• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.15 no.2
• /
• pp.137-143
• /
• 2003

In the forming of an integrated system of radiant floor cooling and dehumidifying, chilled coil can be used for cooling and dehumidification. Therefore, it is necessary to find the efficient control method which can eliminates latent load efficiently. This study has been conducted to find this method by dividing the dehumidification system into 3 types according to the control variables and analyzing characteristics of each system. To prevent the floor surface condensation, the amount of condensation can be manipulated by water temperatures, water flow rates in chilled coil, and air flow rates passing by it. So dehumidification system control can be divided into constant air flow control and variable air flow control. Regarding dehumidification control, variable air flow control, which eliminates latent load rather than sensible load, is preferable to constant flow control.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.60 no.1
• /
• pp.1-7
• /
• 2011

Active power control scheme for distributed generation in microgrid consists of feeder flow control and unit power control. Feeder flow control is more useful than the unit power control for demand-side management, because microgrid can be treated as a dispatchable load at the point of common coupling(PCC). This paper presents detailed descriptions of the feeder flow control scheme for the hybrid system in microgrid. It is divided into three parts, namely, the setting of feeder flow reference range for stable hybrid system operation, feeder flow control algorithm depending on load change in microgrid and hysteresis control. Simulation results using the PSCAD/EMTDC are presented to validate the inverter control method for a feeder flow control mode. As a result, the feeder flow control algorithm for the hybrid system in microgrid is efficient for supplying continuously active power to customers without interruption.

• Proceedings of the KIEE Conference
• /
• 1994.11a
• /
• pp.3-5
• /
• 1994

It is shown that the power flow considering the voltage characteristic of the composite load has some difference comparing with conventional load flow in this paper. When the load flow is used in a study of the static voltage stability, it is necessary to consider the voltage characteristic of load, since the composite load of a typical power system bas constant power, constant current, and constant impedance characteristic. The load is modeled to a polynomial form in here, and used in solving the load flow problem. In this way, the effect which the voltage characteristic of the load has on several voltage collapse proximity indicator based on sensitivities is compared with the conventional load flow, or with another load model having a different voltage characteristic. In this paper, the voltage collapse proximity indicator using the sensitivity of real power for transmission loss is also proposed, and compared with other indicators.

• KIEE International Transactions on Power Engineering
• /
• v.4A no.2
• /
• pp.73-78
• /
• 2004

This paper proposes a framework for determining the minimum load shedding for restoring solvability. The framework includes a continuation power flow (CPF) and an optimal power flow (OPF). The CPF parameterizes a specified outage from a set of multiple contingencies causing unsolvable cases, and it traces the path of solutions with respect to the parameter variation. At the nose point of the path, sensitivity analysis is performed in order to achieve the most effective control location for load shedding. Using the control location information, the OPF for locating the minimum load shedding is executed in order to restore power flow solvability. It is highlighted that the framework systematically determines control locations and the proper amount of load shedding. In a numerical simulation, an illustrative example of the proposed framework is shown by applying it to the New England 39 bus system.

• Proceedings of the KIEE Conference
• /
• 2001.07a
• /
• pp.116-118
• /
• 2001

The load bus voltage is controlled by not only using several control device but also generation bus voltage adjustment. This paper deals with a load bus voltage control problem which used optimization and load flow technique. The usage of proposed control algorithm is verified through the comparison with normal load flow on the IEEE 14 sample system. The proposed control algorithm can be used to optimal decision of position and capacity for voltage control device.

• The KSFM Journal of Fluid Machinery
• /
• v.6 no.3 s.20
• /
• pp.28-35
• /
• 2003

This paper presents analysis results for the effect of power control strategies on the part load performance of gas turbine based power generation systems utilizing exhaust heat of the gas turbine such as combined cycle power plants and regenerative gas turbines. For the combined cycle, part load efficiency variations were compared among different single shaft gas turbines representing various technology levels. Power control strategies considered were fuel only control and IGV control. It has been observed that gas turbines with higher design performances exhibit superior part load performances. Improvement of part load efficiency of the combined cycle by adopting air flow modulation was analyzed and it was concluded that since the average combined cycle performance is affected by the range of IGV control as well as its temperature control principle, a control strategy appropriate for the load characteristics of the individual plant should be adopted. For the regenerative gas turbine, it is likewise concluded that maintaining exhaust temperature as high as possible by air flow rate modulation is required to increase part load efficiency.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.12
• /
• pp.1039-1046
• /
• 2002

To investigate the characteristics of orifice as an expansion devices, the experimental apparatus was made and experiments are being peformed using R22 and R290. The main idea of this control method of refrigerant flow rate with coupled orifices is to control the ON/OFF state of T and Ball type orifice corresponding to the subdivided region of thermal load. When system requires minimum thermal load, both T and Ball type orifices are closed, but refrigerant can flow through small hole of T type orifice. In regular thermal load, when ball type orifice is closed, T type orifice is opened and mass flow rate increase more than OFF state of T type orifice, due to large diameter. In maximum thermal load, both T and Ball type orifices are open and the much refrigerant can flow. The flow characteristics on T type orifice and parallel-combined orifice are obtained in the subdivided region of thermal load.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.3
• /
• pp.738-750
• /
• 1994

The load-sensing hydraulic system which was developed to improve energy efficiency of conventional hydraulic systems has its own properties. The instability of system responses, linearity of a servo valve, robustness for variation of external load, and dynamic interference between hydraulic motors are such properties which have much to do with control properties of the system. The load-sensing hydraulic system has instability tendancy because the load-sensing mechanism makes a positive feedback loop between the motor part and the pump part. A flow property of the servo valve can be said to be linear because the flow through the valve has nothing to do with a load pressure and the flow is strictly proportional to a valve opening which is adjusted by a valve command signal. The resultant control property can be said to be robust because the steady-state control performance is independent to the load actuated on the motor shaft. In the case when one pump simultaneously drives more than two hydraulic motors, the pump outlet pressure is determined by a hydraulic motor of the largest load pressure among all of the hydraulic motors, and, thus, the other motors are dominated by the largest load pressure. That is, the other motors can be said to be interfered by the motor of the largest load pressure.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.22 no.2
• /
• pp.156-165
• /
• 2014

This paper is the first investigation on the effect of flow control methods on the part load performance in a spark ignition engine. For comparison of the methods, two control devices, port throttling and masking, were applied to a conventional engine without any design change of the intake port. Steady flow evaluation shows that steady flow rates per unit opening area and swirl ratio are very low compared with the port throttling and saturated from mid-stage valve lift, however, swirl increases slightly as the lift is higher in case of 1/4 masking control. In the part load performance, the effect of simple port throttling on lean misfire limit expansion is limited and insufficient; on the other hand a masking improves the limit considerably without any port modification for increasing swirl. Also the results show that the intake flow control improves the combustion with following two mechanisms: stratification induced by the combination of the flow pattern and the fuel injection timing attribute to ignition ability and the intensified flow ensure fast burn. In addition fuel consumption reduces under the flow controls and the reduction rate is different according to the operation conditions and control methods. At the Stoichiometric and/or low speed and low load the throttling method is more advantageous; however vice versa at lean and high load condition. Finally, the throttling is more efficient for HC reduction than masking, on the other side the NOx emissions increase under the masking and decrease under the port throttling compared with conventional port scheme.

• 제어로봇시스템학회:학술대회논문집
• /
• 2005.06a
• /
• pp.2203-2206
• /
• 2005

A load flow and short circuit fault simulation of AC electrified railway distribution systems is presented with DIgSILENT PowerFactory software. Load flow of electrified railways distribution system with concerning multi train lines and dynamic characteristics of train load is studied for different time laps. The dynamic characteristics of train load in starting and braking conditions with different starting and stopping times and its moving positions makes the load flow complicated so there is a great need in studying the effects of electrified railways on load flow. Short circuit fault transients is also studied and simulated for both power system or traction distribution system and their effects on the operation of the train sets is investigated.