Iratxo Gomez

There are three principal sources of noise and vibration in electrical machines: electromagnetic sources, mechanical sources, and aerodynamic sources. Nowadays, one of the major advantages of permanent-magnet synchronous machines is their torque density. This density is achieved through a high magnetic flux density in the air gap, which is achieved through hard magnets. Unfortunately, in these machines, electromagnetic forces have been identified as the main source of vibration and noise, and high magnetic flux densities make these vibrations and noises more significant. With the aim of better understanding the relationship between electromagnetic forces and design variables, this article, which is the continuation of previous work, firstly describes a study of the sources of magnetic forces in permanent-magnet synchronous machines. Subsequently, an analytical model for the computation of the radial forces originating from electromagnetic sources in permanent-magnet synchronous machines is stated. This model analyzes the forces on both the rotor surface and the base of the stator tooth. The analytical results were corroborated through simulations using the finite element method (FEM) and also by experimental tests performed over two prototypes. The results achieved by the analytical model show good agreement with both FEM results and experimental measurements.

Nowadays, many applications are demanding more and more compact, cost effective and robust electric drives. By using rare earth magnets, it is possible to achieve electrical machines with rather high torque volume ratio, accomplishing this way the compactness requirement. Nevertheless, rare earth permanent magnets are very sensitive to the temperature, so that the risk of being partially demagnetized arises as their working temperature increases. In addition, as it has been seen during the last years, the market of rare earth metals is quite volatile. The price of magnets could rise suddenly, leading to a significant impact on the cost, and so in the competitiveness of Permanent Magnet Machines. Due to this fact, it is essential to reduce the dependency on rare earth market in order to accomplish cost effective drive solutions. Some key points to face this problem can be to reduce the magnet volume, or to use magnets with worse thermal properties (magnets with less dysprosium). Nevertheless, in both cases, the adopted solution would lead to an increase in the risk of demagnetization, affecting to the robustness of the machine. In this paper, a methodology based on Finite Element Analysis and experimental test is proposed to evaluate the demagnetization risk in Permanent Magnet Machines. By applying this methodology, it is possible to accomplish competitive machine designs, achieving a good trade-off between cost and robustness. The proposed methodology has been applied in a practical case, for the optimization of 10 industrial motors, achieving good results.

Nowadays the majority of applications are demanding more and more compact, cost effective and robust solutions for their electric drives. In this context permanent magnet synchronous machines are considered as a good candidate due to their high torque density. This torque density is obtained thanks to high power rare earth magnets with both high remanence and high coercive force. However, the magnets cost has a relevant impact in the final cost of the electrical machine and the uncertainty shown by the rare earth market in the last years has originated high variations in the price of them. Due to that, it is essential to reduce this impact in order to accomplish cost effective drive solutions. Some key points to face this problem are the reduction of the magnets volume or the using of magnets with worse thermal properties (magnets with few dysprosium and with low coercive force). In both cases special attention must be paid on the demagnetization risk of the magnets. To carry out that analysis, in this article a finite element method simulation analysis process for demagnetization of permanent magnets is presented. The developed method has been validated experimentally in a test bench. Good agreement is shown between simulations and experimental results.

In this article a general analytical model for the analysis of permanent magnet synchronous machines with static eccentricity is presented. The model is a continuation of [1] and it is based on Fourier time-space series formulated in 2-D coordinates. The results of the model are corroborated by simulations of finite element method over two different machines. The results of the model show a good agreement with the results obtained from simulations.

In permanent-magnet synchronous machines (PMSMs) electromagnetic forces are identified as the principal source of vibrations and noises. In this article, first of all the sources of magnetic forces in PMSMs are analyzed. Then, an analytical method for the calculation of radial forces on the base of the stator tooth created by electromagnetic sources in PMSMs is presented. Finally finite element method (FEM) is used to corroborate analytical results.