Youn-Hyun Kim

Characteristics of hydrogen co-doped ZnO : Al thin films

ZnO films co-doped with H and Al (HAZO) were prepared by sputtering ZnO targets containing 1 wt% Al2O3 on Corning glass at a substrate temperature of 150 °C with Ar and H2/Ar gas mixtures. The effects of hydrogen addition to Al-doped ZnO (AZO) films with low Al content on the electrical, the optical and the structural properties of the as-grown films as well as the vacuum- and air-annealed films were examined. Secondary ion mass spectroscopy analysis showed that the hydrogen concentration increased with increasing H2 in sputter gas. For the as-deposited films, the free carrier number increased with increasing H2. The Hall mobility increased at low hydrogen content, reaching a maximum before decreasing with a further increase of H2 content in sputter gas. Annealing at 300 °C resulted in the removal of hydrogen, causing a decrease in the carrier concentration. It was shown that hydrogen might exist as single isolated interstitial hydrogen bound with oxygen, thereby acting like an anionic dopant. Also, it was shown that the addition of hydrogen to ZnO films doped with low metallic dopant concentration could yield transparent conducting films with very low absorption loss as well as with proper electrical properties, which is suitable for thin film solar cell applications.

Optimal design of switched reluctance motor using two-dimensional finite element method

Switched reluctance motor (SRM) has some advantages such as low cost, high torque density, etc., but SRM has essentially high torque ripple due to its salient structure. To apply SRM to the industrial field, we have to minimize torque ripple, which is the weak point of SRM. This article introduces optimal design process of SRM using a numerical method such as two-dimensional (2D) finite element method. The electrical and geometrical design parameters have been adopted as 2D design variables. From this work, we can obtain the optimal design, which minimizes the torque ripple. We also can obtain the optimal design, which maximizes the average torque. Finally, this article presents performance comparison of two optimal designs, the minimized torque ripple, and the maximized average torque.

Development of a flux concentration-type linear oscillatory actuator

A novel permanent magnet (PM) flux concentration-type linear oscillatory actuator (LOA) for a compressor is proposed in this paper. The proposed LOA has an embedded PM structure and the structure is effective in magnet flux concentration. The flux concentration has a positive influence on the flux linkage, cogging force, and electromotive force. The superiority of the proposed LOA has been confirmed by comparing the performances between the proposed and conventional LOA.

Effect of alloying elements on the copper-base anode for molten carbonate fuel cells

Abstract The effects of aluminium and chromium on the structural stability and the electrochemical performance of porous CuNi anodes for the molten carbonate fuel cell (MCFC) are examined in a simulated MCFC anode environment (923 K, 80% H2-20% CO2). The addition of aluminium and chromium inhibits porous CuNi anodes from being sintered because of the formation of aluminium oxide and chromium oxide on their surfaces. Electrochemical performance is evaluated in terms of anodic polarization in a half-cell system. At an anodic overpotential of 100 mV, the current density for H2 oxidation of the Cu-Ni-Al anodes is about 85 mA cm−2. The current densities of the CuNi and CuNiCr anodes were, however, 114 and 112 mA cm−2, respectively.

Maximum Power Control of IPMSM Considering Nonlinear Cross-Magnetization Effects

Interior permanent magnet synchronous motor is widening its application compared to other AC machines because of magnetic and reluctance torque. Despite of the advantages, improving control performance with parameter nonlinearity consideration is crucial during the field weakening control. This paper shows a maximum power control method at the field weakening region that considers d, q inductances nonlinearity due to magnetic saturation and d, q mutual inductance. To verify the feasibility of control scheme, FEM simulations and experiments about comparison between linear and nonlinear maximum power control are carried out.

The finite element analysis of switched reluctance motor considering asymmetric bridge converter and DC link voltage ripple

This paper presents a characteristic analysis of switched reluctance motor (SRM) considering hard chopping and dc link voltage ripple by using time-stepped voltage source finite element method in which the magnetic field is combined with drive circuit. We also examine the influence of freewheeling diodes and dc link voltage ripple on the performance of a SRM such as torque ripples and radial force on the surface of the teeth. The freewheeling diodes and dc link voltage ripples must be taken into account in predicting the performance of the SRM.

Software Resolver-to-Digital Converter for Compensation of Amplitude Imbalances using D-Q Transformation

Resolvers are transducers that are used to sense the angular position of rotational machines. The analog resolver is necessary to use resolver to digital converter. Among the RDC software method, angle tracking observer (ATO) is the most popular method. In an actual resolver- based position sensing system, amplitude imbalance dominantly distorts the estimate position information of ATO. Minority papers have reported position error compensation of resolvers output signal with amplitude imbalance. This paper proposes new ATO algorithm in order to compensate position errors caused by the amplitude imbalance. There is no need premeasured off line data. This is easy, simple, cost-effective, and able to work on line compensation. To verify feasibility of the proposed algorithm, simulation and experiments are carried out.

Finite element analysis of magnetic field in high temperature bulk superconductor

This paper presents the analysis of magnetic field in high temperature bulk superconductor (HTSC). The macroscopic field equations constructed on the basis of the critical state model and levitation forces are simulated between permanent magnets (PM) and HTSC using a 3D axisymmetric finite element method. The force computations are obtained by using the Lorentz force equation. An iteration method is used to determine the current distribution of HTSC, because the J-E relation in HTSC is extremely nonlinear. The numerical results show that the presented method is comparatively accurate by comparing the measured levitation forces and the simulation ones.

The effectiveness of anisotropic iron-core material on a switched reluctance motor

In this paper, the effectiveness of the proposed SRM model which has anisotropic iron-core material structure was investigated. The material of stator poles is the anisotropic steel sheets.

Advanced torque control of switched reluctance motor

This paper proposes a new torque control strategy for switched reluctance motor (SRM). Most of the established torque control methods implemented with pre-measured or pre-analyzed data, such as phase currents, rotor position and torque. The established methods require hard efforts and time for the repetitious measurement and analysis. Therefore, this paper suggests the torque control method that is possible to control the SRM directly without the various data. The proposed control method uses the real-time estimated torque that is based on the linearized mechanical work operation (LMWO). To verify the accuracy of the estimated torque by the LMWO, the estimated torque compares with the calculated torque by finite element method (FEM). From the experiment the effectiveness of the proposed torque control method has been confirmed. From these simulation and experiment results, its known that the proposed torque control can be effectively used without performance data.