• Current Optics and Photonics
• /
• v.3 no.4
• /
• pp.298-303
• /
• 2019

We propose a photonic quasi-crystal fiber (PQF) for supporting up to 14 orbital angular momentum (OAM) modes with low and ultra-flat dispersion characteristics over the C+L bands. The designed PQF which consists of a large hollow center and quasi structural small air holes in the clad region exhibits low confinement losses and a large effective index separation (>$10^{-4}$) between the vector modes. This proposed fiber could potentially be exploited for mode division multiplexing and other OAM mode applications in fibers.

• Korean Journal of Mathematics
• /
• v.29 no.3
• /
• pp.631-638
• /
• 2021

In this paper, some sharp inequalities for ordinary derivative P'(z) and polar derivative D_αP(z) = nP(z) + (α - z)P'(z) are obtained by including some of the coefficients and modulus of each individual zero of a polynomial P(z) of degree n not vanishing in the region |z| > k, k ≥ 1. Our results also improve the bounds of Turán's and Aziz's inequalities.

• 제어로봇시스템학회:학술대회논문집
• /
• 1997.10a
• /
• pp.195-198
• /
• 1997

This paper proposes the effective compensation method of the rotor time constant of induction motor. An indirect vector control method is highly dependent on the motor parameters. To solve the problem of performance degradation due to parameter variation in an indirect vector control of induction motor, we compensate the rotor time constant by current error feedback. The proposed method is a simple on-line rotor time constant compensation method using the information from terminal voltages and currents. As the current error, difference between current command and estimated current, approaches to zero, the value of rotor time constant in an indirect vector controller follows the real value of induction motor. This scheme is valid transient region as well as steady state region regardless of low or high speed. This method is verified by computer simulation. For this, we constructed the simulation model of induction motor, indirect vector controller and current regulated PWM (CRPWM) voltage source inverter (VSI) using SIMULINK in MATLAB.

• Journal of Industrial Technology
• /
• v.21 no.B
• /
• pp.59-66
• /
• 2001

In this paper, a novel overmodulation strategy for PWM inverters to extend linearity region is presented. The proposed strategy uses the concept of space-vector PWM(SVPWM) based on the zero sequence signal(offset voltage) injection principle. So, by modifying the pole voltage simply, the linear control of inverter output voltage over the whole overmodulation range can be achieved easily. The proposed strategy is so simple that its practical implementation is easy. The validity of the proposed strategy is confirmed by the experimental results.

• Proceedings of the IEEK Conference
• /
• 1998.10a
• /
• pp.35-38
• /
• 1998

In this paper we fabricated QMSAs for 850MHz band on the teflon substrate with $\varepsilon_1-2.6, $ $t=1.6mm(\pm0.08)(CGP-500).$ We measured the resonant frequency and the return loss with cutting the gap region between radiation patch and ground plate by a 5mm length step by step. As a result we found that the measured data was not so bad unlike other papers when the gap region was closer to zero, especially under 10mm.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.315-318
• /
• 1995

In this paper, an optimal trunk trajectory for stable walking of biped robots is expressed as a simple differential equation, which is then solved by numerical methods. We used ZMP (Zero Moment Point), the virtual total ground reaction point within the region of the supporting food, as the criterion of stability of biped robot walking. If the ZMP is located outside of the stable region in dynamic walking, biped robots fall down. The biped robot considered in this paper consists of two legs and a trunk. The trajectories of the two legs and the ZMP of the biped robot are determined such that they are similar ti those of a human. Based upon those trajectories, the trunk trajectory is solved by numerically integrating differential dynamic equations. Leg motions are controlled by the computed torque control method. The effectiveness of control algorithm as well as the trajectories is confirmed by computer simulations.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.25 no.12
• /
• pp.82-87
• /
• 2011

In this paper, a sensorless speed control system is designed for the next generation high speed railway at zero and low speed region. The applied vector control scheme is a maximum torque per ampere(MTPA) method to utilize reluctance torque of IPMSM. The designed sensorless control scheme is a rotating high frequency voltage signal injection method. To verify the designed system, a simulator for the vector controller and sensorless controller is implemented using Matlab/simulink.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.52 no.11
• /
• pp.496-500
• /
• 2003

A low-cost, large area, random, maskless texturing scheme independent of crystal orientation is expected to significantly impact terrestrial photovoltaic technology. We investigated silicon surface microstructures formed by reactive ion etching (RIE) in Multi-Hollow cathode system. Desirable texturing effect has been achieved when radio-frequency (rf) power of about 20 Watt per one hollow cathode glow is applied for our RF Multi-Hollow cathode system. The black silicon etched surface shows almost zero reflectance in the visible region as well as in near IR region. The etched silicon surface is covered by columnar microstructures with diameters from 50 to 100 nm and depth of about 500 nm. We have successfully achieved 11.7% efficiency of mono-crystalline silicon solar cell and 10.2% multi-crystalline silicon solar cell.

• Proceedings of the KIEE Conference
• /
• 1999.07f
• /
• pp.2487-2489
• /
• 1999

This paper proposes a wide speed range sensorless vector control strategy. At low speed region, the difference of high frequency impedances is used in order to estimate the rotor flux angle. At high speed region this algorithm is combined with the adaptive observer. It enables the stable operation even at zero speed under the rated load condition This is verified by experimental results.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.34D no.11
• /
• pp.30-36
• /
• 1997

AlGaAs/GaAs HBTs are developed well enough to be commercialized as an active device in optical transmission system, but there remains the unanswered questions about reliability. In this paper we applied the reverse constant current stress at the high voltage in avalanche region for a long time to find out a new degradation mechanism of junctrion I-V. The unction off-set voltage at which the current vanishes to zero was shifted to the negative direction of applied bias due to the increment of leakage current as the stress time increases. It was identified that the degradation was induced by the hot carriers which were generated at space charge region and trapped at the interface between GaAs base and the passivation nitride enhancing the electric field across the nesa edge.