Fabio Luise

Potentials and limits of high-speed PM motors

This paper illustrates the potentials and limits of high-speed permanent-magnet (PM) motors. The effect of the material choice, including PM, stator core and retaining sleeve is highlighted. Slotted and slotless configurations are taken into account and compared, computing magnetic, electrical, mechanical and thermal quantities by means of both an analytical and a finite element approach. In particular, the thermal and the PM demagnetization limits and the rotor losses are evaluated. A criteria of optimisation of the motor structure is described, with the diameter ratio and the iron flux density as main design variables.

Analysis and design of a PM Brushless Motor for high-speed operations

This paper deals with the design of a 1-kW permanent-magnet (PM) brushless motor operating in the speed range of 20-40 k r/min. The design procedure involves a parametrical investigation of the most adequate motor configuration by means of a coupled thermal and electromagnetic analysis. The design procedure takes advantage of an analytical study based on Maxwells equations and is refined by finite-element analysis. Both slotted and slotless motor configurations have been taken into account, with different PM materials for an overall comparison of the motor performance.

Potentials and limits of high speed PM motors

This paper illustrates the potentials and limits of high-speed permanent-magnet (PM) motors. The effect of the material choice, including PM, stator core and retaining sleeve is highlighted. Slotted and slotless configurations are taken into account and compared, computing magnetic, electrical, mechanical and thermal quantities by means of both an analytical and a finite element approach. In particular, the thermal and the PM demagnetization limits and the rotor losses are evaluated. A criteria of optimisation of the motor structure is described, with the diameter ratio and the iron flux density as main design variables.

Analysis and design of a brushless motor for high speed operation

This paper presents the design of a 1 kW permanent magnet brushless motor operating at 20-40 krpm. The design procedure involves parametrical research of the most convenient motor configuration through a coupled thermal and electromagnetic analysis. The preliminary design is based on the solution of Maxwells equations and is followed by a finite element analysis. A slotted and a slotless motor configurations have been taken into account, with different permanent magnet materials for an overall comparison of the motor performance.

An Analytical-Numeric Method for Stator End-Coil Leakage Inductance Computation in Multi-Phase Electric Machines

In this paper an analytical-numeric method for stator end-coil leakage inductance computation is presented based on the solution of Neumann integrals. The method extends an approach already introduced for three-phase machines to the case of an arbitrary phase number and arrangement. Moreover, some original contributions are proposed to enhance the calculation of end-coil self inductances, for which Neumann integrals cannot be directly used. Measurements on three machines with different numbers of poles and phases are presented to assess the accuracy of the method.

Design Optimization and Testing of High-Performance Motors: Evaluating a Compromise Between Quality Design Development and Production Costs of a Halbach-Array PM Slotless Motor

This article has reported on an industrial R&D project aimed at identifying a cost-effective response to the more and more challenging high-speed motor requirements that presently come from the gas industry sector. To meet the very high efficiency, dynamic performance, and reliability standards required by cutting-edge turbomachinery drive applications, a special PM synchronous motor prototype has been developed. The identified technology includes AMBs for rotor levitation, a slotless stator design, and a Halbach-array PM rotor. Motor design optimization through genetic algorithms has been presented as a tool to search for the best tradeoff between performance targets and industrial production cost reduction. Extensive prototype testing under converter supply has been reported as a successful validation of the selected technology.

A contextual parameter identification method for the equivalent circuit of induction machine

The classic single-phase equivalent circuit is used to predict the steady-state operation of symmetrical induction machines under balanced sinusoidal supply. Its scope can be extended by considering variable parameters depending on the main influencing quantities, thus allowing to account also for secondary phenomena affecting the machine operation, such as magnetic saturation and skin effect. This paper presents a contextual identification method using analytical elaborations and one standstill pseudo-time-harmonic FEM simulation per each operation condition, permitting to estimate simultaneously all of the parameters and thus achieving a better coherency.

Design for manufacturability of an off-shore direct-drive wind generator

Direct-drive generators to be used in off-shore wind farms are very large low-speed electric machines which pose remarkable design and manufacturing challenges. Demand forecasts for this kind of machines are urging manufacturers to work out design and technological solutions that can facilitate series production at competitive costs. This paper presents the development of an interior-permanent magnet generator design and technology aimed at reducing series manufacturing costs while preserving high performance levels. The proposed solutions are validated through the construction and testing of a 780 kVA generator prototype conceived for easy scalability to higher power ratings (up to around 2.5 MVA) by core length increase.

Design for Manufacturability of an Off-Shore Direct-Drive Wind Generator: An Insight into Additional Loss Prediction and Mitigation

Direct-drive generators to be used in off-shore wind farms are very large low-speed electric machines, which pose remarkable design and manufacturing challenges. Demand forecasts for this kind of machines are urging manufacturers to work out design and technological solutions capable of facilitating series production at competitive costs. This paper presents the development of an interior permanent-magnet generator design and technology aimed at reducing series manufacturing costs while preserving good performance levels. The focus is on two of the most critical issues in the machine design and analysis, namely, the prediction and reduction of eddy-current losses in stator conductors and in permanent magnets. The proposed design solutions are validated through the construction and testing of a 780 kVA generator prototype conceived for easy scalability to higher power ratings (up to around 2.5 MVA) by core length increase.

Investigation into electrical resonance phenomena in the field circuit of wound-rotor synchronous machines

The field circuit of wound-rotor synchronous machines can be supplied in various ways, including brushed and brushless excitation systems. Regardless of whether the synchronous machine is equipped with a rotating exciter or not, the external excitation power source necessarily injects some high-frequency harmonics into the field circuit. The frequency of these harmonics can be particularly large if Pulse-Width-Modulated (PWM) converters are used as excitation voltage supply. This paper investigates the possibility that the excitation supply harmonics can produce electrical resonance phenomena resulting in possibly harmful overvoltages. The investigation is carried out through different approaches: by experiments on a low-voltage salient-pole 20-kVA laboratory prototype; by experiments on a large (multi-MW) round-rotor synchronous motor; through an analytical model. The results obtained from the analytical model are shown to well match measurements provided that a resistive parameter (affected by eddy-current loss effects) is properly calibrated. Another important conclusion is that the possible overvoltages due to electrical resonance would occur between internal points of the field (not between its terminals) and would not be thereby damped by conventional field circuit protection devices.