E. Santini

Multi-stage axial-flux PM machine for wheel direct drive

The design of direct-drive wheel motors must comply with a diameter restriction due to housing the motor in a wheel rim, and must allow the achievement of very high torque density and overload capability. Slotless axial-flux permanent magnet machines (AFPMs) prove to be one of the best candidates for application in electric vehicles as direct-drive wheel motors, as in comparison with conventional machines they allow designs with higher compactness, lightness and efficiency. The paper presents a newly-conceived AFPM which has multi-stage structure and water-cooled ironless stator. In the proposed new machine topology, the space formerly occupied by the toroidal core becomes a water duct, which removes heat directly from the interior surface of the stator winding. The high efficiency of the machine cooling arrangement allows long-term 100% overload operation and great reduction of the machine weight. The multistage structure of the machine is suited to overcome the restriction on the machine diameter and meet the torque required at the wheel shaft. The paper gives guidelines for the design of a multi-stage AFPM with water-cooled ironless stator, and describes characteristics of a two-stage prototype machine rated 220 Nm, 1100 RPM.

Performance of coreless-winding axial-flux permanent-magnet generator with power output at 400 Hz-3000 rev/min

An axial-flux permanent magnet machine (AFPM) topology with a coreless winding is proposed for generator units required aboard ships, aircraft or hybrid-electric vehicles. In the proposed AFPM configuration, the winding consists of rhomboidal shaped coils encapsulated in fibre-reinforced epoxy resin. The coils have a double-layer arrangement to leave space for a cooling water duct being used to remove heat directly from the interior surface of the winding. The overall machine structure has high compactness and lightness, and because of the lack of the iron core generator operation with power output at 400 Hz can be accomplished with high efficiency and acceptable voltage regulation. The paper discusses the basic design and construction of AFPM generators with coreless winding and experimental results taken from a 16 poles machine prototype rated 70 kW, 3000 rev/min are finally reported.

Compact wheel direct drive for EVs

Concerning the application of slotless axial-flux PM motor (AFPMs) in electric vehicle drives, this article deals with the development of a 16-pole AFPM prototype which is used in the propulsion system of an electrical scooter. The proposed AFPM prototype has 45 Nm peak torque and 6.8 kg mass of active materials, and it is coupled directly to the scooters rear wheel. In the following, the authors discuss the design and construction of the motor prototype and report experimental results taken from machine laboratory tests. Finally, they give details concerning the motor drive arrangement used in an electrical scooter prototype.

Basic principle and design criteria of axial-flux PM machines having counter-rotating rotors

Axial-flux PM machines are particularly suitable for application in electrical drives devoted to ship propulsion, since they allow the elimination of the large-power gearbox used in conventional systems. In consideration of that, this paper deals with a novel slotless axial-flux PM machine topology which is characterised by the synchronous counter rotation of the two machine rotors. Such a new machine topology can find application in the direct driving of two counter-rotating propellers, which may be used in propulsion systems to recover energy from rotational flow of the main propeller slip stream. In this case, the use of an axial-flux machine having counter-rotating rotors allows an improvement in terms of weight and efficiency, since the epicyclic gear otherwise required for the motion reversal can be avoided. The paper discusses the stator winding arrangement which allows the opposite motion of the machine rotors and reports experimental results taken from a small-size machine prototype.<<ETX>>

Innovative solutions for stand alone system powering

In the paper, possible hybrid configurations of low power stand alone systems based on renewable energy sources (RES) and alternative sources, suitable for applications in remote areas not connected to the grid such as radio base stations for mobile phone communications, are described and compared. As practical case, different alternative solutions for the powering of a radio base station (RBS) are analysed: the wind-solar technology including also a PEM fuel cell, supplying a conventional refrigeration system or an absorption system for the equipment cooling; a thermally insulated pre-fabricated system that uses the natural air circulation for the equipment cooling.

Rotor bars breakage in railway traction squirrel cage induction motors and diagnosis by MCSA technique Part II : Theoretical arrangements for fault-related current sidebands

In a companion paper (Part I) the bar breakages for a 1.13 MW induction motor used in high speed railway traction drives were studied, by simulating the whole system (converter + motor) and by analyzing frequencies and amplitudes of current sidebands, for various loads (both active and inertial) and with increasing fault severity. It was recognized that faults can be characterized by (1-2s)f sideband, but results vary with load torque and drive inertia. Other sidebands appear less dependent from these disturbs, like (5+2s)f. Unfortunately, no works presented simple and general formulas about sidebands. In this paper, theoretical formulations for computation and prediction of rotor fault-related sideband frequencies and amplitudes are given, aiming to obtain relations useful for diagnostic purposes (fault severity assessment by MCSA), and by using Part I as a case-study. A decomposition by multiphase symmetrical components is performed, taking in account space harmonics. Formulas for (1-2s)f sideband amplitude are carried out, extendable to many other sidebands.

Synchronous generator eccentricities modeling by improved MWFA and fault signature evaluation in no-load E.M.F.s and current spectra

In this paper an accurate modeling of air-gap length function in polar and interpolar regions of non- isotropic synchronous generators is presented, for use in the MWFA (modified winding function approach), to obtain accurate machine simulations with eccentricities. Air-gap in interpolar regions is usually poorly modeled in current literature. Inductances obtained by the improved MWFA have been compared with 3D-FEM model obtained ones. External no-load e.m.f. and current spectra have been evaluated for a medium-power alternator with non-aligned rotor, and with various static and dynamic eccentricity degrees. Fault signatures appear all over the spectra, with variable entities, whose comprehensive evaluation can be used for fault severity assessment.

Influence of the radial variation of the magnet pitch in slotless permanent magnet axial flux motors

The design of slotless axial-flux machines is different from that of conventional radial-flux machines, due to their topology. In particular, the active conductors are subjected to different conditions of magnetic field along their radial length. This is enhanced in machines where the shape of the magnets is different from that of the stator poles. This paper provides a numerical approach (2D FEM) for keeping into account this configuration: the described technique allows accurate evaluation of the instantaneous torque and of the mean torque, as well as all the quantities (such as back EMF, efficiency, and so on) that characterise the machine. The algorithm is validated by means of comparisons with the experimental results from an existing machine.

High-efficiency low-volume starter/alternator for automotive applications

The amount of electric and electronic equipment in automobiles has grown continuously bringing generating requirements more in line with starting requirements, thereby increasing the appeal of combined starter/alternator (S/A) systems. As surface mounted permanent magnet machines achieve high torque and power densities, which are very attractive for S/A applications, this paper outlines the solutions adopted for the development of a direct-drive axial-flux PM (AFPM) S/A including design characteristics and experimental data taken from a 3 kW prototype. This machine topology, having a reduced axial length and low phase reactance, is particularly suited for S/A systems where reduced room along the engine shaft is available and low voltage drop in generating mode of operation is required. Moreover by using a Litz wire winding good efficiency is reached along the whole operating frequency range.

Static and dynamic rotor eccentricity on-line detection and discrimination in synchronous generators By No-Load E.M.F. space vector loci analysis

In this paper a study about the different effects of static and dynamic rotor eccentricities on the external electric variables of a salient-pole synchronous generator is presented. Air-gap irregularities and related monitoring techniques have been studied in the past mainly about large hydro-generators (with practical applications), but similar problems have been recognized for on-board ship synchronous generators. These latter require a different approach, i.e. non-invasive monitoring. Static and dynamic rotor eccentricities were simulated in this work, for a ship-application sized generator, by using a dynamic model including inductances computed by parametric 3D FEM analysis of the faulty machine. Current, voltage, and no-load e.m.f. steady-state waveforms were analyzed by FFT and space-vector approach. No-load e.m.f. space vector is a sensitive fault indicator since its amplitude largely increases with the level of absolute eccentricity; furthermore, it is possible to discriminate the static eccentricity from the dynamic eccentricity utilizing the space vector loci ovality.