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Wide bandgap semiconductors, SiC and GaN-based power devices represent key candidates in the development of more efficient devices due to their superior electrical and thermal properties compared to silicon. To achieve maximal performance from WBG semiconductors, new packaging technologies and thermo-electric designs must be developed to ensure efficient and fast switching of devices while minimizing losses. The paper aims to investigate the thermal and mechanical behavior of new prepackage embedding technologies by finite element simulation. The focus is on insulated substrates including direct bonded copper (DBC) with various dielectrics such as AlN, Al 2O 3, Si3N 4 and new insulated metal substrates (IMS) with emphasis on commercially available materials and thicknesses. This study proposes a thermo-mechanical pareto-optimization methodology able to identify the best substrate configuration. The sintered silver layer (in both sides of the chip), which is the most prone to failure due to delamination, has been modelled with a temperature-dependent bilinear hardening model to account for plasticity. Pareto-optimization accounts for the module thermal resistance and the plastic strain or Von Mises Stress in the sintered layer. Results demonstrate that the best candidate from the thermo-mechanical point of view is the DBC with AlN showing a thermal resistance of 0.34 K/W, accumulative plastic strain of 0.18 % and Von Mises stress of 274 MPa. Finally, the parasitic inductance of multiple pre-packages is evaluated to scale the power of the module. Proper design allows to achieve a stray inductance as small as 1.23 nH for two prepackages and 2.85 nH for four prepackages.
Horizontal chip cracks have been reported in various scientific publications on PCB embedded power semiconductor devices. This study investigates in detail the root cause of the cracks. Experimental evidence indicates that the chip fractures in the mechanical grinding process during preparation of the cross-sections. Here, two different factors are relevant: First, the mechanical fracture strength of the semiconductor die decreases when grinding its edge. The use of P320 sand paper reduces the characteristic fracture strength from 719 MPa to 211 MPa. Second, the tensile stresses in the chip edge increase considerably when, part of the die and package is removed by grinding. Both effects together result in a failure probability of 100%. The use of finer grain sandpaper for target preparation helps to reduce the probability of generating horizontal chip cracks during cross-sectioning.
Safety of the Intended Functionality (SOTIF) addresses sensor performance limitations and deep learning-based object detection insufficiencies to ensure the intended functionality of Automated Driving Systems (ADS). This paper presents a methodology examining the adaptability and performance evaluation of the 3D object detection methods on a LiDAR point cloud dataset generated by simulating a SOTIF-related Use Case. The major contributions of this paper include defining and modeling a SOTIF-related Use Case with 21 diverse weather conditions and generating a LiDAR point cloud dataset suitable for application of 3D object detection methods. The dataset consists of 547 frames, encompassing clear, cloudy, rainy weather conditions, corresponding to different times of the day, including noon, sunset, and night. Employing MMDetection3D and OpenPCDET toolkits, the performance of State-of-the-Art (SOTA) 3D object detection methods is evaluated and compared by testing the pre-trained Deep Lea rning (DL) models on the generated dataset using Average Precision (AP) and Recall metrics.
The following paper points out the key role of IT in the future of car development. At the moment a fundamental change in the structure of automotive IT organizations can be observed. The fact that software update cycle in automotive, about 1 year, in comparison with Apple, Google or Tesla is too much. The entertainment industry is constantly proceeding ahead much faster than the automotive industry. On top of this, new emerging platforms like Apple CarPlay and Android Auto are providing the look and the feel of a mobile phone regarding the control of the car. The vehicle itself is getting more and more as an “ultimate mobile application or app”. This shows the need of speeding up the Time-to-Market of new innovations in automotive industry.
The structure of IT departments has to support these process. No wonder that CIOs of car manufacturers are looking for new structures in their IT departments that enable faster cycle update for automotive applications taking in consideration safety and security requirements.
This only represents a particular interest, as for Apple and Google, we can see that Google has already a fleet of 23 self-driving cars in place which has already autonomously driven more than one million miles with only 12 accidents on public roads and Apple is said to work under the project name "Titan" on its own electric car.
Another important aspect is the software running in the car itself, e.g. the software that “fuses” data from sensors into a comprehensible form: objects have to be accurately located in the environment model of the socalled ego vehicle as a basis for decisions making either by the driver himself or even by the software that can determine within a fraction of a second what the car is going to do. High definition maps also play a very important role in enabling autonomous driving, being developed and maintained by companies such as Nokia HERE, with accuracy of only a few centimeters are thought to be of strategic importance for Advanced Driver Assistance Systems and Self Driving Cars.
“We’re the engine room of the system,” says Mr. Ristevski, vice president of reality capture and processing for former Nokia’s mapping unit named HERE. To be independent from Apple and Google maps and with that from possible competitors, it is said to be the main reason why the German premium car manufacturer Audi, BMW and Daimler bought the online map service for about € 2.5 bn. This is only the first step in the restructuring of the automotive industry.
Trajectory Modelling for Autonomous Driving: Investigating the Artificial Potential Field Method
(2024)
Although the focus of autonomous driving is on maximizing safety and efficiency, comfort and familiarity will play a key role in the adoption of autonomous driving. Therefore, it is important to develop algorithms that can mimic human driving skills and adapt to individual driving styles. The potential field method (PFM) is an obstacle avoidance algorithm for autonomous driving that uses a repulsive potential field, as a environment model, to navigate the vehicle to the lowest risk potential. In this paper, the PFM is used in a overtake scenario at high speed, to test the impact of using prediction when calculating the ideal yaw rate. Analysis is done on how the potential field can be used for lane keeping while following a car and then for overtaking it. A driving simulator is used to record human driving data and compare it with automated driving using a PFM as is proposed by [3], with modifications to enable future prediction.
This paper reports the findings of an online between subject study that investigated the effectiveness of a non-humanoid socially assistive robot in providing positive reinforcement feedback to aid in improving performance on a cognitively demanding task. Four different feedback conditions were used, including verbal, expressive, neutral, and text-based feedback, to identify which type of feedback could positively influence behaviour. Results showed no significant differences in task performance, perceived workload or robot perception.
Produkte werden heutzutage immer variantenreicher und individueller. Für die industrielle Fertigung wachsen die Anforderungen, die Produkte effizient zu fertigen und schnell auf sich verändernde Marktbedingungen zu reagieren. Entsprechend rapide steigt die Nachfrage nach flexiblen Produktionslösungen, die sich möglichst autonom an die neuesten Marktanforderungen anpassen. Wandlungsfähige und modulare Produktionssysteme sollen es ermöglichen, auch bei großer Variantenvielfalt effizient zu produzieren - sogar bis zur Losgröße 1. Unterstützt wird die Produktion durch digitale Lösungen, die bereits an vielen Stellen zum Einsatz kommen.
Durch globale Unsicherheiten, steigende Variantenvielfalt und den Kundenbedarf nach ökologisch nachhaltig produzierten Produkten nehmen die Anforderungen an heutige Produktionssysteme stetig zu. Dies stellt bisherige Produktionsformen wie die Linienproduktion zunehmend vor Herausforderungen. Als hochflexible Produktionsform bietet sich die Matrixproduktion als alleinige oder in Kombination mit der Linie als hybride Produktionsform an.
The spectrometer-free chromatic confocal measurement technique enables 3D surface measurements with just one exposure and without scanning. To reduce the need for a spectrometer for the spectral analysis of the reflected light composition and thus the extraction of the local surface height, an optical spectral analysis unit is used. This unit determines the first momentum of the spectral composition reflected from the surface under probe for a large number of lateral measurement points simultaneously. This work investigates the impact of the spectral composition and light power of the light source on the sensitivity and accuracy of this method. A thorough optimization of the light source will be conducted, demonstrating the impact of various spectral compositions and light source power on the system performance, taking into account the system-related etendue. In addition, the optimization of the spectral transmission filter used in the optical spectral analysis unit and its influence on the accuracy and sensitivity of the system over the entire measurement range is shown.
The spectrometer free areal chromatic confocal metrology (ChromaCAM) is an optical 3D surface measurement technology, which allows a simultaneous measurement of a large array of measuring points within a single exposure. In this work, we investigate the accuracy of a first prototype sensor system utilizing this new singleshot 3D measurement technique. It is found that surface height measurement errors smaller 1μm within a total measurement range of about 1000 μm are achievable. Furthermore, several influential factors are investigated showing the advantages and limits of the presented system. Investigating different surface materials it is found that frame rates up to approximately 800 fps for highly reflecting surfaces and up to 30 fps for ceramics, aluminum, and plastics are achievable.
A considerable amount of enabling technologies are being explored in the era of fifth generation (5G) mobile system. The dream is to build a wireless network that substantially improves the existing mobile networks in all performance metrics. To address this 5G design targets, massive MIMO (multiple input multiple output) and mmWave (millimeter wave) communication are also candidate technologies. Luckily, in many respects these two technologies share a symbiotic integration. Accordingly, a logical step is to integrate mmWave communications and massive MIMO to form mmWave-massive MIMO which substantially increases user throughput, improve spectral and energy efficiencies, increase the capacity of mobile networks and achieve high multiplexing gains. Thus, this work analyses the concepts, performances, comparison and discussion of these technologies called: massive MIMO, mmWave Communications and mmWave-massive MIMO systems jointly. Besides, outcomes of extensive researches, emerging trends together with their respective benefits, challenges, proposed solutions and their comparative analysis is addressed. The performance of hybrid analog-digital beamforming architecture with a fully digital and analog beamforming techniques are also analyzed. Analytical and simulation results show that the low-complexity hybrid analog-digital precoding achieves all round comparable precoding gains for mmWave-Massive MIMO technology.
This study investigated the thermal performance of a packaging solution designed to manage the electrical isolation and cooling of high voltage ( ) SiC power semiconductor > 3300 V devices. The proposed packaging merges the ceramic substrate and the heat exchanger into a single component, streamlining the overall design. Specifically, a novel heat exchanger is developed for a multi-chip module (20 kV), utilizing a combination of jet impingement and channel- flow cooling techniques. Computational fluid dynamics (CFD) simulations and experimental validation are conducted on a multi-chip module to assess the thermal resistance of this new cooling solution. The results demonstrate a
low thermal resistivity of 0.118 cm2K/W, indicating the potential for improved cooling performance in high voltage and power density semiconductor applications.
The goal for solving the expansion planning (EP) problem in electrical systems involves the search for the optimal allocation of output power among available generators to serve the system load in a given time horizon. Currently, environmental aspects and the continuing search for alternative energy sources, push for the integration of wind power generators in the EP problem. In order to fulfill this new requirement, this paper developes a long-term energetic analysis for expansion planning under high wind power penetration scenarios in Colombia and its effect in neighboring countries. The simulations were developed using SDDP ™ software package, a tool based in stochastic dual dynamic programming technique for hydrothermal-wind least-cost dispatch.
The control of mechanical power in wind turbogenerators involves the participation of many subsystems. One of them is related to pitch mechanism, which usually employs conventional PI strategies. This paper presents an alternative for estimating the parameters of this PI controller, using Fuzzy Logic (FL). Matlab-Simulink™ software was used in order to verify the performance of the FL-based parameter estimator in some general cases.
One goal of research activities is finding ways to manage the growing complexity of embedded systems using self- configuration methods. While autonomous configuration could potentially be used in safety-critical and real-time systems, the basic requirements are not yet in place. This paper will outline a concept for the real autonomous configuration of TDMA-based communication processes, which currently does not exist. The paper initially addresses the TDMA-specific framework conditions and a potential solution. The issue of the mandatory a-priori known schedule is resolved using a generic schedule, because a simple method based on "free-slot-reserved-for- further-nodes" is not feasible. The most difficult part the startup was implemented through the generic schedule and an ID-based collision resolution process. To demonstrate the viability of the concept, the configuration method was implemented using a FlexRay communication system. This also satisfied the goal of eliminating the need for additional hardware and preserving the fault tolerant multimaster structure of the FlexRay system. The functionality of the concept was validated under different scenarios. The configuration times were analyzed, the results of which are also detailed here.
This work constitutes the second part of a study that aims to analyze the technical and economic implications of the penetration of wind power in the Colombian Interconnected System (SIN). In the previous part of the work, steady state studies were carried out (loading at transmission corridors, short circuit and the most important contingencies were applied). A summary with the main problems encountered and their respective solutions were proposed. In this second part, the same group of wind farms and time horizon were employed, while dynamic models were fit to ensure the proper operation of controls against the contingences. Using the software DigSilent™, studies of stability (with and without controls), power quality (flicker analysis), and voltage ride through capability (VRT) were addressed. Finally, technical recommendations and further work are presented.
This work is the first part of a study that aims to analyze the technical and economic implications of the penetration of wind power in the Colombian Interconnected system (SIN). Using the software DigSilent™, studies of steady state, contingencies and short-circuit were conducted in order to identify problems of stress, overload, voltage profiles, transmission bottlenecks and the most neuralgic elements for the operation of the proposed wind parks. Additional electrical studies, such as stability, power quality, voltage ride through capability, and the development of some indicators associated with the penetration of wind power in Colombia, will be addressed on a second part of this work.
This paper deals with the development of a system established on a telematic rehabilitation exerciser, a plug-PC and a real-time web-animation. An easy to use device, which allows a telematically controlled training at home is target of this project. It is thereby based on the diagnosis and therapy platform COMES ® of the Heinz Nixdorf-Lehrstuhl für Medizinische Elektronik of the Technische Universität München. In COMES ® mobile measured vital parameters are intelligently evaluated by an expert system before they are provided to the user along with medical information and trends. A Java application allows the real-time data, which is sent by a telematic exerciser and received over the Bluetooth interface of the plug-PC to be filtered and transmitted over a SQL-connection on, to a database. These data is retrieved by the animation and evaluated in form of a game. To visualize this web-animation, the screen of a potential terminal device is splitted in two and taking only a small horizontal part, this animation is shown on the screen. The other part could be filled by a TV-programm, Video or Skype window depending on the abilities of the terminal device which could be any device with an internet browser (e.g. a Smart TV).
No cost software tools and low cost measurement equipment enables improved teaching of circuit design. This paper presents results incorporating models, simulation and measurement together in teaching and laboratory. Comparison of circuit equations with measurement and simulation data addresses different learning styles and promotes advance in reflective judgment stages. It is closer to industrial work style and gives the student a feel for variations and accuracy in circuit design and measurement. A low cost electrical laboratory board (Electronic Explorer), a circuit simulator (LTSPICE) and a spreadsheet program can be used during lecture, laboratory and at home to align results and motivate students for a deep learning approach. This paper presents necessary modification for lecture and laboratory and looks at the results using these tools.
This paper deals with the development of a new mobility concept for disabled and elderly people. The focus of our project is a wheelchair which can climb stairs. In order to give the user maximum freedom regarding absolute mobility, the wheelchair has to suitable for indoor and outdoor usage and therefore be extremely manoeuvrable. A further goal is the integration of the wheelchair into a car. With its help the user is able to travel longer distances independently by car.
Telematic rehabilitation 2.0
(2013)
Today, the compliance of device-based therapy for extended periods lies often below 50 percent [1]. Furthermore every second household is equipped with both a powerful computer and a flat-screen TV ([3], [4]). This project is motivated by the idea to connect these facts. For an increased motivation to use the daily hours of media consumption simultaneously for rehabilitation, a data animation is combined with a browser window or media player. With the COMES® 1 interface, a therapist has additionally the possibility to interact with the user and animation. Moreover a usability test has been made, to examine the acceptance of both patients and therapists for a media supported rehabilitation. The objective of this project is to reduce the motivational threshold of a daily training and thus increase the compliance in long term rehabilitation.
Outcomes based teaching and learning requires monitoring of teaching and students learning. So far teaching can be monitored by video, document camera or screen recordings or by a coach. This creates hard to edit video content. Also static questionnaires are used for outcome monitoring and problem solving purposes. This paper presents a new approach using dynamic HTML5 web pages with JavaScript enabling creating editable and searchable open source content on the fly in real time during lecture. Data can easily be transferred from the web page to data processing tools. This allows explorations by students. Based on this automated problem generation and solving is shown in an example of root mean square voltage calculation. Results can be sent to a server to implement a live feedback system. All data and programs are embedded in the web document. Therefore it is much easier to reuse content, evaluate style and improve lectures increasing efficiency of teaching.
This article describes a design for integrating a telemedical rehabilitation system into a smart home concept. The focus thereby lies on the interface communication, the user benefit and the challenges of combining these complex systems. The objective of this project is, to create an easy-to-use and user-orientated system, which shows the potential of combining smart-home technology with a telemedical rehabilitation system for the user's benefit. Difficulties as well as best-practice solutions are further discussed in this article.
An open access minimum automatic task generation live feedback system for electrical engineering
(2015)
An open online electrical engineering automatic task generation tool with minimum hardware requirements and programming effort is presented. This system can be run on portable Linux access points with php or on a linux web server. Users can do the tasks with handheld devices or PCs also as live feedback system. A novel feature is a pre task submission use rid management system allowing open access to all exercises and selected evaluation of results. Results of use for exercises in a basic electrical engineering class are presented. The openness of the system allows reusability, customization and easy task creation in HTML and evaluation. Data analysis gives professor feedback about proficiency of students.
Writing software is as much a skill as it needs knowledge. Skills come by practice and effective practice needs repetitions and variations. However, many students are not always intrinsically motivated to practice enough and often not able to apply appropriate variations in practicing. This paper describes the principle of an online platform with the goal to generate the necessary amount of practicing and meaningful exercise variations in order to attain the required skills in programming for students in engineering courses. The platform offers a unique combination of ubiquitous availability, runtime modes, peer group data and instant feedback. Additionally it describes the results of a comparative study with and without using this tool.
The paper presents an approach for modelling a Battery Energy Storage System (BESS). This approach consists of four stages. In the first stage a detailed model is developed taking into consideration all the electrical details of the original system. In stage two the detailed model will be validated using real measurements. In the third stage the complexity of the detailed model is reduced resulting in a simplified model which is able to represent the relevant electrical dynamics of the original system and to decrease the simulation time significantly. In the last stage the simplified model is validated by a comparison with simulation results of the detailed model.
Impact of Load Matching Algorithms on the Battery Capacity with different Household Occupancies
(2019)
Due to an increasing use of renewable energy sources in the power grid, it is of high importance to balance supply and demand for grid utilities and microgrid operators. If there are mismatches in the balancing, microgrids with islanded operation capabilities would be preferrable. In islanded mode, nearly zero energy buildings commonly use a stand-alone photovoltaics power supply with a battery storage. A battery storage is expensive and the capacity in case of off-grid operation depends on the electricity consumption of the dwelling's occupants. Using thermostatically controlled appliances like a freezer, water heater and space heating as additional storage systems can reduce the capacity of the battery storage system or increase the operation time in islanded mode for a fixed battery size. This paper analyzes the battery capacity dependency both on the control algorithms for the thermal storages and on the occupancy of the dwelling. Possible battery reductions for different selected occupancies are presented in this work by comparing the simulation results of different load matching algorithms to each other and between the different occupancies. The analysis of those results enables recommendations on the most suitable algorithm for most occupancy scenarios of an existing dwelling with respect to a minimized battery capacity. This can be particularly useful, for example, for dwelling and apartment owners who are renting out dwellings.
Increasing shares of renewable energy sources in combination with rising popularity of demand response applications and flexibility programs forces higher awareness for production and consumption balancing. Accurate models for forecasting are not just necessary for PV- or wind power sources in smart cities, but also the prediction of loads respectively consumption, which can be based on time series analysis or machine learning methods. Three of those methods, namely a linear regression (LM), a long short-term memory network (LSTM) and a neural network model (NN), have been selected to see their performance on predicting the load of a large smart city on the example of the Estonian electricity consumption data. Hourly data of the year 2019 was used as training data to predict the first 20 days of 2020. For this kind of prediction, the LM showed the lowest root mean square error (RMSE) and had the lowest computational time. The neural network was slightly less accurate. The LSTM showed the worst performance in terms of accuracy and computational time. Thus, LSTM is not the preferred method for this kind of prediction and the recommendation for forecasting such loads would be a LM because the RMSE and computational effort needed are lower than for a NN
Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAV) have been a high potential topic in the aerospace industry during the last decades due to its multirotor and fixed-wing nature of the aircraft. Besides, having the ability to rapidly deploy from a tight airstrip and gathering Intelligence, Surveillance, and Reconnaissance (ISR) information is the best way to be one step ahead of the enemy. In this paper, we present the implementation and development of gasoline-electric hybrid propulsion VTOL Unmanned Aerial vehicle respectively. The Hybrid propulsion VTOL UAV offers image and real-time video transmission to the ground station with fully autonomous control to get the best view of the enemy from the sky. The gasoline-electric hybrid propulsion system provides long flight endurance with efficient power consumption. The fundamentals of the multirotor and the conventional fixed-wing aircraft present the theoretical background of the aircraft. The accomplished design consists of high-performance multirotor motors with an efficient gasoline engine. Furthermore, the control system architecture, avionics, and power distribution system presented with addressing cost-effective trending design techniques. The performance of the system has been improved using commercially off-the-shelf (COTS) hardware.
Oxygen scavengers are used to reduce the oxygen permeation of packaging (active barrier) and to absorb oxygen from its direct environment, e.g., a headspace of packaged food. Few oxygen scavenger coatings have been developed. Therefore, in this study, a novel oxygen scavenger coating has been developed. It is based on inorganic–organic polymers (ORMOCER®). The oxygen absorption reaction is activated by UV light. The scavenger was synthesized, coated on aluminum foil, subsequently dried and afterwards laminated with a polyethylene sealing layer. UV light activates the oxygen scavenging reaction. The oxygen absorption capacity, measured at 23 °C and 0% r.h., was 242 ± 8 mg oxygen/g scavenger coating. When the oxygen scavenger coating layer was laminated by using a two-component polyurethane laminating adhesive, the absorption capacity was hardly reduced, with a measured absorption capacity of 223 ± 18 mg oxygen/g scavenger coating. In an experimental packaging sample with the oxygen scavenger coating with a thickness (dry) of 3 µm and 18 µm, near-zero mbar oxygen partial pressure was reached by the non-laminated oxygen scavenger coatings within two days, and within about 20 days when laminated with a polyurethane laminating adhesive and a PE-layer on the oxygen scavenger layer. The oxygen partial pressure was kept near zero mbar for 500 days, whereas in the experimental packaging without oxygen scavenger, the oxygen partial pressure increased to 110 mbar during this time. The developed oxygen scavenger based on inorganic–organic polymers can be applied as wet chemical coating on various surfaces with standard application procedures. Application scenarios are oxygen-sensitive goods such as food, pharmaceutical products and cosmetics.
An artifact appearing during the cathodic transient of cyclic voltammograms (CVs) of low-loaded platinum on carbon (Pt/C) electrodes in proton exchange membrane fuel cells (PEMFCs) was examined. The artifact appears as an oxidation peak overlapping the reduction peak associated to the reduction of platinum oxide (PtOx). By varying the nitrogen (N2) purge in the working electrode (WE), gas pressures in working and counter electrode, upper potential limits and scan rates of the CVs, the artifact magnitude and potential window could be manipulated. From the results, the artifact is assigned to crossover hydrogen (H2X) accumulating in the WE, once the electrode is passivated towards hydrogen oxidation reaction (HOR) due to PtOx coverage. During the cathodic CV transient, PtOx is reduced and HOR spontaneously occurs with the accumulated H2X, resulting in the overlap of the PtOx reduction with the oxidation peak. This feature is expected to occur predominantly in CV analysis of low-loaded electrodes made of catalyst material, whose oxide is inactive towards HOR. Further, it is only measurable while the N2 purge of the WE is switched off during the CV measurement. For higher loaded electrodes, the artifact is not observed as the electrocatalysts are not fully inactivated towards HOR due to incomplete oxide coverage, and/or the currents associated with the oxide reduction are much larger than the spontaneous HOR of accumulated H2X. However, owing to the forecasted reduction in noble metal loadings of catalyst in PEMFCs, this artifact is expected to be observed more often in the future.
We present a model of the cathode catalyst layer morphology before and after loading a porous catalyst support with Pt and ionomer. Support nanopores and catalyst particles within pores and on the support surface are described by size distributions, allowing for qualitative processes during the addition of a material phase to be dependent on the observed pore and particle size. A particular focus is put on the interplay of pore impregnation and blockage due to ionomer loading and the consequences for the Pt/ionomer interface, ionomer film thickness and protonic binding of particles within pores. We used the model to emulate six catalyst/support combinations from literature with different porosity, surface area and pore size distributions of the support as well as varying particle size distributions and ionomer/carbon ratios. Besides providing qualitatively and quantitatively accurate predictions, the model is able to explain why the protonically active catalyst surface area has been reported to not increase monotonically with ionomer addition for some supports, but rather decrease again when the optimum ionomer content is exceeded. The proposed model constitutes a fast translation from manufacturing parameters to catalyst layer morphology which can be incorporated into existing performance and degradation models in a straightforward way.
In this work, flatbed screen printing is evaluated regarding its capability to produce catalyst layers of PEM fuel cells. In the field of printed electronics, screen printing is regarded as robust and high-throughput coating technology. The possibility of in-plane structuring could be an additional degree of freedom, enabling more complex designs of catalyst layers in the future. In this study, process parameters are varied to investigate their effect on resulting layer thickness, homogeneity, and Pt-loading. With the usage of different screens, the Pt-loading can be adjusted. Additionally, two different pastes with and without water content are investigated. The catalyst paste without water showed a better process stability during printing and performed best under dry conditions (RH = 40%) and worst under wet conditions (RH = 100%) during electrochemical in-situ testing. Overall, the reproducibility of the CCM production process was verified. The viscosity of the catalyst paste with 19.55 wt% water in solvent was higher compared to the paste without water. Furthermore, a carbon paste (Pt-free) is developed in a similar viscosity range as the catalyst pastes. The main challenge of screen printing process development lies in the paste optimization to prevent evaporation effects over time, ensuring sufficient wetting of the paste on the substrate and sufficient fuel cell performance.
Due to an increasing share of renewable energy sources the balancing of energy production and consumption is getting a lot of interest considering future smart grids. In this context, many investigations on demand-response programs are being conducted to achieve flexibility from different energy storages and loads. As space heating is an important schedulable load for flexibility simulations, there are different modelling approaches due to its interdisciplinary nature. Models can be built from the civil engineering or electrical engineering point of view, depending on the computational expense and accuracy level. Scheduling optimizations need a lot of simulations, preferably with computationally light models. Thus, this work will use a computationally light neural network load prediction model for space heating which is based on a detailed civil engineering model. Simulations with different scheduling times were conducted to see the long- and short-term effects of the demand response action. Results show, that applying the same demand response action at different times results in different behaviors of the system resp. energy consumption, which requires further studies for developing optimized scheduling methods.
Massive MIMO is one of the 5G nominee technologies that provides high energy and bandwidth efficiencies. Precoding at the basestation is compulsory to ensure such efficiencies in the performance and design of massive MIMO. This work investigates the performance of all recent massive MIMO linear precoding techniques called: Zero Forcing, Maximum Ratio Transmission, Regularized Zero Forcing, Truncated Polynomial Expansion and Phased Zero Forcing. The performance metrics which are used for their performance assessment are: bit error rate, signal to noise ratio, spectral efficiency and energy efficiency for a single cell downlink massive MIMO network; where the base station has ideal channel state information. Analytical expressions are formulated to each performance metric for the evaluation of these linear precoding techniques. Besides, the relationship between the number of base station antennas, users and signal to noise ratio with the achievable rates are revealed. The simulation result shows that Zero Forcing is the optimum linear precoding scheme both in bandwidth and power efficiency. However, its computational complexity is very high relative to other linear precoders. As far as the overall performance is concerned, Phased Zero Forcing approaches to Zero Forcing with low computational complexity.
To address 5G design targets, massive MIMO and mmWave communication are enabling technologies. Luckily, in many respects these two technologies share a symbiotic integration. Accordingly, a logical step is to integrate mmWave communications and massive MIMO to form ”mmWave-massive MIMO” which substantially increases user throughput, improve spectral and energy efficiencies, increase the capacity of mobile networks and achieve high multiplexing gains. Thus, this work analyses the concepts, performances, comparison and discussion of these technologies called: massive MIMO, mmWave Communications and mmWave-massive MIMO systems jointly. Besides, outcomes of extensive researches, emerging trends together with their respective benefits, challenges, proposed solutions and their comparative analysis is addressed. The performance of hybrid beamforming architecture with a fully digital and analog beamforming techniques are also analyzed. Analytical and simulation results show that the low-complexity hybrid analog-digital precoding achieves all round comparable precoding gains for mmWave-Massive MIMO technology.
The fifth-generation (5G) wireless communication system requires massive connectivity with high data rates and low latency. One of the technologies to meet these requirements is mm Wave massive MIMO. This work, therefore, aspires to have an in-depth look at the channel estimation and beamforming techniques jointly with their respective architectures for mm Wave massive MIMO system. In particular; sparse, compressed sensing, machine learning and array signal processing based channel estimation are addressed from 5G channel estimation techniques. On the other hand, beamforming techniques like hybrid beamforming and the low-complexity hybrid block diagonalization schemes with their mathematical analysis are included. This work also discusses in detail the challenges, optimization methods and mitigation techniques of pilot contamination, signal detection, channel estimation and hybrid beamforming for mm Wave massive MIMO system. The result asserts that partially connected block-diagonal hybrid bema forming with array signal processing based channel estimation is more optimal than the others with respect to over all performance, complexity and energy consumption. Finally, open research directions and challenges are pointed out.
To reduce greenhouse gas emissions, volatile energy production from renewable sources is highly encouraged by international agreements. This leads to balancing challenges of demand and supply which can be addressed with smart grids or even smart city concepts. Demand side management control strategies for flexibility harvesting often include energy storage systems, like flywheel- (FESS) and battery (BESS) storages. To investigate different control strategies for a hybrid energy storage system with a flywheel and battery storage in an islanded microgrid, an existing flywheel is modernized with state-of-the-art components to support real time power hardware in the loop simulations. Testing a load levelling control strategy with this test bench showed that the cyclic lifetime of the battery storage system could be increased with peak shaving due to a reduced amount of charging and discharging operations. An excessive energy buffering control method could increase the islanded operation time by using nearly 10% of the otherwise lost energy. However, these results with the testbench showed limited use for research with the current setup due to low capacity and high self-discharge rate of the existing FESS. But due to the MATLAB-based programming interface, it is perfectly suitable as an educational setup for the demonstration of possible implementations of the European Green Deal.
This work investigates a packaging solution for high power density semiconductors (> 200 W/cm 2), allowing for a dramatic reduction in size and complexity of power electronics modules. The multiple layers in standard packaging structures degrade the cooling efficiency due as they lengthen the path between dies and heatsinks. Here, we reduce the layer count by merging the ceramic substrate and the heat exchanger in a single part. CFD simulations and experimental validation are performed on a single-chip cooling packaging, and demonstrate a 10-20 % reduction in thermal resistance over more traditional cooling solutions.
This work investigates a packaging solution for high voltage semiconductors (20 kV), allowing for a dramatic reduction in size and complexity of power electronics modules. The standard packaging structures typically introduce a competition between electrical insulation (which requires thick insulating layers) and thermal performance (where thin, high thermal conductivity layers are preferred). Here, we introduce a concept which addresses this competition and is based on direct cooling using dielectric liquid. Single-chip heatsinks are designed, optimized using computational fluid dynamics (CFD), built and tested.
Es wird auf die Unterschiede von trafobehafteten und trafolosen Wechselrichtern und die daraus resultierenden, wesentlichen Merkmale eingegangen. Die kapazitiven Umladeströme, hervorgerufen durch die im Solargenerator befindlichen Kapazitäten machen eine bipolare Taktung bei der H-Brücke oder eine andere Topologie notwendig. Daraus resultieren auch unterschiedliche Belastungen in den passiven Bauelementen. Hier wird im Wesentlichen auf die Zwischenkreisströme eingegangen.
The performance of an automated driving system is crucially affected by its environmental perception. The vehicle's perception of its environment provides the foundation for the automated responses computed by the system's logic algorithms. As perception relies on the vehicle's sensors, simulating sensor behavior in a virtual world constitutes virtual environmental perception. This is the task performed by sensor models. In this work, we introduce a real-time capable model of the measurement process for an automotive lidar sensor employing a ray tracing approach. The output of the model is point cloud data based on the geometry and material properties of the virtual scene. With this low level sensor data as input, a vehicle internal representation of the environment is constructed by means of an occupancy grid mapping algorithm. By using a virtual environment that has been constructed from high-fidelity measurements of a real world scenario, we are able to establish a direct link between real and virtual world sensor data. Directly comparing the resulting sensor output and environment representations from both cases, we are able to quantitatively explore the validity and fidelity of the proposed sensor measurement model.
The paper presents the effect of network impedances on the transient stability of Low Voltage (LV) microgrids intended for islanded operation. A simulation model is developed using simplified models of Distributed Generations (DGs). These simplified models are used to simulate electrical (excluding switching) as well as control dynamics for each DG to setup and facilitate system level simulations [1]–[3]. The paper focuses on the operation of DGs in grid forming mode using a droop based primary control. This approach is applied on a real microgrid which is set up within the pebbles research project framework. These DGs are connected through cable impedances to a resistive load bank at the point of common coupling (PCC). The effect of varying individual impedances between DGs and PCC under loading conditions on the microgrid stability is investigated. The location of load between DGs and its impact is also discussed. Finally, a control modification utilizing concept of virtual impedances (VIs) in Voltage Source Inverters (VSI) is proposed to improve the transient stability of the discussed microgrid.
This paper addresses the analysis of aircraft control capabilities during the cruise phase (flying at the established level with practically constant configuration and speed) in the presence of windshears. The study uses a point-mass aircraft model describing flight in a vertical plane. The problem is formulated as a differential game against wind disturbances. The first player, autopilot, controls the angle of attack and the power setting, whereas the second player, wind, produces dangerous gusts. The state variables of the model are subjected to constraints expressing aircraft safety conditions. Namely, the altitude, path inclination, and velocity are constrained. Viability theory is used to find the so-called viability kernel, the maximal subset of the state constraint where the aircraft trajectories can remain arbitrary long if the first player utilizes an appropriate feedback control, and the second player generates any admissible disturbances. The computations are based on grid methods developed by the authors and implemented on a multiprocessor computer system.