Sang-Moon Hwang

Various design techniques to reduce cogging torque by controlling energy variation in permanent magnet motors

Using energy method, this paper analytically reveals that the cogging torque can be reduced by controlling N/sub L/th harmonic components of the square of airgap permeance function and flux density function, where N/sub L/ denotes the least common multiple of number of poles and number of slots. As for design tools, it introduces various design techniques to reduce cogging torque with analytical formulation and FEM examples.

Comparison of magnetic forces for IPM and SPM motor with rotor eccentricity

The permanent magnet motor is often the most important element in many precision rotor applications and also a frequent source of vibration and acoustic noise. The eccentricity between stator and rotor is inevitably introduced during manufacturing process, such as mass unbalance, shaft bow and bearing tolerances. This paper investigates radial force density and magnetic unbalanced force for IPM and SPM motors when rotor eccentricity exists. For the magnetic field analysis, a finite element method is used to account for the magnetic saturation and rotor eccentricity. The radial force density and magnetic unbalanced force are analyzed by Maxwell stress tensor and discrete Fourier transform. An IPM BLDC motor, mostly chosen to realize high speed operation, is significantly affected by rotor eccentricity due to magnetic saturation.

A Novel Design of Linear Synchronous Motor Using FRM Topology

This paper proposes design and analysis of a new linear motor called flux reversal linear synchronous motor (FRLSM), which is cost effective for long stroke applications. Passive rotor configuration of a typical flux reversal machine (FRM) can be utilized for a linear machine with less permanent magnet (PM). Three different design choices are investigated and compared both in thrust and normal force. The investigation shows extremely low force ripple and good thrust linearity through skewing and three-phase sinusoidal control. Reduced PM configuration generates about 21% higher thrust even with half amount of PM.

Optimal Design for Noise Reduction in Interior Permanent Magnet Motor

This paper presents methods to reduce acoustic noise in an interior permanent-magnet motor during the design stage. Mechanical and magnetic sources are considered to reduce noise of the machine, and structural and electromagnetic designs are performed. In the structural-design stage to reduce mechanical source, the structural resonances are moved to higher frequency for enhancement of stiffness. Then, in the electromagnetic-design stage to reduce exciting forces, the harmonic amplitude of magnetic forces and torque ripple are reduced by using an optimal design method, respectively. Two models are designed according to each objective function, and the validity of the design process and objective functions is confirmed by their simulated and experimental results.

Finite element analysis and design in stainless steel sheet forming and its experimental comparison

Abstract Bending and drawing processes are analyzed in stainless steel sheet forming using solid element and finite-strain formulation by the Finite Element Code MARC. In bending deformation, the springback increases through augmentations of the clearance between punch and workpiece. Divergences between theoretical and experimental results occur due to the simplification of the contact condition at the die–workpiece interface. For the square cup deep drawing process which includes bending and drawing deformation modes, the lubrication conditions are critical factors for producing sound products. All the results derived from the FEM analysis show reasonable agreement with the experimental data.

Analysis of vibration for permanent magnet motors considering mechanical and magnetic coupling effects

Vibration of a rotor-bearing system driven by an electric motor is a coupled phenomena between mechanical characteristics and magnetic origins through the airgap. With the advent of new high energy magnetic material together with high precision motor applications, magnetic sources of vibration are becoming more serious. This paper investigates the transient whirl responses of a rotor system with purely mechanical origins and compares it with that of magnetically coupled origins. The results show that magnetically coupled sources significantly affect the vibration of the rotor-motor system.

Comparison of dynamic responses for IPM and SPM motors by considering mechanical and magnetic coupling

The permanent magnet motor is often the most important element in high performance rotor applications and also a frequent source of vibration and acoustic noise. Because of manufacturing imprecision such as mass unbalance, shaft bow and bearing tolerances, rotor eccentricity extensively exists in all kinds of electric machines. This paper investigates magnetic unbalanced forces for IPM and SPM motors which are widely used in a washing machine due to high average torque and dynamic responses of a rotor motor system when rotor eccentricity exists. For the magnetic field analysis, a finite element method is used to account for the magnetic saturation and rotor eccentricity. An IPM motor, mostly chosen to realize high speed operation, shows a worse effect on magnetic unbalanced forces and dynamic responses compared with SPM motor due to magnetic saturation when the eccentricity exists.

Finite Element Analysis of Multi-Stage Deep Drawing Process for High Precision Rectangular Case with Extreme Aspect Ratio

Abstract Deep drawing process for rectangular drawn section is different with that for axisymmetric circular one. Therefore deep drawing process for rectangular drawn section requires several intermediate steps to generate the final configuration without any significant defect. In this study, finite element analysis for multi-stage deep drawing process for high-precision rectangular cases is carried out especially for an extreme aspect ratio. The results of analysis show that the irregular contact condition between blank and die affects the occurrence of failure, and the difference of aspect ratio in the drawn section leads to non-uniform metal flow, which may cause failure. A series of experiments for multi-stage deep drawing process for the rectangular cases are conducted, and the deformation configuration and the thickness distribution of the drawn rectangular cases are investigated by comparing with the results of the numerical analysis. The numerical analysis with an explicit time integration scheme shows good agreement with the experimental observation.

Comparison of vibration sources between symmetric and asymmetric HDD spindle motors with rotor eccentricity

The permanent magnet motor is often the most important element in hard disk drive (HDD) spindles and also a frequent source of vibration and acoustic noise. The eccentricity between stator and rotor is inevitably introduced during manufacturing process, such as mass unbalance, shaft bow and bearing tolerances. This paper analytically discusses effects of rotor eccentricity on motor performances for symmetric and asymmetric motors, such as local traction, unbalanced force, cogging torque, back EMF, phase current and torque ripple. An asymmetric motor, mostly chosen to reduce the cogging torque, shows a worse effect on cogging torque and unbalanced force when the eccentricity exists. It also adversely affects the flux linkage and introduces variation of the phase back EMF depending on winding and rotating eccentricity, thus yielding increased mutual torque ripple.

A Feasibility Study on a New Doubly Salient Permanent Magnet Linear Synchronous Machine

Permanent magnet linear synchronous motors (PMLSMs) have been successfully adopted in a wide variety of industry applications due to improved servo-capability and outstanding dynamic characteristics. However, the conventional PMLSMs need a large amount of permanent magnet (PM) material in the stator resulting in significant cost rise. This paper proposes and analyzes a new doubly salient PM linear synchronous machine (DSPMLSM). The proposed configuration consists of consequent pole stator to reduce PM material and modular mover structure to reduce force ripples. Four different models are chosen and compared by two-dimensional finite element analysis (FEA). The analysis reveals that the proposed DSPMLSM uses only a half amount of PMs, while retaining almost the same characteristics as the conventional PMLSMs.