Martina Baumann

Novel three-phase AC-DC-AC sparse matrix converter

A novel three-phase AC-DC-AC sparse matrix converter (SMC) having no energy storage elements in the DC link and employing only 15 IGBTs as opposed to 18 IGBTs of a functionally equivalent conventional AC-AC matrix converter (CMC) is proposed. It is shown that the realization effort could be further reduced to only 9 IGBTs (ultra sparse matrix converter, USMC) in case the phase displacement of the fundamentals of voltage and current at the input and at the output is limited to /spl plusmn//spl pi//6. The dependency of the voltage and current transfer ratios of the systems on the operating parameters is analyzed and a space vector modulation scheme is described in combination with a zero current commutation procedure. Furthermore, a safe multi-step current commutation concept is treated briefly. Conduction and switching losses of the SMC and USMC are calculated in analytically closed form. Finally, the theoretical results are verified in Part II of the paper by digital simulations and results of a first experimental investigation of a 10 kW/400 V SMC prototype are given.

Comprehensive Design of a Three-Phase Three-Switch Buck-Type PWM Rectifier

A three-phase three-switch buck-type pulsewidth modulation rectifier is designed for telecom applications in this paper. The rectifier features a constant 400-V output voltage and 5-kW output power at the three-phase 400-V mains. The principle of operation and the calculation of the relative on-times of the power transistors are described. Based on analytical relationships the stresses of the active and passive components are determined and the accuracy of the given calculations is verified by digital simulations. Exemplarily, a 5-kW power converter is then designed based on the analytical expressions and on switching loss measurements from a hardware prototype constructed with insulated gate bipolar transistor/diode power modules. The loss distribution of the components, the total efficiency, and the junction temperatures of the semiconductors are then evaluated in dependency on the operating point. Finally, the trade-off between the selected switching frequency and the admissible power range for the realized design is shown and a total efficiency of 95.0% is measured on the hardware prototype, where an excellent agreement with the theoretically evaluated efficiency is shown

Parallel Connection of Two Three-Phase Three-Switch Buck-Type Unity-Power-Factor Rectifier Systems With DC-Link Current Balancing

Connecting three-phase rectifier systems in parallel shows many advantages as compared to a single rectifier system with higher output power, such as higher reliability, smaller current and voltage ripple components, lower filtering effort, or higher system bandwidth. However, current unbalance or circulating currents can occur for modular design. In this paper, the parallel connection of two three-phase three-switch buck-type unity-power-factor pulsewidth-modulation rectifier systems is experimentally investigated for a 10-kW digital-signal-processor-controlled prototype. A space vector modulation scheme is employed showing all the advantages of an interleaved operation. Three control schemes for active dc-link current balancing are described employing an additional free-wheeling state that allows to influence the rate of change of the dc-link currents and can therefore be used for dc-link current balancing. The control schemes differ concerning control action and additional switching losses. Simulation and experimental results confirm the theoretical considerations: The dc-link current-balancing capability of the different control methods is compared, and the influence of the additional free-wheeling state on switching losses and operation behavior is investigated. The most advantageous control method, which employs a hysteresis controller and shows limited switching losses, is selected. The analysis of the mains behavior shows an improvement as compared to a single rectifier operation.

New wide input voltage range three-phase unity power factor rectifier formed by integration of a three-switch buck-derived front-end and a DC/DC boost converter output stage

A new three-phase unity power factor rectifier with a three-switch buck-derived input stage and a DC/DC boost converter output stage is presented. This system has a wide input voltage range and a continuous sinusoidal time behavior of the input currents lying in phase with the input voltages which is also guaranteed in case of a failure in one phase of the mains. The input currents are controlled using a switching state sequence showing minimum switching losses. A multi-loop system control is realized by an outer output voltage controller and an inner-loop buck+boost inductor current controller. Furthermore active damping of the input filter resonance is provided. For increasing the output power of the system a parallel connection of two interleaved units is proposed. There, a low input current ripple is achieved, and the cut-off frequency of the input filter can be shifted to higher frequencies (resulting in improved control dynamics and a more compact design downsizing of the inductors and of the input filter).

Comparative evaluation of modulation methods for a three-phase/switch buck power factor corrector concerning the input capacitor voltage ripple

For a three-phase three-switch buck-type PWM rectifier with unity power factor, the RMS value of the input filter capacitor voltage ripple is calculated for different modulation methods. A modulation method being optimal concerning the occurring switching losses and the RMS value of the capacitor voltage ripple is identified and guidelines for the dimensioning of the input filter are derived.

A novel control concept for reliable operation of a three-phase three-switch buck-type unity-power-factor rectifier with integrated boost output stage under heavily unbalanced mains condition

In this paper the reliable operation of a three-phase three-switch buck-type pulsewidth-modulation unity-power-factor rectifier with integrated boost output stage under heavily unbalanced mains, i.e., mains voltage unbalance, loss of one phase, short circuit of two phases, or earth fault of one phase is investigated theoretically and experimentally. A brief description of the principle of operation and the most advantageous modulation method are given. The analytical calculation of the relative on-times of the active switching states and of the dc-link current reference value is treated in detail for active and deactivated boost output stage. Based on the theoretical considerations a control scheme which allows for controlling the system for any mains condition without changeover of the control structure is described. Furthermore, digital simulations as well as experimental results are shown which confirm the proposed control concept for different mains failure conditions and for the transition from balanced mains to a failure condition and vice versa. The experimental results are derived from a 5-kW prototype (input voltage range (280...480) V/sub rms/ line-to-line, output voltage 400 V/sub DC/) of the rectifier system, where the control is realized by a 32-bit digital signal processor.

Understanding Self-Assembled Amphiphilic Peptide Supramolecular Structures from Primary Structure Helix Propensity

Small amphiphilic peptides are attractive building blocks to design biocompatible supramolecular structures via self-assembly, with applications in, for example, drug delivery, tissue engineering, and nanotemplating. We address the influence of systematical changes in the amino acid sequence of such peptides on the self-assembled macromolecular structures. For cationic-head surfactant-like eight-residue peptides, the apolar tail amino acids were chosen to systematically vary the propensity to form an alpha-helical secondary structure while conserving the overall hydrophobicity of the sequence. Characterization of the supramolecular structures indicates that for short peptides a beta-sheet secondary structure correlates with ribbonlike assemblies while random-coil and alpha-helical secondary structures correlate with assembly of rods.

Advances in nanopatterned and nanostructured supported lipid membranes and their applications.

Abstract Lipid membranes are versatile and convenient alternatives to study the properties of natural cell membranes. Self-assembled, artificial, substrate-supported lipid membranes have taken a central role in membrane research due to a combination of factors problem are seemingly incompatible with each other. For example, methods to produce spacers which give suitable wetting conditions of the substrate will be more compatible with for example spotting arrays than other patterning methods. And it is likely that spreading of membranes on polymer cushions opens up new ways of creating artificial replicas of complex natural membranes which have been challenging on solid supports, as it already seems that tethered membranes can help prepare and improve stability of, for example, aperture spanning membranes. The merger of these approaches has only just started. In summary, SLBs combine added stability, defined localization and application of surface sensitive and on the nanoscale localized measurement techniques, which ensures that they will continue to attract much attention and research effort in the years to come. And while there is no shortage of remaining scientific challenges in the field, there is also no lack of creative solutions being developed to meet these challenges.

Pleckstrin homology-phospholipase C-δ1 interaction with phosphatidylinositol 4,5-bisphosphate containing supported lipid bilayers monitored in situ with dual polarization interferometry.

We have determined the kinetics and affinity of binding of PH-PLCδ(1) to the PIP(2) headgroup lipids using an optical surface-sensitive technique in a time-resolved manner. The use of dual polarization interferometry to probe supported lipid bilayers (SLBs) of different compositions allowed determination of accurate affinity constants and a layer structure of the peptide binding to the model membrane platform. In addition, the platform enabled us to monitor the detailed adsorption kinetics characterized by a strong initial electrostatic attraction of the peptide to the SLB surface followed by rearrangement and loss of possibly clustered peptides upon specific binding to the phosphoinositide headgroup. These kinetics differed substantially from adsorption kinetics for nonspecific binding to similarly charged control SLBs.

A novel control concept for reliable operation of a three-phase three-switch buck-type unity power factor rectifier with integrated boost output stage under heavily unbalanced mains condition

In this paper the reliable operation of a three-phase three-switch buck-type PWM unity power factor rectifier with integrated boost output stage under heavily unbalanced mains, i.e. mains voltage unbalance, loss of one phase, short circuit of two phases or earth fault of one phase is investigated theoretically and experimentally. The analytical calculation of the relative on-times of the active switching states and of the DC link current reference value is treated in detail for active and deactivated boost output stage. Based on the theoretical considerations a control scheme which allows to control the system for any mains condition without change-over of the control structure is described. Furthermore, digital simulations as well as experimental results are shown which confirm the proposed control concept for different mains failure conditions and for the transition from balanced mains to a failure condition and vice versa. The experimental results are derived from a 5 kW prototype, input voltage range 208-480 V/sub rms/ line-to-line, output voltage 400 V/sub DC/ of the rectifier system, where the control is realized by a 32-bit digital signal processor.