Jere Kolehmainen

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.

Modeling Magnet Length In 2-D Finite-Element Analysis of Electric Machines

Two-dimensional finite-element-method (2-D FEM) calculations are widely used in electric machine modeling instead of three-dimensional calculations because of their faster calculation time and simplicity. However, the 2-D calculations ignore end effects, causing a large error in calculating eddy currents in permanent magnets of synchronous machines. In this paper, we develop three analytical models and one curve-fitting model based on numerical calculations. The models improve the eddy-current loss calculation accuracy in 2-D FEM. The method adjusts the resistivity of a magnet material according to magnet dimensions. The adjustment takes into account the resistivity, the temperature dependence, and anisotropy of the resistivity of rare-earth magnet materials. We compare the models against FEM calculations in two and three dimensions and show that all the models improve the eddy-current loss calculation accuracy significantly, especially when the time-harmonic caused eddy-current losses in permanent magnets are considered.

Synchronous Reluctance Motor With Form Blocked Rotor

A novel type of mechanically robust synchronous reluctance rotor structure is proposed for medium speed synchronous reluctance machines. A machine utilizing the construction is built, tested, and compared to another machine with the common synchronous reluctance rotor structure. The machine is also simulated using the finite element method and the results are compared to the tested values. The obtained results demonstrate the feasibility of the construction.

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.

Optimal Dovetail Permanent Magnet Rotor Solutions for Various Pole Numbers

A buried magnet rotor structure, which is supported only by permanent magnets, is proposed for medium-speed permanent magnet machines. Many design aspects of the dovetail-shaped rotor structure have been found. Various machine solutions, with pole numbers 6 to 14, are studied with electromagnetic and structural finite element simulations. A simple model is created for making comparison with the different pole numbers easier. Main dimensions of the machine are kept the same. Optimal solutions for various pole numbers are searched and discussed. It is shown that for lower pole numbers, the structure is electrically better, while for higher pole numbers, the structure is mechanically stronger against centrifugal forces. In addition, the optimal electromagnetic structures for each pole number are shown to be similar to the optimal mechanical structures. Electrically and mechanically critical areas are also shown to be almost the same. The optimized results are also compared to three manufactured prototypes. The obtained results demonstrate the feasibility of the construction and the design method.

Application of Calorimetric Method for Loss Measurement of a SynRM Drive System

Synchronous reluctance motors (SynRMs) are gaining in popularity in industrial drives due to their permanent magnet-free, competitive performance, and robust features. This paper studies the power losses in a 90-kW converter-fed SynRM drive by a calorimetric method in comparison of the traditional input-output method. After the converter and the motor were measured simultaneously in separate chambers, the converter was installed inside the large-size chamber next to the motor and the total drive system losses were obtained using one chamber. The uncertainty of both measurement methods is analyzed and discussed.

Uncertainty in motor efficiency measurements

Results of five induction motor efficiency measurements according IEC 60034-2-1 are presented. The uncertainty of the measurements is analyzed using scientific and numerical methods.

Dovetail permanent magnet rotor solutions with different pole numbers

A buried magnet rotor structure, which is supported only by permanent magnets, is proposed for medium speed permanent magnet machines. Different solutions with pole numbers six to fourteen are studied with electromagnetic and structural finite element simulations. An optimal solution with optimal pole number is discussed.