Dae-Seok Rho

Optimal Operation Methods of Protection Devices in Distribution Systems with PV Systems

This paper deals with the technical problems of protection devices in distribution systems with connected photovoltaic systems by developing a test device of protection coordination for photovoltaic systems. In order to analyze the operational characteristics of the protection devices in a distribution system connected with photovoltaic systems, in which bi-directional power flow could be supplied, this paper develops a test device that is composed of a model distribution system, protection device, and model PV system. By performing a simulation for operational characteristics of the protection devices based on the test device, this paper proposes a malfunction mechanism for the protection devices. The simulation results show that this paper is practical and effective for the technical guideline for the PV systems.

Optimal Operation System of Step Voltage Regulator in Primary Feeders with Distributed Generations

This paper deals with the optimal operation algorithm of SVR(Step Voltage Regulator) which is located with primary feeders and proposes the optimal operation system to evaluate customer voltage. The existing algorithm of SVR adapts the constant sending voltage method, which may cause the power quality problems such as overvoltage and under voltage variations in case where the distributed generations are interconnected with the primary feeders. Therefore, this paper proposes the optimal algorithm of LDC method for SVR using least square method to obtain the optimal setting values. Also, this paper presents the optimal evaluation system based on the former algorithm. The simulation results according to the types and capacities of distributed generations shows the effectiveness.

Development of State of Charge and Life Cycle Evaluation Algorithm for Secondary Battery

This paper deals with the state of charge(SOC) and life cycle evaluation algorithm for lead-acid battery, which is essential factor of the electric vehicle(EV) and the stabilization of renewable energy in the smart grid. In order to perform the effective operation of the lead-acid battery, SOC and life cycle evaluation algorithm is required. Specific gravity with the change of electrolyte temperature inside battery case should be obtained to evaluate the SOC of lead-acid battery, however it is difficult to measure the electrolyte temperature of sealed type lead-acid battery. To overcome this problem, this paper proposes the equation of thermal transmission to compensate internal temperature of the lead-acid battery. Also, it is difficult to exactly evaluate the life cycle of battery, depending on the operation conditions of lead-acid battery such as charging and discharging state, self discharging rate and environmental issue. In order to solve the problem, this paper presents the concept for gravity accumulation of charge and discharge cycle, which is the value converted at . By using the proposed algorithm, this paper propose the test device based on the Labview software. The simulation results show that it is a practical tool for the maintenance of lead-acid battery in the field of industry.

A Study on Fault Characteristics of Wind Power in Distribution Feeders

Abstract Korea Ministry of Knowledge Economy has estimated that wind power (WP) will be occupied 37% in 2020 and 42% in 2030 of the new energy sources, and also green energies such as photovoltaic (PV) and WP are expected to be interconnected with the distribution system because of Renewable Portfolio Standard (RPS) starting from 2012. However, when a large scale wind power plant (over 3[MW]) is connected to the traditional distribution system, protective devices (mainly OCR and OCGR of re-closer) will be occurred mal-function problems due to changed fault currents it be caused by Wye-grounded/Delta winding of interconnection transformer and %impedance of WPs turbine. Therefore, when Double-Fed Induction Generator (DFIG) of typical WP‘sGenerator is connected into distribution system, this paper deals with analysis three-phase short, line to line short and a single line ground faults current by using the symmetrical components of fault analysis and PSCAD/EMTDC modeling. Key Words :

A Study on the Countermeasure Algorithm for Power System Disturbance in Large Scale Fuel Cell Generation System

Recently, fuel cell generation system with high energy efficiency and low CO2 emission is energetically interconnected with distribution power system. Especially, MCFC(molten carbonate fuel cell) operating at high temperature conditions is commercialized and installed as a form of large scale power generation system. However, it is reported that power system disturbances such as harmonic distortion, surge phenomenon, unbalance current, EMI(Electromagnetic Interference), EMC (Electromagnetic Compatibility) and so on, have caused several problems including malfunction of protection device and damage of control devices in the large scale FCGS(Fuel Cell Generation System). Under these circumstances, this paper proposes countermeasure algorithms to prevent power system disturbances based on the modelling of PSCAD/EMTDC and P-SIM software. From the simulation results, it is confirmed that proposed algorithms are useful method for the stable operation of a large scale FCGS.

A Study on the Modeling of Step Voltage Regulator and Energy Storage System in Distribution System Using the PSCAD/EMTDC

In order to maintain customer voltage within allowable limit(220±13V), tap operation of SVR(step voltage regulator) installed in primary feeder could be carried out according to the scheduled delay time(30 sec) of SVR. However, the compensation of BESS(battery energy storage system) is being required because the customer voltages during the delay time of SVR have a difficultly to maintain within allowable limit when PV system is interconnected with primary feeder. Therefore, this paper presents modeling of SVR to regulate voltage with the LDC(line drop compensation) method and modeling of BESS to control active and reactive power bi-directionally. And also, this paper proposes the coordination control modeling between BESS and SVR in order to overcome voltage problems in distribution system. From the simulation results based on the modeling with the PSCAD/EMTDC, it is confirmed that proposed modeling is practical tool for voltage regulation analysis in distribution system.

Development of Evaluation Simulator of New Power Sources Using the LabVIEW Software

This paper deals with a evaluation simulator which is composed of distribution system simulator, PV systems simulator, and control and monitoring systems with the LabVIEW S/W. The simulator can analyze the customer voltage characteristics of normal conditions, considering the 3 parameters of the introduction capacity for PV systems, system configuration and load factor. Also, the simulator can provide the analysis of the power quality problems in distribution systems, when new power sources like photovoltaic (PV) systems are interconnected. By performing the simulation for power quality operation characteristic, this paper presents the optimal countermeasures for power quality for the new distributed power sources(NDS).

A Study on the Optimal Method for Malfunction of Protection Devices in Distribution Systems Interconnected with Photovoltaic Systems

Recently, new dispersed generation systems such as photovoltaic, wind power, fuel cell etc. are energetically interconnected and operated in the distribution systems, as one of the national projects for alternative energy with the provision against oil crisis. The technical guidelines on the interconnection of dispersed generation systems have been established and conducted positively. However, protection devices (Re-closer) in primary feeder of distribution system interconnected with photovoltaic generation may cause problems with mis-operation, and then many customers could have problems like an interruption. So, this paper presents the optimal method to minimize the impact of interruption, using both the symmetric method and MATLAB/SIMULINK. And, also this paper shows the effectiveness of proposed method by simulating at the real distribution systems.

A Study on the Voltage Stabilization Method of Distribution System Using Battery Energy Storage System and Step Voltage Regulator

In order to maintain customer voltages within the allowable limit(220±13V) as much as possible, tap operation strategy of SVR(Step Voltage Regulator) which is located in primary feeder, is widely used for voltage control in the utilities. However, SVR in nature has operation characteristic of the delay time ranging from 30 to 150 sec, and then the compensation of BESS (Battery Energy Storage System) during the delay time is being required because the customer voltages in distribution system may violate the allowable limit during the delay time of SVR. Furthermore, interconnection of PV(Photovoltaic) system could make a difficultly to keep customer voltage within the allowable limit. Therefore, this paper presents an optimal coordination operation algorithm between BESS and SVR based on a conventional LDC (Line Drop Compensation) method which is decided by stochastic approach. Through the modeling of SVR and BESS using the PSCAD/EMTDC, it is confirmed that customer voltages in distribution system can be maintained within the allowable limit.

A Study on the Coordination Control Algorithm of Step Voltage Regulator and Battery Energy Storage System for Voltage Regulation in Distribution System

In order to maintain customer voltages within allowable limit() as much as possible, tap operation strategy of SVR(Step Voltage Regulator) installed in distribution system is very important, considering the scheduled delay time(30 sec) of SVR. However, the compensation of BESS(Battery Energy Storage System) during the delay time of SVR is being required because the customer voltages in distribution system interconnected with PV(Photovoltaic) system have a difficultly to be kept within allowable limit. Therefore, this paper presents the optimal voltage stabilization method in distribution system by using coordination operation algorithm between BESS and SVR. It is confirmed that customer voltage in distribution system can be maintained within allowable limit().