Ki-Seok Jeong

Coordinated Voltage and Reactive Power Control Strategy with Distributed Generator for Improving the Operational Efficiency

This study proposes a voltage and reactive coordinative control strategy with distributed generator (DG) in a distribution power system. The aim is to determine the optimum dispatch schedules for an on-load tap changer (OLTC), distributed generator settings and all shunt capacitor switching on the load and DG generation profile in a day. The proposed method minimizes the real power losses and improves the voltage profile using squared deviations of bus voltages. The results indicate that the proposed method reduces the real losses and voltage fluctuations and improve receiving power factor. This paper proposes coordinated voltage and reactive power control methods that adjust optimal control values of capacitor banks, OLTC, and the AVR of DGs by using a voltage sensitivity factor (VSF) and dynamic programming (DP) with branch-and-bound (B&B) method. To avoid the computational burden, we try to limit the possible states to 24 stages by using a flexible searching space at each stage. Finally, we will show the effectiveness of the proposed method by using operational cost of real power losses and voltage deviation factor as evaluation index for a whole day in a power system with distributed generators.

EMTP simulation of a STATCOM-Shunts-OLTC coordination for local voltage control

This paper proposes coordinative control method between STATCOM installed within substation and other reactive power resources including Shunt Reactors and Shunt Capacitors and OLTC. Voltage/Reactive power control has various difficult aspects to control because of analysis and system dynamics error. This coordinative control method suggests practical algorithm regarding system voltage and reactive power status which is easy to implement in substation basis. In normal status, STATCOM-Shunts-OLTC are in operation. The proposed algorithm is tested and verified in EMTP/RV. And this is expected to be applied to control multiple reactive power devices combined with SCADA/EMS system.

Conceptual Design for Lifetime Test System for LED Headlamps on Rolling Stock

LED luminaires as a lighting system have attracted much research attention due to their high efficiency and long lifetimes. However, disappointing outcomes have been noted in terms of performance levels and lifetimes as compared to desired system requirements in practice due to certain electrical and thermal characteristics of LEDs. LM-80 and TM-21 established by IESNA are the best known standards for lifetime test procedures and estimation techniques. However, they only handle LED light sources without guaranteeing the LED luminaire in a reliability test. They also operate for more than 6,000 hours and undergo various stresses, such as the operating current and temperature. Therefore, a lifetime standard for LED luminaires has not yet been established. This paper proposes a conceptual design of a lifetime test system for LED headlamps depending on the operating environment. Eventually, this method can assist with evaluations of the validity of lifetime standard tests of LED headlamps.

The System Design and Demonstration for Autonomous Microgrid Operation

The autonomous microgrid is a system that is autonomously operated depending on the grid and internal load condition, without the operator’s intervention. In this study, a control algorithm for the microsource and an operation algorithm for the microgrid are proposed to realize the autonomous microgrid system. In addition, a microgrid operation system based on the operation algorithm is proposed. The electromagnetic transient program is used by the proposed microsource control algorithm for simulation, and the validity of the algorithm is verified. The proposed operation system is verified based on a case study using a simulator and test devices.

Performance Assessment of a Temperature Control Unit used in a Lifecycle Testing System for LED Headlamps on Locomotives

현재 대부분 LED제품의 수명특성은 LED소자의 수명시험으로 추정하고 있으나 완제품 단계의 수명특성이 소자단계에서 측 정된 수명특성과 동일하다 볼 수 없어 현재의 LED소자 단계의 수명 시험은 완제품 단계의 운용과 수명을 예측하는 데는 한계 를 가진다[1]. LED 조명제품의 최종 수명은 LED 패키지, 방열판, 전원공급장치 등의 특성을 반영해야 함으로, 기존의 LED 패 키지 단위의 수명시험 뿐만 아니라 완제품 단위에서 수명특성을 확인하는 연구가 필요하다[2]. 특히, 철도, 선박 등의 특수 분 야에 적용되는 수만~수십만 칸델라(cd: candela) LED전조등의 경우 방열설계에 따른 온도 특성과 전원공급장치의 구동전류 유 지 기술이 실제 수명에 중요한 요소로 작용하고 있다. 최근 전력전자 기술을 발달로 LED모듈로 공급되는 정전류원의 전력품질이 향상되어 안정적인 전류 공급이 가능케 되었다. 기존의 할로겐램프와 동등한 수준의 성능을 갖는 LED광원은 입력전력의 약 85%가 열에너지로 변환되며, 발열로 인해 수명감 소, 성능저하 등의 문제를 발생시킨다[3]. 따라서 LED제품의 수명은 주로 온도에 의해 결정되므로, 원하는 기준온도를 에이징 기간 동안 허용범위 내로 유지하도록 제어장치의 설계 및 검증이 요구된다. 현재까지 LED광원/모듈/패키지 등에 대한 구체적인 수명시험 방법은 북미조명학회의 LM-80에서 미국 LED제조업체들의 방 대한 수명시험 데이터를 바탕으로 제시하고 있으며, 온도유지에 대한 기준온도 및 허용범위 등에 대한 기준을 포함하고 있다 [4,5]. LED제품의 경우 기준온도 및 허용범위에 대한 규정이 마련되지 않았기 때문에 사전에 온도특성시험을 통해 기준값을 마 Abstract LED light sources have been known to have a long life and good energy efficiency compared to traditional light sources. Recently, headlamps using LED light sources have ensured the forward visibility and safe operation of high-speed rolling stock. However, assessing the lifespan of LED headlamps based on real test data is not easy because it depends on the multiple stress factors such as a fixed driving current, junction temperature, vibration and so on. Generally, LED headlamps have failed before their advertised life span mainly due to temperature. Thus, the performance assessment of a temperature control unit should be done before a life cycle test of LED headlamps. This study attempted to develop a prototype temperature control module for a lifecycle test system using a commercial LED headlight and verified the system through experiments.

Optimal Voltage and Reactive Power Scheduling for Saving Electric Charges using Dynamic Programming with a Heuristic Search Approach

With the increasing deployment of distributed generators in the distribution system, a very large search space is required when dynamic programming (DP) is applied for the optimized dispatch schedules of voltage and reactive power controllers such as on-load tap changers, distributed generators, and shunt capacitors. This study proposes a new optimal voltage and reactive power scheduling method based on dynamic programming with a heuristic searching space reduction approach to reduce the computational burden. This algorithm is designed to determine optimum dispatch schedules based on power system day-ahead scheduling, with new control objectives that consider the reduction of active power losses and maintain the receiving power factor. In this work, to reduce the computational burden, an advanced voltage sensitivity index (AVSI) is adopted to reduce the number of load-flow calculations by estimating bus voltages. Moreover, the accumulated switching operation number up to the current stage is applied prior to the load-flow calculation module. The computational burden can be greatly reduced by using dynamic programming. Case studies were conducted using the IEEE 30-bus test systems and the simulation results indicate that the proposed method is more effective in terms of saving electric charges and improving the voltage profile than loss minimization.

An Under-Frequency Load Shedding Scheme Design for a Large Steelworks with Self-Generation System

This paper presents a load-shedding scheme for a large steelworks with several self-generation units. The power system of the steelworks can be separated from a utility grid in case of disturbances. Also, some substations with generators in the steelworks can be isolated due to the tie line tripping. These situations cause an under-frequency events as the result of the imbalance between generation and load. A system stabilizing controller (SSC) system is the core of the proposed load shedding scheme for the frequency stabilization. The SSC system performs a pre-calculation for load-shedding (LS) quantity before an event and a post-calculation to provide against a deficient load-shedding in the pre-calculated load-shedding. The back-up protection system is used to counteract situations in which the SSC system does not operate normally. Also, the load-shedding by frequency calculation is carried out for subsequent disturbance such as an additional generator tripping. The hardware based proposed scheme has been applied to the steelworks. The several under-frequency events causing a load-shedding are examined through the transient stability analysis by using ETAP. The simulation results show that the proposed scheme effectively stabilizes the frequency within the continuous frequency operation range of generators.

Optimal Capacity Determination of BESS for Customer using Investment Cost and Electric Cost

Abstract - This study presents the estimation method for the optimal capacity of BESS(Battery Energy Storage System) in order to reduce the electric charges of common consumer. The daily optimal charge and discharge plan of BESS which satisfies the given constraints is established using linear programming through the change of rated output/rated capacity of the time that shows the electric charges in the highest reduced rate has been selected. There will be a problem to compare only reduced rate because the bigger the rated capacity, the more reduced rate is increased. Therefore, rated output/rated capacity of the time when the reduced amount of electric charges for a year is higher than the investment cost of BESS was selected.Key Words : Electric cost savings rate, Optimal charge and discharge control, Battery energy storage system, Investment cost* Dept. of Electrical Engineering, Kyungpook National University, Korea.** Metropolitan Transit System Research Division, Korea Railroad Research Institute, Korea*** Dept. of Electrical Engineering, Koje College, Korea.† Corresponding Author : Dept. of Electrical Engineering, Kyungpook National University, Korea.E-mail : ysbaek@knu.ac.krReceived : November 24, 2014; Accepted : January 26, 2015

A Study on Cooperative Control Method to Secure the Reactive Power in the Power System

This paper proposes the cooperative control method between reactive power compensation devices for securing the reactive reserve power of the FACTS in the power system. The Cooperative control consists of the two different methods, such as concurrent and sequence control. This proposed method is used different method according to the normal and abnormal state. The concurrent control is applied for maintaining the bus voltage in desired level when the load of power system has been remarkably increased or decreased. This control method is operated at once by calculating necessary active power capacity based on the voltage difference to each substation voltage and reference voltage in the power system. The sequence control has been used to secure momentary reactive power. The momentary reactive power is processed with the fast control characteristics. Therefore, this control has been managed for improving the voltage stability in the power system. Also, it has been demonstrated by the PSS/E and the Python programs.

Coordination of UPFC and Reactive Power Sources for Steady-state Voltage Control

Abstract - This paper presents a new method of local voltage control to achieve coordinative control among UPFC(Unified Power Flow Controller) and conventional reactive compensation equipments , such as switched-shunt and ULTC(Under-Load Tap Changing) transformer. Reactive power control has various difficult aspects to control because of difficulty of system analysis. Recently, the progress of power electronics technologies has lead to commercial availability of several FACTS(Flexible AC Transmission System) devices. The UPFC(Unified Power Flow Controller) simultaneously allows the independent control of active and reactive power flows as well as control of the voltage profile. When conventional reactive power sources and UPFC are used to control system voltage , the UPFC reacts to the voltage deviation faster than the conventional reactive power sources. Keeping reactive power reserve in an UPFC during steady-state operation is always needed to provide reactive power requirements during emergencies. Therefore, coordination control among UPFC and conventional reactive power sources is needed. This paper describe the method to keep or control the voltage of power system of local area and to manege reactive power reserve using PSS/E with Python. The result of simulation shows that the proposed method can control the local bus voltage within the given voltage limit and manege reactive power reserve. Key Words : Coordinative control, UPFC, ULTC, Switched-shunt, PSS/E, Python† 교신저자, 정회원 : 경북대 전기공학과 시간강사․공박E-mail : pjh@ee.knu.ac.kr* 정 회 원 : 경북대 대학원 전자전기컴퓨터학부 박사과정** 펠로우회원 : 경북대 전기공학과 교수․공박***정 회 원 : 거제대 선박전기과 조교수․공박 접수일자 : 2011년 3월 2일 최종완료 : 2011년 4월 26일