• Journal of Power Electronics
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• v.17 no.2
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• pp.551-560
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• 2017

The present study proposes an angle droop controller for converter interfaced (dispatchable) distributed generation (DG) resources in the islanded mode of operation. Due to the necessity of proper real and reactive power sharing between different types of resources in microgrids and the ability of systems to respond properly to abnormal conditions (sudden load changes, load uncertainty, load current disturbances, transient conditions, etc.), it is necessary to produce appropriate references for all of the mentioned above conditions. The proposed control strategy utilizes a current controller in addition to an angle droop controller in the discrete time domain to generate appropriate responses under transient conditions. Furthermore, to reduce the harmonics caused by switching at converters' output, a LCL filter is used. In addition, a comparison is done on the effects that LCL filters and L filters have on the performance of DG units. The performance of the proposed control strategy is demonstrated for multi islanded grids with various types of loads and conditions through simulation studies in the DigSilent Power Factory software environment.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.4
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• pp.313-320
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• 2003

This paper deals with the optimal design of a elevator inverter system based on the customized IPM. The proposed method reduces dv/dt and di/dt, which resulted in the minimized conducted EMI noise without an additional circuitry. It only optimizes the value of gate resistor in the IGBT embedded in the IPM. In order to optimize the customized IPM to a elevator system, we simulated and measured the spike voltage and the motor surge voltage including the temperature variation due to the switching losses at the IPM case and heat-sink. As a result, thanks to the optimized value of the gate resister in the IPM, the conducted EMI noise is reduced approx. 5∼10 [dB$\mu$V] in a particular frequency domain.

• Journal of Magnetics
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• v.15 no.3
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• pp.116-122
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• 2010

An accurate analytical equation for the total energy in the framework of the single domain model is used to study the thermal stability of nanostructured synthetic ferrimagnets. Elliptical cells are considered that have lateral dimensions of 160 nm (long axis)$\times$80 nm (short axis) and varying values of thickness asymmetry for the two magnetic layers. The direction of the applied magnetic field, which points to the $45^{\circ}$ direction, is in the opposite direction to the thicker layer magnetization. A significant difference is observed in the applied magnetic field dependencies of the equilibrium magnetic configuration and the magnetic energy barrier when using the simplifying assumption that the self-demagnetizing field is identical in magnitude to the dipole field. At a small thickness asymmetry of 0.2 nm, for example, the magnetic energy barrier is reduced from 68 kT (T=300 K) to 6 kT at the remanent state and a progressive switching behavior changes into a critical behavior, as the simplifying assumption is used. The present results clearly demonstrate the need for an accurate analytical equation for the total energy in predicting the thermal stability of nanostructured synthetic ferrimagnets.

• Journal of the Microelectronics and Packaging Society
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• v.20 no.4
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• pp.69-74
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• 2013

In this paper, the impact of integrating large number of I/O (Input-Output) and Core power Delivery Network (PDN) on a 6 layers Flip-Chip Ball Grid Array (FCBGA) package is investigated. The impact of core induced supply noise on high-speed I/O interfaces, and high-speed I/O interface's supply noise coupling to adjacent high-speed I/O interfaces' jitter impact are studied. Concurrent stress validation software is used to induce SSO noise on each individual I/O interfaces; and at the same time; periodic noise is introduced from Core PDN into the I/O PDN domain. In order to have the maximum coupling impact, a prototype package is designed to merge the I/O and Core PDN as one while impact on jitter on each I/O interfaces are investigated. In order to understand the impact of the Core to I/O and I/O to I/O noise, the on-die noise measurements were measured and results were compared with the original PDN where each I/O and Core PDN are standalone and isolated are used as a benchmark.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.6
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• pp.72-80
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• 1998

A method is proposed for directional vector quantization using the wavelet packets. After partitioning the wavelet packet coefficients into 9 edges according to the corresponding directions, it encodes and transmits locally dominant edges. The directions of the edges are encoded with a variable length coding and conditional switching of codebooks, while the contents of them with the vector quantization followed by the variable length index coding. The proposed algorithm is superior to various conventional image coding algorithms in the sense of PSNR, which is relatively more significant at very low bit rate such as 0.1~0.3 bpp. As the proposed algorithm preserves the edges which is the most important for the human visual system, it also provides the reconstructed images of good subjective quality even at very low bit rate.

• Journal of the Korea Society of Computer and Information
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• v.8 no.4
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• pp.126-131
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• 2003

While the advantages of multicast delivery over multiple unicast deliveries is undeniable, the deployment of the IP multicast protocol has been limited to network domains under single administrative control. Deployment of inter-domain multicast delivery has been slow due to both technical and administrative reasons. For this reasons overlay multicasting technologies are recently proposed. We propose a End-Host Multicast Tree Protocol (EMTP) that searches two levels of the tree at a time until reaching to a leaf node and can select the nearest node that a new node try to join in the tree. Even if there is no available degree of the desirable node that a new node want to join, selecting the node as a potential parent by EMTP can reduce the number of tree switching with robustness of the tree and bring to ruduce the data delivery time.

• Journal of Power Electronics
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• v.18 no.3
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• pp.802-816
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• 2018

A digital direct phase-shift control (DDPSC) method based on the phase-shifted full-bridge LLC (PSFB-LLC) converter is presented. This work combines DDPSC with the conventional linear control to obtain a hybrid control strategy that has the advantages of linear control and DDPSC control. The strategy is easy to realize and has good dynamic responses. The PSFB-LLC circuit structure is simple and works in the fixed frequency mode, which is beneficial to magnetic component design; it can realize the ZVS of the switch and the ZCS of the rectifier diode in a wide load range. In this work, the PSFB-LLC converter resonator is analyzed in detail, and the concrete realization scheme of the hybrid control strategy is provided by analyzing the state-plane trajectory and the time-domain model. Finally, a 3 kW prototype is developed, and the feasibility and effectiveness of the DDPSC controller and the hybrid strategy are verified by experimental results.

• Journal of Magnetics
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• v.8 no.1
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• pp.24-31
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• 2003

The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grunberg, the Giant Magneto Resistance by Fert and Grunberg and a large tunneling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunneling resistance, where a strong dependence of the tunneling current on an external magnetic field can be found. We will briefly address important basic properties of these junctions like thermal, magnetic and dielectric stability and discuss scaling issues down to junction sizes below 0.01 $\mu\textrm{m}$$^2$with respect to single domain behavior, switching properties and edge coupling effects. The second part will give an overview on applications beyond the use of the tunneling elements as storage cells in MRAMs. This concerns mainly field programmable logic circuits, where we demonstrate the clocked operation of a programmed AND gate. The second 'unconventional' feature is the use as sensing elements in DNA or protein biochips, where molecules marked magnetically with commercial beads can be detected via the dipole stray field in a highly sensitive and relatively simple way.

• The Journal of Information Technology
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• v.5 no.4
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• pp.155-164
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• 2002

MPLS is a integrated technology by using routing function and label swapping in the network layer. Based on the previous forwarding equivalence classes, it adds the fixed length label in ingress of the MPLS domain. For the routing, without the packet header information, it uses label for the forwarding decisions. In this paper, traffic engineering requirements in the MPLS internet will be setup. The traffic engineering function have to be performed previously with the network topology. In addition to, we presents the IP network topology and main function with MPLS signaling protocol.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.277-280
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• 2005

This paper dealt with the development of a surge protection device (SPD) that can protect high speed computer network devices from overvoltages caused by switching operations or lightning surges. The designed SPD is a form of hybrid circuit which is composed of a gas tube having large current diverting capability, high response bi-directional avalanche diodes, and fast recovery diodes to reduce insertion loss on high frequency domain. Surge protection and signal transmission characteristics of the fabricated SPD was tested according to the international standards, IEC 61000-4-5 and IEC 61643-21. From the test results, the SPD is satisfied with the international standards and the high cut-off frequency was 204MHz. Also, the SPD showed a good performance without an insertion loss on a field test of 100Mbps class Local Area Network