Won-Wook Jung

Operation Schemes of Smart Distribution Networks With Distributed Energy Resources for Loss Reduction and Service Restoration

The integration of Distributed Energy Resources (DERs) into the future Smart Distribution Network (SDN) has challenging issues regarding the successful development of smart grids. The SDN offers new opportunities in the improvement of the efficiency of power distribution networks. The DERs will be distributed in the existing distribution networks, interconnected in customer areas and operated on its own schedule without communication to the control center of the existing distribution system. The DER units have both positive and negative effects regarding SDN operations. With the appropriate operation of the DER units in the SDN, losses can be reduced during normal operations and they can support local loads during abnormal conditions. Thus, the positive effects of the DER units need to be enabled in the SDN by adopting advanced operation schemes. In this paper, the smart control functions for the DER units in the SDN are defined and classified. In addition, the integration schemes for the SDN with DER units are introduced. The proposed operation strategies will be implemented into the Korean Smart Distribution Management System (KSDMS) as operation schemes used for loss reduction and service restoration. A sample case study shows the effectiveness of the proposed operation schemes to achieve smart operation functions for the SDN with DER units.

Simulation and Analysis of Existing MPPT Control Methods in a PV Generation System

Maximum Power Point Tracking (MPPPT) techniques are employed in PV systems to make full utilization of PV array output power which depends on solar irradiation and temperature. Recently, many MPPT algorithms and control schemes of PV system have been proposed, but different control methods and different PID controller parameters lead to different output efficiency and dynamic response. Therefore, in this paper, a PSCAD/EMTDC user defined module of the solar array is established to easily simulate its inherent characteristics with the basic specification data. Moreover, we also compare the advantages and weakness of the existing MPPT control methods by simulations to give a reference to the Grid-Connected Photovoltaic System (GCPS) designers.

The Coordinate Control Method of LTC Transformer and Capacitor Banks at Distribution Substation

The Load Tap Changing (LTC) transformer and Shunt Capacitor (SC) bank are major devices for voltage and reactive power control in a distribution substation. Thus, the coordination operation of a LTC transformer and a SC bank is required to achieve better voltage and reactive power compensation at a distribution substation in the same time. This paper proposes coordinate control method of LTC transformer and SC bank to achieve better voltage and reactive power compensation and operation times of these two devices in the same time. The mathematical formulations of the proposed coordinate control method are introduced. Sample case studies are shown to verify the effectiveness of the proposed coordinate control method.

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.

Development and test of conservation voltage reduction application for Korean Smart Distribution Management System

Korea Electric Power Corporation (KEPCO) developed a Korean Smart Distribution Management System (K-SDMS) to address many issues of distribution system control, including the lack of receptivity of distributed generations (DGs). Voltage-VAR control (VVC) program is one of the K-SDMS real-time mode applications. VVC calculates the references of voltage and reactive power control equipment, which minimize the power loss while satisfying a number of operational constraints. The VVC application is upgraded to have a new control objective, i.e. conservation voltage reduction (CVR). CVR is based on the simple premise that reduction of the voltage will lead to reduced energy consumption by the end-use loads. This paper presents the algorithm of developed CVR function and the test results. The CVR function calculates the references of the voltage control devices such that the bus voltages are maintained at as close to the lower operation limit as possible. Firstly, the system is divided into small sections. Secondly, the reactive power references of the DGs are determined such that the voltage profile of the section is flattened. Finally, the tap references of the on-load tap changers (OLTCs) and step voltage regulators (SVRs) are calculated. The effectiveness of the CVR is presented with case studies using the K-SDMS simulator.

Modeling and MPPT Control in DFIG-Based Variable-Speed Wind Energy Conversion Systems by Using RTDS

AbstractThe generating systems use Doubly-Fed Induction Generators (DFIGs) to achieve high conversion efficiency and to reduce the installation cost. This paper presents a modeling and Maximum Power Point Tracking (MPPT) control method of DFIG-based variable-speed wind energy conversion system. The generator considered is a wound rotor induction machine whose stator is connected directly to the grid and the rotor is fed through back-to-back Pulse-Width Modulation (PWM) converters. Stator flux-oriented vector control is applied to control the active and reactive current loops independently. The MPPT control method in a Wind Energy Conversion System (WECS) is proposed. The proposed control solution aims at driving the position of the operating point near to optimality. This is a very important aspect to maintain DFIGs efficiently in a variable wind speed. The wind generator is modeled in RSCAD program which is interfaced with the Real Time Digital Simulator (RTDS).

Development of simulation platform of distribution systems with DGs and SVR for voltage control studies

In this paper, we develop the simulation platform of the distribution systems with distributed generations (DGs). The detailed simulation models of a DG and a step voltage regulator (SVR) are developed as PSCAD user defined model (UDM). The control schemes of SVR and DGs to regulate the local voltages are proposed and implemented as a function block in the PSCAD platform. Some case studies to verify the effectiveness of the control schemes are performed in the developed simulation platform.

A Study on Optimal Planning of Microgrid with Actual Loading

AbstractMicroGrids are small power supply system located on-site that can supply both the electricity and the hot-water simultaneously. MicroGrid system that consists of Distributed Energy Resources system, such as wind, solar, fuel-cell and co-generation, has been developed greatly during the last 10 years. Its 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. For example this cell could be controlled as a single dispatchable load, which can respond in seconds to meet the needs of the transmission system. It can be also designed to meet their special need; such as, enhance local reliability, reduce feeder losses. This paper introduces the case study of engineering to construct Microgrid with actual loading in KEPRI