Kyoung-Jin Ko

Improved Analytical Model for Electromagnetic Analysis of Axial Flux Machines With Double-Sided Permanent Magnet Rotor and Coreless Stator Windings

This paper deals with the experimental verification and electromagnetic analysis of an axial flux machine with a double-sided permanent magnet (PM) rotor and coreless stator windings, based on analytical field computation. Employing a magnetic vector potential and a 2-D analytical model, magnetic fields produced by PMs are obtained. The 3-D problem is solved by introducing a special function for the radial position. Then, the analytical solutions for back emf, electromagnetic torque, and efficiency of the PM-type axial flux machines are derived by using the magnetic field solutions and considering simple equivalent circuits. The analytical results are validated extensively by 3-D FE results. Test results such as back-emf, torque, and efficiency measurements are also presented to show the effectiveness of the analyses.

Magnet Pole Shape Design of Permanent Magnet Machine for Minimization of Torque Ripple Based on Electromagnetic Field Theory

This paper deals with the magnet pole shape design of permanent magnet machines for the minimization of torque ripple based on electromagnetic field theory. On the basis of a magnetic vector potential and a two-dimensional (2-D) polar system, analytical solutions for flux density due to permanent magnet (PM) and current are obtained. In particular, the analytical solutions for mathematical expressions of magnets with different circumferential thicknesses can be solved by introducing improved magnetization modeling techniques, resulting in accurate calculations of electromagnetic torque. The analytical results are validated extensively by nonlinear finite element method (FEM). Test results such as back-emf measurements are also given to confirm the analyses. Finally, on the basis of derived analytical solutions, a reduction of torque ripple can be achieved.

Electromagnetic Performance Analysis of Wind Power Generator With Outer Permanent Magnet Rotor Based on Turbine Characteristics Variation Over Nominal Wind Speed

In this paper, we investigate the electromagnetic performance of wind power generators with outer permanent magnet rotors on the bases of variations in the turbine characteristics over nominal wind speeds by employing various proposed analytical techniques. We have employed an electromagnetic analytical method for calculating electrical parameters such as back EMF constant, synchronous inductance, and phase resistance on the basis of the magnetic field distribution calculated in previous studies. Moreover, curve fitting and finite element methods have been used for core losses analysis, while the d-q model employing the coordinate transformation theorem has been used for analyzing generation performances. To validate our techniques, we compared the performance results obtained using our analytical methods with those obtained by experimental setups. In addition, we propose optimized wind turbine characteristics for our model from the analysis results of electromagnetic performances obtained by considering three types of turbine characteristics.

Rotor Natural Frequency in High-Speed Permanent-Magnet Synchronous Motor for Turbo-Compressor Application

For permanent-magnet synchronous motors driven by high-frequency drives, the rotor speed is normally above 30 000 rpm, and it may exceed 100 000 rpm. Designing high-speed motors from both in an electromagnetic and a mechanical aspect requires a different approach from designing conventional motors with low-medium operation speeds. This paper deals with rotor natural frequencies that are particular to high-speed permanent-magnet synchronous motors for turbo-compressor applications. It is very important to accurately predict rotor natural frequencies at the design stage in order to minimize operational failure. On the basis of the finite element method (FEM), this paper predicts the natural frequencies of a designed and manufactured permanent magnet rotor. The experimental results confirm the validity of the FEM calculations of the proposed design process.

Design and Experimental Evaluation of Synchronous Machine Without Iron Loss Using Double-Sided Halbach Magnetized PM Rotor in High Power FESS

The rotational loss is one of the most important problems in high-power flywheel energy storage system (FESS) which supplies the electrical energy from the mechanical rotation energy. In our FESS with PM synchronous motor/generator (PMSM/G) and non-contacting system, the rotational loss is mainly generated in the laminated iron stator when PM rotor mounted on the flywheel is rotated. Therefore, this paper presents design and evaluation of a PMSM/G model composed of double-sided Halbach magnetized PM rotor and ironless 3-phase winding stator to minimize speed reduction of the flywheel. For one such motor structure we give analytical formulae for its magnetic field and back-electromotive force in a uniform way via the magnetic vector potential. As a result of experiment, dynamic performance of a manufactured double-sided PMSM/G is evaluated by comparison with those of the slotless PMSM/G in the idling mode. The result shows that the presented PMSM/G can be applicable to the high-power FESS.

Analysis and comparison for rotor eddy current losses of permanent magnet synchronous generator according to dc and ac load conditions

This paper presents an analytical procedure for the calculation of the eddy current losses of permanent magnet synchronous generator (PMSG). The dc and ac loading effects on the eddy current is examined through the suggested analytical procedure that considers the radial and tangential flux density waveform through a phase current harmonic analysis. The corresponding test results are also presented to quantify and compare those loading effects on the eddy current. The results verified the suggested analytical procedures and show that the rotor eddy current losses for PMSG with the dc loads turned out to be more significant than those with the ac loads.

Electromechanical Parameters Calculation of Permanent Magnet Synchronous Motor Using the Transfer Relations Theorem

This paper presents an analytical solution to predict magnetic field distribution and to calculate parameters of permanent magnet (PM) synchronous motor equipped with surface-mounted magnet using an electromagnetic transfer relations theorem (TRT) in terms of 2-D model in polar co-ordinates system. The analytical results are validated by comparison with finite element (FE) analyses and experimental results

Characteristics analysis of a high speed permanent magnet synchronous generator using the transfer relations theorem and equivalent circuit method

This paper presents analytical methods to predict the magnetic field distribution, electrical parameters, and output characteristics of a high speed synchronous generator equipped with surface-mounted permanent magnet. In order to analyze the magnetic field distribution and to estimate the electrical parameters, electromagnetic transfer relation (TR) theorem is employed. Moreover, output characteristics for variable resistive load and the operating speed are also obtained by solving the permanent magnet machine’s equivalent circuit equation. The analytical results are validated extensively by nonlinear finite element analysis and experimental results.

Optimum DC Link Voltage Extraction Based on Dynamic Performance Analysis and Design Parameters of Slotless Double-Sided Permanent Magnet Linear Synchronous Motor

This paper deals with the influence of design parameters and dc link voltage on dynamic performance of slotless double-sided permanent magnet linear synchronous motor (PMLSM). Generally, the dc link voltage is not a design target to motor designers because of a fixed power by commercial voltage. However, in this paper, we will consider the dc link voltage from a different point of view for system efficiency and optimum dynamic performance. As the first procedure, the design parameters of the PMLSM are derived by electromagnetic analysis considering space harmonics. And then the dc link voltage is defined by d-q transformed electrical dynamic equation and the design parameters according to switching scheme of voltage source inverter to satisfy the required mover speed and thrust. Finally, experimental verification for dynamic characteristic is performed by field orient speed control using design parameters according to the dc link voltage. Therefore, this paper can offer motor designers an insight for the effect of design parameters and dc link voltage on dynamic performance. The electromagnetic field analysis and dynamic characteristics are verified through the finite element method and experiment result, respectively.

Experimental Works and Power Loss Calculations of Surface-Mounted Permanent Magnet Machines

Surface-mounted permanent magnet (PM) machines were examined experimentally and theoretically, through power loss measurements and calculations. Windage, friction and copper losses were calculated using simple analytical equations and finite element (FE) analyses. Stator core losses were calculated by determining core loss coefficients through curve-fitting and magnetic behavior analysis through non-linear FE calculations. Rotor eddy current losses were calculated using FE analyses that considered the time harmonics of phase current according to load. Core, windage and friction open-circuit losses and copper loss were determined experimentally to test the validity of the analyses.