In this article, a process for reducing the electromagnetic vibration and noise by changing the shape of the stator is presented. Although the fundamental wave of the air gap magnetic flux density contributes to the average torque of the motor, other spatial harmonics which were except the fundamental wave of that cause vibration and enfeeble the output of the motor. Therefore, it is important to reduce the spatial harmonics for performance of the motor. Through the proposed process, it is possible to obtain an objective function to reduce the specific harmonics by assigning weights to each spatial harmonic. The reduction in the fundamental wave is minimized and it is possible to reduce the spatial harmonics that have an adverse impact on vibration. After the process, a model can be found that maintains the electromagnetic performance as much as possible while optimally reducing the vibration. To verify the process, the electromagnetic vibrations by a radial force of the proposed and conventional models were compared, and it was confirmed that the electromagnetic vibration of the proposed model was reduced. The validity of the analysis was proved through finite-element analysis.

Generators are a key technological element of wind power generation systems. The use of synchronous generators that employ heavy rare-earth permanent magnets is increasing owing to the demand for higher efficiencies. However, these magnets are expensive and undergo an unbalanced supply and demand. Therefore, spoke-type structures have been developed and used in various fields to compensate for the deficient performance when using a ferrite magnet, which is inexpensive and provides a stable supply and demand. However, permanent magnet synchronous generators (PMSGs) with adopted spoke-type structures and an output power of 1 kW or higher have not been studied and practically applied sufficiently. Additionally, new designs must consider differences between the target specifications of a generator and wind turbine. In this study, we designed and analyzed the characteristics of an alternative bridge spoke-type PMSG modeling a generator for a 3-kW class wind turbine. We analyzed the performance of the existing spoke-type generator and proposed an alternative bridge spoke shape with an improved performance by removing the leakage flux of the bridge. The performance of the existing spoke model was compared using the finite element method (FEM), and the performance of the proposed model was verified more accurately by performing a three-dimensional (3D) analysis considering the 3D effect. Additionally, we analyzed the voltage fluctuation rate according to the number of stator slots and overhang structure and designed a final model. Considering the characteristics of the ferrite magnet used in the spoke-type design, the irreversible demagnetization characteristics of the conventional and final models were compared using simulations, followed by a comparison between the stiffness characteristics of the two models. Finally, a prototype was manufactured, and the feasibility of the final design was verified using the performance tests.

The interior permanent magnet synchronous motor (IPMSM) has a structure, in which a permanent magnet is inserted inside the rotor and cogging torque is generated in its structure. To solve this problem, various methods for reducing the cogging torque are being studied. The first method is to reduce the cogging torque by increasing the air-gap length by applying tapering to the rotor or stator core. However, in case of reducing the cogging torque above a certain level, the tapering application method may cause a decrease in output because the position and shape of the permanent magnet are restricted. The second method is to apply skew to the stator or rotor. This is the most reliable way to reduce the cogging torque, but the magnetization rate of the permanent magnet is low, so the manufacturability is low. In this article, we describe a rotor with rotational tapering that fuses the advantages of tapering and skew and offsets the disadvantages. The motor design used 3-D finite element analysis (FEA), and the validity of this article was verified by making the final model and comparing it with the simulation results.

Interior permanent magnet synchronous motors have the advantage of being applicable to various fields owing to their high torque density and wide operating range but have the disadvantage of large electromagnetic vibrations. To calculate the electromagnetic vibration, analysis of the magnetic flux density of the air gap using the finite element method (FEM) is essential. This process requires a significant amount of time because of the use of many analysis models. The radial force, which is the source of vibration, is expressed as the square of the air gap magnetic flux density, the vibration can be predicted in advance by calculating the waveform of the air gap magnetic flux density using a formula. In this paper, a new air gap relative permeance formula is proposed when an offset is applied to the outer diameter of the rotor to reduce electromagnetic vibration. By calculating the waveform of the air gap magnetic flux density using the proposed air gap relative permeance formula, a model with a minimum total harmonic distortion is selected. The validity of the formula was confirmed by comparing the FEM result with the waveform of the air gap magnetic flux density calculated using the proposed formula. The proposed model minimized the vibration and was confirmed using FEM. Using the proposed formula, vibration can be easily and quickly predicted in analytic way. The prototype of the final model was developed and compared using FEM, and the validity of the analysis result was confirmed.

When a magnetic bearing is used in the design of a high-speed motor, no friction and wear occur because of the principle of magnetic levitation; however, the size of the entire system increases. An integrated magnetic bearing motor is a motor with a magnetic bearing inserted inside the rotor that can minimize the increase in the size of the entire system. In this study, a method to reduce the bearing force ripple and torque ripple of an integrated magnetic bearing motor through parameters for a Halbach array and permanent magnet tapering is proposed. When designing an integrated magnetic bearing motor, because the magnetic bearing is located inside the rotor, the influence of the magnetic flux of the rotor and stator on the magnetic flux of the magnetic bearing should be minimized. By combining the magnetic fluxes of the magnetic bearing, rotor, and stator at the rotor back yoke, magnetic saturation occurs, and the performance of the bearing force and torque ripples decreases. The bearing force and torque according to the Halbach array and permanent magnet tapering were analyzed using finite element analysis. The average bearing force and torque were maximized, and the ripple was minimized through the rotor parameters. Thus, the validity of the main design variables selected to improve the output characteristics was confirmed.

In an interior permanent magnet synchronous motor, an adhesive such as bond is generally injected into the magnet tolerance to prevent vibration of the permanent magnet within the insertion space. In this case, a disadvantage is that the magnet tolerance does not contribute to the performance. In this paper, ferrofluid is inserted to improve the torque density, utilizing the magnet tolerance. When inserting ferrofluid into the magnet tolerance, it is important to fix the magnet because conventional adhesives are not used, and it is important that the ferrofluid does not act as a leakage path within the insertion space. In this study, a new rotor configuration using a plastic barrier that satisfies these considerations was introduced. The analysis was conducted through finite element analysis (FEA), and this technique was verified by comparing the simulation results and the experimental results through a dynamo test. It was confirmed that the no-load back electromotive force in the final model increased through ferrofluid injection.