• Ocean Systems Engineering
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• v.4 no.1
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• pp.63-82
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• 2014

Declutching control is applied to a hemispherical wave energy converter with direct linear electric Power-Take-Off systems oscillating in heave direction in both regular and irregular waves. The direct linear Power-Take-Off system can be simplified as a mechanical spring and damper system. Time domain model is applied to dynamics of the hemispherical wave energy converter in both regular and irregular waves. And state space model is used to replace the convolution term in time domain equation of the heave oscillation of the converter due to its inconvenience in analyzing the controlled motion of the converters. The declutching control strategy is conducted by optimal command theory based on Pontryagin's maximum principle to gain the controlled optimum sequence of Power-Take-Off forces. The results show that the wave energy converter with declutching control captures more energy than that without control and the former's amplitude and velocity is relatively larger. However, the amplification ratio of the absorbed power by declutching control is only slightly larger than 1. This may indicate that declutching control method may be inapplicable for oscillating wave energy converters with direct linear Power-Take-Off systems in real random sea state, considering the error of prediction of the wave excitation force.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.446-451
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• 2003

This paper presents some examples of active control of flow-induced vibration using piezoelectric actuators. The flutter phenomenon, which is the dynamic instability of structure due to mutual interaction among inertia, stiffness, and aerodynamic forces, may cause catastrophic structural failure, and therefore the active flutter suppression is one of the main objectives of the aeroelastic control. Active flutter control has been numerically and experimentally studied for swept-back lifting surfaces using piezoelectric actuation. A finite element method, a panel aerodynamic method, and the minimum state space realization are involved in the development of the governing equation, which is efficiently used for the analysis of the system and design of control laws with modern control framework. The active control suppressed flow-induced vibrations and extended the flutter speed around by 10%. Another representative flow-induced vibration phenomenon is the oscillation of blunt bodies due to the vortex shedding. In general, it is quite difficult to set up the numerical model because of the strong non-linearity of the vortex shedding structure. Therefore, we applied adaptive positive position feedback controller, which requires no pre-determined model of the plant, and successfully suppressed the flow-induced vibration.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.5
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• pp.395-403
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• 2020

This study presents a stable start-up strategy for v/f scalar-controlled permanent magnet synchronous motors (PMSMs). The v/f-controlled PMSMs easily lose synchronism under low-speed conditions if an insufficient stator voltage is applied to the machine due to errors in measured motor parameters and inverter nonlinearity, such as inverter dead time and on-state voltage drop. The proposed method adopts the I/f control method to ensure a stable start at low speeds and then switches to the v/f control method at medium speeds. A smooth transition method from I/f control to v/f control is proposed to minimize the oscillation of the stator current and rotor speed during transition. Moreover, the stability of the I/f and v/f control methods is analyzed using a small-signal model. Simulation and experimental results are provided to verify the performance of the proposed control strategy.

• Korean Journal of Soil Science and Fertilizer
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• v.31 no.2
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• pp.85-94
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• 1998

Due to relatively high permittivity of water in soils, we placed the soil condenser into soils to measure the soil moisture content. The soil condenser was made with two insulated iron sticks. The capacitance of the soil condenser was determined by the pulse period from RC type oscillation circuit and the highest voltage output accepting 10MHz pulse. After zero point adjustment, the measured relative capacitance percentage (RCS) to the standard condenser obtained by the oscillation circuit almost linearly correlated with the end depth of the sensor submerged in water. The RC type oscillation was disturbed by many sensor installed in a close distance in one place, presumably resulting in that the sensor sticks played as a interfering antennas generating or accepting electron waves from them. The temperature dependance of the output from the sensors could be corrected through experimentally determined revision function. Although lineal correlation was found between soil moisture and RCS, users should derive their own correlation function for every sensor to measure soil moisture, because the outputs were influenced by the installation depth and layout in the soil. The voltage type sensor responded inversely with soil moisture content and so was not suitable to the accurate measurement of soil moisture, but allows high economic benefit in various application such as simplified measurement of soil moisture and irrigation line control because of its low component count. The voltage type moisture sensor could be reinforced by relay controlling circuit to open and to close the solenoid valves respectively at optimal limits of the least and the most soil moisture according to user's adjustment.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.451-454
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• 2000

Invasive methode and Non-invasive methode are used in blood pressure measurement. The Invasive methode can Set the correct measured blood pressure but, it has patient feels uncomfortable. So most of cases use Non-invasive methode. The Oscillometric method is commonly apply to modem electric sphygmomanometer and using various algorithm. In this paper describe about a algorithm it control and to determinate the cuff pressure, and filtering that data for measure the blood pressure. The communicating with personal computer can pressure deflation is by Solenoid valve and it uses RS-232 system in packet communication. The main using algorithm for blood pressure measurements are maximum amplitude algorithm and oscillometric algorithm. MAA(maximum amplitude algorithm) has various measured oscillation it depend on patient's age, height, weight and arm circumference size. In this paper, 1 studied the various measured oscillation apply to characteristic ratio and can get the result of systolic blood pressure, diastolic blood pressure, mean blood pressure. It was not used same ratio to measuring oscillation. In the MAA(maximum amplitude algorithm), we hope for reduce the difference with the real blood pressure and the measured blood pressure, when it applied with various specific ratio.

• Korean Journal of Food Science and Technology
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• v.28 no.4
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• pp.624-631
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• 1996

Effect of fluctuation range and intervals of defrosting temperature on quality of frozen foods stored in a domestic refrigerator equipped with an automatic defrost system was evaluated. As defrost system was operated, temperatures of domestic refrigerators were elevated from $-18^{\circ}C\;to\;-5^{\circ}C\;and\;-15^{\circ}C$, and fluctuation intervals were l6 hrs and 30 hrs, respectively. Quality deterioration such as protein denaturation, vitamin loss, exudate production and changes in appearance of frozen foods was minimized by reducing temperature oscillation during storage. Considerable effects of thermal oscillation on ice crystal sizes were observed for frozen beef tissue and ice cream. TTI (time temperature indicator) system also proved that the temperature control of defrost system in domestic refrigerator can improve the quality of foods during storage.

• Journal of Electrical Engineering and Technology
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• v.10 no.5
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• pp.1989-2000
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• 2015

In this paper, digital peak current mode control for single phase H-bridge inverters is developed and implemented. The digital peak current mode control is achieved by directly controlling the PWM signals by cycle-by-cycle current limitation. Unlike the DC-DC converter where the output voltage always remains in the positive region, the output of DC-AC inverter flips from positive to negative region continuously. Therefore, when the inverter operates in negative region, the control should be changed to valley current mode control. Thus, a novel control logic circuit is required for the function and need to be analyzed for the hardware to track the sinusoidal reference in both regions. The problem of sub-harmonic instability which is inherent with peak current mode control is also addressed, and then proposes the digital slope compensation in constant-sloped external ramp to suppress the oscillation. For unipolar PWM switching method, an adaptive slope compensation in digital manner is also proposed. In this paper, the operating principles and design guidelines of the proposed scheme are presented, along with the performance analysis and numerical simulation. Also, a 200W inverter hardware prototype has been implemented for experimental verification of the proposed controller scheme.

• Journal of Power System Engineering
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• v.14 no.2
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• pp.34-39
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• 2010

Recently, technical trend for machine tools is focused on enhancement of speed and accuracy. High speedy processing causes thermal and structural deformation of objects from the machine tools. Water cooler has to be applied to machine tools to reduce the thermal negative influence with accurate temperature controlling system. Existing On-Off control type can't control temperature accurately because compressor is operated and stopped repeatedly and causes increment of power consumption and decrement of the expected life of compressor. The goal of this study is to minimize temperature error in steady state. In addition, control period of an electronic expansion valve were considered to increment of lifetime of the machine tools and quality of product with a water cooler. PI controller is designed using type of hot-gas bypass for precise control of temperature. Gain of PI is decided easily by method of critical oscillation response, excellent performance of control is shown with 4.24% overshoot and ${\pm}0.2^{\circ}C$error of steady state. Also, error range of temperature is controlled within $0.2^{\circ}C$although disturbance occurs.

• Journal of Auto-vehicle Safety Association
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• v.13 no.1
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• pp.6-13
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• 2021

This paper presents yaw moment control for modification of steering characteristic in rear-driven vehicle with front in-wheel motors (IWMs). The proposed control algorithm is designed to modify yaw rate response of the test vehicle. General approach for modification of steering characteristic is to define the desired yaw rate and track the yaw rate. This yaw rate tracking method can cause the chattering problem because of the IWM actuator response. Large overshoot and settling time in IWM torque response can amplify the oscillation in control input and yaw rate. To resolve these problems, open-loop IWM controller for cornering agility was designed to modify the understeer gradient of the vehicle. The proposed algorithm has been investigated via the computer simulations and the vehicle tests. The performance evaluation has been conducted on dry asphalt using E-segment test vehicle. The performance of the proposed algorithm has been compared to general yaw rate tracking algorithm in the vehicle tests. It has been shown that the proposed control law improved the cornering agility without chattering problem.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.298-305
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• 2006

The flow around a circular cylinder which oscillates rotationally with a relatively high forcing frequency has been investigated experimentally using flow visualization and hot-wire measurements. Dominant parameters are Reynolds number (Re), oscillation amplitude $({\theta}_A)$, and frequency ratio $F_R=f_f/f_n$, where $f_f$ is the forcing frequency and $f_n$ is the natural frequency of vortex shedding. Experiments were carried out under the conditions of $Re=4.14{\times}10^3,\;{\theta}_A={\pi}/6$, and $0{\leq}F_R{\leq}2$. The effect of frequency ratio $F_R$ on the flow structure of wake was evaluated by measuring wake velocity profile and spectral analysis of hot-wire signal. Depending on the frequency ratio $F_R$, the cylinder wake has 5 different flow regimes. The vortex formation length and vortex shedding frequency are changed significantly before and after the lock-on regime. The drag coefficient was reduced under the condition of $F_R<1.0$ and the maximum drag reduction is about 33% at $F_R=0.8$. However, the drag is increased as $F_R$ increases beyond $F_R=1.0$. This active flow control method can be effective in aerodynamic applications, if the forcing parameters are selected optimally.