High voltage DC power conversion system and method of operating the same

• US 9,407,157 B2
• Filed: 09/13/2013
• Issued: 08/02/2016
• Est. Priority Date: 09/13/2013
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Gupta, Ranjan Kumar, Zhou, Rui
• Primary Examiner(s): PATEL, RAJNIKANT B
• Application Number:
  US14/026,737
• Publication Number:
  US 20150078046A1
• Time in Patent Office: 1,054 Days
• Field of Search: 307/21, 307/39, 307/40, 307/43, 307/52, 307/63, 307/153, 363/17, 363/34, 363/37, 363/40, 363/41, 363/71, 363/132
• US Class Current: 1/1
• CPC Class Codes: H02J 1/102 being switching converters H02J1/108, H02J1/12 take precedence
• CPC Class Codes: H02J 2300/28 The renewable source being wind energy wind motors F03D
• 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: H02M 1/0077 Plural converter units whose outputs are connected in series
• CPC Class Codes: H02M 7/04 by static converters
• 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

A fraction rated conversion system for coupling a plurality of high voltage direct current (HVDC) power strings in parallel to an HVDC transmission system includes at least one fraction rated power converter coupled to the plurality of HVDC power strings and at least one capacitive device coupled to the at least one fraction rated power converter. The at least one fraction rated power converter and the at least one capacitive device regulate a differential voltage across each HVDC power string of the plurality of HVDC power strings to be substantially similar to each other.

Claims

1. An electric power conversion system coupled to a high voltage direct current (HVDC) transmission system, said electric power conversion system comprising:

a first HVDC transmission conduit having a first polarity;

a second HVDC transmission conduit having a second polarity;

a plurality of HVDC power strings extending in parallel between said first HVDC transmission conduit and said second HVDC transmission conduit;

a fraction rated conversion system comprising;

at least one fraction rated power converter coupled to said plurality of HVDC power strings; and

at least one capacitive device coupled to said at least one fraction rated power converter, said at least one fraction rated power converter and said at least one capacitive device regulate a differential voltage across each HVDC power string of said plurality of HVDC power strings to be substantially similar to each other.

2. The electric power conversion system in accordance with claim 1 further comprising a plurality of power converters, each of said power converters coupled to one of an alternating current (AC) power source and a DC power source.

3. The electric power conversion system in accordance with claim 1 further comprising a plurality of power converters, each of said power converters coupled to one HVDC power string of said plurality of HVDC power strings.

4. The electric power conversion system in accordance with claim 3, wherein at least one HVDC power string of said plurality of HVDC power strings comprises a group of said plurality of power converters coupled in series.

5. The electric power conversion system in accordance with claim 1, wherein said at least one fraction rated power converter is configured to receive at least a portion of DC current transmitted through each HVDC power string of said plurality of HVDC power strings and regulate DC current transmitted through each of said HVDC power strings.

6. The electric power conversion system in accordance with claim 1, wherein said at least one fraction rated power converter is configured to circulate DC current received from each HVDC power string of said plurality of HVDC power strings to regulate DC current transmitted through each of said HVDC power strings to be substantially similar to each other.

7. The electric power conversion system in accordance with claim 1, wherein said at least one capacitive device and said at least one fraction rated power converter are configured to induce a supplemental voltage to each HVDC power string of said plurality of HVDC power strings.

8. The electric power conversion system in accordance with claim 1, wherein said at least one fraction rated power converter is configured to induce a supplemental voltage for each HVDC power string of said plurality of HVDC power strings, such induced supplemental voltages have predetermined values such that when added to existing voltages induced across said plurality of HVDC power strings the total voltages induced across each of said HVDC power strings are substantially similar to each other.

9. The electric power conversion system in accordance with claim 8, wherein the sum of all supplemental voltages induced by said at least one fraction rated power converter is approximately zero.

15. The electric power conversion system in accordance with claim 1, wherein the at least one fraction rated power converter comprises a bi-directional power converter.

16. The electric power conversion system in accordance with claim 4, wherein each of said group of said plurality of power converters is an AC-to-DC converter and is coupled to an AC electric power generation device such that said group of said plurality of power converters are coupled in parallel on the AC side of each of said group of said plurality of power converters.

17. The electric power conversion system in accordance with claim 1, wherein the said at least one capacitive device is maintained at a predetermined, substantially constant voltage.

18. The electric power conversion system in accordance with claim 7, further comprising:

a supervisory control and data acquisition system configured to receive electric current values for each of the plurality of HVDC power strings and command the fraction rated conversion system to induce the supplemental voltages.

19. The electric power conversion system in accordance with claim 18, wherein the supervisory control and data acquisition system measures values of differential voltages of each HVDC power string and compares the measured values of differential voltages to a predetermined voltage of a HVDC electric power transmission grid comprising the first and second HVDC transmission conduits.

20. The electric power conversion system in accordance with claim 19, wherein a sum of the supplemental voltages that the supervisory control and data acquisition system commands the fraction rated conversion system to induce is approximately zero.

10. A method of operating an electric power conversion system, the electric power conversion system coupled to a high voltage direct current (HVDC) transmission system, the electric power conversion system including a first HVDC transmission conduit having a first polarity and a second HVDC transmission system having a second polarity, a plurality of HVDC power strings extending in parallel between the first HVDC transmission conduit and the second HVDC transmission conduit, and a fraction rated conversion system including at least one fraction rated power converter coupled to the plurality of HVDC power strings and at least one capacitive device coupled to the at least one fraction rated power converter, said method comprising:

sensing a differential voltage value across each of the HVDC power strings, thereby determining a plurality of differential voltage values;

comparing the plurality of differential voltage values to a predetermined reference differential voltage value; and

regulating at least one differential voltage value such that the differential voltage values sensed across each of the HVDC power strings are substantially similar to each other.

11. The method in accordance with claim 10 further comprising:

sensing, a DC current value through each of the HVDC power strings, wherein regulating at least one differential voltage value comprises regulating DC current transmitted through at least one HVDC power string;

transmitting at least a portion of DC current transmitted through each HVDC power string to the at least one fraction rated power converter; and

circulating DC current received from each HVDC power string to regulate DC current transmitted through each HVDC power string to be substantially similar to each other.

12. The method in accordance with claim 10, wherein regulating at least one differential voltage value comprises inducing a supplemental voltage on at least one HVDC power string.

13. The method in accordance with claim 12, wherein inducing a supplemental voltage on at least one HVDC power string comprises:

inducing a supplemental voltage for each HVDC power string, each induced supplemental voltage has a determined value related to the comparison of each differential voltage value for each HVDC power string to the predetermined reference differential voltage value; and

adding each induced supplemental voltage to the sensed differential voltage value across each associated HVDC power string.

14. The method in accordance with claim 12, wherein inducing a supplemental voltage for each HVDC power string comprises inducing a plurality of supplemental voltages having values that are at least one of positive, negative, and zero, such that the sum of all supplemental voltages induced by the at least one fraction rated power converter is approximately zero.