• Journal of Power Electronics
• /
• v.17 no.1
• /
• pp.282-293
• /
• 2017

There exists a strong coupling between real and reactive power owing to the complex impedances in droop based islanded microgrids (MGs). The existing virtual impedance methods consider improvements of the impedance matching for sharing of the voltage controlled power (VCP) (reactive power for Q-V droop, and real power for P-V droop), which yields a 1-DOF (degree of freedom) tunable virtual impedance. However, a weak impedance matching for sharing of the frequency controlled power (FCP) (real power for $P-{\omega}$ droop, and reactive power for $Q-{\omega}$ droop) may result in FCP overshoots and even oscillations during load transients. This in turn results in VCP oscillations due to the strong coupling. In this paper, a 2-DOF tunable adaptive virtual impedance method considering impedance matching for both real and reactive power (IM-PQ) is proposed to improve the power sharing performance of MGs. The dynamic response is promoted by suppressing the coupled power oscillations and power overshoots while realizing accurate power sharing. In addition, the proposed power sharing controller has a better parametric adaptability. The stability and dynamic performances are analyzed with a small-signal state-space model. Simulation and experimental results are presented to investigate the validity of the proposed scheme.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.34D no.11
• /
• pp.76-82
• /
• 1997

The characteristics of optical waeguides and IDT electrodes fabricated for acousto-optic tunable filters (AOTE) used for optical communications were analyzed. A $Ti:LiNbO_3$ in-diffusion method was employed for the formation of the optical waveguide with a dimension of width $8\mu\textrm{m}$, length $30000\mu\textrm{m}$, and thickness $1150{\AA}$. The diffusion was carried at $1050^{\circ}C$ for 8 houss to pattern the optical waveguide with Ti. The resulted waveguide exhibited a single mode at a 1550nm wavelength range and its propagation loss was less than 0.5dB/cm. The width of IDT, with 10 SAW periods, was $5000\mu\textrm{m}$, S11 reflection characteristics and impedances of th eelectrodes deposited with Au were analyzed using a network analyzer; $48.1\Omega$ at th ecenter frquency of 193MHz for Au deposition thickness of $1500{\AA}$ and $50.7\Omega$ at the center frequency of 192MHz for au deposition thickness of $1600{\AA}$.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.8 no.4
• /
• pp.25-30
• /
• 1971

Fabrication and measurements of the magnetically tunable YIG band pass or stop filter at X-band are discussed. Using two YIG spheres located at the region of r-f circularly polarized magnetic field between the strip lines, the pass or stop characteristics of the filter are obtained. In the case of band stop, the output level is typically 25db lower than the input power. Contrarily for the pass band, the pass band level is 22db higher than the stop frequency region. The experimental results are in good agreement with the theoretical values of FMR. Further it is shown that the structure can be used for a directional coupler.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.39 no.1
• /
• pp.58-66
• /
• 2002

Acousto-optical wavelength tunable optical filters in LiNbO$_3$ have been demonstrated using taperd directional weighted coupling acoustic waveguides and Ti double diffusion technique. Conversion efficiency in excess of 61%, 86% and sidelobe intensity of -14.29㏈, -14.99㏈ were measured at a wavelength of 1551.1nm RF frequency of 173.58MHz and RF power of 35㎽ for both TE and TM input polarizations, respectivelv. A spectral width of ~l.8nm and linear tuning late of 8.6nm/MHz were demonstrated. A 2.82$mutextrm{s}$ switching time has been measured. With two channels with 2.5nmseparation, channel cross-talk was lower than -l4㏈ for single wavelength filtering due to sidelobe.

• Journal of the Korean Institute of Telematics and Electronics C
• /
• v.35C no.11
• /
• pp.57-62
• /
• 1998

In this paper, tunable transconductor shows good linearity over a wide input voltage range are proposed. The proposed transconductor employ operating in the nonsaturation(ie., linear) region to improve circuit simplicity and tunability and 6.8V$\_$p-p/ wide input range. Also the circuit employ source-coupled differential pair to provide true differential input and can achieve both positive and negative transconductance values. The proposed circuits are implemented using a 1.2 $\mu\textrm{m}$ single poly double metal n-well CMOS technology. The THD characteristic of proposed circuit is less than 1% for a differential input voltage of up to 6V$\^$p-p/ when supply bias condition is V$\_$DD/=-V$\_$ss/=5V, I$\_$B/=20, 40${\mu}$A, and frequency of input signal is 1KHz.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.46 no.3
• /
• pp.31-35
• /
• 2009

In this paper, tunable 4th order SC(switched capacitor) bandpass ${\sigma}-{\Delta}$(Sigma-Delta) modulator with advanced architecture that can adjust the IF by two coefficient values is proposed for data conversion in the wireless communication. Its architecture can optionally adjust all the 4th order noise transfer function in comparison with the conventional architecture. In order to adjust the IF, the conventional architecture needs the four variable coefficients values, basic clocks and eight clocks. On the other hand, the proposed architecture can adjust the IF by two variable coefficient values and basic clocks only.

• Progress in Superconductivity
• /
• v.1 no.1
• /
• pp.36-41
• /
• 1999

Methods for mode identification and accurate measurements of the unloaded Q ($Q_0$) of a dielectric-loaded $TE_{01{\delta}}$ mode cavity resonator with HTS endplates are proposed. A resonator with a sapphire rod and $YBa_2Cu_3O_{7-x}$(YBCO) endplates was prepared and its microwave properties were studied at temperatures above 30 K. The $TE_{01{\delta}}$ mode $Q_0$ of the resonator, designed to work as a tunable resonator with variations in the gap distance (s) between the sapphire rod and the top YBCO, was more than 1000000 at s = 0 mm and at 30 K with the resonant frequency of 19.56 GHz. The $TE_{01{\delta}}$ mode $Q_0$ decreases as s increases for s < 2 mm until mode couplings between the $TE_{01{\delta}}$ mode and other modes appeared at s = 2 mm. Significant dependence of the $TE_{01{\delta}}$ mode $Q_0$ on the input and output coupling constants was also observed. Applications of the open-ended $TE_{01{\delta}}$ mode cavity resonator for a tunable resonator with a very high Q as well as a characterization tool for the surface resistance measurements of HTS films are described.

• Journal of electromagnetic engineering and science
• /
• v.4 no.2
• /
• pp.87-92
• /
• 2004

A millimeter-wave distributed frequency doubler has been designed with distributed block and frequency tunable output reflectors. The simulated conversion loss of 9.5 ㏈ to 7.7 ㏈ from 54.6 ㎓ to 62.4 ㎓ output frequencies is achieved with fundamental and third harmonic signal rejections of more than 10 ㏈c. The fabricated chip has the size of 1.2 mm${\times}$1.0 mm. Some measured results of frequency and bias dependent characteristics are presented for the fabricated PHEMT MMIC frequency doubler. The designed doubler has two transistors, and if one of the transistors fails the doubler unit still operates with reduced gain. The failure effect of the PHEMT has been simulated, and compared to the measured data of which one PHEMT is not operating properly.

• Journal of IKEEE
• /
• v.15 no.1
• /
• pp.57-63
• /
• 2011

This paper presents a tunable band pass filter (BPF) for multi bio-signal detection. The bandwidth can be controlled by the bias current of transconductance (gm), while conventional BPF exploited switchable capacitor array for band selection. With this design technique, the die area of proposed BPF reduced to at least one tenth the area of conventional design. The simulation results show the high cut-off frequency tuning range of from 100Hz to 1Khz. The circuit was implemented with a 0.18um CMOS standard technology. Total current consumption is 1uA at the supply voltage of 1V with sub-threshold design technique.

• Korean Journal of Optics and Photonics
• /
• v.15 no.1
• /
• pp.1-5
• /
• 2004

Tunable diode laser absorption spectroscopy was performed for analysis of the H$_2$$^{18}$ O/H$_2$$^{16}$ O isotope ratio of a water sample which was enriched by the membrane distillation method. In order to improve the signal-to-noise ratio, the wavelength modulation spectroscopic method was used with a lock-in amplifier. The fringe noise could be suppressed by using the FFT (Fast Fourier Transform) lowpass filter and the optimization of the modulation depth of the laser frequency. The maximum deviation of $\delta$-value was measured to be$\pm$4$\textperthousand$.