Harmonic load flow calculation method of alternating current and direct current hybrid power distribution network considering photovoltaic access

Abstract

The invention discloses an AC / DC hybrid power distribution network harmonic load flow calculation method considering photovoltaic access. The method comprises the following steps: S1, constructing load flow calculation models of various types of branches of an AC / DC power distribution network for calculating fundamental power and harmonic current of the various types of branches; s2, constructing an AC / DC power distribution network harmonic load flow calculation model considering photovoltaic access; and S3, calculating the harmonic power flow of the AC / DC power distribution network to finally obtain a fundamental voltage and a harmonic voltage for analyzing the harmonic power flow of the AC / DC hybrid power distribution network system. According to the method, loss distribution can be calculated, equipment type selection and operation optimization can be guided, harmonic distribution after a newly added load or a distributed power supply is connected can be predicted, and filtering measures can be planned in advance. Through precise modeling and harmonic power flow analysis, the electric energy quality and reliability of the hybrid power grid can be significantly improved, and high-proportion new energy access and intelligent development requirements are supported.

Description

Technical Field

[0001] The present invention relates to the technical field of AC-DC hybrid distribution networks, and particularly to a harmonic power flow calculation method and system for an AC-DC hybrid distribution network considering photovoltaic access. Background Art

[0002] With the rapid development of distributed generation technology, a large number of distributed power sources are connected to the distribution network, which has significantly changed the structure of the traditional distribution network, presenting a new form of AC-DC hybrid distribution network. This change in the grid structure not only increases the complexity of the distribution network but also poses new challenges to the operation and control of the grid.

[0003] In an AC-DC hybrid distribution network, the harmonic problem becomes particularly prominent. The accuracy of harmonic power flow is crucial for the safe and stable operation of the grid and the improvement of power quality. The existence of harmonic power flow will affect the normal operation of grid equipment, increase equipment losses and heating, reduce the transmission efficiency of the grid, and may even cause problems such as resonance, threatening the safe and stable operation of the grid. However, current research on AC-DC hybrid distribution networks mostly focuses on the analysis and calculation of fundamental waves, with relatively little consideration of harmonics. When analyzing the power flow of an AC-DC hybrid distribution network, existing research usually only considers the fundamental wave component and ignores the impact of harmonics on grid operation. This research method to a certain extent limits the comprehensive understanding and solution of harmonic problems in AC-DC hybrid distribution networks. Therefore, in-depth research on the harmonic power flow calculation method in AC-DC hybrid distribution networks, considering the impact of harmonics on the grid, is of great significance for improving the operation efficiency and power quality of the grid. Summary of the Invention

[0004] The purpose of the present invention is to provide a harmonic power flow calculation method and system for an AC-DC hybrid distribution network considering photovoltaic access, and to analyze the harmonic power flow of the AC-DC hybrid distribution network system through a calculation model.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] On the one hand, the present invention provides a harmonic power flow calculation method for an AC-DC hybrid distribution network considering photovoltaic access, including the following steps:

[0007] S1. Construct a power flow calculation model for each type of branch in the AC-DC distribution network to calculate the fundamental wave power and harmonic current of each type of branch;

[0008] S2. Construct a harmonic power flow calculation model for the AC-DC distribution network considering photovoltaic access;

[0009] S3. Calculate the harmonic power flow of the AC-DC distribution network:

[0010] S31. Calculate the nodal admittance matrix and initialize the nodal injection power of harmonics;

[0011] S32. Solve the fundamental power flow considering the access of PV;

[0012] S33. Solve the harmonic power flow considering the access of PV;

[0013] S34. Update the nodal injection power of harmonics. If the convergence condition is satisfied, output the calculation results. If the convergence condition is not satisfied, repeat steps S32 - S34 until convergence;

[0014] Finally, obtain the fundamental voltage and harmonic voltage, which are used to analyze the harmonic power flow of the AC - DC hybrid distribution network system.

[0015] In some embodiments, in S1, establish the power flow calculation models of the various types of branches according to the following topological structures:

[0016] Two AC nodes are directly connected; two DC nodes are connected; an AC node and a DC node are connected via an AC - DC converter; a DC node and an AC node are connected via a DC - AC converter; two AC nodes are successively connected via an AC - DC converter and a DC - AC converter.

[0017] In some embodiments, the power flow calculation model for the direct connection of two AC nodes is:

[0018]

[0019] The fundamental power obtained according to the model is:

[0020]

[0021] The harmonic current is:

[0022]

[0023] In the formula, are the fundamental active power and reactive power considering node classification respectively; N i is the type of the i - th node, N i = 0 is an AC node, N i = 1 is a DC node; N j is the type of the j - th node, N j = 0 is an AC node, N j = 1 is a DC node; L ij is the type of branch ij, L ij = 0 is an AC branch, L ij = 1 is a DC branch; The real and imaginary parts of the harmonic current between the $i$-th node and the $j$-th node considering node classification when two AC nodes are directly connected, respectively; The real and imaginary parts of the fundamental current between the $i$-th node and the $j$-th node, respectively; The fundamental active power and reactive power between the $i$-th node and the $j$-th node, respectively; The fundamental conductance and susceptance between the $i$-th node and the $j$-th node, respectively; The real and imaginary parts of the fundamental voltage of the $i$-th node, respectively; The real and imaginary parts of the fundamental voltage of the $j$-th node, respectively; The $h$-th harmonic conductance and susceptance between the $i$-th node and the $j$-th node, respectively; The real and imaginary parts of the $h$-th harmonic voltage of the $i$-th node, respectively; The real and imaginary parts of the $h$-th harmonic voltage of the $j$-th node, respectively.

[0024] In some embodiments, the power flow calculation model for the connection of the two DC nodes is:

[0025]

[0026]

[0027] In the formula, is the fundamental active power considering node classification; The real and imaginary parts of the harmonic current between the $i$-th node and the $j$-th node considering node classification when two DC nodes are directly connected, respectively.

[0028] In some embodiments, the power flow calculation model for the connection of the AC node and the DC node through an AC-DC converter is:

[0029]

[0030] In the formula, The fundamental active power and reactive power considering node classification, respectively; The real and imaginary parts of the harmonic current between the $i$-th node and the $j$-th node considering node classification when the AC node is connected to the DC node; $\eta$ ij is a constant of the converter efficiency; $V$ max 、$V$ min are the upper and lower limits of the converter voltage, respectively; $Q$ VSC,max is the upper limit of the converter reactive power; Regarding the AC-DC converter as a harmonic source, The real and imaginary parts of the $h$-th harmonic current injected by the AC-DC converter, respectively; $M1$ is the pulse width modulation ratio.

[0031] In some embodiments, the power flow calculation model in which the DC node is connected to the AC node through a DC-AC converter is as follows:

[0032]

[0033]

[0034] where is the fundamental active power considering node classification; are the real part and imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when the DC node is connected to the AC node, respectively. Regarding the AC-DC converter as a harmonic source, are the real part and imaginary part of the h-th harmonic current injected by the DC-AC converter, respectively; M2 is the pulse width modulation ratio.

[0035] In some embodiments, the power flow calculation model in which the two AC nodes are connected through an AC-DC converter and a DC-AC converter in sequence is as follows:

[0036]

[0037] where are the fundamental active power and reactive power considering node classification, respectively; are the real part and imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when the AC nodes are connected through an inverter, respectively.

[0038] In some embodiments, in S2, the harmonic power flow calculation model of the AC-DC distribution network includes:

[0039] Power balance model:

[0040]

[0041] Fundamental node injection power model:

[0042]

[0043] Harmonic current balance model:

[0044]

[0045] Node injection current model:

[0046]

[0047] where are the fundamental node injection active power and node injection reactive power of the i-th node, respectively; The active power and reactive power injected into the node of the h-th harmonic of the i-th node, respectively; The active power of the generator and the reactive power injected into the node of the i-th node, respectively; The active load and reactive load of the i-th node, respectively; The active power and reactive power injected by the photovoltaic at the i-th node; The real part and imaginary part of the injected current of the h-th harmonic node at the i-th node, respectively; The real part and imaginary part of the h-th harmonic current injected by the load at the i-th node, respectively; The real part and imaginary part of the h-th harmonic current injected by the photovoltaic at the i-th node, respectively; The real part and imaginary part of the h-th harmonic current injected by the generator at the i-th node, respectively.

[0048] In some embodiments, the calculation expression for updating the harmonic power injected into the node in S34 is:

[0049]

[0050] In the formula, The active power and reactive power injected into the node of the h-th harmonic of the i-th node, respectively; The real part and imaginary part of the h-th harmonic voltage of the i-th node, respectively; The real part and imaginary part of the injected current of the h-th harmonic node at the i-th node, respectively;

[0051] The convergence condition is:

[0052]

[0053] In the formula, Is the change in the real part of the injected current of the h-th harmonic node at the i-th node; Is the change in the imaginary part of the injected current of the h-th harmonic node at the i-th node.

[0054] On the other hand, the present invention provides a harmonic power flow calculation system for an AC-DC hybrid distribution network considering photovoltaic access, using the above method, including:

[0055] AC-DC distribution network various types of branch power flow calculation module: used to calculate the fundamental wave power and harmonic current of various types of branches;

[0056] AC-DC distribution network harmonic power flow calculation module considering photovoltaic access: used to calculate power balance, fundamental wave node injection power, harmonic current balance, and node injection current;

[0057] Calculation module: used to calculate the harmonic power flow of the AC-DC distribution network;

[0058] Output module: Output the obtained fundamental voltage and harmonic voltage for analyzing the harmonic power flow of the AC-DC hybrid distribution network system.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] The present invention establishes a harmonic interaction model for the coupling network, realizes the power flow calculation of harmonic voltage / current, and fills the technical gap in the quantization evaluation method of harmonic power flow in the existing AC-DC distribution network. Description of the Drawings

[0061] Figure 1 It is a schematic diagram of the overall process of the present invention;

[0062] Figure 2 It is a schematic diagram of the harmonic power flow calculation process of the AC-DC distribution network of the present invention;

[0063] Figure 3 It is a schematic diagram of the 13-node AC-DC hybrid distribution network system of the present invention. Detailed Embodiments

[0064] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0065] Embodiment 1:

[0066] Please refer to Figure 1 - Figure 2 , a method for calculating the harmonic power flow of an AC-DC hybrid distribution network considering photovoltaic access, comprising the following steps:

[0067] S1. Construct a power flow calculation model for each type of branch in the AC-DC distribution network to calculate the fundamental power and harmonic current of each type of branch.

[0068] The various types of branches include the following five topological structures:

[0069] Two AC nodes are directly connected, two DC nodes are connected, an AC node and a DC node are connected via an AC-DC converter, a DC node and an AC node are connected via a DC-AC converter, and two AC nodes are successively connected via an AC-DC converter and a DC-AC converter.

[0070] 1. Two AC nodes are directly connected:

[0071] In this topological structure, both node i and node j are AC nodes, and the two nodes are directly connected. The line admittance between the nodes is as follows:

[0072] Y ij = G ij + jB ij ;

[0073] In the formula, Y ij is the line admittance between node i and node j; G ij is the line conductance between node i and node j; B ij is the line susceptance between node i and node j; j is the imaginary unit of the complex number (the j in front of B).

[0074] The power flow equations of this branch are shown in Formulas (1)-(2). Among them, the calculation method of the fundamental wave power is shown in Formula (3), and the calculation method of the harmonic current is shown in Formula (4).

[0075]

[0076] 2. Two DC nodes are connected:

[0077] In this topological structure, both node i and node j are DC nodes, and the two nodes are directly connected. The line admittance between the nodes is as follows:

[0078] Y ij = G ij ;

[0079] The power flow equations of this branch are shown in Formulas (5)-(6). Among them, the calculation method of the fundamental wave power is shown in Formula (7), and the calculation method of the harmonic current is shown in Formula (8).

[0080]

[0081] 3. An AC node and a DC node are connected through an AC-DC converter:

[0082] In this topological structure, node i is an AC node and node j is a DC node, and the two nodes are connected through an AC-DC converter. The power flow equations of this branch are shown in Formulas (9)-(10). Among them, the calculation method of the fundamental wave power is shown in Formula (11), and the calculation method of the harmonic current is shown in Formula (12).

[0083]

[0084] 4. A DC node and an AC node are connected through a DC-AC converter:

[0085] In this topological structure, node i is a DC node and node j is an AC node. The two nodes are connected by a DC-AC converter. The line admittance between the nodes is:

[0086] Y ij = G ij ;

[0087] The power flow equations of this branch are shown in Eqs. (13)-(14). Among them, the calculation method of fundamental power is shown in Eq. (15), and the calculation method of harmonic current is shown in Eq. (16).

[0088]

[0089] 5. Two AC nodes are connected successively through an AC-DC converter and a DC-AC converter:

[0090] In this topological structure, both node i and node j are AC nodes. The two nodes are connected successively through an AC-DC converter and a DC-AC converter. The line admittance between the nodes is:

[0091] Y ij = G ij ;

[0092] The power flow equations of this branch are shown in Eqs. (17)-(18). Among them, the calculation method of fundamental power is shown in Eq. (19), and the calculation method of harmonic current is shown in Eq. (20).

[0093]

[0094] S2. Build a harmonic power flow calculation model for AC-DC distribution network considering photovoltaic access to calculate power balance, fundamental node injection power, harmonic current balance and node injection current.

[0095] Power balance:

[0096]

[0097] Fundamental node injection power:

[0098]

[0099] Harmonic current balance:

[0100]

[0101] Node injection current:

[0102]

[0103] The harmonic power flow model of the AC-DC distribution network considering photovoltaic access of the present invention is constituted by the above formulas (1)-(24).

[0104] S3. Calculate the harmonic power flow of the AC-DC distribution network: Due to the complexity of the model, the alternating iteration method is used to solve the harmonic power flow.

[0105] S31. Initialize the active power injection and reactive power injection at the nodes of the h-th harmonic, and let Calculate the fundamental power flow according to formulas (1), (3), (5), (7), (9), (11), (13), (15), (17), (19), (21), (22).

[0106] S32. Calculate the harmonic power flow according to formulas (2), (4), (6), (8), (10), (12), (14), (16), (18), (20), (23), (24).

[0107] S33. Calculate the active power injection and reactive power injection at the nodes of the h-th harmonic according to formula (25).

[0108]

[0109] S34. Calculate the fundamental power flow according to formulas (1), (3), (5), (7), (9), (11), (13), (15), (17), (19), (21), (22), and repeat steps S32 - S34 until the convergence condition shown in formula (26) is satisfied.

[0110]

[0111] Through the above calculation model, the present invention realizes the analysis of the harmonic power flow of the AC-DC hybrid distribution network system. Applying this model can calculate the loss distribution, guide equipment selection and operation optimization, predict the harmonic distribution after the access of new loads or distributed power sources, and plan filtering measures in advance. Through accurate modeling and analysis, the power quality and reliability of the hybrid power grid can be significantly improved, supporting the needs of high-proportion new energy access and intelligent development.

[0112] In a specific embodiment, as Figure 3 shown, the present invention verifies the feasibility of the above model through a 13-node AC-DC hybrid distribution network system. The system simultaneously includes the above five topological structures and can well reflect the effectiveness of the present invention.

[0113] Node 10 is connected to Node 12 successively through an AC-DC inverter and a DC-AC inverter. Node 11 is connected to Node 4 through an AC-DC inverter. Node 6 is connected to Node 13 through a DC-AC inverter. In addition, distributed power sources are connected to Nodes 3 and 8 respectively, and a photovoltaic system is planned to be connected to Node 5, with the power as shown in the figure. Among them, the system base power is 10 MW, the AC base voltage is 4.16 kV, and the DC base voltage is 6.8 kV. The line impedances of each node are shown in Table 1.

[0114] Table 1 Line Impedance Table of IEEE 13 System

[0115] Node i Node j Resistance (Ω) Reactance (Ω) Node i Node j Resistance (Ω) Reactance (Ω) 1 2 0.1256 0.1273 5 6 0.0655 0.1924 1 9 0.0706 0.1132 6 13 0.0754 0.0764 2 3 0.0754 0.0764 7 8 0.0754 0.0422 3 10 0.1310 0.3848 7 12 0.0706 0.1132 3 11 0.2030 0.0775 7 13 0.2030 0.0775 4 5 0.1310 0.3848 8 9 0.1256 0.1273 4 11 0.0751 0.0769 10 12 0.1367 0.1490

[0116] The harmonic currents injected by the inverters are shown in Table 2.

[0117] Table 2 Harmonic Current Injection Table of Each Harmonic Source

[0118]

[0119]

[0120] Through the above data, substituting into the formula for calculation, the power flow calculation results shown in Table 3 are obtained.

[0121] Table 3 Power Flow Calculation Result Table

[0122] Node Fundamental voltage 3rd harmonic voltage 5th harmonic voltage 7th harmonic voltage 1 1.05 -0.0145-j0.0160 -0.0172-j0.0185 -0.0159-j0.0180 2 1.01-j0.04 -0.0236-j0.0214 -0.0271-j0.0257 -0.0248-j0.0253 3 1.00-j0.04 -0.0293-j0.0257 -0.0335-j0.0318 -0.0307-0.0315 4 1.00 -0.0321-j0.0273 -0.0365-j0.0339 -0.0335-j0.0339 5 1.00 -0.0329-j0.0274 -0.0371-j0.0338 -0.0340-j0.0338 6 0.99 -0.0333-j0.0274 -0.0374-j0.0338 -0.0343-j0.0338 7 0.95-j0.12 -0.0348-j0.0294 -0.0387-j0.0362 -0.0353-j0.0363 8 1.00-j0.05 -0.0358-j0.0317 -0.0399-j0.0394 -0.0365-j0.0398 9 1.00-j0.04 -0.0239-j0.0229 -0.0273-j0.0271 -0.0250-j0.0267 10 0.99-j0.07 -0.0343-j0.0293 -0.0383-j0.0359 -0.0348-j0.0358 11 0.99-j0.06 -0.0316-j0.0273 -0.0361-j0.0339 -0.0332-j0.0340 12 0.96-j0.09 -0.0345-j0.0291 -0.0384-j0.0358 -0.0349-j0.0357 13 0.95-j0.10 -0.0339-j0.0275 -0.0379-j0.0338 -0.0346-j0.0338

[0123] The method proposed in the present invention can calculate the harmonic power flow of the AC-DC hybrid distribution network. According to the results, indicators such as harmonic distortion degree and three-phase unbalance degree can be calculated, providing a reference for the feasibility of photovoltaic access to the system.

[0124] Example 2:

[0125] A harmonic power flow calculation system for an AC-DC hybrid distribution network considering photovoltaic access, using the method described above, includes:

[0126] AC-DC distribution network various types of branch power flow calculation module: used to calculate the fundamental power and harmonic current of various types of branches;

[0127] AC-DC distribution network harmonic power flow calculation module considering photovoltaic access: used to calculate power balance, fundamental node injection power, harmonic current balance, and node injection current;

[0128] Calculation module: used to calculate the harmonic power flow of the AC-DC distribution network;

[0129] Output module: output the obtained fundamental voltage and harmonic voltage, used to analyze the harmonic power flow of the AC-DC hybrid distribution network system.

[0130] A harmonic power flow calculation system for an AC-DC hybrid distribution network considering photovoltaic access according to the present invention can be installed in a computer device. The computer device includes a processor, a memory, and a computer program stored in the memory and executable on the processor, such as a harmonic power flow calculation program for an AC-DC hybrid distribution network considering photovoltaic access. Among them, the memory includes at least one type of readable storage medium, and the readable storage medium includes flash memory, mobile hard disk, multimedia card, card-type memory (such as SD or DX memory, etc.), magnetic memory, magnetic disk, optical disk, etc. The processor is the control core of the electronic device, connecting various components of the entire computer device through various interfaces and lines, and by running or executing the programs or modules stored in the memory, and calling the data stored in the memory, to perform various functions of the computer device and process data.

[0131] The module according to the present invention refers to a series of computer program segments that can be executed by the processor of a computer device and can complete fixed functions, and are stored in the memory of the computer device.

[0132] Those skilled in the art will readily think of other embodiments of the present application after considering the specification and practicing the content disclosed herein. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field not disclosed in the present application.

Claims

1. A harmonic power flow calculation method for AC-DC hybrid distribution network considering photovoltaic access, characterized in that Including the following steps: S1. Construct the power flow calculation models for various types of branches in the AC-DC distribution network to calculate the fundamental power and harmonic current of each type of branch; S2. Construct the harmonic power flow calculation model of the AC-DC distribution network considering the access of photovoltaic power; S3. Calculate the harmonic power flow of the AC-DC distribution network: S31. Calculate the nodal admittance matrix and initialize the nodal injection power of harmonics; S32. Solve the fundamental power flow considering the access of photovoltaic power; S33. Solve the harmonic power flow considering the access of photovoltaic power; S34. Update the nodal injection power of harmonics. If the convergence condition is met, output the calculation results. If the convergence condition is not met, repeat steps S32 - S34 until convergence; Finally, obtain the fundamental voltage and harmonic voltage for analyzing the harmonic power flow of the AC-DC hybrid distribution network system.

2. A harmonic power flow calculation method for an AC-DC hybrid distribution network considering photovoltaic access according to claim 1, characterized in that, In S1, establish the power flow calculation models for various types of branches according to the following topological structures: Two AC nodes are directly connected; two DC nodes are connected; an AC node and a DC node are connected through an AC-DC converter; a DC node and an AC node are connected through a DC-AC converter; two AC nodes are successively connected through an AC-DC converter and a DC-AC converter.

3. A harmonic power flow calculation method for an AC-DC hybrid distribution network considering photovoltaic access according to claim 2, characterized in that, The power flow calculation model for two directly connected AC nodes is: The fundamental power obtained according to the model is: The harmonic current is: Wherein, are the fundamental active power and reactive power considering node classification when two AC nodes are directly connected; N i is the type of the i-th node, N i = 0 represents an AC node, N i = 1 represents a DC node; N j is the type of the j-th node, N j = 0 represents an AC node, N j = 1 represents a DC node; L ij is the type of branch ij, L ij = 0 represents an AC branch, L ij = 1 represents a DC branch; are the real part and imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when two AC nodes are directly connected; are the fundamental active power and reactive power between the i-th node and the j-th node; are the fundamental conductance and susceptance between the i-th node and the j-th node; are the real part and imaginary part of the fundamental voltage of the i-th node; are the real part and imaginary part of the fundamental voltage of the j-th node; are the real part and imaginary part of the harmonic current between the i-th node and the j-th node; are the h-th harmonic conductance and susceptance between the i-th node and the j-th node; are the real part and imaginary part of the h-th harmonic voltage of the i-th node; are the real part and imaginary part of the h-th harmonic voltage of the j-th node.

4. A harmonic power flow calculation method for an AC-DC hybrid distribution network considering photovoltaic access according to claim 2, characterized in that The power flow calculation model for two connected DC nodes is: Wherein, is the fundamental active power considering node classification when two DC nodes are directly connected; N i is the type of the i-th node, N i = 0 represents an AC node, N i = 1 represents a DC node; N j is the type of the j-th node, N j = 0 represents an AC node, N j = 1 represents a DC node; L ij is the type of branch ij, L ij = 0 represents an AC branch, L ij = 1 represents a DC branch; is the fundamental active power between the i-th node and the j-th node; are respectively the real part and the imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when two DC nodes are directly connected; are respectively the real part and the imaginary part of the harmonic current between the i-th node and the j-th node; is the fundamental conductance between the i-th node and the j-th node; are respectively the real part and the imaginary part of the fundamental voltage of the i-th node; are respectively the real part and the imaginary part of the fundamental voltage of the j-th node; are respectively the real part and the imaginary part of the h-th harmonic voltage of the i-th node; are respectively the real part and the imaginary part of the h-th harmonic voltage of the j-th node; is the h-th harmonic conductance between the i-th node and the j-th node.

5. A harmonic power flow calculation method for an AC-DC hybrid distribution network considering photovoltaic access according to claim 2, characterized in that The power flow calculation model for an AC node and a DC node connected through an AC-DC converter is: Wherein, are the fundamental active power and reactive power considering node classification when the AC node is connected to the DC node; N i = 0 represents an AC node, N i = 1 represents a DC node; N j is the type of the j-th node, N j = 0 represents an AC node, N j = 1 represents a DC node; L ij is the type of branch ij, L ij = 0 represents an AC branch, L ij = 1 represents a DC branch; are the fundamental active power and reactive power between the i-th node and the j-th node respectively; are the real part and imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when the AC node is connected to the DC node; are the real part and imaginary part of the harmonic current between the i-th node and the j-th node respectively; V i 1 and V j 1 are the fundamental voltage amplitudes of the i-th node and the j-th node respectively; η ij is a constant of the converter efficiency; is the fundamental conductance between the i-th node and the j-th node; V max and V min are the upper and lower limits of the converter voltage respectively; Q VSC,max is the upper limit of the converter reactive power; Regarding the AC-DC converter as a harmonic source, are the real part and the imaginary part of the h-th harmonic current injected by the AC-DC converter respectively; is the h-th harmonic conductance between the i-th node and the j-th node; are the real part and the imaginary part of the h-th harmonic voltage of the i-th node respectively; are the real part and the imaginary part of the h-th harmonic voltage of the j-th node respectively; M1 is the pulse width modulation ratio.

6. A harmonic power flow calculation method for an AC-DC hybrid distribution network considering photovoltaic access according to claim 2, characterized in that The power flow calculation model for a DC node and an AC node connected through a DC-AC converter is: Wherein, is the fundamental active power considering node classification when the DC node is connected to the AC node; N i = 0 represents an AC node, N i = 1 represents a DC node; N j is the type of the j-th node, N j = 0 represents an AC node, N j = 1 represents a DC node; L ij is the type of branch ij, L ij = 0 represents an AC branch, L ij = 1 represents a DC branch; is the fundamental active power between the i-th node and the j-th node; are respectively the real part and the imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when the DC node is connected to the AC node; are respectively the real part and the imaginary part of the harmonic current between the i-th node and the j-th node; V i 1 、V j 1 are respectively the fundamental voltage amplitudes of the i-th node and the j-th node; is the fundamental conductance between the i-th node and the j-th node; Regarding the AC-DC converter as a harmonic source, are respectively the real part and the imaginary part of the h-th harmonic current injected by the DC-AC converter; is the h-th harmonic conductance between the i-th node and the j-th node; are respectively the real part and the imaginary part of the h-th harmonic voltage of the i-th node; are respectively the real part and the imaginary part of the h-th harmonic voltage of the j-th node; M2 is the pulse width modulation ratio.

7. A harmonic power flow calculation method for an AC-DC hybrid distribution network considering photovoltaic access according to claim 2, characterized in that, The power flow calculation model for two AC nodes successively connected through an AC-DC converter and a DC-AC converter is: Wherein, are respectively the fundamental active power and reactive power considering node classification when AC nodes are connected through inverters; N i = 0 represents an AC node, N i = 1 represents a DC node; N j is the type of the j-th node, N j = 0 represents an AC node, N j = 1 represents a DC node; L ij is the type of branch ij, L ij = 0 represents an AC branch, L ij = 1 represents a DC branch; are respectively the fundamental active power and reactive power between the i-th node and the j-th node; are respectively the real part and imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when AC nodes are connected through inverters; are respectively the real part and imaginary part of the harmonic current between the i-th node and the j-th node; V i 1 、V j 1 are respectively the fundamental voltage amplitudes of the i-th node and the j-th node; η ij is a constant of the converter efficiency; is the fundamental conductance between the i-th node and the j-th node; M1 and M2 are both pulse width modulation ratios; V max 、V min are respectively the upper and lower limits of the converter voltage; Q VSC,max is the upper limit of the converter reactive power; Regarding the AC-DC converter as a harmonic source, are the real and imaginary parts of the h-th harmonic current injected by the AC-DC converter respectively; are the real and imaginary parts of the h-th harmonic current injected by the DC-AC converter respectively; is the h-th harmonic conductance between the i-th node and the j-th node; are the real and imaginary parts of the h-th harmonic voltage of the i-th node respectively; are the real and imaginary parts of the h-th harmonic voltage of the j-th node respectively.

8. A harmonic power flow calculation method for an AC-DC hybrid distribution network considering photovoltaic access according to claim 1, characterized in that, In S2, the harmonic power flow calculation model of the AC-DC distribution network includes: Power balance model: Fundamental nodal injection power model: Harmonic current balance model: Nodal injection current model: wherein, are respectively the fundamental active power injected into the node and the reactive power injected into the node of the i-th node; are respectively the active power injected into the node and the reactive power injected into the node of the h-th harmonic of the i-th node; are respectively the active power of the generator and the reactive power injected into the node of the i-th node; are respectively the active load and the reactive load of the i-th node; is the active power and reactive power injected by the photovoltaic of the i-th node; are respectively the fundamental active power considering node classification when two AC nodes are directly connected, the fundamental active power considering node classification when two DC nodes are directly connected, the fundamental active power considering node classification when an AC node is connected to a DC node, the fundamental active power considering node classification when a DC node is connected to an AC node, and the fundamental active power considering node classification when an AC node is connected through an inverter; are respectively the real part and the imaginary part of the h-th harmonic node injection current of the i-th node; are respectively the real part and the imaginary part of the h-th harmonic current injected by the load of the i-th node; are respectively the real part and the imaginary part of the h-th harmonic current injected by the photovoltaic of the i-th node; are respectively the real part and the imaginary part of the h-th harmonic current injected by the generator of the i-th node; are respectively the real part and the imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when two AC nodes are directly connected; are respectively the real part and the imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when two DC nodes are directly connected; are respectively the real part and the imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when an AC node is connected to a DC node; are respectively the real part and the imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when a DC node is connected to an AC node; are respectively the real part and the imaginary part of the harmonic current between the i-th node and the j-th node considering node classification when an AC node is connected through an inverter.

9. A harmonic power flow calculation method for an AC-DC hybrid distribution network considering PV access according to claim 1, characterized in that The calculation expression for updating the nodal injection power of harmonics in S34 is: wherein, are respectively the active power and reactive power injected into the node of the h-th harmonic of the i-th node; are respectively the real part and imaginary part of the voltage of the h-th harmonic of the i-th node; are respectively the real part and imaginary part of the current injected into the node of the h-th harmonic of the i-th node; The convergence condition is: In the formula, is the change in the real part of the injected current at the h-th harmonic node of the i-th node; is the change in the imaginary part of the injected current at the h-th harmonic node of the i-th node.

10. A harmonic power flow calculation system for an AC-DC hybrid distribution network considering PV access, using the method according to any one of claims 1-9, characterized in that, Including: Power flow calculation module for various types of branches in the AC-DC distribution network: used to calculate the fundamental power and harmonic current of various types of branches; Harmonic power flow calculation module of the AC-DC distribution network considering the access of photovoltaic power: used to calculate power balance, fundamental nodal injection power, harmonic current balance, and nodal injection current; Calculation module: used to calculate the harmonic power flow of the AC-DC distribution network; Output module: output the obtained fundamental voltage and harmonic voltage for analyzing the harmonic power flow of the AC-DC hybrid distribution network system.

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