Electrical power generation in aircraft: review, challenges and opportunities

The constant growth of air traffic, the demand for performance optimization and the need for decreasing both operating and maintenance costs have encouraged the aircraft industry to move towards more electric solutions. As a result of this trend, electric power required on board of aircraft has significantly increased through the years, causing major changes in electric power system architectures. Considering this scenario, the paper gives a review about the evolution of electric power generation systems in aircraft. The major achievements are highlighted and the rationale behind some significant developments discussed. After a brief historical overview of the early DC generators (both wind- and engine-driven), the reasons which brought the definitive passage to the AC generation, for larger aircraft, are presented and explained. Several AC generation systems are investigated with particular attention being focused on the voltage levels and the generator technology. Further, examples of commercial aircraft implementing AC generation systems are provided. Finally, the trends towards modern generation systems are also considered giving prominence to their challenges and feasibility

Influence of Insulation Thermal Aging on the Temperature Assessment in Electrical Machines

Thermal modeling and temperature assessment of electrical machines often rely on the use of lumped-parameter thermal networks. A historic limitation of analytical thermal models is their need for an experimental fine-tuning, necessary for selecting the appropriate values of thermal conductivity and convection heat transfer coefficients. This evaluation procedure is commonly carried out at the design stage of a new machine, by assuming that its thermal behavior will remain unchanged throughout its whole lifetime. This paper demonstrates, through an in-depth experimental investigation, how the capability of heat extraction from a machine's hot spot towards the coolant can be strongly affected by the level of thermal aging of its insulation system. Based on the experimental findings, a decrement of the winding equivalent thermal conductivity is noted as the thermal aging accumulates, with a corresponding progressive increment in hot-spot temperature

Physics of failure as a technology enabler for electrical machines in transportation: reliability-oriented design of low voltage insulation systems

In modern electrical machines there is an-ever-increasing push towards high power density and efficiency, which are thus considered as main design objectives. On the other hand, electrical machines used in certain applications, such as in the transport industry, are also required to be highly reliable and robust. In order to achieve the much needed power density performances, “extra” stresses are being experienced by the insulation systems of these machines, often resulting in accelerated components degradation and compromised system-level reliability figures. In general, the lifetime consumption evaluation and the reliability assessment of electrical machines components, including the insulation system, are still evaluated through outdated methods. These are often based on historical data and adopt constant failure rates, derived by statistically post-processing the failure times of a large number of built prototypes. This is of course a very time-consuming and expensive process. In application fields such as automotive and aerospace, the reliability assessment procedures can then negatively affect the development timeline of an electrical product, especially for certification. This Thesis therefore argues for the development of new processes, based on comprehensive physics of failure methodologies, for assessing the lifetime consumption and degradation of insulation systems for electrical machines. This will enable the electrical machine designer to make reliability considerations a main design objective, right from the very start of the design process. As a result of this work, this Thesis also shows how the proposed advanced philosophy will allow manufacturers to design insulation systems without relying on outdated, traditional “safety factors” and over-engineering concepts. The proposed processes focus on the development of new lifetime prediction models for electrical machines. The core of the Thesis is focused on thermal considerations and stresses. The novel models, developed in this work, seek to achieve significant improvements in terms of accuracy of lifetime prediction, by combining the cumulative damage law with the conventional Arrhenius model. The Thesis also includes considerations on partial discharges and ensuing insulation electrical stresses

Moving Toward a Reliability-Oriented Design Approach of Low-Voltage Electrical Machines by Including Insulation Thermal Aging Considerations

© 2020 IEEE. Electrical machines (EMs) are required to consistently perform their intended mission over a specified timeframe. The move toward transportation electrification made the EMs' reliability an even stringent and predominant requirement, since a failure might cause severe economic losses, as well as endanger human lives. Traditionally, the design procedure of motors conceived for safety-critical applications mainly relies on over-engineering approaches. However, a paradigm shift is recently taking place and physics of failure approaches/methodologies are employed to meet the reliability figures, while delivering an optimal design. This article proposes and outlines a reliability-oriented design for low-voltage EMs. Thermal accelerated aging tests are preliminarily carried out on custom-built specimens. Once the aging trend of the turn-to-turn insulation system is assessed, the thermal endurance graph at several percentile values is determined and lifetime models are developed, for both constant and variable temperature operations. Finally, these models are used to predict the turn-to-turn insulation lifetime of motors meant for aerospace and automotive applications

Influence of Comfort Expectations on Building Energy Need

Increase thermal comfort is considered as one of the main benefits of a deep renovation right after energy saving. However, an increase in thermal comfort could be seen as a behavioural change caused by the energy efficiency improvement that reduces expected energy saving: the so-called rebound effect. This paper shows how building energy need is correlated to comfort category, defined in EN 15251. The study is conducted via dynamic simulations performed by TRNSYS 17 software using 3D multi-zone models. Models are tailored on occupant behaviour and driven by thermal comfort constraints. Calculations of energy need for space heating and space cooling is done both before and after a deep renovation. The effect of building and user characteristics is evaluated too. Users are differentiated by number of persons and occupancy schedule. The relation between thermal comfort, set-point temperature and energy need is investigated, focusing attention on changes that occur after the building has been thermally insulated. Computational results are critically discussed and compared with an empirical study on building renovation that includes a survey on thermal comfort perception and user behaviour. Finally, rebound effect is discussed and its magnitude is evaluated

Application of Dynamic Numerical Simulation to Investigate the Effects of Occupant Behaviour Changes in Retrofitted Buildings

The term rebound effect is commonly used in literature to identify the gap between the estimated and the real energy savings due to changes in the occupant behaviour after a building energy retrofit. In the present article, the rebound effect for some Italian residential building types is investigated through dynamic simulation. The energy efficiency measures determining the highest rebound effect are identified and discussed. The results point out that the major renovation generally leads to the highest benefits as the efficiency measures are mutually reinforced. In contrast, single measures may lead to the opposite goal of increasing the energy consumption

Enhancing Prediction in Cyclone Separators through Computational Intelligence

Pressure drop prediction is critical to the design and performance of cyclone separators as industrial gas cleaning devices. The complex nonlinear relationship between cyclone Pressure Drop Coefficient (PDC) and geometrical dimensions suffice the need for state-of-the-art predictive modelling methods. Existing solutions have applied theoretical/semi-empirical techniques which fail to generalise well, and some intelligent techniques have also been applied such as the neural network which can still be improved for optimal equipment design. To this end, this paper firstly introduces a fuzzy modelling methodology, then presents an alternative Extended Kalman Filter (EKF) for the learning of a Multi-Layer Neural Network (MLNN). The Lagrange dual formulation of Support Vector Machine (SVM) regression model is deployed as well for comparison purposes. For optimal design of these models, manual and grid search techniques are used in a cross-validation setting subsequent to training. Based on the prediction accuracy of PDC, results show that the Fuzzy System (FS) is highly performing with testing mean squared error (MSE) of 3.97e-04 and correlation coefficient (R) of 99.70%. Furthermore, a significant improvement of EKF-trained network (MSE = 1.62e-04, R = 99.82%) over the traditional Back-Propagation Neural Network (BPNN) (MSE = 4.87e-04, R = 99.53%) is observed. SVM gives better prediction with radial basis kernel (MSE = 2.22e-04, R = 99.75) and provides comparable performance to universal approximators. In comparison to conventional theoretical and semi-empirical models, intelligent approaches can provide far better prediction accuracy over a wide range of cyclone designs, while the EKFMLNN performance is noteworthy

The rebirth of the current source inverter: advantages for aerospace motor design

It is well known and widely accepted that the voltage source inverter (VSI) now dominates the world of electrical drives. Its success is probably due to its simplicity, high efficiency, and the widespread availability of VSs. This popularity has, in turn, influenced the evolution of the semiconductor industry, which has focused in recent years on devices tailored for VSIs. Thus, products such as depletion devices (normally off) and those without reverse voltage blocking have been widely marketed and used

Thermal analysis of fault-tolerant electrical machines for more electric aircraft applications

For safety critical applications, electrical machines need to satisfy several constraints, in order to be considered fault-tolerant. In fact, if specific design choices and appropriate control strategies are adopted, fault-tolerant machines can operate safely even in faulty conditions. However, particular care must be taken for avoiding uncontrolled thermal overload, which can cause severe failures. This study describes the thermal modelling of a three-phase, synchronous machine for aerospace applications, analysing the machine's thermal behaviour under open-circuit fault conditions. A particular winding's layout is chosen with the purpose of satisfying fault-tolerance constraints. The winding temperature is evaluated by using a simplified thermal model, which was experimentally validated. Copper and iron losses, necessary for the thermal simulations, are calculated analytically and through electromagnetic finite element analysis, respectively. Finally, an aerospace study case is presented and the machine's thermal behaviour is analysed during both healthy and open-circuit conditions

Reliability-Oriented Design of Electrical Machines: The Design Process for Machines' Insulation Systems MUST Evolve

As the world of transportation keeps moving toward greater electrification, the main design objectives in terms of power density and efficiency of system components are becoming increasingly important. Meanwhile, transportation applications are also very safety critical. The extra stresses being seen by important components, such as electrical machines (EMs) and their insulation systems, to achieve the required performances, are accelerating the degradation of components, making them less reliable and shorting their lives. In general, lifetime consumption and degradation of components, such as for insulation systems of EMs, is still assessed through statistical methods (i.e., recording the number of imposed cycles until failure of a built prototype). This is a very timeconsuming and expensive process. In the mobile applications, such assessments can be the major bottleneck in the development timeline of an electrical product, especially for certification