L. Del Ferraro

AC brushless drive with low-resolution Hall-effect sensors for surface-mounted PM Machines

An ac brushless drive in which Hall-effect sensors are used as rotor position sensors is presented in this paper. Three different methods to obtain a high-resolution position estimation from the low-resolution sensors are described and compared through simulation and experimental testing. The proposed control algorithms most innovative feature is its adaptability to the entire speed range, including startup, when using any of the three estimation algorithms. The control algorithm has been implemented and tested in order to drive a slotless axial-flux permanent-magnet (PM) machine for domestic appliance applications.

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.

Axial-flux PM starter/alternator machine with a novel mechanical device for extended flux weakening capabilities

In modern vehicles, the demand for on-board electric energy generation is rapidly growing in order to satisfy new requirements for passengers comfort and safety. This growth, which is predicted to reach 6 kW in the very next years, is forcing manufacturers to explore new solutions concerning the whole electrical system inside the vehicle. In particular, novel topologies of alternators are under research since the currently used Lundell type (claw-pole) alternator is reaching its power limits. In this paper an original torque dependant mechanical device is proposed in order to extend the speed range of an axial flux PM machine. This device displaces the rotors realizing a mechanical flux weakening with constant output power in generation. Simulations and experimental tests on a prototype realized in the lab are fully discussed.

Three-wheeled electric maxi-scooter for improved driving performances in large urban areas

In the last years a growing number of four-stroke vehicles, called maxi-scooters, came into European market as a solution to solve mobility problems in large urban areas. On the other hand, in the field of purely electric vehicles, only low-performance electric scooter solutions have been presented in the past. Aim of this paper is to present a new, high performance, prototype of a three-wheeled electric scooter with extended driving range. This prototype is propelled by two AFPM wheel-motors placed on the rear wheels and includes integrated linear Hall effect position sensors. This solution provides a low cost alternative to traditional encoders and resolvers, which are not viable in traction applications.

Stability conditions for multi-converter power systems

The development of power electronic system has brought the application of solid-state power converters in a variety of new fields of application. For example, the number of power converter varies from a few converters in a conventional car to hundreds in a international space station. A multi-converter power system is composed by the presence of different solid-state power converters integrated together in order to form an interconnected system, generally very complex. In this work stability conditions are investigated, starting at first from a conventional mathematical model derived using state-space averaging method. Preliminary experimental tests, however, proved the importance of parasitic parameters on the stability of the whole system. A more complete model that takes into account real parameters is then introduced, in order to obtain more precise predictions on critical load values. Final experimental test verified the validity of the model and the accordance with predictions.

Coil and Magnet Shape Optimization of an Ironless AFPM Machine by Means of 3D FEA

Coreless permanent magnet (PM) machines can be a viable solution for applications where light-weight and high- efficiency are requested, as the absence of an iron core in the stator reduces machine weight and losses at high-frequency losses. Due to the large airgap, main flux is not driven by a magnetic path into the stator, hence a 3D field analysis is necessary. In this paper, an AFPM ironless machine has been optimized in terms of maximum torque produced per joule losses. Several topologies of coils and magnets have been proposed and investigated with 3D FEA.

Aluminium Multi-Wire for High-Frequency Electric Machines

In order to limit losses in high-frequency transformers and inductor windings, special and expensive solutions such as Litz Wire are often adopted. The high cost of these wires is due to the complex process needed for realizing a thin insulating coating for each of the several single copper wires that form the strand. In this paper, an aluminium multi-wire is proposed as a low cost alternative to Litz Wire. Insulation between conductors is achieved by anodization, which is a commonly used process in the aluminium industry. Hence, the proposed solution can potentially drop the cost in electrical machines and in many other applications operating at high-frequency.

Measurement of traction current harmonics on the track circuits of the Rome-Naples high-speed railway

The new high speed railway lines, under construction in Italy, are electrified in 2times25 kHz - 50 Hz and, in order to avoid interference problems between traction and signaling current, make use of a signaling system based on audio frequency track circuits (AF-TC), ranging from 2.1 kHz to 16.5 kHz. Problems could arise from the fact that traction currents required by high-speed locomotives, equipped with electronic static converters, show a harmonic spectrum which includes audio frequencies. Since the tracks are means of propagation of both traction and signaling currents, interference problems in the standard operation can occur with possible impact on transportation regularity. Thus, preliminary studies of the compatibility between traction and signaling system (where the traction load is a disturbance source and the signaling circuit is a disturbance victim), under standard and failure conditions, are required. In this context, a measurement campaign on the AF-TC of the new high speed railway system Rome-Naples has been made and some results are reported in this paper