Min-Mo Koo

Characteristic Analysis of Permanent Magnet Synchronous Machines Under Different Construction Conditions of Rotor Magnetic Circuits by Using Electromagnetic Transfer Relations

This paper presents a comparative analysis of the characteristics of high-speed permanent magnet synchronous machines (PMSMs) with diametrically magnetized rotors under different construction conditions of the rotor magnetic circuit. An analytical method is adopted to predict the magnetic field distribution and to calculate the electrical parameters by using the transfer relations based on a two-dimensional model in a polar coordinate system. In addition, three types of PMSMs with diametrically magnetized permanent magnets are proposed in this work. The electrical parameters are estimated and the magnetic field distribution is analyzed for those models, and these results are compared with those obtained using the finite element method; the two sets of results are found to be in good agreement. On the basis of the analysis results, a real model manufactured and the validity of our results is demonstrated by performing suitable experiments.

Electromagnetic Vibration Analysis and Measurements of Double-Sided Axial-Flux Permanent Magnet Generator With Slotless Stator

This paper examines the effects of the electromagnetic source on the vibration of a double-sided axial permanent magnet generator with a slotless stator depending on the ac and dc-load conditions. The slotless machine has no cogging torque. Most of the vibration originates from the torque ripple and axial force distributions, which result from the current load conditions. The 3-D finite element analysis results are compared with voltage, current, and torque measurements. The order tracking analysis of the vibration test data clearly demonstrates the dependence of the critical harmonics on the load conditions.

Comparative Investigation on Integrated System of Permanent Magnet Synchronous Generator and Power Converter Based on Machine Topology for Small-Scale Wind Power Application

This paper presents the comparative analysis and test results of permanent magnet (PM) synchronous generators based on machine topology for small-scale wind power application. For reasonable comparison, various design considerations, such as flux direction, rotor position, slot existence and PM materials, are dealt with under specific machine size limitation. Among the analysis models, five machines are manufactured for experimental verification, and the generators are integrated with AC-DC-DC converter to convert originally generated AC power to DC power. With our constructed experimental set, the electromagnetic characteristics based on measured current, and their performance are comparatively investigated under constant output voltage control condition.

Characteristic Analysis on the Influence of Misaligned Rotor Position of Double-Sided Axial Flux Permanent Magnet Machine and Experimental Verification

While axial flux permanent magnet (AFPM) machines are manufactured, their wrong assembly can be possible, such as misaligned PM rotor position of double-sided machine. Once the machines are assembled, detecting the misaligned rotor is hard, so the designers are required to have deep insight in its related and unexpected characteristics to prevent them focusing on other possible errors. Therefore, this paper deals with the characteristic analysis on the influence of the misaligned rotor position of double-sided AFPM machine and its experimental verification. In general, the AFPM machines have been analyzed by 3-D finite-element method (3-D FEM) due to their structural features, but it requires very long analysis time to consider various factors. For this reason, analytical approach is presented in order to consider all the cases of the misaligned rotor positions, and it is confirmed to be practical to detect the positions and to reduce analysis time with high reliability. With the analytical approach, the misaligned rotor position characteristics, such as back-emf and its total harmonic distortion are analyzed. Furthermore, all the analysis results are validated by 3-D FEM results and experimental verification.

Influence of Rotor Overhang Variation on Generating Performance of Axial Flux Permanent Magnet Machine Based on 3-D Analytical Method

This paper presents an analytical method based on transfer relations for an axial flux permanent magnet machine. The method takes the overhang length into account. Although considering the overhang structure is a very attractive way to increase the output power of the machine, optimization of its length has a heavy analytical burden when only the 3-D finite element method is employed for characterization of the electromagnetic field. Therefore, we derive accurate analytical solutions to dramatically reduce the time needed for analysis, and we present an experimental verification using a fabricated sample.

Characteristic Analysis of Tubular-Type Permanent-Magnet Linear Magnetic Coupling Based on Analytical Magnetic Field Calculations

This paper presents a characteristic analysis of a tubular-type permanent-magnet (PM) linear magnetic coupling (TLMC) based on analytical magnetic field calculations. First, the analytical solutions for magnetic fields generated by PM are derived on the basis of a magnetic vector potential and a 2-D polar coordinate system. Next, the magnetic force is also determined on the basis of these solutions. The magnetic field and force obtained by the analytical method are compared with those obtained by the finite-element analysis and experiment, which validates the analysis methods presented in this paper.

Comparative Analysis of Eddy-Current Loss in Permanent Magnet Synchronous Machine Considering PM Shape and Skew Effect Using 3-D FEA

In this paper, eddy-current loss in permanent magnets (PMs) due to the armature reaction field of a PM synchronous machine was analyzed. Various techniques, including numerical techniques such as finite element analysis (FEA), enable the accurate prediction and analysis of magnetic field distribution with saturation effects. Furthermore, the eddy-current loss can be easily analyzed using a commercial software. 3-D FEA is essential when considering the stator skew effect. In particular, the influence of time harmonics in armature current and space harmonics due to distributed magnetomotive force on the eddy current loss is thoroughly investigated and discussed on the basis of 3-D FEA.

Characteristic Analysis of Direct-Drive Wind Power Generator considering Permanent Magnet Shape and Skew Effects to Reduce Torque Ripple Based on Analytical Approach

In this study, the design for a direct-drive permanent magnet (PM) wind power generator is presented, and its characteristics are analyzed based on analytical approach. In order to confirm their influence on the torque ripple characteristics, both the shape design and the skew effects of the PM are thoroughly studied. In particular, we performed an analytically based electromagnetic field analysis in order to investigate the influence of the AC/DC load conditions on our model. By manufacturing a model using an experimental construction setup, we validate the results of our analytical approach.

Comparative analysis of eddy current loss in permanent magnet synchronous generator considering PM shape and skew effect for wind power generation

Summary form only given. This paper analyzes the eddy current loss in permanent magnets (PMs) caused by the armature reaction field of a PM synchronous generator (PMSG) on the basis of three-dimensional finite element (3D FE) analysis. The eddy current loss in PMs is the main source of thermal issues. It can result in the irreversible demagnetization of PMs because of direct thermal conduction. Furthermore, because the eddy current loss significantly increases with increasing output power, accurate analysis is an important issue. The analysis models used and the machine manufactured for the experiment is shown. The machine consists of a stator and PM rotor. The stator is of a slotted type employing concentrated winding, and 1 slot-pitch skew is applied. The PM rotor has multi poles, and chamfered PMs are used. The rotor and stator have identical stack lengths of 101 mm; as a result, no overhang exists. In addition, we applied 3D FE analysis for the eddy current loss analysis of the PMSG. 3D FE analysis was adopted to consider the magnetic field distribution resulting from the armature reaction field in PMs. Because the analysis model applied the stator skew structure mentioned previously, it has a different magnetic field distribution along with axial length in comparison with machines without skew structure. The chamfered PM rotor influences the magnetic distribution along the tangential direction. In particular, edge effects should be thoroughly investigated as the PM demagnetizes relatively easily owing to the concentrated magnetic field at both edges of the PM. The edge effects are due to complicated electromagnetic field phenomena such as fringing flux and leakage flux in coil end turns; therefore, 3D analysis is required to accurately take them into account in the analysis. There are 3 categories of the armature reaction field according to the operation mode. They are the current of motoring mode and that of generating mode in both AC and DC load conditions. As the back-to-back test is generally applied for evaluating the performance of PM machines, the current in motoring mode is also considered. In this paper, for better understanding, the back-to-back test uses two identical machines: one operated as a motor and the other as a generator. Furthermore, the electrical input power and output power are subtracted to measure the power losses in both machines. Owing to the different harmonic components in each phase current according to the operation modes, their electromagnetic losses have difference, so the losses are also required to be thoroughly investigated as performed. The experimentally measured current according to the operation mode is shown. As the eddy current loss is difficult to measure, it was calculated by FE analysis on the basis of the measured current. Each current characteristic analyzed by FFT is compared. The motoring mode has the highest THD because the employed SVPWM inverter produces a high chopping frequency. Owing to the influence of the harmonic components, the motoring mode has the highest eddy current loss. It can also be confirmed that the skew structure is useful in reducing the eddy current losses. It is clear that the overall value as well as the distribution of eddy current loss requires thorough investigation. In the full paper, the eddy current distribution derived from 3D FE analysis will be presented in detail.

No-Load Analysis of PMLSM With Halbach Array and PM Overhang Based on Three-Dimensional Analytical Method

This paper presented a 3-D analytical method, based on transfer relations for permanent-magnet (PM) linear synchronous machine (PMLSM). The PMLSMs in this paper have a double-sided mover structure with Halbach array PMs and a slotless stator core. In addition, in order to complement the leakage and fringing flux density, we use a PM overhang in the mover structure. The analysis of this methods phenomenon is the proposed 3-D analytical method in this paper. Furthermore, we present experimental verification using a prototype model.