• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.27-27
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• 2011

For the design of real applicable molecular devices, current-voltage properties through molecular nanostructures such as metal-molecule-metal junctions (molecular junctions) have been studied extensively. In thiolate monolayers on the gold electrode, the chemical bonding of sulfur to gold and the van der Waals interactions between the alkyl chains of neighboring molecules are important factors in the formation of well-defined monolayers and in the control of the electron transport rate. Charge transport through the molecular junctions depends significantly on the energy levels of molecules relative to the Fermi levels of the contacts and the electronic structure of the molecule. It is important to understand the interfacial electron transport in accordance with the increased film thickness of alkyl chains that are known as an insulating layer, but are required for molecular device fabrication. Thiol-tethered RuII terpyridine complexes were synthesized for a voltage-driven molecular switch and used to understand the switch-on mechanism of the molecular switches of single metal complexes in the solid-state molecular junction in a vacuum. Electrochemical voltammetry and current-voltage (I-V) characteristics are measured to elucidate electron transport processes in the bistable conducting states of single molecular junctions of a molecular switch, Ru(II) terpyridine complexes. (1) On the basis of the Ru-centered electrochemical reaction data, the electron transport rate increases in the mixed self-assembled monolayer (SAM) of Ru(II) terpyridine complexes, indicating strong electronic coupling between the redox center and the substrate, along the molecules. (2) In a low-conducting state before switch-on, I-V characteristics are fitted to a direct tunneling model, and the estimated tunneling decay constant across the Ru(II) terpyridine complex is found to be smaller than that of alkanethiol. (3) The threshold voltages for the switch-on from low- to high-conducting states are identical, corresponding to the electron affinity of the molecules. (4) A high-conducting state after switch-on remains in the reverse voltage sweep, and a linear relationship of the current to the voltage is obtained. These results reveal electron transport paths via the redox centers of the Ru(II) terpyridine complexes, a molecular switch.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1869-1883
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• 2016

In recent years, some converter structures and analyzing methods for the voltage regulation of stand-alone self-excited induction generators (SEIGs) have been introduced. However, all of them are concerned with the three-phase voltage control of three-phase SEIGs or the single-phase voltage control of single-phase SEIGs for the operation of these machines under balanced load conditions. In this paper, each phase voltage is controlled separately through separated converters, which consist of a full-bridge diode rectifier and one-IGBT. For this purpose, the principle of the electronic load controllers supported by fuzzy logic is employed in the two-different proposed converter structures. While changing single phase consumer loads that are independent from each other, the output voltages of the generator are controlled independently by three-number of separated electronic load controllers (SELCs) in two different mode operations. The aim is to obtain a rated power from the SEIG via the switching of the dump loads to be the complement of consumer load variations. The transient and steady state behaviors of the whole system are investigated by simulation studies from the point of getting the design parameters, and experiments are carried out for validation of the results. The results illustrate that the proposed SELC system is capable of coping with independent consumer load variations to keep output voltage at a desired value for each phase. It is also available for unbalanced consumer load conditions. In addition, it is concluded that the proposed converter without a filter capacitor has less harmonics on the currents.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.5
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• pp.456-463
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• 2015

Nowadays, small quantity batch production, which is so-called a flexible manufacturing system, is a major trend in the modern factory automation industry. The demands for new transportation system are increased gradually, with which multiple passive carriers carrying materials and semi-products are precisely and individually controlled along a single closed rail. Thus, a new type of permanent magnet linear synchronous motor (PMLSM), which consists of state coils on a single rail and PM movers as many as carriers, is proposed in this paper. The rail can be segmented as modules with pairs of coils and a current amplifier, which makes the transportation system simple; therefore, the rail can be easily extended and repaired. A design method of the new PMLSM with a single carrier is proposed, which can be thought as a new version of PMLSM, a coil-segmented coreless PMLSM (CS-CLPMLSM). Experimental setup for it is made, and propulsion results show that with the help of a new effective coil selection and switching algorithms, the conventional current-based vector control is sufficient to fulfill the position and velocity control of the new PMLSM. The proposed PMLSM is expected to fulfill seamless servo-control of multiple carriers also in process line, such as a new generation of flat panel display manufacturing line.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1066-1071
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• 2005

This paper presents the two lossless auxiliary inductors-assisted voltage source type half bridge (single ended push pull: SEPP) series resonant high frequency inverter for induction heated fixing roller in copy and printing machines. The simple high-frequency inverter treated here can completely achieve stable zero current soft switching (ZCS) commutation for wide its output power regulation ranges and load variations under its constant high frequency pulse density modulation (PDM) scheme. Its transient and steady state operating principle is originally described and discussed for a constant high-frequency PDM control strategy under a stable ZCS operation commutation, together with its output effective power regulation characteristics-based on the high frequency PDM strategy. The experimental operating performances of this voltage source SEPP ZCS-PDM series resonant high frequency inverter using IGBTs are illustrated as compared with computer simulation results and experimental ones. Its power losses analysis and actual efficiency are evaluated and discussed on the basis of simulation and experimental results. The feasible effectiveness of this high frequency inverter appliance implemented here is proved from the practical point of view.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.1
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• pp.143-148
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• 2013

When the fault occurs in power system, the fault-current exceeds breaking capacity of the circuit breaker. So, reliablity of the power system is decreased sharply. Superconducting fault-current limiter (SFCL) is operated without impedance in normal state. The fault-current is limited by its impedance during the fault condition. However, the SFCL has several weak points such as huge size, high-price, liquid-nitrogen operation for the real power system. In this paper, We suggested the high-speed interrupter to limit the fault-current in case of the single line-to-ground fault. In addition, we compared the high-speed interrupter with the SFCL to ensure the operation reliability. The proposed interrupter detected the fault-current through the CT, and the power was supplied by operation of the SCR control system. In this experiment, the power of high-speed interrupter was applied after the 4.8[msec] from fault instant. The on-off operation of the interrupter was started after half-cycle from the fault. The fault-current was flowed into the impedance element by the switching operation of the high-speed interrupter. So, the fault current was limited within one cycle, and then it didnt exceed the capacity of a circuit breaker. We confirmed that there was slight difference between the SFCL with high-speed interrupter in terms of limiting-time of the fault-current and switching speed of the SCR. The high-speed interrupter was considered to be more efficient than the SFCL in size, cost or reliability.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.11a
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• pp.415-420
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• 2005

This paper presents the two lossless auxiliary inductors-assisted voltage source type half bridge (single ended push pull: SEPP) series resonant high frequency inverter for induction heated king roller in copy and printing machines. The simple high-frequency inverter treated here can completely achieve stable zero current soft switching (ZCS) commutation for wide its output power regulation ranges and load variations under its constant high frequency pulse density modulation (PDM) scheme. Its transient and steady state operating principle is originally described and discussed for a constant high-frequency PDM control strategy under a stable ZCS operation commutation, together with its output effective power regulation characteristics-based on the high frequency PDM strategy. The experimental operating performances of this voltage source SEPP ZCS-PDM series resonant high frequency inverter using IGBTs are illustrated as compared with computer simulation results and experimental ones. Its power losses analysis and actual efficiency are evaluated and discussed on the basis of simulation and experimental results. The feasible effectiveness of this high frequency inverter appliance implemented here is proved from the practical point of view.

• Transactions on Electrical and Electronic Materials
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• v.13 no.2
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• pp.73-77
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• 2012

Operation of liquid crystal displays (LCDs) can be improved by monolithic integration of the pixel transistors with light emitting diodes (LEDs) on a single substrate. Conventional LCDs make use of filters to control the backlighting which reduces the overall efficiency. These LCDs also utilize LEDs in series which impose failure and they require high voltage for operation with a power factor correction. The screen of small hand-held devices can operate from moderate brightness. Therefore, III-V nanowires that are grown along with transistors over Silicon substrates can be utilized. Control of nanowire LEDs with nanowire transistors will significantly lower the cost, increase the efficiency, improve the manufacturing yield and simplify the structure of the small displays that are used in portable devices. The steps to grow nanowires on Silicon substrates are described. The vertical n-type and p-type nanowire transistors with surrounding gate structures are characterized. While biased at 0.5 V, nanowire transistors with minimum radius or channel width have an OFF current which is less than 1pA, an ON current more than 1 ${\mu}A$, a total delay less than 10 ps and a transconductance gain of more than 10 ${\mu}A/V$. The low power and fast switching characteristics of the nanowire transistor make them an ideal choice for the realization of future displays of portable devices with long battery lifetime.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.1
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• pp.1-9
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• 2013

This paper presents a new control algorithm for dynamic control of a unicycle robot. The unicycle robot motion consists of a pitch that is controlled by an in-wheel motor and a roll that is controlled by a reaction wheel pendulum. The unicycle robot doesn't have any actuator for a yaw axis control, which makes the derivation of the dynamics relatively simple. The Euler-Lagrange equation is applied to derive the dynamic equations of the unicycle robot to implement the dynamic speed control of the unicycle robot. To achieve the real time speed control of the unicycle robot, the sliding mode control and LQ regulator are utilized to guarantee the stability while maintaining the desired speed tracking performance. In the roll controller, the sigmoid-function based sliding mode controller has been adopted to minimize the chattering by the switching function. The LQR controller has been implemented for the pitch control to drive the unicycle robot to follow the desired velocity trajectory in real time using the state variables of pitch angle, angular velocity, angle and angular velocity of the wheel. The control performance of the two control systems form a single dynamic model has been demonstrated by the real experiments.

• Journal of Magnetics
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• v.15 no.3
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• pp.116-122
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• 2010

An accurate analytical equation for the total energy in the framework of the single domain model is used to study the thermal stability of nanostructured synthetic ferrimagnets. Elliptical cells are considered that have lateral dimensions of 160 nm (long axis)$\times$80 nm (short axis) and varying values of thickness asymmetry for the two magnetic layers. The direction of the applied magnetic field, which points to the $45^{\circ}$ direction, is in the opposite direction to the thicker layer magnetization. A significant difference is observed in the applied magnetic field dependencies of the equilibrium magnetic configuration and the magnetic energy barrier when using the simplifying assumption that the self-demagnetizing field is identical in magnitude to the dipole field. At a small thickness asymmetry of 0.2 nm, for example, the magnetic energy barrier is reduced from 68 kT (T=300 K) to 6 kT at the remanent state and a progressive switching behavior changes into a critical behavior, as the simplifying assumption is used. The present results clearly demonstrate the need for an accurate analytical equation for the total energy in predicting the thermal stability of nanostructured synthetic ferrimagnets.

• Journal of Power Electronics
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• v.16 no.2
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• pp.654-665
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• 2016

The pumping of electric power from photovoltaic (PV) farms is normally carried out using transformers, which require heavy mounting structures and are thus costly, less efficient, and bulky. Therefore, transformerless schemes are developed for the injection of power into the grid. Compared with the H4 inverter topology, the H6 topology is a better choice for pumping PV power into the grid because of the reduced common mode current. This paper presents how the perturb and observe (P&O) algorithm for maximum power point tracking (MPPT) can be implemented in the H6 inverter topology along with the improved sinusoidal current injected to the grid at unity power factor with the average current mode control technique. On the basis of the P&O MPPT algorithm, a power reference for the present insolation level is first calculated. Maintaining this power reference and referring to the AC sine wave of bus bars, a sinusoidal current at unity power factor is injected to the grid. The proportional integral (PI) controller and fuzzy logic controller (FLC) are designed and implemented. The FLC outperforms the PI controller in terms of conversion efficiency and injected power quality. A simulation in the MATLAB/SIMULINK environment is carried out. An experimental prototype is built to validate the proposed idea. The dynamic and steady-state performances of the FLC controller are found to be better than those of the PI controller. The results are presented in this paper.