• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.3
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• pp.624-631
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• 2011

In this paper, the RCF method is used in sensitivity analysis problems of the discrete power systems including both series FACTS equipments such as TCSC in transmission lines and generator controllers such as Exciter and PSS in generator terminal. To apply the RCF method in small signal stability problems of discrete power systems, state transition equations of controllers and TCSC are derived and the sensitivity calculation algorithm using state transition equations in discrete time domain is devised. The results of eigenvalue analysis showed that the variations of eigenvalues after periodic switching operations of TCSC can be calculated exactly by the RCF method and the change of firing angles in TCSC have important effect to determine the stability of power systems.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.6
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• pp.569-576
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• 2011

This paper proposes a new dead time compensation method for a PWM inverter. Recently, PWM inverters are extensively used for industry applications, such as ac motor drives, distributed grid-connected systems and a static synchronous compensator (STATCOM). Nonlinear characteristics of the switch and the inverter dead time cause a current distortion and deterioration of power quality. The dominant harmonics in the output current are the $5^{th}$ and $7^{th}$ harmonics in the stationary frame, and the $6^{th}$ harmonics in the synchronous rotating frame. In this paper, a resonant controller which compensates the $6^{th}$ harmonics in the synchronous rotating frame is proposed. This method does not require any off-line experimental measurements, additional hardware and complicated mathematical computations. Furthermore, the proposed method is easy to implement and does not cause any stability problem.

• Journal of the Korean Solar Energy Society
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• v.23 no.3
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• pp.45-53
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• 2003

This paper presents a study on the power factor improvement of V47- 660 [kW] Wind Turbine Generation System (WTGS) in Jeju wind farm, as a model system in this paper. In this system, the power factor correction is controlled by the conventional method with power condensor banks. Also, this system has only four bank steps, and each one capacitor bank step is cut in every one second when the generator has been cut in. This means that it is difficult to compensate the reactive power exactly according to the variation of them. Actually, model system has very low power factor in the area of low wind speed, which is almost from 4 to 6 [m/s]. This is caused by the power factor correction using power condenser bank. To improve the power factor in the area of low wind speed, we used the static var compensator(SVC) using current controlled PWM power converter using IGBT switching device. Finally, to verify the proposed method, the results of computer simulation using Psim program are presented to support the discussions.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.179-190
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• 2010

This paper describes a new stochastic heuristic algorithm in engineering problem optimization especially in power system applications. An improved particle swarm optimization (PSO) called adaptive particle swarm optimization (APSO), mixed with simulated annealing (SA), is introduced and referred to as APSO-SA. This algorithm uses a novel PSO algorithm (APSO) to increase the convergence rate and incorporate the ability of SA to avoid being trapped in a local optimum. The APSO-SA algorithm efficiency is verified using some benchmark functions. This paper presents the application of APSO-SA to find the optimal location, type and size of flexible AC transmission system devices. Two types of FACTS devices, the thyristor controlled series capacitor (TCSC) and the static VAR compensator (SVC), are considered. The main objectives of the presented method are increasing the voltage stability index and over load factor, decreasing the cost of investment and total real power losses in the power system. In this regard, two cases are considered: single-type devices (same type of FACTS devices) and multi-type devices (combination of TCSC, SVC). Using the proposed method, the locations, type and sizes of FACTS devices are obtained to reach the optimal objective function. The APSO-SA is used to solve the above non.linear programming optimization problem for better accuracy and fast convergence and its results are compared with results of conventional PSO. The presented method expands the search space, improves performance and accelerates to the speed convergence, in comparison with the conventional PSO algorithm. The optimization results are compared with the standard PSO method. This comparison confirms the efficiency and validity of the proposed method. The proposed approach is examined and tested on IEEE 14 bus systems by MATLAB software. Numerical results demonstrate that the APSO-SA is fast and has a much lower computational cost.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.114-123
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• 2018

Recently, as one of the countermeasures to reduce carbon dioxide($CO_2$) for global warming problems, operation methods in micro-grid systems replacing diesel generator with renewable energy sources including wind power(WP) and photovoltaic(PV) system have been studied and presented in energetic manners. However, it is reported that some operation problems in micro-grid systems without diesel generator for carbon-free island are being occurred when large scaled WP systems are at start-up. To overcome these problems, this paper proposes an operation strategy in micro-grid systems by adapting control devices such as CVCF(constant voltage constant frequency) ESS(energy storage system) for constant frequency and voltage regulation, load control ESS for balancing demand and supply and SVC(static-var compensator) for reactive power compensation. From the simulation results based on the various operation scenarios, it is confirmed that the proposed operation strategy in micro-grid systems without diesel generators is a useful tool to perform a stable operation in micro-grid systems without diesel generator and also make a contribution to reduce carbon dioxide in micro-grid systems.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.6
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• pp.626-633
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• 2005

This paper proposes a new 2MVA SSFG(Sag Swell Flicker Generator) injecting voltage by using series inverter. The proposed SSFG composes series inverter, DC capacitor as energy storage, rectifier and voltage clamp circuit. This SSFG is designed to generate typical power disturbances, such as voltage sag/swell, over/under voltage and voltage flicker. Also it is designed to generate unexpected voltage phase jumping waveform by controlling the series inverter. In this paper, three kinds of control methods for the proposed 2MVA SSFG we investigated by PSIM simulation. Also typical voltage sag, swell, flicker waveforms are implemented by adopting effective control method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.3
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• pp.57-66
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• 2001

This paper resents a control approach for designing a fuzzy-PI controller for a synchronous generator excitation and SVC system A combination of thyristor-controlled reactors and fixed capacitors (TCR-FC) type SVC is recognized as having the must fiexible control and high speed response, which has been widely utilized in power systems, is considered and designed to improve the response of a synchronous generator, as well as controlling the system voltage A Fuzzy-PI controller for SVC system was proposed in this paper. The PI gain parameters of the proposed Fuzzy-PI controller which is a special type of PI ones are self-tuned by fuzzy inference technique. It is natural that the fuzzy inference technique should be barred on humans intuitions and empirical knowledge. Nonetheless, the conventional ones were not so. Therefore, In this paper, the fuzzy inference technique of PI gains using MMGM(Min Max Gravity Method) which is very similar to humans inference procedures, was presented and allied to the SVC system. The system dynamic responses are examined after applying all small disturbance condition.