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Four-port power electronic transformer based on hybrid modular multilevel converter

  • US 9,960,666 B2
  • Filed: 03/16/2016
  • Issued: 05/01/2018
  • Est. Priority Date: 01/27/2016
  • Status: Active Grant
First Claim
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1. A four-port power electronic transformer based on a hybrid modular multilevel converter (MMC), comprising:

  • a hybrid MMC, direct current (DC)/DC converters, and an inverter, whereinthe DC/DC converter comprises a front stage part, a high frequency transformation part, and a back stage part, wherein an alternating current (AC) side of the front stage part is connected to a primary side of the high frequency transformation part, and a secondary side of the high frequency transformation part is connected to an AC side of the back stage part;

    the inverter is a three-phase four-bridge arm inverter;

    the MMC has three phases, each phase having two bridge arms, and each bridge arm comprising X first submodules, Y second submodules, and an inductor, wherein X+Y≥

    N, N being the minimum number of modules required when the MMC works normally;

    the first submodule comprises two half-bridge structures connected in series, comprising a DC capacitor C1, a DC capacitor C2, and four insulated gate bipolar transistors T1, T2, T3 and T4 with anti-paralleled diodes;

    the T1, T2, T3, and T4 have collectors respectively connected to cathodes of their respective freewheeling diodes and emitters respectively connected to anodes of their respective freewheeling diodes;

    an emitter of the T1 and a collector of the T2 are connected and used as an AC port A of the first submodule, a collector of the T1 and a positive electrode of the C1 are connected and used as a positive electrode port C of the first submodule, an emitter of the T2, a negative electrode of the C1, a collector of the T4, and a positive electrode of the C2 are connected and used as a port I of the first submodule, an emitter of the T4 and a collector of the T3 are connected and used as an AC port B of the first submodule, and an emitter of the T3 and a negative electrode of the C2 are connected and used as a negative electrode port D of the first submodule;

    the positive electrode port C and the negative electrode port D of the first submodule are respectively connected to a positive electrode port and a negative electrode port of the front stage of the DC/DC converter connected to a DC side of the module;

    the second submodule comprises a DC capacitor C3, a DC capacitor C4, and five insulated gate bipolar transistors T5, T6, T7, T8, and T9 with anti-paralleled diodes;

    the T5, T6, T7, T8, and T9 have collectors respectively connected to cathodes of their respective freewheeling diodes and emitters respectively connected to anodes of their respective freewheeling diodes;

    in the second submodule, an emitter of the T5 and a collector of the T6 are connected and used as an AC port E of the second submodule, a collector of the T5 and a positive electrode of the C3 are connected and used as a positive electrode port G of the second submodule, an emitter of the T6, an emitter of the T9, and a negative electrode of the C3 are connected, an emitter of the T7 and a collector of the T8 are connected and used as an AC port F of the second submodule, a collector of the T7, a collector of the T9, and a positive electrode of the C4 are connected and used as a port J of the second submodule, and an emitter of the T8 and a negative electrode of the C4 are connected and used as a negative electrode port H of the second submodule;

    the positive electrode port G and the negative electrode port H of the second submodule are respectively connected to a positive electrode port and a negative electrode port of the front stage of the DC/DC converter connected to a DC side of the second submodule;

    without considering redundancy, X+Y=N, (2X+2Y)Vc=Vdc, and vm=(2X+2Y)Vc, where Vdc is a voltage at a high-voltage DC side, Vc is a voltage of each DC capacitor, and vm is a phase voltage amplitude at a high-voltage AC side;

    considering redundancy, the following relationship needs to be satisfied;

    X+Y≥

    N;

    when the MMC has a DC fault ride-through capability, without considering redundancy, X and Y satisfy the following relationship;

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