• Journal of Power System Engineering
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• v.2 no.2
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• pp.55-59
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• 1998

In practice, the property of nonlinearity is contained in all physical systems. In other word, all physical systems are nonlinear to some degree. Therefore it is important that we acquires a facility for analyzing feedback control systems with varying degrees of nonlinearity. To operate the system linearly over wide range of variation of signal amplitude and frequency, the system requires components of an extremely high quality. Such a system would probably be impractical in the view points of cost, space and weight. In this context of view, it is worth noting that the nonlinearities may be intentionally introduced into a system in order to compensate for the effects of other undesirable nonlinearities or to obtain better performance than what could be achieved using linear element only. A simple example of an intentional nonlinearity is the use of a nonlinear damped system to optimize response in accordance with the magnitude of error. In this paper, an on-off type nonlinear controller is introduced and the applicability and validity of a simple on-off controller are presented by the experimental result.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.5
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• pp.457-462
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• 2014

Given their low cost, single rolling piston compressors (SRPC) are utilized in low-power room air-conditioning systems. The SRPC cycle is composed of one compression and discharge process per mechanical rotation. The load torque is high during the compression process of the refrigerants and low during the discharge process of the refrigerants. This load torque variation induces a speed ripple and severe vibration, which cause fatigue failures in the pipes and compressor parts, particularly under low-speed conditions. To reduce the vibration, the compressor usually operates at a high-speed range, where the rotor and piston inertia reduce the vibration. At a low speed, a predefined feed-forward load torque compensator is used to minimize the speed ripple and vibration. However, given that the load torque varies with temperature, pressure, and speed, a predefined load torque table based on one operating condition is not appropriate. This study proposes an online load torque compensator for SRPC. The proposed method utilizes the speed ripple as a load torque ripple factor. The speed ripple is transformed into a frequency domain and compensates each frequency harmonic term in an independent feed-forward manner. Experimental results are presented to verify the proposed method.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.414-418
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• 1999

Typical metal oxide thin films having optical and electrical properties are widely used as inorganic functional materials. Liquid phase deposition(LPD) method, a new low temperature process, has been developed for the several advantages of no vacuum system, low cost, high throughput, and low processing temperature(<$50^{\circ}C$). Silica powder was added to 40wt% hydrofluoro-silicic acid($H_2$SiF\ulcorner) to obtain an immersing solution of silica-saturated hydrofluorosilicic acid solution. Boric acid solution was continuously added in the range from 0 to 0.05M to prepare supersaturated hydrofluorosilicic acid solution. LPD $SiL_2$film was formed with the variation of added amount of $H_2$O. The SiO$_2$thin film could be prepared from hydrofluorosilicic acid by LPD method. The thickness of LPD $_SiO2$film was influenced by the boric acid concentration and added amount of $H_2$O. Silicon in thin film existed as SiF\ulcorner by Raman spectrum.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.7
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• pp.734-740
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• 2003

In this paper, A Vector Modulator based a wideband analog phase shifter is realized with four P-I-N diode attenuators, an asymmetric coupled line coupler, a symmetric coupled line coupler, and a power combiner. Simple configuration to have advantages in cost, size, power, and the number of passive circuits is presented. The phase variation due to phase and amplitude error of a P-I-N diode attenuator is derived and used to optimize the overall circuit. The phase shifter shows a total phase shift of 360$^{\circ}$, a 8.2$^{\circ}$maximum phase error, and a 16${\pm}$2.5 dB insertion loss over the wide frequency range of 1 GHz to 3 GHz.

• Geomechanics and Engineering
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• v.14 no.1
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• pp.91-98
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• 2018

Length of a vehicle is an important variation to generate different variants of an automotive platform. This parameter is usually adjusted by embedding dimensional flexibility into different components of the Body in White (BIW) including the floor pan. Due to future uncertainties, it is not necessarily possible to define certain values of wheelbase for the future products of a platform. This work is performed to add flexibility into the design process of a length-variable floor pan. By means of this analysis, the cost and time consuming process of optimization is not necessary to be performed for designing the different variants of a product family. Stiffness and mass of the floor pan are two important functional requirements of this component which directly affect the occupant comfort, dynamic characteristics, fuel economy and environmental protection of the vehicle. A combination of Genetic algorithm, GMDH-type of artificial neural networks and TOPSIS methods is used to optimally design the floor pan associated with arbitrary length of the variant in the defined system range. The correlation between the optimal results shows that for a constant mass of the floor pan, the first natural frequency decreases by increasing the length of this component.

• ETRI Journal
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• v.33 no.3
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• pp.335-343
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• 2011

The pad pitch of modern radio frequency integrated circuits is in the order of few tens of micrometers. Connecting a large number of high-speed I/Os to the outside world with good signal fidelity at low cost is an extremely challenging task. To cope with this requirement, we need reflection-free transmission lines from an on-chip pad to on-board SMA connectors. Such a transmission line is very hard to design due to the difference in on-chip and on-board feature size and the requirement for extremely large bandwidth. In this paper, we propose the use of narrow tracks close to chip and wide tracks away from the chip. This narrow-to-wide transition in width results in impedance discontinuity. A step change in substrate thickness is utilized to cancel the effect of the width discontinuity, thus achieving a reflection-free microstrip. To verify the concept, several microstrips were designed on multilayer FR4 PCB without any additional manufacturing steps. The TDR measurements reveal that the impedance variation is less than 3 ${\Omega}$ for a 50 ${\Omega}$ microstrip and S11 better than -9 dB for the frequency range 1 GHz to 6 GHz when the width changes from 165 ${\mu}m$ to 940 ${\mu}m$, and substrate thickness changes from 100 ${\mu}m$ to 500 ${\mu}m$.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.372-378
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• 2012

This paper deals with a 3-phase voltage disturbance generator for a performance test of custom power devices such as dynamic voltage restorers (DVR), dynamic uninterruptable power supplies (UPS), etc. The operating principle of the proposed circuit is described in each mode of voltage sag, swell, outage, and unbalance. The main components of the proposed disturbance generator are silicone controlled rectifier (SCR) thyristors, variable autotransformers, and transformers. Therefore, the disturbance generator can be implemented with a considerably low cost compared to the conventional pulse width modified (PWM) inverter and converter type generators. Furthermore, it has good features of high reliability with simple structure, high efficiency caused by no PWM switching of the SCR thyristors, and easy control with a wide variation range. To verify the validity of the proposed scheme, simulations and experiments are carried out.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1682-1686
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• 2004

A slit-flow apparatus with laser diffraction method has been developed with significant advances in ektacytometry design, operation and data analysis. In the slit-flow ektacytometry (or laser-diffractometry), the deformation of red blood cells subjected to continuously decreasing shear stress in slit flow is measured. A laser beam traverses a diluted blood suspension flowing through a slit and is diffracted by RBCs in the volume. The diffraction patterns are captured by a CCD-video camera, linked to a frame grabber integrated with a computer, while the differential pressure variation is measured by a pressure transducer. Both measurements of laser-diffraction image and pressure with respect to time enable to determine deformation index and the shear stress. The range of shear stress of 0 ${\sim}$ 35 Pa and measuring time is less than 2 min. When deforming under decreasing shear stress, RBCs change gradually from the prolate ellipsoid towards a circular biconcave morphology. The Deformation Index (DI) as a measure of RBC deformability is determined from an isointensity curve in the diffraction pattern using an ellipse-fitting program. The advantages of this design are simplicity, i.e., ease of operation and no moving parts, low cost, short operating time, and the disposable kit which is contacted with blood sample.

• Journal of Electrical Engineering and Technology
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• v.3 no.2
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• pp.152-161
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• 2008

This paper deals with a new wave shaping technique for cost effective harmonic mitigation in ac-dc converter feeding Vector Controlled Induction Motor Drives(VCIMD's) for improving power quality at the point of common coupling(PCC). The proposed harmonic mitigator consists of a polygon connected autotransformer based twelve-pulse ac-dc converter and a small rating passive shunt filter tuned for $11^{th}$ harmonic frequency. This ac-dc converter eliminates the most dominant $5^{th},\;7^{th},\;and\;11^{th}$ harmonics and imposes the reduction of other higher order harmonics from the ac main current, thereby improving the power quality at ac mains. The design of autotransformer is carried out for the proposed ac-dc converter to make it suitable for retrofit applications, where presently a 6-pulse ac-dc converter is used. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter in a wide operating range of the drive. Experimental results obtained on the developed laboratory prototype of the proposed harmonic mitigator are used to validate the model and design of the ac-dc converter.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.8 no.2
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• pp.90-95
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• 2009

All-optical fiber-type gain flattening filer (GFF) for an EDFA (Erbium doped fiber amplifier) were fabricated by using a FBT (fiber biconical tapered) process and the performance of the GFF was tested and athermal package was proposed. Historically, the chief contributor to gain unevenness has been the EDFA. Due to the inherent gain response of the EDFA's operation, there is always a modest imbalance in the gain applied as a function of wavelength. FBT methods have been used to make fiber type couplers and WDM filter since 1980. Attractivity of this methods was simple, cost effective and thermal stability. Simulation program tool is made to design target GFF profile for this paper. Fiber coupler manufacturing machine is modified for the GFF process. The final GFF is obtained by cascading 4 unit filter that has 6 taper stage. Test result shows 1 dB of wavelength flatness in the C band. Polarization dependent loss is under 0.15dB. The center wavelength variation is below ${\pm}$0.35nm at the temperature range of $20^{\circ}C$ to $70^{\circ}C$.