DC CONNECTION SCHEME FOR WINDFARM WITH INTERNAL MVDC COLLECTION GRID

• US 20130197704A1
• Filed: 02/01/2012
• Published: 08/01/2013
• Est. Priority Date: 02/01/2012
• Status: Active Grant

• Current Assignee: Hitachi Energy Limited (Hitachi, Ltd.)
• Original Assignee: ABB Research Ltd. (ABB Limited)
• Inventors: PAN, Jiuping, SRIVASTAVA, Kailash, QI, Li, LI, Jun, REZA, Muhamad
• Granted Patent: US 9,048,694 B2
• Time in Patent Office: Days
• US Class Current: 700/287
• CPC Class Codes: H02J 2300/28 The renewable source being wind energy
• CPC Class Codes: H02J 3/36 Arrangements for transfer of electric power between ac networks via a high-tension dc link
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects
• 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

Connection schemes for offshore power generation with an internal collection grid include a power generation system which includes a plurality of generator-rectifier subsystems. The scheme further includes a medium voltage DC (MVDC) collection network with positive pole cables and negative pole cables connected to the DC outputs of the generator-rectifier subsystems. At least one offshore substation includes a positive bus bar and a negative bus bar correspondingly connected to the positive pole cables and negative pole cables of the MVDC collection network and a plurality of main DC-DC converters. Each main DC-DC converter includes multiple modules connected to the MVDC bus bars and each module has a positive and a negative output such that the modules'"'"' outputs are serially connected to one another. The schemes may also include a high voltage DC (HVDC) transmission system connected to the modules'"'"' outputs and at least one DC/AC converter at an onshore substation.

Claims

1. A connection scheme for offshore power generation with an internal collection grid, comprising:

a power generation system including a plurality of generator-rectifier subsystems, said subsystems having at least one generator with an active rectifier, each said active rectifier having a positive DC voltage output and a negative DC voltage output;

a medium voltage DC (MVDC) collection network comprising positive pole cables and negative pole cables, and connected to said DC outputs of generator-rectifier subsystems;

at least one offshore substation comprising;

a positive bus bar and a negative bus bar correspondingly connected to said positive pole cables and negative pole cables of said MVDC collection network; and

a plurality of main DC-DC converters, each said main DC-DC converter comprising multiple modules connected to said MVDC bus bars, each said module having a positive output and a negative output such that said modules'"'"' outputs are serially connected to one another; and

a high voltage DC (HVDC) transmission system comprising at least two DC transmission lines connected to said modules'"'"' outputs.

2. The scheme according to claim 1, wherein said generator-rectifier sub-system comprises:

at least two turbine generators;

an active AC/DC rectifier associated with each of said turbine generators, each said rectifier having a positive DC output and a negative DC output, wherein said DC outputs of AC/DC rectifiers are connected to each other in series, wherein a positive output of a first AC/DC rectifier is connected to one of said positive pole cables in a feeder system, and a negative output of a last AC/DC rectifier is connected to said negative pole cable in a feeder system.

3. The scheme according to claim 1, wherein said generator-rectifier subsystem comprises:

a single turbine generator having at least two sets of stator windings;

an active AC/DC rectifier associated with each set said generator windings, each said AC/DC rectifier having a positive DC output and a negative DC output, wherein said DC outputs of AC/DC rectifiers are connected to each other in series, wherein positive output of a first AC/DC rectifier is connected to one of said positive pole cables in a feeder system, and a negative output of a last AC/DC rectifier is connected to said negative pole cable in said feeder system.

4. The scheme according to claim 1, wherein said active rectifiers comprise modular multi-level converter topology which has distributed energy storage inside and provides almost sinusoidal line-line voltage at generator side.

5. The scheme according to 1, wherein said MVDC collection network comprises multiple feeders, each said feeder comprising one of said positive pole cables and one of said negative pole cables, and said feeder connecting to at least one said generator-rectifier subsystem.

6. The scheme according to claim 1, further comprising:

a high voltage transmission system comprising a HVDC positive pole cable connected to said positive output of one said main DC/DC converters, and a HVDC negative pole cable connected to said negative output of another of said main DC/DC converters.

7. The scheme according to claim 1, wherein said plurality of main DC-DC converters are connected in parallel to said positive and negative bus bars.

8. The scheme according to claim 1, further comprising:

a high voltage transmission system comprising a HVDC positive pole cable connected to said positive output of one said main DC/DC converters, a HVDC negative pole cable connected to said negative output of another said main DC/DC converters, and a return cable connected to a negative output of one of said main DC/DC converters and a positive output of another of said main DC/DC converters different than said positive and negative outputs connected to said HVDC pole cables.

9. The scheme according to claim 1, further comprising:

an onshore station comprising;

a positive pole DC/AC converter connected to a positive pole HVDC cable;

a negative pole DC/AC converter connected to a negative pole HVDC cable;

two parallel three-phase converter transformers connected to said positive and negative pole converters and to a main power grid, wherein said HVDC transmission system comprises said positive pole and negative pole HVDC cables.

10. The scheme according to claim 9, wherein said pole DC/AC converters each have a positive DC terminal and a negative DC terminal , wherein said negative terminal of said positive pole converter and said positive terminal of said negative pole converter are connected together and grounded.

11. The scheme according to claim 1, further comprising:

an onshore station comprising a single DC/AC converter connected to HVDC positive and negative pole cables wherein said HVDC transmission system comprises said positive pole and negative pole HVDC cables.

12. The scheme according to claim 1, wherein said offshore substation further comprises:

an energy storage system connected to said bus bars.

13. The scheme according to claim 1, wherein said plurality of main DC-DC converters are connected in parallel to said positive and negative bus bars, said scheme further comprising:

a ground connection connected to a negative output of one of said main DC-DC converters and a positive output of another said main DC-DC converters different than said positive and negative outputs connected to said HVDC transmission lines.

14. The scheme according to claim 1, wherein said at least one offshore substation comprises one offshore substation with two MVDC bus sections, wherein each MVDC bus section comprises at least two main DC/DC converters,

the scheme further comprising:

a high voltage transmission system having a HVDC positive pole cable and a HVDC negative pole cable, wherein said at least one main DC/DC converter from said both first and second MVDC bus sections are connected in parallel to said HVDC positive pole cable and said at least one main DC/DC converter from said both first and second MVDC bus sections are connected in parallel to said HVDC negative pole cable.

15. The scheme according to claim 1, wherein said at least one offshore substation comprises:

two offshore substations;

wherein each offshore substation comprises at least two main DC/DC converters;

the scheme further comprising;

a high voltage transmission system having a HVDC positive pole cable and a HVDC negative pole cable, wherein said at least one main DC/DC converter from both said first and second offshore substations are connected in parallel to said HVDC positive pole cable and said at least one main DC/DC converter from both said first and second offshore substations are connected in parallel to said HVDC negative pole cable.

16. The scheme according to claim 1, further comprising:

a master controller connected to a substation controller associated with each said offshore substation, each said offshore substation having at least two main DC/DC converters connected in parallel between said bus bars and HVDC transmission lines, and each said main DC/DC converter generating an I_o, each said substation controller comprising;

an input voltage controller receiving a V_in signal and a V_in,ref signal and generating an I_o,ref signal; and

a current controller receiving said I_o signal and said I_o,ref signal, said current controller generating a duty cycle signal for receipt by each said main DC/DC converter.

17. The scheme according to claim 1, further comprising:

a master controller connected to a substation controller associated with each said offshore substation, each said offshore substation having at least two MVDC bus sections and at least two main DC/DC converters connected in parallel between each said MVDC bus section and said HVDC transmission lines, and each said main DC/DC converter generating an I_o, each said substation controller comprising;

an input voltage controller receiving a V_in signal, a V_in,ref signal and a P<sub>in—

ref</sub> vector singal, and generating an I_o,ref vector signal; and

a current controller receiving said I_o vector signal and said vector I_o,ref signal, said current controller generating a duty cycle vector signal for receipt by said main DC/DC converters.