Hae-Joong Kim

Estimation of Acoustic Noise and Vibration in an Induction Machine Considering Rotor Eccentricity

In this paper, a static rotor eccentricity analysis method is proposed. Electromagnetic noise by static eccentricity occurs in the course of manufacturing. The increase in errors is attributed to manufacturing errors of the components: the assembly and the torsional errors caused by shrink fitting. For these reasons, the rotor is displaced from the center of the stator bore, but it still turns on its own axis. Accordingly, in this paper, the acoustic noise using the electromagnetic excitation force was analyzed according to the rotor eccentricity. Finite-element analysis was used to analyze the rotor eccentricity considering the electrical and mechanical characteristics. To verify the proposed method, an induction machine was fabricated and an experiment was conducted.

Characteristics of IPMSM According to Rotor Design Considering Nonlinearity of Permanent Magnet

As materials with various properties have been developed for the improvement of performance and lowering the material cost of permanent magnet (PM) motors, the properties of the materials have become major factors in determining the motor performance. As such a material, the recently developed anisotropic bonded NdFeB PM showed a nonlinear demagnetization curve. Thus, in this paper, by considering the nonlinear property of the PM, a process to calculate the operating point, coupled with a nonlinear analysis of the core, is proposed, and by applying this process, the characteristics of interior PM synchronous motor according to different rotor designs are investigated.

Structure of Concentrated-Flux-Type Interior Permanent-Magnet Synchronous Motors Using Ferrite Permanent Magnets

Interior permanent magnet synchronous motors (IPMs) usually use NdFeB for achieving high-torque and high-efficiency performance. This paper reviews the performance of concentrated-flux-type ferrite magnet motors (CFFMs) that use ferrite, as an alternative to the general type of IPMs that use NdFeB. A structure to reduce the motor volume and improve the torque density of CFFMs is suggested in this paper. The characteristics of CFFMs for different rotor types are analyzed. The motor parameters are analyzed. Using 2-D finite element analysis (FEA), the efficiency and size of the CFFMs are compared with each other. This paper discusses the results of stress analysis for each rotor type using 2-D FEA. Finally, it suggests a CFFM structure to replace the general type of IPMs that use NdFeB. The proposed LC-type has the highest torque density among all the ferrite rotor types. It is seen that the proposed LC-type ferrite-model replacement for the Nd model is the best choice of all the types.

Characteristic Analysis for Concentrated Multiple-Layer Winding Machine With Optimum Turn Ratio

Three-phase fractional slot concentrated winding synchronous machines (FCSM) has excellent electrical properties of high torque density, low cogging torque, and torque ripple, yet in armature, as vibration/noise characteristics are not good due to asymmetric MMF, and due to the presence of subspace harmonics in MMF, eddy-current loss of permanent magnet is increased. If multiple-layer winding with optimum turn ratio is applied to three-phase FCSM, this can improve these problems. In this paper, the turn ratio in concentrated multiple-layer winding machine is proposed to be applied. Considering the turn ratio, a general formula is derived to calculate the winding factor. Using the induced formula, the winding factor changes according to the changes in the turn ratio are calculated, and the turn ratio to remove the harmonic components that the MMF has is determined. To verify improvement in the motor characteristics for the proposed method, turn ratio is applied to motors of 16 pole 18 slot and 10 pole 12 slot. For the two models, MMF distribution in the air gap using FEM is calculated, and through harmonic analysis, reduction or removal of a particular harmonic is verified. In addition, through FEM transient analysis, reduced eddy-current loss in permanent magnet is to be identified, and improvements in vibration/noise are to be verified by deformation/acoustic noise analysis of stator.

Proposition of Structures for Brushless Hybrid-Excitation Synchronous Motors With Improved Rotor

Recently, studies on the hybrid excitation synchronous motor using permanent magnet (PM) together with field windings have been actively conducted. In this regard, this paper seeks to investigate brushless hybrid excitation synchronous motors with improved rotors. The design was performed using an equivalent magnetic circuit to determine the best of four possible different structures. Using a finite-element analysis (FEA), the back electromotive force (EMF) per PM usage and the phase back EMF of each type were calculated and compared, and the design that can best reduce costs and increase torque density was determined. A detailed design of one of the four structures with excellent characteristics was performed, and the associated characteristics and problems were verified. An improved rotor structure was proposed to resolve the identified problems and improve performance. The phase back EMF and the total harmonic distortion of the phase back EMF, cogging torque, load torque, and torque ripple of the improved rotor structure were verified through the application of the FEA. In addition, the prototype motor was fabricated, and a no-load test was conducted to compare the test results and analysis results on the phase back EMF. The reliability of the analysis results was confirmed by comparison between test results and analysis results on the input current, line to line voltage, and efficiency under the same output conditions through the load test.

Dynamic Characteristics of a Hard Disk Drive Spindle System Due to Imperfect Shaft Roundness

This paper proposes a modified Reynolds equation for the coupled journal and thrust fluid dynamic bearings (FDBs) to include variable film thickness due to imperfect roundness of a rotating shaft. A finite element method is used to solve the modified Reynolds equation to calculate the pressure. Reaction force, moment, and friction torque of FDBs are calculated by integrating the pressure and shear stress along the fluid film. The dynamic behavior of a hard disk drive (HDD) spindle system is investigated by solving the equations of motion with six degrees of freedom using the Runge-Kutta method. This research shows that the imperfect roundness of the shaft increases the nonlinearity of FDBs. Imperfect roundness of the shaft generates harmonics of the groove number plusmn 1 in the bearing reaction force and the displacement of the HDD spindle system even in the case of stationary grooved FDBs.

Influence of manufacturing tolerances on cogging torque of IPMSM for EPS application

This paper examines a study of an unexpected cogging torque due to the manufacturing tolerances. During the manufacturing, to reduce the cogging torque, various design techniques can be chosen. However, some techniques, which are effective cogging torque reduction methods, can become ineffective. Also, if the manufacturing tolerances exist, they can cause an increase in the cogging torque magnitude. In this paper, the influence of manufacturing defects on the cogging torque is analyzed. For this purpose, the finite-element (FE) analyses are utilized and validated by the experimental measurements.

Simple Size Determination of Permanent-Magnet Synchronous Machines

Today, performance improvements such as reducing the time response and enhancing the efficiency of the electrical motor are one of the most important challenges. In the design of a permanent-magnet (PM) motor, the variables for sizing include the shape ratio (SR), the torque per rotor volume (TRV), and the torque density (TD), and these variables are important for determining the mechanical and electrical characteristics of the motor. This study investigated the changing patterns of the motor parameters (back electromotive force, inductance, resistance, etc.) and the motor characteristics with the changes in the SR, TRV, and TD with respect to the PM synchronous motor, and sought to determine the SR and TRV values. Toward these ends, this study proceeded with the initial design of the spoke-type (flux-concentrated) PM motor. Then, the motor parameters of the initial model were calculated using finite-element analysis. Based on the motor parameters of the initial model, the changing patterns of the electrical and mechanical characteristics of the motor according to the changes in the SR, TRV, and TD were investigated. In addition, the SR, TRV, or split ratio that can enhance the mechanical characteristics and efficiency of the motor were determined and reflected in the design.

Estimation of Rotor Type Using Ferrite Magnet Considering the Magnetization Process

This paper deals with the post-assembly magnetization process of motors using ferrite permanent magnets (PMs). In order to meet the needs of mass production, most motors are magnetized post assembly. However, increasing complex shapes are required to maximize the flux of PMs. As a result, certain locations in the magnet are not fully magnetized by the magnetizing fixture due to insufficient magnetomotive force. Therefore, an analysis concerning the post-assembly magnetization is needed. In this paper, the concentrated flux spoke-type synchronous motor is analyzed with regard to the magnetization process. Owing to more flux, this motor is designed as a V-shape PM. Therefore, it is not fully magnetized according to magnet shape. By identifying the effect of the magnet shape, the magnetization level is compared by the amount of flux linkage between post assembly and at full magnetization. Finally, the back electromotive force is estimated by the post-assembly magnetization method according to the magnet shape.

Design of In-Wheel Motor for Automobiles Using Parameter Map

Electric Vehicle (EV) can be categorized by the driving method into in-wheel and in-line types. In-wheel type EV does not have transmission shaft, differential gear and other parts that are used in conventional cars, which simplifies and lightens the structure resulting in higher efficiency. In this paper, design method for in-wheel motor for automobiles using Parameter Map is proposed, and motor with continuous power of 5 kW is designed, built and its performance is verified. To decide the capacity of the in-wheel motor that meets the automobiles requirement, Vehicle Dynamic Simulation considering the total mass of vehicle, gear efficiency, effective radius of tire, slope ratio and others is performed. Through this step, the motors capacity is decided and initial design to determine the motor shape and size is performed. Next, the motor parameters that meet the requirement is determined using parametric design that uses parametric map. After the motor parameters are decided using parametric map, optimal design to improve THD of back EMF, cogging torque, torque ripple and other factors is performed. The final design was built, and performance analysis and verification of the proposed method is conducted by performing load test.