• Journal of Power Electronics
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• 제16권4호
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• pp.1256-1267
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• 2016

Distributed stray inductance exerts a significant influence on the turn-off voltages of power switching devices. Therefore, the design of low stray inductance bus bars has become an important part of the design of high-power converters. In this study, we first analyze the operational principle and switching transient of a T-type converter. Then, we obtain the commutation circuit, categorize the stray inductance of the circuit, and study the influence of the different types of stray inductance on the turn-off voltages of switching devices. According to the current distribution of the commutation circuit, as well as the conditions for realizing laminated bus bars, we laminate the bus bar of the converter by integrating the practical structure of a capacitor bank and a power module. As a result, the stray inductance of the bus bar is reduced, and the stray inductance in the commutation circuit of the converter is reduced to more than half. Finally, a 10 kVA experimental prototype of a T-type converter is built to verify the effectiveness of the designed laminated bus bar in restraining the turn-off voltage spike of the switching devices in the converter.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.124-126
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• 2002

The general capacitor placement problem is a combinatorial optimization problem having an objective function composed of power losses and capacitor installation costs subject to bus voltage constraints. In this paper, the method employing the chaos search algorithm is proposed to solve optimal capacitor placement problem with reducing computational effort and enhancing optimality of the solution. Chaos method in optimization problem searches the global optimal solution on the regularity of chaotic motions and easily escapes from local or near optimal solution than stochastic optimization algorithms. The chaos optimization method is tested on 9 buses and 69 buses system to illustrate the effectiveness of the proposed method.

• Journal of Electrical Engineering and Technology
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• 제9권1호
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• pp.45-51
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• 2014

Distribution system is a critical link between customer and utility. The control of power loss is the main factor which decides the performance of the distribution system. There are two methods such as (i) distribution system reconfiguration and (ii) inclusion of capacitor banks, used for controlling the real power loss. Considering the improvement in voltage profile with the power loss reduction, later method produces better performance than former method. This paper presents an advanced evolutionary algorithm for capacitor inclusion for loss reduction. The conventional sensitivity analysis is used to find the optimal location for the capacitors. In order to achieve a better approximation for the current candidate solution, Opposition based Differential Evolution (ODE) is introduced. The effectiveness of the proposed technique is validated through 10, 33, 34 and85-bus radial distribution systems.

• 전기학회논문지P
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• 제58권4호
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• pp.404-409
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• 2009

A DC power system has many loads with various functions. In particular, these sizable loads take the form of power electronic converters. When they are tightly regulated, the loads appear as constant power loads and result in negative incremental input impedance. Under certain conditions the effect of such loads on the power system is causes instability. In this paper, converter with a large storage capacitor and a lag compensator is proposed as a DC bus conditioner to mitigate the voltage transients on the bus. In addition, the proposed control approach has the advantage of performing both the functions of mitigating the voltage bus transients and maintaining the level of energy stored. Simulation and experimental results showed that the proposed control method was operated well in a small-scale DC power system that contained subsystems with constant power characteristics, such as DC/DC converters and electrical drives.

• 전기학회논문지P
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• 제61권4호
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• pp.186-191
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• 2012

DC Bus Electrolytic capacitors have been widely used in power conversion system because they can achieve high capacitance and voltage ratings with volumetric efficiency and low cost. This type of capacitors have been traditionally used for filtering, voltage smoothing, by-pass and other many applications in power conversion circuits requiring a cost effective and volumetric efficiency components. Unfortunately, electrolytic capacitors are some of the weakest components in power electronic converter. Many papers have proposed different methods or algorithms to determinate the ESR and/or capacitance C for fault diagnosis of the electrolytic capacitor. However, both ESR and C vary with frequency and temperature. Accurate knowledge of both values at the capacitors operating conditions is essential to achieve the best reference data of fault judgement. According to parameter analysis, the capacitance increases with temperature and the ESR decreases. Higher frequencies make the ESR and C to decrease. Analysis results show that the proposed electrolytic capacitor parameter estimation technique can be applied to reference signal of capacitor diagnosis systems successfully.

• 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.

• Journal of Power Electronics
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• 제9권3호
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• pp.386-395
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• 2009

In this paper, a new control algorithm for the dynamic voltage restorer (DVR) is proposed to regulate the load terminal voltage during various power quality problems that include sag, swell, harmonics and unbalance in the voltage at the point of common coupling (PCC). The proposed control strategy is an Adaline (Adaptive linear element) Artificial Neural Network (ANN) and is used to control a capacitor supported DVR for power quality improvement. A capacitor supported DVR does not need any active power during steady state because the voltage injected is in quadrature with the feeder current. The control of the DVR is implemented through derived reference load terminal voltages. The proposed control strategy is validated through extensive simulation studies using the MATLAB software with its Simulink and SimPower System (SPS) toolboxes. The DVR is found suitable to support its dc bus voltage through the control under various disturbances.

• 전기학회논문지
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• 제57권2호
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• pp.164-171
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• 2008

This paper proposes the planning method for placement of capacitors in a distribution system. The main objectives in the planning for capacitor allocation are the reduction of installation costs and electric power loss. In the proposed method, the life time of each device is considered in calculating installation costs, and the optimal operation status of devices is found by genetic algorithm. Then, the optimal numbers and locations are determined based on the optimal operation status. Simulation results in the 69-bus distribution system show that the proposed method performs better than conventional methods.

• Journal of Electrical Engineering and Technology
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• 제8권3호
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• pp.428-435
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• 2013

Flexible AC Transmission System (FACTS) application study on enhancing the flexibility of AC power system has continued to make progress. A thyristor-controlled series capacitor (TCSC) is a useful FACTS device that can control the power flow by adjusting line impedances and minimize the loss of power flow and voltage drop in a transmission system by adjusting line impedances. Reduced power flow loss leads to increased loadability, low system loss, and improved stability of the power system. This study proposes the optimal location and compensation rate method for TCSCs, by considering both the power system loss and voltage drop of transmission systems. The proposed method applies a multi-objective function consisting of a minimizing function for power flow loss and voltage drop. The effectiveness of the proposed method is demonstrated using IEEE 14- and a 30-bus system.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.914-919
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• 1998

A Capacitor Commutated Converter (CCC) has less difficulty of commutation failure in comparison to the conventional line commutated converter. This paper proposes the Ar1R control of the CCC in the inverter operation, which deserves as the Ar1R of the conventional converter. The CCC can be operated in high power factor area by using the proposing Ar1R control. The voltage stability at an AC bus connected the CCC inverter is investigated and estimated its ability of preventing the AC voltage collapse. To estimate the voltage stability, this paper developed the simplified converter mathematical model and led the VSF index. The results shows that the AC voltage stability is guaranteed and enables the interconnection to an weak AC system, when compensation factor of the compensation capacitor is higher than 200%.