Yulia Alexandrova

Unequal Teeth Widths for Torque Ripple Reduction in Permanent Magnet Synchronous Machines With Fractional-Slot Non-Overlapping Windings

Permanent magnet synchronous machines (PMSMs) with fractional-slot non-overlapping windings, also known as tooth-coil winding PMSMs (TCW PMSM), have been under intensive research during the latest decade. There are many optimization routines explained and implemented in the literature to improve the characteristics of this machine type. This paper introduces a new technique for torque ripple minimization in TCW PMSM. The source of torque harmonics is also described. The low-order torque harmonics can be harmful for a variety of applications, such as direct drive wind generators, direct drive light vehicle electrical motors, and for some high-precision servo applications. The reduction of the torque ripple harmonics with the lowest orders (6th and 12th) is realized by machine geometry optimization technique using finite element analysis. The presented optimization technique includes the stator geometry adjustment in TCW PMSMs with rotor surface permanent magnets and with rotor embedded permanent magnets. Influence of the permanent magnet skewing on the torque ripple reduction and cogging torque elimination was also investigated. It was implemented separately and together with the stator optimization technique. As a result, the reduction of some torque ripple harmonics was attained.

Inductance Calculation of Tooth-Coil Permanent-Magnet Synchronous Machines

Analytical calculation methods for all the major components of the synchronous inductance of tooth-coil permanent-magnet synchronous machines are reevaluated in this paper. The inductance estimation is different in the tooth-coil machine compared with the one in the traditional rotating field winding machine. The accuracy of the analytical torque calculation highly depends on the estimated synchronous inductance. Despite powerful finite element method (FEM) tools, an accurate and fast analytical method is required at an early design stage to find an initial machine design structure with the desired performance. The results of the analytical inductance calculation are verified and assessed in terms of accuracy with the FEM simulation results and with the prototype measurement results.

Multidisciplinary Design of a Permanent-Magnet Traction Motor for a Hybrid Bus Taking the Load Cycle into Account

An electrical and mechanical design process for a traction motor in a hybrid bus application is studied. Usually, the design process of an electric machine calls for close cooperation between various engineering disciplines. Compromises may be required to satisfy the boundary conditions of electrical, thermal, and mechanical performances. From the mechanical point of view, the stress values and the safety factors should be at a reasonable level and the construction lifetime predicted by a fatigue analysis. In a vehicle application, the motor has to be capable of generating high torque when accelerating, and in normal operation, the losses of the machine should be low to be able to cool the machine. Minimization of the no-load iron losses becomes a very important electrical design requirement if the traction motor and the generator are mechanically connected with an internal combustion engine when it is operating as the only source of torque. The manufacturing costs of the motor are also taken into account in this paper.

The design of rotor geometry in a permanent magnet traction motor for a hybrid bus

The paper addresses the electrical and mechanical design process of a traction motor for a hybrid bus application. In general, the design process of the electric motors requires intimate co-operation between different engineering disciplines. Often compromises are needed in order to satisfy both the electrical and mechanical performance specifications. From the mechanical point of view the stress values should be on reasonable level and safety factors should be taken into account. From the electrical point of view the torque level should be high while accelerating the traction motor and the losses of the machine should be small in order to be able to cool the machine and sustain high efficiency. In traction use the no-load iron losses will be loading the overall system all the time - also while driving direct with diesel engine. While selecting the best rotor design also the costs will be taken into account - one expensive part of the motor is the permanent magnet material. Therefore, the material price is estimated when selecting the rotor design.

Wind power electrical drives for permanent magnet generators — Development in Finland

The use of permanent magnets offers freedom in machine design and the highest possible efficiencies for wind power machines. Although full power converters must be used with permanent magnet machines, these converters make it possible to fulfill even the strictest grid codes. If appropriate care is taken in selecting the exact magnetic material composition, Neodymium-Iron-Boron magnets are compatible with long term generator use. However, rare earth material prices have been so volatile lately that highpower applications using lower strength ferrite magnet materials are being studied. For wind power applications, the three basic types of PM generator include direct-drive generators (10-20 min-1), medium-speed generators (100-300 min-1), and high-speed generators (1000-2000 min-1). Finnish companies such as Neorem Magnets, ABB, and The Switch have been very active in the development of permanent magnet technology for wind power. Moreover, Finnish wind turbine manufacturers operating today use the most modern PM technologies in their products.