• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.11
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• pp.1031-1036
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• 2013

The motor-driven water pump boiler for a water circulating mattress generates noise and vibration as it supplies a large water flow rate. A non-pump boiler can reduce such noise and vibration, however, the water circulation flow rate becomes lesser than that in motor-driven water pump boilers, and a large temperature deviation occurs between the inlet and the outlet of the mattress. In this research, a new non-pump boiler for water circulating mattress is developed and its performance is experimentally validated and compared with the existing non-pump boilers. The experimental results show that temperature response time is improved and temperature deviation is reduced.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.1
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• pp.55-65
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• 2016

This paper proposed a new control method which is capable of controlling circulating current considering current capacity of switching device. In the unbalanced voltage conditions, active power and reactive power have double line frequency. Thus, in order to provide active power without ripple, it is necessary to inject the negative sequence current components. However, when the negative current components is injected, it increases the total current flowing in the Arm, and in the Sub-module(SM) the current more than rated is impressed, which leads to destroy the system. Also, in impressing the circulating current reference of each arm, conventional control method impressed applicable $i_{dck}/3$ in the case of balanced voltage conditions. In the case of unbalanced conditions, as arm circulating current of three phase show difference due to the power impressed to each arm, reference of each arm is not identical. In this study, in the case of unbalanced voltage, within permitted current, the control method to decrease the ripple of active power is proposed, through circulating current control and current limitations. This control method has the advantage that calculates the maximum active power possible to generate capacity and impressed the current reference for that much. Also, in impressing circulating current reference, a new control method proposes to impress the reference from calculating active power of each phase. The proposed control method is verified through the simulation results, using the PSCAD/EMTDC.

• Journal of Veterinary Science
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• v.22 no.5
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• pp.75.1-75.10
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• 2021

Background: Programmed cell death protein-1 (PD-1) and programmed cell death ligand-1 (PD-L1) have important roles in tumor evasion of the immune system. Objectives: This study aimed to assess the diagnostic utility of circulating PD-1 and PD-L1 levels in healthy dogs and dogs with tumors. Methods: Circulating PD-1 and PD-L1 levels in the serum of 71 dogs with tumors were compared with those of 52 healthy dogs by performing enzyme-linked immunosorbent assay (ELISA). Results: The ELISA results revealed higher circulating PD-1 and PD-L1 levels in dogs with tumors (2.9 [2.2-3.7] ng/mL; median [IQR] and 2.4 [1.4-4.4] ng/mL, respectively) than in healthy dogs (2.4 [1.9-3.0] ng/mL; p = 0.012 and 1.4 [0.9-2.1] ng/mL; p < 0.001, respectively). Especially, there was a significant difference in circulating PD-1 levels between healthy dogs and dogs with malignant epithelial tumors (2.4 [1.9-3.0] ng/mL and 3.1 [2.6-4.4] ng/mL, respectively; p < 0.01). In addition, there was a significant difference in circulating PD-L1 levels between healthy dogs and dogs with lymphomas (1.4 [0.9-2.1] ng/mL and 2.7 [1.6-5.8] ng/mL, respectively; p < 0.001). Conclusion: This study indicates that circulating PD-1 and PD-L1 have potential as tumor diagnostic biomarkers in dogs with tumors.

• Journal of Power Electronics
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• v.8 no.4
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• pp.332-344
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• 2008

High frequency AC (HFAC) power distribution systems delivering power through a high frequency AC link with sinusoidal voltage have the advantages of simple structure and high efficiency. In a multiple module system, where multiple resonant inverters are paralleled to the high frequency AC bus through connection inductors, it is necessary for the output voltage phase angles of the inverters be controlled so that the circulating current among the inverters be minimized. However, the phase angle of the resonant inverters output voltage can not be controlled with conventional phase shift modulation or pulse width modulation. The phase angle is a function of both the phase of the gating signals and the impedance of the resonant tank. In this paper, we proposed a pulse phase modulation (PPM) concept for the resonant inverters, so that the phase angle of the output voltage can be regulated. The PPM can be used to minimize the circulating current between the resonant inverters. The mechanisms of the phase angle control and the PPM were explained. The small signal model of a PPM controlled half-bridge resonant inverter was analyzed. The concept was verified in a half bridge resonant inverter with a series-parallel resonant tank. An HFAC power distribution system with two resonant inverters connected in parallel to a 500kHz, 28V AC bus was presented to demonstrate the applicability of the concept in a high frequency power distribution system.

• Particle and aerosol research
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• v.9 no.4
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• pp.239-246
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• 2013

The purpose of this study is to determine the feasibility of dry-type desulfurization process for actual application to coal-fired power plant. We used actual exhaust gas from Facility Y, Plant #2 to fabricate a demo-scale testing device to attempt to improve the efficiency of desulfurization. A spout-bed circulating dry scrubber convergence system connecting turbo reactor with bag filter was devised, then analyzed for performance characteristics of $SO_2$ removal for Ca/S mole ratio, superficial gas velocity, and ammonia injection, and for secondary reaction characteristics of the non-reactive sorbent at the bag filter. As a result, the installation of spout-bed circulating dry scrubber convergence system showed better economy and efficiency for removing sulfur than the existing wet/semidry-type desulfurization process. In addition, the best efficiency for desulfurization occurred when connected to the bag filter, with differential pressure maintained at 150 $mmH_2O$.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2294-2305
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• 2016

The introduction of a high-voltage direct-current (HVDC) system based on a modular multilevel converter (MMC) for wind farm integration has stimulated studies on methods to control this type of converter. This research article focuses on the control of the AC voltage and circulating current for a wind-farm-side MMC (WFS-MMC). After theoretical analysis, emotional learning (EL) controllers are proposed for the controls. The EL controllers are derived from the learning mechanisms of the amygdala and orbitofrontal cortex which make the WFS-MMC insensitive to variance in system parameters, power change, and fault in the grid. The d-axis and q-axis currents are respectively considered for the d-axis and q-axis voltage controls to improve the performance of AC voltage control. The practicability of the proposed control is verified under various conditions with a point-to-point MMC-HVDC system. Simulation results show that the proposed method is superior to the traditional proportional-integral controller.

• Journal of Power Electronics
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• v.19 no.2
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• pp.529-539
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• 2019

The modular multilevel converter (MMC) has become a promising topology for high-voltage direct current (HVDC) transmission systems. To control a MMC system properly, the ac-side current, circulating current and submodule (SM) capacitor voltage are taken into consideration. This paper proposes a low-computation indirect model predictive control (IMPC) strategy that takes advantages of the conventional MPC and has no weighting factors. The cost function and duty cycle are introduced to minimize the tracking error of the ac-side current and to eliminate the circulating current. An optimized merge sort (OMS) algorithm is applied to keep the SM capacitor voltages balanced. The proposed IMPC strategy effectively reduces the controller complexity and computational burden. In this paper, a discrete-time mathematical model of a MMC system is developed and the duty ratio of switching state is designed. In addition, a simulation of an eleven-level MMC system based on MATLAB/Simulink and a five-level experimental setup are built to evaluate the feasibility and performance of the proposed low-computation IMPC strategy.

• New & Renewable Energy
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• v.5 no.3
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• pp.32-39
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• 2009

The Samcheonpo ocean small hydropower plant (SHP) has a special feature of using marginal hydraulic head of circulating water system of fossil fuel power plant as a power source and having the characteristics of general hydropower generation and tidal power generation as well. Also, it contributes to reducing green house gases and developing clean energy source by recycling circulating water energy otherwise dissipated into the ocean. The efficiency of small hydropower plant is directly affected by effective head and flow rate of discharged water. Therefore, the efficiency characteristics of ocean hydropower plant are analyzed with the variation of water level and flow rate of discharged water, which is based on the accumulated operation data of the Samcheonpo hydropower plant. After the start of small hydropower plant operation, definite rise of water level was observed. As a result of flow pattern change from free flow to submerged flow, the instability of water surface in overall open channel is increased but it doesn't reach the extent of overflowing channel or having an effect on circulation system. Performance evaluation result shows that the generating power and efficiency of small hydropower exceeds design requirements in all conditions. Analysis results of CWP's water flow rate verify that the amount of flowing water is measured less and the highest efficiency of small hydropower plant is achieved when the effective head has its maximum value. In conclusion, efficiency curve derived from water flow rate considering tidal level shows the best fitting result with design criteria curve and it is verified that overall efficiency of hydropower system is satisfactory.

• Journal of Bio-Environment Control
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• v.11 no.4
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• pp.168-174
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• 2002

A new circulating hydroponic system was invented for oriental melons grown in the greenhouse. For developing nutrient solution management techniques, we examined the changes of nutrient contents of circulating solution in three different types of new hydroponic systems. The yield and fruit quality of oriental melons in Hydroponics were better than those in soil culture. The substrate culture was appropriate fer hydroponics of oriental melons, and NFT was turned to be the opposite due to the physiological disorder during hot seasons. Yamazaki's melon solution with EC 2.0dS.m$^{[-10]}$ was the most appropriate for oriental melons. The new circulating hydroponic system seemed to be appropriate for oriental melons because of the stable EC, pH and the macro- and micro-element contents. NO$_3$-N, Ca and Mg contents in the circulating solution kept a good balance in all types of hydroponics. However, p content, compared to other types, decreased by the degree of 1 me.L$^{[-10]}$ in perlite medium. K content showed irregular status in perlite but showed the stable status in cocopeat. Generally, microelements, except Mo, showed stable absorption in the substrate culture. However, in NET, most of the elements showed irregular absorption except B and Mn. Microelement absorption, especially Cu, Zn and Mo, decreased during hot seasons.

• Journal of the Korean Solar Energy Society
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• v.22 no.2
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• pp.11-17
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• 2002

This paper is concerned with the development of a new method for making, separating ice and storage floated ice by installing an evaporation plate at under-water within a storage tank. In a conventional harvest-type ice storage system, a tank saves ice by separating an ice from an installed evaporation plate, which is located above an ice storage tank as an ice storage system. Developed new harvest-type method shows good heat transfer efficiency than a convectional method. It is because the evaporation panel is directly contacted with water in a storage tank. Also, at a conventional system a circulating pump, a circulating water distributor and a piping are installed, however these components are not necessary in a new method. In this study ice storage systems are experimentally investigated to study the charge and discharge of thermal energy. The results show the applicable possibility and performance enhancement of a new type.