearing forces for achieving magnetic levitation, and drive forces for producing the needed pump torque. The generation of these forces requires bearing and drive windings, which can be realized as separate bearing and drive coils or as identical, combined coils on the stator claws. In this paper, a detailed comparison between these two winding concepts is undertaken, whereby the copper losses, the power electronics losses, and the achievable pump output pressure are evaluated for both concepts. For each criterion a ratio of improvement is calculated analytically which allows evaluation of the performance of the two winding concepts for any given pump operating point and design. Finally, also practical features such as control complexity, cabling effort and manufacturability are discussed and measurements on prototype systems are carried out to validate the considerations.

Double-stage gate drive circuit for parallel connected IGBT modules

Abstract: Solid state modulators are increasingly being used in pulsed power applications. In these applications IGBT modules must often be connected in parallel due to their limited power capacity. In a previous paper, we introduced a control method for balancing the currents in the IGBTs. In this paper, we investigate techniques to minimize the modules' rise and fall times, which can positively impact the modulator's output pulse parameters, which in turn must meet the application's specifications. Further, a reduction in rise and fall times lowers switching losses and thus increases the modulator's efficiency. To reduce the voltage rise time of the pulse without increasing the maximal over-voltage of the parallel IGBTs we have investigated a double-stage gate driver with protection circuits to avoid over-voltages and over-currents. Additionally voltage edge detection has been implemented to improve current balancing. Our measurement results reveal the dependency of the rise-time and turnoff losses on the design parameters of the gate drive. We show that our design achieves a 62% reduction in the turn-off rise time, and a 32% reduction in the turn-off losses.

Balancing circuit for a 5kV/50ns pulsed power switch based on SiC-JFET Super Cascode

Abstract: In many pulse power applications there is a trend to modulators based on semiconductor technology. For these modulators high voltage and high current semiconductor switches are required in order to achieve a high pulsed power. Therefore, often high power IGBT modules or IGCT devices are used.

Theoretical and experimental results of a mesoscale electric power generation system from pressurized gas flow

Abstract: In many process applications where throttling is used to reduce pressure, the potential to obtain net work output is sacrificed to the throttling process. Examples are throttling valves of gas pipelines and conventional throttles in automotive applications or turbo expanders as used in cryogenic plants. With a new pressure reduction system that produces electricity while expanding the gas, the lost potential to obtain work output can be recovered. To achieve a high power density, this energy generation system requires an increased operating speed of the electrical machine and the turbomachinery. This paper presents a miniature compressed-air-to-electric-power system, based on a radial turbine with a rated rotational speed of 490 000 rpm and a rated electric power output of 150 W. A comprehensive description including turbine, diffuser and permanent magnet (PM) generator is given. Finally, measurements of the compressed-air-to-electric-power system with a maximum rotational speed of over 600 000 rpm, a maximum electric output power of 170 W, a maximum torque of 5.2 mN m and a turbine efficiency of 52% are presented.

Design and Development of a 26-Pole and 24-Slot Bearingless Motor

Abstract: Several processes in chemical, pharmaceutical, biotechnology and semiconductor industry require contactless levitation and rotation through a hermetically closed process chamber. A highly interesting topology for these applications is the ldquobearingless slice motorrdquo concept, where already some research has been done in the past. This paper presents the design, optimization and development of a 26-pole and 24-slot bearingless motor, which promises high acceleration and bearing performance and an ultra-compact setup. A prototype with a large rotor diameter and a large air-gap has been built to verify the simulation results by experiments.

A Three-Phase Delta Switch Rectifier for More Electric Aircraft Applications Employing a Novel PWM Current Control Concept

Abstract: In the course of the More Electric Aircraft program active three-phase rectifiers in the power range of 5 kW are required. A comparison with other rectifier topologies shows that the three-phase ?-switch rectifier (comprising three ?-connected bidirectional switches) is well suited for this application. The system is analyzed using space vector calculus and a novel PWM current controller concept is presented, where all three phases are controlled simultaneously; the analysis shows that the proposed concept yields optimized switching sequences. To facilitate the rectifier design, analytical relationships for calculating the power components average and rms current ratings are derived. Furthermore, a laboratory prototype with an output power of 5 kW is realized. Measurements taken from this prototype confirm the operation of the proposed current controller. Finally, initial EMI-measurements of the system are also presented.