METHODS AND APPARATUS FOR CONTROLLING CURRENT IN AN ELECTRICAL MACHINE

• US 20080106098A1
• Filed: 11/02/2006
• Published: 05/08/2008
• Est. Priority Date: 11/02/2006
• Status: Active Grant

• Current Assignee: GE Infrastructure Technology, LLC (General Electric Company)
• Original Assignee: General Electric Company
• Inventors: Delmerico, Robert William, Miller, Nicholas Wright, Larsen, Einar
• Granted Patent: US 7,417,333 B2
• Time in Patent Office: Days
• US Class Current: 290/44
• CPC Class Codes: F03D 9/25 the apparatus being an electrical generator F03D9/22 takes precedence
• CPC Class Codes: H02J 2300/28 The renewable source being wind energy wind motors F03D
• CPC Class Codes: H02J 3/1871 Methods for planning installation of shunt reactive power compensators
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/50 Controlling the sharing of the out-of-phase component
• CPC Class Codes: H02P 21/22 Current control, e.g. using a current control loop
• CPC Class Codes: Y02E 10/72 Wind turbines with rotation axis in wind direction
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects

Abstract

A method for determining electric currents for an electrical machine includes generating a first real power current demand signal and a first reactive power current demand signal. The method also includes determining at least one of a second real power current demand signal and a second reactive power current demand signal by prioritizing a second real power current demand signal over a second reactive power current demand signal. Alternatively, the method also includes determining at least one of a second real power current demand signal and a second reactive power current demand signal by prioritizing the second reactive power current demand signal over the second real power current demand signal. The method further includes comparing at least one of the first real power current demand signal and first reactive power current demand signal to at least one electrical machine current limit signal.

Claims

1. A method for determining electric currents for an electrical machine, said method comprising:

generating a first real power current demand signal and a first reactive power current demand signal; and

determining at least one of a second real power current demand signal and a second reactive power current demand signal by;

prioritizing at least one of a second real power current demand signal over a second reactive power current demand signal and the second reactive power current demand signal over the second real power current demand signal; and

comparing at least one of the first real power current demand signal and first reactive power current demand signal to at least one electrical machine current limit signal.

2. A method in accordance with claim 1 wherein prioritizing at least one of the second real power current demand signal over the second reactive power current demand signal and the second reactive power current demand signal over the second real power current demand signal comprises selecting at least one of a real power current demand signal functional logic block and a reactive power current demand signal functional logic block.

3. A method in accordance with claim 2 wherein selecting at least one of the real power current demand signal functional logic block and the reactive power current demand signal functional logic block comprises at least one of:

shifting at least one discrete switch configured to shift between the real power current demand signal functional logic block and the reactive power current demand signal functional logic block substantially using operator prerogative; and

using a substantially automated selection logic block configured to shift between at least the real power current demand signal functional logic block and the reactive power current demand signal functional logic block.

4. A method in accordance with claim 3 wherein using the substantially automated selection logic block comprises:

using at least one total current demand signal algorithm to calculate a total current demand signal, the at least one total current demand signal algorithm configured to receive the first real power current demand signal and the first reactive power current demand signal;

using at least one first comparison algorithm to compare the total current demand signal and the at least one electrical machine current limit signal, thereby generating a first result signal;

using at least one reactive power current algorithm to calculate a reactive power current signal, the at least one reactive power current algorithm using at least one of a reactive power signal, an apparent power signal, and the at least one electrical machine current limit signal;

using at least one second comparison algorithm to compare an absolute value of the reactive power current signal and an absolute value of the total current demand signal, thereby generating a second result signal;

using at least one real power current algorithm to calculate a real power current signal, the at least one real power current signal algorithm using at least one of a real power signal, an apparent power signal, and the at least one electrical machine current limit signal;

using at least one third comparison algorithm to compare the real power current signal and the total current demand signal, thereby generating a third result signal;

using at least one of the first, second and third result signals to modulate at least one of;

the real power current demand signal within a first band and a reactive power current demand signal within a second band, said first band greater than said second band; and

the reactive power current demand signal within a third band and a real power current demand signal within a fourth band, said third band greater than said fourth band.

5. A method in accordance with claim 1 wherein determining a second real power current demand signal comprises determining an upper real power current limit signal using at least one of:

the first reactive power current demand signal; and

the at least one electrical machine current limit signal.

6. A method in accordance with claim 5 wherein determining an upper real power current limit signal using the at least one electrical machine current limit signal comprises comparing the at least one electrical machine current limit signal with at least one of the first real power current demand signal and the first reactive power current demand signal using at least one of the following algorithms:

the operating upper real power current limit signal=√

((the at least one electrical machine current limit signal)²−

(the first real power current demand signal)²); and

the operating upper real power current limit signal=√

((the at least one electrical machine current limit signal)²−

(the first reactive power current demand signal)²).

7. A method in accordance with claim 1 wherein determining a second reactive power current demand signal comprises determining at least one of an upper reactive power current limit signal and a lower reactive power current limit signal using at least one of:

at least one electrical machine voltage;

the at least one electrical machine current limit signal;

at least one electrical machine voltage limit signal;

the first reactive power current demand signal; and

the first real power current demand signal.

8. A method in accordance with claim 7 wherein determining at least one of an upper reactive power current limit signal and a lower reactive power current limit signal using the at least one electrical machine current limit signal comprises comparing the at least one electrical machine current limit signal with the real power current demand signal using at least the following algorithm:

the operating upper real power current limit signal=√

((the at least one electrical machine current limit signal)²−

(the first real power current demand signal)²).

9. A control system for determining electric currents for an electrical machine comprising:

at least one real power current demand signal functional logic block configured to modulate a real power current demand signal within a first band and modulate a reactive power current demand signal within a second band, wherein said first band is greater than said second band;

at least one reactive power current functional logic block configured to modulate a reactive power current demand signal within a third band and modulate a real power current demand signal within a fourth band, wherein said third band is greater than said fourth band; and

at least one selection mechanism configured to select at least one of said real power current demand signal functional logic block and said reactive power current demand signal functional logic block.

10. A control system in accordance with claim 9 wherein said at least one selection mechanism comprises at least one of:

at least one discrete switch, said switch configured to shift between selecting said real power current demand signal functional logic block and said reactive power current demand signal functional logic block substantially using operator prerogative; and

at least one substantially automated selection logic block configured to shift between at least said real power current demand signal functional logic block and said reactive power current demand signal functional logic block.

11. A control system in accordance with claim 10 wherein said at least one substantially automated selection logic block further comprises:

at least one total current demand signal algorithm configured to calculate a total current demand signal;

at least one first comparison algorithm configured to compare said total current demand signal and at least one electrical machine current limit signal;

at least one reactive power current algorithm configured to calculate a reactive power current signal;

at least one second comparison algorithm configured to compare an absolute value of said reactive power current signal and an absolute value of said total current demand signal;

at least one real power current algorithm configured to calculate a real power current signal; and

at least one third comparison algorithm configured to compare said real power current signal and said total current demand signal.

12. A control system in accordance with claim 11 wherein said at least one electrical machine current limit signal comprises a value substantially equivalent to at least one of:

at least one electric machine temperature-dependent current limit;

at least one hard real power current limit;

at least one hard reactive power current limit; and

at least one electric machine voltage limit.

13. A control system in accordance with claim 9 further comprising:

at least one reactive power current demand signal bounding function configured to receive at least one bounding signal from at least one of;

said at least one real power current demand signal functional logic block; and

said at least one reactive power current demand signal functional logic block.

14. A control system in accordance with claim 9 further comprising:

at least one real power current demand signal bounding function configured to receive at least one bounding signal from at least one of;

said at least one real power current demand signal functional logic block; and

said at least one reactive power current demand signal functional logic block.

15. A wind turbine generator comprising:

a rotor comprising a hub, at least one rotor blade coupled to said hub, and a rotor shaft coupled to said hub for rotation therewith;

at least one electrical generator coupled to said rotor shaft;

at least one frequency converter electrically coupled to said electrical generator; and

a control system for determining electric currents in at least one of said at least one electrical generator and said at least one frequency converter, said control system comprising at least one real power current demand signal functional logic block, at least one reactive power current functional logic block, and at least one selection mechanism, said at least one real power current demand signal functional logic block configured to modulate a real power current demand signal within a first band and modulate a reactive power current demand signal within a second band, wherein said first band is greater than said second band, said at least one reactive power current functional logic block configured to modulate a reactive power current demand signal within a third band and modulate a real power current demand signal within a fourth band, wherein said third band is greater than said fourth band, said at least one selection mechanism configured to select at least one of said real power current demand signal functional logic block and said reactive power current demand signal functional logic block.

16. A wind turbine generator in accordance with claim 15 wherein said at least one selection mechanism comprises at least one of:

at least one discrete switch, said switch configured to shift between selecting said real power current demand signal functional logic block and said reactive power current demand signal functional logic block substantially using operator prerogative; and

at least one substantially automated selection logic block configured to shift between at least said real power current demand signal functional logic block and said reactive power current demand signal functional logic block.

17. A wind turbine generator in accordance with claim 16 wherein said at least one substantially automated selection logic block further comprises:

at least one total current demand signal algorithm configured to calculate a total current demand signal;

at least one first comparison algorithm configured to compare said total current demand signal and at least one electrical machine current limit signal;

at least one reactive power current algorithm configured to calculate a reactive power current signal;

at least one second comparison algorithm configured to compare an absolute value of said reactive power current signal and an absolute value of said total current demand signal;

at least one real power current algorithm configured to calculate a real power current signal; and

at least one third comparison algorithm configured to compare said real power current signal and said total current demand signal.

18. A wind turbine generator in accordance with claim 17 wherein said at least one electrical machine current limit signal comprises a value substantially equivalent to at least one of:

at least one electric machine temperature-dependent current limit;

at least one hard real power current limit;

at least one hard reactive power current limit; and

at least one electric machine voltage limit.

19. A wind turbine generator in accordance with claim 15 further comprising:

at least one reactive power current demand signal bounding function configured to receive at least one bounding signal from at least one of;

said at least one real power current demand signal functional logic block; and

said at least one reactive power current demand signal functional logic block.

20. A wind turbine generator in accordance with claim 15 further comprising:

at least one real power current demand signal bounding function configured to receive at least one bounding signal from at least one of;

said at least one real power current demand signal functional logic block; and

said at least one reactive power current demand signal functional logic block.