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US-20260128666-A1 - POWER CONVERSION SYSTEM AND FAULTY UNIT SEPARATION METHOD FOR POWER CONVERSION SYSTEM

US20260128666A1US 20260128666 A1US20260128666 A1US 20260128666A1US-20260128666-A1

Abstract

An object of the present invention is to separate a failure-detected cell from an SST type power conversion system while suppressing overvoltage and overcurrent. In the system in which a plurality of power converter units (cells) each having an AC/DC converter, an isolated DC/DC primary converter, and an isolated DC/DC secondary converter, are provided, and AC-side terminals of the units (cells) are connected in series, and DC-side terminals of the units (cells) are connected in parallel, a switch SWin to short-circuit the AC-side terminals and a switch SWout to disconnect parallel connection of the DC-side terminals are provided. A short-circuit detected location in each converter in each cell is determined (step S 11 ). After a gate of a short-circuit detected converter is blocked (S 12 a , S 12 b ), a gate of a short-circuit undetected converter is blocked (S 13 a , S 13 b ). AC-side switch SWin is turned on (S 14 ), and DC-side switch SWout is turned off (S 15 ).

Inventors

  • Hayato Higa

Assignees

  • MEIDENSHA CORPORATION

Dates

Publication Date
20260507
Application Date
20240308
Priority Date
20230518

Claims (4)

  1. 1 . A power conversion system of an SST (Solid State Transformer) type, the power conversion system configured by a plurality of power converter units, each power converter unit including: an AC/DC converter configured to convert AC power into DC power; a primary single-phase power converter whose DC side is connected to a DC side of the AC/DC converter and whose AC side is connected to a primary winding of an isolated transformer; a secondary single-phase power converter whose AC side is connected to a secondary winding of the isolated transformer; a primary capacitor connected between DC-side positive and negative terminals of the primary single-phase power converter; and a secondary capacitor connected between DC-side positive and negative terminals of the secondary single-phase power converter, and AC-side terminals of the plurality of power converter units being connected in series, and DC-side terminals of the plurality of power converter units being connected in parallel, the power conversion system comprising: an input-side system separation switch provided at an input side of each of the plurality of power converter units, and configured to short-circuit the AC-side terminals; an output-side system separation switch provided at an output side of each of the plurality of power converter units, and configured to disconnect parallel connection of the DC-side terminals; a short-circuit detection unit configured to detect a short-circuit failure of any of the converters provided in each power converter unit; a gate block unit configured to, when a short-circuit failure is detected by the short-circuit detection unit, after blocking a gate of a semiconductor switch of a short-circuit detected converter among the AC/DC converter, the primary single-phase power converter and the secondary single-phase power converter in a short-circuit detected power converter unit, block gates of semiconductor switches of short-circuit undetected converters, or block gates of semiconductor switches of all the converters in the short-circuit detected power converter unit simultaneously; and a switch on/off unit configured to, after performing the gate-blocking by the gate block unit, turn on the input-side system separation switch, and turn off the output-side system separation switch.
  2. 2 . The power conversion system as claimed in claim 1 , wherein the power converter unit is configured by a unidirectional power supply type power converter, and the switch on/off unit is configured to, after turning on the input-side system separation switch, turn off the output-side system separation switch.
  3. 3 . The power conversion system as claimed in claim 1 , wherein the power converter unit is configured by a bidirectional power supply type power converter using a DAB (Dual Active Bridge) converter, or a bidirectional power supply type power converter using an LLC resonant converter, when a short-circuit failure is detected during power conversion from AC into DC by the short-circuit detection unit, the gate block unit is configured to, when performing the blocking of the gates of the semiconductor switches of the short-circuit undetected converters, first, block a gate of a semiconductor switch of one of the short-circuit undetected converters, then, block a gate of a semiconductor switch of the other of the short-circuit undetected converters, and the switch on/off unit is configured to, after turning on the input-side system separation switch, turn off the output-side system separation switch, and when a short-circuit failure is detected during power conversion from DC into AC by the short-circuit detection unit, the gate block unit is configured to, when performing the blocking of the gates of the semiconductor switches of the short-circuit undetected converters, first, block a gate of a semiconductor switch of the other of the short-circuit undetected converters, then, block a gate of a semiconductor switch of one of the short-circuit undetected converters, and the switch on/off unit is configured to, after turning off the output-side system separation switch, turn on the input-side system separation switch.
  4. 4 . A method of separating a failure unit of a power conversion system of an SST (Solid State Transformer) type, the power conversion system configured by a plurality of power converter units, each power converter unit including: an AC/DC converter configured to convert AC power into DC power; a primary single-phase power converter whose DC side is connected to a DC side of the AC/DC converter and whose AC side is connected to a primary winding of an isolated transformer; a secondary single-phase power converter whose AC side is connected to a secondary winding of the isolated transformer; a primary capacitor connected between DC-side positive and negative terminals of the primary single-phase power converter; and a secondary capacitor connected between DC-side positive and negative terminals of the secondary single-phase power converter, and AC-side terminals of the plurality of power converter units being connected in series, and DC-side terminals of the plurality of power converter units being connected in parallel, the method of separating the failure unit of the power conversion system comprising: a short-circuit detection step of detecting a short-circuit failure of any of the converters provided in each power converter unit; a gate block step of, when a short-circuit failure is detected by the short-circuit detection step, after blocking a gate of a semiconductor switch of a short-circuit detected converter among the AC/DC converter, the primary single-phase power converter and the secondary single-phase power converter in a short-circuit detected power converter unit, blocking gates of semiconductor switches of short-circuit undetected converters, or blocking gates of semiconductor switches of all the converters in the short-circuit detected power converter unit simultaneously; and a switch on/off step of, after performing the gate-blocking by the gate block step, turning on an input-side system separation switch provided at an input side of each of the plurality of power converter units and configured to short-circuit the AC-side terminals, and turning off an output-side system separation switch provided at an output side of each of the plurality of power converter units and configured to disconnect parallel connection of the DC-side terminals.

Description

TECHNICAL FIELD The present invention relates to a method of safely disconnecting a cell that has been failed and detected from an SST (Solid State Transformer) type power conversion system configured by a plurality of power converter units (cells) connected in series or in parallel. BACKGROUND ART An example of a circuit configuration of the SST type power conversion system is shown in FIG. 1. In FIG. 1, a reference numeral 11 denotes an AC/DC converter that converts AC power into DC power. An AC side of the AC/DC converter 11 is connected to AC-side terminals 10a and 10b. An AC-side switch Swin (an input-side system separation switch) to short-circuit the AC-side terminals 10a and 10b is connected between the AC-side terminals 10a and 10b. A reference numeral 12 denotes an isolated DC/DC converter. The isolated DC/DC converter 12 includes, as will be described later, a primary single-phase power converter whose DC side is connected to a DC side of the AC/DC converter 11, an isolated transformer whose primary winding is connected to an AC side of the primary single-phase power converter, and a secondary single-phase power converter whose AC side is connected to a secondary winding of the isolated transformer. Positive and negative terminals of a DC output-side (the secondary single-phase power converter) of the isolated DC/DC converter 12 are connected to DC-side terminals 10c and 10d via a DC-side switch SWout (an Output-side system separation switch). The AC-side switch SWin, the AC/DC converter 11, the isolated DC/DC converter 12, and the DC-side switch SWout constitute one power converter unit (hereinafter, also referred to as a cell) 10. Here, an AC-side capacitor (a primary capacitor) C1, which is omitted in FIG. 1 though, is connected between DC-side positive and negative lines connecting the AC/DC converter 11 and the isolated DC/DC converter 12. Also, a DC-side capacitor (a secondary capacitor) C2, which is omitted in FIG. 1 though, is connected between DC output-side positive and negative terminals of the isolated DC/DC converter 12. A plurality of power converter units 10 (cell No. 1 to cell No. n) are provided. The AC-side terminals 10a and 10b of one power converter unit 10 are connected to the AC-side terminals 10a and 10b of next power converter unit 10 in series (so that the AC-side terminal 10b of the cell No. 1 is connected to the AC-side terminal 10a of the cell No. 2). The DC-side terminals 10c and 10d of one power converter unit 10 are connected to the DC-side terminals 10c and 10d of the other power converter units 10 in parallel (so that the DC-side terminals 10c of the cell No. 1 to the cell No. n are connected in common, and the DC-side terminals 10d of the cell No. 1 to the cell No. n are connected in common). It is noted that, in a case where each power converter unit 10 is not disconnected (separated), the AC-side switch SWin is turned off (is in an open circuit state), and the DC-side switch SWout is turned on (is in a closed circuit state). Next, examples of a circuit configuration of the power converter unit (the cell) 10 will be described with reference to FIGS. 2A to 2C. In FIGS. 2A to 2C, the same element or component as that in FIG. 1 is denoted by the same reference symbol. FIG. 2A illustrates a circuit configuration of the power converter unit of a unidirectional power supply type using an LLC resonant converter. A reference numeral 11 denotes an AC/DC converter configured by bridge-connected semiconductor switches SW1 to SW4. An AC-side capacitor (a primary capacitor) C1 is connected between DC-side positive and negative terminals of the AC/DC converter 11. A reference numeral 121 denotes an isolated DC/DC primary converter (a primary single-phase power converter) configured by bridge-connected semiconductor switches SW5 to SW8. A DC side of the isolated DC/DC primary converter 121 is connected to a DC side of the AC/DC converter 11. An AC side of the isolated DC/DC primary converter 121 is connected to a primary winding of a current resonance transformer Tr via reactors L1 and L2 and current resonance capacitors C3 and C4. The reactors L1 and L2 may be omitted. The primary and secondary windings of the current resonance transformer Tr have a winding ratio of 1:N. The secondary winding is connected to an AC side of an isolated DC/DC secondary converter (a secondary single-phase power converter) 122a configured by bridge-connected diodes D1 to D4. A DC-side capacitor (a secondary capacitor) C2 is connected between DC-side positive and negative terminals of the isolated DC/DC secondary converter 122a. FIG. 2B illustrates a power converter of a bidirectional power supply type using a DAB (Dual Active Bridge) converter. An AC/DC converter 11, an AC-side capacitor C1, and an isolated DC/DC primary converter 121 are configured in the same manner as in FIG. 2A. An AC side of the isolated DC/DC primary converter 121 is connected to a primary winding of a transformer T via reac