Young-Sik Baek

Improvement of a power quality of microgrid system interconnected to distribution system in emergency condition

In todays world, according as interest about renewable energy source rises, many researches are progressing about energy source development and power distribution system configuration for improving renewable energy sources efficiency. The microgrid is small power system that consists of several consumers loads and small size Distributed resources and accomplishes one independent system. It is operated by interconnecting with power distribution system and could be islanding operation according to situation. Therefore, the control of microgrid makes microgrid can be connected to the power distribution system without equipment correction of power distribution system, and can compensate voltage quality and must satisfy dynamic request of loads as active and reactive power are controlled independently. Specially, when consumers load includes sensitive loads, consumer is going to expect very high reliability from microgrid. In this paper, we studied about effects that get to power distribution system relationship emergency condition this microgird using EMTP/RV modeling and simulation. And we proposed microsources control algorithm and simulated to improve power quality that is supplied in microgird interior load in emergency situation of power distribution system. This shows that microgird can provide local high quality power supply or voltage compensation ability.

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.

Coordination Control of Voltage Between STATCOM and Reactive Power Compensation Devices in Steady-State

This paper proposes a new coordinated voltage control scheme between STATCOM (Static Synchronous Compensator) and reactive power compensation devices, such as shunt elements(shunt capacitor and shunt reactor) and ULTC(Under-Load Tap Changer) transformer in a local substation. If STATCOM and reactive power compensators are cooperatively used with well designed control algorithm, the target of the voltage control can be achieved in a suddenly changed power system. Also, keeping reactive power reserve in a STATCOM during steady-state operation is always needed to provide reactive power requirements during emergencies. This paper describes the coordinative voltage control method to keep or control the voltage of power system in an allowable range of steady-state and securing method of momentary reactive power reserve using PSS/E with Python. In the proposed method of this paper, the voltage reference of STATCOM is adjusted to keep the voltage of the most sensitive bus to the change of loads and other reactive power compensators also are settled to supply the reactive power shortage in out range of STATCOM to cope with the change of loads. As the result of simulation, it is possible to keep the load bus voltage in limited range and secure the momentary reactive power reserve in spite of broad load range condition.

Performance Verification and Improvement of UHF Sensor for the Lncreasement of the Partial Discharge Detection Reliability

Abstract - GIS(Gas Insulated Switchgear) is important power apparatus which have strong dielectric strength, supply electric power and is a part of the power system. Most substation type is configured as GIS. Recently, because of continuous increasement of GIS demand resulted from high quality & big capacity of electric power, the necessity of the preventive & diagnosis system is being expanded gradually. GIS partial discharge occurred on the UHF band is detected effectively by the method to IEC 60270 that recommend to be able to detect the apparent minimum discharge, 5 pC. Additionally, the UHF sensor should be installed to detect PD signal if Partial discharge signal, 5 pC occur in every part of GIS. Currently PD diagnosis system applying UHF sensor for GIS with various voltage level like 154 kV, 345 kV, 765 kV have been operated. And it is necessary to measure and analyze insulation breakdown phenomenon of inside GIS exactly. In this paper, we proposed Fat-dipole patch UHF sensor that is developed and more sensitive, excellent wide-range characteristic than the exising UHF sensor. And we performed KERI (Korea Electrotechnology Research Institute) reference test, which showed the excellent result for the all tests.Key Words : GIS(Gas Insulated Switchgear), Fat-dipole patch, PD(Partial Discharge), UHF sensor†Corresponding Author : Dept. of Electronics and Electrical Engineering, Kyungpook National University, Korea.E-mail : ysbaek@knu.ac.kr*Dept. of Electronics and Electrical Engineering, Kyungpook National University, Korea.**Hyosung Corporation Power System Performance UnitReceived : August 12, 2014; Accepted : September 23, 2014

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.

Development of power system stabilization program using optimization method

Various protective equiptments are used for the power system control and protection. Numerous facilities are monitored at the same time in real time and introduction of optimization method and analysis of the method are required for generation control and facility management considering the demand fluctuations. However, the existing system analysis programs are difficult to link with the other sw and there are some problems with user convenience. To solve these problems the present conditions of the system are figured out in real time and the equipment insert method was estimated by optimization method, and the system that showed the system analysis program is developed. PSS/E has been used as system anlysis program for stabilizing system development which applied the optimization. method and Python language is applied in order to link the input and output values with the DB automatically. Lastly, DLL of matlab has been made included in C++ for solving the objective function using opmization method.By linking this to DB, power flow was calculated in PSS/E and the result was represented by Intouch screen.

Optimal Operation of Reactive Power Compensation Devices for Voltage Control of Emegency Status

This paper proposes a method for solving running cost problem by minimizing switching reactive power compensation devices. An objective function was modeled by calc ulating the weighting value of cost, and a solution was derived using ILP. This paper suggests optimal coordinative control method between FACTS, Shunt Reactors, Capacitors and OLTC. Therefore, it is valuable for decision maker in determini ng order and capacity of devices which gaining a voltage stabilization. As a result, the objectives of voltage stabiliza tion and cost minimization were achieved simultaneously. This realizes the economic efficiency of the system. We start by showing how to solve systems of linear equations using the language of pivots and tableaus. The effectiveness of this technique is demonstrated in modified PSS/E MIGUM 45 bus system. The simulation results show the effectiveness of this algorithm by comparing the outcome withseveral established methods.

Performance verification and improvement of the frequency analysis unit for GIS Preventive & Diagnostic Monitoring System

Abstract – This paper shows the design improvement and test model of FAU (Frequency Analysis Unit) in PDD (Partial Discharge Diagnosis system) for 800kV GIS (Gas Insulated Switchgear). We found some problems during operation of previous FAU, such as the aging of fiber-optic converter that can cause communication error, the malfunction of signal analysis circuit etc. And then we solved those problems by design improvement and verified the performance through type test. To monitor partial discharge, the performance of UHF sensor is important but the performance of frequency analysis unit is also very important. So we solved communication error, the malfunction of signal analysis circuit and then increased the operation reliability of FAU by improving fiber-optic converter and signal analysis circuit. Accredited testing laboratory carried out the performance verification test according to performance test criteria and procedure of reliability test standards, IEC-60225, 61000 and 60068 etc. We confirmed the test results which correspond with the performance test criteria.Key Words : GIS, PDMS, PD, UHF (Ultra High Frequency), FAU (Frequency analysis Unit)† Corresponding Author : Dept. of Electronics and Electrical Engineering, Kyungpook National University, Korea.E-mail : ysbaek@knu.ac.kr* Dept. of Electronics and Electrical Engineering, Kyungpook National University, Korea.** Hyosung Corporation Power System Performance UnitReceived : December 18, 2014; Accepted : January 29, 2015

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