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The insertion of permanent magnets (PMs) within the rotor slots of Synchronous Reluctance Machines (SyRM) is the most common design strategy used to increase significantly their performance. In this paper it is shown how a permanent magnet assisted synchronous reluctance machine (PMaSyRM) can be optimized to satisfy all the electromagnetic and structural constraints arising as the maximum operating speed increases. This is done considering a variety PMs material. This work, the second of two companion papers, briefly recalls the novel systematic design approach proposed in Part I, and then describes the characteristics of the optimal machines achieved considering a maximum speed ranging from 1 to 140 krpm with and without the assistance of ferrite and neodymium based PMs. The reasons behind the performance deterioration as the speed increases are all investigated along with the geometrical variations of the optimal designs. The selection of the design solution to be manufactured is justified as well as the final structural and electromagnetic refinement stages leading to the final prototype. All the reported considerations are experimentally validated testing an 8.5kW at 80krpm PMaSyRM, comparing the measured and expected performance in terms of torque and internal power factor.

With the increasing electrical energy demands in aviation propulsion systems, the increase in the onboard generators’ power density is inevitable. During the flight, forces coming from the gearbox or gyroscopic forces generated by flight manoeuvres like take-off and landing can act on the generator’s bearings, which can lead to wear and fatigue in the bearings. Utilizing the radial force control concept in the electrical machine can relieve loads from the bearings that not only minimize the bearing losses but also increase the bearings’ life. The objective of the MAGLEV project (Measurement and Analysis of Generator Bearing Loads and Efficiency with Validation) is to study, demonstrate, and test a new class of high-speed generators with radial force control. The concept is developed in an electrical machine and is validated on a test rig by measuring required parameters like shaft displacement, vibrations and bearings’ temperature. Additionally, the friction moment of each generator’s bearings is measured and validated in a separate test rig with a precise friction force measurement system under comparable conditions to the bearings’ loads in the generator. In this paper design steps of this type of generator and its test rig are presented and the measurement methodology used for radial force control is explained.

This paper shares with the aerospace community a case study of turboprop mild hybridisation using a recently developed integrated drive system in the University of Nottingham, UK, within the ACHIEVE project under EU H2020 CleanSky 2 program (project No. 737814). The developed drive system enables green taxiing of a turboprop aircraft while on the ground with its engine off, and as an electrical generator when the turboprop is in the air. The entire system is designed to be able to integrate within the power auxiliary gear box (PAGB) of a turboprop aircraft. Some of the key features of the developed system include a high-speed permanent magnet machine (up to 14,200rpm) with dual three-phase design, SiC-based high power density (11.8kW/L for the power converter, 35.3kW/L and 7.2kW/kg for the machine active parts), integrated cooling design for high-temperature operation (>130ºC ambient temperature), fault tolerance consideration with dual channel operation capabilities and sensorless control for entire operational conditions. This paper is giving an overview of the design process of the electrical machine, power converters, and its cooling of the entire drive. Numerical analysis (FEM and CFD) and some experimental results are presented to demonstrate the effectiveness and the desired performance of the developed integrated drive system.

Thermal management is often considered a bottleneck in the pursuit of the next generation electrical machines for electrified transportation with a step change in power density. Slot-channel cooling is considered to be an effective cooling technique, either as an independent method or as a secondary heat transfer path which compliments traditional cooling systems. The slot-channel specific geometry and position effects on the thermal benefits are not thoroughly investigated in literature, while previous work focuses on passing fluid through the un-used space left in between coils forming concentrated windings. In this paper, slot-channel cooling is implemented within an oil-flooded cooling system for a high power density motor used as a pump. A flexible and detailed lumped parameter thermal network (LPTN) is proposed for the cooling system, with the LPTN used to optimize the slot-channel dimensions and location for obtaining maximum thermal benefits. Finally, a surface-mount permanent magnet (SPM) machine with the optimized slot channel geometry is built and tested to validate the thermal model, experimentally achieving an armature continuous current density in excess of 30A/mm2.

The slot thermal condition is critical for thermal management of high performance electrical machines, due to the high heat losses and poor heat transfer ability within the slot. With a part of the back-iron projected radially downwards into the slot, back-iron extension (BIE) shortens the heat dissipation path from the slot coil to the back-iron and was proven to be an effective thermal improvement technique. The relationship between BIE thermal benefits and various electrical machines’ parameters remains to be investigated. Based on an existing concentrated-wound machine, the relationship between the equivalent slot thermal conductivity (ESTC) and the back-iron extension effectiveness is researched in this paper. Utilizing a developed 3D thermal model, the equivalent slot thermal conductivity effects on the temperature reduction with BIE are indicated with simulation results and verified with experimental tests. BIE is reported to provide temperature reductions ranging from 48°C down to 18°C across the plausible range of ESTC values considered. Guidelines are given in the final part to suggest the situations under which BIE is more effective.

Interior permanent magnet synchronous machines (IPMSMs) with V-shaped permanent magnet (PM) rotors are widely used as traction motors in electric vehicles because of their high torque density and high efficiency. However, the V-shape IPMSMs have the disadvantages of inevitable torque ripple due to the non-sinusoidal air-gap flux density distribution and the utilisation of the reluctance torque. In this study, with the aim of improving the torque ripple characteristics, a modified V-shaped IPMSM rotor configuration with bridges extended inwards towards the pole centre is proposed to generate a more sinusoidal air-gap flux density waveform. The proposed topology, referred to as ‘Type C’ within this study, is compared with baseline rotor configuration references, namely ‘Type A’ which is a conventional V-shaped PM rotor, as well as ‘Type B’ which is a related configuration with a mechanically non-uniform air gap. The analysis results show that the rotor ‘Type C’ exhibits significant advantages in terms of reducing cogging torque, torque ripple and radial force, without incurring additional air-gap friction losses. Finally, a prototype of the IPMSM with the proposed rotor configuration is manufactured and tested, verifying the predicted benefits experimentally.

Alumina films (~2??m thick) were deposited with a mixed Cu/Al interlayer onto copper. Direct current (DC)/Pulsed DC (PDC) magnetron sputtering techniques were independently compared for reactive alumina sputtering. In DC sputtered films, elemental aluminium of 9.2 at.% and nano-crystallites were present within the x-ray amorphous matrix, resulting from target arcing. Defects lead to premature dielectric breakdown/increased current leakage. PDC sputtering improved film quality by removing crystallites, metallic clusters and through thickness cracking. Time dependent dielectric breakdown (TDDB) measurements were carried out using conductive atomic force microscopy identified an improvement in dielectric strength (166 to 310?V??m?1) when switching from DC to PDC deposition power. TDDB suggested that at high applied field the dominant pre-breakdown conduction mechanism was Fowler-Nordheim tunnelling in DC films. Tensile pull-off adhesion ranged from 56 to 72?MPa and was highest following incorporation of an Cu/Al blended interfacial layer. Scratch testing indicated various cracking/buckling failures.

Electrical starter/generator (ESG) system is one of the key innovations of more-electric aircraft initiative. The ESG cranks the engine and accelerates it up to self-sustained speed using electric energy (starter mode) and then runs as a generator to supply onboard loads. Three-level neutral point clamped (NPC) converter have been identified as a preferable choice for ESG applications due to high power quality as well as efficiency. However, the application of three-level NPC converter in the ESG systems has certain challenges. One of which is the low frequency neutral point voltage ripple, especially in generation mode when running at high speeds such that the flux weakening control is required. The paper proposes an advanced modulation scheme which can balance the neutral point voltage for the full range of speeds and loading conditions. Using the proposed technique, zero neutral point voltage deviation within each switching period is achieved by introducing a sharing factor computed in a deadbeat predictive approach. The proposed technique is validated with simulation results.

This paper investigates the influence of the slot/pole (S/P) combination on inter-turn short-circuit (SC) current in fault-tolerant permanent magnet (FT-PM) machines. A 2-D sub-domain field computational model with multi-objective genetic algorithm is used for the design and performance prediction of the considered FT-PM machines. The electromagnetic losses of machines, including iron, magnet, and winding losses are systematically computed using analytical tools. During the postprocessing stage, a 1-D analysis is employed for turn-turn fault analysis. The method calculates self-and mutual inductances of both the faulty and healthy turns under an SC fault condition with respect to the fault locations, and thus SC fault current, considering its location. Eight FT-PM machines with different S/P combinations are analyzed. Both the performance of the machine during normal operation and induced currents during a turn-turn SC fault are investigated. To evaluate the thermal impact of each S/P combination under an inter-turn fault condition, a thermal analysis is performed using finite element computation. It is shown that low-rotor-pole-number machines have a better fault tolerance capability, while high-rotor-pole-number machines are lighter and provide higher efficiency. Results show that the influence of the S/P selection on inter-turn fault SC current needs to be considered during the design process to balance the efficiency and power density against fault-tolerant criteria of the application at hand.

This paper looks at a novel optimisation approach to the design of surface mounted permanent magnet (SMPM) machines with self-sensing capabilities. A methodology will be presented which will look at the use of genetic algorithms (GA) to contemporarily maximise the output torque and the self sensing properties of such machines. A GA optimisation environment has been grafted with a finite element analysis (FEA) environment to enable the designer to account for both geometrical and saturation saliencies for an effective determination of the machine's self sensing characteristics. Satisfactory results were obtained in terms of torque maximization and self sensing capability. In addition sensitivity of the major geometrical parameters of the machine will be discussed in terms torque density and the self-sensing.

In this article, a novel post fault control algorithm based on the space vector method is presented and applied to a bearingless multisector permanent magnet synchronous machine with a triple three-phase winding. First, the expressions of the current space vectors, as a function of the electromagnetic suspension force and motoring torque, are introduced. Then, the open-circuit fault is described and a new post-fault algorithm is introduced. The introduced post-fault algorithm, based on the minimization of the stator copper losses, is compared at simulation level with an existing one, where the above-mentioned loss minimization was not considered. The simulation results show a remarkable improvement in the performance when the novel post-fault algorithm is employed. Finally, the developed control algorithm is experimentally validated on a prototype of a bearingless multisector permanent magnet synchronous machine.

The transportation electrification process is rapidly demanding for drivers with enhanced performance. Modern systems are moving from fossil fuel technologies toward hybrid and fully electric solutions. Consequently, in automotive and motorcycle sectors the complete electrification process requires significant power and energy capabilities, and high efficiency. Also, to minimize the mechanical power loss and save the battery energy, the weight and volume of the vehicle have to be minimized. These features are significantly stressed in race applications, where the power density of the drive and its efficiency has to push the limits of state of the art. In this work, a multiphase machine with dual rotor architecture is employed, aiming at maximizing the performance of a full electric motorcycle (E-Bike). In particular, it is already known that in multi-phase machines it is possible to inject high frequency current component to increase the power density of the drive. Therefore, the analytical model for the injection of a third harmonic in the currents waveforms is presented for a case study of E-Bike featuring a dual rotor with Halback permanent magnet array. The third current harmonic is injected keeping the same peak current, when compared with the control technique without injection. The three-phase and multiphase winding layout of the machine are compared with and without current injection control by means of analytical equations. Finally, finite element results are shown in order to validate the model, the advantage of the multiphase winding and the current injection technique.

A new advanced fault tolerant control technique for a triple three-phase Surface Permanent Magnet (SPM) machine is investigated in this paper. The machine has a nine-phase winding arranged in three sectors and supplied by three different Voltage Source Inverters (VSIs). The proposed current control technique is firstly exploited to avoid the radial force appearance in case of open winding of one machine sector. Then, the radial force fault tolerant control is improved to compensate for a bearing fault or another source of radial force in this open winding condition. Finite element simulations are used to validate the two proposed control techniques. Finally, advantages and drawbacks of the solution are highlighted.

The radial force control technique for a triple three-phase Surface Permanent Magnet (SPM) machine is investigated in this paper. The machine has a nine-phase winding arranged in three sectors and supplied by three different Voltage Source Inverters (VSI). A machine model is developed, based on the multi space vector approach. The multi space vector current control technique is exploited to control the torque and the radial force. The radial force control can be useful to compensate for a bearing fault or for a rotor eccentricity. Finite element simulations are used to validate the model and the control technique. Finally, criticalities of the control and modelling aspects are discussed.

A new multiphase Surface Permanent Magnet (SPM) machine design is investigated in this paper. The machine has a nine-phase winding arranged in three sectors and supplied by three different Voltage Source Inverters (VSI). Stator segmentation between these sectors is analyzed to improve the machine performance and fault tolerant behaviour. A new adaptable control technique is developed for the different segmentation geometries. Finite element simulations are used in order to validate the model and analyse possible layouts. Finally, an optimized design is proposed and the criticalities of the segmentation solution are explained.

Diseño de un generador eléctrico de imanes permanentes para bicicleta eléctrica sin conexión mecánica, es decir, sin cadena.