• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2008년 영문 학술대회
• /
• pp.602-605
• /
• 2008

The anode sheath structure in the hollow anode of an anode-layer type Hall thruster was numerically computed using a fully kinetic 2D3V Particle-in-Cell and Direct Simulation Monte Carlo(PIC-DSMC) code. By treating both ions and electrons as particles, anode surface region, which is electrically non-neutral, was analyzed. In order to analyze in detail, the calculation code was parallelized using Message Passing Interface (MPI). The code successfully simulated the discharge current oscillation. In the low magnetic induction case, ion sheath appears in the anode surface because ionization is enough to maintain the plasma occurs in the anode hollow. As the magnetic induction increases, main ionization region move to outside of the anode. At the same time, anode sheath voltage decreases. In the high magnetic induction case, electron sheath appears on the anode surface periodically because the ionization occurs mainly in the discharge channel. This anode sheath condition shift can be explained using the simple sheath model.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2019년도 전력전자학술대회
• /
• pp.186-188
• /
• 2019

현재 신재생에너지 발전원은 계속 증가되고 있으며, 발전기의 용량 또한 점점 증가하고 있다. 늘어나는 신재생에너지 발전원에 의해 계통 연계의 중요성이 증대되고 있고 아울러 계통에서 발생할 수 있는 여러 가지 사고로 인한 발전기의 PCS의 고장에 대한 문제 또한 중요해지고 있다. 본 논문에서는 신재생발전원의 용량이 증가함에 따라서 각 스위치의 전기적 스트레스를 줄일 수 있는 3-level NPC 타입의 컨버터회로를 기반으로 이중 전류 제어기를 이용하였고, 계통 사고시에도 강인한 위상 추종 특성을 가지는 DDSRF(Decoupled Double Synchronous Reference Frame 이하 DDSRF)방식의 PPL을 채택하여 시뮬레이션을 진행하였다. 현재 계통의 사고에 의한 사고전압은 ABC 분류에 의해서 크게 A~G 타입으로 나타내고 있다. 본 논문에서는 각 타입별 사고전압의 불평형 지수(Imbalance Factor, 이하 IF)에 따른 중성점 전류의 고조파 성분을 분석하여 도식화 하고자 한다. 이는 계통사고 발생 시 계통연계형 컨버터의 제어 및 계통탈락 여부에 활용 할 수 있을 것으로 예상된다.

• 대한약학회:학술대회논문집
• /
• 대한약학회 2003년도 Proceedings of the Convention of the Pharmaceutical Society of Korea Vol.1
• /
• pp.293.1-293.1
• /
• 2003

Electroosmotic flux during iontophoresis originates due to the net negative charge of the current passing channels (pores) in skin at physiological pH (pH 7.4). Thus, the channels are permselective to cations, and this causes the convective solvent flow from anode to cathodal direction. This solvent flow facilitates the flux of cations (from anode), inhibits that of anions (from cathode), and enables theenhanced transport of neutral, polar solutes. (omitted)

• 대한약학회:학술대회논문집
• /
• 대한약학회 2003년도 Proceedings of the Convention of the Pharmaceutical Society of Korea Vol.2-2
• /
• pp.233.3-234
• /
• 2003

Electroosmotic flux during iontophoresis originates due to the net negative charge of the current passing channel (pores) in skin at physiological pH (pH 7.4). Thus, the channel is permselective to cations, and this causes the convective solvent flow, from anode to cathode direction. This solvent flow facilitates the flux of cations (from anode), inhibits that of anions (from cathode), and enables the enhanced transport of neutral, polar solutes. In this work, we have investigated the effect of a series of polyethylene glycols (PEGs) with different molecular weights on the electroosmtic flow to get more detail understanding of this phenomena. (omitted)

• 한국수소및신에너지학회논문집
• /
• 제34권6호
• /
• pp.562-574
• /
• 2023

Carbon neutrality has been suggested to overcome the global climate crisis caused by global climate change. Hydrogen energy is a major way to achieve carbon neutrality, and the developments and policies of hydrogen technology have been proposed to achieve this goal. To commercialize hydrogen energy resources, it is necessary to understand the overall value chain composed of hydrogen production, storage, and utilization and to present the direction of technological developments. In this paper the hydrogen strategies of major countries, including Europe, the United States, Japan, China, and South Korea will be analyzed, and hydrogen technologies by value chain will also be explain. This paper will contribute to understanding the overall hydrogen policy and technology, as both policy and technology are summarized.

• 공업화학
• /
• 제9권5호
• /
• pp.734-741
• /
• 1998

본 연구에서는 전극전위 분석법을 사용하여 중성운반체로 dibenzo-18-crown-6(D18Cr6)와 valinomycin(Val)을 이용하여 $K^+$ 이온선택성 PVC막 전극의 막과 용액계면에서의 전극특성을 검토하였다. PVC막에서 감응물질(운반체)에 기본전해질의 혼입 (doping)여부, 감응물질의 종류와 함량, 가소제, 막두께 및 이온의 활동도변화에 따른 전극의 기울기, 선형응답범위 한계측정농도 및 방해이온에 따른 선택계수 등 전극특성을 검토하였다. 중성운반체로 D18Cr6, Val을 $K^+$ 이온으로 착체형성하여 사용하였고, 가소제로 dibutylphthalate(DBP), dioctyl sebacate(DOS) 및 dibutyl sebacate(DBS)를, 혼입제인 기본전해질로 potassium tetraphenylborate (KTPB) 및 용매로 THF를 지지체로 PVC를 이용하여 막을 제조하였다. 운반체의 최적 함량은 D18Cr6와 Val의 경우 3.23 wt %이었고, 가소제는 DBP가 가장 적절한 가소제이었다. 막두께에 대한 영향은 최적 막두께 이상에서는 막두께가 얇아질수록 전극특성이 좋아졌으나, 막두께가 이 이하로 얇아지면 운반체의 용출, 막의 강도 등이 작용하여 전극특성이 나빠짐을 알 수 있었다. D18Cr6의 경우 $K^+$ 이온에 대한 혼합용액법에 의한 선택계수 서열은 다음과 같았다: $NH_4{^+}>Ca^{2+}>Mg^{2+}>Na^+$.

• 전기학회논문지
• /
• 제67권2호
• /
• pp.233-238
• /
• 2018

This paper proposes a seamless MPPT operation mode transfer method of photovoltaic system. The photovoltaic system consists of a DC-DC boost converter, a DC-Link, and a 3-level neutral point clamp (NPC) type inverter. The PV voltage fluctuates due to the output characteristics of the solar pane1 depending on the irradiation amount and the temperature. The photovoltaic system requires seamless MPPT mode transfer method that the discontinuity does not occur in order to supply the stable power to system without affecting the fluctuation of the PV voltage. MPPT operation is divided into two modes by the voltage reference. Under the condition that the PV voltage is below 650V, the DC-DC boost converter performs MPPT through duty control based on perturb & observe (P&O) method, and the inverter conducts DC-link voltage and grid current controls in synchronous reference frame. On the other hand, when the PV voltage exceeds above 650V, inverter performs MPPT in accordance with the variation of DC-link voltage control while the converter stops operating. Two MPPT operation modes is smoothly transferred through the proposed method that DC-link voltage or grid current commands are appropriately adjusted from the certain criteria. The feasibility of the MPPT operation mode transfer method is verified using a 10kW solar photovoltaic system, experimental results have good performances that the fluctuation of PV current is reduced to 100%.

• 전기학회논문지P
• /
• 제58권4호
• /
• pp.391-396
• /
• 2009

In this paper, a control algorithm for DC-Link voltage unbalancing compensation of a four-switch inverter for a three-phase BLDC motor drive is proposed. Compared with a conventional six-switch inverter, the split source of the four-switch inverter can be obtained by splitting DC-link capacitor into two capacitors to drive the three phase BLDC motor. The voltages across each of two capacitors are not always equal in steady state because of the unbalance in the impedance of the DC-link capacitors $C_1$ and $C_2$ or the variable current flowed into the capacitor's neutral point in motor control. Despite the unbalance, if the BLDC motor may be run for a long time the voltage across one of the capacitors is more increased. So the unbalance in the capacitors voltages will be accelerated. As a result, The current ripple and torque ripple is increased due to the fluctuation of input current which flows into 3-phase BLDC motor. According to that, the vibration of motor will be increased and the whole system will be instable. This paper presents a control algorithm for DC-Link voltage unbalancing compensation. The sampling from the voltages across each of two capacitors is used to perform the voltage control of DC-Link by using the feedforward controller.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2004년도 전력전자학술대회 논문집(1)
• /
• pp.77-81
• /
• 2004

In this paper a novel line interactive UPS (Uninterruptible Power Supply) using the two 4-leg VSCs and AC line reactor is proposed. The 4-leg Voltage Source Converter(VSC) can use the DC link voltage effectively by the 3-D SVPWM method. Hence the DC battery voltage can be reduced by $15\%$ in comparison to that of the conventional line-interactive UPS system. One VSC is in parallel with the AC line reactor of the power source side, and the other is in series with the load. The parallel 4-leg voltage source inverter controls three-phase line voltage independently in order to control the line reactor current indirectly. It eliminates the neutral line current and the active ripple power of the source side using the pqr theory so that unity power factor and the sinusoidal source current can be achieved even though both the source and the load voltages have zero sequence components. The series 4-leg voltage source inverter compensates the line voltage and allows the load voltage to be balanced and harmonic-free. Both of parallel and series 4-leg voltage source inverters always act as independently controllable voltage sources, so that three-phase output voltage shows a seamless transition to the backup mode. The feasibility of the proposed UPS system has been investigated and verified through computer simulation results.

• 전력전자학회논문지
• /
• 제20권1호
• /
• pp.1-10
• /
• 2015

This paper proposes a control algorithm for permanent magnet synchronous generators with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage off-shore wind power system under unbalanced grid conditions. Specifically, the proposed control algorithm compensates for unbalanced grid voltage at the PCC (Point of Common Coupling) in a collector bus of an off-shore wind power system. This control algorithm has been formulated based on symmetrical components in positive and negative synchronous rotating reference frames under generalized unbalanced operating conditions. Instantaneous active and reactive power is described in terms of symmetrical components of measured grid input voltages and currents. Negative sequential component of AC input current is injected into the PCC in the proposed control strategy. The amplitude of negative sequential component is calculated to minimize the negative sequential component of grid voltage under the limitation of current capability in a voltage source converter. The proposed control algorithm enables the provision of balanced voltage at the PCC resulting in the high quality generated power from off-shore wind power systems under unbalanced network conditions.