Publications

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To meet the Paris Agreement target of limiting global warming to 1.5°C, the International Energy Agency stresses the urgent need for rapid and transformative actions in all sectors. In 2022, transportation accounted for about 25% of global CO2 emissions, making decarbonization a critical priority. Among transportation modes, rail is the least carbon-intensive and is expanding significantly worldwide. High-speed rail, in particular, provides a viable alternative to short- and medium-haul flights, helping reduce aviation-related emissions. Innovative, sustainable transportation technologies are gaining interest as complementary solutions to rail expansion. They diversify land transportation and help reduce aviation-related emissions. Governments, especially the European Commission, have shown renewed commitment to advancing high-speed systems. This political interest has brought back interest in established but underutilized technologies like Hyperloop and maglev trains. The propulsion of maglev and Hyperloop systems is typically achieved using Linear Electrical Machines (LEMs), which are types of electrical machines that produce linear motion by generating a direct and contactless thrust force along a straight-line path. Among various types of LEMs, Linear Induction Motors (LIMs) stand out as promising candidates for maglev propulsion. LIMs correspond to the linear counterpart of conventional Rotating Induction Motors (RIMs) and may offer significant advantages compared to other LEMs, such as simpler construction, lower cost, and scalability. However, LIMs have traditionally been restricted to low-speed, short-haul applications due to their lower efficiency and gravimetric force densities than other LEMs. This thesis explores the potential of LIMs for medium- to high-speed maglev ground transportation systems, focusing on the integration of Propulsion and Levitation (PL) or Propulsion and Guidance (PG) functionalities into a single motor for an all-in-one maglev system. The core of the thesis is the development of a highly accurate and computationally efficient analytical model of LIMs that allows for the calculation of motor electromagnetic fields, forces, and efficiency. The proposed analytical model has been validated through comparisons with Finite Element Analysis (FEA) simulations and measurements from a custom-made experimental platform, demonstrating excellent accuracy and superior computational efficiency compared to FEA models. The proposed analytical model is utilized in the thesis to enhance the performance of Single-Sided LIMs (SLIMs), focusing particularly on increasing their gravimetric force densities, and to demonstrate the potential of SLIMs for a MHS maglev system with PL or PG functionalities integrated into the same motor. The thesis also proposes an optimization framework for the design of SLIMs, in which the developed analytical model and the performance enhancement techniques mentioned above have been combined into a multiobjective optimization problem. The objective is to maximize the Levitation-to-Weight Ratio (LWR) and the efficiency of SLIMs for a reduced-scale Hyperloop prototype operated at the EPFL Hyperloop test infrastructure. Finally, a control strategy is proposed to achieve a decoupled, simultaneous, and electromagnetic drag-less control of PL in SLIMs, thereby unlocking their potential to combine these functionalities into a single motor.

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Thanks to the rapid growth of multiphase drives (MPDs), multiphase (MP) rotating electrical machines have gained popularity in the scientific community, demonstrating several advantages compared to traditional three-phase ones. Although MP rotating machines have been extensively studied in the literature, little research has been carried out on MP linear electrical machines and their application in the transportation sector. In this context, this article proposes a highly accurate and computationally efficient analytical model of MP single-sided linear induction motors (SLIMs) validated through comparison with finite-element analysis (FEA) simulations over a large interval of operational speeds (i.e., 0 mathrm m cdot mathrm s^-1 łeq v_m łt 150 mathrm m cdot mathrm s^-1 ). The proposed model, obtained by extending the one published in previous works by the authors, is used to analyze the performance of different MP SLIMs in terms of forces (i.e., thrust and normal force) and efficiency. A comparison with a three-phase SLIM is presented too. Furthermore, the effect of an iron appendix installed at the rear of the motor, which has been shown to increase the levitation force of SLIMs at high speed, has been added to the presented analysis. The results of the analysis demonstrate that an MP supply greatly affects the forces developed by the SLIMs and represents a solution to integrate propulsion and levitation (PL) functionalities into a single LIM for magnetic levitation (maglev) vehicles.

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Traditional magnetic levitation trains (maglev) generally use two or three separate systems to perform propulsion, levitation, and guidance (PLG) functionalities. Linear electromagnetic motors (LEMs) may be used for propulsion, electromagnetic suspension (EMS), or electrodynamic suspension (EDS) for levitation and guidance. Although considerable effort has been made to integrate these functionalities in a single LEM, a maglev with combined PLG is not yet available. This article proposes a solution to increase the levitation force of a singlesided linear induction motor (SLIM) at medium-to-high speed by adding an appendix of ferromagnetic material to its rear section. The appendix’s role is to conserve the magnetic flux density at the SLIM rear, which would otherwise be unexploited, and use it to generate additional levitation. The impact of the tail size on the levitation force has been modeled and added to an analytical model developed in previous works. The accuracy of the proposed model has been numerically and experimentally validated through f.e.m. and measurements from a custom-made test bench. A sensitivity analysis on the appendix length for a realistic-size SLIM is finally carried out, proving the effectiveness of the proposed solution and demonstrating the potential of SLIMs for combined PLG for medium-to-high-speed magnetic levitation vehicles.

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This article describes a simultaneous and decoupled scheme for the control of levitation and propulsion forces of single-sided linear induction motors (SLIMs). The proposed control scheme utilizes a highly accurate SLIM analytical model to ensure the operation of the motor at the best efficiency point while achieving lift and thrust forces decoupling through a multi-frequency supply strategy adapted from the literature. The described control scheme has been implemented and validated in MATLAB Simulink.

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This article describes a field-based analytical model of single-sided linear induction motors (SLIMs) that explicitly considers the following effects altogether: finite motor length, magnetomotive force mmf space harmonics, slot effect, edge effect, and tail effect. The derived closed-form solution of the system’s differential equations makes the model computationally more efficient than traditional finite elements (f.e.m.) models, and, therefore, more suitable for SLIM design optimization processes. The computational performance and accuracy of the proposed analytical model are validated through numerical simulations (via COMSOL Multiphysics) and experimental measurements carried out through a dedicated test bench.

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Literature on linear induction motors (LIMs) has proposed several approaches to model the behavior of such devices for different applications. In terms of accuracy and fidelity, field analysis-based models are the most relevant. Closed-form or numerical solutions can be derived, based on the complexity of the model and the underlying hypotheses. In terms of simplicity, equivalent circuit-based models are the most effective, since they can be easily integrated into optimization frameworks. To the best of the authors’ knowledge, the literature has not yet provided a computationally efficient LIM analytical model that considers the main characteristics of this type of motor altogether (i.e. finite motor length, magnetomotive force (mmf) space harmonics, slot effect, edge effect, and tail effect) and that is numerically and experimentally validated, especially at high speed (i.e. v ≃ 100ms -1 ). Within this context, this paper proposes a field analysis-based pseudo-three-dimensional model of LIMs that explicitly takes into account the above-mentioned effects. The derived closed-form solution makes the model computationally more effective than traditional f.e.m. models and, therefore, suitable to be coupled with optimization frameworks for optimal LIM design. The performance and accuracy of the proposed model are assessed through numerical simulations and experimental measurements, carried out by means of a dedicated test bench.

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Linear electromagnetic motors (LEMs) have been proposed, developed and used to propel high-speed (i.e. speed > 100 m/s) levitating vehicles. However, few real implementations have demonstrated the feasibility of these machines at such speeds. Furthermore, LEMs are expected to be enabling technologies for levitating vehicles traveling at near sonic speed, such as the Hyperloop concept. This paper presents a systematic review of modeling, design and performance assessment of LEMs used (or proposed) for the propulsion of levitating high-speed vehicles. Among all the possibilities, those that have received the most attention since the 1960s, along with the first magnetic levitation train concepts, are discussed. Classified by operating principle and topology, the LEMs are compared in terms of design and performance via specific key performance indicators. The performance of the various proposed LEMs is assessed on the basis of data available in the literature.

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The thorough development of the hyperloop system does require the availability of reduced-scale models. They can be used for the fast prototyping of various components, as well as for studying critical phenomena that takes place in this peculiar transportation system without the need to develop complex and expensive full-scale setups. In this respect, in this paper, we present a process for the optimal assessment of the scaling factor; it is to be used for the development of a reduced-scale hyperloop model, starting from the knowledge of the technical characteristics of its full-scale counterpart. The objective of the proposed process is the minimisation of the difference between the normalized power profiles associated with the reduced-scale and full-scale models of a hyperloop capsule traveling along a pre-defined trajectory with a pre-determined speed profile. By considering the hyperloop full-scale model as a reference, we propose a set of equations that link the above-mentioned metric with the constraints dictated by the kinematics of the hyperloop capsule, the capsule’s battery-energy storage and propulsion systems, the capsule’s aerodynamics, and the operating environmental conditions. We then derive a closed-form expression for the assessment of the optimal scaling factor and eventually use it to study the scaled-down version of an application example of a realistic hyperloop system.

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We present an operational-driven optimal-design framework of a Hyperloop system. The novelty of the proposed framework is in the problem formulation that links the operation of a network of Hyperloop capsules, the model of the Hyperloop infrastructure, and the model of the capsule’s propulsion and kinematics. The objective of the optimisation is to minimize the energy consumption of the whole Hyperloop system for different operational strategies. By considering a network of energy-autonomous capsules and various depressurization control strategies of the Hyperloop infrastructure, the constraints of the optimisation problem represent the capsule’s battery energy storage system response, the capsule’s propulsion system and its kinematic model linked with the model of the depressurization system of the Hyperloop infrastructure. Depending on the operational scheme and lengths of the trajectories, the proposed framework determines optimal operating pressures of the Hyperloop infrastructure between 1.5-80mbar along with the maximum capsules cruising speeds. Furthermore, the proposed framework determines maximum operational power of the capsule’s propulsion system in the range between 1.7-5MW with a minimum energy need of 25Wh/passenger/km.

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The paper assesses the influence of equivalent circuit battery models on the optimal design of the propulsion system of an energy-autonomous Hyperloop capsule. By knowing a pre-determined payload to be transported along pre-determined trajectories, the problem minimizes the total number of battery cells supplying the capsule propulsion along with the maximization of its performance. The constraints of the problem embed numerically- tractable models of the main components of the electrical propulsion systems and of the battery. Although the optimization problem is non-convex, its constraints are formulated to exhibit a good numerical tractability. After having determined the solutions influenced by a weighting factor with two different battery models, dominant solutions are identified using specific metrics with the purpose of assessing the impact of the battery model on the determined solutions.

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In this article, we focus on the assessment of the optimal design of the propulsion system (PS) of an energy-autonomous Hyperloop capsule supplied by batteries. The novelty in this article is to propose a sizing method for this specific transportation system and answer the question whether the energy and power requirements of the Hyperloop propulsion are compatible with available power-electronics and battery technologies. By knowing the weight of a predetermined payload to be transported along predetermined trajectories, the proposed sizing method minimizes the total number of battery cells that supply the capsule’s propulsion and maximizes its performance. The constraints embed numerically tractable and discrete-time models of the main components of the electrical PS and the battery, along with a kinematic model of the capsule. Although the optimization problem is nonconvex due to the adopted discrete-time formulation, its constraints exhibit a good numerical tractability. After having determined multiple solutions, we identify the dominant ones by using specific metrics. These solutions identify PSs characterized by energy reservoirs with an energy capacity in the order of 0.5 MWh and a power rating below 6.25 MW and enable an energy consumption of 10-50 Wh/km/passenger depending on the length of the trajectory.