Jouni Ikäheimo

Interdependence of Demagnetization, Loading, and Temperature Rise in a Permanent-Magnet Synchronous Motor

The demagnetization of permanent magnets in permanent-magnet machines has been under discussion in many publications lately. Demagnetization models have been used, for example, to optimize the machine structures but there have been no studies on how the demagnetization is coupled with the loading and temperature-rise of the machine and how this coupling should be modeled. In this paper, we model the dynamics of the demagnetization of a dovetail machine under a constant load torque. We show that the thermal model should be included in the demagnetization calculations. The demagnetization will cause an increase of the copper losses, which will increase the temperatures of the machine. This will cause more demagnetization and might lead even to a stall in a situation in which a model neglecting the thermal effects predicts stable operation without additional demagnetization.

Synchronous High-Speed Reluctance Machine With Novel Rotor Construction

A new mechanically robust construction for an ultrahigh-speed synchronous reluctance rotor is presented. The two-pole rotor design incorporates soft magnetic flux guides inside nonmagnetic matrix material. Two prototypes based on the concept were constructed and tested. This paper describes the electromagnetic and mechanical design principles of the novel rotor concept.

Motors With Buried Magnets for Medium-Speed Applications

A novel type of mechanically robust buried magnet rotor structure is proposed for medium speed permanent magnet machines. A machine utilizing the construction is built, tested, and compared to another machine with traditional V-shaped poles. The machine is also simulated using finite element method and the results are compared to tested values. The obtained results demonstrate the feasibility of the construction.

Demagnetization Testing for a Mixed-Grade Dovetail Permanent-Magnet Machine

A dovetail machine is a novel design developed to solve the strength problems of traditional buried magnet machines. A mixed-grade construction can be easily applied to a dovetail machine, because a dovetail machine has several magnets in a single pole in different positions. The basic idea of the mixed-grade construction is to use high intrinsic coercivity material in the positions of the high demagnetization risk and high remanence material in the positions of low demagnetization risk. We have developed a demagnetization model that takes into account the temperature dependence of the properties of the permanent-magnet materials to model a dovetail permanent-magnet motor with mixed-grade construction. We compared the model with a real motor. By comparing the testing and the calculations, we show that our demagnetization model can predict the demagnetization of the permanent magnets with reasonable accuracy. We discuss the benefits of the mixed-grade construction in a dovetail machine.

Adaptive mesh generation in 2D magnetostatic integral formulations

A new type of adaptive h-version mesh refinement associated with magnetostatic integral formulations is proposed. In this method the magnetic field due to a locally estimated error in the magnetization is integrated in a region where high accuracy is required, such as in the air gap. This remote error (i.e. the contribution of each element to the error in a remote region) is then used to determine the need for the element subdivision. The presented results indicate that the magnetic fields in the apertures of the dipole and quadrupole magnets can be computed with high accuracy using small number of elements.

Analysis of Direct-On-Line Synchronous Reluctance Machine Start-Up Using a Magnetic Field Decomposition

Direct-on-line synchronous reluctance machines combine the characteristics of induction machines and synchronous reluctance machines. Saturation of core materials, the eddy currents, and the asymmetry of the rotor core and cage make it difficult to predict which kind of loads a machine can synchronize. In this paper, the start-up of a direct-on-line synchronous reluctance machine is analyzed with a magnetic field decomposition that makes it possible to quantify and isolate forces between any two distinct parts of an electric machine using a transient time-stepping finite element field solution. The results show explicitly which portion of the torque is produced by the rotor core and which by the rotor cage. Compared with conventional average torque analyses (also known as pseudo-constant-speed or quasi-steady-state analyses) used to distinguish between the torque on the rotor core and cage, the proposed method makes no assumptions on the state of the machine. This results in a more detailed view of the starting transient.

Analysis of direct-on-line synchronous reluctance machine (DOLSynRM) start-up using a magnetic field decomposition

Direct-on-line synchronous reluctance motors (DOLSynRM) combine the characteristics of the induction motor (IM) and the synchronous reluctance motor (SynRM). Saturation of core materials, the eddy currents, and the asymmetry of the rotor core and cage make it difficult to predict to which kind of loads the motor can synchronize. In this paper, the DOLSynRM start-up is analyzed with a magnetic field decomposition that makes it possible to quantify and isolate forces between any two distinct parts of an electric machine using a time-stepping finite element (FE) field solution. The results show explicitly, which portion of the motor torque is produced by the rotor core and which by the rotor cage. Compared to conventional static and quasi-stationary analyses used to distinguish between the torque on rotor core and cage, the presented method gives a more detailed view.

Domain Decomposition Approach for Efficient Time-Domain Finite-Element Computation of Winding Losses in Electrical Machines

Finite-element (FE) analysis of winding losses in electrical machines can be computationally uneconomical. Computationally lighter methods often place restrictions on the winding configuration or have been used for time-harmonic problems only. This paper proposes a domain decomposition-type approach for solving this problem. The slots of the machine are modeled by their impulse response functions and coupled together with the rest of the problem. The method places no restrictions on the winding and naturally includes all resistive ac loss components. The method is then evaluated on a 500-kW induction motor. According to the simulations, the method yields precise results 70–100 faster compared with the established FE approach.