Woo-Kyu Chae

Cooperative operation method of two battery systems at Microgrid system

The grid-interconnected Microgrid must be able to operate without the utilitys grid to supply electricity in case of outage. To operate in standalone mode, the Microgrid must control electricity demand or supply to maintain the frequency. The Microgrid EMS (Energy Management System) could control supply and demand with the AGC (Auto Generation Control) function using a communication line. Note, however, that the period of AGC is too slow to maintain the frequency if there is rapid variation in loads or generation. Moreover, the transition of operation mode could fail if there is too much power flow at PCC (Point of Common Coupling). In this paper, we propose a method of improving the stability of the grid-interconnected Microgrid using BESS (Battery Energy Storage System) and super capacitor. The cooperative control method between BESS and super capacitor uses droop, which is used at the generator. BESS could operate as UPC (Unit Power Control) or FFC (Feeder Flow Control) depending on Microgrids operation strategy. We simulate the cooperative control method using PSCAD/EMTDC to verify the validity of the method. As a result, Microgrids stability is improved using the cooperative control method, and the life span of BESS could be prolonged.

Application of Directional Over Current Protection Schemes Considering the Fault Characteristics in the Distribution System with Dispersed Generation

Penetration of distributed generator(DG) to power distribution system can cause malfunction of existing protection schemes. Because grid interconnected DG can contribute fault currents and make bidirectional current flows on the system, fault contributions from DG can cause an interference of protection relay operation. Therefore, over current protection device of the distribution system with DGs need directional protection schemes. In this paper, improved directional protection algorithms are proposed for the distribution system with DG considering their fault characteristics. And than, these directional protection algorithms are tested and validated in various fault conditions. From the simulation results, it can be seen that the proposed directional protection algorithms are practically efficient for the radial distribution system with DG.

Autonomous Micro-grid Design for Supplying Electricity in Carbon-Free Island

In island and backcountry areas, electrical power is usually supplied by diesel generators. It is difficult for small scale diesel generators to have an economy of scale owing to the usage of fossil fuels to produce electricity. Also, there is a problem of carbon dioxide emissions that brings some environmental pollution to the entire region of the area. For solving those, this paper proposes a design method of autonomous micro-grid to minimize the fossil fuels of diesel generator, which is composed of diesel generator, wind turbine, battery energy storage system and photovoltaic generation system. The proposed method was verified through computer simulation and micro-grid operation system.

Frequency Control Method of Grid Interconnected Microgrid Operating in Stand Alone Mode

Microgrid is a new electrical energy system that composed of various generators, renewable energy, batteries and loads located near the electrical customers. When Microgrid is interconnected with large power system, Microgrid don`t need to control the frequency. But in case of the outage or faults of power system, Microgrid should control the frequency to prevent the shutdown of Microgrid. This paper presents the frequency control methods using the droop function, being used by synchronous generators and EMS(Energy Management System). Using droop function, two battery systems could share the load based on locally measured signals without any communications between batteries. Also, we suggest that EMS should control the controllable distributed generators as P/Q control modes except batteries to overcome the weakness of droop function. Finally we suggest the two batteries systems to prolong the battery`s life time considering the economical view. The validation of proposed methods is tested using PSCAD/EMTDC simulations and field test sites at the same time.

Optimal interconnection device for distributed energy resources of customer

This paper proposes a smart switch panel (SSP) that can link distributed generations more economically and actively to improve power quality for customers, prevent power failure through independent operation in case of power failure in electric power systems (EPS), and trade electricity with Smart Grid operation systems as they become more widespread. For the economical interconnection of distributed generations and to reduce installation spaces, a power converter was installed in the switch panel, and the power converter was proposed in a form wherein diverse distributed generations share the DC link and inverter. A static transfer switch (STS) was installed so that customers can prevent power failure through independent operation even in case of EPS failure. An intelligent electronic device (IED) was installed so that power can be exchanged with EPS or nearby customers and to enable protection control so that all current standards for the interconnection of distributed generations are met.

An Optimization of the Distributed Generator Combination for Microgrid using Linear Programming

MG(Microgrid) is a small power supply system located on-site that can supply both the electricity and the hot-water simultaneously. Engineering S/W is requested to construct Microgrids economically. We developed Engineering S/W that can combine DERs (Distributed Energy Resources) most economically using the linear programming and estimate of the economic. Developed S/W was programed using GAMS(General Algebraic Modeling System) and it is composed of the optimal DER combination module and forecasting module of renewable energy`s output. We embody it based on MS Excel considering the user`s convenience and we show its validity through a case study. We think that developed S/W will be very useful for planning MGs and energy supply.

A Fault Analysis on AC Microgrid with Distributed Generations

As the penetration of different types of renewable energy sources (RES) and energy storage systems (ESS) increases, the importance of stability in AC microgrid is being emphasized. Especially, RES and ESS which are operated using power electronics have difference in output characteristics according to control structures. When faults like single-line-to-ground fault or islanding operation occur, this means that a fault should be interpreted in different way. Therefore, it is necessary to analyze fault characteristics in AC microgrid in case of grid-connected mode and standalone mode. In this paper, the fault analysis for AC microgrid is carried out using PSCAD/EMTDC and an overvoltage problem and the countermeasures were proposed.

Automatic Generation Control System for Operation Mode in Microgrid

The microgrid concept assumes a cluster of loads and microsources operating as a single controllable system that provides a new paradigm for defining the operation of distributed generation. This system can be operated as both grid-connected mode and islanded mode. In other words, the microgrid can be operated to meet their special need; such as economics in steady state and local reliability in islanded mode due to the grid fault. This paper presents the AGC (Automatic Generation Control) method for microgrid with EMS (Energy Management System).

A Study on the Application of SVR at the Distribution Line Interconnected with Wind Turbine

It is expected that distribution system, interconnected with wind turbines, would experience the voltage problem due to WT`s output. But most papers just consider this problem using the simulation or the theory only. In this paper, we verify this problem through the measurement at the distribution system and wind turbine. We explain the method for voltage management at distribution system. And we verify that the voltage of D/L interconnected with WTs could not be maintained properly using pole transformer`s tap only. We consider some method to solve this problem and we propose the installation of SVR(step voltage regulator). Finally we show this method`s validity through the simulation.

A Study on the Limit Analysis of the LED Lighting Subsidy Program Considering the Perspective of Individual Building Clients

Various DSM (Demand Side Management) programs have been developed and carried out to use the limited energy resources of human-beings reasonably. LED lighting is one of essential DSM programs and the development of technologies is ongoing vigorously. Recently, one-person households have been increased and the electricity consumption pattern is different with conventional households because residents live as a single. On the other hand, owners of the one-person households tend to not prefer to install high efficient appliances due to the cost increasement. Therefore, the existing DSM subsidy programs should be revaluated so that the owners decide to install high efficient appliances.