• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6B
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• pp.559-568
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• 2002

In this paper, we studied on combining the control of transmission fates and power for the real system where a finite set of transmission rates are used. In [1], the combined control of transmission rates and power was first researched, and suggested the Selective Power Control (SPC) algorithm. However, it can't guarantee the minimum rate to each user and results in frequent changes of rate due to oscillation of the SIR (Signal to Interference Ratio) values. As a main purpose of this paper, we derive a formulation model and propose a distributed iteration algorithm to solve these problems. To evaluate the performance of the proposed algorithm, we carried out numerical analysis and computational experiments. The results indicate that the proposed algorithm achieves better throughput than conventional one by keeping the low average transmission power.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.154-156
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• 1999

A Linear Stepping Motor(LSM) can operate open loop control mode similarly to a rotary stepping motor. The linear motion without any mechanical linkage in the LSM results in several advantages for precise positioning actuators. However, to realize the more stable and higher speed control without hunting, it is necessary to derive an equivalent circuit to explain the steady-state and transisent characteristics in order to find an adequate control rule for high performance control of the LSM. In this paper, magnetic equivalent circuit is obtained, based on the structure of the LSM, and then the electric equivalent circuit of the LSM is derived by solving equations for the magnetic equivalent circuit. The 1-step response characteristic of the LSM is analyzed by the ACSL with the voltage equations, the force equations, the force equations and the kinetic equation.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.4
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• pp.134-141
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• 1999

Ths paper describes on the stability improvement of output voltage control on the power suwJy for railway. On the transient states such as input voltage sudden change, the inpJt and output voltage beccxre unstable by L-C resonance occurred due to constant output voltage control. In this paper, the new clamping circuit for system stability is proposed, and control method using band attenuated filter and feed-forward terms is introduced. The propoesd damping circuit is composed with sma1l size R-L. Also, the 3 level PWM method is adopted to decrease distortion of output voltage. The output voltage is controlledl with variation under 10% without oscillation at transient states and have total hanmnic distortion under 3%.der 3%.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.10
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• pp.1426-1431
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• 2015

Piezoelectric pump can be considered as R-C load and it needs something special driver because the output voltage does not become 0 even though the applied voltage is 0 with common converter. This operating system consists of fly-back converter to increase the input voltage and energy recovery inverter to apply square voltage to the piezoelectric pump. The energy recovery inverter can charge and discharge the energy of capacitive load. In this paper, to enhance performance of the driver, a few elements or circuits are added and modified. To drive the inverter safely, current limit resister is added and adjusted the value to valance the charging and discharging current. In addition, a current limit inductor is added to the input side to limit the input current and enhance the efficiency. Inductor only may make oscillation and another resister is added parallel to the inductor to solve this problem. The converter and inveter are assembled to one board for compactness. The appropriateness is proved with simulation and experiments.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.3
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• pp.1083-1095
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• 1996

Shock wave/boundary layer interaction frequently causes the shock wave to oscillate violently and thus the global flow field to unstabilize. In order to stabilize the shock wave system in the diffuser of a supersonic wind tunnel, the present study attempted to control the shock oscillations by using a passive control. A porous wall with the porosity of 19.6% was mounted on a shallow cavity. Experiment was made by means of schlieren optical observation and wall pressure measurements. The flow Mach number just upstream the shock system and Reynolds number based on the turbulent boundary layer thickness were 2.1 and 1.8 * 10$\^$6/, respectively. The results show that the present passive control method on the shock wave/boundary layer interaction in the supersonic diffuser can significantly suppress the oscillations of shock system, especially when the shock system locates at the porous wall.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.6
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• pp.546-554
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• 2012

This paper suggests a design method of an improved phase control loop for tracking resonant frequency of solid type precision resonant gyroscope. In general, a low cost MEMS gyroscope adapts the automatic gain control loops by taking a velocity feedback configuration. This control technique for controlling the resonance amplitude shows a stable performance. But in terms of resonant frequency tracking, this technique shows an unreliable performance due to phase errors because the AGC method cannot provide an active phase control capability. For the resonance control loop design of a solid type precision resonant gyroscope, this paper presents a phase domain control loop based on linear PLL (Phase Locked Loop). In particular, phase control loop is exploited using a higher order PLL loop filter by extending the first order active PI (Proportion-Integral) filter. For the verification of the proposed loop design, a hemispherical resonant gyroscope is considered. Numerical simulation result demonstrates that the control loop shows a robust performance against initial resonant frequency gap between resonator and voltage control oscillator. Also it is verified that the designed loop achieves a stable oscillation even under the initial frequency gap condition of about 25 Hz, which amounts to about 1% of the natural frequency of a conventional resonant gyroscope.

• Nuclear Engineering and Technology
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• v.44 no.4
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• pp.369-378
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• 2012

A load-following operation in APR+ nuclear plants is necessary to reduce the need to adjust the boric acid concentration and to efficiently control the control rods for flexible operation. In particular, a disproportion in the axial flux distribution, which is normally caused by a load-following operation in a reactor core, causes xenon oscillation because the absorption cross-section of xenon is extremely large and its effects in a reactor are delayed by the iodine precursor. A model predictive control (MPC) method was used to design an automatic load-following controller for the integrated thermal power level and axial shape index (ASI) control for APR+ nuclear plants. Some tracking controllers employ the current tracking command only. On the other hand, the MPC can achieve better tracking performance because it considers future commands in addition to the current tracking command. The basic concept of the MPC is to solve an optimization problem for generating finite future control inputs at the current time and to implement as the current control input only the first control input among the solutions of the finite time steps. At the next time step, the procedure to solve the optimization problem is then repeated. The support vector regression (SVR) model that is used widely for function approximation problems is used to predict the future outputs based on previous inputs and outputs. In addition, a genetic algorithm is employed to minimize the objective function of a MPC control algorithm with multiple constraints. The power level and ASI are controlled by regulating the control banks and part-strength control banks together with an automatic adjustment of the boric acid concentration. The 3-dimensional MASTER code, which models APR+ nuclear plants, is interfaced to the proposed controller to confirm the performance of the controlling reactor power level and ASI. Numerical simulations showed that the proposed controller exhibits very fast tracking responses.

• Journal of Power Electronics
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• v.16 no.1
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• pp.227-237
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• 2016

A novel digital current control strategy for digitally controlled DC-DC switching converters, referred to as Adjacent Cycle Sampling (ACS), is proposed in this paper. For the ACS current control strategy, the available time interval from sampling the current to updating the duty ratio, is approximately one switching cycle. In addition, it is independent of the duty ratio. As a result, the contradiction between the processing speed of the hardware and the transient response speed can be effectively relaxed by using the ACS current control strategy. For digitally controlled buck DC-DC switching converters with trailing-edge modulation, digital current control algorithms with the ACS control strategy are derived for three different control objectives. These objectives are the valley, average, and peak inductor currents. In addition, the sub-harmonic oscillations of the above current control algorithms are analyzed and eliminated by using the digital slope compensation (DSC) method. Experimental results based on a FPGA are given, which verify the theoretical analysis results very well. It can be concluded that the ACS control has a faster transient response speed than the time delay control, and that its requirements for hardware processing speed can be reduced when compared with the deadbeat control. Therefore, it promises to be one of the key technologies for high-frequency DC-DC switching converters.

• Journal of computational fluids engineering
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• v.21 no.4
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• pp.90-95
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• 2016

Leidenfrost drops with ellipsoidal shaping can control the bouncing height by adjusting the aspect ratio(AR) of the shape at the moment of impact. In this work, we focus on the effect of the AR and the impact Weber number(We) on the non-axisymmetrical spreading dynamics of the drop, which plays an important role in the control of bouncing. To understand the impact dynamics, the numerical simulation is conducted for the ellipsoidal drop impact upon the perfect non-wetting solid surface by using volume of fluid method, which shows the characteristics of the spreading behavior in each principal axis. As the AR increases, the drop has a high degree of the alignment into one principal axis, which leads to the consequent suppression of bouncing height with shape oscillation. As the We increases, the maximum spreading diameters in the principal axes both increase whereas the contact time on the solid surface rarely depends on the impact velocity at the same AR. The comprehensive understanding of the ellipsoidal drop impact upon non-wetting surface will provide the way to control of drop deposition in applications, such as surface cleaning and spray cooling.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.5
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• pp.41-47
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• 2009

Numerical computations were carried out to analyze the effect of a sub-cavity at several inlet Mach numbers on the control of cavity-induced pressure oscillations in two-dimensional supersonic flow. The present passive control method, the sub-cavity applied to the front wall of a square cavity, was studied for the inlet Mach numbers of 1.50, 1.83 and 2.50. The results show that the sub-cavity is effective in reducing the oscillations, and a resultant amount of the reduction depended on the inlet Mach number, the length of flat plate, and the depth of sub-cavity used as an oscillation suppressor.