An interval harmonic power flow calculation method using relative distance measure

Abstract

The application discloses a kind of interval harmonic power flow calculation method using relative distance measure, first input the parameter of power grid and network fluctuation, construct the node admittance matrix of fundamental wave and harmonic, set the RDM initial value of node voltage and carry out fundamental wave power flow iteration calculation, in the process of fundamental wave power flow iteration, the correction of reactive power injection and voltage is carried out to PV node, after meeting convergence condition, the RDM number of the fundamental wave voltage and injection current of whole network is output. After that, the harmonic power flow iteration part in decoupling method is further simplified by using simple solution method. The harmonic current is calculated at harmonic source node in combination with harmonic spectrum, and then the harmonic admittance matrix in RDM form is established based on the harmonic model of each element in the whole network, and the harmonic voltage RDM value of each node is obtained through the harmonic voltage equation. Finally, the interval number is converted through the conversion principle of RDM number, and the harmonic voltage interval range of the whole network is obtained, which can be applied to harmonic analysis and treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of power quality, and in particular to an interval harmonic power flow calculation method using relative distance measurement. Background Art

[0002] Due to the recent influx of distributed power sources and various nonlinear loads connected to power systems, harmonic pollution in power grids has become increasingly severe. Grid harmonics pose a significant threat to the economic and stable operation of power equipment and power systems, making harmonic analysis and harmonic mitigation research of paramount importance. Harmonic flow calculation is an effective method for conducting harmonic analysis. By establishing an accurate harmonic source model based on known network structure and parameters, harmonic flow calculation can effectively determine the harmonic distribution at each node in the power grid.

[0003] However, modern power grids are subject to numerous uncertainties, such as uncertainty in renewable energy generation output and the size and quantity of connected loads. This leads to uncertainty in grid harmonics, making traditional deterministic harmonic analysis methods difficult to apply. While interval arithmetic can effectively represent uncertainty, it suffers from a severe interval expansion effect in power flow calculations, resulting in high conservatism and low engineering practical value. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for calculating interval harmonic power flow using relative distance measurement, which can calculate the harmonic voltage intervals of the entire network to facilitate subsequent power quality index calculation and harmonic planning and management.

[0005] To achieve the above object, the present invention adopts the following technical solution: a method for calculating interval harmonic power flow using relative distance measurement, comprising the following steps:

[0006] Step S1: Construct the fundamental wave and harmonic wave model of the power grid to build the node harmonic admittance matrix of the power grid, and set the initial value of the RDM number of the voltage for initialization;

[0007] Step S2: Based on step S1, uncertainty is added to the constructed fundamental and harmonic components to model the relative distance measurement so that accurate positioning can be achieved within the interval while retaining the uncertainty factor;

[0008] Step S3: Combining the parameters and equations obtained in steps S1 and S2, an iterative solution method for fundamental power flow is performed for the load power fluctuation and generator output fluctuation range. RDM modeling is performed on the PQ and PV nodes. Reactive power and voltage correction are injected into the PV nodes to calculate the fluctuation range of the fundamental voltage and current of the power grid.

[0009] Step S4: Combined with the RDM number of the fundamental power flow obtained in step S3, a constant current source model of the harmonic source is established through the harmonic source spectrum and combined with the power grid harmonic equation to calculate the harmonic power flow;

[0010] Step S5: Based on step S3 and step S4, the obtained RDM harmonic voltage is converted into intervals to obtain the harmonic voltage range of the entire network.

[0011] In a preferred embodiment, in step S1, the parameters of the power grid and the network model are constructed to construct the fundamental and harmonic models, the node harmonic admittance matrix of the power grid is built, and the initial value of the RDM number of the voltage is set to initialize the fundamental power flow calculation.

[0012] In a preferred embodiment, in step S2, RDM modeling is performed on the nodes after considering the uncertainty of generator output and load fluctuation, and then substituted into the power flow iterative calculation.

[0013] In a preferred embodiment, in step S3, the RDM modeling method of the PV node of the power grid is specifically as follows: the injected reactive power of the PV node is calculated by a simplified node admittance matrix; after each iteration, the injected reactive power of the PV node is corrected using the obtained voltage amplitude deviation and reactive power deviation; the PV node is corrected according to the above steps to obtain the power of the PV node, and the PV node is converted into a PQ node, thereby obtaining the corresponding harmonic equivalent model according to the calculation formula using the parallel load; when the reactive correction value is When it is a negative number, there is a subtraction operation at the PV node, and the RDM interval model is used to reduce the conservatism of the interval solution;

[0014] PQ node RDM modeling

[0015]

[0016]

[0017]

[0018] Where, The RDM value of active and reactive power injected into node i, is the RDM value of the injected complex power, is the upper limit of the injection power interval, P G 、 Q G is the lower limit of the interval of injected power, α is the RDM metavariable of the interval power, and its value range is [0, 1];

[0019] RDM modeling of PV nodes

[0020] The injected reactive power of the PV node is calculated by a simplified node admittance matrix; assuming that there are N+1 nodes in the system, wherein 1~n are PV nodes, the node equation of the system is:

[0021]

[0022] Y" matrix in the formula is a fundamental wave admittance matrix containing only PV nodes, RDM value of the fundamental wave current, RDM value of the fundamental wave node voltage, as shown in the following formula:

[0023]

[0024]

[0025] In the formula, I and U represent the lower limit of the interval fundamental wave current and fundamental wave voltage, and represent the upper limit of the interval fundamental wave current and fundamental wave voltage;

[0026] The node grid equation is expressed by variables, as shown in the following formula:

[0027]

[0028] The per-unit value of the distribution network node voltage is close to 1.0, and the phase angle is very small, and only reactive power is injected at the PV node, so the following approximation is made:

[0029]

[0030] Expansion is as follows:

[0031]

[0032] The matrix M is the imaginary part of the simplified node admittance matrix Y"; after each iteration, the obtained voltage amplitude deviation is used to correct the injected reactive power of the PV node, and the corrected injected reactive power is as follows:

[0033]

[0034] In the formula, k is the iteration number, is the reactive power correction amount.

[0035] In a preferred embodiment, in the step S4, the harmonic current RDM value injected by the harmonic current source is calculated by the harmonic spectrum.

[0036] In a preferred embodiment, the convergence condition of the power flow iteration established in step S3 in step S4 is divided into four conditions, namely the upper limit of the real part, the lower limit of the real part, the upper limit of the imaginary part, and the lower limit of the imaginary part; when all four conditions are less than the set precision, the iteration stops.

[0037] In a preferred embodiment, the RDM harmonic voltage is obtained by solving the harmonic grid equation, and finally converted into interval numbers through RDM number, and finally the interval range of the harmonic voltage of the whole grid is obtained, which is applied to subsequent harmonic analysis and treatment.

[0038] The RDM number initial value of the voltage is set to initialize the fundamental power flow calculation, wherein the node voltage equation is

[0039]

[0040] Then

[0041]

[0042] In the formula, is the RDM value of the node fundamental voltage; is the node injected fundamental current; n is the total number of grid nodes, and node n is the balance node; Y in and Y ni are the block matrices composed of the mutual admittance between node n and other nodes, and are transposed to each other; Y nn is the self-admittance of node n; Y is the block matrix of the entire grid node admittance matrix after removing Y in , Y ni , and Y nn .

[0043] In the power flow calculation, the given operating variable is the injected power of each node, and the relationship between them is as follows:

[0044]

[0045] Expanding it can be obtained

[0046]

[0047] When the iteration result satisfies the convergence condition shown in the following formula, the iteration process is stopped, and thus the RDM value of each node voltage can be obtained:

[0048]

[0049] Where Δ is a very small positive number, generally taken as 1e-4-1e-6; are the lower limit of the real part, the upper limit of the real part, the lower limit of the imaginary part, and the upper limit of the imaginary part of the voltage of node i in the kth iteration, respectively;

[0050] RDM harmonic power flow calculation

[0051]

[0052] In the formula represents the RDM harmonic admittance matrix, Represents the RDM value of the harmonic current injected into the interval, Represents harmonic voltage.

[0053] Finally, according to the principle of RDM number, it is converted into interval number to obtain the harmonic voltage fluctuation range of the whole network.

[0054] In a preferred embodiment, in step S5, the obtained voltage RDM number is converted into an interval number, and indicators such as the total harmonic voltage distortion rate and the total harmonic current distortion rate are calculated to perform harmonic evaluation and analysis.

[0055] Compared with the existing technology, the present invention has the following beneficial effects: The present invention proposes a new uncertain harmonic flow calculation method, which can realize the harmonic flow calculation on a complex multi-node power supply network. This method applies relative distance measurement to the calculation of uncertain harmonic flow in the power system, so that the harmonic voltage amplitude fluctuation range of the entire network can be obtained. When the operating conditions of the power grid fluctuate greatly, it can obtain the harmonic data and voltage fluctuation range of non-measurement points more quickly and accurately than the traditional interval flow algorithm. It can be applied to online monitoring of power grid harmonics, while reducing the cost of the measuring device. It can guide power grid staff to perform harmonic pollution analysis and harmonic control through accurate harmonic data. In addition, the research results in this area can also be applied to the reliability assessment of new energy power generation access, accurately predict and evaluate the harmonic pollution and voltage fluctuation degree of the power grid caused by the grid connection of new energy power generation, and thus propose a more reasonable grid connection plan. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a specific flow chart of a preferred embodiment of the present invention.

[0057] Figure 2 This is a simulation diagram in an embodiment of the present invention, which compares the results of the fundamental power flow calculation based on the relative distance measure (RDM) with those of the traditional interval power flow algorithm and the Monte Carlo method.

[0058] Figure 3 This is a simulation diagram in an embodiment of the present invention. The results of calculating the 5th harmonic voltage amplitude of the entire network using relative distance measure (RDM) are compared with the results of traditional interval harmonic power flow algorithm and Monte Carlo method. DETAILED DESCRIPTION

[0059] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0060] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0061] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form, and it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0062] A method for calculating interval harmonic power flow using relative distance measurement, refer to Figures 1 to 3 , including the following steps:

[0063] Step S1: Construct the fundamental wave and harmonic wave model of the power grid to build the node harmonic admittance matrix of the power grid, and set the initial value of the RDM number of the voltage for initialization;

[0064] Step S2: Based on step S1, uncertainty is added to the constructed fundamental and harmonic components to model the relative distance measurement so that accurate positioning can be achieved within the interval while retaining the uncertainty factor;

[0065] Step S3: Combining the parameters and equations obtained in steps S1 and S2, an iterative solution method for fundamental power flow is performed for the load power fluctuation and generator output fluctuation range. RDM modeling is performed on the PQ and PV nodes. Reactive power and voltage correction are injected into the PV nodes to calculate the fluctuation range of the fundamental voltage and current of the power grid.

[0066] Step S4: Combined with the RDM number of the fundamental power flow obtained in step S3, a constant current source model of the harmonic source is established through the harmonic source spectrum and combined with the power grid harmonic equation to calculate the harmonic power flow;

[0067] Step S5: Based on step S3 and step S4, the obtained RDM harmonic voltage is converted into intervals to obtain the harmonic voltage range of the entire network.

[0068] In step S1, the parameters of the power grid and the network model are constructed to construct the fundamental and harmonic models, the node harmonic admittance matrix of the power grid is built, and the initial value of the RDM number of the voltage is set to initialize and perform fundamental power flow calculation.

[0069] In step S2, RDM modeling is performed on the nodes after considering the uncertainty of generator output and load fluctuation, and then substituted into the power flow iterative calculation.

[0070] In step S3, the PV node RDM modeling method of the power grid is specifically as follows: the injected reactive power of the PV node is calculated by a simplified node admittance matrix; after each iteration, the injected reactive power of the PV node is corrected by using the obtained voltage amplitude deviation and reactive power deviation; the PV node is corrected according to the above steps to obtain the power of the PV node, and the PV node is converted into a PQ node, so as to obtain the corresponding harmonic equivalent model according to the calculation formula using the parallel load; when the reactive correction value is When it is a negative number, there is a subtraction operation at the PV node, and the RDM interval model is used to reduce the conservatism of the interval solution;

[0071] PQ node RDM modeling

[0072]

[0073]

[0074]

[0075] Where, The RDM value of active and reactive power injected into node i, is the RDM value of the injected complex power, is the upper limit of the injection power interval, P G 、 Q G is the lower limit of the interval of injected power, α is the RDM metavariable of the interval power, and its value range is [0, 1];

[0076] RDM modeling of PV nodes

[0077] The injected reactive power of the PV node is calculated using a simplified node admittance matrix. Assuming that there are N+1 nodes in the system, where 1 to n are PV nodes, the node equation of the system is:

[0078]

[0079] The Y″ matrix in the formula is the fundamental wave admittance matrix containing only PV nodes, Indicates the RDM value of the fundamental current, The RDM value representing the fundamental node voltage is shown in the following equation:

[0080]

[0081]

[0082] Where, I and U Indicates the lower limit of the interval fundamental current and fundamental voltage, and Indicates the upper limit of the interval fundamental current and fundamental voltage;

[0083] The node grid equation is expressed using variables as follows:

[0084]

[0085] The per-unit value of the distribution network node voltage is close to 1.0, the phase angle is very small, and only reactive power is injected at the PV node. Therefore, the following approximation is obtained:

[0086]

[0087] Expanded to:

[0088]

[0089] The matrix M is the imaginary part of the simplified node admittance matrix Y″. After each iteration, the voltage amplitude deviation is used to correct the injected reactive power of the PV node. The corrected injected reactive power is as follows:

[0090]

[0091] Where k is the number of iterations, is the reactive power correction value.

[0092] In step S4, the harmonic current RDM value injected by the harmonic current source is calculated from the harmonic spectrum.

[0093] In step S4, the convergence conditions of the power flow iteration established in step S3 are divided into four conditions, namely, the upper limit of the real part, the lower limit of the real part, the upper limit of the imaginary part, and the lower limit of the imaginary part; when all four conditions are less than the set accuracy, the iteration stops.

[0094] The RDM harmonic voltage is obtained by solving the harmonic grid equation, and finally converted into an interval number through the RDM number, and finally the harmonic voltage interval range of the entire network is obtained, which is used in subsequent harmonic analysis and control;

[0095] Set the initial value of the voltage RDM number to initialize the fundamental wave power flow calculation, where the node voltage equation is:

[0096]

[0097] Then there is

[0098]

[0099] Where, is the node fundamental voltage RDM value; Inject fundamental current into the node; n is the total number of grid nodes, node n is the balance node; Y in and Yni is the block matrix composed of mutual admittance between node n and other nodes, and is transposed to each other; Y nn is the self-admittance of node n; Y is the block matrix after Y in , Y ni , Y nn .

[0100] In the power flow calculation, the given operating variable is the injection power of each node, and the relationship between them is as follows:

[0101]

[0102] Expansion can be obtained

[0103]

[0104] When the iteration result meets the convergence condition shown in the following formula, the iteration process is stopped, and thus the RDM value of each node voltage can be obtained:

[0105]

[0106] Where Δ is a very small positive number, generally taken as 1e-4-1e-6; The real part lower limit, the real part upper limit, the imaginary part lower limit, and the imaginary part upper limit of the voltage of node i in the kth iteration, respectively;

[0107] RDM harmonic power flow calculation

[0108]

[0109] In the formula RDM harmonic admittance matrix, RDM value of interval injection harmonic current, Harmonic voltage.

[0110] Finally, according to the principle of RDM number, it is converted into interval number to obtain the harmonic voltage fluctuation range of the whole network.

[0111] In the step S5, the obtained voltage RDM number is converted into interval number, and indexes such as total harmonic voltage distortion rate and total harmonic current distortion rate are calculated to perform harmonic evaluation and analysis.

[0112] The above is only the preferred embodiment of the present application, and does not limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application, and the generated function effect does not exceed the range of the technical scheme of the present application, should be included in the protection scope of the present application.

Claims

1. A method for calculating interval harmonic power flow using relative distance measurement, characterized in that: The following steps are involved: Step S1: Construct the fundamental wave and harmonic wave model of the power grid to build the node harmonic admittance matrix of the power grid, and set the initial value of the RDM number of the voltage for initialization; Step S2: Based on step S1, uncertainty is added to the constructed fundamental and harmonic components to model the relative distance measurement so that accurate positioning can be achieved within the interval while retaining the uncertainty factor; Step S3: Combining the parameters and equations obtained in steps S1 and S2, an iterative solution method for fundamental power flow is performed for the load power fluctuation and generator output fluctuation range. RDM modeling is performed on the PQ and PV nodes. Reactive power and voltage correction are injected into the PV nodes to calculate the fluctuation range of the fundamental voltage and current of the power grid. Step S4: Combined with the RDM number of the fundamental power flow obtained in step S3, a constant current source model of the harmonic source is established through the harmonic source spectrum and combined with the power grid harmonic equation to calculate the harmonic power flow; Step S5: Based on steps S3 and S4, the obtained RDM harmonic voltage is converted into an interval to obtain the harmonic voltage range of the entire network; In step S3, the RDM modeling method of the PV node of the power grid is specifically to calculate the injected reactive power of the PV node through a simplified node admittance matrix; After each iteration, the injected reactive power of the PV node is corrected using the obtained voltage amplitude deviation and reactive power deviation; According to the above steps, the PV node is corrected to obtain the power of the PV node, and the PV node is converted into a PQ node, thereby obtaining the corresponding harmonic equivalent model according to the calculation formula using the parallel load; when the reactive correction value is When it is a negative number, there is a subtraction operation at the PV node, and the RDM interval model is used to reduce the conservatism of the interval solution; PQ node RDM modeling: Where, The RDM value of active and reactive power injected into node i, is the RDM value of the injected complex power, is the upper limit of the injection power interval, P G , Q G is the lower limit of the interval of injected power, α is the RDM metavariable of the interval power, and its value range is [0, 1]; RDM modeling of PV nodes: The injected reactive power of the PV node is calculated using a simplified node admittance matrix. Assuming that there are N+1 nodes in the system, where 1 to n are PV nodes, the node equation of the system is: The Y″ matrix in the formula is the fundamental wave admittance matrix containing only PV nodes, Indicates the RDM value of the fundamental current, The RDM value representing the fundamental node voltage is shown in the following equation: Where I and U represent the lower limits of the interval fundamental current and fundamental voltage, and Indicates the upper limit of the interval fundamental current and fundamental voltage; The node grid equation is expressed using variables as follows: The per-unit value of the distribution network node voltage is close to 1.0, the phase angle is very small, and only reactive power is injected at the PV node. Therefore, the following approximation is obtained: Expanded to: The matrix M is the imaginary part of the simplified node admittance matrix Y″; After each iteration, the voltage amplitude deviation is used to correct the injected reactive power of the PV node. The corrected injected reactive power is as follows: Where k is the number of iterations, is the reactive power correction value.

2. The interval harmonic power flow calculation method using relative distance measurement according to claim 1 is characterized in that: In step S1, the parameters of the power grid and the network model are constructed to construct the fundamental and harmonic models, the node harmonic admittance matrix of the power grid is built, and the initial value of the RDM number of the voltage is set to initialize and perform fundamental power flow calculation.

3. The interval harmonic power flow calculation method using relative distance measurement according to claim 1 is characterized in that: In step S2, RDM modeling is performed on the nodes after considering the uncertainty of generator output and load fluctuation, and then substituted into the power flow iterative calculation.

4. The interval harmonic power flow calculation method using relative distance measurement according to claim 1 is characterized in that: In step S4, the harmonic current RDM value injected by the harmonic current source is calculated from the harmonic spectrum.

5. The interval harmonic power flow calculation method using relative distance measurement according to claim 1 is characterized in that: In step S4, the convergence conditions of the power flow iteration established in step S3 are divided into four conditions, namely, the upper limit of the real part, the lower limit of the real part, the upper limit of the imaginary part, and the lower limit of the imaginary part; when all four conditions are less than the set accuracy, the iteration stops.

6. The interval harmonic power flow calculation method using relative distance measurement according to claim 5, characterized in that: The RDM harmonic voltage is obtained by solving the harmonic grid equation, and finally converted into an interval number through the RDM number, and finally the harmonic voltage interval range of the entire network is obtained, which is used in subsequent harmonic analysis and control; Set the initial value of the voltage RDM number to initialize the fundamental wave power flow calculation, where the node voltage equation is: Then there is Where, is the RDM value of the fundamental node voltage; is the RDM value of the fundamental current; n is the total number of grid nodes, and node n is the balancing node; Y in and Y ni is the block matrix composed of the mutual admittance between node n and other nodes, which are transposed to each other; Y nn is the self-admittance of node n; Y is the admittance matrix of the entire grid node excluding Y in 、Y ni 、Y nn The block matrix after In power flow calculations, the given operating variable is the injected power at each node, and the relationship between the two is as follows: Expand to get When the iteration result meets the convergence condition shown in the following formula, the iteration process is stopped, and the RDM value of each node voltage can be obtained: Where Δ is a small positive number, take 1e -4 -1e -6 ; are the real lower limit, real upper limit, imaginary lower limit and imaginary upper limit of the voltage of node i in the kth iteration respectively; RDM harmonic power flow calculation: In the formula represents the RDM harmonic admittance matrix, Represents the RDM value of the harmonic current injected into the interval, represents harmonic voltage; Finally, according to the principle of RDM number, it is converted into interval number to obtain the harmonic voltage fluctuation range of the whole network.

7. The interval harmonic power flow calculation method using relative distance measurement according to claim 1 is characterized in that: In step S5, the obtained voltage RDM number is converted into an interval number, and the total harmonic voltage distortion rate and the total harmonic current distortion rate indicators are calculated to perform harmonic evaluation and analysis.

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