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Boost converters suffer from a bandwidth limitation caused by the right-half plane zero (RHPZ), which occurs in the control-to-output transfer function. In contrast, there are many applications that require superior dynamic behavior. Further, size and cost of boost converter systems can be minimized by reduced voltage deviations and fast transient responses in case of large signal load transients. The key idea of the proposed ΔV/Δt-intervention control concept is to adapt the controller output to its new steady state value immediately after a load transient by prediction from known parameters. The concept is implemented in a digital control circuit, consisting of an ASIC in a 110 nm-technology and a Xilinx Spartan-6 field programmable gate array (FPGA). In a boost converter with 3.5V input voltage, 6.3V output voltage, 1.2A load, and 500 kHz switching frequency, the output voltage deviations are 2.8x smaller, scaling down the output capacitor value by the same factor. The recovery times are 2.4x shorter in case of large signal load transients with the proposed concept. The control is widely applicable, as it supports constant switching frequencies and allows for duty cycle and inductor current limitations. It also shows various advantages compared to conventional control and to selected adaptive control concepts.
This article proposes several modified quasi Z-source dc/dc boost converters. These can achieve soft-switching by using a clamp-switch network comprised of an active switch and a diode in parallel with a capacitor connected across one of the inductors of the Z-source network. In this way, ringing at the transistor switching node is mitigated, and the voltage at the turn-on of the transistor is reduced. Even a zero voltage switching (ZVS) of the main transistor is possible if the capacitor in the clamp-switch network is adequately chosen. The proposed circuit structure and operating mode are described and validated through simulations and measurements on a low-power prototype.
Der elektrische Wirkungsgrad stellt eines der wichtigsten Bewertungskriterien für BHKW dar, da über diese Größe ausgedrückt wird, wie viel des Wertproduktes „elektrische Energie“ bezogen auf die eingesetzte oder aufzuwendende Brennstoffenergie produziert werden kann. Ein hoher elektrischer Wirkungsgrad ist somit gleichbedeutend mit hohen Erlösen aus dem Verkauf der erzeugten elektrischen Energie und damit eine grundlegende Voraussetzung für einen wirtschaftlichen Betrieb eines BHKWs. Folglich sind die Hersteller von BHKW bestrebt, den elektrischen Wirkungsgrad ihrer Geräte kontinuierlich zu verbessern und nach oben zu treiben. Dieses Bemühen zeigt sich eindrucksvoll an der Entwicklung der mechanischen Effizienz von Gasmotoren der Firma GE Jenbacher. Während mit Motoren der Baureihe 6 im Leistungsbereich 1,8 – 4,4 MWel im Jahr 1988 eine mechanische Effizienz von 34% erreichbar war, liegt dieser Wert mittlerweile bei etwa 47,5%. Diese enorme Steigerung konnte im Wesentlichen durch eine Erhöhung des mittleren effektiven Zylinderarbeitsdrucks von etwa 10 bar im Jahr 1988 auf derzeit 24 bar erzielt werden. Dabei hilft der Magerbetrieb, der gleichzeitig ein Zurückdrängen der NOx-Emissionen bewirkt, die Klopfgrenze zu höheren Drücken hin zu verschieben. Eine sichere Zündung des Gas-Luft-Gemisches wird durch die Vorkammerzündung erreicht.
”I have never seen one who loves virtue as much as he loves beauty,” Confucius once said. If beauty is more important as goodness, it becomes clear why people invest so much effort in their first impression. The aesthetic of faces has many aspects and there is a strong correlation to all characteristics of humans, like age and gender. Often, research on aesthetics by social and ethic scientists lacks sufficient labelled data and the support of machine vision tools. In this position paper we propose the Aesthetic-Faces dataset, containing training data which is labelled by Chinese and German annotators. As a combination of three image subsets, the AF-dataset consists of European, Asian and African people. The research communities in machine learning, aesthetics and social ethics can benefit from our dataset and our toolbox. The toolbox provides many functions for machine learning with state-of-the-art CNNs and an Extreme-Gradient-Boosting regressor, but also 3D Morphable Model technolo gies for face shape evaluation and we discuss how to train an aesthetic estimator considering culture and ethics.
Today the optimization of metal forming processes is done using advanced simulation tools in a virtual process, e.g. FEM-studies. The modification of the free parameters represents the different variants to be analysed. So experienced engineers may derive useful proposals in an acceptable time if good initial proposals are available. As soon as the number of free parameters growths or the total process takes long times and uses different succeeding forming steps it might be quite difficult to find promising initial ideas. In metal forming another problem has to be considered. The optimization using a series of local improvements, often called a gradient approach may find a local optimum, but this could be far away from a satisfactory solution. Therefore non-deterministic approaches, e.g. Bionic Optimization have to be used. These approaches like Evolutionary Optimization or Particle Swarm Optimization are capable to cover a large range of high dimensional optimization spaces and discover many local optima. So the chance to include the global optimum increases when using such non-deterministic methods. Unfortunately these bionic methods require large numbers of studies of different variants of the process to be optimized. The number of studies tends to increase exponentially with the number of free parameters of the forming process. As the time for one single study might be not too small as well, the total time demand will be inacceptable, taking weeks to months even if high performance computing will be used. Therefore the optimization process needs to be accelerated. Among the many ideas to reduce the time and computer power requirement Meta- and Hybrid Optimization seem to produce the most efficient results. Hybrid Optimization often consists of global searches of promising regions within the parameter space. As soon as the studies indicate that there could be a local optimum, a deterministic study tries to identify this local region. If it shows better performance than other optima found until now, it is preserved for a more detailed analysis. If it performs worse than other optima the region is excluded from further search. Meta-Optimization is often understood as the derivation of Response Surfaces of the functions of free parameters. Once there are enough studies performed, the optimization is done using the Response Surfaces as representatives e.g. for the goal and the restrictions of the optimization problem. Having found regions where interesting solutions are to be expected, the studies available up to now are used to define the Response Surfaces. In many cases low degree polynomials are used, defining their coefficients by least square methods. Both proposals Hybrid Optimization and Meta-Optimization, sometimes used in combination often help to reduce the total optimization processes by large numbers of variants to be studied. In consequence they are highly recommended when dealing with time consuming optimization studies.
Verification of an active time constant tuning technique for continuous-time delta-sigma modulators
(2022)
In this work we present a technique to compensate the effects of R-C / g m -C time-constant (TC) errors due to process variation in continuous-time delta-sigma modulators. Local TC error compensation factors are shifted around in the modulator loop to positions where they can be implemented efficiently with finely tunable circuit structures, such as current-steering digital-to-analog converters (DAC). We apply our technique to a third-order, single-bit, low-pass continuous-time delta-sigma modulator in cascaded integrator feedback structure, implemented in a 0.35-μm CMOS process. A tuning scheme for the reference currents of the feedback DACs is derived as a function of the individual TC errors and verified by circuit simulations. We confirm the tuning technique experimentally on the fabricated circuit over a TC parameter variation range of ±20%. Stable modulator operation is achieved for all parameter sets. The measured performances satisfy the expectations from our theoretical calculations and circuit-level simulations.
The coupling of the heat and power sector is required as supply and demand in the German electricity mix drift further and further apart with a high percentage of renewable energy. Heat pumps in combination with thermal energy storage systems can be a useful way to couple the heat and power sectors. This paper presents a hardware-in the-loop test bench for experimental investigation of optimized control strategies for heat pumps. 24-hour experiments are carried out to test whether the heat pump is able to serve optimized schedules generated by a MATLAB algorithm. The results show that the heat pump is capable of following the generated schedules, and the maximum deviation of the operational time between schedule and experiment is only 3%. Additionally, the system can serve the demand for space heating and DHW at any time.
Universelle OTA-Testbench
(2014)
Es wird eine universell einsetzbare Testbench zur Simulation von integrierten Schaltungen innerhalb der OTA-Schaltungsklasse (Operational Transconductance Amplifier; Transkonduktanzverstärker) vorgestellt. Transkonduktanzverstärker sind in der analogen Schaltungstechnik weit verbreitet und daher von großer Bedeutung. Sie treten sowohl als eigenständige Schaltungen innerhalb eines Chips, sowie als Bestandteil anderer Schaltungen (z.B. als erste und zweite Stufe von Operationsverstärkern) auf. Es kann davon ausgegangen werden, dass heute kaum ein analoger oder Mixed-Signal-Chip gefertigt wird, in dem keine Transkonduktanzverstärker verbaut sind. Die Entscheidungsfindung des Entwicklers bei der Auslegung eines OTAs beruht maßgeblich auf einer anwendungsspezifischen Simulation. Die Erstellung einer eigenen Testbench für jede Anwendung bedeutet allerdings einen hohen Zeitaufwand und erschwert den Vergleich der Simulationsergebnisse unterschiedlicher Schaltungsvarianten. Durch eine universelle Testbench kann zum einen der Zeitaufwand verringert werden, zum anderen können nun Simulationsergebnisse direkt miteinander verglichen werden. Hierdurch wird die Entscheidungsfindung des Entwicklers objektiviert und beschleunigt. Neben dem Vergleich unterschiedlicher Schaltungen innerhalb einer Technologie ist auch der Vergleich einer Schaltung in unterschiedlichen Technologien denkbar. Die Idee einer universell anwendbaren Testbench lässt sich auch auf andere analoge Schaltungsklassen anwenden und damit als Prinzip verallgemeinern.
The experimental characterization of the thermal impedance Zth of large power MOSFETs is commonly done by measuring the junction temperature Tj in the cooling phase after the device has been heated, preferably to a high junction temperature for increased accuracy. However, turning off a large heating current (as required by modern MOSFETs with low on-state resistances) takes some time because of parasitic inductances in the measurement system. Thus, most setups do not allow the characterization of the junction temperature in the time range below several tens of μs.
In this paper, an optimized measurement setup is presented which allows accurate Tj characterization already 3 μs after turn-off of heating. With this, it becomes possible to experimentally investigate the influence of thermal capacitances close to the active region of the device. Measurement results will be presented for advanced power MOSFETs with very large heating currents up to 220 A. Three bonding variants are investigated and the observed differences will be explained.
This paper aims at presenting a solution that enables end customers of the energy system to participate in new local micro-energy-markets by providing them with a distributed, decentralized, transparent and secure Peer to Peer (P2P) payment system, which functions automatically applying new concepts of Machine to Machine (M2M) communication technologies. This work was performed within the German project VK_2G, funded by the DBU. The key results were: Providing means to perform microtransactions in a P2P fashion between end consumers and prosumers in local communities at low cost in a transparent and secure manner; Developing a platform with pre-defined smart contracts able to be tailored to different end customers ‘needs in an easy way and; Integrating both the market platform as well as the local control of generation and loads. This solution has been developed, integrated and tested in a laboratory prototype. This paper discusses this solution and presents the results of the first test.
The aim of this work is the development of artificial intelligence (AI) application to support the recruiting process that elevates the domain of human resource management by advancing its capabilities and effectiveness. This affects recruiting processes and includes solutions for active sourcing, i.e. active recruitment, pre-sorting, evaluating structured video interviews and discovering internal training potential. This work highlights four novel approaches to ethical machine learning. The first is precise machine learning for ethically relevant properties in image recognition, which focuses on accurately detecting and analysing these properties. The second is the detection of bias in training data, allowing for the identification and removal of distortions that could skew results. The third is minimising bias, which involves actively working to reduce bias in machine learning models. Finally, an unsupervised architecture is introduced that can learn fair results even without ground truth data. Together, these approaches represent important steps forward in creating ethical and unbiased machine learning systems.
In this work, a comparison between different brushless harmonic-excited wound-rotor synchronous machines is performed. The general idea of all topologies is the elimination of the slip rings and auxiliary windings by using the already existing stator and rotor winding for field excitation. This is achieved by injecting a harmonic airgap field with the help of power electronics. This harmonic field does not interact with the fundamental field, it just transfers the excitation power across the airgap. Alternative methods with varying number of phases, different pole-pair combinations, and winding layouts are covered and compared with a detailed Finite-Element-parameterized model. Parasitic effects due to saturation and coupling between the harmonic and main windings are considered.
The increase in distributed energy generation, such as photovoltaic systems (PV) or combined heat and power plants (CHP), poses new challenges to almost every distribution network operator (DNO). In the low-voltage (LV) grids, where installed PV capacity approaches the magnitude of household load, reverse power flow occurs at the secondary substa-tions. High PV penetration leads to voltage rise, flicker and loading problems. These problems have been addressed by the application of various techniques amongst which is the deployment of step voltage regulators (SVR). SVR can solve the voltage problem, but do not prevent or reduce reverse power flows. Therefore, the application of SVR in low voltage grids can result in significant power losses upstream. In this paper we present part of a research project investi-gating the application of remote-controlled cable cabinets (CC) with metering units in a low-voltage network as a possible alternative for SVR. A new generation of custom-made remote-control cable cabinets has been deployed and dynamic network reconfigurations (NR) have been realized with the following objectives: (i) reduction of reverse power flow through the secondary substation to the upstream network and therefore a reduction of upstream losses, (ii) reduction of the voltage rise caused by distributed energy resources and (iii) load balancing in the low-voltage grid. Secondary objec-tives are to improve the DNO's insight into the state of the network and to provide further information on future smart grid integration.
In der Mikroelektronik werden Chips häufig in Mold-Gehäusen verpackt. Die elektrischen Verbindungen vom Chip zu den Anschlussbeinchen des Gehäuses werden mit Bonddrähten realisiert. Für die Berechnung der Gleichgewichtstemperatur in einem Bonddraht bei konstantem Strom sowie von Temperaturverläufen bei transienten Strömen ist die herkömmliche FEM-Methode langsam und unhandlich. Daher wurde der Bondrechner entwickelt, der ein zylindersymmetrisches Ersatz-Modell für das Package in geeigneten mathematischen Gleichungen abbildet.
Im Gegensatz zum Bondrechner der ersten Generation [1], der auf den Gleichungen von [2] basiert, bietet ein neuer mathematischer Ansatz die Möglichkeit, eine endliche effektive Package-Größe, sowie einen endlichen Wärmeübergang zwischen Bonddraht und Mold-Masse zu berücksichtigen. Ebenso wurde die Berechnung der Interaktion von mehreren benachbarten Drähten verfeinert. Die Berechnung von beliebigen transienten Pulsformen mittlerer Länge wurde ebenfalls verbessert. Eine quadratische Komponente in der Temperaturabhängigkeit des spezifischen Widerstandes des Drahtmaterials kann jetzt ebenfalls berücksichtigt werden.
Die Ergebnisse wurden erfolgreich mit FEM-Berechnungen verglichen und die Geschwindigkeit der Berechnung ist um Größenordnungen schneller als mit kommerziellen FEM-Programmen.
Electromigration (EM) is becoming a progressively severe reliability challenge due to increased interconnect current densities. A shift from traditional (post-layout) EM verification to robust (pro-active) EM aware design - where the circuit layout is designed with individual EM-robust solutions - is urgently needed. This tutorial will give an overview of EM and its effects on the reliability of present and future integrated circuits (ICs). We introduce the physical EM process and present its specific characteristics that can be affected during physical design. Examples of EM countermeasures which are applied in today’s commercial design flows are presented. We show how to improve the EM-robustness of metallization patterns and we also consider mission proiles to obtain application-oriented current density limits. The increasing interaction of EM with thermal migration is investigated as well. We conclude with a discussion of application examples to shift from the current post layout EM verification towards an EM aware physical design process. Its methodologies, such as EM-aware routing, increase the EM-robustness of the layout with the overall goal of reducing the negative impact of EM on the circuit’s reliability.
Electronic design automation approaches can roughly be divided into optimizers and procedures. While the former have enabled highly automated synthesis flows for digital integrated circuits, the latter play a vital (but mostly underestimated role) in the analog domain. This paper describes both automation strategies in comparison, identifying two fundamentally different automation paradigms that reflect the two basic design practices known as “top-down” and “bottom-up”. Then, with a focus on the latter, the history of procedural approaches is traced from their
early beginnings until today’s evolvements and future prospects to underline their practical importance and to accentuate their scientific value, both in itself and in the overall context of EDA.
Most Question-answering (QA) systems rely on training data to reach their optimal performance. However, acquiring training data for supervised systems is both time-consuming and resource-intensive. To address this, in this paper, we propose TFCSG, an unsupervised similar question retrieval approach that leverages pre-trained language models and multi-task learning. Firstly, topic keywords in question sentences are extracted sequentially based on a latent topic-filtering algorithm to construct unsupervised training corpus data. Then, the multi-task learning method is used to build the question retrieval model. There are three tasks designed. The first is a short sentence contrastive learning task. The second is the question sentence and its corresponding topic sequence similarity judgment task. The third is using question sentences to generate their corresponding topic sequence task. The three tasks are used to train the language model in parallel. Finally, similar questions are obtained by calculating the cosine similarity between sentence vectors. The comparison experiment on public question datasets that TFCSG outperforms the comparative unsupervised baseline method. And there is no need for manual marking, which greatly saves human resources.
3D assisted 2D face recognition involves the process of reconstructing 3D faces from 2D images and solving the problem of face recognition in 3D. To facilitate the use of deep neural networks, a 3D face, normally represented as a 3D mesh of vertices and its corresponding surface texture, is remapped to image-like square isomaps by a conformal mapping. Based on previous work, we assume that face recognition benefits more from texture. In this work, we focus on the surface texture and its discriminatory information content for recognition purposes. Our approach is to prepare a 3D mesh, the corresponding surface texture and the original 2D image as triple input for the recognition network, to show that 3D data is useful for face recognition. Texture enhancement methods to control the texture fusion process are introduced and we adapt data augmentation methods. Our results show that texture-map-based face recognition can not only compete with state-of-the-art systems under the same precon ditions but also outperforms standard 2D methods from recent years.