• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.263-269
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• 2018

In this study, a selective inverter operation between a 2-level voltage source converter (VSC) and a 3-level T-type VSC (3LT VSC) is proposed to improve the efficiency of a 3LT VSC. The 3LT VSC topology, except for its neutral-point switches, has similar operations as that of the 2-level VSC. If an operation mode is changed according to efficiency, the efficiency can be improved because efficiencies of each methods are depending on current and MI (Modulation Index). The proposed method calculates the power losses of the two topologies and operates as the having lower losses. To calculate the losses, the switching and conduction losses based on the operation mode of each topology were analyzed. The controller determined the operation mode of the 2- or 3-level VSC based on the power loss calculated during every cycle. The validity of the proposed control scheme was investigated through simulation and experiments. The waveform and average efficiency of each method were compared.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 전력전자학술대회 논문집
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• pp.341-342
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• 2014

VSC-HVDC system based on Modular Multilevel Converter (MMC) is an emerging technology since compared to the conventional VSC-HVDC system an MMC presents several advantages such as modularity, low dv/dt, low harmonics, and low switching losses. In this paper, a comprehensive control strategy of an MMC-based VSC-HVDC system is proposed. In contrast to the conventional system control strategy, the DC side of the MMC operates as a controlled voltage source by the proposed method, and the dynamics of the transmission line voltage and current can be actively controlled. Validity of the proposed strategy was verified by 201-level full-scale computer simulation.

• Journal of Power Electronics
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• 제7권2호
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• pp.146-158
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• 2007

A multi-pulse GTO based voltage source converter (VSC) topology together with a fundamental frequency switching mode of gate control is a mature technology being widely used in static synchronous compensators (STATCOMs). The present practice in utility/industry is to employ a high number of pulses in the STATCOM, preferably a 48-pulse along with matching components of magnetics for dynamic reactive power compensation, voltage regulation, etc. in electrical networks. With an increase in the pulse order, need of power electronic devices and inter-facing magnetic apparatus increases multi-fold to achieve a desired operating performance. In this paper, a competitive topology with a fewer number of devices and reduced magnetics is evolved to develop an 18-pulse, 2-level $\pm$ 100MVAR STATCOM in which a GTO-VSC device is operated at fundamental frequency switching gate control. The inter-facing magnetics topology is conceptualized in two stages and with this harmonics distortion in the network is minimized to permissible IEEE-519 standard limits. This compensator is modeled, designed and simulated by a SimPowerSystems tool box in MATLAB platform and is tested for voltage regulation and power factor correction in power systems. The operating characteristics corresponding to steady state and dynamic operating conditions show an acceptable performance.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권2호
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• pp.70-78
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• 2012

Due to the variable nature of renewable energy resources and power demand by consumers, it is difficult to operate a power system installed with only one type of renewable energy resource. Grid-based renewable generation may be the only solution to overcome this problem. The conventional approach based on a low-voltage converter with power frequency transformer is commonly employed for grid connection of offshore renewable energy systems. Because of the heavy weight and large size of the transformer, the system can be expensive and complex in terms of installation and maintenance. In this paper, an 11-kV series connected H-bridge (SCHB) multilevel voltage source converter (VSC) is proposed to achieve a compact and light direct grid connection of renewable energy systems. This paper presents the design, simulation and analysis of a five level (5L)-SCHB and an eleven level (11L)-SCHB VSC for 11-kV grid-based renewable energy systems. The performance, cost, modulation scheme and harmonic spectra of the converter are analyzed.

• Journal of Electrical Engineering and Technology
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• 제3권2호
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• pp.254-262
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• 2008

This paper presents an active use of doubly-fed induction-generator(DFIG)-based variable-speed wind-turbine for voltage control in power system operation. For reasonable simulation studies, a detail dynamic model of a DFIG-based wind-turbine grid-connected system is presented. For the research objective, an innovative reactive power control scheme is proposed that manipulates dynamically the reactive power from the voltage source converter(VSC) with taking into account its operating state and limits.

• 한국초전도ㆍ저온공학회논문지
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• 제20권4호
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• pp.55-59
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• 2018

Currently, the development of industry makes needs larger electric supply. Providers must consider the efficiency about losses and reliability of the system. In this case, DC power system can save electrical energy; long-distance transmission line losses. Relevance to switch technology with a voltage-source converter (VSC) in AC-DC conversion system have been researched. But, protection device of DC-link against fault current is still needed to study much. VSC DC power system is vulnerable to DC-cable short-circuit and ground faults, because DC-link has a huge size of capacitor filter which releases extremely large current during DC faults. Furthermore, DC has a fatal flaw that current zero crossing is nonexistence. To interrupt the DC, several methods which make a zero crossing is used; parallel connecting self-excited series LC circuit with main switch, LC circuit with power electronic device called hybrid DC circuit breaker. Meanwhile, self-excited oscillator needs a huge size capacitor that produces big oscillation current which makes zero crossing. This capacitor has a quite effective on the price of DCCB. In this paper, hybrid self-excited type superconducting DCCB which are using AC circuit breaker system is studied by simulation tool PSCAD/EMTDC.

• 전력전자학회논문지
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• 제26권2호
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• pp.150-157
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• 2021

Nowadays, a DC microgrid that can link various distributed power sources is gaining much attention. Accordingly, research on fault situations, such as line-to-line and line-to-ground faults of the DC microgrid, has been conducted to improve grid reliability. However, the blackout of an AC system and the oscillation of a DC bus voltage have not been reported or have not been sufficiently verified by previous research. In this study, a 20 kW DC microgrid testbed using a power HIL simulation technique is proposed. This testbed can simulate various fault conditions without any additional grid facilities and dangerous experiments. It includes the blackout of the DC microgrid caused by the AC utility grid's blackout, a drastic load increment, and the DC bus voltage oscillation caused by the LCL filter of the voltage source converter. The effectiveness of the proposed testbed is verified by using Opal-RT's OP5707 real-time simulator with a 3 kW prototype three-port dual-active-bridge converter.

• Journal of Power Electronics
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• 제8권1호
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• pp.81-90
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• 2008

This paper presents an investigation of a voltage and frequency controller for an isolated asynchronous generator (IAG) driven. by a wind turbine and supplying 3-phase 4-wire loads to the isolated areas where a grid is not accessible. The control strategy is based on the indirect current control of the VSC (voltage source converter) using the frequency PI controller. The proposed controller consists of three single-phase IGBT (Insulated Gate Bipolar Junction Transistor) based VSC, which are connected to each phase of the IAG through three single phase transformers and a battery at their DC link. The controller has the capability of controlling reactive and active powers to regulate the magnitude and frequency of the generated voltage, harmonic elimination, load balancing and neutral current compensation. The proposed isolated system is modeled and simulated in MATLAB using Simulink and PSB (Power System Block-set) toolboxes to verify the performance of the controller.

• 전기전자학회논문지
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• 제23권4호
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• pp.1140-1149
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• 2019

전압형 컨버터의 다양한 전압 합성 방법을 구현하기 위해서, 옵셋 전압을 주입하는 방법이 널리 사용되고 있다. 즉, 전압 변조 방식(pulse width modulation; PWM)들은 교류 측 전압 지령에 적절한 옵셋 전압을 주입하는 것과 수학적으로 동일하다. 이러한 옵셋 전압을 이용한 AC 단 출력 전압 합성 방법에 따라 DC 단 전압의 전압 이용률이 달라지며, 이는 모듈형 다단 컨버터(modular multilevel converter; MMC) 시스템에서도 동일하다. 따라서, DC 단의 용량이 정해져 있는 고압 직류(high voltage DC; HVDC) 송전 시스템의 경우에도 AC 단에 옵셋 전압을 이용함에 따라 AC 단으로 공급 가능한 최대 무효 전력의 크기를 변화시킬 수 있다. 본 논문에서는 대표적인 전압 변조 방식을 적용한 옵셋 전압 주입 시 합성된 AC 측 출력 전압에 따라 MMC 시스템의 레그 에너지 맥동을 수학적으로 분석하였다. 또한, 이를 실제 스케일의 400MVA급 MMC 시스템 시뮬레이션을 통해 수학적 분석의 경향성을 검증하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.243-245
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• 1994

A PWM forced-commutated converter with DC voltage source is studied in this paper. This PWM-VSC using spacs vector modulation permits to control bi-directional power exchange between the AC mains and the DC source. The principle of the active and reactive power control is presented. In transient operation, the analysis of reactive component current is performed. Finally, the simulation results are also presented and discussed.