WO2020052104A1

WO2020052104A1 - Method for determining power flow of dg-connected distribution network and computer storage medium

Info

Publication number: WO2020052104A1
Application number: PCT/CN2018/118729
Authority: WO
Inventors: 杨洛; 徐陆飞; 陈天华; 陈建华; 杜磊
Original assignee: 国电南瑞科技股份有限公司; 国电南瑞南京控制系统有限公司
Priority date: 2018-09-12
Filing date: 2018-11-30
Publication date: 2020-03-19
Also published as: CN109193664B; CN109193664A

Abstract

A method for determining a power flow of a DG-connected distribution network and a computer storage medium. The method comprises: establishing, on the basis of parameters of N nodes in a DG-connected system, a nonlinear power flow equation for the system, and converting the nonlinear power flow equation to a linear-nonlinear hybrid equation for the system (11), wherein N is a positive integer; and determining, on the basis of the definition of a bilinear state variable and a solution of the linear-nonlinear hybrid equation for the system, phase differences between and voltages of the N nodes and phase differences between N-1 nodes (12).

Description

Method for determining power flow of distribution network including DG grid connection and computer storage medium

Technical field

The present application relates to the technical field of power system operation and control, and in particular to a method for determining power flow of a distribution network including DG grid connection and a computer storage medium.

Background technique

Power flow calculation is one of the most basic functions in the energy management system (EMS). Power flow calculation of the distribution network is an important basis for economic operation and system analysis of the distribution network. In terms of topology and operation mode, there are obvious differences between the distribution network and the transmission network. The distribution network has a high R / X ratio (resistance and reactance ratio), more branches, and a radial network structure. In addition, the distribution network is open-loop during normal operation, and only short-term loop network or dual power supply operation occurs when a fault or load is deployed.

Distributed generation (DG) technology has gradually become a hotspot in the field of electric power with its advantages such as small investment, clean and environmental protection, reliable power supply and flexible power generation methods. The combination of distributed power generation and centralized power generation will be the trend of power system development. Commonly used distributed power generation methods are wind power, solar power and fuel cell power.

The introduction of distributed power generation (DG) in the distribution network has a huge impact on the power flow, voltage quality, power loss, reliability and short-circuit capacity. The traditional power flow algorithm cannot be directly applied to distribution networks with DG for the following reasons:

1) The access of DG may change the flow of the tide, and the distribution network is also changed from a single power mode to a multiple power mode;

2) There are only two types of balance nodes and PQ nodes in traditional power flow calculation. Among them, the balance node and PQ node are existing nouns, the balance node is given the voltage amplitude and phase, and its injected active power and The active power is the quantity to be calculated; the PQ node is the active power P and the reactive power Q of the node are given, and the voltage and phase of the node are the quantities to be calculated.

Summary of the Invention

The purpose of this application is to overcome the shortcomings of the prior art, and to provide a method for determining the power flow of a distribution network containing DG grid-connected, to improve the speed of solving the power flow calculation of the power grid containing DG, and to improve the calculation convergence.

In order to solve the above technical problems, this application provides a method for determining power flow of a distribution network including DG grid connection, including the following steps:

Based on the parameters of N nodes included in the DG grid-connected system, a non-linear power flow equation for the system is established, and the non-linear power flow equation is converted into a linear-nonlinear mixed equation for the system; where N is a positive integer;

Based on the definition of the bilinear state variable and the solution of the linear-nonlinear mixed equation for the system, the phase difference and voltage between the N nodes and the phase difference between N-1 nodes are determined.

The present application provides a computer storage medium that stores computer-executable instructions. When the computer-executable instructions are executed, the steps of the foregoing method are implemented.

Compared with the prior art, the beneficial effect of this application is that this application uses bilinear transformation technology to introduce bilinear state variables, thereby transforming the non-linear power flow equations into linear-nonlinear mixed equations. In combination with the operating characteristics of DG's distribution network, a reasonable approximation of the Jacobian matrix of the mixed equation is made, thereby making the Jacobian matrix constant and speeding up the solution. The method of the patent is simple and easy to implement, and can effectively calculate the speed and accuracy of DG power distribution network load flow calculation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first flowchart of the method of the present application;

FIG. 2 is the second flowchart of the method of the present application.

detailed description

This application is further described below. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and cannot be used to limit the protection scope of the present application.

A method for determining the power flow of a distribution network containing a DG grid connected to the present application, by introducing a bilinear state variable through a bilinear transformation technology, thereby transforming a non-linear power flow equation system into a linear-nonlinear mixed equation. Further, Combined with the operating characteristics of DG's distribution network, a reasonable approximation of the Jacobian matrix of the mixed equation is made, thereby making the Jacobian matrix constant and speeding up the solution.

This application provides a method for determining the power flow of a distribution network including a DG grid, as shown in FIG. 1, including the following steps:

Step 11: Based on the parameters of the N nodes included in the DG grid-connected system, establish a non-linear power flow equation for the system, and convert the non-linear power flow equation into a linear-nonlinear mixed equation for the system; where N is positive Integer

Step 12: Based on the definition of the bilinear state variable and the solution of the linear-nonlinear mixed equation for the system, the phase difference and voltage of N nodes and the phase difference between N-1 nodes.

A method for determining the power flow of a distribution network including DG grid connection in this application, the specific process is as follows:

Establishing a non-linear power flow equation for the system based on the parameters of the N nodes included in the DG grid-connected system, and converting the non-linear power flow equation into a linear-nonlinear mixed equation for the system, including:

The N-node DG grid-connected system is used. Node 1 of all the nodes in the system is a balanced node. There are N _PV PV nodes, NN _PV -1 PQ nodes, and b branches. (I, j) indicates Take the node i as the head and j as the branch. The admittance of this branch is y _ij = g _ij + jb _ij , where g _ij is the branch conductance and b _ij is the branch susceptance.

According to the basic principles of the power system, the power balance equation of node i is:

Where N is the number of system nodes, P _i is the active power injected at node i, Q _i is the reactive power injected at node i, G _ii is the self-conductance of node i, B _ii is the self- _{susceptibility} of node i, and G _ij is node i, j Mutual conductance, B _ij is the mutual admittance between nodes i, j, these are known quantities, U _i is the voltage amplitude of node i, δ _ij is the phase difference between nodes i, j, these two types The variable is the quantity to be sought.

Since U _i U _j cosδ _ij , U _i U _j sinδ _ij and U _i ² all appear in a fixed overall form in formula (1), for any branch (i, j), the following bilinearity can be defined State variables:

R _ij = U _i U _j cosδ _ij

I _ij = U _i U _j sinδ _ij (2)

Here, R _ij , I _ij , and K _i are all intermediate variables. Obviously R _ij = R _ji , I _ij = -I _ji , R _ij ² + I _ij ² = 2K _i K _j .

Bringing the intermediate variables R _ij , I _ij , K _i defined in (2) into the power flow equilibrium equation (1) has:

Then the power flow equation is transformed into the following linear-nonlinear mixed equations.

(3) The variables in the system of equations are R _ij , I _ij , K _i ,

Is a set of linear equations about R _ij , I _ij , K _i , and R _ij ² + I _ij ² = 2K _i K _j is a set of nonlinear equations about R _ij , I _ij , K _i .

The above description is for a single node i and branch (i, j). For the nodes and branches of the entire network, the above-mentioned bilinear transformation can still be used to form a system of linear-nonlinear equations:

This application uses Newton's method to solve the above nonlinear-linear equations, and the solution form is:

among them:

△ R = [△ R _ij ] i, j are nodes at both ends of any branch of the entire network;

△ I = [△ I _ij ] i, j are nodes at both ends of any branch in the whole network

△ K = [△ K _i ] i is an arbitrary PQ node

△ P = [△ P _i ] i is any node in the whole network

△ Q = [△ Q _i ] i is any node in the whole network

△ S = [△ S _ij ] i, j is any node in the whole network

J is the Jacobian matrix of the system nonlinear-linear equations, and its specific form will be given below.

For linear equations

The solution process does not need to iterate, so the convergence speed is fast. For the nonlinear equations R _ij ² + I _ij ² = 2K _i K _j , the solution is difficult. This application combines the operating characteristics of the distribution network to solve the problem. Simplify the solution, the principle is as follows:

Non-linear mapping f (I, R) = R _ij ² + I _ij ² -2K _i K _j Partial differentiation into R _ij , I _ij , K _i is:

Due to the small transmission power of the DG-containing distribution network line, the phase difference between the nodes at both ends of the branch can still be considered δ _ij = 0, and according to the operating characteristics of the power system, the voltage of the node (including the load node and the DG grid-connected node) is approximately rated Voltage 1p.u, using the above assumption, then R _ij = U _i U _j cosδ _ij ≈1, I _ij = U _i U _j sinδ _ij ≈0,

Then the non-linear equations f (I, R) = R _ij ² + I _ij ² -2K _i K _j can be approximated as:

Therefore, the Jacobian matrix J of equation (4) can be approximated as:

It can be seen that through the above processing, the Jacobian matrix has become a sparse matrix with constant elements. Therefore, only a factor table needs to be formed during the solution process (because the factor table is a mature technology, this application will not be described in detail), without iteration at each step Repeat the inversion in the process.

The method for determining the power flow of a distribution network including DG grid connection in this application is shown in FIG. 2. The detailed solution steps are:

1. Form the Jacobian matrix according to the node admittance matrix Y = G + jB

And form a factor table of J;

2. Set the initial voltage of the PQ node to 1p.u, the phase to 0, and the number of iterations k = 0.

3. The k-th iteration solves the following linear-nonlinear equations:

Its Newton method iterative equations form

Correction of bilinear state variables can be obtained according to the factor table

Here

4.Update the k-th iteration bilinear state variable

Here

5, use

Update the k + 1th iteration

The update form is:

6. Repeat the above steps 3-5, set the convergence threshold ξ> 0, until the correction amount for two consecutive iterations is

Then get the solution of the above linear-nonlinear mixed equations

7, according to

The voltage amplitude U _{i of} node i can be obtained,

according to

Available

Furthermore, U _j can be obtained.

This application uses bilinear transformation technology to introduce bilinear state variables, thereby transforming the power flow non-linear equations into linear-nonlinear mixed equations, and based on the characteristics of the DG distribution network, the Jacobian matrix in the mixed equations is rationalized This makes the Jacobian matrix constant, so that only a small number of variable elements need to be calculated repeatedly, which reduces the amount of calculation, speeds up the solution speed, and improves the calculation efficiency. The method of the patent is simple and easy to implement, and can effectively calculate the speed and accuracy of DG power distribution network load flow calculation.

A computer storage medium provided in the embodiments of the present application. The computer storage medium stores computer-executable instructions. When the computer-executable instructions are executed, the method steps of the foregoing embodiments are implemented.

In the embodiment of the present application, if the foregoing device is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the embodiments of the present application that are essentially or contribute to the existing technology can be embodied in the form of software products. The computer software product is stored in a storage medium and includes several instructions for A computer device (which may be a personal computer, a server, or a network device) is caused to perform all or part of the methods described in the embodiments of the present application. The foregoing storage medium includes various media that can store program codes, such as a U disk, a mobile hard disk, a read-only memory (ROM, Read Only Memory), a magnetic disk, or an optical disk. In this way, the embodiments of the present application are not limited to any specific combination of hardware and software.

Although the preferred embodiments of the present application have been disclosed for illustrative purposes, those skilled in the art will recognize that various improvements, additions, and substitutions are also possible, and therefore, the scope of the present application should not be limited to the above embodiments.

The above is only the preferred implementation of the present application. It should be pointed out that, for those of ordinary skill in the art, without departing from the technical principles of the present application, several improvements and modifications can be made. These improvements and modifications It should also be regarded as the scope of protection of this application.

Claims

Method for determining power flow of distribution network with DG grid connection, including the following steps:

Based on the parameters of N nodes included in the DG grid-connected system, a non-linear power flow equation for the system is established, and the non-linear power flow equation is converted into a linear-nonlinear mixed equation for the system; where N is a positive integer;

Based on the definition of the bilinear state variable and the solution of the linear-nonlinear mixed equation for the system, the phase difference and voltage between the N nodes and the phase difference between N-1 nodes are determined.
The method according to claim 1, wherein, based on the parameters of N nodes included in the DG grid-connected system, a non-linear power flow equation for the system is established, and the non-linear power flow equation is converted into a linearity for the system- Non-linear mixed equations, including:

The DG grid-connected system with N nodes is set as a balanced node among all nodes. The DG grid-connected system includes N PV PV nodes, NN PV -1 PQ nodes, and b branches. (I, j) represents the branch with node i as the head and j as the end. The admittance of this branch is y ij = g ij + jb ij , where g ij is the branch conductance and b ij is the branch electrical Accept

According to the basic principles of the power system, the power balance equation of node i is determined as:

Where N is the number of system nodes, P i is the active power injected at node i, Q i is the reactive power injected at node i, G ii is the self-conductance of node i, B ii is the self- susceptibility of node i, and G ij is node i, j Mutual conductance, B ij is the mutual admittance between nodes i and j, U i is the voltage amplitude of node i, and δ ij is the phase difference between nodes i and j;

Since U i U j cosδ ij , U i U j sinδ ij and U i 2 all appear in a fixed overall form in (1), for any branch (i, j), the following bilinear state is defined variable:

Among them, R ij , I ij , and K i are intermediate variables, R ij = R ji , I ij = -I ji , R ij 2 + I ij 2 = 2K i K j ;

Bringing the intermediate variables R ij , I ij , K i defined in (2) into the power flow equilibrium equation (1) has:

The power flow equation is transformed into the following linear-nonlinear mixed equations:

(3) The variables in the system of equations are R ij , I ij , K i ,
Is a set of linear equations about R ij , I ij , K i , and R ij 2 + I ij 2 = 2K i K j is a set of nonlinear equations about R ij , I ij , K i ;

For the nodes and branches of the entire network, the above-mentioned bilinear transformation is still used to form the system's linear-nonlinear equations:
The method according to claim 1, wherein, based on the parameters of N nodes included in the DG grid-connected system, a non-linear power flow equation for the system is established, and the non-linear power flow equation is converted into a linearity for the system- After the nonlinear mixed equation, the method further includes:

Approximating the overall Jacobian matrix of the linear-nonlinear mixed equation;

The approximated linear-nonlinear mixed equation is solved to obtain a solution of the linear-nonlinear mixed equation.
The method according to claim 3, wherein the approximating the overall Jacobian matrix of the linear-nonlinear mixed equation comprises:

The overall Jacobian matrix J of the power flow equation is approximated as:
The method according to claim 4, wherein approximating the overall Jacobian matrix J of the power flow equation comprises:

The phase difference between the nodes at both ends of the branch δ ij = 0, and the node voltage is approximately the rated voltage 1p.u, so for f (I, R) = R ij 2 + I ij 2 -2K i K j , its partial difference is :

Since R ij = U i U j cosδ ij ≈ 1, I ij = U i U j sinδ ij ≈ 0,

Then f (I, R) = R ij 2 + I ij 2 -2K i K j The approximate Jacobian is:

Thus the overall Jacobian matrix J of the power flow equation is:
The method according to claim 1, further comprising:

Newton's method is used to solve linear-nonlinear equations.
The method according to claim 6, wherein solving the linear-nonlinear equation is:

1) Form the Jacobian matrix according to the node admittance matrix Y = G + jB
And form a factor table of J;

2) Let the initial voltage of the PQ node be 1 p.u, the phase be 0, and the number of iterations k = 0;

3) The k-th iteration solves the following linear-nonlinear equations:

Its Newton method iterative equations form
The correction amount of the bilinear state variable can be obtained according to the factor table
Here

4) Update the k-th iteration bilinear state variable
Here

5) Use
Update the k + 1th iteration
The update form is:

6) Repeat the above steps 3-5, set the convergence threshold ξ> 0, until the correction amount for two consecutive iterations is satisfied
Then get the solution of the above linear-nonlinear mixed equations

7) According to
The voltage amplitude U i of node i can be obtained,

according to
Available

At this point, the full network voltage and node phase can be obtained.
The method according to claim 7, wherein the convergence threshold value ranges from ξ> 0.
A computer storage medium stores computer-executable instructions, and when the computer-executable instructions are executed, the steps of the method according to any one of claims 1-8 are implemented.