F. Caricchi

Study of bi-directional buck-boost converter topologies for application in electrical vehicle motor drives

The use of a bi-directional DC-DC converter in motor drives devoted to EVs allows a suitable control of both motoring and regenerative braking operations. In particular, during motoring operations of a battery-fed DC motor drive, a DC-DC converter is to be used to adjust the motor current in order to follow the torque reference signal. On the other hand, a bi-directional arrangement of the converter is needed for the reversal of the power flow, in order to recover the vehicle kinetic energy in the battery by means of motor drive regenerative braking operations. This paper deals with the study and comparison of two bi-directional buck-boost converter topologies. Each of them allows stepping the battery voltage level either up or down, according to motor drive modes of operation. For each converter topology computer simulations of modes of operation are presented together with experimental test results.

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.

20 kW water-cooled prototype of a buck-boost bidirectional DC-DC converter topology for electrical vehicle motor drives

In brushless DC motor drives devoted to electric vehicles (EVs) a bi-directional DC-DC power converter can be used to control suitably both motoring and regenerative braking operations in order to improve the motor drive performance. In consideration of such an application, this paper deals with the experimental study of a buck-boost bi-directional DC-DC power converter topology which has been conceived for the use in EVs propelled by means of wheel-direct-coupling axial-flux PM motor drives. The paper discusses the power converter modes of operation and reports experimental results taken from a 20 kW water-cooled prototype of the proposed power converter topology.<<ETX>>

Experimental study of a bidirectional DC-DC converter for the DC link voltage control and the regenerative braking in PM motor drives devoted to electrical vehicles

The use of a bidirectional DC-DC converter operating in the DC link of CRPWM-inverter-fed motor drives devoted to electric vehicles (EVs) application allows a suitable control of both motoring and regenerative braking operations, and it can contribute to a significant increase of the motor drive overall efficiency. This paper deals with the experimental study of a bidirectional DC-DC converter prototype which has been designed for application in small-size EVs propelled by axial-flux PM motor drives. The paper discusses the converter modes of operation and reports the experimental results taken from a converter prototype which has been constructed using an IGBTs power module rated 600 V, 50 A.<<ETX>>

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.

Permanent-magnet, direct-drive, starter/alternator machine with weakened flux linkage for constant-power operation over extremely wide speed range

As consequence of the considerable increase of the electrical power demand in vehicles, the adoption of a combined direct-drive starter/alternator system is being seriously pursued and a new generation of vehicle alternators delivering power up to 6 kW over the entire range of the engine speed is soon expected for use with connection to a 42 V bus. The surface permanent magnet (SPM) machines offer many of the features sought for such future automotive power generation systems, and thereby a substantial improvement in the control of their output voltage would allow the full exploitation of their attractive characteristics in the direct-drive starter/alternator application without significant penalties otherwise resulting on the machine-fed power converter. Concerning that, this paper reports on the original solution adopted in a proof-of-concept axial-flux permanent magnet machine (AFPM) prototype to provide weakening of the flux linkage with speed and thereby achieve constant-power operation over a wide speed range. The principle being utilized is introduced and described, including design dimensions and experimental data taken from the proof-of-concept machine 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>>

Sinusoidal brushless drive with low-cost linear Hall effect position sensors

This paper presents a low-cost AC brushless drive, which is obtained by the employment of linear Hall effect ICs for the generation of current references in the three-phase stationary reference frame. In this way, the traditionally adopted position sensor (i.e. absolute or incremental encoder, resolver, etc.) can be eliminated, thus obtaining a considerable gain in terms of costs and reliability. Moreover, if the back EMF presents some harmonic content, the same drive allows incrementing the output power with respect to a conventional sinusoidal drive. Finally, it can be directly employed also in DC brushless drives, without any modification and maximising power output.

Prototype of electric vehicle drive with twin water-cooled wheel direct drive motors

The availability of new high-energy permanent magnets at a reasonable cost has opened up the possibility of developing very compact brushless permanent magnet motors with substantially improved overload capability for wheel direct drive applications. Concerning the development of an electric propulsion system for a newly-conceived dual-power city car, this paper discusses the design, construction and laboratory testing of a twin wheel direct drive prototype based on a novel topology of water-cooled axial-flux permanent magnet motor.