Massimo Barcaro

Permanent-Magnet Optimization in Permanent-Magnet-Assisted Synchronous Reluctance Motor for a Wide Constant-Power Speed Range

A permanent-magnet (PM)-assisted synchronous reluctance (PMASR) machine exhibits both high efficiency and high flux-weakening (FW) range. However, the best performance is achieved after a machine design optimization. In industry applications, the design of PMASR machines requires to satisfy an increasing number of limitations. The key points are lamination geometry, material property, and control strategy. This paper analyzes the influence of PM volume (flux level) on the motor performance, although lamination geometry and stack length are kept fixed. Thus, the PM volume inset in the rotor is optimized. The considered PMASR motor is designed for a very high FW speed range. The study is based on a finite-element (FE) analysis. The accuracy of the FE simulations is verified comparing their results with measurements on a prototype. The FE model is then used to study the different cases.

Analysis and Tests of a Dual Three-Phase 12-Slot 10-Pole Permanent-Magnet Motor

In order to increase the fault tolerance of a motor drive, multiphase systems are adopted. Since custom solutions are expensive, machines with dual three-phase windings supplied by two parallel converters seem to be more convenient. In the event of a fault, one of the two three-phase windings (the faulty winding) is disconnected, and the motor is operated by means of the healthy winding only. A fractional-slot permanent-magnet (PM) motor with 12 slots and 10 poles is considered with two different rotor topologies: the interior PM (IPM) rotor and the surface-mounted PM rotor. Various winding configurations of dual three-phase windings are taken into account, comparing average torque, torque ripple, mutual coupling among phases, overload capability, and short-circuit behavior. Considerations are given regarding the winding arrangements so as to avoid excessive torque ripple and unbalanced radial forces in faulty operating conditions. An IPM motor prototype has been built, and experimental results are carried out in order to verify the numerical predictions.

Faulty Operations of a PM Fractional-Slot Machine With a Dual Three-Phase Winding

The permanent-magnet (PM) machine with dual three-phase windings is proposed for applications requiring continuous operating even under a partial fault. The two windings are supplied by two separate inverters. Thus, in the event of a fault of one winding, this is disconnected, and the machine continues to be operated by means of the healthy winding. This paper investigates the PM machine with dual three-phase windings and its capabilities during faulty operating conditions. A fractional-slot interior PM machine with 12 slots and 10 poles is taken into account. Its performance is investigated according to different winding configurations. The torque behavior, overload capability, and thermal limits are evaluated under open-circuit and short-circuit faults. A finite-element analysis as well as experimental tests is carried out on a prototype of such a machine.

Optimization of Interior PM Motors With Machaon Rotor Flux Barriers

Interior permanent magnet (IPM) motors are normally designed with two or more flux barriers per pole. The form of such flux barriers has a direct impact on the torque developed by the IPM motor, with regards to both its average value and ripple. The Machaon structure includes flux barriers of different shape, aimed at reducing the torque ripple. Their shape depends on the number of poles, number of slots, winding arrangements, and PM volume used in the rotor. An optimization technique is adopted in order to determine the best shape of the flux barriers with the objective of achieving a smooth torque with a high average value.

Six-Phase Supply Feasibility Using a PM Fractional-Slot Dual Winding Machine

The growing interest in fault-tolerant drives requires new solutions avoiding the adoption of custom and expensive configurations. The machine with a dual three-phase winding is an interesting candidate. It is provided with two windings, each of them fed by one converter of half power. With a proper mechanical and electrical arrangement, the machine can be exactly a six-phase machine, obtaining higher performance during healthy conditions. In the event of a fault, one of the two three-phase windings (the faulty one) is disconnected, and the machine is operated by means of the healthy winding only. This paper analyzes the feasibility of this dual winding configuration applied to a nonoverlapped-coil fractional-slot winding permanent-magnet machine. The star of slots is applied to highlight the proper winding candidates. The more interesting windings are deeply analyzed.

Rotor Flux-Barrier Geometry Design to Reduce Stator Iron Losses in Synchronous IPM Motors Under FW Operations

The interior permanent-magnet (IPM) synchronous motor is characterized by a high rotor anisotropy. Such an anisotropy is the cause of a high harmonic content of the air-gap flux density distribution, almost independent of the main flux. As a consequence, there are fluctuations of the flux density in the stator iron and, consequently, eddy-current iron losses. This aspect is prominently evident during flux-weakening operations, when the armature current weakens the permanent magnet flux and the motor runs above the base speed. This paper presents a complete study of such a phenomenon, including an analytical model and a finite element validation, as well as an experimental confirmation of the predicted stator tooth flux waveforms. Finally, some suggestions are given in order to design an IPM motor exhibiting reduced iron losses during all operating conditions.

Design of a Low-Torque-Ripple Fractional-Slot Interior Permanent-Magnet Motor

Despite a strong nonlinear behavior and a complex design, the interior permanent-magnet (IPM) machine is proposed as a good candidate among the PM machines owing to its interesting peculiarities, i.e., higher torque in flux-weakening operation, higher fault tolerance, and ability to adopt low-cost PMs. A second trend in designing PM machines concerns the adoption of fractional-slot (FS) nonoverlapped coil windings, which reduce the end winding length and consequently the Joule losses and the cost. Therefore, the adoption of an IPM machine with an FS winding aims to combine both advantages: high torque and efficiency in a wide operating region. However, the combination of an anisotropic rotor and an FS winding stator causes some problems. The interaction between the magnetomotive force harmonics due to the stator current and the rotor anisotropy causes a very high torque ripple. This paper illustrates a procedure in designing an IPM motor with the FS winding exhibiting a low torque ripple. The design strategy is based on two consecutive steps: at first, the winding is optimized by taking a multilayer structure, and then, the rotor geometry is optimized by adopting a nonsymmetric structure. As an example, a 12-slot 10-pole IPM machine is considered, achieving a torque ripple lower than 1.5% at full load.

IPM Machine Drive Design and Tests for an Integrated Starter-Alternator Application

This paper deals with an integrated starter-alternator (ISA) drive which exhibits a high torque for the engine start, a wide constant-power speed range for the engine speedup, and a high-speed generator mode operation for electric energy generation. Peculiarities of this ISA drive are thus its flux-weakening capability and the possibility to large torque overload at low speed. The focus on the design, analysis, and test of an interior permanent-magnet motor and drive for a prototype of ISA is given in this paper. In details, this paper reports on the design of stator and rotor geometries, the results of finite-element computations, the description of control system, and the experimental results of prototype tests.

Interior PM Machines Using Ferrite to Replace Rare-Earth Surface PM Machines

Since the cost of rare-earth permanent magnets (PMs), such as NdFeB and SmCo, is more and more increasing, there is a great interest in designing PM machines without adopting such rare-earth PMs, i.e., replacing them with cheaper ferrite magnets. Referring to the interior PM (IPM) machines, the expected performance reduction is limited owing to the anisotropic structure: The reluctance (REL) torque component compensates for the use of low-energy PMs. This paper investigates the convenience of adopting ferrite magnets in an IPM machine (sometimes also referred to as PM-assisted synchronous REL machine), instead of a rare-earth surface-mounted PM machine. It is shown that, even though a lengthening of the stack length is required, the anisotropic PM machine that adopts ferrite magnets may represent a valid competitor of a surface PM machine with rare-earth PMs.

IPM Machine Drive Design and Tests for an Integrated Starter–Alternator Application

This paper deals with an integrated starter-alternator (ISA) drive which exhibits a high torque for the engine start, a wide constant-power speed range for the engine speedup, and a high-speed generator mode operation for electric energy generation. Peculiarities of this ISA drive are thus its flux-weakening capability and the possibility to large torque overload at low speed. The focus on the design, analysis, and test of an interior permanent-magnet motor and drive for a prototype of ISA is given in this paper. In details, this paper reports on the design of stator and rotor geometries, the results of finite-element computations, the description of control system, and the experimental results of prototype tests.