• KEPCO Journal on Electric Power and Energy
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• v.6 no.4
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• pp.419-425
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• 2020

DC distribution system has been evaluated as an excellent one in comparison with existing AC distribution network because it needs fewer power conversion stages and the full capacity of the equipment can be used without consideration for power factor. Recently, research and development on the implementation of DC distribution networks have been progressed globally based on the rapid advancement in power-electronics technology, and the technological developments from the viewpoint of infrastructure are also in progress. However, to configure a distribution network which is a distribution line for DC, more accurate and rapid introduction of analysis technology is needed for the monitoring, control and operation of the system, which ensure the system run flexible and efficiently. However, in case of a bipolar DC distribution network, there are two buses acting as slack buses, so the Jacobian matrix cannot be configured. Without solving this problem, DC distribution network cannot be operated when the network is unbalanced. Therefore, this paper presented a comprehensive method of analysis with consideration of operating elements which are directly connected between neutral electric potential caused by the unbalanced of load in DC distribution network with bipolar structure.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.948-953
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• 2011

In AC railway feeding system, three phase received from the network is changed to two phase power sources with different phases. The main circuit breaker installed train is automatically open by track signal when the train passes the neutral section. In order to continuously supply power source to train, the changeover system was used in Japan. Therefore, the train is able to operate under powering condition when it was passing through the neutral section. We investigated the control method to reduce the inrush current flowing main transformer in train. To examine the inrush current and operate the static semiconductor switch such as thyristor, we manufactured the small scale the changeover system and carried out performance tests.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.577-580
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• 2010

In case of connecting the weak AC system, a detailed attentions are needed. In particular, since HVDC system can control the flow of AC network freely, have to contain the range of stability and safe operation range. This paper deals with HVDC control algorithms, which are operated within 1 second on viewpoint of time domain, that is, transient stability. The target of HVDC introduced in this paper is Jindo-Cheju HVDC system, which will be operated at 2011. The introduced algorithm can be actually implemented to Jindo-Cheju HVDC system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.381-384
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• 1997

This paper describes the method of diagnosing the degradation by void defects of insulator inside in operation. Needle-shape void specimens, made from LDPE, were used to generate an electrical tree under ac voltage. The method uses a neural network system with input signal of AE patterns. AE pattern consists of the pulse count and average amplitude according to the phase angle. After the learning process was over, unknown emission patterns were put into the network. It was shown that the network discriminates the void deflects well. The effectiveness of the neural network system for partial discharge recognition was shown.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.9
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• pp.1514-1522
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• 2010

This paper dealt with the HVDC concept design of Cheju HVDC #2, which will be operated at 2011. The concept design is the first step of HVDC design procedures and the contents which were presented in this paper, are HVDC operation conditions based on the reliability of HVDC and AC network conditions, short circuit ratios(SCR) to related to HVDC stability and overvoltage and interactions between AC network including FACTS and generators, and HVDC system. The results of this paper are a keystone of HVDC #2 design.

• Proceedings of the KIEE Conference
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• 2002.07d
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• pp.2158-2160
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• 2002

In this paper, we designed the adaptive fuzzy controller(AFLC) using neural network and tabu search. We tuned the weights of neural network changing adaptively input/output gain of fuzzy logic controller and the gain of fuzzy logic controller using tabu search. To evaluate the proposed method's effectiveness, we apply the proposed AFLC to the speed control of an actual AC servomotor system. The experimental results show that AFLC has the better control performance than PI controller in terms of settling time, rising time and overshoot.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.8
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• pp.420-426
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• 2003

This paper deals with the effect of exciter parameters on the torsional stress of turbine-generator. The excitation system effects on the AC network stability and the turbine-generator stress. However. it, until now, have not reported that any parameter among exciter parameters is related to the stability and the stress. In order to verify those CIGRE HVDC model was used. Since the AC network with HVDC has the voltage stability problem due to big capacitor, the worst condition to analyze the stress can considered. The EMTDC program is used for the simulation studies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.817-825
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• 2017

The AC-common bus microgrid system can overcome several weaknesses of the DC microgrid system by interconnecting the DC/AC inverters used for renewable energy with an AC network. Nevertheless, the unbalanced loads inherent in the electric power systems of island and small communities can deteriorate the performance of the AC microgrid system. This is because of the limited voltage regulation capability and mixed power flow in the voltage source inverter. In order to overcome the unbalanced load condition, this paper proposes a voltage and current control algorithm for the 4-leg inverter based on the single phase d-q control method, as well as the modeling of the voltage controller using Matlab/Simulink S/W. From the S/W simulation and experiment of the 250KW proto-type inverter, it is confirmed that the proposed algorithm is a useful tool for the design and operation of the AC microgrid system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.12 no.3
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• pp.139-146
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• 1998

In this paper, we proposed the hybrid intelligent control method for fast response time and precise speed control of the AC Servo system. The proposed system first used the fuzzy-neural network control methods for fast response time and when the error reaches the preset value, used the PLL control method. In order to verify the advantage of he proposed method, the system is implemented. The results of the simulation and the experiment of speed control to use the 3-phase induction motor as a plant, we verified excellency of the proposed control method to compare with the conventional fuzzy-neural network control method.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.659-665
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• 2023

The exciter of a ship generator adjusts the magnetic flux through excitation current control to maintain the output terminal voltage constant. The voltage controller inside the exciter typically uses a proportional integral control method. however, the response characteristics determined by the gain and time constant produce unwanted output owing to an inappropriate setting value that can reduce the quality and stability of power within the ship. In this study, a neural network circuit is learned using stable input/output data that can be obtained through the AC4A type exciter model provided by IEEE, and the simulation is performed by replacing the existing proportional integral control type voltage controller with the learned neural network circuit controller. Consequently, overshooting was improved by up to 9.63% compared with that of the previous model, and excellence in stable response characteristics was confirmed.