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Active magnetic bearings are commonly applied in high-speed rotors in the medium to high power range to replace rolling-element or oil-film bearings. They require less maintenance and provide a number of unique benefits owing to their contactless suspension and active control. A rotor construction with integrated compressors or turbines results in predictable and controllable rotor dynamics, where model-based controllers can be used. Model-based centralized controllers outperform decoupled transfer function controllers, but they require accurate plant models. For integrated impellers on a single rotor, the control models comprise a rigid rotor and the lowest frequency bending modes. The bending mode frequency and parameters related to node locations can be identified, yielding controllers tuned to the application. This work introduces drivetrain modeling and magnetic levitation control of a 2 MW rotor and an external load attached to the electric machine rotor with a radially stiff but flexural coupling. The model-based control is tested in an experimental setup, and the drivetrain frequency responses are compared with the modeled multirotor drivetrain dynamics.

Permanent Magnet Synchronous Machines (PMSMs) are commonly employed in applications demanding a high specific power. To achieve high specific power values, a high pole pair number PMSM with very thin yokes can be built. Such a design leads to a high operating frequency. At high operating frequencies, AC losses can more than double the DC losses if solid hairpin technology or traditional bunches of nontransposed round enameled wires are used in the stator windings of machines with a considerable power. Against this negative effect, the emerging Litz wire coil technology with prefabricated coils can be used. In this study, firstly, alternative stator slot geometries required when using prefabricated Litz wire coils are evaluated. A symmetric semi-closed slot is not suitable for inserting such prefabricated Litz wire coils into the stator slots. Instead, an asymmetric semi-closed slot can be used, and it may even offer a better performance than the symmetric open slot. After showing that the asymmetric semi-closed slot provides a better performance, it is investigated how this asymmetric stator slot geometry can be used beneficially. The findings were first studied with finite element analysis (FEA) and then experimentally verified on a high-specific-power machine.

High-speed electric machines aim for compact, direct-driven elevated speed applications and highly efficient operation, especially when a gearbox can be avoided. The design of these types of machines is highly iterative, combining multiphysics optimization and leading to custom types of machines that fulfill the application-specific requirements. The Axially Laminated Synchronous Reluctance Machine (ALASynRM) with a solid rotor is one of the motor types that can be considered for high-speed applications. An axially laminated solid rotor structure combines magnetic and nonmagnetic layers rigidly bonded to each other by vacuum brazing, hot isostatic pressing, soldering, explosion welding, or even additive manufacturing. In this study, six nonmagnetic materials and nine magnetic materials are cross-compared. The results show clear differences in performance, efficiency, and physical properties of the rotor when made of different material combinations and can thereby suggest the best pairs when the application-specific performance criteria are known. The study is carried out on a 12 kW machine with a maximum speed of 24000 rpm.

The stability of a wind turbine-rotated synchronous generator must be maintained during a sudden change in wind speed or direction. In integral slot winding machines this task is taken care of by rotor damper windings. Tooth-coil permanent magnet generators cannot, however, have a damper winding in the rotor because of the high harmonic content of the air gap. In this paper, we study a possibility to stabilize PMSG damperless synchronous operation by dividing the generator stator winding into two parts - power winding (PW) and control winding (CW). We call this machine a dual-port PMSG (DPPMSG). The PW is directly connected to the grid. Therefore, the generator rotates, in average, at a fixed speed. On the other hand, the CW is connected to the grid through a four-quadrant power converter. The CW has three different tasks: It is responsible for the startup process, damping of speed oscillations and, of course, power generation. Electrical and magnetic decoupling of the winding sets is ensured by concentrated wound coils. The number of stator coils allocated to a winding set determines its power level. Different power levels of winding sets are analytically analyzed for wind gust speeds according to the IEC 61 400 standard. The results are verified by experimental tests.

The effects of manufacturing stresses on the overall magnetic properties of electrical steel core applied in the stator and transversally-laminated rotor of Synchronous Reluctance motors are studied. In addition, it is investigated how the -manufacturing-degraded electrical steel core affects the electromagnetic performance of two different Synchronous Reluctance motors. The traditional transversally-laminated rotor of this kind of a machine requires the adoption of mechanical elements (inner and tangential ribs) to maintain its mechanical integrity. Especially, for high-speed applications, the number of rotor ribs must be increased to make the rotor withstand higher centrifugal forces. Lamination manufacturing typically affects the magnetic properties of electrical steel by reducing its permeability at the machined edge. This machining effect is greater when the overall core layer area surrounded by the machined edges is small i.e., the machined surface area ratio to the total core area is high. Considering this, the degradation of the core magnetic properties in the ribs could improve the performance of the machine, and this effect would be more visible when the machine is designed with a higher number of narrow ribs with the adoption of Topology Optimization. The paper aims to propose some guidelines for the simulation of these effects starting from the measurements on defined core samples and then based on the measured results the simulation model should be updated accordingly. The samples are manufactured from several assembled sheets in order to modify the width of the cut area while maintaining the same external geometry.

The energy efficiency of non-road mobile machinery can be improved by using e.g., an electric drive system as a servo controller of a hydraulic machine to get an efficient electro-hydraulic (EH) converter. However, the cooling of EH devices require more understanding and new innovations. This work presents a design of a 7-kW integrated EH machine and studies its electric motor heat transfer phenomena both experimentally and numerically. Further, to better match the torque and speed performances of the permanent magnet synchronous motor (PMSM) and the hydraulic machine a planetary step-down gear is utilized to triple the output torque of the PMSM. The integrated motor and gear system is then connected to a bent axis piston hydraulic machine, which is capable of operating both as a motor and a pump. Two different electric motor cooling approaches are investigated. The first cooling approach is to use some hydraulic oil inside the motor-gear chamber to let it flow freely as a result of the rotor rotation and move the losses to the surface of the converter cover, which is equipped with some air cooling fins. In the second approach, the oil flows through the converter and removes the losses more effectively. Motor losses and thermal behaviour are studied within these two cooling approaches. Computational fluid dynamic (CFD) simulations are performed to find how the coolant is distributed inside the machine and how heat is distributed in the device.