Method and system for detecting stand-alone operation of a distributed generating system

• US 20050146224A1
• Filed: 12/29/2003
• Published: 07/07/2005
• Est. Priority Date: 12/29/2003
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Liu, Yung-Hsiang, Lin, Jeu-Min, Huang, Shyh-Jier, Luor, Tain-Syh
• Granted Patent: US 7,342,758 B2
• Time in Patent Office: Days
• US Class Current: 307/69
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/388 Islanding, i.e. disconnection of local power supply from the network

Abstract

A method and a system for detecting stand-alone operation of a distributed generating system having a generating source connected in shunt with an independent power distribution system via a first branch breaker are proposed. A voltage or a frequency signal on the independent power distribution system is read. The wavelet transformation is performed on the voltage or frequency signal to form a time versus high-frequency component window and a time versus low-frequency component window for conveniently detecting the perturbation in the time domain of the signal. Next, whether the absolute value of the high-frequency component is greater than a threshold value and whether the duration is longer than another threshold value are determined. If both answers are yes, a stand-alone operation occurs. An alarm signal is immediately generated and sent to the first branch breaker to release the connection between the generating source and the power distribution system.

Claims

1. A method for detecting stand-alone operation of a distributed generating system, said distributed generating system having a generating source connected in shunt with an independent power distribution system via a first branch breaker, said method comprising the steps of:

a. reading a voltage signal or a frequency signal on said independent power distribution system;

b. performing the wavelet transformation to said voltage or frequency signal to form a time versus high-frequency component window and a time versus low-frequency component window for conveniently detecting the perturbation in a transient time domain of said signal;

c. determining whether an absolute value of the high-frequency component is greater than a threshold value and whether a duration is longer than another threshold value and deciding that a stand-alone operation occurs if both answers are yes; and

d. generating an alarm signal and sending said alarm signal to said first branch breaker to drive said first branch breaker to release a parallel connection between said generating source and said power distribution system.

2. The method for detecting stand-alone operation of a distributed generating system as claimed in claim 1, wherein a voltage comparator is used to input said voltage or frequency signal to said power distribution system.

3. The method for detecting stand-alone operation of a distributed generating system as claimed in claim 1, further comprising the following step after said Step a:

a′

. amplifing said voltage or frequency signal for convenient observation of the high-frequency component of the wavelet transformation.

4. The method for detecting stand-alone operation of a distributed generating system as claimed in claim 1, wherein perturbation in said voltage signal, said frequency signal, or both is is detected in said Step b.

5. The method for detecting stand-alone operation of a distributed generating system as claimed in claim 1, wherein said threshold values include a time threshold value and a threshold value for the absolute value of the high-frequency component in said Step c.

6. The method for detecting stand-alone operation of a distributed generating system as claimed in claim 5, wherein said time threshold value is set to 0.13 sec and said threshold value for the absolute value of the high-frequency component is set to 0.01.

7. The method for detecting stand-alone operation of a distributed generating system as claimed in claim 1, wherein the perturbation is determined to be due to other electric phenomena if said perturbation is not greater than said threshold value.

8. A system for detecting stand-alone operation of a distributed generating system, said distributed generating system forming an independent power distribution system connected in shunt with the public electric power grid, said detection system comprising:

a generating source for providing power for said independent power distribution system;

a first branch breaker connected between said generating source and said independent power distribution system;

a voltage/frequency input device connected to said independent power distribution system and used to input a voltage signal or a frequency signal in said independent power distribution system; and

a calculating processing device for performing the wavelet transformation of said voltage or frequency signal on said independent power distribution system to determine whether stand-alone operation occurs on said independent power distribution system, said first branch breaker being controlled to release a parallel connection between said generating source and said independent power distribution system if stand-alone operation occurs on said independent power distribution system.

9. The system for detecting stand-alone operation of a distributed generating system as claimed in claim 8, wherein said distributed generating system is a cogeneration generating system, a solar generating system or a wind generating system.

10. The system for detecting stand-alone operation of a distributed generating system as claimed in claim 8, further comprising a second branch breaker connected between said independent power distribution system and said public electric power grid, said second branch breaker being controlled by the power company to release a connection between said independent power distribution system and said public electric power grid.

11. The system for detecting stand-alone operation of a distributed generating system as claimed in claim 8, wherein said voltage/frequency input device is a voltage comparator.

12. The system for detecting stand-alone operation of a distributed generating system as claimed in claim 8, wherein said calculating processing device has a microprocessor.

13. The system for detecting stand-alone operation of a distributed generating system as claimed in claim 8, wherein said voltage signal, said frequency signal or both are decomposed into a time versus high-frequency component window and a time versus low-frequency component window by the wavelet transformation for observation of the perturbation in said signals, and a stand-alone operation is determined to be occurring in said distributed generating system if an absolute value of the high-frequency component is greater than a threshold value and a duration is higher than another threshold value.

14. The system for detecting stand-alone operation of a distributed generating system as claimed in claim 13, wherein said threshold values include a time threshold value and a threshold value for the absolute value of the high-frequency component.

15. The system for detecting stand-alone operation of a distributed generating system as claimed in claim 14, wherein said time threshold value is set to 0.13 sec, and said threshold value for the absolute value of the high-frequency component is set to 0.01.