Fabio Giulii Capponi

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.

Recent Advances in Axial-Flux Permanent-Magnet Machine Technology

This paper reviews the progress that has been made in the analysis and design of axial-flux permanent-magnet machines over the past decade, with particular attention to aspects such as electromagnetic and thermal modeling, materials, manufacturing, pulsating torque, and extended speed range. Comparisons with other machine types and applications are also reviewed.

Experimental study on reducing cogging torque and no-load power loss in axial-flux permanent-magnet machines with slotted winding

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 winding are the most promising candidate for use in wheel-motor drives. In consideration of that, this paper deals with an experimental study devoted to investigate a number of technical solutions to be used in AFPMs having a slotted winding in order to achieve substantial reduction of cogging torque and power loss in the stator core. To conduct such an experimental study, a laboratory machine was purposely built incorporating facilities that allow easy-to-achieve off-line 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.

Erratum to "Implementation Issues and Performance Evaluation of Sinusoidal, Surface-Mounted PM Machine Drives With Hall-Effect Position Sensors and a Vector-Tracking Observer"

This paper presents the implementation and evaluation of a high-resolution position estimation system for sinusoidal, surface phase modulation machines based on Hall-effect sensors and a vector-tracking observer. First, the tuning of the observer is presented and a speed-dependent gain scheduling strategy is proposed. Then various harmonic decoupling strategies are investigated to improve the performance of the observer, particularly at low speeds. Stability analysis is performed leading to the definition of local stability limits, within which the actual position is tracked with bounded estimation error. Both simulation and experimental testing illustrate the performance and limitations of the proposed observer topology and of the drive when this observer is used for state feedback.

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.

Axial-Flux Permanent-Magnet Generator for Induction Heating Gensets

This paper presents a single-phase slotless axial-flux permanent-magnet synchronous machine for induction heating gensets. A full-scale prototype of the machine (110 kVA, 400 Hz, 690 A) has been designed and subsequently analyzed through finite element analysis (FEA). Induced current distributions in the permanent magnets and in the rotors have also been calculated through FEA, showing that the resulting losses are kept at bay due to the low armature reaction. An effective way of achieving regulation of the power transferred to the load has been analytically derived. The prototype has also been built, and experimental tests confirm the aforesaid analyses.

No-Load Performance of Axial Flux Permanent Magnet Machines Mounting Magnetic Wedges

Axial flux permanent magnet (AFPM) machines are being increasingly used in a variety of industrial, direct drive applications which benefit from their extreme axial compactness. In particular, slotted AFPM machines are of great interest, since they allow to achieve high torque densities together with an adequate constant power speed range. This paper analyzes a particular aspect related to the design of such machines, i.e. the use of soft magnetic composite (SMC) wedges to close stator slots. Magnetic circuit-based analyses and 2-D and 3-D finite-element analyses are performed on a 10 kW AFPM machine; various magnetic wedge configurations are adopted; the no-load performance is compared with that of the same machine using nonmagnetic wedges in terms of flux linkage, cogging torque, and no-load losses. Finally, experimental tests and results on a full-scale prototype machine mounting magnetic wedges are reported.

Active Output Voltage Regulation for an Ironless Axial-Flux PM Automotive Alternator with Electromechanical Flux Weakening

Aim of the paper is to present a solution for active output voltage regulation in PM automotive alternators, though mechanical flux weakening. An AFPM ironless machine is investigated, composed of two stators connected in series which can be shifted one with respect to the other, thus allowing a theoretically infinite constant power speed range. The paper focuses on the aspects related to layout, sizing and control of the shifting mechanism, which are critical for accurate output voltage regulation. Experimental tests on a 2 kW prototype will validate the capabilities of the proposed solution, both during steady-state and during transient operating conditions.

On the Use of Magnetic Wedges in Axial Flux Permanent Magnet Machines

Axial flux permanent magnet (AFPM) machines are being increasingly used in a variety of industrial direct drive applications which benefit from their extreme axial compactness. In particular, slotted AFPM machines are of great interest since they allow to achieve high torque densities together with an acceptable constant power speed range. This paper analyzes a particular aspect related to the design of such machines, i.e., the use of soft-magnetic-composite wedges to close stator slots. This paper is the continuation of a previous investigation dedicated to the analysis of the no-load performance variation introduced by the magnetic wedges. Here, the attention is focused on the load performance by studying the effect of the wedges on d-q-axis stator flux linkages, torque production, and losses. The 2-D and 3-D finite element analyses are performed on a 10-kW AFPM machine, various magnetic wedge configurations are studied, and the load performance is compared with that of the same machine using nonmagnetic wedges, in terms of stator flux linkage, average and ripple torque, and magnetic losses. Finally, experimental tests and results on a full scale prototype machine mounting magnetic wedges are reported.

Ironless Axial Flux PM Machine With Active Mechanical Flux Weakening For Automotive Applications

Because of their high compactness and lightness, together with high efficiency, axial-flux PM (AFPM) machines are among the most suitable candidates for several automotive applications. As a drawback, they are limited in speed range because voltage rises linearly with speed. For this reason, they are generally considered not well-suited for applications such as starter/alternators. As a solution, in this paper an AFPM ironless machine prototype with extended flux weakening capabilities is proposed. Flux weakening, and therefore output voltage regulation, is achieved mechanically through a small-sized actuator that displaces each other the two adjacent windings that compose the stator