CN108983045B - Passive island detection method - Google Patents
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Abstract
The invention relates to a passive island detection method, which comprises the following steps: after the power generation system is in grid-connected operation, the relationship between the period value deviation of the grid-connected point voltage and a set value is judged in each grid period, meanwhile, whether the effective value and the average value of the total harmonic voltage of a plurality of continuous grid periods meet preset conditions is judged, the corresponding island occurrence counting variable is counted in the process, and finally whether an island state occurs is judged according to the counting result of the island occurrence counting variable. The invention solves the problem that the conventional island detection method influences the quality of electric energy by using an active disturbance mode or uses a passive mode but has a larger dead zone. The island state can be rapidly detected without dead zones by combining two parameter characteristics of the grid-connected point voltage period and the harmonic, and the electric energy quality is not influenced because of a passive mode.
Description
Technical Field
The invention belongs to the field of distributed power generation (such as photovoltaic power generation), and particularly relates to an island detection method related to grid-connected safety regulations of an inverter.
Background
Most of the existing island detection methods are active disturbance detection modes, and the active detection modes can influence the quality of output electric energy. The existing passive detection methods are generally phase change and frequency change detection methods, and the methods have the problem of overlarge dead zone.
Disclosure of Invention
The invention aims to provide a passive island detection method which does not affect the quality of electric energy and reduces dead zones,
in order to achieve the purpose, the invention adopts the technical scheme that:
a passive island detection method comprises the following steps: after the grid-connected operation of the power generation system, the following steps are executed in each grid cycle:
step 1: setting the current as the Nth power grid period, and acquiring the Nth power grid period value T of the voltage of the grid-connected pointNAnd the N-2 power grid period value TN-2Calculating the deviation Td of the period value, and then executing the step 2;
step 2: judging the size relation between the period value deviation Td and a set value, executing a step 3 when the period value deviation Td is larger than the set value, and executing a step 4 when the period value deviation Td is smaller than or equal to the set value;
and step 3: adding 1 to the island occurrence count variable, and then executing the step 9;
and 4, step 4: obtaining the total harmonic voltage effective value VHT [ m ] of the grid-connected point voltage of the Nth grid cycle and the forward continuous X grid cycles]And m is N, N-1, N-2, …, N-X, and the average value VHT of the total harmonic voltage effective values of the grid-connected point voltages from the Nth cycle to the Nth-X + t grid cycle is calculatedavgWherein X is [4, 6]]Integer within the range, t being a positive integer less than X, then performing step 5;
and 5: setting the judgment conditions as follows: total harmonic voltage effective value VHT [ N ] of grid-connected point voltage in Nth power grid cycle]And the average value VHT of the total harmonic voltage effective value of the grid-connected point voltageavgDifference value of (1), total harmonic voltage effective value VHT [ N-1] of grid-connected point voltage in the N-1 th power grid cycle]And the average value VHT of the total harmonic voltage effective value of the grid-connected point voltageavg…, and a total harmonic voltage effective value VHT [ N-X + t + 1] of the grid-connected point voltage of the (N-X + t + 1) th grid cycle]And the average value VHT of the total harmonic voltage effective value of the grid-connected point voltageavgAll the difference values are simultaneously greater than the corresponding preset values; judging whether the judgment condition is met, if so, executing a step 6, and otherwise, executing a step 7;
step 6: adding 2 to the island occurrence count variable, and then executing a step 9;
and 7: judging whether the island occurrence count variable is greater than 0, if so, executing a step 8, otherwise, executing a step 9;
and 8: subtracting 1 from the island occurrence count variable, and then executing a step 9;
and step 9: judging whether the island occurrence counting variable is larger than or equal to a preset frequency value, if so, executing the step 10, otherwise, ending;
step 10: detecting an island occurrence state, and zeroing an island occurrence counting variable; and then ends.
In the step 1, Td is TN-TN-2。
In the step 4, the total harmonic voltage effective value VHT [ N ] of the grid-connected point voltage in the Nth grid cycle is calculated and stored, and then the total harmonic voltage effective values VHT [ N-1], VHT [ N-2], … and VHT [ N-X ] of the grid-connected point voltage in the previous continuous X grid cycles are extracted;
the method for calculating the total harmonic voltage effective value VHT [ N ] of the grid-connected point voltage in the Nth power grid period comprises the following steps: the method comprises the steps of firstly extracting a voltage effective value VH [ h ] of multiple harmonics of grid-connected point voltage in an Nth power grid period, and then calculating a total harmonic voltage value VHT [ N ] according to the voltage effective value of the multiple harmonics of the grid-connected point voltage in the Nth power grid period, wherein h is the harmonic frequency.
In step 4, a correlation method is used to extract a voltage effective value VH [ h ] of multiple harmonics of the grid-connected point voltage in the nth grid cycle:
wherein,
n is the number of sampling points, and n is 0, 1, 2, …, and M-1;
m is the total number of sampling points in one power grid period;
f1for rated electric networkFrequency;
h is the harmonic frequency;
x [ nT ] is a sampling voltage value obtained by sampling the voltage of the grid-connected point in the Nth power grid period;
ah is h-order voltage harmonic cosine amplitude;
bh is the h-order voltage harmonic sine amplitude.
In said step 4, use is made of
The total harmonic voltage value VHT [ N ] is calculated.
h＝2，3，4，5，6，7。
In said step 4, use is made of
VTHavg＝(VHT[N-X]+VHT[N-X+1]+…+VHT[N-X+t])/(t+1)
Calculating the average value VTH of the total harmonic voltage effective values of the grid-connected point voltages from the Nth cycle to the Nth-X + t grid cycleavg。
In step 4, X is 5 and t is 2.
In the step 9, the preset sub-value is 4.
In the step 10, after the island state is detected, the grid-connected relay is disconnected.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages: the island detection method solves the problem that the conventional island detection method influences the quality of electric energy by using an active disturbance mode or uses a passive mode but has a larger dead zone. The island state can be rapidly detected without dead zones by combining two parameter characteristics of the grid-connected point voltage period and the harmonic, and the electric energy quality is not influenced because of a passive mode.
Drawings
Fig. 1 is a schematic flow chart of a passive island detection method according to the present invention.
Detailed Description
The invention will be further described with reference to examples of embodiments shown in the drawings to which the invention is attached.
The first embodiment is as follows: as shown in fig. 1, a passive island detection method includes: after the grid-connected operation of the power generation system, the following steps are executed in each grid cycle:
step 1: setting the current as the Nth power grid period, and acquiring the Nth power grid period value T of the voltage of the grid-connected pointNAnd the N-2 power grid period value TN-2And calculating the period value deviation Td ═ TN-TN-2Then, step 2 is performed.
Step 2: and (3) judging the size relation between the period value deviation Td and the set value, executing the step (3) when the period value deviation Td is larger than the set value, and executing the step (4) when the period value deviation Td is smaller than or equal to the set value.
In the step, the set value is determined according to the actual power grid frequency jitter state, and the islanding state is not detected by mistake.
And step 3: the islanding occurrence count variable is incremented by 1 and then step 9 is performed.
And 4, step 4: obtaining the total harmonic voltage effective value VHT [ m ] of the grid-connected point voltage of the Nth grid cycle and the forward continuous X grid cycles]And m is N, N-1, N-2, …, N-X, and the average value VHT of the total harmonic voltage effective values of the grid-connected point voltages from the Nth cycle to the Nth-X + t grid cycle is calculatedavgWherein X is [4, 6]]Integer within the range, t being a positive integer less than X, and then step 5 is performed.
In the step 4, the total harmonic voltage effective value VHT [ N ] of the grid-connected point voltage in the Nth grid cycle is calculated and stored, and then the total harmonic voltage effective values VHT [ N-1], VHT [ N-2], … and VHT [ N-X ] of the grid-connected point voltage in the previous continuous X grid cycles are extracted.
Specifically, the method for calculating the total harmonic voltage effective value VHT [ N ] of the grid-connected point voltage in the Nth power grid cycle comprises the following steps: firstly, extracting a voltage effective value VH [ h ] of multiple harmonics of the grid-connected point voltage of the Nth power grid period by using a correlation method. Is based on
Calculating to obtain a voltage effective value VH [ h ] of multiple harmonics of the grid-connected point voltage of the Nth power grid period,
n is the number of sampling points, and n is 0, 1, 2, …, and M-1;
m is the total number of sampling points in one power grid period;
f1is the rated grid frequency;
h is the harmonic frequency;
x [ nT ] is a sampling voltage value obtained by sampling the voltage of the grid-connected point in the Nth power grid period;
ah is h-order voltage harmonic cosine amplitude;
bh is the h-order voltage harmonic sine amplitude.
In this embodiment, h is 2, 3, 4, 5, 6, 7, that is, the second to seventh harmonics are calculated to obtain voltage effective values VH [2], VH [3], VH [4], VH [5], VH [6], and VH [7] of the second to seventh harmonics of the grid-connected point voltage.
Calculating the effective voltage value VH [ h ] of multiple harmonics of the grid-connected point voltage in the Nth power grid period, and then utilizing the effective voltage value of multiple harmonics of the grid-connected point voltage in the Nth power grid period
The total harmonic voltage value VHT [ N ] is calculated. Therefore, in the present embodiment, the first electrode is,
in the step 4, the total harmonic voltage effective value VHT [ N ] of the grid-connected point voltage of the Nth grid cycle is calculated, and the total harmonic voltage effective values VHT [ N-1], VHT [ N-2], … and VHT [ N-X ] of the grid-connected point voltage of the previous continuous X grid cycles are extracted and then continuously utilized
VTHavg＝(VHT[N-X]+VHT[N-X+1]+…+VHT[N-X+t])/(t+1)
Calculating the average value VTH of the total harmonic voltage effective values of the grid-connected point voltages from the Nth cycle to the Nth-X + t grid cycleavg。
In this embodiment, X is 5 and t is 2. Therefore, the total harmonic voltage effective values of the grid-connected point voltages corresponding to 6 grid cycles are extracted in total and are respectively VHT [ N ], VHT [ N-1], VHT [ N-2], VHT [ N-3], VHT [ N-4] and VHT [ N-5 ]. Then, the effective values of the total harmonic voltage VHT [ N-3], VHT [ N-4] and VHT [ N-5] of the grid-connected point voltage corresponding to the first three power grid periods are taken and utilized
VTHavg＝(VHT[N-5]+VHT[N-4]+VHT[N-3])/3
To calculate the average value VTH of the effective value of the total harmonic voltage of the grid-connected point voltageavg。
And 5: setting the judgment conditions as follows: total harmonic voltage effective value VHT [ N ] of grid-connected point voltage in Nth power grid cycle]Average value VHT of total harmonic voltage effective values of grid-connected point voltageavgDifference value of (1), total harmonic voltage effective value VHT [ N-1] of grid-connected point voltage in the N-1 th power grid cycle]Average value VHT of total harmonic voltage effective values of grid-connected point voltageavg…, and a total harmonic voltage effective value VHT [ N-X + t + 1] of the grid-connected point voltage of the (N-X + t + 1) th grid cycle]Average value VHT of total harmonic voltage effective values of grid-connected point voltageavgAll the differences are simultaneously greater than the corresponding preset values.
In this embodiment, the total harmonic voltage effective value VHT [ N ] of the grid-connected point voltage of the nth grid cycle needs to be determined]Average value VHT of total harmonic voltage effective values of grid-connected point voltageavgDifference value of (VHT [ N ]]-VHTavgAnd the total harmonic voltage effective value VHT [ N-1] of the grid-connected point voltage of the N-1 th power grid cycle]Average value of total harmonic voltage effective values of grid-connected point voltageVHTavgDifference of (VHT) N-1]-VHTavgAnd the total harmonic voltage effective value VHT [ N-2] of the grid-connected point voltage of the Nth-2 th power grid cycle]Average value VHT of total harmonic voltage effective values of grid-connected point voltageavgDifference of (VHT 2)]-VHTavgThe three differences are respectively in size relation with corresponding preset values. The preset value is determined according to actual conditions, in this embodiment, VHT [ N ]]-VHTavgCorresponding to a preset value of 2.0V, VHT [ N-1]]-VHTavgCorresponding to a preset value of 2.0V, VHT [ N-2]]-VHTavgThe corresponding preset value is 0.5V.
Judging whether the current condition is satisfied, i.e. judging
VHT[N]-VHTavg＞2.0V
VHT[N-1]-VHTavg＞2.0V
VHT[N-2]-VHTavg＞0.5V
And if the determination result is positive, executing the step 6, otherwise executing the step 7.
Step 6: and if the harmonic voltage change reflected by the difference meets the judgment condition, adding 2 to the island occurrence count variable, and executing the step 9. The reason for counting 2 is that the islanding state can be determined with high probability by not changing the frequency greatly but changing the voltage harmonic greatly, so 2 counts are added to the islanding generation variable, and the islanding state is detected as soon as possible.
And 7: judging whether the island occurrence count variable is greater than 0, if so, executing a step 8, otherwise, executing a step 9;
and 8: subtracting 1 from the island occurrence count variable, and then executing a step 9;
and step 9: and judging whether the island occurrence counting variable is larger than or equal to a preset number value, wherein the preset number value is 4, judging whether the island occurrence counting variable is larger than or equal to 4, if so, executing the step 10, and if not, finishing.
Step 10: detecting the island occurrence state, disconnecting the grid-connected relay and zeroing an island occurrence counting variable; and then ends.
The island detection method is a passive detection mode, and does not affect the quality of electric energy; the problem of large dead zone of a conventional passive detection algorithm is solved by a method for simultaneously detecting the voltage period and the higher harmonic of the grid-connected point.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (10)
1. A passive island detection method is characterized in that: the passive island detection method comprises the following steps: after the grid-connected operation of the power generation system, the following steps are executed in each grid cycle:
step 1: setting the current as the Nth power grid period, and acquiring the Nth power grid period value T of the voltage of the grid-connected pointNAnd the N-2 power grid period value TN-2Calculating the deviation Td of the period value, and then executing the step 2;
step 2: judging the size relation between the period value deviation Td and a set value, executing a step 3 when the period value deviation Td is larger than the set value, and executing a step 4 when the period value deviation Td is smaller than or equal to the set value;
and step 3: adding 1 to the island occurrence count variable, and then executing the step 9;
and 4, step 4: obtaining the total harmonic voltage effective value VHT [ m ] of the grid-connected point voltage of the Nth grid cycle and the forward continuous X grid cycles]And m is N, N-1, N-2, …, N-X, and the average value VHT of the total harmonic voltage effective values of the grid-connected point voltages from the Nth cycle to the Nth-X + t grid cycle is calculatedavgWherein X is [4, 6]]Integer within the range, t being a positive integer less than X, then performing step 5;
and 5: setting the judgment conditions as follows: total harmonic voltage effective value VHT [ N ] of grid-connected point voltage in Nth power grid cycle]And the average value VHT of the total harmonic voltage effective value of the grid-connected point voltageavgDifference value of (1), total harmonic voltage effective value VHT [ N-1] of grid-connected point voltage in the N-1 th power grid cycle]And the point of connectionAverage value VHT of total harmonic voltage effective value of voltageavg…, and a total harmonic voltage effective value VHT [ N-X + t + 1] of the grid-connected point voltage of the (N-X + t + 1) th grid cycle]And the average value VHT of the total harmonic voltage effective value of the grid-connected point voltageavgAll the difference values are simultaneously greater than the corresponding preset values; judging whether the judgment condition is met, if so, executing a step 6, and otherwise, executing a step 7;
step 6: adding 2 to the island occurrence count variable, and then executing a step 9;
and 7: judging whether the island occurrence count variable is greater than 0, if so, executing a step 8, otherwise, executing a step 9;
and 8: subtracting 1 from the island occurrence count variable, and then executing a step 9;
and step 9: judging whether the island occurrence counting variable is larger than or equal to a preset frequency value, if so, executing the step 10, otherwise, ending;
step 10: detecting an island occurrence state, and zeroing an island occurrence counting variable; and then ends.
2. A passive island detection method according to claim 1, wherein: in the step 1, Td is TN-TN-2。
3. A passive island detection method according to claim 1, wherein: in the step 4, the total harmonic voltage effective value VHT [ N ] of the grid-connected point voltage in the Nth grid cycle is calculated and stored, and then the total harmonic voltage effective values VHT [ N-1], VHT [ N-2], … and VHT [ N-X ] of the grid-connected point voltage in the previous continuous X grid cycles are extracted;
the method for calculating the total harmonic voltage effective value VHT [ N ] of the grid-connected point voltage in the Nth power grid period comprises the following steps: the method comprises the steps of firstly extracting a voltage effective value VH [ h ] of multiple harmonics of grid-connected point voltage in an Nth power grid period, and then calculating a total harmonic voltage value VHT [ N ] according to the voltage effective value of the multiple harmonics of the grid-connected point voltage in the Nth power grid period, wherein h is the harmonic frequency.
4. A passive island detection method according to claim 3, wherein: in step 4, a correlation method is used to extract a voltage effective value VH [ h ] of multiple harmonics of the grid-connected point voltage in the nth grid cycle:
wherein,
n is the number of sampling points, and n is 0, 1, 2, …, and M-1;
m is the total number of sampling points in one power grid period;
f1is the rated grid frequency;
h is the harmonic frequency;
x [ nT ] is a sampling voltage value obtained by sampling the voltage of the grid-connected point in the Nth power grid period;
ah is h-order voltage harmonic cosine amplitude;
bh is the h-order voltage harmonic sine amplitude.
5. A passive island detection method according to claim 4, characterized in that: in said step 4, use is made of
The total harmonic voltage value VHT [ N ] is calculated.
6. A passive island detection method according to any of claims 3 to 5, wherein: h is 2, 3, 4, 5, 6, 7.
7. A passive island detection method according to claim 1, wherein: in said step 4, use is made of
VTHavg＝(VHT[N-X]+VHT[N-X+1]+…+VHT[N-X+t])/(t+1)
Calculating the average value VTH of the total harmonic voltage effective values of the grid-connected point voltages from the Nth cycle to the Nth-X + t grid cycleavg。
8. A passive island detection method according to claim 1, wherein: in step 4, X is 5 and t is 2.
9. A passive island detection method according to claim 1, wherein: in the step 9, the preset sub-value is 4.
10. A passive island detection method according to claim 1, wherein: in the step 10, after the island state is detected, the grid-connected relay is disconnected.
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Address after: 215000 No. 90, Zijin Road, high tech Zone, Suzhou, Jiangsu Patentee after: Goodway Technology Co.,Ltd. Address before: 215163 No.189 Kunlunshan Road, high tech Zone, Suzhou City, Jiangsu Province Patentee before: JIANGSU GOODWE POWER SUPPLY TECHNOLOGY Co.,Ltd. |
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