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In this paper, two methods for flux linkage regulation in a starter/alternator with an axial-flux permanent magnet (AFPM) machine are proposed and compared. Desired regulation is achieved by two different mechanical solutions, each of them capable of modifying the amount of flux linkage through displacement of the two rotors in the AFPM machine. Constant power generation is thus achieved with very inexpensive devices that do not require external energy sources since energy in the airgap doesn't change. The main difference between the two proposed solutions is that the speed dependant device is ideally a constant voltage source while the torque-dependant device behaves as a constant current source. Even if some improvements are still needed, both devices introduce the totally innovative concept of mechanical flux weakening for AFPM power regulation in a wide speed range. Finally, the paper demonstrates that the introduction of these devices doesn't modify machine behavior in starting mode, so that the particular features of AFPM machines in terms of high toque density and overload capability remain unaffected. Index Terms--Axial-flux permanent magnet (AFPM).

In hybrid electric vehicle (HEV) drivetrains an electrical generator is coupled onto the shaft of an internal-combustion engine (ICE) in order to process either the entire or a given fraction of the traction power required by the vehicle wheels. As such an ICE-driven generator is being confined within the vehicle hood and is exposed to heating resulting from ICE operation, high compactness, totally enclosed construction, and suitable machine cooling arrangement become challenging targets the generator design must deal with. Due to unique characteristics such as higher torque per volume and higher efficiency compared to other machine topologies, the axial-field permanent-magnet machine topology was selected for a 15-kW-at-4500-r/min-rated generator prototype that would be utilized in a demonstrator of an HEV drive train. This paper describes the original solutions adopted for the design of such an HEV generator and reports experimental results taken from the prototype machine. Index Terms--Axial-field machines, compact generators, hybrid vehicles, liquid-cooled machines, permanent-magnet (PM) machines.

The axial-flux permanent-magnet machine (AFPM) topology is suited for direct-drive applications and, due to their enhanced flux-weakening capability, AFPMs having slotted windings are the most promising candidates for use in wheel-motor drives. In consideration of this, this paper deals with an experimental study devoted to investigate a number of technical solutions to be used in AFPMs having slotted windings in order to achieve substantial reduction of both cogging torque and no-load power loss in the machine. To conduct such an experimental study, a laboratory machine was purposely built incorporating facilities that allow easy-to-achieve offline modifications of the overall magnetic arrangement at the machine air gaps, such as magnet skewing, angular shifting between rotor discs, and accommodation of either PVC or Somaloy wedges for closing the slot openings. The paper discusses experimental results and gives guidelines for the design of AFPMs with improved performance. Index Terms--Axial-flux machines, cogging torque, wheel motors.

This paper deals with design and construction of two twin prototypes of slotless axial-flux permanent-magnet motor drives jointly developed by SIMINOR Ascenseurs and the University of Rome for application in direct-drive elevator systems without machine room. Each prototype of pulley-direct-drive motor is rated 5 kW, 95 rev/min, and has a shaft height of 380 mm and overall axial thickness of about 80 mm. Machine design based on unusual specification and original manufacturing solutions adopted for the proposed direct-drive elevator arrangement are discussed throughout the paper, including the leading dimensions and characteristics of the prototype motors. Finally, experimental results taken from the machine prototypes are reported. Index Terms--Direct-drive motors, elevator motor drives, permanent-magnet machines.

An axial-flux permanent-magnet machine (AFPM) topology with 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 fiber-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, due to the lack of the iron core, generator operation with power output at 400 Hz can be accomplished with high efficiency and acceptable voltage regulation. This paper discusses the basic design and construction of AFPM generators with coreless winding and experimental results taken from a 16-pole machine prototype rated 230 N-m, 3000 r/min are finally reported. Index Terms - Aerospace power generation, on-board electric generators, permanent-magnet machines.

The variable-speed driven pump can result in significant energy conservation where reduced flow rates are required for long periods of time. In regard to adjustable-speed pump drives, one major contribution of this paper is the demonstration that a permanent magnet (PM) motor based on the slotless axial-flux permanent magnet machine (AFPM) topology can be a suitable candidate to advantageously compete with the induction motor for such a low-cost drive application. For the purpose of a cost comparison, the paper discusses design and construction of a prototype machine which has been conceived to replace a 1.2-hp induction motor being used in a standard adjustable-speed pump drive. Results taken from laboratory tests of the prototype machine are reported, together with an assessment of the machine manufacturing cost. Index Terms - AC adjustable-speed drives, axial-flux permanent magnet machines, brushless motor drives.

The design of direct-drive wheel motors must comply with diameter restriction due to housing the motor in a wheel rim and allow the achievement of very high torque density and overload capability. Slotless axial-flux permanent magnet machines (AFPM's) prove to be the best candidate 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 a multistage structure and a water-cooled ironless stator. In the proposed new topology of the machine 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 multistage AFPM with water-cooled ironless stator, and describes characteristics of a two-stage prototype machine rated 215 N[center dot]m, 1100 r/min.

The average torque of concentrated winding PM machines can be increased significantly by supplying current waveforms matching in full the trapezoidal back EMF. However, such current supply arrangements involve a large harmonic current flowing into the machine neutral. This paper presents an innovative converter topology to overcome the problem. This new configuration extends the standard layout of conventional PWM-VSI by adding a fourth branch devoted to control the voltage of the machine neutral. The inverter modes of operation resulting from the modulation of the machine neutral are discussed, and the paper reports the experimental results achieved from a converter prototype which has been constructed using IGBTs. Results show that the new inverter configuration allows significant benefits in the machine average torque, as well as the fact that the machine neutral modulation introduces an additional degree of freedom in the machine torque control.

This paper presents a new system, the mercury-gap ring collector (MGRC), for supplying current to the rotating armature of the double-armature generator (DAG). The MGRC can be considered as a valid alternative to conventional collector rings with solid brushes. It offers several advantages over sliding contacts with carbon brushes, especially when the machine has high rating currents and high rotating speed. The design of a prototype is presented in this paper; the experimental tests are reported and a comparison between the MGRC and a conventional carbon brush collector is discussed.

This paper outlines the original solutions adopted for powering a nonconventional three-wheel electric vehicle. This is a lightweight vehicle for use in urban mobility with mission tasks such as 50-km/h cruising speed and 80-kin range of autonomy. The propulsion system is based on a lead-acid battery-fed wheel direct drive. This is arranged with a 4.5-kW prototype of a slotless axial-flux permanent magnet machine, which has a total weight of 15 kg and is capable of 85-Nm continuous torque and 120 -Nm peak torque over 2 min. The motor is totally enclosed in the single front wheel of the vehicle and fed through an IGBT bidirectional power converter, which allows the control of both motoring and regenerative braking operations. Design characteristics and experimental data taken from the prototype of wheel direct drive are given. Index Terms--Axial-flux permanent-magnet (PM) motor, regenerative braking, urban mobility, wheel direct-drive motor.

This paper investigates methods to achieve a wide constant power speed range (CPSR) in electric drives using hybrid excitation synchronous machines; five strategies are presented and compared. These range from state-of-the-art flux weakening based on demagnetizing armature current injection, to algorithms based on wound excitation (WE) current regulation, all the way to techniques involving both armature and WE current regulation. It is shown that one of these latter strategies allows a theoretically infinite CPSR and unity power factor operation throughout. This result is also verified experimentally, and a 10:1 range is demonstrated. Finally, a discussion is presented on practical limiting issues such as harmonic flux linkage components, inductance variations, and high-speed iron losses. [ABSTRACT FROM PUBLISHER]