• 전력전자학회논문지
• /
• 제18권1호
• /
• pp.103-109
• /
• 2013

The conventional LCL filter design method of the utility interactive inverter considers only harmonics attenuation of the current injected to the grid. However, in case of utility-interactive inverter with critical load the voltage quality of the critical load should also be considered for LCL filter design. Also, considering cost and volume of LCL filters. it is important to have minimum values of inductance and capacitance as far as the harmonic standards are satisfied. In this paper a LCL filter design method is proposed to satisfy not only the harmonic standards of the grid current during the grid-connected mode but the voltage quality of the critical load during grid-connected mode and stand-alone mode. With the proposed method optimized values of LCL filters could be obtained by applying weighting factor to voltage ripple across the critical load, inductor volume, amount of reactive current and system bandwidth.

• Journal of Power Electronics
• /
• 제16권4호
• /
• pp.1396-1406
• /
• 2016

A novel controller design is presented for the recently proposed electric springs (ESs). The dynamic modeling is analyzed first, and the initial Bode diagram is derived from the s-domain transfer function in the open loop. The design objective is set according to the characteristics of a minimum phase system. Step-by-step optimizations of the Bode diagram are provided to illustrate the proposed controller, the design of which is different from the classical multistage leading/lagging design. The final controller is the accumulation of the transfer function at each step. With the controller and the recently proposed δ control, the critical load voltage can be regulated to follow the desired waveform precisely while the fluctuations and distortions of the input voltage are passed to the non-critical loads. Frequency responses at any point can be modified in the Bode diagram. The results of the modeling and controller design are validated via simulations. Hardware and software designs are provided. A digital phase locked loop is realized with the platform of a digital signal processor. The effectiveness of the proposed control is also validated by experimental results.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 1999년도 추계종합학술대회 논문집
• /
• pp.232-235
• /
• 1999

In this paper, we present a coprocessor that can operate with ARM microprocessors. The coprocessor supports IEEE 754 standard single- and double-precision binary floating point arithmetic operations. The design objective is to achieve minimum-area, low-power and acceleration of processing power of ARM microprocessors. The instruction set is compatible with ARM7500FE. The coprocessor is written in verilog HDL and synthesized by the SYNOPSYS Design Compiler. The gate count is 38,115 and critical path delay is 9.52ns.

• Structural Engineering and Mechanics
• /
• 제66권5호
• /
• pp.583-594
• /
• 2018

A theoretical formulation based on the linearized potential theory, the Descartes' rule and the extremum optimization method is presented to calculate the critical distance of lifting points of the fully balanced hoist vertical ship lift, and to study pitching stability of the ship lift. The overturning torque of the ship chamber is proposed based on the Housner theory. A seven-free-degree dynamic model of the ship lift based on the Lagrange equation of the second kind is then established, including the ship chamber, the wire rope, the gravity counterweights and the liquid in the ship chamber. Subsequently, an eigenvalue equation is obtained with the coefficient matrix of the dynamic equations, and a key coefficient is analyzed by innovative use of the minimum optimization method for a stability criterion. Also, an extensive influence of the structural parameters contains the gravity counterweight wire rope stiffness, synchronous shaft stiffness, lifting height and hoists radius on the critical distance of lifting points is numerically analyzed. With the Runge-Kutta method, the four primary dynamical responses of the ship lift are investigated to demonstrate the accuracy/reliability of the result from the theoretical formulation. It is revealed that the critical distance of lifting points decreases with increasing the synchronous shaft stiffness, while increases with rising the other three structural parameters. Moreover, the theoretical formulation is more applicable than the previous criterions to design the layout of the fully balanced hoist vertical ship lift for the ensuring of the stability.

• 조명전기설비학회논문지
• /
• 제25권8호
• /
• pp.106-113
• /
• 2011

The conventional grounding impedance of a counterpoise is calculated as a function of the length of the counterpoise by use of the distributed parameter circuit model with an application of the EMTP(Electromagnetic Transient Program). The adequacy of the distributed parameter circuit model is examined and verified by comparison of the simulated and the measured results. The conventional grounding impedance of the counterpoise is analyzed for the first short stroke and subsequent short stroke currents. As a result, the simulated results show that the minimum conventional grounding impedance gives at a specified length of the counterpoise. The shorter the time taken to reach the peak of injected currents, the shorter the length of the counterpoise having the minimum conventional grounding impedance. We also present the critical lengths of the counterpoise for short stroke currents as a function of soil resistivity. Based on these results, it is necessary to compute the length of the counterpoise in a specified soil resistivity which satisfies both the low conventional grounding impedance requirement whilst also providing a suitable ground resistance in order to obtain an economical design and installation of the counterpoise.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1999년도 하계학술대회 논문집 C
• /
• pp.1221-1223
• /
• 1999

The safety loads in a nuclear power plant perform a critical function to plant safety. The design of the electrical auxiliary system should ensure the availability and adequacy of the power supply, and therefore, the frequency and voltage relaying schemes should be installed on the system to monitor and protect against the degraded system condition. If unforeseen contingencies degrade the switchyard frequency and voltage to below the minimum values, the safety related bus should properly be transferred to alternate power source. This paper presents guidelines associated with the protection of nuclear power plants during frequency/voltage decay and the steady-state and dynamic analysis of auxiliary power system that should be performed to support the degraded voltage relay(second level undervoltage relay) setting.

• Journal of Mechanical Science and Technology
• /
• 제15권1호
• /
• pp.10-20
• /
• 2001

The leak before break(LBB) concept is difficult to apply to a structure with a thin tube that is immersed in a water environment. A heat exchanger in a nuclear power plant is such a structure. The present paper addresses an application of the LBB concept to a heat exchanger in a nuclear power plant. The minimum leaked coolant amount(approximately 37.9 liters) containing the radioactive material which can activate the radiation detector device installed in near the heat exchanger is assumed. A postulated initial flaw size that can not grow to a critical flaw size within the time period to activate the radiation detector is justified. In this case, the radiation detector can activate the warning signal caused by coolant leakage from initially postulated flaws of the heat exchanger. The nuclear plant can safely shutdown when this occurs. Since the postulated initial flaw size can not grow to the critical flaw size, the structural integrity of the heat exchanger is not impeded. Particularly the informational scenario presented in this paper discusses an actual nuclear plant.

• 한국작물학회지
• /
• 제47권2호
• /
• pp.127-131
• /
• 2002

Critical nitrogen concentration (Nc), which is defined as the minimum % N in shoots required to maintain the maximum growth rate of top dry weight (W) at any time, was determined for rice plant. Using two rice varietal groups, japonica varieties and an indica $\times$ japonica "Dasanbyeo", 18 data points fulfilling the statistical criteria for determining Nc were obtained through eight N-fertilization experiments over two years at Suwon (37$^{\circ}$16'N), Korea. Nc dilution curve for each variety was obtained by fitting the Nc-W relationship to power function. However, The critical nitrogen curves for the two variety groups were not different statistically. Thus, a Nc dilution curve was fitted for the Nc data points pooled over the two variety groups and proposed in rice as: Nc=4.08, where W＜1.73 t h $a^{-1}$ , Nc=5.197 $W^{0.425}$3/ ($R^2$=0.964), where 1.73 t h $a^{-1}$ ＜W＜12 t h $a^{-l}$. The Nc for W＜1.73 t h $a^{-l}$ were estimated as a constant value of 4.08%, the mean value of the maximum N concentration for N-limiting condition and the minimum N concentration for N non-limiting condition. The model for Nc is applicable to diagnosing the nitrogen nutrition status during the rice growth period from emergence to heading stage. The Nc curve well discriminated the 144 data points between the N limiting and the N non-limiting groups regardless of varieties, cultural methods, and years.-limiting groups regardless of varieties, cultural methods, and years.

• 대한전기학회논문지:전력기술부문A
• /
• 제50권12호
• /
• pp.575-583
• /
• 2001

Dynamic Voltage Restorer(DVR) which is installed between the supply and a critical load can restore voltage disturbances in distribution system. The restoration is based on injecting the same voltages as voltage sags. The ideal restoration is compensation to make the load voltages be unchanged. But voltage restoration involves real power or energy injection and the capability of energy storage is limited. So it must be considered how injection energy can be minimized and voltages can be made close to the voltages before fault. This paper describes conventional restoration techniques, which draw minimum energy from the DVR in order to correct a given voltage sag or swell. And this paper proposes a new concept of restoration technique to inject minimum energy. The proposed method is based on the definition of voltage tolerance in load side. Hence using the proposed method a particular disturbance can be corrected with less amount of storage energy compared to those of conventional methods.

• Ocean Systems Engineering
• /
• 제14권2호
• /
• pp.141-156
• /
• 2024

The turbine system converts the kinetic energy of water flow to electricity by rotating the rotor in a restricted waterway between the seabed and free surface. A turbine system's immersion depth and rotation direction are significantly critical in the turbine's performance along with the shape of the rotor. This study has investigated the hydrodynamic performance of the Savonius hydrokinetic turbine (SHT) according to the immersion depth and rotation direction using computational fluid dynamics (CFD) simulations. The instantaneous torque, torque coefficient, and power coefficients are calculated for the immersion ratios Z/D ranging [0.25, 3.0] and both clockwise (CW) and counterclockwise (CCW) rotations. A flow visualization around the rotor is shown to clarify the correlation between the turbine's performance and the flow field. The CFD simulations show that the CCW rotation produces a higher power at shallow immersion, while the CW rotation performs better at deeper immersion. The immersion ratio should be greater than the minimum of Z/D=1.0 to obtain the maximum power production regardless of the rotation direction.