• Journal of Power Electronics
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• v.2 no.1
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• pp.46-54
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• 2002

In this paper a neural network controller for achieving maximum power tracking as well as output voltage regulation, for a wind energy conversion system (WECS) employing a permanent magnet synchronous generator is proposed. The permanent magnet generator (PMG) supplies a dc load via a bridge rectifier and two buck-boost converters. Adjusting the switching frequency of the first buck-boost converter achieves maximum power tracking. Adjusting the switching frequency of the second buck-boost converter allows output voltage regulation. The on-time of the switching devices of the two converters are supplied by the developed neural network (NN). The effect of sudden changes in wind speed and/ or in reference voltage on the performance of the NN controller are explored. Simulation results showed the possibility of achieving maximum power tracking and output voltage regulation simulation with the developed neural network controllers. The results proved also the fast response and robustness of the proposed control system.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1558-1565
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• 2018

Three-phase current is reconstructed from the dc-link current in an AC machine drive with a single current sensor. Switching pattern modification methods, in which the magnitude of the effective voltage vector is secured over its minimum, are investigated to accurately reconstruct the three-phase current. However, the existing methods that modify the switching pattern cause voltage and current distortions that degrade sensorless performance. This paper proposes a variable-magnitude voltage signal injection method based on a high frequency voltage signal injection. The proposed method generates a voltage reference vector that ensures the minimum magnitude of the effective voltage vector by varying the magnitude of the injection signal. This method can realize high quality current reconstruction without switching pattern modification. The proposed method is verified by experiments in a 600W Interior permanent magnet synchronous machine (IPMSM) drive system.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.656-659
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• 2001

In this paper a neural network controller for achieving maximum power tracking as well as output voltage regulation, for a wind energy conversion system(WECS) employing a permanent magnet synchronous generator, is proposed. The permanent magnet generator (PMG) supplies a dc load via a bridge rectifier and two buck-boost converters. Adjusting the switching frequency of the first buck-boost converter achieves maximum power tracking. Adjusting the switching frequency of the second buck-boost converter allows output voltage regulation. The on-times of the switching devices of the two converters are supplied by the developed neural network(NN). The effect of sudden changes in wind speed ,and/or in reference voltage on the performance of the NN controller are explored. Simulation results showed the possibility of achieving maximum power tracking and output voltage regulation simultaneously with the developed neural network controller. The results proved also the fast response and robustness of the proposed control system.

• Journal of Korea Trade
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• v.23 no.8
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• pp.45-72
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• 2019

Purpose - This study examines the mediating effect of switching costs (economic risk costs and setup costs) on the relationships of country image with product attitude and product attachment. Switching-cost effects for the Korean Wave, which are insufficiently addressed in the literature, were investigated using the country image of Korea as a proxy for the Korean Wave. Moreover, this study examined the economic effects of the Korean Wave and the negative effect of the Terminal High Altitude Area Defense (THAAD) deployment on these economic effects. Design/methodology - A total of 302 Chinese consumers were surveyed using a questionnaire. Because this was an exploratory study and was not based on a classical model, the PLS-SEM method was employed to test the stability of the model and its hypotheses. Findings - Switching costs had mediating effects on the relationships of country image with product attitude and product attachment. The switching-cost effects for the Korean Wave were verified. However, neither the economic image nor cultural image of Korea had significant effects on the economic risk costs. Moreover, the economic image of Korea had no significant effect on the set-up costs. Originality/value - This study broadened the understanding of the relationships among country image, switching costs, product attitude, and product attachment and advanced the knowledge of relevant theories. The results contribute theoretically to the literature on switching-cost effects for the Korean Wave. The results confirmed the negative effect of THAAD deployment on the economic effects of the Korean Wave. In the rapidly developing international environment, these research results could serve as theoretical reference guidelines for suppliers when developing marketing strategies.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.8
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• pp.105-113
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• 2004

MRAM uses magneto-resistance material as a storage element, which stores cell data as a polarization of spin in a free magnetic layer. This magneto-resistance material has hysteresis, asteroid curve at the thermal variation, and R-V characteristics for switching the data. Therefore, a macro-model which can reproduce these characteristics is required for MRAM simulation. We propose a macro-model of TMR (Tunneling Magneto Resistance) that can reproduce all of these characteristics on HSPICE. Also we propose a novel sensing scheme, which generates reference resistance having the medium value, ( $R_{H}$+ $R_{L}$)/2, for a wide range of applied voltage and present simulation results based on the HSPICE macro-model of MTJ that we have developed.d.d.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.3
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• pp.84-93
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• 2000

In PWM voltage source inverters operated by conventional switching method, the dead time is inserted in switching signals to prevent tile short circuit of the DC voltage source. The dead time causes detrimental effects to the control performance of the inverter system. So we need to compensate the dead time effects. And the dead time minimization switching method can be considered as the best way to avoid the dead time effects fundamentally. In this paper, a new switching strategy is proposed which is a kind of dead time minimization switching methods. According to the proposed switching method, very short dead time is adopted in only once when the current polarity is changing. And the adopted dead time is equal to the turn off time of the swtiching device or shorter than it. As the proposed method can be done with the polarity information of the reference current in case that the output current of the inverter is controlled, it is easy to solve some problems in comparison with the case that the real current is used to get the polarity changing time； level detection difficulty, noise problem and so on

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.11
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• pp.1139-1145
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• 2008

A robust position sensing system is proposed in this paper for a ubiquitous mobile robot which moves indoors as well as outdoors. The Differential GPS (DGPS) which has a position estimation error of less than 5 m is a general solution when the mobile robot is moving outdoor, while an active beacon system (ABS) with embedded ultrasonic sensors is reliable as an indoor positioning system. The switching from the outdoor to indoor or vice versa causes unstable measurements on account of the reference coordinates and algorithm changes. To minimize the switching time in the position estimation and to stabilize the measurement, a robust position sensing system is proposed. In the system, to minimize the switching delay, the door positions are stored and updated in a database. Using the database, the approaching status of the mobile robot from indoor to outdoor or vice versa has been checked and the switching conditions are prepared before the mobile robot actually moves out or moves into the door. The reliability and accuracy of the robust positioning system based on DGPS and ABS are verified and demonstrated through the real experiments using a mobile robot prepared for this research.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.5
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• pp.269-277
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• 1999

In this paper, a novel dead time minimization algorithm is proposed for improving the output waveform of an inverter. The adverse effects of the dead time are mainly described by the voltage drop and the distortion factor of waveforms. The principle of the proposed algorithm is organized with forbidding unnecessary firings fo the inverter switches which are not conducted even though the gate signal is impressed. The proposed methods are explained with the conduction mode of output currents. The H/W and S/W implementation method of the proposed algorithm are also presented. The validity of the proposed algorithm is verified by comparing the simulation and experimental results with conventional methods. It can be concluded from the results that the proposed algorithm has the advantage which is able to reduce the harmonics in the output voltages and which the output voltage can nearly be equal to the reference value. Another advantage of the proposed method is the reduction of total numbers of switching so that the switching losses of inverter drives can be minimized.

• Journal of Power Electronics
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• v.17 no.3
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• pp.674-685
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• 2017

The conventional model predictive direct torque control (MPDTC) method uses all of the voltage vectors available from a two level voltage source inverter for the prediction of the stator flux and stator current, which leads to a heavy computational burden. This paper proposes an improved model predictive direct torque control method. The stator flux predictive controller is obtained from an analysis of the relationship between the stator flux and the torque, which can be used to calculate the desired voltage vector based on the stator flux and torque reference. Then this method only needs to evaluate three voltage vectors in the sector of the desired voltage vector. As a result, the computational burden of the conventional MPDTC is effectively reduced. The time delay introduced by the computational time causes the stator current to oscillate around its reference. It also increases the current and torque ripples. To address this problem, a delay compensation method is adopted in this paper. Furthermore, the switching frequency of the inverter is significantly reduced by introducing the constraint of the power semiconductor switching number to the cost function of the MPDTC. Both simulation and experimental results are presented to verify the validity and feasibility of the proposed method.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.6
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• pp.873-879
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• 2016

A charge pump circuit with very short turn-on time is presented for minimizing reference spurs in CMOS PLL frequency synthesizers. In the source switching charge pump circuit, applying proper voltages to the source nodes of the current source FETs can significantly reduce the unwanted glitch at the output current while not degrading the rising time, thus resulting in low spur at the synthesizer output spectrum. A 1.1-1.6 GHz PLL synthesizer employing the proposed charge pump circuit is fabricated in 65 nm CMOS. The current consumption of the charge pump is $490{\mu}A$ from 1 V supply. Compared to the conventional charge pump, it is shown that the reference spur is improved by dB through minimizing the turn-on time. Theoretical analysis is described to show that the measured results agree well with the theory.