Multiphysic Design and Modeling of Rotating Electrical Machines

This paper presents a general overview on design process of electrical machines considering a multiphysic point of view, and a road map for a comprehensive design approach is drawn. The objective multi-physical criterion including electromagnetism and mechanics physics, thermodynamics, fluid dynamics, structural dynamics, noise and vibration are discussed. Also, various modelling methodologies are presented and compared in terms of computational-time resources and accuracy. Current state of art in this approach will be presented highlighting the advantages and disadvantages of such methodologies

Electromagnetic and Thermal Evaluation of Surface-Mounted PM Vernier Machines

This study investigates the electromagnetic and thermal performance of surface-mounted permanent magnet vernier machines. In particular, different losses and thermal behaviour of PM vernier machines are evaluated considering different gear ratios and the obtained results are compared with a baseline conventional PM machine. In order to have a fair evaluation of the studied machines, the stator and rotor dimensions, as well as current density in the slots, are kept constant, while the stator winding poles and the PM poles mounted on the rotor are varied. The performances of all the machines are evaluated using 2D finite element analyses. Back-EMF, output torque, torque ripple, losses and efficiency are evaluated for the studied machines together with their weight / volume comparison. Finally, thermal analyses are carried out and the impact of temperature on the machines is investigated

Non-Invasive Measurements and FEM Analyses for Estimating the Rotor Bar-Lamination Contact Resistance

This research work investigates the phenomenon of interbar currents in induction motors equipped with die-cast alu- minum cages. Flowing in the lamination and distorting the bar current distributions, the interbar currents cause additional stray losses as well as an increase of the joule loss in the cage bars. The contact resistance between the bars and the rotor lamina- tions is the key modeling element for a correct prediction of the interbar currents and the related extra losses. The study presents a new noninvasive method to obtain a reliable estimation of the contact resistance. The proposed hybrid approach is based on a mix of experimental data and Finite Element method (FEM)-based simulation results. A reliable three-dimensional FEM model of a four-pole 15-kW induction motor with closed rotor slots has been used to investigate the impact of variable contact resistance on the interbar currents, rotor joule losses, and the voltage drops along the bars, opening a new perspective for this complex phenomenon and its impact on the stray losses. Finally, the proposed methodologies are critically discussed and the obtained results compared with other relevant research works

Enhanced Stray-Load Loss Measurements Through a Zig-Zag Variable Load Test Approach

This article proposes an enhanced procedure for executing the standard variable load test that allows obtaining high correlation factors for indirectly measured stray-load loss during efficiency tests of induction motors. This helps to achieve the minimum values required by the international standards to consider the variable load test well executed, avoiding unwelcome test repetitions and leading to significant amount of time saved. With the machine at steady-state temperature, the enhanced procedure consistsofalternativelyapplyingloadlevelshigherandlowerthan the rated load, so that the stator winding temperature zigzags aroundtheratedvalue.Hence,multiplereadingscanbeperformed for each load point, having the machine in isothermal conditions. This allows averaging many measurements of the same load point to mitigate the impact of instrumentation and reading errors. The article includes load tests conducted on different induction motor sizesandpolecounts,applyingboththestandardvariableloadtest procedure and the proposed approach. The experimental results show that theproposed technique allows achieving higher correlation factors on the stray-load losses than the standard procedure

Design and Analysis of High-Speed Induction Machines for Submerged Cryogenic Pumps

This paper discusses the electromagnetic design and loss analysis of a 15 kW, 13500 rpm induction machine for a single-stage submerged cryogenic pump. The study starts from an existing machine driving a three-stage cryogenic pump, rated 7.5 kW at 7300 rpm. The new motor design is approached by increasing the rotating speed of the reference machine at fixed outer diameter, aiming at an optimum between efficiency and power factor. Experimental investigations are carried out on the reference machine to analyze its thermal behavior. The results allow to obtain initial values for the electrical loadability of cryogenic induction machines. The electromagnetic design of the high-speed motor is successfully carried out with the help of detailed numerical simulations, particularly devoted to a precise analysis of the losses active in the machine. Special care is given to the iron losses, estimated with two different approaches

Off-Line Efficiency Mapping of Induction Motors Operated in Wide Torque-Speed Ranges

In the context of a progressive component virtualization for energetic assessments in variable speed and load operations, this paper presents a methodology for computing the efficiency maps of three-phase induction motors. The proposed approach is based on the conventional machine equivalent circuit to quickly obtain a set of efficiency maps at different machine temperatures and supply voltage levels. The well-known no-load and locked-rotor tests are used to determine the motor parameters at different frequencies and voltages, taking into account the machine nonlinearities and the iron losses. The approach has been validated on an 11 kW, 4 poles, 50 Hz induction motor tested in different operating conditions

Accurate Induction Machines Efficiency Mapping Computed by Standard Test Parameters

The extensive electrification process that is taking hold in several applications makes increasingly necessary the virtualization of electric components for energetic and performance assessments during the system design stage. For this purpose, this paper proposes a straightforward methodology for computing the efficiency maps of induction machines operated in wide torque-speed ranges. The modeling approach is based on the induction machine equivalent circuit defined in the rotor dq coordinates. The procedure allows computing a set of efficiency maps at different machine temperatures and supply voltage levels, both for motor and generator operation modes. The equivalent circuit parameters at different frequencies and voltages are determined by means of the well-known no-load and locked-rotor tests, thus including in the modelling the machine nonlinearities, skin effect and the iron losses. The proposed methodology has been validated on a 10 kW, 4-pole induction machine. The comparison between computed and experimental efficiency maps for different operating conditions, confirm the validity of the proposed methodology

Simplified Thermal Model of Disk-Shaped Automotive Smart Braking Actuators

This paper articulates the challenges in the thermal modelling of surface-mounted permanent magnet motors for automotive brake-by-wire systems, which operate by injecting high dc currents in two of the three phases for short time intervals. This unconventional operation requires dedicated thermal models for the prediction of uneven heat distributions inside the machine. This study extends a previous work conducted on slender-shaped motors to a disk-shaped machine where the edge effects could compromise the model accuracy. Additionally, here efforts have been made to minimize the number of experimental tests needed for the correct calibration of the proposed phase-split lumped-parameters thermal models

Losses Analysis of Induction Motors under Ambient and Cryogenic Conditions

Cryogenic induction machines have been re-emerging as a potential solution to increase the current power density for challenging specific power applications. Compared with an ambient temperature operation, cryogenic conditions allow higher power density and increased efficiency due to the decrease of electric resistivity of conducting materials and increased cooling capability. This work focuses on the losses analysis of induction machines immersed in liquid nitrogen. Under ambient and cryogenic conditions, experimental tests are performed and presented for two induction machines, a 90 W 40 V induction machine, and a 550 W 400 V induction machine, to evaluate the mechanical, iron and residual losses, and the change of their equivalent circuit parameters

Outcomes of COVID-19 patients treated with continuous positive airway pressure outside ICU

Aim We aim at characterizing a large population of Coronavirus 19 (COVID-19) patients with moderate-to-severe hypoxemic acute respiratory failure (ARF) receiving CPAP outside intensive care unit (ICU), and ascertaining whether the duration of CPAP application increased the risk of mortality for patients requiring intubation. Methods In this retrospective, multicentre cohort study, we included COVID-19 adult patients, treated with CPAP outside ICU for hypoxemic ARF from March 1 st to April 15th, 2020. We collected demographic and clinical data, including CPAP therapeutic goal, hospital length of stay (LOS), and 60- day in-hospital mortality. Results The study includes 537 patients with a median age of 69 (IQR, 60-76) years. Males were 391 (73%). According to predefined CPAP therapeutic goal, 397 (74%) patients were included in full treatment subgroup, and 140 (26%) in the do-not intubate (DNI) subgroup. Median CPAP duration was 4 (IQR, 1-8) days, while hospital LOS 16 (IQR, 9-27) days. Sixty-day in-hospital mortality was overall 34% (95%CI, 0.304-0.384), and 21% (95%CI, 0.169-0.249) and 73% (95%CI, 0.648-0.787) for full treatment and DNI subgroups, respectively. In the full treatment subgroup, in-hospital mortality was 42% (95%CI, 0.345-0.488) for 180 (45%) CPAP failures requiring intubation, while 2% (95%CI, 0.008- 0.035) for the remaining 217 (55%) patients who succeeded. Delaying intubation was associated with increased mortality [HR, 1.093 (95%CI, 1.010-1.184)]. Conclusions We described a large population of COVID-19 patients treated with CPAP outside ICU. Intubation delay represents a risk factor for mortality. Further investigation is needed for early identification of CPAP failures