• Applied Microscopy
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• v.2 no.1
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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'.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.3
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• pp.279-288
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• 2013

This paper proposes a improved speed control system for five-phase squirrel-cage induction motor(IM) injecting 3rd. current harmonic components with field oriented control (FOC) A five-phase IM drives present unique characteristics due to the additional degrees of freedom and also drives possess many others advantage compared with the traditional three-phase motor drive system, such as reducing a amplitude of torque pulsation at low frequency and increasing the reliability. In order to maximize the torque per ampere, the proposed motor has concentrated windings. The produced back-electromotive force is almost trapezoidal, and the motor is supplied with the combined sinusoidal plus third harmonic of currents. There is necessary to controlled 3rd harmonic current in order to high response characteristics. For presenting the superior performance of the proposed the speed control system, experimental results are presented using a 32-bit fixed point TMS320F2812 DSP with 1.5[kW] induction motor.

• Journal of Power Electronics
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• v.15 no.5
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• pp.1264-1273
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• 2015

An inverter output power control based power factor correction (PFC) strategy is being extensively used for permanent magnet synchronous motor (PMSM) drives in appliances because such a strategy can considerably reduce the cost and size of the inverter. In this strategy, PFC circuits are removed and large electrolytic DC-link capacitors are replaced with small film capacitors. In this application, the PMSM d-q axes currents are controlled to produce ripples, the frequency of which is twice that of the AC main voltage, to obtain a high power factor at the AC mains. This process indicates that the PMSM operates under periodic magnetic saturation conditions. This paper proposes a back electromotive-force (back-EMF) estimator for the high-speed sensorless control of PMSM operating under periodic magnetic saturation conditions. The transfer function of the back-EMF estimator is analyzed to examine the effect of the periodic magnetic saturation on the accuracy of the estimated rotor position. A simple compensation method for the estimated position errors caused by the periodic magnetic saturation is also proposed in this paper. The effectiveness of the proposed method is experimentally verified with the use of a PMSM drive for a vacuum cleaner centrifugal fan, wherein the maximum operating speed reaches 30,000 rpm.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.3
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• pp.284-291
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• 2006

Recently with the motorizing of electric home appliances and car systems, there is increasing interest in high efficiency electric motors. Thus, the present study described the operating characteristics of coreless AFPM motor that is highly efficient in high speed driving, and discussed its electric characteristics from the perspective of design. In particular, we examined back electromotive force and the magnetic field characteristic in slits, which have significant effects on the characteristic of the motor, and conducted simulation and experiment on control characteristic according to inductance characteristic. This study analyzed torque speed and efficient operation characteristic as well as control characteristic through comparing the result of motor design with the result of output characteristic experiment based on the electric network method. Furthermore, we evaluated vibration and noise that may occur due to the absence of core.

• Journal of Sensor Science and Technology
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• v.15 no.3
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• pp.168-172
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• 2006

Potentiometric $CO_{2}$ sensors were fabricated using a NASICON ($Na_{1+x}Zr_{2}Si_{X}P_{3-X}O_{12}$, 1.8 < x < 2.4) thick film and auxiliary layers. The powder of a precursor of NASICON with high purity was synthesized by a sol-gel method. By using the NASICON paste, an electrolyte was prepared on the alumina substrate by screen printing and then sintered at $1000^{\circ}C$ for 4 h. A series of $Na_{2}CO_{3}-CaCO_{3}$ auxiliary phases were deposited on the Pt sensing electrode. The electromotive force (emf) values were linearly dependent on the logarithm of $CO_{2}$ concentration in the range between 1,000 and 10,000 ppm. The device attached with $Na_{2}CO_{3}-CaCO_{3}$ (1:2 in mol.%) showed good sensing properties in the low temperatures.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.12
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• pp.2125-2130
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• 2010

The neutral section on electric railway system is significant sector in order to prevent short circuit of two electric powers. However, while electric trains pass the neutral section, those speed is decreased and the accident of AC electric traction system and the electric train would be occurred. So the countermeasures are urgently needed. The automatic power switching technology system that is current being research and development is system to improve these problems. Because main object of this system is power change using static switch in the neutral section, it's expected to cause a variety of transients. Especially, onboard transformer inrush current for electric railway train can be occurred more than rated current according to switching time. Therefore, the analysis and improvement are needed to ensure the stability of this system. In this paper, we analyze the operating characteristics of the automatic power switching technology system. Especially, it reviews inrush current according to the closing phase angle. And we propose control plan of inrush current considering the case that voltage is maintained due to counter electromotive force and regenerative braking operation of electric railway train. Finally, the proposed control scheme was reviewed using the transient analysis program.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.764-767
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• 2004

This paper present the temperature control of aluminum plate using Peltier element. Peltier effect is heat pumping phenomena by electric energy as one of the thermoelectric effect. So if current is asserted to Peltier element, it absorbs heat from low temperature side and emits to high temperature side. In this experiment, Peltier element is used to control the temperature of small aluminum plate with ON/OFF control scheme and fan ON/OFF. As the result of experiments, it is proper to act fan only while cooling duration and there exist a proper cooling current to drop temperature rapidly. It takes about 100sec to increase to 7$0^{\circ}C$ and drop to 35$^{\circ}C$ of aluminium plate temperature and about 90sec to increase to 7$0^{\circ}C$ and drop to 4$0^{\circ}C$ in ambient temperature 3$0^{\circ}C$ while fan is on only in cooling duration. Future aim is to realize more rapid temperature control and develop SMHA(special metal hydride actuator) by using Peltier element to heating and cooling.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.10
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• pp.1403-1407
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• 2013

This paper presents the method to calculate the motor parameters considering skew in EPS Interior Permanent Magnet Synchronous Motor (IPMSM). The skew is applied to stator or rotor by general technology used for design of reducing noise and vibration in motor. The characteristics analysis of motor including the skew is mostly used by 3D Finite Element Analysis (FEA), though, this analysis is a very time-consuming to perform. Besides, The reliability lacks due to the considerable change of motor characteristics according to the number of elements in 3D FEA. However, analysis time and effort can be saved by characteristic analysis considering skew using 2D FEA. Therefore, in this paper, a quick and accurate method for the calculations of motor parameters considering skew is suggested. The proposed method is verified by the comparison of calculated and experimental results.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.9
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• pp.1325-1333
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• 2017

The sensorless control of blushless DC motor(BLDCM) is based on the $120^{\circ}$ control in which the back electromotive force(Back EMF) for estimating the position of the rotor can be detected. However, the $120^{\circ}$ control has a disadvantage that the torque constant is small as compared with $180^{\circ}$ control which can not detect the back EMF. The $150^{\circ}$ control which complements these problems makes it possible to detect the back EMF and improve the torque constant by 12.5% compared to the $120^{\circ}$ control. Therefore, this paper compares the output characteristics of BLDCM through finite element method analysis (FEA) by the conventional and proposed control methods of BLDCM for water circulation system and proposes design for downsizing and weight reduction of BLDCM according to secured torque constant. The validity of the proposed control and design proposal is proved through simulation and experimental results by comparing the output characteristics of $120^{\circ}$ control and $150^{\circ}$ control.

• Journal of Power Electronics
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• v.9 no.6
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• pp.911-918
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• 2009

This paper presents a new sensorless control method for single-phase switched reluctance motors using induced electromotive force (EMF) due to the residual flux both on the stator and the rotor during phase commutation. The induced EMF falls to zero when the rotor pole moves away from the overlap with the stator pole. By detecting this instant, the speed and position of the rotor can be simply estimated. This method is very simple to implement and it is insensitive to variations in the system parameters as it does not require any stored magnetic data or offline inductance measurements but requires only measurements of the terminal voltage and a simple analog circuit. The proposed method is implemented on a 6/6 single-phase switched reluctance motor. However, it can also be implemented on a multiphase SRM regardless of the size, operation speed and switching mode of the motor hence making the proposed method viable to many applications. Simulation and experimental verification is provided to demonstrate the feasibility of the proposed method.