Browsing by Department "Energie-Umweltmanagement"
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- PublicationA Case Study of Socially-Accepted Potentials for the Use of End User Flexibility by Home Energy Management Systems(MDPI, 2020-12-25)
; ; ; ; ; Due to the increase of volatile renewable energy resources, additional flexibility will be necessary in the electricity system in the future to ensure a technically and economically efficient network operation. Although home energy management systems hold potential for a supply of flexibility to the grid, private end users often neglect or even ignore recommendations regarding beneficial behavior. In this work, the social acceptance and requirements of a participatively developed home energy management system with focus on (i) system support optimization, (ii) self-consumption and self-sufficiency optimization, and (iii) additional comfort functions are determined. Subsequently, the socially-accepted flexibility potential of the home energy management system is estimated. Using methods of online household survey, cluster analysis, and energy-economic optimization, the socially-accepted techno-economic potential of households in a three-community cluster sample area is computed. Results show about a third of the participants accept the developed system. This yields a shiftable load of nearly 1.8 MW within the small sample area. Furthermore, the system yields the considerably larger monetary surplus on the supplier-side due to its focus on system support optimization. New electricity market opportunities are necessary to adequately reward a systemically useful load behavior of households.175 1Scopus© Citations 7 - PublicationA fast test technique for life time estimation of ultrasonically welded Cu-Cu interconnectsIn this research the quality of the interconnects of the ultrasonically welded Cu terminals to the Cu substrate in the IGBT-module has been investigated. An ultrasonic resonance fatigue system in combination with a laser Doppler vibrometer and a special specimen design was used for shear fatigue testing of these large ultrasonic Cu-Cu welds (about 0.5 cm2). Fatigue life curves up to 109 loading cycles were obtained in a very short period of time. Using this technique it was possible to evaluate the fatigue strength of these interconnects for the first time. The microstructural features of the interconnects were characterized and their crack growth behaviour was studied. Fracture analysis of the fatigued specimen shows that failure occur due to the propagation of the crack beneath the welding interface into the copper substrate. Additionally performed finite element simulations offer an insight into the stress and strain concentrations during the mechanical fatigue tests. As this method is not restricted to the welding geometry, material joints with larger interconnects can be tested likewise. Thus this new technique can be used as a practical and valid fatigue testing method for evaluation of various interconnects.
50 2Scopus© Citations 1 - PublicationA New Algebraic Reynolds Stress Turbulence Model for Prediction of Wall-Affected Three Dimensional Room AirflowsIn the past various experimental investigations about room airflows were published. But most investiagtions are limited regarding measurements positions (restricted gflow patttern) and the availability of turbulent quantities (Reynolds-Stresses, entrainment, macroscopic instabilities etc.) based on the avaiable experimental data a targeted improvement of turbulence models is difficult. Therefore a complex three dimensional room airflow situation was investigatedwith three-dimensional Particle Image Velocmetry. Detailed informatiom of the floww, the Reynolds-stress distribution and the entertainment are presented. Based on the experimental results the behaviour of RANS-based turbulence models in predicting roomairflow is discussed. In this context, it is shown that intensive anisotropic Reynolds stresses near the wall arise and influences the airflow pattern. For this reason a new algebraic Reynolds stress turbulence model - which can in princible reproduce the turbulence anisotropic behaviour- is proposed. Compared with the linear eddy viscoity turbulence models the new nonlinear model agrees clearly better with the presented experimental findings.
128 1 - PublicationA New Approach for Evaluation of Fatigue Life of Al Wire Bonds in Power Electronics(Elsevier, 2014-03)
; ;Khatibi, Golta ;Kotas, Agnieszka Betzwar ;Weiss, BrigitteLederer, MartinUltrasonically bonded Al wire bonds on Al metallization pads are widely used in power semiconductors. The required long time reliability of the devices is highly dependent on the interfacial quality of Al wire and the bond pad. Reliability of wire bonds is commonly assessed by thermal and power cycling tests. Accelerated mechanical fatigue testing can be used as an alternative to these time consuming procedures. In the present study, lifetime of thick Al wedge bonds on Si substrates was investigated using a novel mechanical fatigue testing technique operating at high frequencies and elevated temperatures. The influence of microstructure, testing temperature and frequency on lifetime of Al wire bonds was investigated. Finite element analysis was applied to calculate the stress distribution at the interfacial region and to establish life time prediction curves. The results of mechanical isothermal fatigue curves were compared and correlated with thermal cycling data of Al wire bonds. © 2014 The Minerals, Metals & Materials Society.45 1Scopus© Citations 6 - PublicationA new approach for evaluation of fatigue life of al wire bonds in power electronics(Elsevier, 2014-02-16)
; ;Khatibi, Golta ;Lederer, Martin ;Kotas, Agnieszka BetzwarWeiss, BrigitteUltrasonically bonded A1 wire bonds on A1 metallization pads are widely used in power semiconductors. The required long time reliability of the devices is highly dependent on the interfacial quality of A1 wire and the bond pad. Reliability of wire bonds is commonly assessed by thermal and power cycling tests. Accelerated mechanical fatigue testing can be used as an alternative to these time consuming procedures. In the present study, lifetime of thick A1 wedge bonds on Si substrates was investigated using a novel mechanical fatigue testing technique operating at high frequencies and elevated temperatures. The influence of microstructure, testing temperature and frequency on lifetime of A1 wire bonds was investigated. Finite element analysis was applied to calculate the stress distribution at the interfacial region and to establish life time prediction curves. The results of mechanical isothermal fatigue curves were compared and correlated with thermal cycling data of Al wire bonds. Copyright © 2014 by The Minerals, Metals & Materials Society.72 1Scopus© Citations 2 - PublicationA novel approach for evaluation of material interfaces in electronics(2016-03-05)
; ;Khatibi, Golta ;Lassnig, Alice ;Lederer, Martin ;Nicolics, Johann ;Magnien, JulienSuhir, EphraimThe rapid technological advancements and market demands in electronic sector requires application of highly accelerated, still practice relevant reliability assessment methods. At present, accelerated power and temperature cycling tests count as the state of the art for qualification of the devices. However due to physical characteristics of the devices, there are limitations to accelerated thermal and power cycling tests. Further acceleration by exceeding a critical temperature or time reduction may result in occurrence of failure mechanisms other than those encountered in real application or suppressing these failures. An alternative approach for further acceleration of the testing procedures is based on the application of isothermal mechanical fatigue testing at high frequencies (AMT). The principle idea of this approach is replacement of thermally induced strains by means of equivalent mechanical strains. Based on a physics of failure approach, the relevant failure modes in the material interfaces are induced enabling detection of weak sites of the devices in a very short duration of time. In addition of time saving factor a further advantage of mechanical fatigue testing is the possibility of decoupling of thermal, mechanical and environmental stress factors for a more effective investigation and diagnosis. This paper presents an overview of our recent reliability studies on different types of electronic components by using the proposed methodology with the aim to give an insights into the advantages and some restrictions of AMT for qualification of electronic devices.61 1Scopus© Citations 4 - PublicationA novel linear predictive control approach for auxiliary energy supply to a solar thermal combistorage(Elsevier, 2014)
;Pichler, Martin Felix ;Lerch, Werner ;Heinz, Andreas; ;Schranzhofer, HermannRieberer, RenéThis paper presents and investigates a novel, hybrid model predictive approach to control the auxiliary heating for a combistorage. Faulty design, as well as suitable design schemes cause situations in which solar energy supply has to “compete against” the auxiliary energy supply. This research demonstrates a feasible method to remedy such situations with the utilization of weather forecast data. The developed approach is modular and expandable to be used with additional heat sources. A suitable disturbance-prediction, which approximates the expected solar energy flux into the storage, in connection with a linear model predictive control (MPC), can prevent the auxiliary system to switch on at an early stage and thus reduce the auxiliary energy demand and keep storage capacity for solar thermal energy supply. Results obtained through simulations for selected months show a reduction of auxiliary energy demand up to 40%, when facilitating this approach for a solar thermal combisystem for a single family house. Monthly solar fractions (Fs) increase by approximately 4% points or 5% with respect to the base case.68 1Scopus© Citations 17 - Publication
154 965 - PublicationA Thermal Flow Sensor Based on Printed Circuit Technology in Constant Temperature Mode for Various Fluids(MDPI, 2019)
;Glatzl, Thomas ;Beigelbeck, Roman ;Cerimovic, Samir ;Steiner, Harald; ;Sauter, Thilo ;Treytl, AlbertKeplinger, FranzWe present a thermal flow sensor designed for measuring air as well as water flow velocities in heating, ventilation, and air conditioning (HVAC) systems. The sensor is designed to integrate the flow along the entire diameter of the pipe also quantifying the volume flow rate of the streaming fluid where the calorimetric principle in constant temperature operation is utilized as a readout method. In the constant temperature mode, a controller keeps a specific excess temperature between sensing elements at a constant level resulting in a flow dependent heater voltage. To achieve cost-effective sensors, the fabrication of the transducer is fully based on printed circuit board technology allowing low-cost mass production with different form factors. In addition, 2D-FEM simulations were carried out in order to predict the sensor characteristic of envisaged setups. The simulation enables a fast and easy way to evaluate the sensor’s behaviour in different fluids. The results of the FEM simulations are compared to measurements in real environments, proving the credibility of the model.452 1Scopus© Citations 8 - PublicationAccelerated mechanical fatigue interconnect testing method for electrical wire bonds(2018-04-25)
; Khatibi, GoltaEvery new development in device performance and packaging design, can drastically affect the reliability of devices due to implementation of new materials and design changes. High performance and high reliability demands in power electronics over several decades and a short time to market development, raise the need for very fast reliability testing methods. In this study a mechanical fatigue testing method is presented for evaluating the interfacial fatigue resistance of heavy Al wire bonded interconnects in high power modules. By separating the concurrent thermal, mechanical and environmental failure mechanisms a selective investigation of the desired failure mode is possible. The setup is designed to reproduce the thermo-mechanical shear stresses by mechanical means, while provoking the same lift-off failure mode as in power cycling tests. With a frequency variable test setup of a few Hz up to several kHz, measurements from 103 up to 108 loading cycles and determining the influence of the testing frequency on the fatigue life are possible. A semi-automated bond wire fatigue tester operating at 60 kHz is presented which is suitable for rapid screening and qualification of a variety of wire bonds at the stages of development and during the production. © 2018 Walter de Gruyter GmbH, Berlin/Boston.60 1Scopus© Citations 19 - Publication
60 1Scopus© Citations 21 - PublicationAn interdisciplinary approach of a local peer-to-peer energy trading model for a more sustainable power grid(SDEWES Centre, 2021-10)
; ; ; ; ; This work investigates a novel distance-based electricity tariff applicable to energy communities. Based on a mixed integer linear optimization model computational studies are conducted to investigate the effects of this tariff on a small-scale community consisting of 22 consumers and 5 prosumers. Additionally, the potential of electric storage systems supporting the use of locally produced energy is investigated. The results of the computational model prove that an energy community generates incentives photovoltaic plants and the installation of energy storage systems. Complementary to the simulations, the flexibility options are supported by a user survey focusing on technology attributes for local energy market models, proving that there is a significant awareness for the use of energy storage systems.562 34251 - PublicationApplication of in-situ non-invasive failure detection methods for wire bonds(2020-09-15)
; ;Chavan, Vinayak ;Gasser, Christoph ;Rosc, JördisKhatibi, GoltaTwo in-situ failure detection methods by measuring acoustic emissions and transducer responses are presented to investigate the wire bond degradation failure during a highly accelerated mechanical fatigue test. This BAMFIT fatigue test is used to induce cyclic shear stresses in the bond interface until wire bond lift-off, operating at 60 kHz. The task was to incorporate non-invasive failure detection to identify the degree of degradation prior to end of life as an extension to the BAMFIT method and a possible quality control method. The acoustic emission investigations uses a Fabry Perot interferometer to detect high frequency emissions in the vicinity of the wire bond and detecting changes in the first three harmonics to identify a bond degradation. The transducer response approach observes systematic changes in the vibration and the damping behavior of the coupled resonance system by using the transducer as a piezo sensor. The results have shown that defective bond interconnect can be identified as early as ~50% of end of life, using high power but very short vibration pulses, and at ~80% for low power and completely non-invasive pulses. The obtained responses from the presented methods were correlated to the degree of degradation of the bond wire interface, by completing BAMFIT tests until end of life, cross section analysis as well as non-destructive X-ray computer tomography.68 1Scopus© Citations 1 - PublicationAssessing the technical feasibility of value chains for Reed based biofuels(2015)
; ;Kitzler, Hannes ;Beckmann, Georg; ;Pfeifer, Christoph259 1355 - PublicationAssessment and optimisation of energy efficiency in heat treatment plants(2013)
; ;Buchner, KlausAltena, Herwig153 1