• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1610-1620
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• 2015

A major problem in conventional multilevel inverter is that an increase in power semiconductor switches causes an increase in cost and switching losses of the inverter. The multicarrier strategy adopted for the multilevel inverters has become more popular due to reduced cost, lower harmonic distortion, and higher voltage capability than the conventional switching strategy applied to inverters. Various topologies and modulation strategies have been reported for utility and drive applications. Level shifted based pulse width modulation techniques are proposed to investigate the performance of the multilevel inverter. The proposed work focuses on reducing the utilized switches so that the cost and the switching losses of the inverter do not go up and the consistent efficiency could be achieved. This paper presents the detailed analysis of these topologies. The analysis is based on the number of switches, DC sources, output level, maximum voltage, and the efficiency. As an illustration, single phase cascaded multilevel inverter topologies are simulated using MATLAB/SIMULINK and the experimental results demonstrate the viability of these inverters.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.206-209
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• 2003

AC loss is an important issue in the design of high-T$_{c}$ superconducting power cables which consist of a number of Bi-2223 tapes wound on a former. In the cables, the tapes have different critical currents intrinsically. And they are electrically connected to each other and current leads. These make loss measurements considerably complex, especially for short samples of laboratory size. So special cautions are required in the positioning of voltage leads for measuring the true loss voltage. In this work we have prepared a conductor composed of three Bi-2223 tapes with different critical currents. The ac loss characteristics in the conductor have experimentally investigated. The loss tests indicate that the ac loss is dependent on arrangements of voltage leads but not on their contact positions. The measured losses in the conductor also agree well with the sum of the transport losses measured in each Bi-2223 tape.e.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.7-10
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• 2003

AC loss is an important issue in the design of high-T$_{c}$ superconducting power cables which consist of a number of Bi-2223 tapes wound on a former. In the cables, the tapes have different critical currents intrinsically. And they are electrically connected to each other and current leads. These make loss measurements considerably complex, especially for short samples of laboratory size. So special cautions are required in the positioning of voltage leads for measuring the true loss voltage. In this work we have prepared a conductor composed of three Bi-2223 tapes with different critical currents. The ac loss characteristics in the conductor have experimentally investigated. The loss tests indicate that the ac loss is dependent on arrangements of voltage leads but not on their contact positions. The measured losses in the conductor also agree well with the sum of the transport losses measured in each Bi-2223 tape.e.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.276-280
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• 2003

This paper presents a zero voltage and zero current switching (ZVZCS) interleaving two-transistor forward converter for high input voltage and high power application. A phase shift has a disadvantage that a circulating current and RMS current stress, conduction losses of transformer and switching devices increases. Due to this circulating current and RMS current stress, conduction losses of transformer and switching devices increases. To alleviate these problems, we propose an improved interleaving two-transistor forward Zero Voltage and Zero Current Switching (ZVZCS) dc/dc converter using a tapped inductor a snubber capacitor and two snubber diodes attached at the secondary side of transformer. The proposed ZVZCS converter is verified on a 1.8kW, 5kHz experimental prototype.

• Transactions on Electrical and Electronic Materials
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• 제7권6호
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• pp.319-323
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• 2006

The problem of the partial discharge (PD) extinction is investigated. The transient process takes place in a small spherical inclusion which is located in the dielectric. Both the losses caused by polarization and ohmic losses as the dielectric parameters are taken into account. From the inclusion standpoint the dielectric is considered as an active two-pole element (equivalent generator) and inclusion represents by own current-voltage curve. PD extinction voltage was shown to depend on the polarization loss tangent.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 A
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• pp.9-11
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• 2003

In power system planing and operation, voltage and reactive power control are very important. The voltage deviation and system losses can be reduced through control of reactive power sources. In general, there are several different reactive power sources, we used UPFC and switched shunt capacitor to improve the voltage profile and to reduce system losses in this study. Since there are many switched shunt capacitors in power system, so it is necessary to coordinate these switched shunt capacitors. In this study, Genetic Algorithm(GA) is used to find optimal coordination of UPFC and switched shunt capacitors in a local area of power system. In case study, the effectiveness of the proposed method is demonstrated in KEPCO's power system. The simulation is performed by PSS/E.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 전력전자학술대회 논문집
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• pp.367-368
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• 2014

This paper investigates characteristics of high power semiconductor device losses in 5MW-class Permanent Magnet Synchronous Generator (PMSG) Medium Voltage (MV) wind turbines. High power semiconductor device of press-pack type IGCT of 6.5kV is considered in this paper. Analysis is performed based on neutral point clamped (NPC) 3-level back-to-back type voltage source converter (VSC) supplied from grid voltage of 4160V. This paper describes total loss distribution at worst case under inverter and rectifier operating mode for the power semiconductor switches. The loss analysis is confirmed through PLECS simulations. In addition, the loss factors due to di/dt snubber and ac input filter are presented. The investigation result shows that IGCT type semiconductor devices generate the total efficiency of 97.74% under the rated condition.

• 한국철도학회논문집
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• 제17권3호
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• pp.171-177
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• 2014

PWM컨버터 차량은 전압벡터제어방식에 의해 부하역률 1.0에 가까운 운전이 가능하므로 기존 저역률의 위상제어방식 차량에 비해 급전선로 전압강하 측면에서 우수한 부하특성을 나타낸다. 그러나 이 경우에도 급 전구간 내의 운전밀도가 높거나 연장급전 구간에서는 선로손실의 증가 및 전압강하 현상이 심각한 수준으로 나타날 수 있다. 본 논문은 PWM컨버터 차량의 역률을 1.0으로 고정하여 운행하는 대신 차량의 운전 조건에 따라 가변적으로 최적 제어함으로써 급전선로의 손실을 최소화 하고 전압 프로파일을 개선하는 방법을 기술하였다. 제시된 방법은 동일 급전구간 내에 운행중인 차량을 대상으로 최대 경사법에 의해 선로의 무효전력손실이 최소화되는 개별 차량의 무효전력 보상량을 결정하게 되며, 이 방법을 표본 계통에 대해 시뮬레이션 한 결과 선로손실의 감소와 함께 전압 프로파일도 상당한 수준으로 개선됨을 알 수 있었다.

• 전기의세계
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• 제15권5호
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• pp.6-12
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• 1966

As a power system gets complicated and the number of regulating points increases, the voltage reactive power control tends to be more complex and more difficult. In the past, we took only the voltage regulation into account for this voltage control problem. pay attention not only to the voltage regulation but also to the rational system operation which minimizes transmission losses. Considering the rehuirements mentioned above we aim developing a method of coordination of these regulating equipments and also present some preliminary discussions aboutcomputer control of power systems which is now frequently available with the progress of digital computer technique.

• Journal of Power Electronics
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• 제18권6호
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• pp.1729-1750
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• 2018

Voltage source inverters (VSIs) are widely used to drive induction motors in industry applications. The quality of output waveforms depends on the switching sequences used in pulse width modulation (PWM). In this work, all existing optimal space vector pulse width modulation (SVPWM) switching strategies are studied. The performance of existing SVPWM switching strategies is optimized to realize a tradeoff between quality of output waveforms and switching losses. This study generalizes the existing optimal switching sequences for total harmonic distortions (THDs) and switching losses for different modulation indexes and reference angles with a parameter called quality factor. This factor provides a common platform in which the THDs and switching losses of different SVPWM techniques can be compared. The optimal spatial distribution of each sequence is derived on the basis of the quality factor to minimize harmonic current distortions and switching losses in a sector; the result is the minimum ripple loss SVPWM (MRSLPWM). By employing the sequences from optimized switching maps, the proposed method can simultaneously reduce THDs and switching losses. Two hybrid SVPWM techniques are proposed to reduce line current distortions and switching losses in motor drives. The proposed hybrid SVPWM strategies are MRSLPWM 30 and MRSLPWM 90. With a low-cost PIC microcontroller (PIC18F452), the proposed hybrid SVPWM techniques and the quality of output waveforms are experimentally validated on a 2 kVA VSI based on a three-phase two-level insulated gate bipolar transistor.