• Journal of Power Electronics
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• 제17권1호
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• pp.161-171
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• 2017

To enhance the reliability of two-motor drive systems, this paper proposes an improved direct torque control (DTC) scheme (P-DTC) for five-leg dual-PMSM drive systems. First, the topology of a five-leg dual-PMSM drive system is illustrated. To clarify the analysis of the P-DTC, the standard DTC scheme for three-phase drive systems is presented. The operation of a five-leg dual-PMSM drive system is classified into three situations according to the definitions of the switching-vector unions. Compared with the existing DTC scheme (R-DTC), the P-DTC can minimize the replacement of active switching-vectors to zero switching-vectors. When this replacement cannot be avoided, the P-DTC uses a proposed master-slave selection principle to minimize the system error. Comparing with the R-DTC, the P-DTC has lower torque ripples, a wider speed range and a faster torque increasing response. Experiments have been carried out in the coupling and independent modes, and the effectiveness of the P-DTC is verified by the obtained results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 하계종합학술대회 논문집
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• pp.16-20
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• 1989

In this paper, we describe the optimal driving method and magnetic flux distribution of permanent magnet which enhance torque characteristics in small-sized 3-phase brushless DC motors. The disadvantages of conventional $120^{\circ}$ constant current drive method are torque ripple, switching noise and spike voltage due to the inductance of stator coil. This shortcommings can be avoided by the switching slew-rate of driving current which is called linear voltage driving method. The aim of this study is to analyze linear voltage driving method quantatively and to determine optimal drive current waveform through computer simulation. The selection of commutation angle and slew rate of a new driving current at switching instants makes torque ripple index minimize and average torque maximize. And the validity of this new driving method was assured by Fourier analysis. Considering two dimensional nonlinear magnetic flux distribution on the permanent magnet, we suggest optimal flux distribution according to the presented driving method which improves torque characteristics.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 춘계학술대회 논문집
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• pp.788-793
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• 2005

This paper presents harmonic evaluation of an IAT(Intra Airport Transit) system in Incheon International Airport. It will be used electric vehicles with 80 kW per car that are produced Mitsubishi Heavy Industries Ltd, and one car is constructed with SIV(Static Inverter), VVVF(Variable Voltage and Variable Frequency) and two induction motor. The operated vehicles in the IAT system are rapidly changing DC load, and at a feeding substation, 3-phase electric power is transferred to DC 750 V by rectifier. Since, vehicles are also changing continuously, the voltages for the DC load fluctuate in the IAT system, and moreover, the fluctuating voltages generate high-order harmonics. This means that there is the difficulty in maintaining power quality in KEPCO systems' side. Therefore, the power quality of the IAT system in Incheon International Airport is evaluated using PSCAD/EMTDC simulator in the paper. The THD(Total Harmonic Distortion) of voltages and TDD(Total Demand Distortion) of currents, indices are calculated for the IAT system using the results of PSCAD/EMTDC dynamic simulation.

• 전기학회논문지
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• 제66권4호
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• pp.733-739
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• 2017

Research on fuel cell systems attracting attention as an environmentally friendly energy source has been actively conducted. And research is being conducted on railway vehicles that use direct current power generated by a fuel cell as an energy source. In this paper, a two-phase interleaved bidirectional DC-DC converter has been proposed which can supply electric energy of a battery to a traction motor during powering and charge the battery with regenerative energy during braking. Therefore, the topology of the energy storage system applied to the railway vehicle was analyzed, and the simulation was performed by constructing the power conversion system by this topology. Experiments were also conducted through hardware design and fabrication based on the simulation analysis results, and the validity of the hardware implementation was verified.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(2)
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• pp.677-680
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• 2003

The control of the SRM(Switched Reluctance Motor) is usually based on the non-linear inductance profiles with positions. So determination of optimal switching angle is very different. we present self-tuning control of SRM for maximum torque and efficiency with phase current and shaft position sensor During the sample time, micro-controller checks the number of pre-checked pulse. After micro-controller calculates between two data, it move forward or backward turn-off angle. When the turn-off angle is fixed optimal turn-off angle, turn-on angle moves forward or backward by a step using self-tuning control method. And then, optimal turn-off angle is searched once again. As such a repeating process, turn-on/off angle is moves automatically to obtain the maximum torque and efficiency. The experimental results are presented to validate the self-tuning algorithm.

• 한국통신학회논문지
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• 제15권5호
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• pp.384-398
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• 1990

本 硏究는 電壓源 인버어터의 펄스信號를 發生시키기 위한 PWM 方式의 特性 및 長短點을 比較하여 提示하였다. 電壓源 인버어터를 PTR로 設計하여 VSD을 構成한 후 各 PWM 方式으로 誘導電動機를 可變速 運轉시켜 騷音레벨, 線間電壓 및 電流 波形, 電流 高周波 스펙트럼을 測定하였다. 그 結果, Suboptimal PWM 方式은 高周波 影響이 Optimal PWM 方式과 類似한 結果로 良好하게 나타나며 microprocessor 應用이 可能하였고, TP PWM 方式은 3相中 2相만 制御하기 때문에 CPO에 要하는 處理負擔을 줄일 수 있으며 出力電壓을 擴大시킬 수 있는 優秀한 方式임을 알 수 있었다.

• Journal of Power Electronics
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• 제13권3호
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• pp.419-428
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• 2013

The modular multilevel cascade converter (MMCC) is a new family of multilevel power converters with modular realization and a cascaded pattern for submodules. The MMCC family can be classified by basic configurations and submodule types. One member of this family, the Hexverter, is configured as Double-Delta Full-Bridge (DDFB). It is a novel multilevel AC/AC converter with direct power conversion and comparatively fewer required components. It is appropriate for connecting two three-phase systems with different frequencies and driving an AC motor directly from a utility grid. This paper presents the dq model of a Hexverter with both of its AC systems by state-space representation, which then simplifies the continuous time-varying model into a periodic discrete time-invariant one. Then a generalized multivariable optimal control strategy for regulating the Hexverter's independent currents is developed. The resulting control structure can be adapted to other MMCCs and is flexible enough to include other control criterion while guaranteeing the original controller performance. The modeling method and control design are verified by simulation results.

• Transactions on Electrical and Electronic Materials
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• 제9권5호
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• pp.181-185
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• 2008

Using the extensional vibration mode of PZT ring, a piezopump is successfully made. The PZT ring is polarized with thickness direction. The traveling extensional wave along the circumference of the ring is obtained by dividing two standing waves which are temporally and spatially phase shifted by 90 degrees from each other. The proposed piezopump is consisted of coaxial cylindrical shells that are bonded piezoelectric ceramic ring. The pump takes an unobtrusive operation into the simple displacing mechanism using peristaltic traveling waves without the physical moving parts. The finite elements analysis on the proposed pump model is carried out to verify its operation principle and design by the commercial FEM software. Components of piezopump were made, assembled, and tested to validate the concepts of the proposed pump and confirm the simulation results. The performance of the proposed piezopump is about 580 ${\mu}l/min$ in flow rate with the highest pressure level of 0.85 kPa, when the driving voltage is 150 $V_p$, 57 kHz.

• 전력전자학회논문지
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• 제24권2호
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• pp.71-77
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• 2019

This study proposes a circulating current reduction method that uses high-frequency voltage compensation when carrier phase difference occurs between two inverters in MSIS. In MSIS, inverters are configured in parallel to increase power capacity and to increase efficiency by using inverters only as needed. However, in the parallel inverter structure, circulating current is inevitably generated. Circulating current increases the stress on the switch, adversely affects the current control performance, and renders load sharing difficult. The proposed method compensates for the output voltage reference of the slave module by using the high-frequency voltage so that the switching pattern of each module is matched even in asynchronous carriers. The validity of the proposed method is verified by simulations and experiments with 600 W IPMSM.

• 국제물리치료학회지
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• 제12권2호
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• pp.2365-2369
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• 2021

Background: Patients with dysphagia after stroke are treated with neuromuscular electrical stimulation (NMES), but its effect on masseter muscle thickness and bite force in the oral phase is not well known. Objectives: To investigated the effect of NMES on masseter muscle thickness and occlusal force in patients with dysphagia after stroke. Design: Two group, pre-post design. Methods: In this study, 25 patients with dysphagia after stroke were recruited and allocated to either the experimental or the control groups. Patients in the experimental group were treated with NMES to the masseter muscle at the motor level for 30 minutes and were additionally treated with traditional swallowing rehabilitation for 30 minutes. In contrast, patients in the control group were only treated with traditional swallowing rehabilitation for 30 minutes. Masseter muscle thickness was measured using ultrasonography before and after intervention, and bite force was measured using an bite force meter. Results: The experimental group showed significant improvement in masseter muscle thickness and bite force compared to the control group. Conclusion: NMES combined with traditional dysphagia rehabilitation is effective in improving masseter muscle thickness and bite force in patients with dysphagia after stroke.