Fractional-slot concentrated-winding (FSCW) synchronous permanent magnet (PM) machines have been gaining interest over the last few years. This is mainly due to the several advantages that this type of windings provides. These include high-power density, high efficiency, short end turns, high slot fill factor particularly when coupled with segmented stator structures, low cogging torque, flux-weakening capability, and fault tolerance. This paper is going to provide a thorough analysis of FSCW synchronous PM machines in terms of opportunities and challenges. This paper will cover the theory and design of FSCW synchronous PM machines, achieving high-power density, flux-weakening capability, comparison of single- versus double-layer windings, fault-tolerance rotor losses, parasitic effects, comparison of interior versus surface PM machines, and various types of machines. This paper will also provide a summary of the commercial applications that involve FSCW synchronous PM machines.

Fractional-Slot Concentrated-Windings Synchronous Permanent Magnet Machines: Opportunities and Challenges

This paper deals with the design criteria for a high-efficiency permanent magnet synchronous motor. The goal is not pursued by a trivial reduction of the electric and magnetic loadings (which decrease motor losses) but optimizing a set of motor design variables, without increasing the overall dimensions, which are typically imposed as design constraints. The effect of the number of slots and of the inner-to-outer diameter ratio on motor losses is investigated. The possibility of designing a stator with a tooth length lower than the total core length, using soft magnetic composites, is studied. Finally, a criterion is proposed to evaluate the convenience of using a nonoverlapping winding. An analytical approach is adopted so as to allows the obtained results to be useful for a wide variety of permanent magnet machines.

Design criteria for high-efficiency SPM synchronous motors

The universal or AC commutator motor, widely used in hand tools or domestic appliances, generally uses a two-pole stator with a concentrated winding and an armature with interlocked coils elements. The copper volume and the axial length of the end windings of such conventional structures are then usually very important. In this paper, the authors present a new universal motor structure based on an efficient use of the isotropic magnetic properties of the soft magnetic composites (SMC) and on the concentrated winding technique. The stator core presents a claw pole structure and the armature has a concentrated winding with several coils wound around the same tooth. With this new AC commutator motor structure, a reduction of the total volume by a ratio equal to 200% is obtained when compared to classical universal motor structure with nearly identical performance.

A new structure of universal motor using soft magnetic composites

This paper deals with the magnetic analysis and the design of fractional slot PM motors with non overlapped coils. A particular care is given to the stator current reaction and the computation of the self and mutual inductances. The effort of this paper is to give an analytical prediction of these quantities. Simple but effective rules are given to a rapid choice of the motor geometry, with a special care of the combinations of number of poles and number of slots, as well as the winding types. Finite element simulations and experimental results confirm the analytical predictions. The effort of this paper is to find a method for the choice of the combination of the number of slot and poles of the machine.

Magnetic loading of fractional-slot three phase PM motors with non-overlapped coils

Soft magnetic composite (SMC) materials and their uses in electrical machines have undergone significant development in the past decade. The major advantages of the materials include isotropic magnetic and thermal properties, very low eddy current loss and relatively low total core loss at medium and higher frequencies, and low cost fabrication with good tolerance and surface finish using the well developed powder metallurgical techniques that require no further machining. It is even anticipated that the application of SMC may lead to a revolutionary development in the electrical machine manufacturing industry. This paper reviews the application of SMC in electrical machines. Both successful experiences and existing difficulties are discussed, and possible further work required for the commercial success of SMC machines is proposed.

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Applications of soft magnetic composite materials in electrical machines: A review

The armatures of conventional brush DC motors are using windings with interlocked coils elements With this kind of distributed winding, the axial length of the end-windings is usually very important and their copper volume is large In this paper, the authors present new structures of brush DC motor armature using a concentrated winding with a plurality of simple coils wound around the same tooth The copper volume is about 60% lower than in the classical winding armature and the current commutation remains efficient This kind of structure is well adapted to the use of soft magnetic composite materials for the realization of the magnetic circuit and can be used over a wide power range The design method and a synthesis of these machines with concentrated winding armatures are presented A prototype of concentrated winding brush DC motor is compared to a conventional motor used in a typical automotive application The performance of the new structure in terms of torque to copper volume ratio is much higher than in the case of the classical structure

A. Halila

Papers

Brush DC motors with concentrated windings and soft magnetic composites armatures