Jin-Wan Jung

Crystalline mesoporous molecular sieves have long been sought as solid acid catalysts for organic reactions involving large molecules. We synthesized a series of mesoporous molecular sieves that possess crystalline microporous walls with zeolitelike frameworks, extending the application of zeolites to the mesoporous range of 2 to 50 nanometers. Hexagonally ordered or disordered mesopores are generated by surfactant aggregates, whereas multiple cationic moieties in the surfactant head groups dire

In a high-speed operation of a vector-controlled induction motor, coupling between d-q current dynamics impairs the characteristics of torque response. The feedforward decoupling scheme does not perform well if an error exists in the motor parameter estimation. We derive a dynamic decoupling condition when the two additional proportional integral current controllers are used. A great advantage of this dynamic decoupling controller is the robustness to the motor parameter estimation errors. Furth

The authors propose a new power converter control scheme for a converter-inverter system. The strategy is to fully utilize the inverter dynamics in controlling the converter dynamics. The authors obtain the power dynamics for both converter and inverter systems, and control the converter power so that it matches the required inverter power exactly. Then, in the ideal case, no power flows through the DC-link capacitors and, thus, the DC-link voltage does not fluctuate even though a very small amo

This paper addresses a control method of reducing the size of the DC-link capacitors of a converter-inverter system. The main idea is to utilize the inverter operation status in the current control of the converter. Specifically, the information on the load power is incorporated in synthesizing the converter current control input so that a proper DC voltage level is maintained. We describe the dynamics of load current and apply feedback linearization theory to obtain an input output linearized s

Multiammonium surfactants exhibited a remarkable capping effect for zeolite synthesis in the forms of nanoparticles, nanorods, and nanosponges in cases where common monovalent surfactants failed. A nanorod-shaped mordenite zeolite synthesized in this manner showed significantly enhanced catalytic lifetimes in acid-catalyzed cumene synthesis reactions.

Zeolite MFI nanosheets have been hydrothermally synthesized using a surfactant with the formula [C18H37–N+(CH3)2–C6H12–N+(CH3)2–C6H12–N+(CH3)2–C18H37][Br−]3 as the zeolite structure-directing agent. These nanosheets correspond to a slice of MFI zeolite crystal of 1.5 nm thickness in the b-direction. Each nanosheet is composed of a monolayer of micropores, which is thinner than a single crystal unit-cell dimension (2.0 nm). Such a single-pore zeolite nanosheet still exhibits high thermal stabilit

Electric vehicle (EV) motors are characterized by their low inductance and high current density, so that they run at high speed and produce a high starting torque. Due to the low inductance coil design, the current ripple caused by pulsewidth modulation (PWM) switching makes a significant amount of eddy-current loss and hysteresis loss, especially in high-speed operation. If one simply neglects the iron loss, the overall vector controller is detuned, resulting in an error in the torque control.

In the high-speed operation of a vector controlled induction motor, decoupling current control is a very important problem. However, the conventional decoupling scheme does not perform well when there are mismatches in the motor parameters. The authors propose a PI type decoupling current controller. A great advantage of this PI type decoupling controller is its robustness to motor parameter errors. Hence, the proposed scheme appears suitable for practical applications where the exact parameters

Internet of things (IoT) technologies have been widely used in various applications, especially in industrial field, which often require energy efficiency, high reliability, and low delay. Recently, Time Slotted Channel Hopping (TSCH) that operates based on TDMA with channel hopping has been standardized to achieve such multiple goals. Based on TSCH protocol, the nodes are scheduled at slots by scheduling algorithm, where there is a trade-off between energy efficiency and contention among the se

<div class="htmlview paragraph">Fuel cell is one of alternative power sources, which can replace the conventional internal combustion engine. But, it has some drawbacks such as low efficiency at high power output and inability of energy regeneration. So, hybridization of the fuel cell has been proposed to overcome these drawbacks. And the fuel cell hybrid system is preferred in a viewpoint of cost and performance.</div> <div class="htmlview paragraph">HMC's fuel cell hybrid sys

This paper presents GateScatter, the first backscatter-based gateway connecting commodity IoT to WiFi. The backscatter design of GateScatter is an economic option towards pervasive Internet connectivity for ever-growing IoT. The carefully designed tag optimally reshapes ZigBee IoT packets with an arbitrary payload into an 802.11b WiFi packet over the air, such that the payload can be reliably retrieved at the WiFi receiver (hence a gateway). Gate-Scatter is highly compatible - it works with a wi

In the case of GTO inverter, the conventional dead-time compensation methods do not work well, since the terminal voltage of a leg is not constant during the dead-time due to the presence of the snubber circuit. We propose a dead-time compensation method that regulates the voltage error caused by the dead-time. The terminal voltage of each leg is measured by a voltage sensor during the dead-time and its time-average is used for calculating the actual terminal voltage. We obtain an error by subtr

In the case of voltage-source gate-turn-off thyristor (GTO) inverters, the conventional dead-time compensation methods do not work well, since the terminal voltage of an inverter leg is not constant during the dead-time period, due to the presence of the snubber circuit. We propose a closed-loop dead-time compensation method that regulates the voltage error by a proportional-integral (PI)-type compensator. We show its superior performance by the reduction in current ripple and in the sixth harmo