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

• US 7,342,758 B2
• Filed: 12/29/2003
• Issued: 03/11/2008
• Est. Priority Date: 12/29/2003
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Luor, Tain-Syh, Lin, Jeu-Min, Huang, Shyh-Jier, Liu, Yung-Hsiang
• Primary Examiner(s): Sherry; Michael
• Assistant Examiner(s): HOANG, ANN THI
• Application Number:
  US10/745,619
• Publication Number:
  US 20050146224A1
• Time in Patent Office: 1,534 Days
• Field of Search: 361/62
• US Class Current: 361/62
• 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 a wavelet transformation to the signal read in step a to form high and low frequency components of the transformed signal, a time versus high-frequency component window for the high frequency component and a time versus low-frequency component window for the low frequency component for detecting a perturbation in a transient time domain of said read signal;

c. determining whether an absolute amplitude value of the high-frequency component is greater than an amplitude threshold value and whether the amplitude threshold value is exceeded for a duration longer than a time 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 read 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. amplifying said read signal for 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 read signal 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 time threshold value is set to 0.13 sec and said amplitude threshold value for the absolute value of the high-frequency component is set to 0.01.

6. 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 amplitude threshold value.

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

a″

. introducing a perturbation to at least a frequency or a voltage of said generator source.

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 a 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 read signal, which is either a voltage signal or a frequency signal, in said independent power distribution system; and

a calculating processing device for performing a wavelet transformation of said read 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;

wherein;

said, calculating processing device includes means for decomposing said read signal into a high-frequency component and a low frequency component by the wavelet transformation for observation of a perturbation, and means for determining a stand-alone operation to be occurring in said distributed generating system if an absolute amplitude value of the high-frequency component is greater than an amplitude threshold value for a duration greater than a time threshold value.

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 time threshold value is set to 0.13 sec, and said amplitude threshold value for the absolute value of the high-frequency component is set to 0.01.