CN103969549B - The island detection method of power-supply device and isolated island detecting device - Google Patents

Abstract

The invention discloses an islanding detection method and an islanding detection device for power supply equipment. The method obtains the actual working frequency of a power distribution system , and calculate the corresponding power frequency period ; After that, obtain the sampling frequency at the common connection point PCC between the power distribution system and the distributed power supply or the microgrid , and according to the sampling frequency frequency cycle be divided into period, and , then each time period ; After that, collect PCC points in each period Corresponding voltage sampling data ; Afterwards, integrate the voltage sampling data and obtain the integral value , the ;Finally, detect Threshold value for occurrence of island phenomenon size, if > , indicating that islanding occurs. The detection method of the present invention is not affected by conventional interference factors during detection, and the integral of the entire cycle of the power frequency from any moment can be used as a basis for judgment; only one power frequency cycle is required to obtain the judgment result, and the detection speed is fast and effective. It is beneficial to quickly isolate faults and ensure the reliability of power distribution system operation.

Description

Islanding detection method and islanding detection device for power supply equipment

technical field

The invention relates to the field of electric power, in particular to an islanding detection method and an islanding detection device for power supply equipment.

Background technique

At present, distributed power generation represented by wind power and solar power generation has attracted extensive attention from academia and industry due to its advantages of flexibility, low carbon and environmental protection. At the same time, the penetration rate of distributed power generation in power distribution systems is increasing year by year. . Distributed power can be connected to the power distribution system in a decentralized manner, and can also be connected to the power distribution system in the form of a microgrid. For power distribution systems, most distributed power sources are uncontrollable power sources, and their output power is often affected by natural conditions and has strong random characteristics. In order to ensure the reliability of system operation, the distributed power supply or micro-grid is required to have an island detection function, so as to isolate the fault in time when the internal fault of the power distribution network or micro-grid occurs. Among many island detection methods, the phase shift method has been widely used because of its good sensitivity. By detecting the zero-crossing point of the grid-connected point voltage waveform, the waveform phase can be quickly obtained within half the power frequency cycle, thereby quickly completing the islanding detection. This zero-crossing detection method has a high detection accuracy when the measured waveform is relatively smooth, and the power grid will inevitably be affected by various disturbances such as load changes, component switching, and motor startup during actual operation, so that the detection point The voltage waveform is distorted and glitches are generated. In this way, several voltage zero points may be continuously detected before and after the power frequency voltage zero crossing point, resulting in inaccurate or even wrong phase detection, which can easily lead to the malfunction of the island detection unit, thereby affecting the reliability of the distribution system run.

Contents of the invention

In order to solve the above problems, the purpose of the present invention is to provide an islanding detection method and an islanding detection device for power equipment, which can automatically eliminate the influence of glitches in the collected voltage and improve the accuracy of islanding detection.

The technical scheme that the present invention solves its problem adopts is:

An islanding detection method for power supply equipment, the power supply equipment includes distributed power supplies that are dispersedly connected to a power distribution system or a micro-grid power supply that is composed of distributed power supplies and connected to a power distribution system, and the method includes:

(1) Obtain the actual operating frequency of the power distribution system , and calculate the corresponding power frequency period ;

(2) Obtain the sampling frequency at the common connection point PCC between the power distribution system and the distributed power supply or microgrid , and according to the sampling frequency frequency cycle be divided into period, and , then each time period ;

(3) Collect PCC points in each period Corresponding voltage sampling data ;

(4) Integrate the voltage sampling data and obtain the integral value , the ;

(5) Detection Threshold value for occurrence of island phenomenon size, if > , it indicates that the island phenomenon occurs, otherwise, go to step (3) for loop detection.

An island detection device for power supply equipment, the power supply equipment includes distributed power sources that are dispersedly connected to the power distribution system or micro-grid power sources that are connected to the power distribution system composed of distributed power sources, and the device includes:

Parameter initialization module, used to obtain the actual operating frequency of the power distribution system , calculate the corresponding power frequency period , and according to the sampling frequency at the point of common connection PCC , the power frequency cycle be divided into period, and , then each time period ;

Acquisition module, used to collect PCC points in each time period Corresponding voltage sampling data ;

The processing module is used to integrate the voltage sampling data and obtain the integral value , the , and judge the integral value Threshold value for occurrence of island phenomenon the size of;

The alarm module is used to detect in the processing module > , to issue an island alarm message.

The beneficial effects of the present invention are:

The invention adopts an island detection method and an island detection device for power supply equipment, adopts an orthogonal integration method for the collected sampling voltage, automatically eliminates the influence of burrs in the waveform, and uses the result of numerical integration as a criterion for island detection to improve The accuracy of detection; the present invention does not need to use the zero-crossing point as a phase reference, and the integral of the entire power frequency cycle from any moment can be used as a basis for judgment; the present invention only needs one power frequency cycle to obtain the judgment result, which is conducive to rapid isolation of faults and guarantee the reliability of power distribution system operation.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and example.

Fig. 1 is a schematic diagram of the island detection method of the present invention;

Fig. 2 is a phase voltage waveform diagram at the PCC point described in the present invention;

Fig. 3 is a schematic diagram of orthogonal integration when the islanding phenomenon occurs in the present invention.

detailed description

As shown in Figure 1, the islanding phenomenon means that when the power supply of the power grid is interrupted due to a fault accident or power outage maintenance, the distributed grid-connected power generation systems (such as: photovoltaic power generation, wind power generation, fuel cell power generation, etc.) It detects the power failure state and cuts itself off from the mains network, forming a self-sufficient power supply island composed of distributed power station grid-connected power generation systems and surrounding loads. At this time, a separate distributed power supply DG will supply power alone. Once the island is generated, it will endanger the safety of maintenance personnel on the power grid transmission line; affect the action program of the protection switch on the power distribution system, impact the power grid protection device; affect the quality of transmitted power, and the power supply voltage and frequency in the power island area will be unstable; When the grid power supply is restored, the phases will be out of sync; the single-phase distributed power generation system will cause the three-phase load of the system to lose phase power supply. Therefore, for a grid-connected system, it is necessary to be able to perform anti-islanding detection.

Among many islanding detection methods, the phase shift method is widely used because of its good sensitivity. By detecting the zero-crossing point of the grid-connected point voltage waveform, the waveform phase can be quickly obtained within half the power frequency cycle, thereby quickly completing the islanding detection. This zero-crossing detection method has high detection accuracy when the measured waveform is relatively smooth, and the power grid will inevitably be affected by various disturbances such as load changes, component switching, and motor startup during actual operation, so that the detection point The voltage waveform is distorted and glitches are generated. In this way, several voltage zero points may be continuously detected before and after the power frequency voltage zero crossing point, resulting in inaccurate or even wrong phase detection, which can easily lead to the malfunction of the island detection unit, thereby affecting the reliability of the distribution system run. Referring to Figure 2, this is the voltage waveform diagram obtained by actually detecting the voltage when the power distribution system is running normally. It can be seen from the figure that when the power frequency voltage crosses zero, the common connection point PCC of the distributed power supply is located The measured voltage is not a standard power frequency sine wave, but contains certain harmonics. These harmonics cause the voltage waveform to have multiple zero-point voltages when it crosses the zero point. Refer to the enlarged graph in Figure 2, which produces Three zero-point voltages P1, P2, and P3. If phase detection is used at this time, it will obviously lead to inaccurate detection or even detection errors.

Referring to Figure 3, under normal circumstances, the voltage measured at the common connection point PCC The waveform is shown in the figure, considering the harmonic voltage, the voltage measured at the common connection point PCC It is expressed by Fourier series expansion, as shown in the following formula (1):

in, is the DC component, and respectively The magnitude and phase angle of the subharmonic voltage, is the power frequency angular frequency. make , , , , then formula (1) can be rewritten as:

, as formula (2).

According to formula (2), the following trigonometric function system is constructed:

, which is formula (3).

It can be seen from the above It can be regarded as a trigonometric series generated by a system of trigonometric functions. According to the characteristics of the orthogonality of the trigonometric function system, the following relationship is established:

(4)

(5)

In the formula, is the start time of the detection cycle, is the period of the power frequency voltage, and is a non-negative integer.

Therefore, any term in the trigonometric function system of formula (3) is taken as , with the left and right sides of equation (2), and in a power frequency cycle Integral, will get a fixed value that does not change with time, the integral result is recorded as . For example, take , then there are:

(6)

When to take When, there are:

(7)

In order to reduce the calculation amount of numerical integration, the present invention takes , that is, integrate according to formula (7). In the formula .

In this way, when the power distribution system is running normally, the non-smooth waveform containing integer harmonics takes the value of 0 after the integral operation of a power frequency cycle.

When the power distribution system fails and the corresponding feeder switch trips, the fundamental frequency of the island changes due to the mismatch between the distributed power supply and the load in the island, and the voltage waveform at the PCC detection point is distorted, as shown in Figure 3 of shown in the figure Indicates the moment when the island occurred.

According to the above description, similarly, the It is also expanded into the form of Fourier series, then:

(8)

In the formula, for the DC component of and are the waveforms after islanding occurs of The magnitude and phase angle of the subharmonic voltage, for the fundamental frequency. , , ,

Pick , for the voltage waveform in Figure 3 from arrive Integrate, and the integral result is recorded as , since the voltage waveform changes from arrive A transformation is made so:

(9)

because , so the integral result is not zero, as shown in the shaded part in Figure 3. because The magnitude of is related to the degree of frequency offset or phase offset, therefore, islanding can be identified with the help of this feature.

In view of this, the present invention provides an islanding detection method for power equipment by adopting the above islanding identification method. grid power, the method comprising:

(1) Obtain the actual operating frequency of the power distribution system , and calculate the corresponding power frequency period ;

(2) Obtain the sampling frequency at the common connection point PCC between the power distribution system and the distributed power supply or microgrid , and according to the sampling frequency frequency cycle be divided into period, and , then each time period ;

(3) Collect PCC points in each period Corresponding voltage sampling data ;

(4) Integrate the voltage sampling data and obtain the integral value , the ;

(5) Detection Threshold value for occurrence of island phenomenon size, if > , it indicates that the island phenomenon occurs, otherwise, go to step (3) for loop detection.

The detection method provided by the present invention is not affected by conventional interference factors (such as normal load fluctuations) during detection, and solves the influence of the zero-crossing detection method by waveform glitches; compared with zero-crossing detection, the present invention is more flexible and simple in detection , and there is no need to use the zero-crossing point as a phase reference, the integral of the power frequency full cycle from any moment can be used as a judgment basis; the detection method of the present invention can obtain the judgment result only in one power frequency cycle, and the detection speed is fast, which is beneficial to Quickly isolate faults and ensure the reliability of power distribution system operation.

As another protection form of the present invention, the present invention provides an islanding detection device for power supply equipment, and the device includes:

Parameter initialization module, used to obtain the actual operating frequency of the power distribution system , calculate the corresponding power frequency period , and according to the sampling frequency at the point of common connection PCC , the power frequency cycle be divided into period, and , then each time period ;

Acquisition module, used to collect PCC points in each time period Corresponding voltage sampling data ;

The processing module is used to integrate the voltage sampling data and obtain the integral value , the , and judge the integral value Threshold value for occurrence of island phenomenon the size of;

The alarm module is used to detect in the processing module > , to issue an island alarm message.

For the specific implementation method of the device, refer to the content described in the above method. The device is a kind of physical protection for adopting the method described in the present invention. within the scope of protection of the invention.

The above descriptions are only preferred embodiments of the present invention, and the present invention is not limited to the above-mentioned embodiments, as long as they achieve the technical effect of the present invention by the same means, they should all belong to the protection scope of the present invention.

Claims (2)

1. The island detection method of the power supply equipment, the power supply equipment comprises a distributed power supply which is dispersedly connected into a power distribution system or a micro-grid power supply which is composed of the distributed power supply and is connected into the power distribution system, and the island detection method is characterized by comprising the following steps:

(1) obtaining actual operating frequency of power distribution systemAnd calculating the corresponding power frequency period；

(2) Acquiring sampling frequency of PCC (point of common coupling) of power distribution system and distributed power source or microgridAnd according to the sampling frequencyPeriod of power frequencyIs divided intoA period of time, andeach time interval；

(3) Collecting PCC points in each time intervalCorresponding voltage sampling data；

(4) Integrating the voltage sampling data to obtain an integral valueSaid；

(5) Detection ofThreshold value related to islandingSize of (1), if>If not, the step (3) is carried out for circular detection.

2. Power supply equipment's island detection device, power supply equipment is including distributed power source of decentralized access distribution system or the microgrid power source of access distribution system who constitutes by distributed power source, its characterized in that, the device includes:

a parameter initial module for acquiring the actual working frequency of the power distribution systemCalculating the corresponding power frequency periodAnd according to the sampling frequency at the point of common coupling PCCThe power frequency periodIs divided intoA period of time, andeach time interval；

An acquisition module for acquiring the PCC points in each time intervalCorresponding voltage sampling data；

A processing module for integrating the voltage sampling data and obtaining an integral valueSaidAnd determining the integral valueThreshold value related to islandingThe size of (d);

an alarm module for detecting in the processing module>And sending out island alarm information.