An implementation method of a variable amplitude harmonic power directional element

Abstract

The application discloses an implementation method of a variable-amplitude harmonic power direction element, and comprises the following steps: synchronously sampling current signals of each branch of an installation point, and calculating a high-frequency harmonic current vector; comparing the harmonic with a change amount in a certain time, and forming a starting criterion of the power direction element; when the harmonic current change amount of any branch meets the starting criterion, recording the harmonic current change amount of each branch at the current time, so as to form an action criterion of the harmonic direction element, the method comprises the following steps: calculating the current vector in real time, judging whether the starting criterion is met, recording the harmonic current change amount of each branch, then judging whether the current of any branch meets the direction criterion, when it is judged that any branch meets the direction criterion, the branch is determined as a harmonic generation point, otherwise, the branch is determined as not a harmonic generation point, since only a current collection loop is needed, field installation is convenient, and the application of a portable harmonic source positioning device is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of power system automation, and specifically relates to a method for implementing a proportional harmonic power directional element. Background Technology

[0002] With the increasing number of nonlinear power electronic components in the power grid, harmonic problems are also gradually increasing. Harmonics in the power grid increase losses in motor equipment and shorten its lifespan, thus necessitating the location and mitigation of harmonics. In advanced applications of harmonic source location, most sampling power direction devices determine the harmonic power direction of each branch. Currently, the widely used sampling method combines voltage and current power direction algorithms. However, these direction devices require connection to the voltage acquisition circuit, necessitating power outage installation, and such devices need to be installed at every node in the power grid. This increases investment in power grid secondary equipment. Summary of the Invention

[0003] To address the drawback of requiring a power outage to install a voltage acquisition circuit for harmonic source location and harmonic power direction determination, this invention proposes a method for implementing an amplitude-comparison harmonic power direction element. This method only requires collecting current data from multiple branches at the grid connection point, calculating the change in harmonic current, and forming an amplitude-comparison harmonic current direction criterion to determine the harmonic power direction. The main technical solution is described below: A method for implementing an amplitude-comparison harmonic power direction element, comprising the following steps:

[0004] The current signals of each branch at the installation point are sampled synchronously to calculate the high-frequency harmonic current vector.

[0005] By comparing the changes in harmonics with those from a certain time ago, a starting criterion for the power direction element is formed.

[0006] When the change in harmonic current of any branch meets the start-up criterion, the change in harmonic current of each branch at the current moment is recorded to form the action criterion of the harmonic direction element.

[0007] As an improvement of the present invention, the method includes real-time calculation of the current vector, and when the start-up criterion is met, recording the change in harmonic current of each branch, and then determining whether the current of any branch satisfies the direction criterion.

[0008] As an improvement of the present invention, when any branch satisfies the direction criterion, the branch is determined to be a harmonic generation point; otherwise, the branch is determined not to be a harmonic generation point.

[0009] As an improvement to the present invention, the step of calculating the high-frequency harmonic current vector in the method includes the following formula:

[0010]

[0011]

[0012] In equation (1), real m imag represents the real component of the m-th harmonic. m The m-th harmonic represents the imaginary component; N represents the number of sampling points within the data window, x i Represents the instantaneous sampled value. denoted by , where 1j represents the vector of the m-th harmonic current, and 1j denotes the imaginary part.

[0013] As an improvement to the present invention, the method uses the following formula to compare the change of harmonics with that before a certain time to form the start-up criterion for the power direction element:

[0014]

[0015] In equation (2), This represents the m-th harmonic current change of the i-th branch at the k-th sampling point. This represents the m-th harmonic current of the i-th branch at the k-th sampling point. I represents the m-th harmonic current of the i-th branch in the first 200ms. op This indicates the startup threshold.

[0016] As an improvement of the present invention, when the harmonic current change of any branch satisfies the start-up criterion, the harmonic current change of each branch at the current moment is recorded by the following formula:

[0017]

[0018] In equation (3), k represents the m-th harmonic current change of the i-th branch. rel It is the reliability coefficient of the floating threshold.

[0019] As an improvement of the present invention, after recording the change in harmonic current of each branch at the current moment, the branch with the largest change in harmonic current is determined to form the action criterion of the harmonic direction element.

[0020] As an improvement to the present invention, according to the above formula (3), when the harmonic current of a certain branch i is greater than the current of all other branches... If the sum of all branch vectors is given, then the harmonic source is determined to be on that branch.

[0021] Compared to existing technologies, the advantages of this invention are as follows: This invention only requires current information at the installation point to determine the direction of harmonic current, eliminating the need for power outages when installing a voltage acquisition circuit; the reprocessing of harmonic current utilizes its variation, minimizing the impact of system operation; and the addition of a floating threshold criterion to the direction element's criteria further enhances the criterion's sensitivity. Since only a current acquisition circuit is needed, on-site installation is convenient, facilitating the application of portable harmonic source positioning devices. Attached Figure Description

[0022] Figure 1 This is an equivalent schematic diagram of the power grid harmonic component network in this embodiment.

[0023] Figure 2 This is an equivalent schematic diagram of the variable harmonic component network in this embodiment.

[0024] Figure 3 This is a vector diagram of the harmonic components of the branch variation in this embodiment.

[0025] Figure 4 This is a flowchart of the implementation method in this embodiment. Detailed Implementation

[0026] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0027] Example: Figure 1 As shown, Figure 1 This is an equivalent schematic diagram of the harmonic component network of the power grid. Since harmonics are high-frequency components, and the system can be considered as an infinite power frequency source that does not provide harmonic components, the system power supply side is grounded in the equivalent diagram. Due to the nonlinear characteristics of power electronic devices in the power grid and the magnetic saturation of motor equipment, a certain amount of harmonics will be generated during equipment operation. In the harmonic network, this is equivalent to a high-frequency harmonic source existing at the equipment installation point. This harmonic source may exist at multiple points, and the power direction cannot be determined solely by steady-state harmonics. Furthermore, the state of the equipment during operation cannot remain constant. Once there is a small disturbance, according to the superposition theorem, an equivalent small power source is formed only at the point of change in the changing harmonic network. The power direction can be determined by comparing the amplitude of the change in harmonic current at the grid connection point. The equivalent schematic diagram of the changing harmonic component network of branch 1 is shown below. Figure 2 As shown. The specific steps of this invention are as follows. Figure 4 As shown, a method for implementing a harmonic power directional element with amplitude ratio is provided, the method comprising the following steps:

[0028] The current signals of each branch at the installation point are sampled synchronously to calculate the high-frequency harmonic current vector.

[0029] By comparing the changes in harmonics with those from a certain time ago, a starting criterion for the power direction element is formed.

[0030] When the change in harmonic current of any branch meets the start-up criterion, the change in harmonic current of each branch at the current moment is recorded to form the action criterion of the harmonic direction element.

[0031] Furthermore, the method includes real-time calculation of the current vector, and when the start-up criterion is met, recording the change in harmonic current of each branch, and then determining whether the current of any branch meets the direction criterion.

[0032] Furthermore, if any branch satisfies the direction criterion, then the branch is determined to be a harmonic generation point; otherwise, the branch is determined not to be a harmonic generation point.

[0033] Furthermore, the step of calculating the high-frequency harmonic current vector in the method includes the following formula:

[0034]

[0035]

[0036] In equation (1), real m imag represents the real component of the m-th harmonic. m The m-th harmonic represents the imaginary component; N represents the number of sampling points within the data window, x i Represents the instantaneous sampled value. denoted by , where 1j represents the vector of the m-th harmonic current, and 1j denotes the imaginary part.

[0037] As an improvement to the present invention, the method uses the following formula to compare the change of harmonics with that before a certain time to form the start-up criterion for the power direction element:

[0038]

[0039] In equation (2), This represents the m-th harmonic current change of the i-th branch at the k-th sampling point. This represents the m-th harmonic current of the i-th branch at the k-th sampling point. I represents the m-th harmonic current of the i-th branch in the first 200ms. op This indicates the start threshold, where the start threshold means that if the value is greater than the set value, the direction determination process will begin.

[0040] As an improvement of the present invention, when the change in harmonic current of any branch satisfies the starting criterion, i.e. At that time, the change in harmonic current of each branch is recorded by the following formula. Taking branch 1 as an example, the vector of the change in harmonic current of each branch is as follows: Figure 3As shown, it can be observed that the harmonic current variation is largest in this branch. The operating criterion for forming the harmonic direction element is:

[0041]

[0042] In equation (3), The m-th harmonic current change represents the i-th branch. krel is the floating threshold reliability coefficient, which is a constant and is set to avoid sampling errors and zero drift.

[0043] As an improvement of the present invention, after recording the change in harmonic current of each branch at the current moment, the branch with the largest change in harmonic current is determined to form the action criterion of the harmonic direction element.

[0044] As an improvement to the present invention, according to the above formula (3), when the harmonic current of a certain branch i is greater than the current of all other branches... If the sum of all branch vectors is given, then the harmonic source is determined to be on that branch.

[0045] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A method for implementing a harmonic power directional element of amplitude ratio, characterized in that, The method includes the following steps: The current signals of each branch at the installation point are sampled synchronously to calculate the high-frequency harmonic current vector. The steps for calculating the high-frequency harmonic current vector include the following formulas: （1）， In equation (1), This represents the real component of the m-th harmonic. represents the imaginary component of the m-th harmonic; N represents the number of sampling points within the data window. Represents the instantaneous sampled value. This represents the vector of the m-th harmonic current. Indicates the imaginary part symbol; By comparing the changes in harmonics with those from a certain time ago, a starting criterion for the power direction element is formed. The starting criterion for the power direction element is formed by comparing the change of harmonics with that of a certain time ago using the following formula: （2）， In equation (2), This represents the m-th harmonic current change of the i-th branch at the k-th sampling point. This represents the m-th harmonic current of the i-th branch at the k-th sampling point. This represents the m-th harmonic current of the i-th branch in the first Zms. Indicates the start threshold; When the change in harmonic current of any branch meets the start-up criterion, record the change in harmonic current of each branch at the current moment to form the action criterion of the harmonic direction element. When the change in harmonic current of any branch meets the start-up criterion, the change in harmonic current of each branch at the current moment is recorded by the following formula: （3）， In equation (3), represents the m-th harmonic current change of the i-th branch, and krel is the floating threshold reliability coefficient.

2. The method for implementing a ratio-type harmonic power directional element according to claim 1, characterized in that, The method includes real-time calculation of the current vector, recording the change in harmonic current of each branch when the start-up criterion is met, and then determining whether the current of any branch meets the direction criterion.

3. The method for implementing a ratio-type harmonic power directional element according to claim 2, characterized in that, If any branch satisfies the direction criterion, then the branch is determined to be a harmonic generation point; otherwise, the branch is determined not to be a harmonic generation point.

4. The method for implementing a ratio-type harmonic power directional element according to claim 3, characterized in that, After recording the changes in harmonic current in each branch at the current moment, the branch with the largest change in harmonic current is determined to form the criterion for the operation of the harmonic direction element.

5. A method for implementing a ratio-type harmonic power directional element according to claim 4, characterized in that, According to equation (3) above, when the harmonic current of a certain branch i is greater than the current of all other branches... If the sum of all branch vectors is given, then the harmonic source is determined to be on that branch.

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