Start-Up and Dynamic Modeling of the Multilevel Modular Capacitor-Clamped Converter

Electr. & Comput. Eng. Dept., Univ. of Utah, Salt Lake City, UT, USA
IEEE Transactions on Power Electronics (Impact Factor: 5.73). 03/2010; DOI: 10.1109/TPEL.2009.2025273
Source: IEEE Xplore

ABSTRACT This paper will present the analytical proof of concept of the multilevel modular capacitor-clamped converter (MMCCC). The quantitative analysis of the charge transfer mechanism among the capacitors of the MMCCC explains the start-up and steady-state voltage balancing. Once these capacitor voltages are found for different time intervals, the start-up and steady-state voltages at various nodes of the MMCCC can be obtained. This analysis provides the necessary proof that explains the stable operation of the converter when a load is connected to the low-voltage side of the circuit. In addition, the analysis also shows how the LV side of the converter is (1/ N )th of the HV side excitation when the conversion ratio of the circuit is N . In addition to the analytical and simulation results, experimental results are included to support the analytical proof of concept.

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    ABSTRACT: This paper presents two novel topologies on precharge and submodule capacitor voltage balancing schemes of Modular Multilevel Converter (MMC) for VSC-HVDC application respectively. Firstly, A traditional precharge process of MMC was modeled in PSCAD/EMTDC, its drawbacks were summarized and a novel topology was proposed based on submodules charged synchronously; Secondly, we analyzed the principles of a traditional submodule capacitor voltage balancing scheme, clarified its limitations and another novel topology based on the essential objectives of the balancing schemes was proposed. The topology is with Double DC Bus Bars, external DC voltage source and antiparallel thyristors. Detailed analysis and simulations indicated that the two topologies presented here not only can make up the drawbacks of the conventional schemes to a certain extent, but also have great potentiality in the application of VSC-HVDC projects in the future.
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    ABSTRACT: This paper presents a double-wing multilevel modular capacitor-clamped (DW-MMCCC) dc-dc converter. Compared to the traditional single-wing (SW) MMCCC with the same voltage conversion ratio, the capacitor voltage stress of DW-MMCCC is reduced by half. And the switch and capacitor current stress, the switch voltage stress of the SW-MMCCC and the DW-MMCCC are the same. When the conversion ratio is equal to N, the total device and capacitor number of the even conversion ratio DW-MMCCC is 3N-2 and N, which is the same with the corresponding SW-MMCCC. The total device and capacitor number of odd conversion ratio DW-MMCCC is 3N-1 and N+1 respectively. By using the distributed stray inductance existing in the circuit, zero current switching (ZCS) can be achieved for all the switches of DW-MMCCC. And by using multi-phase DW-MMCCC, the input current ripple and input capacitor size can be reduced significantly. Compared with the traditional multilevel dc-dc converter, the power density of DW- MMCCC could be increased by about ten times. A 100 W three- phase 3X-ZCS-DW-MMCCC prototype has been built and tested. The simulation and experimental results are provided to verify the validity of the proposed converter. Index Terms—Multilevel, Switched-Capacitor DC-DC, Modular, ZCS.
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    ABSTRACT: The multilevel modular capacitor clamped converter (MMCCC) topology overcomes the difficulties of the multilevel switched capacitor (SC) based dc-to-dc converters in high conversion ratio applications. MMCCC is completely modular and has many other advantageous features. Like most other SC converters, MMCCC suffers from limited voltage regulation. The conversion ratio of an ideal MMCCC converter in step-up mode is an integer, and this integer conversion ratio depends on the number of active modules. The maximum conversion ratio in step-up configuration for a k-module MMCCC is (k+1). It has already been shown in literature that different integer CRs can be achieved by changing the number of active modules of an MMCCC. Achieving voltage regulation by lowering the operating frequency is another well known technique for switched capacitor converters. However, the output voltage ripple increases in inverse proportion of the frequency. In this paper, a new switching scheme is proposed for MMCCC to achieve continuously variable CRs. The proposed switching scheme requires introducing a small inductor in each module of the MMCCC without altering the modular structure of the converter. This additional inductor can be realized using the stray inductance distributed in the circuit or small external inductors. It has been shown that continuous CR variation with lower output ripple can be achieved without lowering the operating frequency of the converter. This proposed method introduces another degree of freedom in order to achieve variable CR using MMCCC. Simulation results and experimental results obtained from an MMCCC prototype have been used to validate the new control scheme.
    Control and Modeling for Power Electronics (COMPEL), 2012 IEEE 13th Workshop on; 01/2012


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