• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 F
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• pp.2515-2517
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• 1999

In this paper we analysis DC bus voltage stress at high line voltage and light load in $S^4$-PFC Isolated AC/DC converter with DC bus voltage feedback using coupling in transformer. In this converter, the principle of operation and the practical problems in the design are considered. Simulation and experimental results are presented to verify the operation and performance of the $S^4$-PFC converter with DC bus voltage feedback. Experimental sets are performed in the conditions; switching frequency 100 kHz, output of 5 V, 60W, and universal line input voltage.

• Journal of Electrical Engineering and Technology
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• 제4권4호
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• pp.429-437
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• 2009

This paper proposes a hybrid voltage controller based on a hierarchical control structure for implementation in the Jeju power system. The hybrid voltage controller utilizes the coordination of various reactive power devices such as generators, switched shunt devices and LTC to regulate the pilot voltage of an area or zone. The reactive power source can be classified into two groups based on action characteristics, namely continuous and discrete. The controller, which regulates the pilot bus voltage, reflects these characteristics in the coordination of the two types of reactive power source. However, the continuous type source like generators is a more important source than the discrete type for an emergency state such as a voltage collapse, thereby requiring a more reactive power reserve of the continuous type to be utilized in the coordination in order to regulate the pilot bus voltage. Results show that the hybrid controller, when compared to conventional methods, has a considerable improvement in performance when adopted to control the pilot bus voltage of the Jeju island system.

• 대한전기학회논문지
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• 제39권2호
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• pp.133-141
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• 1990

In the operation of an electric power system, the voltage security of the system has acquired more significant importance after the occurrence of large system black-outs caused by voltage collapse several times. This paper describes a fast contingency screening method concerning voltage security. The method defines a voltage-sensitive buses where significant voltage changes would occur as a result of the contingency to reduce the number of bus voltages to be solved for continngency screening. This method is based on the observation that it is not necessary to solve the entire network in most contingency cases because boltage changes actually occur around the contingency. The P-Q decoupled linearized model and the fast error correction method are also adopted in the method to define voltage-sensitive buses and to calculate voltage magnitude on the selected voltage-sensitive buses fastly and reliably. The method suggested in this papaer has been tested in IEEE 30-bus model system and KEPCO 130-bus actual system and its effectiveness for practical use has also been confirmed.

• 항공우주기술
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• 제9권2호
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• pp.57-62
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• 2010

저궤도 인공위성에서 SAR 위성 탑재체의 전류 소모량이 약 150A로 예측된다. 이러한 높은 전류 소모는 배터리-위성버스-탑재체로 이루어진 인터페이스에서 전압 강하를 유기하여 위성 본체의 전장품과 탑재체의 동작 전압을 낮추게 되어 정상 동작을 보장하지 못하게 된다. 따라서, 탑재체 동작에 따른 버스 전압과 탑재체 입력 전압 강하의 예측이 반드시 필요하다. 본 해석에서는 전압강하의 요인이 될 수 있는 하니스 및 접촉 저항에 대한 worst case analysis를 수행하여 탑재체 동작시 발생할 수 있는 전압 강하를 예측한다.

• Journal of Power Electronics
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• 제12권4호
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• pp.567-577
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• 2012

This paper introduces a new scheme to balance the DC bus voltages of a cascaded H-bridge converter which is used as a Distribution Static Synchronous Series Compensator (D-SSSC) in electrical distribution network. The aim of D-SSSC is to control the power flow between two feeders from different substations. As a result of different cell losses and capacitors tolerance the cells DC bus voltage can deviate from their reference values. In the proposed scheme, by individually modifying the reference PWM signal for each cell, an effective balancing procedure is derived. The new balancing procedure needs only the line current sign and is independent of the main control strategy, which controls the total DC bus voltages of cascaded H-bridge. The effect of modulation index variation on the capacitor voltage is analytically derived for the proposed strategy. The proposed method takes advantages of phase shift carrier based modulation and can be applied for a cascaded H-bridge with any number of cells. Also the system is immune to loss of one cell and the presented procedure can keep balancing between the remaining cells. Simulation studies and experimental results validate the effectiveness of the proposed method in the balancing of DC bus voltages.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.797-799
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• 1996

This paper presents a simple method for evaluating of voltage stability using the line flow equation. Line flow equations($P_{ij}$, $Q_{ij}$) are comprised of state variable, $V_i$, ${\delta}_i$, $V_j$ and ${\delta}_j$, and line parameter, r and x. Using the feature of polar coordinate, these equations become one equation with two variables, $V_i$ and $V_j$. Moreover, if bus j is slack bus or generator bus, which is specified voltage magnitude, it becomes One equation with one variable $V_i$, that is, may be formulated with the second-order equation for $V_i^2$. Therefore, solutions are obtained with simple computation. Solutions obtained are used for evaluating of voltage stability through sensitivity analysis. Also, considering of reactive power source, method for evaluating the voltage stability is introduced. The proposed method was validated to 2-bus and IEEE 6-bus system.

• Journal of Electrical Engineering and Technology
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• 제8권6호
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• pp.1305-1309
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• 2013

The application of the superconducting fault current limiter (SFCL) in a power distribution system is expected to contribute the voltage-sag suppression of the bus line as well as the fault-current reduction of the fault line. However, the application effects of the SFCL on the voltage sag of the bus line including the fault current are dependent on its application location in a power distribution system. In this paper, we investigated the fault current limiting and the voltage sag suppressing characteristics of the SFCL due to its application location such as the outgoing point of the feeder, the bus line, the neutral line and the 2nd side of the main transformer in a power distribution system, and analyzed the trace variations of the bus-voltage and fault-feeder current. The simulated power distribution system, which was composed of the universal power source, two transformers with the parallel connection and the impedance load banks connected with the 2nd side of the transformer through the power transmission lines, was constructed and the short-circuit tests for the constructed system were carried out. Through the analysis on the short-circuit tests for the simulated power distribution system with the SFCLs applied into its representative locations, the effects from the SFCL's application on the power distribution system were discussed from the viewpoints of both the suppression of the bus-voltage sag and the reduction of the fault current.

• 대한전기학회논문지
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• 제43권6호
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• pp.869-876
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• 1994

This paper presents an efficient method to calculate voltage collapse point and to avoid voltage instability. To evaluate voltage stability in power systems, it is necessary to get critical loading points. For this purpose, this paper uses linear programming to calculate efficiently voltage collapse point. Also, if index value becomes larger than given threshold value, voltage stability is improved by compensation of reactive power at selected bus. This algorithm is verified by simulation on the IEEE 14-bus sample system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 춘계학술대회 논문집 전력기술부문
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• pp.74-76
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• 2001

When a Bus voltage is low, the Load-Flour is generally blown up. If Bus voltage is normalized. the convergence of Load-flow is improved. This paper introduces virtual bus with tap. In that case, the Bus admittance will be considered. And the convergence of Load-Flow in applying virtual bus is debated.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 D
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• pp.1118-1120
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• 1997

This paper presents a simple method for evaluating of voltage stability using the line flow equation. Line flow equations ($P_{ij}$, $Q_{ij}$) are comprised of state variable, $V_i$, ${\delta}_i$, $V_j$ and ${\delta}_j$, and line parameter, r and x. Using the feature of polar coordinate, these becomes one equation with two variables, $V_i$ and $V_j$. Moreover, if bus j is slack or generater bus, which is specified voltage magnitude, it becomes one equation with one variable $V_i$, that is, may be formulated with the second-order equation for $V_i^2$. Therefore, multiple load flow solutions may be obtained with simple computation, and the formulated equation used for approximately evaluating of voltage stability limit considering line flow sensitivity. The proposed method was validated to 2-bus and IEEE 6-bus system.