Plant for transmitting electric power, including VSC-converter and DC/DC-converter

• US 6,144,567 A
• Filed: 09/20/1999
• Issued: 11/07/2000
• Est. Priority Date: 03/24/1997
• Status: Expired due to Fees

• Current Assignee: Asea Brown Boveri AB (ABB Limited)
• Original Assignee: Asea Brown Boveri AB (ABB Limited)
• Inventors: Asplund, Gunnar, Eriksson, Kjell
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/381,355
• Time in Patent Office: 414 Days
• Field of Search: 363/34, 363/35, 363/36, 363/37, 363/97, 363/98, 363/131, 363/132
• US Class Current: 363/37
• CPC Class Codes: H02J 3/36 Arrangements for transfer of electric power between ac networks via a high-tension dc link
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H02M 7/219 in a bridge configuration
• CPC Class Codes: Y02E 60/60 Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Abstract

A plant for transmitting electric power comprises at least one VSC-converter (1). It comprises also at least one DC/DC-converter (33, 34) having two current valves connected in series and an inductance connected to a midpoint therebetween. The DC/DC-converter is through said inductance connected to a first of the poles of the direct voltage side of the converter and through a first output terminal connected to one of the current valves to the second of the poles so as to obtain an unbalanced step-up-transformation of the direct voltage between the two poles while obtaining a potential having a higher value on the second output terminal (27) of the DC/DC-converter connected to the second current valve than on said first output terminal (28).

Claims

1. A plant for transmitting electric power comprising:

at least first and second VSC-converters, each adapted to convert direct voltage into alternating voltage and convert alternating voltage into direct voltage, and each having an alternating voltage side to which at least one phase of an alternating voltage network is connected and a direct voltage side having first and second poles with a direct voltage thereacross;

each of said VSC-converters being connected to first and second DC/DC-converters, respectively, each of said first and second DC/DC-converters having two current valves connected in series and an inductance connected to a midpoint therebetween;

said first DC/DC-converter being connected through said inductance to said first pole in said first VSC-converter and through a first output terminal connected to one of the current valves and to said second pole in said first VSC-converter;

said second DC/DC-converter being connected through said inductance to said first pole in said second VSC-converter and through a first output terminal connected to one of the current valves and to said second pole in said second VSC-converter;

whereby an unbalanced step-up-transformation of the direct voltage between the two poles in each of said first and second VSC-converters is produced while obtaining a potential of a higher magnitude on a second output terminal of each of said first and second DC/DC-converters, respectively, connected to the other current valve than on said first output terminal; and

wherein

said second poles of said first and second VSC-converters are each connected to an output terminal of a first additional said DC/DC-converter in common thereto, the inductance of said first additional DC/DC converter being connected to ground for defining a zero potential level, and wherein poles having opposite polarities form said second poles of said first and second VSC-converters and said first and second DC/DC-converters are adapted to deliver potentials having mutually opposite polarities on the second output terminals thereof.

2. A plant according to claim 1, wherein said first and second DC/DC-converters are adapted to deliver potentials of different signs but having the same magnitude on said second output terminals.

3. A plant according to claim 1, wherein at least one of said first and second VSC-converters is replaced by a plurality of VSC-converters which are connected in parallel at the direct voltage side thereof with direct voltage poles in common connected to said DC/DC-converters.

4. A plant according to claim 1, wherein said first and second VSC-converters, said first and second DC/DC-converters and the first additional DC/DC-converter form a unit, and wherein the plant comprises two said units having the second output terminal of one of the DC/DC-converters of each unit connected to a second additional DC/DC-converter each at an output terminal thereof, and wherein the inductance of the second additional DC/DC-converter is connected to ground for defining a zero potential level, the second output terminals connected to said additional second DC/DC-converter having different polarity signs, and wherein the remaining second output terminal of the DC/DC-converter of the respective unit is connected to the inductance of a separate additional third said DC/DC-converter, the first output terminal of which is connected to the same output terminal of the additional second DC/DC-converter as the unit in question through a said second output terminal is connected to so as, on said second output terminal of the respective third additional DC/DC-converter, to deliver a potential step-up-transformed further with respect to the input of this converter of an opposite sign for the respective unit.

5. A plant according to claim 1, wherein at least some of the converters are intended to be remotely arranged with respect to each other at sources for generating electric power delivered thereto through the alternating voltage network connected thereto, and wherein these VSC-converts are adapted to transfer this electric power to a direct voltage network in common arranged on the direct voltage side thereof.

6. A plant according to claim 5, wherein the converters are arranged connected to different generators of electric power driven by wind power.

7. A plant according to claim 1, comprising means for defining a zero potential level connected to at least one of the poles of the VSC-converter.

8. A plant according to claim 7, wherein said means is formed by a connection in series of two current valves each consisting of a semiconductor element of turn-off type and rectifier diode connected in anti-parallel therewith and an inductance connected to the midpoint between the two valves, the opposite end of which with respect to said midpoint being connected to ground.

9. A plant according to claim 1, wherein said first and second DC/DC-converters have each a pole of the direct voltage side of the converter connected to the inductance thereof and the opposite pole to the first output terminal thereof for delivering a potential of a higher magnitude at the second output terminals thereof than at the first output terminals.

10. A plant according to claim 9, wherein said first and second DC/DC-converters are adapted to deliver potentials of the same magnitude but with opposite signs at the second output terminals thereof.

11. A plant according to claim 9, comprising a plurality of DC/DC-converters connected in a cascade connection, with the first output terminal of a first cascaded DC/DC-converter being connected to the a second output terminal of a first of two cascaded DC/DC-converters and the inductance of said first cascaded DC/DC converter being connected to a second output terminal of the second of the two cascaded DC/DC converters for a continued unbalanced step-up-step-transformation of the direct voltage between said second output terminals.

12. A plant according to claim 1, wherein said VSC-converter is connected to an alternating voltage network having three phases and comprises therethrough a six-pulse-bridge.

13. A plant according to claim 1, wherein a direct voltage network for high voltage direct current (HVDC) is directly or indirectly connected to said direct voltage side of said first and second VSC-converters.