Distributed generation system and power system stabilizing method

• US 7,948,217 B2
• Filed: 01/22/2010
• Issued: 05/24/2011
• Est. Priority Date: 10/27/2005
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Fukuda, Shoji, Ichinose, Masaya, Futami, Motoo, Matsutake, Mitsugu, Oohara, Shinya
• Primary Examiner(s): Cuevas; Pedro J.
• Application Number:
  US12/691,790
• Publication Number:
  US 20100117606A1
• Time in Patent Office: 487 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 distributed generation connected with a power system,

a static var compensator connected with the power system at a point of connection between the distributed generation and the power system, and

control means for detecting an output of the distributed generation and for controlling the static var compensator according to the detected output so that a voltage fluctuation developed at the point of connection attributable to the distributed generation is suppressed,

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

means for obtaining, based on the voltage fluctuation, a target value α

for ratios P/Q of the active power P to a reactive power Q, both generated by the distributed generation and the static var compensator; and

means for calculating a reactive power command Q* to be generated by the static var compensator on the basis of the target value α

;

wherein the control means controls the static var compensator according to the reactive power command Q*.

2. A distributed generation system as claimed in claim 1, wherein the control means controls the static var compensator such that a ratio P/Q of an active power P generated by the distributed generation to a reactive power Q generated by the static var compensator, is varied with time according to the detected output.

3. A distributed generation system as claimed in claim 1, wherein the control means controls the static var compensator such that a ratio P/Q of an active power P to a reactive power Q both generated by the distributed generation and the static var compensator, is varied with time according to the detected output, the active power P and reactive power Q being a combined output of the distributed generation and the static var compensator.

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

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

a voltage detector for detecting a voltage V developed at the point of connection; and

means for calculating a fluctuating component Δ

P of the active power P and a fluctuating component Δ

V of the voltage V developed at the point of connection;

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

P of the active power P and the fluctuating component Δ

V of the voltage V developed at the point of connection, the active power P and reactive power Q being a combined output of the distributed generation and the static var compensator.

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

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 static var compensator such that a ratio P/Q of the active power P to the reactive power Q both generated by the distributed generation and by the static var compensator, is varied with time on the basis of the short period fluctuating component Δ

P of the active power.

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

a load connected also with the power system near the point of connection,

wherein the control means detects a total output of the distributed generation and the load, and controls the static var compensator according to the detected output such that the voltage fluctuation developed at the point of connection attributable to the total output is suppressed.

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

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