• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.22 no.2
• /
• pp.252-257
• /
• 2011

A compact microstrip dual-band bandpass filter with controllable bandwidth for each passband is proposed. Each passband is independently designed using two different dual-mode resonators. The proposed dual-band bandpass filter has three transmission zeros. Two transmission zeros are generated by each dual-mode resonator. An additional transmission zero is generated by input/output port coupling. The dual-band bandpass filter application is designed for 2.4/5.7 GHz WLAN. Experimental results are presented to validate theory.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.2
• /
• pp.390-396
• /
• 2010

An 80MHz surface acoustic wave (SAW)-based gyroscope utilizing a progressive wave was developed on a piezoelectric substrate. The developed sensor consists of two SAW oscillators in which one is used for sensing element and has metallic dots in the cavity between input and output IDTs. The other is used for a reference element. Coupling of mode (COM) modeling was conducted to determine the optimal device parameters prior to fabrication. According to the simulation results, the device was fabricated and then measured on a rate table. When the device was subjected to an angular rotation, oscillation frequency differences between the two oscillators were observed because of the Coriolis force acting on the metallic dots. Depending on the angular rate, the difference of the oscillation frequency was modulated. The obtained sensitivity was approximately 52.35 Hz/deg.s within the angular rate range of 0~1000 deg/s. The performances of devices with three IDT structures for two kinds of piezoelectric substrates were characterized. Good thermal stability was also observed during the evaluation process.

• Journal of Electrical Engineering and Technology
• /
• v.13 no.2
• /
• pp.711-721
• /
• 2018

This paper presents a single-phase asymmetric half-bridge cascaded multilevel inverter based series active power filter (SAPF) for harmonic voltage compensation. The effect of level number on performance of the proposed SAPF is examined in terms of total harmonic distortion (THD) and system efficiency. Besides, the relationship between the level number and the number of switching device are compared with the other multilevel inverter topologies used in APF applications. The paper is also aimed to demonstrate the capability of the SAPF for compensating harmonic voltages alone, without using a passive power filter (PPF). To obtain the required output voltage, a new switching algorithm is developed. The proposed SAPF with levels of 7, 15 and 31 is used in both simulation and experimental studies and the harmonic voltages of the load connected to the point of common coupling (PCC) is compensated under two different loading conditions. Furthermore, very high system efficiency values such as 98.74% and 96.84% are measured in the experimental studies and all THD values are brought into compliance with the IEEE-519 Standard. As a result, by increasing the level number of the inverter, lower THD values can be obtained even under high harmonic distortion levels while system efficiency almost remains the same.

• Journal of Power Electronics
• /
• v.16 no.3
• /
• pp.1152-1162
• /
• 2016

The unequal impedances of the interconnecting cables between paralleled inverters in the island mode of microgrids cause inaccurate reactive power sharing when the traditional droop control is used. Many studies in the literature adopt low speed communications between the inverters and the central control unit to overcome this problem. However, the losses of this communication link can be very detrimental to the performance of the controller. This paper proposes an improved reactive power-sharing control method. It employs infrequent measurements of the voltage at the point of common coupling (PCC) to estimate the output impedance between the inverters and the PCC and then readjust the voltage droop controller gains accordingly. The controller then reverts to being a traditional droop controller using the newly calculated gains. This increases the immunity of the controller against any losses in the communication links between the central control unit and the inverters. The capability of the proposed control method has been demonstrated by simulation and experimental results using a laboratory scale microgrid.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.20 no.6
• /
• pp.526-533
• /
• 2015

A new algorithm is proposed for the estimation of equivalent grid impedance at the point of common coupling of a grid-tie inverter output. The estimated impedance parameter can be used for the improvement of the performance and the stability of the distributed generation system. The estimation error is inevitable in the conventional estimation method because of the axis rotation due to PLL. In the conventional estimation error, the d-q voltage and current are used for the calculation of the impedance with active and reactive current injections. Conversely, in the proposed algorithm, the negative sequence current is injected, and then the negative sequence voltage is measured for the impedance estimation. As the positive and negative sequence current controller is independent and the PLL is based on the positive sequence component only, the estimation of the equivalent impedance can be achieved with high accuracy. Simulation and experimental results are compared to validate the proposed algorithm.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.22 no.5
• /
• pp.423-430
• /
• 2017

This paper proposes a control methodology for a high efficiency operation of an inductive power transfer (IPT) converter by combining full bridge (FB) and half bridge (HB) controls. To apply the proposed control to the IPT converter, the characteristics of each control method are analyzed. By examining the output voltages of the IPT converter and a theoretical loss analysis, the control shifting points between FB and HB controls are evaluated in accordance with the coupling coefficients and the load. Based on the control shifting points, the FB-HB control algorithm is implemented. By applying FB-HB control, high efficiency operation at the light load condition can be achieved.

• Bulletin of the Korean Chemical Society
• /
• v.26 no.1
• /
• pp.19-31
• /
• 2005

During the last decade, the exploration of nanoscale device and circuitry based on molecules has gained increasing interest. In parallel with this, considerable effort is being devoted to the development of molecular photonic/electronic materials based on various porphyrin arrays. This involves light as an input/output signal and excitation energy migration as a mechanism for signal transmission. Absorption of a photon at the light collector end of the porphyrin array yields the excited state, which migrates among the intervening pigments until reaching the emitter, whereupon another photon is emitted. As a consequence, it is relevant to understand the excitation energy transfer (EET) processes occurring in various forms of porphyrin arrays for the applications as artificial light harvesting arrays and molecular photonic/electronic wires. Since the excitonic (dipole) and electronic (conjugation) couplings between the adjacent porphyrin moieties in porphyrin arrays govern the EET processes, we have characterized the EET rates of various forms of multiporphyrin arrays (linear, cyclic, and box) based on various time-resolved spectroscopic measurements. We believe that our observations provide a platform for further development of molecular photonic/electronic materials based on porphyrin arrays.

• Journal of the Korean Solar Energy Society
• /
• v.23 no.3
• /
• pp.37-44
• /
• 2003

This paper presents the modeling and analysis of V47-660 kW wind turbine generation system(WTGS) in Jeju wind farm using Psim program. Generally, WTGS is composed of complicated machinery. So it is very difficult to present the mathematic model. This means that WTGS has a nonlinear system. Using the real output data from V47 WTGS for one year, it is simply possible to express the rotor and gear coupling system as a torque generator according to wind speed. Also, the modeling of electrical system can be able to present using the data sheet from the company. To analyze the proposed method, results of computer simulation using Psim program are presented to support the discussion.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.15 no.1
• /
• pp.110-118
• /
• 2004

In this paper, a method is presented for the design of an orthomode transducer(OMT) operating at 21/31GHz frequency bands. A square waveguide is used in the common port while the WR-34 standard rectangular waveguide is used in the straight port. The straight port is connected to the common port via a multi-stage quarter-wave impedance transformer. The side port is coupled to the common port through a slot formed along the center line of the common square waveguide. An impedance transformer is employed to match the impedance of the coupling slot with that of the WR-51 waveguide at the output of the side port. Dimensions of the OMT are iteratively optimized employing the theory of waveguide. The validity of the proposed method is verified by fabricating and testing the designed orthomode transducer.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.13 no.8
• /
• pp.783-789
• /
• 2002

In this paper, V-band MMIC coupled oscillator arrays are presented. In the proposed array, two push-pull patch antennas are synchronized by using strong electromagnetic coupling between two antennas. As a result, total size of the array is reduced and the array can be integrated in a single chip. To verify proposed array concept, two 1$\times$2 arrays are designed and fabricated using standard 0.15 um gate length pHEMT MMIC process. The circuits are mounted in an oversized waveguide and measured. The first array shows 0.5 dBm at 56.372 GHz and the second one has an output of 5.85 dBm at 60.147 GHz.