• Journal of Power Electronics
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• 제13권5호
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• pp.854-860
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• 2013

The voltage variation problem at the point of common coupling (PCC) in a grid-connected wind turbine is investigated. The voltage variation problem is one of the most frequent power quality issues for the grid connection of large amounts of input power in a weak grid. Through the simplified modeling of the wind turbine and power network, the magnitude of PCC voltage variation is calculated by using the equivalent circuit parameters and output power of the wind turbine. The required amount of reactive power that can compensate the voltage variation is also presented analytically by using the vector diagram method. The proposed calculation and compensation method of the PCC voltage variation is verified by computer simulations and experiments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권5호
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• pp.1735-1754
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• 2022

The reliability and performance of WiFi need optimization because of the rising number of WiFi users day by day. A highlighted point is saving power while transmitting and receiving packets using WiFi devices. Wake-on-Wlan (WoW) is also implemented to improve energy consumption, but it also needs betterment. This paper will introduce universal ideas to transmit and receive packets using low-power technology like Bluetooth or BLE (Bluetooth low energy). While looking for power-saving ways in this research, WiFi connection and maintenance also take care using lesser power-consuming technology. Identifying different use-cases where low power technology can help save energy and maintain 802.11 connection is part of the research. In addition, the proposed method discuss energy saving with unicast and broadcast/multicast data. Calculation of power-saving and comparison with standalone WiFi usage clearly shows the effectiveness of the proposed method.

• Journal of Power Electronics
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• 제10권6호
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• pp.762-768
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• 2010

This paper describes the development of a new islanding detection method for inverter-based distributed generation systems, which uses a signal cross-correlation scheme between the injected reactive current and the power frequency deviation. The proposed method injects 1% of the reactive current to the rated current which brings about a negligible degradation of the power quality. It discriminates the islanding state, when the calculated cross-correlation index is larger than 0.5. The operational feasibility was verified through computer simulations with PSCAD/EMTDC software and experimental research with a hardware prototype. The proposed method can detect the islanding state without degrading the power quality at the point of common connection. Further study is required to overcome the cancellation of the injected reactive current from multiple distributed generation units interconnected with the utility grid.

• Journal of Power Electronics
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• 제17권2호
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• pp.522-532
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• 2017

This paper presents a novel integrated structure for a cascaded distribution static compensator (D-STATCOM) and distribution transformer for medium-voltage reactive power compensation. The cascaded multilevel converter is connected to a system via a group of special designed taps on the primary windings of the Dyn11 connection distribution transformer. The three-phase winding taps are symmetrically arranged and the connection point voltage can be decreased to half of the line-to-line voltage at most. Thus, the voltage stress for the D-STATCOM is reduced and a compromise between the voltage rating and the current rating can be achieved. The spare capacity of the distribution transformer can also be fully used. The working mechanism is explained in detail and a modified control strategy is proposed for reactive power compensation. Finally, both simulation and scaled-down prototype experimental results are provided to verify the feasibility and effectiveness of the proposed connection structure and control strategy.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2008년도 하계학술대회 논문집
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• pp.562-564
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• 2008

This paper deals with the three phase high voltage power-grid connection topology using multi-level inverter. Due to the multi-level inverter, these are improved effect of fluctuating voltage, problem of EMC and switching loss using suitable switching patterns of device, above all thing, it is easy to realize the system because of using lower voltage rating switch. This topology can be applicable to power-grid connection of wind system, there is a good point about economical efficiency. The simulation results are presented to verify the validity of the proposed topology.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.972-977
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• 1998

This paper deals with stand-alone Photovoltaic system(SPVS) with charge and discharge controller. Main power source of SPVS are generally solar cell and battery. Therefore SPVS can be classified into variable types in accordance with connection method between battery and solar cell array. Mainly used one of them is direct connection type which has advantages such as simple structure and simple controller. However most big drawback of this system is energy loss by voltage disharmony between solar cell array and battery. Therefore SPVS with charge and discharge controller which can operate solar cell array at maximum power point is designed and experimented with a laboratory prototype.

• 조명전기설비학회논문지
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• 제25권5호
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• pp.34-38
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• 2011

The shorter the electric power line is, the less its cost becomes. In this paper, the Steiner tree is applied to find the shortest path of the electric power line to obtain resultant cost reduction. Up to 18.3[%] of length reduction can be expected compared to conventional method when the lines are connected through the Steiner points, which also can result in appreciable cost reduction.

• 전기학회논문지
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• 제57권6호
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• pp.944-950
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• 2008

When small cogenerators are operated in connected with power system, there are many positive aspects such as the reduction of power plant construction, making a improvement of power security etc. At the same time, there are some negative effects or difficulties such as we should make sure of protective coordination, especially, Actually these are not fault, but it is likely to consider the current as the fault. This is one of major causes of malfunctions for protective relays in power distribution system which is including interconnection point. Thus, in this paper, We showed that the directional protection is necessary to the dispersed generation system which is including connection point. We also executed contingency analysis to find out the magnitude of fault current and direction which are classified by fault points, length of line and kinds of faults using ETAP power system analysis program.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 학술대회 논문집 전문대학교육위원
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• pp.208-211
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• 2006

We have analyzed operating characteristics of hybrid-type superconducting fault current limiter (SFCL) according to the parallel connection of secondary windings with $YBa_{2}Cu_{3}O_{7}$ (YBCO) films. The turn ratio between the primary and secondary windings of each reactor was 63:21. Hybrid-type SFCL using a transformer with parallel reactors could reduce the unbalanced quench caused by differences of the critical current density between YBCO films. We found that hybrid-type SFCL having parallel connection induced simultaneous quench between the superconducting elements. The quench-starting point at this time was almost same. When the applied voltage was 200V, the limiting current in the hybrid-type SFCL with a serial connection was lowered to 34 percent than that in the SFCL with a parallel connection. In the meantime, when the voltage generated in the superconducting elements was the same, the current value in the parallel connection was 60 percent less than in the serial connection. The voltage generated in the primary winding also showed the similar behavior. In conclusion, we found that the fault current was limited more effectively in the SFCL with the serial connection but the power burden of the superconducting elements was reduced in the parallel connection.

• 조명전기설비학회논문지
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• 제26권7호
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• pp.70-76
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• 2012

In general, the unidirectional power flow is normal in distribution feeders before activation of distributed power source such as PV. However, the interactive power flow is likely to occur in case of the power system under distributed generation. This interactive power flow can cause an unexpected effect on convectional protection coordination systems designed based only on the unidirectional power flow system. When the power line system encounters a problem, the interactive power flow can be a contributed current source and this makes the fault current bigger or smaller compared to the unidirectional case. The effect of interactive power flow is varied depending on the location of the point to ground fault, relative location of the PV, and connection method. Therefore it is important to analyse characteristics of fault current and interactive flow for various transformer connection and location of the PV. This paper proposes a method of improved protection coordination which can be adopted in the protective device for customers in distribution feeders interconnected with the PV. The proposed method is simulated and analysed using PSCAD/EMTDC under various conditions.