Jae-Sun Huh

A Study on the Application of a Superconducting Fault Current Limiter for Energy Storage Protection in a Power Distribution System

This paper presents the application of a superconducting fault current limiter to energy storage for protection in a power distribution system. An energy storage system is increasingly being used to help renewable energy resources integrate into the grid. It is important to keep an energy storage system interconnected with the grid without interruption and to supply electrical power to the grid. The main objective of this paper is to introduce a superconducting fault current limiter to keep the energy storage system from disconnecting from the grid when ground faults occur. Its effect is analyzed using transient simulation software.

Study on Voltage Unbalance Improvement Using SFCL in Power Feed Network With Electric Railway System

An electric railway system uses a single-phase source that is supplied through a Scott transformer from a three-phase transmission system. In addition, the electric railway system has rapidly changing load characteristics in time. An unbalance is generated owing to the rapidly changing large single-phase loads. Subsequently, the unbalanced load causes an unbalanced transmission line. A voltage unbalance in the source influences the power equipment by causing a reduction in the power generation capacity of the generator and a decrease in the output of the other facilities in the transmission line. In addition, many flexible ac transmission systems are applied to transmission lines to compensate for and control electric power. A voltage unbalance causes a control error in these systems. We propose the application of a superconducting fault current limiter to improve the voltage unbalance in a transmission system linked to a Scott transformer. In addition, we analyzed the effects of the proposed method using transient simulations.

A Study on Siting of HVAC Offshore Substation for Wind Power Plant using Submarine Cable Cost Model

Development of the technologies for offshore wind power is proceeding actively and the installation capacity is continuously increasing because of its many advantages in comparison with the land wind power. Accordingly, project for Southwestern 2.5GW offshore wind power plant is in progress in Korea. Design of electric power systems for offshore wind power plant is very important due to its high investment and operational costs. Hence, it needs to be designed in order to minimize costs. This way can be employed in determining the installation location of offshore substation for HVAC wind power plant. According to the offshore substation site, MV inter-array cable and HV export cable lengths vary and they change a total cost regarding submarine cable. This paper represents cost models with variables which are MV inter-array cable and HV export cable lengths to locate the offshore substation for HVAC wind power plant. It is classified into submarine cable installation cost, reactive power compensator installation cost, ohmic losses, and unsupplied energy cost. By minimizing a total cost, an appropriate installation site of the offshore substation is determined.Development of the technologies for offshore wind power is proceeding actively and the installation capacity is continuously increasing because of its many advantages in comparison with the land wind power. Accordingly, project for Southwestern 2.5GW offshore wind power plant is in progress in Korea. Design of electric power systems for offshore wind power plant is very important due to its high investment and operational costs. Hence, it needs to be designed in order to minimize costs. This way can be employed in determining the installation location of offshore substation for HVAC wind power plant. According to the offshore substation site, MV inter-array cable and HV export cable lengths vary and they change a total cost regarding submarine cable. This paper represents cost models with variables which are MV inter-array cable and HV export cable lengths to locate the offshore substation for HVAC wind power plant. It is classified into submarine cable installation cost, reactive power compensator installation cost, ohmic losses, and unsupplied energy cost. By minimizing a total cost, an appropriate installation site of the offshore substation is determined.

DC-link Voltage Control of HVDC for Offshore Wind Farm using Improved De-loading Method

This paper presents the DC voltage control method in DC link of High Voltage Direct Current(HVDC) for an offshore wind farm in Low Voltage Ride Through(LVRT) situation. Wind generators in an offshore wind farm are connected to onshore network via HVDC transmission. Due to LVRT control of grid side inverter in HVDC, power imbalancing in DC link is generated and this consequentially causes rising of DC voltage. A de-loading scheme is one of the method to protect the wind power system DC link capacitors from over voltage. But the flaw of this method is slow control response time and that it needs long recovery time to pre-fault condition after fault clear. Thus, this paper proposes improved de-loading method and we analyze control performance for DC voltage in LVRT control of HVDC for an offshore wind farm.

Output Control of Wind Farm Side Converter from DC Link for DC Voltage Stabilization with HVDC

This paper presents DC voltage recovery time improvement method in DC link of High Voltage Direct Current (HVDC) with offshore wind farm. The wind farm should be satisfied Low Voltage Ride Through(LVRT) control strategy when grid faults occur. The LVRT control strategy indicates actions which have to be executed according to the voltage dip ratio and the fault duration. However, The LVRT control strategy makes between wind farm and power system through DC Link voltage when grid fault occurs. The de-loading scheme is one of the method to control the DC voltage. But de-loading scheme need to long DC voltage recovery time. Thus, this paper proposes an improved de-loading scheme and we analysis DC voltage and active power reference through a simulation

Control Scheme Using Active Power Regulation for DC Voltage of VSC HVDC Under Unbalanced Voltage

Faced with unbalanced grid operation mode, the high voltage direct current (HVDC) based on voltage source converter (VSC) can be properly controlled by a dual current control scheme. For the modular multilevel converter (MMC) controlling the AC side current is able to limit the arm current which flows along the IGBT of submodule (SM) to rated current. However the limitation of the arm current results in leaving the control range of active power at MMC confined to below the rated capacity. As a result, limiting the arm current causes the problem that the DC side voltage of the HVDC can not be controlled to the reference value since MMC HVDC adjusts the DC side voltage through the active power. In this paper, we propose the algorithm adjusting the active powers of both MMCs to resolve the problem. The back-to-back MMC HVDC applying the algorithm is modeled by PSCAD/EMTDC to verify the algorithm.

Optimal Design of Power Grid and Location of Offshore Substation for Offshore Wind Power Plant

Abstract – This paper presents the methodology for optimal design of power grid for offshore wind power plant (OWPP) and optimum location of offshore substation. The proposed optimization process is based on a genetic algorithm, where the objective cost model is composed of investment, power loss, repair, and reliability cost using the net present value during the whole OWPP life cycle. A probability wind power output is modeled to reflect the characteristics of a wind power plant that produces electricity through wind and to calculate the reliability cost called expected energy not supplied. The main objective is to find the minimum cost for grid connection topology by submarine cables which cannot cross each other. Cable crossing was set as a constraint in the optimization algorithm of grid topology of the wind power plant. On the basis of this method, a case study is conducted to validate the model by simulating a 100-MW OWF.Key Words : GA optimization, Probabilistic wind power model, Offshore su bstation, Offshore wind power grid, Submarine cable crossing†Corresponding Author : School of Electrical Engineering, Soongsil University, KoreaE-mail : jckim@ssu.ac.kr* School of Electrical Engineering, Soongsil University Korea** KEPCO Research Institute, KoreaReceived : June 9, 2915; Accepted : June 25, 2015

A Study on the Adequate Capacity of Substation Transformer for Offshore Wind Farm

This study suggests the methodology to decide the number and adequate capacity of substation transformer in a large-scale offshore wind farm (OWF). The recent trend in transformer capacity of offshore substation is analyzed in many European offshore wind farm sites prior to entering the studies. In order to carry out the economic evaluation for the transformer capacity we present the cost models which consist of investment, operation, and expected energy not supplied (EENS) cost as well as the probabilistic wind power model of wind energy that combines the wind speed with wind turbine output characteristics for a exact calculation of energy loss cost. Economic assessment includes sensitivity analysis of parameters which could impact the 400-MW OWF: average wind speed, availability, discount rate, energy cost, and life-cycle.

New control scheme for a battery energy storage system for output stabilization of a wind generator

Wind power output has the characteristics of being intermittent and low quality, which have a negative effect on the spread of renewable energy sources. To solve these problems, energy storage systems (ESSs) are used. ESSs have demonstrated that high-quality power from renewable energy sources can be supplied through the charge and discharge operation of an ESS. In this paper, ESS control methods are studied to operate a power grid connected wind turbine with stable condition. First, we introduce an output smoothing method to mitigate the unstable system with a wind turbine, and then a moving average method is proposed to obtain the target output. An output-smoothing algorithm considering the constraints of a battery ESS (BESS) is presented. Additionally, this algorithm is simulated by MATLAB with actual wind turbine data.

The Study on Planning of EV Charging Facilities using Prevalence Estimates of EV in the Public Housing

Today, effort to reduce greenhouse gas emissions is to be strengthened worldwide. And environment-friendly vehicle is being magnified because of energy saving and minimization of environmental pollution. In the future, the construction of EV charging facilities will be needed for Prevalence of EV in the Public Housing. So in this paper, we survey and analyze data of power usage and owned vehicles on the existing public housing according to season, day and time. And, we reviewed appropriate configuration ratio according to three kind of case. Besides, we calculate Prevalence Estimates of EV and utilization factor based on analysis result. And finally, we try to study for case model.