Modular multilevel converter sub-module having dc fault current blocking function and method of controlling the same

Patent metadata

Field	Value
Publication number	US-2020366186-A1
Application number	US-202016844447-A
Country	US
Kind code	A1
Filing date	Apr 9, 2020
Priority date	May 14, 2019
Publication date	Nov 19, 2020
Grant date	—

Abstract

Disclosed is a modular multilevel converter sub-module, including: a normal circuit which includes a first switching element and a second switching element connected in series and a first diode and a second diode respectively connected to be parallel to the first switching element and the second switching element to offset a counter electromotive force generated in the first switching element and the second switching element, a fault DC current blocking circuit which includes a capacitor connected to the normal circuit in parallel and applies a capacitor voltage to a DC fault path as a reverse voltage with respect to a fault voltage, and a bypass circuit which includes a third switch element, is connected to the fault DC current blocking circuit in parallel, and determines an output voltage and a direction of an arm current to provide a DC fault current bypass path when a DC fault current occurs.

First claim

1 . A modular multilevel converter sub-module having a direct current (DC) fault current blocking function, comprising:
a normal circuit which includes a first switching element (T 1 ) and a second switching element (T 2 ) connected in series to control the modular multilevel converter sub-module to turn on or off through an on or off operation and a first diode (D 1 ) and a second diode (D 2 ) respectively connected to be parallel to the first switching element (T 1 ) and the second switching element (T 2 ) to offset a counter electromotive force generated in the first switching element (T 1 ) and the second switching element (T 2 ); a fault DC current blocking circuit which includes a capacitor (C) connected to the normal circuit in parallel and applies a capacitor voltage (V cap ) to a DC fault path as a reverse voltage (V Block ) with respect to a fault voltage (V Fault ); and a bypass circuit which includes a third switch element (T 3 ), is connected to the fault DC current blocking circuit in parallel, and determines an output voltage (V SM ) and a direction of an arm current (i ARM ) to provide a DC fault current bypass path when a DC fault current occurs.

2 . The modular multilevel converter sub-module of claim 1 , wherein the bypass circuit includes the third switching element (T 3 ), a third diode (D 3 ), a thyristor (TH 3 ), and a fourth diode (D 4 ), wherein the third switching element (T 3 ), the third diode (D 3 ), and the thyristor (TH 3 ) are connected in parallel and connected to the fourth diode (D 4 ), which is connected to the first switching element (T 1 ), in series to form a fault DC current path.

3 . The modular multilevel converter sub-module of claim 1 , wherein the first switching element (T 1 ), the second switching element (T 2 ), and the third switching element (T 3 ) each include an insulated gate bipolar transistor (IGBT).

4 . The modular multilevel converter sub-module of claim 1 , wherein, in a case in which the direction of the arm current (i ARM ) in a normal operation is positive (i ARM >0), a current always flows through the third diode (D 3 ) of the bypass circuit,
when the first switching element (T 1 ) is switched on, a current flows to the first diode (D 1 ), and the capacitor voltage (V cap ) of the fault DC current blocking circuit is output, and when the second switching element (T 2 ) is switched on, a current flows to the second switching element (T 2 ), and a sub-module voltage becomes zero.

5 . The modular multilevel converter sub-module of claim 1 , wherein, in a case in which the direction of the arm current i ARM in a normal operation is positive (i ARM >0),
when the modular multilevel converter sub-module is turned on, the modular multilevel converter sub-module has a switching state in which the first switching element (T 1 ) is switched on, the second switching element (T 2 ) is switched off, the third switching element (T 3 ) is switched off, and the thyristor (TH 3 ) is switched off, and when the modular multilevel converter sub-module is turned off, the modular multilevel converter sub-module has a switching state in which the first switching element (T 1 ) is switched off, the second switching element (T 2 ) is switched on, the third switching element (T 3 ) is switched off, and the thyristor (TH 3 ) is switched off.

6 . The modular multilevel converter sub-module of claim 1 , wherein, in a case in which the direction of the arm current (i ARM ) in a normal operation is negative (i ARM <0), a current flows through the third switching element (T 3 ) and the thyristor (TH 3 ),
when the first switching element (T 1 ) is switched on, a current flows to the first switching element (T 1 ), and the capacitor voltage (V cap ) of the fault DC current blocking circuit is output, and when the second switching element (T 2 ) is switched on, a current flows to the second diode (D 2 ), and a sub-module voltage becomes zero.

7 . The modular multilevel converter sub-module of claim 1 , wherein, in a case in which the direction of the arm current i ARM in a normal operation is negative (i ARM <0),
when the modular multilevel converter sub-module is turned on, the modular multilevel converter sub-module has a switching state in which the first switching element (T 1 ) is switched on, the second switching element (T 2 ) is switched off, the third switching element (T 3 ) is switched on, and the thyristor (TH 3 ) is switched on, and when the modular multilevel converter sub-module is turned off, the modular multilevel converter sub-module has a switching state in which the first switching element (T 1 ) is switched off, the second switching element (T 2 ) is switched on, the third switching element (T 3 ) is switched on, and the thyristor (TH 3 ) is switched on.

8 . The modular multilevel converter sub-module of claim 1 , wherein, during a fault operation, a current flows in a negative direction (i Fault <0), and when the third switching element (T 3 ) and the thyristor (TH 3 ) are switched off during a fault, a current flows to the fourth diode (D 4 ) and the second diode (D 2 ) so that the capacitor voltage (V cap ) is applied to the DC fault path as the reverse voltage (V Block ) with respect to the fault voltage (V Fault ) to block a fault DC current.

9 . The modular multilevel converter sub-module of claim 1 , wherein, during a fault operation, the modular multilevel converter sub-module has a switching state in which the first switching element (T 1 ) is switched off, the second switching element (T 2 ) is switched off, the third switching element (T 3 ) is switched off, and the thyristor (TH 3 ) is switched off.

10 . A method of controlling a modular multilevel converter sub-module having a direct current (DC) fault current blocking function, which includes a normal circuit which includes a first switching element (T 1 ) and a second switching element (T 2 ) connected in series to control the modular multilevel converter sub-module to turn on or off through an on or off operation and a first diode (D 1 ) and a second diode (D 2 ) respectively connected to be parallel to the first switching element (T 1 ) and the second switching element (T 2 ) to offset a counter electromotive force generated in the first switching element (T 1 ) and the second switching element (T 2 ), a fault DC current blocking circuit which includes a capacitor (C) connected to the normal circuit in parallel and applies a capacitor voltage (V cap ) to a DC fault path as a reverse voltage (V Block ) with respect to a fault voltage (V Fault ), and a bypass circuit which includes a third switching element (T 3 ), a third diode (D 3 ), a thyristor (TH 3 ), and a fourth diode (D 4 ), wherein the third switching element (T 3 ), the third diode (D 3 ), and the thyristor (TH 3 ) are connected in parallel and are connected to the fourth diode (D 4 ) which is connected to the first switching element (T 1 ), in series to form a fault DC current path, the method comprising:
when a fault occurs, switching the third switching element (T 3 ) and the thyristor (TH 3 ) off to allow a current to flow to the fourth diode (D 4 ) and the second diode (D 2 ); and applying the capacitor voltage (V cap ) to the DC fault path as the reverse voltage (V Block ) with respect to the fault voltage (V Fault ) to block a fault DC current.

11 . The method of claim 10 , wherein, when the fault occurs, the modular multilevel converter sub-module has a switching state in which the first switching element (T 1 ) is switched off, the second switching element (T 2 ) is switched off, the third switching element (T 3 ) is switched off, and the thyristor (TH 3 ) is switched off.

12 . The method

Assignees

• Univ Yonsei Iacf

Inventors

• Hur Kyeon
• Kim Heejin
• Kim Sangmin
• Na Jongseo
• Kim Ryangkyu

Classifications

• H02M7/483 Primary

  Converters with outputs that each can have more than two voltages levels · CPC title

• H02M7/4835

  comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage · CPC title

• H02M1/32 Primary

  Means for protecting converters other than automatic disconnection · CPC title

• H02M1/0048

  Circuits or arrangements for reducing losses (using snubbers H02M1/34) · CPC title

• H02M1/322

  Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock · CPC title