Stereoscopic DC-DC converter and grid interconnector

Patent metadata

Field	Value
Publication number	US-9755523-B2
Application number	US-201414412002-A
Country	US
Kind code	B2
Filing date	Feb 25, 2014
Priority date	Jan 20, 2014
Publication date	Sep 5, 2017
Grant date	Sep 5, 2017

Abstract

The present invention discloses a stereoscopic DC-DC converter for power transfer between two DC grids, the converter comprises a first converter, a second converter and a third converter, a positive terminal of the first converter is connected to a positive terminal of a second DC grid, a negative terminal of the first converter is connected to a positive terminal of the second converter, a negative terminal of the second converter is connected to a positive terminal of the third converter, a negative terminal of the third converter is connected to a negative terminal of the second DC grid, in the meantime, a positive terminal of the second converter is also connected to a positive terminal of a first DC grid, and the negative terminal of the second converter is also connected to a negative terminal of the first DC grid. Compared with the conventional DC-DC converter employing the DC-AC-DC converting technology, the DC-DC converter of the invention makes full use of existing DC voltage of the first DC grid, which significantly reduces overall power of converters that are used, and thus cost and power loss caused thereby.

First claim

The invention claimed is:

1. A stereoscopic DC-DC converter for power transfer between a first DC grid ( 8 ) and a second DC grid ( 9 ), comprising a first converter ( 1 ), a second converter ( 2 ), and a third converter ( 3 ), wherein:
a positive terminal of said first converter ( 1 ) is directly connected to a positive terminal of said second DC grid ( 9 );
a negative terminal of said first converter ( 1 ) is connected to a positive terminal of said second converter ( 2 );
a negative terminal of said second converter ( 2 ) is connected to a positive terminal of said third converter ( 3 );
a negative terminal of said third converter ( 3 ) is directly connected to a negative terminal of said second DC grid ( 9 );
said positive terminal of said second converter ( 2 ) is connected, via a DC transmission line, to a positive terminal of said first DC grid ( 8 ); and
said negative terminal of said second converter ( 2 ) is directly connected, via a DC transmission line, to a negative terminal of the first DC grid ( 8 ), wherein at least part of the power transferred between the first DC grid and the second DC grid is transferred via a direct electrical connection between the first DC grid and the second DC grid without DC-AC-DC conversion.

2. The stereoscopic DC-DC converter of claim 1 , wherein each of the first converter ( 1 ), the second converter ( 2 ), and the third converter ( 3 ) comprises an AC terminal, and wherein:
the AC terminals of said first converter ( 1 ) and of said third converter ( 3 ) are connected to an AC grid via first and third transformers, respectively, and the AC terminal of said second converter ( 2 ) is connected to said AC grid via a second transformer or a second phase reactor; or
said AC terminals of said first converter ( 1 ) and of said third converter ( 3 ) are connected to said AC grid via first and third phase reactors, respectively, and said AC terminal of said second converter ( 2 ) is connected to said AC grid via a second transformer.

3. The stereoscopic DC-DC converter of claim 2 , wherein the AC terminals of said first converter ( 1 ), said second converter ( 2 ), and said third converter ( 3 ) are connected to a common AC bus ( 7 ) or to different AC grids, respectively.

4. The stereoscopic DC-DC converter of claim 2 , wherein the AC terminals of said first converter ( 1 ) and of said third converter ( 3 ) are connected to an AC grid via first and third transformers, respectively, and the AC terminal of said second converter ( 2 ) is connected to said AC grid via the second transformer or the second phase reactor, and wherein AC terminals of transformers ( 4 , 5 ) of said first converter ( 1 ) and of said third converter ( 3 ) in the vicinity of a DC side employ delta connection to eliminate unbalanced neutral points of said first converter ( 1 ) and said third converter ( 3 ), and AC terminals of transformers ( 4 , 5 ) of said second converter ( 2 ) in the vicinity of a DC side and terminals of said first converter ( 1 ) and said third converter ( 3 ) in the vicinity of an AC side employ star connection or delta connection.

5. The stereoscopic DC-DC converter of claim 2 , wherein said AC terminals of said first converter ( 1 ) and of said third converter ( 3 ) are connected to said AC grid via first and third phase reactors, respectively, and the AC terminal of said second converter ( 2 ) is connected to said AC grid via the second transformer, and wherein each phase of phase reactor branches ( 13 , 16 ) of said first converter ( 1 ) and said third converter ( 3 ) employs delta connection to eliminate unbalanced neutral points of said first converter ( 1 ) and said third converter ( 3 ).

6. The stereoscopic DC-DC converter of claim 1 , wherein said first converter ( 1 ), said second converter ( 2 ), and said third converter ( 3 ) employ voltage source converters, line commutated converters, or un-controlled rectifying bridges.

7. The stereoscopic DC-DC converter of claim 1 , wherein said first converter ( 1 ) and said third converter ( 3 ) employ thyristor-based line commutated converters to enable unidirectional power flow between said first and second DC grids ( 8 , 9 ), so as to achieve interconnection between two DC grids with unidirectional power flow.

8. The stereoscopic DC-DC converter of claim 1 , wherein a first DC circuit breaker ( 20 ) is serially connected between said negative terminal of said first converter ( 1 ) and said positive terminal of said second converter ( 2 ), and a second DC circuit breaker ( 25 ) is serially connected between said negative terminal of said second converter ( 2 ) and said positive terminal of said third converter ( 3 ), so that said stereoscopic DC-DC converter is not destroyed by over voltage or over-current during DC fault at said first DC grid ( 8 ) and/or said second DC grid ( 9 ).

9. The stereoscopic DC-DC converter of claim 8 , wherein protection of said stereoscopic DC-DC converter during DC fault at said second DC grid ( 9 ) is facilitated by blocking trigger pulses of fully controllable power electronics devices ( 26 ) or thyristors in said first converter ( 1 ), said second converter ( 2 ), and said third converter ( 3 ) to cut off paths of DC fault current provided to fault points of said second DC grid ( 9 ) by said first converter ( 1 ), said second converter ( 2 ), and said third converter ( 3 ) via said fully controllable power electronics devices ( 26 ) or said thyristors, respectively, and by simultaneously opening said first DC circuit breaker ( 20 ) and said second DC circuit breaker ( 25 ) to cut off paths of DC fault current provided to said fault points of said second DC grid ( 9 ) by said first DC grid ( 8 ) via diodes of said first converter ( 1 ) and said third converter ( 3 ).

10. The stereoscopic DC-DC converter of claim 8 , wherein by blocking trigger pulses of fully controllable power electronics devices ( 26 ) or thyristors in said first converter ( 1 ), said second converter ( 2 ), and said third converter ( 3 ) to cut off paths of DC fault current provided to fault points of said first DC grid ( 8 ) by said first converter ( 1 ), said second converter ( 2 ) and said third converter ( 3 ) via said fully controllable power electronics devices ( 26 ) or said thyristors, respectively, and by simultaneously opening said first DC circuit breaker ( 20 ) and said second DC circuit breaker ( 25 ) so that voltage of said second DC grid ( 9 ) is applied to a series connection circuit of said first converter ( 1 ), said first DC circuit breaker ( 20 ), said second DC circuit breaker ( 25 ), and said third converter ( 3 ), said first converter ( 1 ) and said third converter ( 3 ) are protected from being destroyed by over voltage as said first converter ( 1 ) and said third converter ( 3 ) solely endure DC voltage of said second DC grid ( 9 ), and to facilitate protection of said stereoscopic DC-DC converter during DC fault at said first DC grid ( 8 ).

11. The stereoscopic DC-DC converter of claim 8 , wherein:
rated DC voltage of said first DC circuit breaker ( 20 ) and said second DC circuit breaker ( 25 ) is half that of said second converter ( 2 ), and rated current of said first DC circuit breaker ( 20 ) and said second DC circuit breaker ( 25 ) is P|E 1 -P/E 2 , where P is rated transferred power between said first DC grid ( 8 ) and said second DC grid ( 9 ), E 1 is rated DC voltage of said first DC grid ( 8 ), and E 2 is rated DC voltage of said second DC grid ( 9 ).

12. The stereoscopic DC-DC converter of claim 1 , wherein said first converter ( 1 ) and said third converter ( 3 ) operate to control active power thereof, and said second converter ( 2 ) operates to control AC

Assignees

• Univ Huazhong Science Tech

Inventors

• Lin Weixing
• Wen Jinyu
• Cheng Shijie

Classifications

• H02J1/102

  being switching converters (H02J1/108, H02J1/12 take precedence) · CPC title

• H02M3/335

  using semiconductor devices only · CPC title

• H02M2001/0074

  Electricity · mapped topic

• H02M7/7575

  for high voltage direct transmission link · CPC title

• H02M2007/4835

  Electricity · mapped topic