• Journal of electromagnetic engineering and science
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• v.11 no.1
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• pp.5-10
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• 2011

We propose an adaptive cooperative scheme with a multi-relay node that achieves high bandwidth efficiency and achieves better SEP performance. In the proposed protocol, if the quality of the direct channel is better than that of the all channels from relays to destination, the source will transmit directly to the destination. Otherwise, the source broadcasts the signal and then a potential relay will be chosen to help the source. A re-transmission will also occur if the potential relay cannot be detected. The spectral efficiency is first derived by calculating the probability of each mode, i.e., direct and cooperation transmission. Subsequently, the SEP performance of M-PSK modulation for the scheme is analyzed by considering each event where the source transmits data to the destination. Finally, the obtained analytical results are verified through computer simulations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.2
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• pp.333-337
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• 2010

In this paper, an advanced torque control scheme of Switched Reluctance Motor(SRM) using modified non-linear logical TSF (Torque Sharing Function) with PWM is presented. In the proposed control scheme, a simple calculation of PWM duty ratio and switching rules from DITC(Direct Instantaneous Torque Control) can reduce the torque ripple with fixed switching frequency. The proposed control scheme is verified by the computer simulations and experimental results.

• Journal of Power Electronics
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• v.3 no.1
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• pp.24-32
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• 2003

The commutation and control in matrix converters is more complicated as in voltage source converters. Natural freewheeling paths do not exist and the theoretic absent storage elements result in a direct coupled system of load and line currents as well as voltages. The paper offers an overview about staggered commutation and control policies in matrix converters. Based on the knowledge about load current direction and the signs of the line to line input voltages different multi-step commutation policies were derived. This paper examines the application of that policies in the case of space vector modulation and direct control methods with the focus on the resulting effects to the reference output voltage deviation.

• Journal of Power Electronics
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• v.9 no.4
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• pp.535-543
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• 2009

In this paper, pulse-width modulation (PWM) control strategy of various topologies of matrix converters is presented, which is based on direct duty ratio PWM (DDPWM). Because the DDPWM method has the characteristics of the inherent per-phase modular structure, it can be effectively applied to single-phase, two-phase and three-phase four-leg matrix converters as well as the common three-phase to three-phase matrix converter. Also, this paper treats command generation method in each matrix converter. The feasibility and validity of the proposed method are verified by experimental results.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.276-279
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• 2001

Direct torque control(DTC) is known to produce quick response in ac drives. Some drawbacks of the classical DTC are the relatively large torque ripple in a low speed range and notable current pulsation during steady state. They are reflected speed response and increased acoustical noise. In this paper, The DTC quick response are preserved at transient state, while better qualify steady state performance is produced by Space Vector Modulation(SVM). It is able to reduce the acoustical noise, torque ripple and current pulsation during steady state. The system presented are closed loop stator flux and torque observer for wide speed range that inputs are currents and voltages sensing of motor terminal. Simulation results for the 2.2kw general purposed induction motor are presented and discussed.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.259-260
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• 2020

모듈화 멀티레벨 컨버터 (modular multilevel converter, MMC)는 고압직류송전(high-voltage direct current, HVDC)에 대한 기술이 발전함에 따라서 이와 관련된 전력변환 장치로써 많은 연구되어지고 있다. 10kV 이하로 구현되는 중압직류송전(medium-volatge direct current, MVDC) 시스템 및 모터 드라이브에 이용되는 MMC의 경우에는 수백 개의 직렬 서브모듈로 구성된 MMC가 사용되는 HVDC와 다르기 때문에 여러 모듈레이션 방식에서의 다른 장단점을 가지게 된다. 본 논문에서는 전력전자 시뮬레이션 툴인 PSIM을 이용하여 여러가지 모듈레이션의 MVDC으로의 적용에 있어서의 장단점을 분석한다.

• Journal of Power Electronics
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• v.17 no.2
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• pp.368-379
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• 2017

In this paper, a direct torque control algorithm with novel duty cycle-based modulation is proposed for permanent magnet synchronous motor drives fed by neutral-point clamped three-level inverters. Compared with the standard DTC, the proposed algorithm can suppress steady-state torque ripples as well as ensure neutral-point potential balance and smooth vector switching. A unified torque/flux evaluation table with multiple voltage vectors and precise control levels is established and used in this method. This table can be used to evaluate the effects of duty-cycle vectors on torque and flux directly, and the elements of the table are independent of the motor parameters. Consequently, a high number of appropriate voltage vectors and their corresponding duty cycles can be selected as candidate vectors to reduce torque ripples by looking up the table. Furthermore, small vectors are incorporated into the table to ensure the neutral-point potential balance with the numerous candidate vectors. The feasibility and effectiveness of the proposed algorithm are verified by both simulations and experiments.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.4 s.334
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• pp.1-6
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• 2005

For the low power and low cost transceivers, direct sequence spread spec01m frequency-shift keying (DSSS-FSK) is proposed. A transmitter of the DSSS-FSK signal can be implemented by a simple direct modulation using the phase locked loop. Since the DSSS-FSK signal has negligible power around the carrier frequency, low cost direct conversion receiver can be used. Optimum coherent and semi-coherent correlation detection methods for the DSSS-FSK signal are proposed and analyzed. Segmented semi-coherent correlation detection method is proposed to improve the bit error rate performance in the large carrier frequency offset.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.2
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• pp.70-78
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• 2012

Due to the variable nature of renewable energy resources and power demand by consumers, it is difficult to operate a power system installed with only one type of renewable energy resource. Grid-based renewable generation may be the only solution to overcome this problem. The conventional approach based on a low-voltage converter with power frequency transformer is commonly employed for grid connection of offshore renewable energy systems. Because of the heavy weight and large size of the transformer, the system can be expensive and complex in terms of installation and maintenance. In this paper, an 11-kV series connected H-bridge (SCHB) multilevel voltage source converter (VSC) is proposed to achieve a compact and light direct grid connection of renewable energy systems. This paper presents the design, simulation and analysis of a five level (5L)-SCHB and an eleven level (11L)-SCHB VSC for 11-kV grid-based renewable energy systems. The performance, cost, modulation scheme and harmonic spectra of the converter are analyzed.

• International Journal of Stem Cells
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• v.16 no.2
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• pp.156-167
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• 2023

Background and Objectives: Cellular reprogramming in regenerative medicine holds great promise for treating patients with neurological disorders. In this regard, small molecule-mediated cellular conversion has attracted special attention because of its ease of reproducibility, applicability, and fewer safety concerns. However, currently available protocols for the direct conversion of somatic cells to neurons are limited in clinical application due of their complex nature, lengthy process, and low conversion efficiency. Methods and Results: Here, we report a new protocol involving chemical-based direct conversion of human fibroblasts (HF) to matured neuron-like cells with a short duration and high conversion efficiency using temporal and strategic dual epigenetic regulation. In this protocol, epigenetic modulation by inhibition of histone deacetylase and bromodomain enabled to overcome "recalcitrant" nature of adult fibroblasts and shorten the duration of neuronal reprogramming. We further observed that an extended epigenetic regulation is necessary to maintain the induced neuronal program to generate a homogenous population of neuron-like cells. Conclusions: Therefore, our study provides a new protocol to produce neurons-like cells and highlights the need of proper epigenetic resetting to establish and maintain neuronal program in HF.