• Journal of Magnetics
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• 제20권4호
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• pp.432-438
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• 2015

This paper presents an electromagnetic analysis of a tubular linear machine with axially magnetized permanent magnets using improved analytical techniques. Based on the magnetic vector potential and a two-dimensional polar-coordinate system, the magnetic field and armature reaction field can be derived. Using these, equivalent circuit parameters, such as the electromotive force and inductance, can be obtained analytically. Finally, the generating characteristics are derived with the equivalent circuit method. In this study, the finite element method was employed to provide a comparative evaluation, and experiments were conducted to validate the results of the analytical analysis.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권1호
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• pp.1-7
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• 2004

This paper presents a sensorless control strategy of a PMSM(Permanent Magnet Sycchoronous Motor). This method is very simple to compute the position angle of a rotor. A principle and a practical solution are described. A sensorless control algorithm is proposed to remove a mechanical position sensor. The theory is based on the superposition principle. The state equation of a motor is divided into two conditions: one is the state equation of exciting voltage and phase current in a constraint, the other is the state equation of back EMF(Electromotive Force) and phase current in a short circuit. Based on the analysis, short circuit current by back EMF is computed and then the information of position angle is calculated. The proposed method is verified by experimental results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 B
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• pp.1108-1110
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• 2000

The BLDCM(Brushless DC motor) has been the Trapezoidal Back Electromotive Force(EMF) due to a surface magnet rotor with nonlinear distribution and full-pitch windings. Theoretically, it should be fed with rectangular phase current in order to minimize torque ripple. But, because voltage source inverter drives BLDCM, perfectly rectangular phase currents are not available. Now in this paper, using fourier series coefficients, calculating the coefficients of harmonic current within available orders and each harmonic component are controlled on stationary frame. Only using four switches, low cost and small size drive can be made and proposed method will be more useful in industrial. Simulation and experimental results prove the validity of the proposed method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 B
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• pp.1130-1132
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• 2000

In this paper, For Control of the speed sensorless induction motor propose the method which is controled the motor by operating two axis current in input current of the inverter. This method determines frequency of inverter in order to stator electromotive force and E/F ratio for the setting magnetic flux, drives for speed control using a voltage power converter of the induction motor by means of voltage fed converter with current control ability.

• Journal of Electrical Engineering and Technology
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• 제12권3호
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• pp.1166-1176
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• 2017

Estimation errors of the rotor speed and position in sensorless control systems of Permanent Magnet Synchronous Motors (PMSM) will lead to low efficiency and dynamic-performance degradation. In this paper, a parallel-type extended nonlinear observer incorporating the nominal parameters is constructed in the stator-fixed reference frame, with rotor position, speed, and the load torque simultaneously estimated. The stability of the extended nonlinear observer is analyzed using the indirect Lyapunov's method, and observer gains are selected according to the transfer functions of the speed and position estimators. Taking into account the parameter inaccuracies issue, explicit estimation error equations are derived based on the error dynamics of the closed-loop sensorless control system. An equivalent flux error is defined to represent the back Electromotive Force (EMF) error caused by the inaccurate motor parameters, and a compensation strategy is designed to suppress the estimation errors. The effectiveness of the proposed method has been validated through simulation and experimental results.

• Journal of Power Electronics
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• 제10권4호
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• pp.396-404
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• 2010

This paper presents simple schemes used to estimate the initial rotor position and the d- and q-axis inductances for effective Maximum Torque per Ampere (MTPA) operation in a wind-power system using an IPMSM (Interior Permanent Magnet Synchronous Machine). An IPMSM essentially requires an exact coordinate transformation and accurate inductance values to use a reluctance torque caused by the saliency characteristic. In the proposed high-frequency voltage testing method, there is no voltage drop caused by the resistance and the electromotive force. The initial rotor position and the inductance can be measured through an analysis of the stator current without turning the rotor. The experimental results are presented in order to illustrate the feasibility of the proposed method.

• 한국재료학회지
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• 제15권1호
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• pp.47-53
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• 2005

The E.M.F. of the galvanic cell with fused salt was measured to determine the activities of zinc at 720-860 K over the entire composition range of liquid Zn-In and Zn-Sn alloys. The cell used was as follows: $$(-)W{\mid}Zn(pure){\mid}Zn^{2+}(KCl-LiCl){\mid}Zn(in\;Zn-In\;or\;Zn-Sn\;alloy){\mid}W(+)$$ The activities of zinc in the alloys showed positive deviation from Raoult's law over the entire composition range. The activity of cadmium and some thermodynamic functions such as Gibbs free energy, enthalpy and entropy were derived from the results by the thermodynamic relationship. The comparison of the results and the literature data was made. The liquid Zn-In and Zn-Sn alloys are found to be close tn the regular solution. The concentration fluctuations in long wavelength limit, $S_{cc}(o)$, in the liquid alloy were calculated from the experimental results.

• 대한안전경영과학회지
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• 제17권3호
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• pp.363-370
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• 2015

In this paper, the control technique of the stepping motor using back electromotive force(B-EMF) without encoder is investigated. The stepping motor generally uses the rotary encoder to detect the rotor position. Since this method increases the cost and the motor configuration size, the new closed-loop control method applied for the B-EMF was implemented by using current detect circuit, AD-converter, and micro controller unit(MCU). The control loop of stepping motor became very simplified. The current change of stepping motor measured by the amplifier was measured and analyzed, when the missing step is occurred. Based on the data from current feedback, position errors were compensated and confirmed by using AD-converter.

• Applied Microscopy
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• 제2권1호
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• pp.39-46
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• 1972

There are many kinds of microscopes suitable for general studies; optical microscopes(OM), conventional transmission electron microscopes (TEM), and scanning electron microscopes(SEM). The optical microscopes and the conventional transmission electron microscopes are very familiar. The images of these microscopes are directly formed on an image plane with one or more image forming lenses. On the other hand, the image of the scanning electron microscope is formed on a fluorescent screen of a cathode ray tube using a scanning system similar to television technique. In this paper, the features and some applications of the scanning electron microscope will be discussed briefly. The recently available scanning electron microscope, combining a resolution of about $200{\AA}$ with great depth of field, is favorable when compared to the replica technique. It avoids the problem of specimen damage and the introduction of artifacts. In addition, it permits the examination of many samples that can not be replicated, and provides a broader range of information. The scanning electron microscope has found application in diverse fields of study including biology, chemistry, materials science, semiconductor technology, and many others. In scanning electron microscopy, the secondary electron method. the backscattererd electron method, and the electromotive force method are most widely used, and the transmitted electron method will become more useful. Change-over of magnification can be easily done by controlling the scanning width of the electron probe. It is possible. to continuously vary the magnification over the range from 100 times to 1.00,000 times without readjustment of focusing. Conclusion: With the development of a scanning. electron microscope, it is now possible to observe almost all-information produced through interactions between substances and electrons in the form of image. When the probe is properly focused on the specimen, changing magnification of specimen orientation does not require any change in focus. This is quite different from the conventional transmission electron microscope. It is worthwhile to note that the typical probe currents of $10^{-10}$ to $10^{-12}\;{\AA}$ are for below the $10^{-5}$ to $10^{-7}\;{\AA}$ of a conventional. transmission microscope. This reduces specimen contamination and specimen damage due to heatings. Outstanding features of the scanning electron microscope include the 'stereoscopic observation of a bulky or fiber specimen in high resolution' and 'observation of potential distribution and electromotive force in semiconductor devices'.

• Journal of Power Electronics
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• 제17권1호
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• pp.96-105
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• 2017

In this paper, a hybrid modular multilevel converter (MMC) topology with an improved nearest level modulation method is proposed for medium-voltage high-power applications. The arm of the proposed topology contains N series connected half-bridge submodules (HBSMs), one full-bridge submodule (FBSM) and an inductor. By exploiting the FBSM, half-level voltages are obtained in the arm voltages. Therefore, an output voltage with a 2N+1 level number can be generated. Moreover, the total level number of the inserted submodules (SMs) is a constant. Thus, there is no pulse voltage across the arm inductors, and the SM capacitor voltage is rated. With the proposed voltage balancing method, the capacitor voltage of the HBSM is twice the voltage of the FBSM, and each IGBT of the FBSM has a relatively low switching frequency and an equalized conduction loss. The capacitor voltage balancing methods of the two kinds of SMs are implemented independently. As a result, the switching frequency of the HBSM is not increased compared to the conventional MMC. In addition, according to a theoretical calculation of the total harmonic distortion of the electromotive force (EMF), the voltage quality with the presented method can be significantly enhanced when the SM number is relatively small. Simulation and experimental results obtained with a MMC-based inverter verify the validity of the developed method.