• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.324-333
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• 2009

This paper presents a numerical simulation study of the transient behavior of a $2{\times}340MW$ pump-turbine power plant, where the results show an unstable behavior at runaway. First, the modeling of hydraulic components based on equivalent schemes is presented. Then, the 2 pump-turbine test case is presented. The transient behavior of the power plant is simulated for a case of emergency shutdown with servomotor failure on Unit 1. Unstable operation at runaway with a period of 15 seconds is properly simulated using a 1-dimensional approach. The simulation results points out a switch after 200 seconds of the unstable behavior between a period of oscillations initially of 15 seconds to a period of oscillation of 2.16 seconds corresponding to the hydraulic circuit first natural period. The pressure fluctuations related to both the rigid and elastic water column mode are presented for oscillation mode characterization. This phenomenon is described as a switch between a rigid and an elastic water column oscillation mode. The influence of the rotating inertia on the switch phenomenon is investigated through a parametric study.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.6_3
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• pp.1199-1206
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• 2022

Fossil fuels are one of the various energy sources used by humans, and industrial development has been achieved by relying on fossil fuels for a long time in the past. In order to respond to the depletion of fossil fuels and climate change, the world is trying to build an eco-friendly energy ecosystem. Research on efficiency improvement using renewable energy and ESS in various ways for energy conversion is being promoted. In this paper, a microgrid for industrial complexes was designed, constructed, and demonstrated. It was operated in two modes: an independent mode that each plant generates and uses independently and a connected operation mode that allows energy sharing between factories. In the case of independent mode, PV and PCS were intermittently stopped and restarted according to the status change of SoC section of each site. But, in the case of the connected operation mode, stable power supply was confirmed through power transaction through the operation of the entire SoC. This paper presented and verified an algorithm to stably supply power to industrial complexes consisting of various consumers with different load characteristics.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.10 no.1
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• pp.33-39
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• 2011

This paper considers a performance analysis of set-top box (STB) power saving schemes. STB converts the signal into content which is then displayed on the television (TV) screen, and there are typically two operation modes: on mode and stand-by mode. The total energy consumption (TEC), a typical measure of power consumption of STB, is defined by the sum of power consumption in each mode. Recently there are some works of STB power saving schemes that transit STB operation modes efficiently, and the mode transition time point of those schemes can be different. Thus it is required to develop a performance evaluation method that reflects mode transition time points of each scheme to get TEC correctly. This paper proposes a performance evaluation method for STB power consumption using Poisson process to consider the mode transition time point. By modeling STB mode transitions as events of Poisson process, the average time duration of STB mode is computed and accordingly the effect of power saving is evaluated. The performance evaluation result shows that the proposed method achieves 1 to 19% improvement in power consumption compared with a conventional performance evaluation method.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.2309-2318
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• 2010

It is a plan the government increases a railroad section SOC investment, and to activate railroad construction while a railroad wins the spotlight with green transportation. But an error of the demand forecast that is a base of a railroad investment evaluation follows in occurring big, there is it with an operation with an obstacle of a railroad investment. Case of the Incheon International Airport Railroad which went into operation recently, While a present transportation demand showed about 10% than a demand forecasted in a past conference, it was magnified in a social problem. A lot of research was gone on in road project about traffic demand forecast and error, a study to find out the error cause is an insufficient situation although errors of a railroad occurs big. So, this study looked for errors and causes about trip generation model and modes sharing model of railroad demand forecast but it was defined causes so that it can occur similar problems in the future. Especially it investigated causes after comparing rate of development plan for the realization and O/D size in trip generation model and after comparing rate of modes sharing of past and current and conducting a survey for airport users. In conclusion, it suggested method to reduce errors of railroad demand forecasting in the future.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.237-240
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• 2012

This paper describes an implementation of ARIA crypto algorithm which is a KS (Korea Standards) block cipher algorithm. The ARIA crypto-core supports three master key lengths of 128/192/256-bit specified in the standard and the four modes of operation including ECB, CBC, CTR and OFB. To reduce hardware complexity, a hardware sharing is employed, which shares round function in encryption/decryption module with key initialization module. The ARIA crypto-core is verified by FPGA implementation, the estimated throughput is about 1.07 Gbps at 167 MHz.

• Journal of Power Electronics
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• v.8 no.4
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• pp.371-380
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• 2008

This paper describes the Utility Interactive PV (UIPV) system which can improve the peak-cut effect by adding an energy storage device of batteries to the power converter. The proposed system has three possible operation modes depending on relative condition of PV output, which can have the power shaping function covering the peak power for 3 hours. A new power circuit and an application algorithm have been applied to the UIPV system which is based on working PV system during a 3-hour peak time. The energy relationship by the proposed system is analyzed theoretically and experimentally. The proposed system is evaluated at the viewpoint of cost and total spacing, which enables the proposed UIPV system to have the reduction of the peak power demand and hence to improve the power capacity of peak cut.

• Journal of Hydrogen and New Energy
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• v.22 no.6
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• pp.852-858
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• 2011

This paper is aiming to estimate the mutual influence of the stack cooling performances with the operation modes of the thermal management system for the hydrogen fuel cell vehicles. The heat capacity of the thermal management system was measured by varying the operating modes such as stack cooling heat exchanger only (Mode 1), stack cooling and electric devices cooling heat exchangers (Mode 2), and stack cooling and electric devices cooling heat exchangers with an operation of the condenser (Mode 3).As the results, Performance of the thermal management system (TMS) at Mode 3 decreased up to 34.0%, compared with the result of the Mode 1. In addition, in order to optimize the performance of TMS, the entropy change of stack cooling heat exchanger using irreversibility analysis technique was analyzed with the relationship between entropy generation and entering air velocity of the thermal management system.

• Journal of Power Electronics
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• v.15 no.5
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• pp.1318-1328
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• 2015

The photovoltaic (PV) power conditioning system for small-scale applications has gained significant interest in the past few decades. However, the standalone mode of operation has been rarely approached. This paper presents a two-stage multi-level micro-inverter topology that considers the different operation modes. A multi-output flyback converter provides both the DC-Link voltage balancing for the multi-level inverter side and maximum power point tracking control in grid connection mode in the PV stage. A modified H-bridge multi-level inverter topology is included for the AC output stage. The multi-level inverter lowers the total harmonic distortion and overall ratings of the power semiconductor switches. The proposed micro-inverter topology can help to decrease the size and cost of the PV system. Transient analysis and controller design of this micro-inverter have been proposed for stand-alone and grid-connected modes. Finally, the system performance was verified using a 120 W hardware prototype.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.6
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• pp.442-450
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• 2020

A small-signal modeling approach for a three-level boost (TLB) converter and a design methodology for a double-loop controller are proposed in this study. Conventional modeling of TLB converters involves three state variables. Moreover, TLB converters have two operation modes depending on the duty ratio. Consequently, complex mathematical calculations are required for controller design. This study proposes a simple system modeling method that uses two state variables, unlike previous methods that require three state variables. Analysis shows that the transfer functions of the two operation modes can be expressed as identical equations. This condition means that the linear feedback controller can be applied to all operational ranges, that is, for full duty ratios. The design method for a double-loop controller using a PI controller is presented in step-by-step sequences. Simulation and experimental verifications are conducted to verify the effectiveness of the small-signal analysis and control system design.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.4
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• pp.349-360
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• 2006

Controller for doubly-fed induction-type wind generation system should be designed with mechanical power on blade. The controller in this paper consists of upper level controller and lower level controller. The upper level controller determines operating modes according to mechanical input power and calculates proper reference values. There are 4 operating modes - minimum speed control, variable torque control, torque limit control and idle mode. The lower level controller performs current regulated PWM control of rotor-side converter and grid-side inverter. A wind turbine simulator is implemented using doubly-fed induction-type generator and DSP based back-to-back converter to verify the performance of designed controller experimentally.