CN112986675B - Method for detecting frequency change rate - Google Patents
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- CN112986675B CN112986675B CN202110117906.1A CN202110117906A CN112986675B CN 112986675 B CN112986675 B CN 112986675B CN 202110117906 A CN202110117906 A CN 202110117906A CN 112986675 B CN112986675 B CN 112986675B
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Abstract
The invention discloses a method for detecting frequency change rate, which comprises the following steps: firstly, judging whether the detection method of the invention is operated for the first time, and initializing the frequency basic quantity f according to the first and non-first assignment nf The current frequency value f is detected and assignedIs a frequency basis quantity f nf (ii) a Calculating a frequency change rate value delta f/delta t, and performing amplitude limiting treatment on the calculated value; calculating to obtain the frequency variation delta f nf By the amount of frequency change Δ f nf To the frequency basic quantity f nf Updating is carried out; judging whether the value of the frequency change rate delta f/delta t exceeds a limit value, if so, accumulating the duration time, otherwise, clearing the duration time; judging whether the duration time exceeds the error judgment window time, and if the judgment result is true, triggering the fault; otherwise, the detection is finished; the method for detecting the frequency change rate is simple and easy to implement, can be used as a general method in a passive island detection method, and can also be used in combination with other active island detection.
Description
Technical Field
The invention relates to the field of anti-islanding detection of distributed power generation systems, in particular to a frequency change rate detection method.
Background
When the distributed power generation system is in grid-connected operation with a power grid, the frequency is basically unchanged, when an island is formed, serious power unbalance may exist between a power supply and a load, and the frequency of the system can be changed, so that the island can be detected by testing the change rate of the frequency. For example, the part of the safety code EN50549-1, loM, et al, explicitly states that a distributed power generation system should include a frequency rate detection function, but is not limited to including only this function. At present, a general frequency change rate detection method is not described, but a detection method using different frequency change rates directly influences the detection of the functions of the inverter, and the inverter may be frequently tripped due to detection errors.
Therefore, in combination with the above-mentioned technical problems, there is a need to provide a new technical solution.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a general frequency change rate detection method, in particular to a frequency change rate-based detection method in a passive island detection method, and the specific technical scheme is as follows:
s1: reading the value of an initial mark, and if the initial mark is 0, operating the detection method for the first time;
s2: initializing a frequency basis quantity f nf Detecting the current frequency value f and assigning the current frequency value f as the frequency basic quantity f nf While the initial flag is assigned a value of 1;
s3: the frequency rate of change value deltaf/deltat is calculated according to the following formula,
wherein Δ f = f 1 -f 0 ＝f 1 -f nf ，
Wherein f is 0 Is an initial time t 0 Frequency value of time, f 1 Is t 1 The frequency value of the moment and the time interval delta t are obtained by a sampling counting number Rocof _ counter and a sampling frequency Rocof _ adc _ freq;
s4: setting a limit value for the calculated value delta f/delta t of the frequency change rate calculated in the step S3;
s5: the frequency variation Δ f is calculated by the following equation nf ，
Wherein the content of the first and second substances,
is a limit value of the frequency change rate;
change amount of frequency delta f nf Substituting into the frequency basis quantity formula f nf+1 ＝f nf +Δf nf For frequency fundamental quantity f nf Updating to obtain the frequency variation f at the next time nf+1 ；
S6: judging whether the value of the frequency change rate delta f/delta t calculated and obtained in the step S3 exceeds the limit value in the step S4, recording the value exceeding the limit value as true, and recording the value not exceeding the limit value as false;
s7: if the judgment result of the step S6 is true, accumulating the duration time;
s8: judging whether the duration time in the step S7 exceeds the error judgment window time, recording the time exceeding the error judgment window as true, and recording the time not exceeding the error judgment window as false;
s9: and if the judgment result of the step S8 is true, triggering the fault.
Preferably, in step S1, if the initial flag is 1, the detection method is not operated for the first time, and then steps S3, S4, S5, S6, S7, S8, and S9 are sequentially performed.
Preferably, in step S7, the duration amount is cleared if the determination result in step S6 is false.
Preferably, in step S9, if the determination result in step S8 is false, the detection ends.
Preferably, in step S3, the sampling count and the sampling frequency are sampled by an analog-to-digital converter adc.
Preferably, in step S3, the time interval Δ t is calculated by the number of adc samples counted and the adc sampling frequency rocaf _ adc _ freq obtained in the zero-crossing interrupt.
Preferably, in step S4, the limit value is a threshold value FreqChangeMax required in the EN safety specification.
Preferably, in step S4, the frequency change rate calculation value Δ f/Δ t is defined as follows:
preferably, in step S1, the mains frequency is sampled once per mains period, and a detection process of the frequency change rate is executed once.
The frequency change rate detection method has the following beneficial effects:
(1) The method for detecting the frequency change rate is simple in a passive island detection method, easy to implement, capable of serving as a general method and capable of being popularized and used;
(2) The frequency change rate detection method can be used in combination with other active anti-islanding detection.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic diagram of the frequency change rate detection method of the present invention;
fig. 2 is a flow chart of the frequency change rate detection method of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Examples
As shown in fig. 1, fig. 1 is a schematic diagram illustrating the principle of the frequency change rate detection method of the present invention, and the principle is as follows:
t 1 time relative to t 0 The frequency variation Δ f and the time interval Δ t at the time are as follows
Δf＝f 1 -f 0 ＝f 1 -f nf (1)
Δt＝t 1 -t 0 (2)
t 0 And t 1 The interval is a period of a mains supply grid, f 0 Is an initial time t 0 Frequency value of time, f 1 Is t 1 The frequency value of the moment, the time interval Δ t, is obtained by calculating an adc sampling count rocco _ counter and a sampling frequency rocco _ adc _ freq obtained in the zero-crossing interrupt, as follows:
the frequency change rate Δ f/Δ t can be obtained from the formulas (1) and (3), and is represented by the following formula (4):
the calculated frequency change rate delta f/delta t is set with a limiting value FreqChangeMax, and the limiting rule is as follows as formulas (5-1), (5-2) and (5-3):
in an example, the limit value FreqChangeMax is a threshold value required in the EN safety specification.
The frequency change amount Δ f is calculated from the following equation (6) nf ，
Wherein the content of the first and second substances,
is a limit value of the frequency change rate;
the frequency variation Δ f calculated by equation (6) nf Substituting into formula (7), and iterating the frequency basic quantity f by formula nf Updating to obtain the frequency basic quantity f of the next time nf+1 The following:
f nf+1 ＝f nf +Δf nf (7)
preferably, the commercial power frequency value f is sampled once every commercial power period, and a detection process of the frequency change rate is executed once, in an example, the commercial power frequency adopted is 50hz, so that 20ms obtains the primary commercial power frequency. Of course, the detection method provided by the invention is not limited to the mains frequency of 50hz, and is also applicable to other mains frequencies.
As shown in fig. 2, fig. 2 is a flowchart of the method for detecting a frequency change rate according to the present invention, and the flow steps are as follows:
s1: reading the value of an initial mark, and if the initial mark is 0, operating the detection method for the first time; (ii) a
In another embodiment, if the detection method is not run for the first time, step S2 is skipped and steps S3, S4, S5, S6, S7, S8 and S9 are performed in sequence.
S2: initializing a frequency basis quantity f nf Detecting the current frequency value f and assigning the current frequency value f as the frequency basic quantity f nf While the initial flag is assigned a value of 1;
s3: calculating a frequency change rate delta f/delta t value according to the formula (4);
s4: setting a limit value, and setting the limit value for the frequency change rate delta f/delta t calculated in the step S3; in the example, the limit value is a threshold value FreqChangeMax required in the EN safety specification;
s5: the frequency variation Δ f is calculated from equation (6) nf Amount of frequency change Δ f to be calculated nf Calculating the frequency basic quantity f by substituting formula (7) nf And for the frequency base quantity f nf Updating is carried out;
s6: judging whether the value of the frequency change rate delta f/delta t calculated and obtained in the step S3 exceeds the limit value in the step S4, recording the value exceeding the limit value as true, and recording the value not exceeding the limit value as false;
s7: if the judgment result of the step S6 is true, accumulating the duration time; in other embodiments, if the determination result in step S6 is false, the duration is cleared.
S8: judging whether the duration time of the step S7 exceeds the error judgment window time, recording the time exceeding the error judgment window as true, and recording the time not exceeding the error judgment window as false;
s9: and if the judgment result of the step S8 is true, triggering the fault.
In another embodiment, in step S9, if the determination result in step S8 is false, the detection ends.
The method for detecting the frequency change rate has the advantages that:
the method for detecting the frequency change rate is simple and easy to implement, can be used as a general method in a passive island detection method, and can also be used in combination with other active island detection.
In the description of the specification, reference to the description of the term "one embodiment", "some embodiments", "an example", "a specific example" or "some examples", etc., means that a particular feature or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples described in this specification can be combined and combined by one skilled in the art.
While embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and not to be construed as limiting the present invention, and that changes, modifications and variations may be made therein by those of ordinary skill in the art within the scope of the present invention.
Claims (9)
1. A method of detecting a rate of change of frequency, comprising the steps of:
s1: reading the value of an initial mark, and if the initial mark is 0, operating the detection method for the first time;
s2: initializing a frequency basis quantity f nf Detecting the current frequency value f and assigning the current frequency value f as the frequency basic quantity f nf While the initial flag is assigned a value of 1;
s3: the frequency rate of change value deltaf/deltat is calculated according to the following formula,
wherein Δ f = f 1 -f 0 ＝f 1 -f nf ，
Wherein f is 0 Is an initial time t 0 Frequency value of time, f 1 Is t 1 The frequency value of the moment and the time interval delta t are obtained by a sampling counting number Rocof _ counter and a sampling frequency Rocof _ adc _ freq;
s4: setting a limit value for the calculated value delta f/delta t of the frequency change rate calculated in the step S3;
s5: the frequency variation Δ f is calculated by the following equation nf ，
Wherein the content of the first and second substances,
is a limit value of the frequency change rate;
change amount of frequency delta f nf Substituting into the frequency basis quantity formula f nf+1 ＝f nf +Δf nf Iteration of the frequency base quantity f by a formula nf Updating to obtain the frequency basic quantity f of the next time nf+1 ；
S6: judging whether the value of the frequency change rate delta f/delta t calculated and obtained in the step S3 exceeds the limit value in the step S4, recording the value exceeding the limit value as true, and recording the value not exceeding the limit value as false;
s7: if the judgment result of the step S6 is true, accumulating the duration time;
s8: judging whether the duration time in the step S7 exceeds the error judgment window time, recording the time exceeding the error judgment window as true, and recording the time not exceeding the error judgment window as false;
s9: and if the judgment result of the step S8 is true, triggering the fault.
2. The method according to claim 1, wherein in step S1, if the initial flag is 1, and the detection method is not first run, steps S3, S4, S5, S6, S7, S8 and S9 are sequentially performed.
3. The method according to claim 1, wherein in step S7, if the determination result in step S6 is false, the duration is cleared.
4. The method according to claim 1, wherein in step S9, if the determination result in step S8 is false, the detecting ends.
5. The method according to claim 1, wherein in step S3, the number of samplers and the sampling frequency are sampled by an analog-to-digital converter adc.
6. The method of claim 5, wherein in step S3, the time interval Δ t is calculated by the number of adc samples counted taken during the zero-crossing interrupt and the adc sampling frequency Rocof _ adc _ freq.
7. The method as claimed in claim 1, wherein the limit value is a threshold value FreqChangeMax required in EN safety specification in step S4.
8. The method as claimed in claim 7, wherein in step S4, the criterion between the calculated frequency change rate Δ f/Δ t and the limit FreqChangeMax is as follows:
9. the method according to claim 1, wherein in step S1, the commercial power frequency is sampled once per commercial power period, and a frequency change rate detection process is performed once.
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| JP3474350B2 (en) * | 1996-03-07 | 2003-12-08 | 三菱電機株式会社 | Change rate detection relay |
| JP3346171B2 (en) * | 1996-06-07 | 2002-11-18 | 富士電機株式会社 | Frequency measuring method and frequency measuring circuit |
| DE19744691A1 (en) * | 1997-10-10 | 1999-04-15 | Daimler Benz Aerospace Ag | Method for determining the frequency of a signal |
| JP4818188B2 (en) * | 2007-04-18 | 2011-11-16 | 三菱電機株式会社 | Frequency change measuring device, frequency change rate measuring device, and power system control protection device |
| TW201133020A (en) * | 2010-03-18 | 2011-10-01 | O2Micro Inc | Method and device of inspecting carrier frequency of GPS satellite and GPS receiver |
| CN103383412B (en) * | 2013-07-10 | 2015-08-26 | 珠海许继芝电网自动化有限公司 | A kind of method of self-adaptation software and hardware frequency-tracking sampling |
| CN107422196B (en) * | 2017-02-27 | 2019-12-06 | 国电南瑞科技股份有限公司 | Island detection method based on harmonic distortion rate and frequency |
| CN207502605U (en) * | 2017-09-07 | 2018-06-15 | 江汉大学 | A kind of frequency measuring system based on VCXO references |
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