Distributed generation system and power system stabilizing method

• US 7,663,348 B2
• Filed: 10/26/2006
• Issued: 02/16/2010
• Est. Priority Date: 10/27/2005
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Ichinose, Masaya, Futami, Motoo, Matsutake, Mitsugu, Oohara, Shinya, Fukuda, Shoji
• Primary Examiner(s): Ponomarenko; Nicholas
• Assistant Examiner(s): Cuevas; Pedro J
• Application Number:
  US11/586,540
• Publication Number:
  US 20070097565A1
• Time in Patent Office: 1,209 Days
• Field of Search: 290/44, 322/24, 361/62
• US Class Current: 322/24
• CPC Class Codes: H02J 2300/28 The renewable source being wind energy wind motors F03D
• CPC Class Codes: H02J 3/24 Arrangements for preventing or reducing oscillations of power in networks by control effected upon a single generator H02P9/00
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/48 Controlling the sharing of the in-phase component
• CPC Class Codes: H02J 3/50 Controlling the sharing of the out-of-phase component
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects

Abstract

A distributed generation system that can suppress a voltage fluctuation caused by a distributed generation by an apparatus of a small power capacity in the distributed generation itself and stabilize the power system voltage without inserting interharmonic voltage or current into the power system and without interference among a plurality of distributed generations. Parameter α(t) varying with time is estimated based on fluctuating component ΔP of the active power P generated by the distributed generation and the voltage fluctuating component ΔV attributable to the distributed generation developed at the point of connection between the distributed generation and power system. The distributed generation produces reactive power Q=−αP or Q=−αΔP, to thereby suppresses only the voltage fluctuation of the power system attributable to the distributed generation.

Claims

1. A distributed generation system comprising:

a power converter connected to a power system, to generate an output voltage and an output current;

a voltage detector arranged to detect the output voltage outputted from the power converter to the power system;

a current detector arranged to detect the an output current outputted from the power converter to the power system; and

control means for controlling the distributed generation according to the detected voltage and current so as to suppress a voltage fluctuation attributable to the output of the distributed generation and developed at the point of connection between the power system and the distributed generation system,

wherein the power converter is controlled by the control means.

2. A distributed generation system as claimed in claim 1, wherein the control means for controlling the distributed generation is adapted to adjust a ratio P/Q of an active power P to a reactive power Q, both generated by the distributed generation, according to the detected output.

3. A distributed generation system as claimed in claim 1, wherein the control means for controlling the distributed generation such that a ratio P/Q of an active power P to a reactive power Q, both generated by the distributed generation, is varied with time on the basis of the output voltage and the output current.

4. A distributed generation system as claimed in claim 1, comprising:

an active power detecting means for detecting an active power P of the distributed generation; and

means for calculating fluctuating components Δ

P and Δ

V of an active power P and a reactive power Q, respectively;

wherein the control means controls the distributed generation such that a ratio P/Q of the active power P to the reactive power Q, both generated by the distributed generation, is varied with time on the basis of the active power fluctuation Δ

P and the output voltage fluctuation Δ

V.

5. A distributed generation system as claimed in claim 1, comprising:

an active power detecting means for detecting an active power P of the distributed generation; and

means for calculating a short period fluctuating component Δ

P of the active power P;

wherein the control means controls the distributed generation such that a ratio Δ

P/Q of the short period fluctuating component Δ

P and the reactive power Q generated by the distributed generation is varied according to the detected output.

6. A distributed generation system as claimed in claim 1, comprising:

means for operating the distributed generation under a condition that a reactive power command is kept substantially equal to zero;

means for detecting a voltage fluctuation at the point of connection attributable to an active power P of the distributed generation operated under said condition;

means for obtaining, based on the voltage fluctuation, a target value a for the ratio P/Q of the active power P to the reactive power Q, both generated by the distributed generation; and

means for calculating the reactive power command Q* to be generated by the distributed generation on the basis of the target value α

;

wherein the control means controls the distributed generation according to the reactive power command Q*.

7. A distributed generation system as claimed in claim 1, wherein the distributed generation is a wind turbine system.

8. A distributed generation system as claimed in claim 7, wherein the wind turbine system comprises:

at least one wind turbine having three blades; and

means for extracting a short period fluctuating component Δ

P of the active power in a frequency band which approximates three times a rotating frequency of the blades;

wherein the control means controls the wind turbine system such that a ratio Δ

P/Q of the short period fluctuating component Δ

P and the reactive power Q is varied with time according to the detected output.

9. A distributed generation system as claimed in claim 1, comprising:

a plurality of distributed generations connected in parallel with the power system; and

a plurality of control means for detecting the outputs of the respective distributed generations and for controlling the respective distributed generations according to the detected outputs such that the voltage fluctuating components developed at points of connection attributable to the outputs of the respective distributed generations are supressed.

10. A distributed generation system as claimed in claim 1, wherein the power converter converts the alternating power output of the power generator to an AC power of variable voltage/variable frequency;

and the control means controls the power converter according to the detected output.

11. A power system stabilizing method for use with a distributed generation system connected with a power system, comprising:

detecting an output of a distributed generation in the distributed generation system;

detecting a voltage fluctuation develored at the point of connection between the distributed generation system and the power system attributable to the output of the distributed generation; and

controlling the distributed generation according to the detected output of the distributed generation so that the voltage fluctuation developed at the point of connection between the distributed generation system and the power system is supressed.

12. A power system stabilizing method as claimed in claim 11, comprising controlling the output of the distributed generation such that a ratio P/Q of an active power P to a reactive power Q, both generated by the distributed generation, is varied with time according to the detected output.

13. A power system stabilizing method as claimed in claim 11, comprising:

detecting an output voltage V of the distributed generation;

detecting an output current I of the distributed generation; and

controlling the distributed generation such that a ratio P/Q of an active power P to a reactive power Q, both generated by the distributed generation, is varied with time on the basis of the output voltage V and the output current I.

14. A power system stabilizing method as claimed in claim 11, comprising:

detecting an active power P of the distributed generation;

detecting an output voltage V of the distributed generation;

calculating a fluctuating component Δ

P of the active power P and a fluctuating component Δ

V of the output voltage V; and

controlling the distributed generation that a ratio P/Q of the active power P to the reactive power Q, both generated by the distributed generation, is varied with time on the basis of the fluctuating component Δ

P and the fluctuating component Δ

V.

15. A power system stabilizing method as claimed in claim 11, comprising:

detecting an active power P of the distributed generation;

calculating a short period fluctuating component Δ

P of the active power P; and

controlling the distributed generation that a ratio AP/Q of a short period fluctuating component Δ

P to the reactive power Q, both attributable to the distributed generation, is varied with time based on the short period fluctuating component Δ

P of the active power P.