• Journal of Electrical Engineering and Technology
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• v.10 no.6
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• pp.2221-2227
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• 2015

To arrest a frequency nadir, a stepwise inertial control (SIC) scheme generates a constant active power reference signal of a wind turbine generator (WTG) immediately after a disturbance and maintains it for the predetermined time. From that point, however, the reference of a WTG abruptly decreases to restore the rotor speed for the predefined period. The abrupt decrease of WTG output power will inevitably cause a second frequency dip. In this paper, we propose a modified SIC scheme of a doubly-fed induction generator (DFIG) that can prevent a second frequency dip. A reference value of the modified SIC scheme consists of a reference for the maximum power point tracking control and a constant value. The former is set to be proportional to the cube of the rotor speed; the latter is determined so that the rotor speed does not reach the minimum operating limit by considering the mechanical power curve of a DFIG. The performance of the modified SIC was investigated for a 100 MW aggregated DFIG-based wind power plant under various wind conditions using an EMTP-RV simulator. The results show that the proposed SIC scheme significantly increases the frequency nadir without causing a second frequency dip.

• Journal of Preventive Medicine and Public Health
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• v.17 no.1
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• pp.281-287
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• 1984

In search for a method of evaluating the cardiopulmonary function. 74 male and 33 female volunteers ages $18{\sim}25$ were subjected to this study The subjects walked on a treadmill at speed of 2,4,6 and 8km/hr with 0,5,10,15,20 and 25% grade of inclination, respectively, for a measurement of heart rate and oxygen-pulse. Heart rate was measured every 5 seconds at resting state and during walking by telemetric method using Heart Checker 108 System (Senoh Co., Japan). Oxygen concentration was measured by Douglas bag method collecting expired air for 5 minutes at rest, and for 2 minutes at the end of each walking exercise. Oxygen concentration in an expired air was analyzed with Orzat gas analyser and expressed in terms of STPD. Oxygen-pulse was defined as an amount of oxygen consumed at every heart at a cellular level. The followings were the results obtained from this study. 1. Mean values of oxygen-pulse at resting state was $3.1{\pm}0.11ml/beat$ in male and $2.5{\pm}0.87ml/beat$ in female, respectively. 2. Mean values of oxygen-pulse during treadmill walking were increased in proportion with the load of exercise, namely, the speed and grade of inclination, from minimum of 7.1ml/beat upto maximum of 18.2ml/beat in male and from minimum of 4.2ml/beat upto maximum of 12,7ml/beat in female. 3. Both linear and logarithmic regressional relationships between oxygen-pulse and speed of walking and grade of inclination were observed in both sexes. Predicted values of oxygen-pulse by logarithmic regressional formula on speed and on grade of inclination were better coincided with the measured values than those predicted by the linear regressional formula.

• Korean Journal of Agricultural Science
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• v.51 no.2
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• pp.133-146
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• 2024

Selection of gear reduction ratio is essential for machine design to ensure suitable power and speed during agricultural operations. The goal of the study was to evaluate the gear reduction ratio for a 1.6 kW four-wheel-drive (4WD) multi-purpose agricultural electric vehicle platform using workload data under different off-road conditions. A data acquisition system was fabricated to collect workload (torque) of the vehicle acting on the gear shaft. Field tests were performed under three driving surfaces (asphalt, concrete, and grassland), payload operations (981, 2,942, and 4,903 N), and slope conditions (0 - 4°, 4 - 8°, and 8 - 12°), respectively. Commercial speed reduction gear phases were attached to the input shaft of the vehicle powertrain. The maximum required torque was recorded as 37.5 Nm at a 4,903 N load with 8 - 12° slope levels, and the minimum torque was 12.32 Nm at 0 - 4° slope levels with a 981 Nm load for a 4 km/h speed on asphalt, concrete, and grassland roads. Based on the operating load condition and motor torque and rotational speed (TN) curve, the minimum and maximum gear reduction ratios were chosen as 1 : 50 and 1 : 64, respectively. The selected motor satisfied power requirements by meeting all working torque criteria with the gear reduction ratios. The chosen motor with a gear reduction ratio of 1 : 50 was suitable to fit with the motor T-N curve, and produced the maximum speeds and loads needed for driving and off-road activities. The findings of the study would assist in choosing a suitable gear reduction ratio for electric vehicle multi-purpose field operations.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.26-28
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• 2007

The motion estimation is the most important technique in the image compression of the video standards. In the case of next generation standards in the video codec as H.264, a high compression-efficiency can be also obtained by using a motion compensation. To obtain the accurate motion search, a motion estimation should be achieved up to 1/2 pixel and 1/4 pixel uiuts. To do this, the computational complexity is increased although the image compression rate is increased. Therefore, in this paper, we propose the advanced sub-pixel block matching algorithm to reduce the computational complexity by using a statistical characteristics of SAD(Sum of Absolute Difference). Generally, the probability of the minimum SAD values is high when searching point is in the distance 1 from the reference point. Thus, we reduced the searching area and then we can overcome the computational complexity problem. The main concept of proposed algorithm, which based on TSS(Three Step Search) method, first we find three minimum SAD points which is in integer distance unit, and then, in second step, the optimal point is in 1/2 pixel unit either between the most minimum SAD value point and the second minimum SAD point or between the most minimum SAD value point and the third minimum SAD point In third step, after finding the smallest SAD value between two SAD values on 1/2 pixel unit, the final optimized point is between the most minimum SAD value and the result value of the third step, in 1/2 pixel unit i.e., 1/4 pixel unit in totally. The conventional TSS method needs an eight.. search points in the sub-pixel steps in 1/2 pixel unit and also an eight search points in 1/4 pixel, to detect the optimal point. However, in proposed algorithm, only total five search points are needed. In the result. 23 % improvement of processing speed is obtained.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1028-1032
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• 2004

In order to prevent machine tool feed slide system from transient vibrations during operations, machine tool designers usually adopt some typical design solutions; box-in-box typed feed slides, optimizing moving body for minimum weight and dynamic compliance, and so on. Despite all efforts for optimizing design, a feed drive system may experience severe transient vibrations during high-speed operation if its feed rate control is unsuitable. A rough feed rate curve having discontinuity in its acceleration profile causes a serious vibration problem in the feed slides system. This paper presents a feed rate optimization of a ball screw driven machine tool feed slide system for its minimum vibration. Firstly, a ball screw feed drive system was mathematically modeled as a 6-degree-of-freedom lumped parameter system. Next, a feed rate optimization of the system was carried out for minimum vibrations. The main idea of the feed rate optimization is to find out the most appropriate smooth acceleration profile with jerk continuity. A genetic algorithm was used in this feed rate optimization

• Journal of the Korean Society of Safety
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• v.27 no.3
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• pp.63-70
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• 2012

In the hazardous areas where explosive gases, vapor or mists exist, electrical apparatus and installations must be the explosion-proof construction to prevent or limit the danger of the ignition of potentially explosive atmosphere. In Korea, nine types of protection have been specified in the government regulations at present: flameproof enclosure, pressurization, oil immersion, increased safety, intrinsic safety, non-incendive, powder filling, encapsulation, and special types. Among these types, the intrinsic safety has the construction which limit or by-pass igniting the electric energy using electronic devices. This type has lots of merits but at the same time requires a high-degree of technology. In this paper, we investigated several dominating factors which affect the minimum ignition energy; this energy plays a very important role in design and evaluation of the intrinsic safety type electrical apparatus. Electrode material, which is one of the most important factors, was intensively studied for the five sorts of material(Al, Cd, Mg, Sn, and Zn) with performing experiment in a low-voltage inductive circuit using IEC-type(International Electro-technical Commission) spark apparatus. The experimental results show that the minimum ignition energy of electrode material is varied: highest in Cd and lowest in Sn. We also confirmed the effect of electrode make-and-break speed.

• Journal of Ship and Ocean Technology
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• v.9 no.3
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• pp.1-13
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• 2005

A design procedure for a ship with minimum total resistance has been developed using a numerical optimization method called SQP (Sequential Quadratic Programming) to search for optimized hull form and CFD(Computational Fluid Dynamics) technique. The friction resistance is estimated using the ITTC 1957 model-ship correlation line formula and the wave making resistance is evaluated using a potential-flow panel method based on Rankine sources with nonlinear free surface boundary conditions. The geometry of hull surface is represented and modified using B-spline surface patches during the optimization process. Using the Series 60 hull ($C_B$ =0.60) as a base hull, the optimization procedure is applied to obtain an optimal hull that produces the minimum total resistance for the given constraints. To verify the validity of the result, the original model and the optimized model obtained by the optimization process have been built and tested in a towing tank. It is shown that the optimal hull obtained around $13\%$ reduction in the total resistance and around $40\%$ reduction in the residual resistance at a speed tested compared with that of the original one, demonstrating that the present optimization tool can be effectively used for efficient hull form designs.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.913-917
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• 1994

A collision-free geometric path for industrial articulated robot is searched among polyhedral obstacles considering kinematic charcteristics. Then minimum-time control of the geometric path is studied considering dynamic characteristics. The algorithm is simulated on PC for maximum speed, moving time and so forth.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.8
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• pp.953-958
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• 2015

Generally, Urban railway have special characteristics with short distance journey and minimum headway intercity transportation. These days, urban railway operators choose the driverless operation system without driver. On the contrary, Conventional & high speed railway utilize for long distance and high speed running. Because of special conditions of freight railway operation compared with urban railway, operation of conventional & high speed railway is showed very different characteristics. In this paper, We compares different operation scheme of urban railway and conventional & high speed railway and then present condition for train control system based on radio.

• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.284-287
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• 2001

In this paper, we designed and implemented a precise pulse motor control chip that generates the parabolic speed pattern. This chip can control step motor[1], DC servo[2] and AC servo motors at high speed and precisely. It can reduce the mechanical vibration to the minimum at the change point of a degree of acceleration. Because the parabolic speed pattern has the continuous acceleration change. In this paper, we present the pulse generation algorithm and the parabolic pattern speed generation. We verify these algorithm using visual C++. We designed this chip with VHDL(Very High Speed Integrated Circuit Hardware Description Language) and executed a logic simulation and synthesis using Synopsys synthesis tool. We executed the pre-layout simulation and post-layout simulation with Verilog-XL simulation tool. This chip was produced with 100 pins, PQFP package by 0.35 um CMOS process and implemented by completely digital logic. We developed the hardware test board and test program using visual C++. We verify the performance of this chip by driving the servo motor and the function by GUI(Graphic User Interface) environment.