Changhee Cho

Cooperative Control Strategy of Energy Storage System and Microsources for Stabilizing the Microgrid during Islanded Operation

In this paper, the cooperative control strategy of microsources and the energy storage system (ESS) during islanded operation is presented and evaluated by a simulation and experiment. The ESS handles the frequency and the voltage as a primary control. And then, the secondary control in microgrid management system returns the current power output of the ESS into zero. The test results show that the proposed cooperative control strategy can regulate the frequency and the voltage, and the secondary control action can contribute to improve the control capability.

Development of Hardware In-the-Loop Simulation System for Testing Operation and Control Functions of Microgrid

This paper proposes a hardware in-the-loop simulation (HILS) system as a new method to develop and test control algorithms and operation strategies for a microgrid. The HILS system is composed of a real-time digital simulator (RTDS) for real-time simulation of the microgrid, a prototype microgrid management system (MMS) under test, and a communication emulator for interface between the prototype MMS and the RTDS. The prototype MMS is designed to operate microsources of microgrid and to control power flow at the point of common coupling (PCC) in the grid-connected mode, and voltages and frequency in the islanded mode of the microgrid. The MMS is tested in the grid-connected mode and in the islanded mode, respectively, to show the validation of the proposed HILS system.

Development of Simulator System for Microgrids with Renewable Energy Sources

This paper deals with the design and testing of a simulator system for microgrids with distributed generations. This system is composed of a Real Time Digital Simulator (RTDS) and a power amplifier. The RTDS parts are operated for real time simulation for the microgrid model and the distributed generation source model. The power amplifiers are operated for amplification of the RTDSs simulated output signal, which is a node voltage of the microgrid and distributed generation source. In this paper, we represent an RTDS system design, specification and test results of a power amplifier and simulation results of a PV (Photovoltaic) system and wind turbine system. The proposed system is applicable for development and performance testing of a PCS (Power Conversion System) for renewable energy sources.

New Ideas for a Soft Synchronizer Applied to CHP Cogeneration

This paper provides new ideas for the synchronization between an electric power system and a synchronous generator. If an individual ac generator is to be operated with another ac power system, the synchronization is an essential process for the parallel operation. For small combined heat and power cogeneration, the synchronization is a very frequent event and one of the most important jobs in daily operation. There are several types of traditional devices that support or control the breaker closure within the synchronizing criteria. However, the actual break closing is not controlled exactly on a zero point phase-angle difference. In this paper, we introduce new ideas that will lead two ac systems to a smooth and soft synchronization. With these ideas, a soft synchronizer that provides the perfect phase-angle matching is realized. To verify the effectiveness of this newly proposed soft synchronizer, we had conducted simulation studies using MATLAB as well as experimental tests with an actual synchronous diesel generator.

Power control of a grid-connected hybrid generation system with photovoltaic/wind turbine/battery sources

A grid-connected hybrid distributed generation system, composed of PV(photovoltaic) array, wind turbine and BESS (battery energy storage system), is proposed for various power transfer functions to the distribution network. The proposed system has several operation modes which are normal operation, power dispatching, and power averaging, according to coordinate control of the BESS and grid inverter. PV array and wind turbine are individually controlled to operate at the maximum power point for the most use of renewable energy. The BESS operates as an energy buffer to flexibly shift the generation from the renewable energy sources without excessively frequent shifts between battery charging and discharging. A grid interface inverter regulates the generated power injection into the grid. Developed prototype system design and experimental results are presented to demonstrate the performance and to validate the proposed system during its operation modes.

Establishment of a pilot plant for KERI microgrid system based on power IT development program in Korea

This paper introduces a microgrid system having been developed in Korea. Firstly, the Korean Power IT (Information Technology)” development program and its environment are shortly described including the concept of Korean microgrid and characteristics of its components. And then, the microgrid system, the functions of its components and test facilities are explained which are established in KERI (Korea Electrotechnology Research Institute). Finally, some system operation results according to two operational modes are shown.

Real time digital simulator based test system for microgrid management system

This paper presents a real time digital simulator based test system as a new method for testing microgrid management system (MMS). This system is composed of a real time digital simulator and a developed communication emulator. Real time digital simulator runs a simulation case for microgrid model and distributed generation source model. Communication module emulates communication functions of micro-sources in microgrid by transmitting the simulated signals to MMS. The MMS controls operation of micro-sources to control the power flow at the point of common coupling (PCC) and the voltage and frequency of microgrid. A prototype MMS was tested for standalone and grid-connected operation to verify the validation of the developed HILS system.

Study on the Dynamic Synchronizing Control of An Islanded Microgrid

Abstract - A microgrid is an aggregation of multiple distributed generators (DGs) such as renewable energy sources, conventional generators, and energy storage systems that provide both electric power and thermal energy. Generally, a microgrid operates in parallel with the main grid. However, there are cases in which a microgrid operates in islanded mode, or in a disconnected state. Islanded microgrid can change its operational mode to grid-connected operation by reconnection to the grid, which is referred to as synchronization. Generally, a single machine simply synchronizes with the grid using a synchronizer. However, the synchronization of microgrid that operate with multiple DGs and loads cannot be controlled by a traditional synchronizer, but needs to control multiple generators and energy storage systems in a coordinated way. This is not a simple job, considering that a microgrid consists of various power electronics-based DGs as well as alternator-based generators that produce power together. This paper introduces the results of research examining an active synchronizing control system that consists of the network-based coordinated control of multiple DGs. Consequently, it provides the microgrid with a deterministic and reliable reconnection to the grid. The proposed method is verified by using the test cases with the experimental setup of a microgrid pilot plant..Key Words : Microgrid, Synchronization, Static transfer switch, Energy storage system, Microgrid central controller*정 회 원 : 한국전기연구원 선임연구원** 정 회 원 : 한국전기연구원 책임연구원***정 회 원 : 부산대 공대 전기공학과 교수† 교신저자, 정회원 : 한국전기연구원 책임연구원E-mail : chcho@keri.re.kr 접수일자 : 2011년 4월 8일 최종완료 : 2011년 5월 24일

Network-based synchronizing control of a practical microgrid

This application track paper describes the network-based distributed control technology that is applied to practical microgrid application. The paper is dealing with network-based remote sensors, central calculation of control offset signals, and the remote control of distributed generation resources. Through the dynamic modeling and experimental test results, characteristics of the proposed control scheme is shown and the performance is verified.

Development of the integrated controllers for small CHP cogeneration system

Small CHP (Combined Heat & Power) cogeneration system is the dispersed generation system under 1 MW that produces the electricity as well as the heat energy. Currently it is getting the spotlights as a highly efficient power generation system by the fact that it can utilize the previously wasted heat into the usable energy. As a result, the demand for more efficient, peak shaving cogeneration system as well as the high performance, multi-functional controllers has increased. In this paper, we introduce the features of a newly developed 325 kVA CHP cogeneration system and the integrated controllers that supervise the entire system operation.