• Title/Summary/Keyword: Multilevel Converter

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11-kV Series-Connected H-Bridge Multilevel Converter for Direct Grid Connection of Renewable Energy Systems

  • Islam, Md. Rabiul;Guo, Youguang;Zhu, Jian Guo
    • Journal of international Conference on Electrical Machines and Systems
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    • v.1 no.2
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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.

A Flyback-Assisted Single-Sourced Photovoltaic Power Conditioning System Using an Asymmetric Cascaded Multilevel Inverter

  • Manoharan, Mohana Sundar;Ahmed, Ashraf;Park, Joung-Hu
    • Journal of Power Electronics
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    • v.16 no.6
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    • pp.2272-2283
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    • 2016
  • This paper proposes a power conditioning system (PCS) for distributed photovoltaic (PV) applications using an asymmetric cascaded multilevel inverter with a single PV source. One of the main disadvantages of the cascaded multilevel inverters in PV systems is the requirement of multiple isolated DC sources. Using multiple PV strings leads to a compromise in either the voltage balance of individual H-bridge cells or the maximum power point tracking (MPPT) operation due to localized variations in atmospheric conditions. The proposed PCS uses a single PV source with a flyback DC-DC converter to facilitate a reduction of the required DC sources and to maintain the voltage balance during MPPT operation. The flyback converter is used to provide input for low-voltage H-bridge cells which processes only 20% of the total power. This helps to minimize the losses occurring in the proposed PCS. Furthermore, transient analyses and controller design for the proposed PCS in both the stand-alone mode and the grid-connection mode are presented. The feasibility of the proposed PCS and its control scheme have been tested using a 1kW hardware prototype and the obtained results are presented.

Novel Control of a Modular Multilevel Converter for Photovoltaic Applications

  • Shadlu, Milad Samady
    • Transactions on Electrical and Electronic Materials
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    • v.18 no.2
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    • pp.103-110
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    • 2017
  • The number of applications of solar photovoltaic (PV) systems in power generation grids has increased in the last decade because of their ability to generate efficient and reliable power in a variety of low installation in domestic applications. Various PV converter topologies have therefore emerged, among which the modular multilevel converter (MMC) is very attractive due to its modularity and transformerless features. The modeling and control of the MMC has become an interesting issue due to the extremely large expansion of PV power plants at the residential scale and due to the power quality requirement of this application. This paper proposes a novel control method of MMC which is used to directly integrate the photovoltaic arrays with the power grid. Traditionally, a closed loop control has been used, although circulating current control and capacitors voltage balancing in each individual leg have remained unsolved problem. In this paper, the integration of model predictive control (MPC) and traditional closed loop control is proposed to control the MMC structure in a PV grid tied mode. Simulation results demonstrate the efficiency and effectiveness of the proposed control model.

A Selective Voltage Balancing Scheme of a Modular Multilevel DC-DC Converter for Solid-State Transformers (반도체 변압기용 모듈형 멀티레벨 DC-DC 컨버터의 선택적인 전압 균형 제어)

  • Lee, Eui-Jae;Kim, Seok-Min;Lee, Kyo-Beum
    • Journal of IKEEE
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    • v.23 no.2
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    • pp.652-658
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    • 2019
  • This paper proposes the selective voltage balancing scheme of a modular multilevel DC-DC converter for solid-state transformers. In general, the sub-module capacitor voltage can be controlled uniformly by individual feedback controllers, however computation time increases according to the number of modules. The voltage balance control scheme in this paper can reduce the computation time by selecting and controlling sub-module of maximum/minimum voltage momentarily. The performance of the proposed selective voltage balancing scheme is verified by simulation.

Compensation of Individual Voltage Delay for Performance Improvement in Cascaded Multilevel Converter (다단 멀티레벨 컨버터에서의 성능개선을 위한 개별전압 지연보상)

  • Kim, Sang-Hyun;Kim, Tea-Hyung;Kwon, Byung-Ki
    • Proceedings of the KIPE Conference
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    • 2013.07a
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    • pp.532-533
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    • 2013
  • 본 논문에서는 다단 멀티레벨 컨버터(Cascaded Multilevel Converter) 방식으로 개발된 STATCOM에서 Phase-Shifted PWM 시 발생할 수 있는 개별 Cell 인버터의 출력 전압 위상 지연을 보상하여 시스템의 성능을 개선하였다.

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A New Multi Level High Gain Boost DC-DC Converter with Wide Input Voltage Range and Reduced Stress Voltage Capability (넓은 입력 전압 범위와 감소된 스트레스 전압 기능성을 갖는 새로운 승압형 멀티레벨 DC-DC 컨버터)

  • Anvar, Ibadullaev;Park, Sung-Jun
    • The Transactions of the Korean Institute of Power Electronics
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    • v.25 no.2
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    • pp.133-141
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    • 2020
  • The use of high-gain-voltage step-up converters for distributed power generation systems is being popularized because of the need for new energy generation and power conversion technologies. In this study, a new constructed high-gain-boost DC-DC converter was proposed to coordinate low voltage output DC sources, such as PV or fuel cell systems, with high DC bus (380 V) lines. Compared with traditional boost DC-DC converters, the proposed converter can create higher gain and has wider input voltage range and lower voltage stress for power semiconductors and passive elements. Moreover, the proposed topology produces multilevel DC voltage output, which is the main advantage of the proposed topology. Steady-state analysis in continuous conduction mode of the proposed converter is discussed in detail. The practicability of the proposed DC-DC converter is presented by experimental results with a 300 W prototype converter.

A New Snubber Circuit for Four-Level Inverter and Converter (4-레벨 인버터 및 컨버터를 위한 새로운 스너버회로)

  • Kim, In-Dong;No, Ui-Cheol
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.49 no.9
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    • pp.598-606
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    • 2000
  • This paper proposes a new snubber circuit for 4-level inverter and converter. The snubber circuit makes use of Undeland snubber and McMurray efficient snubber as basic snubber unit and can be regarded as a generalized combined Undeland and McMurray efficient snubber. The proposed snubber keeps such good features as fewer number of components improved efficiency due to low snubber loss capability of clamping overvoltage across main switching devices and no unbalance problem of blocking voltage. Furthermore the proposed concept of constructing a snubber circuit for 4-level inverter and converter can apply to any level of converterand inverter.

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A New Ac-to-Dc Power Converter for a Load with Frequent Short Circuits (부하단락이 빈번히 발생하는 경우에 적합한 교류-직류 전력변환기)

  • No, Ui-Cheol;Kim, In-Dong
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.48 no.7
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    • pp.384-390
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    • 1999
  • This paper describes a new ac-to-dc power converter using a multilevel converter. A conventional multilevel ac-to-dc converter has large output dc filter capacitors. When a short circuit happens in a load, the stored energy in the capacitors should be discharged through the load with a high short circuit current. The high current may cause considerable damage to the capacitors and the load. The output dc capacitors of the proposed converter do not discharge even under load short circuit condition. In the case of a load short circuit, the capacitors become a floating state immediately and remain in the state. Then the stored capacitor energy is supplied to the load again as soon as the short circuit has been cleared. Therefore, the rising time of the load voltage can be significantly reduced. This feature satisfies the requirement of a power supply for a load with frequent short circuits. The proposed converter has the characteristics of a simplified structure, a reduced cost, weight, and volume compared with conventional power supplies with frequent output short circuits. Experimental results are presented to verify the usefulness of the proposed converter.

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A Pulsed Mode Operating DC Power Supply Based on Modified Multilevel Converter (Modified 멀티레벨 컨버터 기반 펄스모드 동작 직류전원장치)

  • Ahn J.S.;Nho E.C.;Kim I.D.;Kim H.G.;Chun T.W.
    • Proceedings of the KIPE Conference
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    • 2003.07a
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    • pp.264-268
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    • 2003
  • This paper describes a high voltage high power DC power supply which has the ability of pulsed mode operation. The power supply Is constructed with several series connected power converters based on modified multilevel converters. The modified multilevel converters are suitable for the protection of frequent output short-circuit. The output dc power of the proposed converter can be disconnected from the load within several hundred microseconds at the instant of short-circuit fault. The rising time of the dc load voltage is as small as several hundred microseconds, and there is no overshoot of the do voltage because the dc output capacitors keep undischarged state. Analysis, simulations, and experiments are carried out to Investigate the operation and usefulness of the proposed scheme.

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Discontinuous PWM Scheme for Switching Losses Reduction in Modular Multilevel Converters

  • Jeong, Min-Gyo;Kim, Seok-Min;Lee, June-Seok;Lee, Kyo-Beum
    • Journal of Power Electronics
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    • v.17 no.6
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    • pp.1490-1499
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    • 2017
  • The modular multilevel converter (MMC) is generally considered to be a promising topology for medium-voltage and high-voltage applications. However, in order to apply it to high-power applications, a huge number of switching devices is essential. The numerous switching devices lead to considerable switching losses, high cost and a larger heat sink for each of the switching device. In order to reduce the switching losses of a MMC, this paper analyzes the performance of the conventional discontinuous pulse-width modulation (DPWM) method and its efficiency. In addition, it proposes a modified novel DPWM method for advanced switching losses reduction. The novel DPWM scheme includes an additional rotation method for voltage-balancing and power distribution among sub modules (SMs). Simulation and experimental results verify the effectiveness and performance of the proposed modulation method in terms of its switching losses reduction capability.