Abstract:The demand for alternative fueling methods to reduce the need for fossil fuels is not limited to the electrification of ground vehicles. More-electric and all-electric aircraft pose challenges, with extensive requirements in terms of power density, efficiency, safety, and environmental sustainability. This paper focuses on electrical machines and their components, especially for high-power applications like the main propulsion. The electrical machine is evaluated from different aspects, followed by a closer look at the components and materials to determine the suitability of the current standard materials and advanced technologies. Furthermore, the mechanical and thermal aspects are reviewed, including new and innovative concepts for the cooling of windings and for the use of additive manufacturing. Aircraft have special demands regarding weight and installation space. Following recent developments and looking ahead to the future, the need and the possibilities for light and efficient electrical machines are addressed. All of the approaches and developments presented lead to a better understanding of the challenges to be expected and highlight the upcoming opportunities in electrical machine design for the use of electric motors and generators in future aircraft. Several prototypes of electrical machines for smaller aircraft already exist, such as the electric drive of the Siemens powered Extra 330LE. The focus of this paper is to provide an overview of current technical possibilities and technical interrelations of high performance electric drives for aviation. A 1 MW drive is exemplified to present the possibilities for future drives for airplanes carrying a larger number of passengers. All presented techniques can also be applied to other drive power classes.
In patients with COPD, it has not been comprehensively assessed whether the predictive value of comorbidities for mortality differs between men and women. We therefore aimed to examine sex differences of COPD comorbidities in regard with prognosis by classifying comorbidities into a comorbidome related to extrapulmonary disorders and a pulmorbidome, referring to pulmonary disorders. The study population comprised 1044 women and 1531 men with the diagnosis of COPD from COSYCONET, among them 2175 of GOLD grades 1–4 and 400 at risk. Associations of comorbidities with mortality were studied using Cox regression analysis for men and women separately. During the follow-up (median 3.7 years) 59 women and 159 men died. In men, obesity, hypertension, coronary artery disease, liver cirrhosis, osteoporosis, kidney disease, anaemia and increased heart rate (HR) predict mortality, in women heart failure, hyperuricemia, mental disorders, kidney disease and increased HR (p < 0.05 each). Regarding the pulmorbidome, significant predictors in men were impairment in diffusion capacity and hyperinflation, in women asthma and hyperinflation. Similar results were obtained when repeating the analyses in GOLD 1–4 patients only. Gender differences should be considered in COPD risk assessment for a tailored approach towards the treatment of COPD.Clinical Trial Registration: ClinicalTrials.gov NCT01245933.
This paper is aimed at giving an overview of possible cooling technologies for electrical machines and their assessment for aviation applications, e.g., fan or propeller drives. The most important demand for aircraft is the minimization of the drive system weight comprising electrical machine, power electronics, and the cooling system. The potential of aluminum winding an overview about several cooling technologies with the Rankine or Brayton cycle or utilizing the phase change of the cooling fluid is given. As an alternative approach, the cooling structure inside the machine is studied. A very interesting potential was discovered with direct slot cooling (DSC) removing the heat where it is produced and, thus, simplifying the cooling system effort and its weight. Since it is one of the most promising approaches, this cooling method is studied in depth. Furthermore, it can also be combined with one of the cooling technologies discussed above.In the overview paper [6], focus is set on the most recent progress in thermal management of electric motors for aviation. Besides air cooling, oil bath cooling, water jacket cooling, heat pipe cooling, intra winding cooling channels with a thermal conductive polymer [7], and direct winding cooling with tube-like conductors are cited. In this case, the problem of large pressure drops in the cooling ducts of six bars or more occurs. As experimental results, current densities of 24.7 A/mm 2 and transient current density of more than 40 A/mm 2 with class F insulation were achieved. With class H insulation even higher, values up to 58 A/mm 2 could be possible. By using conductors with integrated cooling channels, current densities possibly reaching 130 A/mm 2 were anticipated. However, the losses increase with the square of the current density and are linear with the volume of the winding even though the temperature is within the limits of the insulation system. The extremely high copper losses will increase weight and size of the cooling system and the reduced efficiency also requires an increase of the on-board power supply (generators and prime movers, fuel tank or energy storages, wiring, switchgear).The weight advantages of such machines can be quickly overcompensated by the weight of the cooling system and the increased power supply. Therefore, an accurately balanced design of the drive system is necessary. A proposal for the improvement of this approach is given in Section 5.A reduction of the winding temperature level by lowering the coolant temperature below standard ambient temperature promises a reduction of the copper losses in the electrical machine and a longer lifetime of the insulation. The higher effort for such cooling systems may be compensated by the higher efficiency of the drive. Due to the usually high temperature drop between winding and cooling fluid, this requires low ambient temperatures-as given in high cruising altitudes-or the use of refrigerant cooling systems, which allow coolant temperatures below ambient temperatures. In a literature study, no pap...
This paper deals with the investigation of a linear generator used in an internal combustion engine. The introduction reviews the state of the art of free-piston linear generators. Then, the mechanical structure of this generator is presented. The main part treats a finite-element-analysis (FEA) of the generator comparing different armature magnetizations with the numeric simulation program FLUX.A cylindrical design with radial, axial and a quasi-Halbach magnetization in Vernier topology is examined. The number of pole-pairs in a Vernier machine differs by one from stator teeth in principle. This paper is focusing on a Vernier machine with five armature pole-pairs coinciding within six stator teeth (Vernier 5/6). Several geometric parameters, like height of the magnets, slot pitch ratio or length of the magnets are varied in order to find the optimal design with regard to a high thrust force and low force ripple. The paper concludes with the determination of losses and electrical efficiency.
Since the significant growth of interest in soft robotics, artificial muscles and biomimetics, soft, capacitive dielectric elastomer sensors (DES) have been in the focus of development. However, when including a sensor into any device, tool or, for example, a machine element, there are several factors which have to be considered, e.g., the ease of embedding the sensor, the maintenance of the functionality of the machine element, as well as the quality of the embedded sensors and their reproducibility. In this work, we will focus on the quality of the sensor and present a procedure for manufacturing multi-layer capacitive strain sensors. In order to assess the influence of different manufacturing processes on the quality of capacitive DES, a variety of thin multi-layer sensors were fabricated. Furthermore, using an LCR meter, the equivalent electrical capacitances (C) at the two sensor contacts were measured. It is shown that C varies depending on the quality of the electrodes. By testing multi-layer DES (ML-DES) with an electrode diameter of d electrode = 3 mm, with three and four electrode layers, a maximum capacitance of C 0 = 6.7 pF and C 0 = 10.5 pF was achieved for the undeformed sensor, respectively. The obtained capacitance values show that following the presented recommendations for creation the electrodes enables to improve the reproducibility and quality of the manufactured ML-DES. The fabricated sensor is soft and deformable due to the compliance of the elastomeric film used. Such a capacitive ML-DES can be used, for example, as a soft strain sensor implemented into the elastic element of a jaw coupling.
Measuring the load current of drive inverters is still inevitable for a precise current control. In common industrial and automotive inverters hall effect based current sensors are widely used.[1] The presented novel current measurement method is based on an inductive current sensor like a Rogowski coil. This can be fabricated much smaller and cheaper than hall based current sensors and can be integrated into drive inverter systems easily. Unlike u evaluation electronic for Rogowski coils, AC and DC components of the load current can be measured using a special evaluation scheme. The arrangement of the sensors also allows them to be used for fast short-circuit detection and di/dt me that some synergies with the gate drive circuitry can be used to create a more compact and reliable system.
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