CN108445326B

CN108445326B - Active reactive island detection method

Info

Publication number: CN108445326B
Application number: CN201810282965.2A
Authority: CN
Inventors: 马保华; 陈旭东
Original assignee: Hangzhou Confirmware Technology Co ltd
Current assignee: Hangzhou Confirmware Technology Co ltd
Priority date: 2018-04-02
Filing date: 2018-04-02
Publication date: 2021-07-27
Anticipated expiration: 2038-04-02
Also published as: CN108445326A

Abstract

The invention discloses an active reactive island detection method; according to the invention, a frequency detection module is added to the active reactive power anti-islanding for active detection, and disturbance quantity does not need to exceed the working range of islanding resonance; through the active disturbance of the scheme, after the active frequency is detected, the magnitude of a disturbance value can be greatly reduced, the disturbance value is only 0.3 percent and is reduced by 20 times compared with the original value, and the response time is faster.

Description

Active reactive island detection method

Technical Field

The invention relates to the field of reactive island detection, in particular to an active reactive island detection method.

Background

The grid-connected power generation system requires an anti-islanding function, and the islanding detection is mainly divided into passive detection and active detection at present. The passive detection has a large non-detection area, and the performance of the product cannot be met by the detection in the mode. The active detection is to lead certain disturbance to the output voltage, phase and frequency by introducing disturbance factors such as harmonic wave, active power, reactive power, frequency shift, phase difference and the like. The active detection precision is high, the non-detection interval is small, but the control is relatively complex, and the main performance of the inverter is affected, such as harmonic quantity increase, low power generation efficiency and the like.

At present, active reactive island detection is achieved by adjusting reactive power output, increasing reactive power mismatching degree, and exceeding a normal working range through continuous change of load frequency.

The magnitude of the idle disturbance quantity directly influences the magnitude of the degradation stratification of the product performance. The existing reactive disturbance has defects, and if the disturbance quantity is large, a blind area does not exist; the present invention addresses these problems.

Disclosure of Invention

In order to solve the defects of the prior art, the invention aims to provide an active reactive island detection method; according to the invention, a frequency detection module is added to the active reactive power anti-islanding for active detection, and disturbance quantity does not need to exceed the working range of islanding resonance.

In order to achieve the above object, the present invention adopts the following technical solutions:

an active reactive island detection method comprises the following steps:

step one, in an inverter, if a reactive power control function needs to be added, the reactive power control ratio is required to be more than or equal to 0.3 percent; if the power grid frequency detection function needs to be added, the detection resolution is required to be 0.001HZ, and the data sampling rate is 100 HZ;

step two, adding a trace amount of reactive power disturbance I_dI is the amplitude of the output current of the inverter, wherein the I is +/-0.3% I;

setting the output current as I ═ I × sin (ω t), adding the disturbed output current I ═ I × sin (ω t) ± 0.003 × I × cos (ω t), and performing positive-negative disturbance switching by 0.5S, namely, the frequency is 1Hz pulse wave;

after reactive disturbance is added, frequency change can occur on the island, a frequency detection module is adopted for detection, the frequency detection resolution of the frequency detection module is 0.001HZ, the sampling frequency is set to be 100HZ, and 100 values are recorded in a circulating mode;

step four, respectively carrying out accumulation calculation and the following calculation on the first 50 values and the last 50 values:

the obtained value is subjected to a difference square operation v ═ f_{Front side}-f_{Rear end})²And if v exceeds 16, judging the island is the island.

In the active reactive island detection method, in step three, the method for detecting by the frequency detection module is as follows: and recording the power grid period by using a counter, wherein the reciprocal of the period is the power grid frequency, the maximum power grid frequency is set to be 60HZ, the detection resolution is 0.001HZ, and the maximum interval time of the counter is (1/60) × 0.001 ═ 16.67 uS.

According to the active reactive island detection method, the island starting time is 4s, the island detection time is 4.9s, and the response time is 0.9 s.

The invention has the advantages that:

active reactive disturbance island detection generally adds reactive power, then detects frequency, and can stop working only when detecting that the frequency exceeds working frequency; according to the invention, a frequency detection module is added to the active reactive power anti-islanding for active detection, and disturbance quantity does not need to exceed the working range of islanding resonance.

The frequency can exceed the working frequency only when the reactive power is added to reach more than 6 percent, so that equipment is required to control the reactive power to reach more than 6 percent; through the active disturbance of the scheme, after the active frequency is detected, the magnitude of a disturbance value can be greatly reduced, the disturbance value is only 0.3 percent and is reduced by 20 times compared with the original value, and the response time is faster.

Drawings

FIG. 1 is a diagram of reactive proportional value control reference pulses in the absence of disturbances in accordance with the present invention;

FIG. 2 is a diagram of reactive proportional value control reference pulses of the present invention with reactive disturbance added beginning at second 3;

FIG. 3 is a graph of the power generation frequency of the invention with the grid disconnected at islanding for 5 seconds;

FIG. 4 is a graph of the power generation frequency log of the present invention with the grid disconnected at islanding and 4 seconds;

FIG. 5 is a graph showing the calculation of f in the case of the grid disconnection at 5 seconds and in the island of the invention_{Front side}Obtaining a frequency numerical diagram;

FIG. 6 is a graph showing the calculation of f in the case of the grid disconnection at 4 seconds in the island of the invention_{Front side}Obtaining a frequency numerical diagram;

FIG. 7 is a graph of f calculation under the condition that the power grid is disconnected at the time of island and 5 seconds according to the invention_{Rear end}Obtaining a frequency numerical diagram;

FIG. 8 is a graph of f calculation for the case of grid loss at 4 seconds in islanding according to the present invention_{Rear end}Obtaining a frequency numerical diagram; square value of frequency difference

FIG. 9 is a numerical diagram obtained by calculating a square value v of a frequency difference under the condition that an electric network is disconnected at the time of an island and 5 seconds;

FIG. 10 is a numerical graph obtained by calculating a square value v of a frequency difference under the condition that an electric network is disconnected at the time of an island and 4 seconds;

FIG. 11 is an islanding response graph for the present invention with the islanding disconnected from the grid at 5 seconds;

fig. 12 is an islanding response diagram of the invention in case of islanding and grid loss at 4 seconds.

Detailed Description

The invention is described in detail below with reference to the figures and the embodiments.

An active reactive island detection method comprises the following steps:

if the output current is I ═ I × sin (ω t), the output current I ═ I × sin (ω t) ± 0.003 × I × cos (ω t) after disturbance is added, and the positive and negative disturbance switching is performed by 0.5S, that is, the frequency is 1Hz pulse wave, as shown in fig. 2, a reactive ratio value control reference pulse diagram of reactive disturbance is added at the 3 rd second;

step three, after reactive disturbance is added, frequency change can occur on the island, as shown in fig. 3 and 4, a frequency detection module is adopted for detection, the frequency detection resolution of the frequency detection module is 0.001HZ, the sampling frequency is set to be 100HZ, and 100 values are recorded in a circulating manner; as an embodiment, the method for detecting by the frequency detection module is as follows: and recording the power grid period by using a counter, wherein the reciprocal of the period is the power grid frequency, the maximum power grid frequency is set to be 60HZ, the detection resolution is 0.001HZ, and the maximum interval time of the counter is (1/60) × 0.001 ═ 16.67 uS. (ii) a It should be noted that the present invention is applicable as long as the accuracy of the frequency detection resolution of the frequency detection module reaches 0.001 HZ.

Step four, as shown in fig. 5, 6, 7 and 8, the first 50 values and the last 50 values are respectively subjected to the accumulation calculation and the following calculation:

the obtained value is subjected to a difference square operation v ═ f_{Front side}-f_{Rear end})²If v exceeds 16, it is determined as an island as shown in fig. 9 and 10.

As shown in fig. 11 and 12, the ordinate 1 indicates that the island is present, the ordinate 0 indicates that the island is not present, the island start time is 4s, the island detection time is 4.9s, and the response time is 0.9 s; the response time is faster than in the prior art.

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It should be understood by those skilled in the art that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by using equivalent alternatives or equivalent variations fall within the scope of the present invention.

Claims

1. The active reactive island detection method is characterized by comprising the following steps:

2. The active reactive island detection method according to claim 1, wherein in step three, the method for detecting by the frequency detection module is: and recording the power grid period by using a counter, wherein the reciprocal of the period is the power grid frequency, the maximum power grid frequency is set to be 60HZ, the detection resolution is 0.001HZ, and the maximum interval time of the counter is (1/60) × 0.001 ═ 16.67 uS.

3. An active reactive island detection method according to claim 1, characterized in that the island start time is 4s, the island detection time is 4.9s, and the response time is 0.9 s.