Multi-port inverter topology derivation method based on even graph

Abstract

The invention discloses a multi-port inverter topology derivation method based on an even graph, and the method comprises the steps: constructing a mapping rule based on the even graph, mapping components in a multi-port inverter into edges in the even graph, and mapping circuit nodes, a DC source and AC ports in the multi-port inverter into points in the even graph; then, basic circuit constraints are converted into graph constraints based on a mapping rule of the even graph, so that the minimum degree of each point is obtained; determining the degree of each point in combination with the handshake theorem, and further deriving an even graph meeting the graph constraint; in addition, topology type and more source expansion can be carried out on the even graph, so that diversified effective even graphs are obtained; and finally, the diversified effective even graph is converted into a topological graph of the multi-port inverter.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic topology, and more specifically, relates to a multi-port inverter topology derivation method based on a dual graph. Background Art

[0002] With the improvement of environmental awareness and the depletion of traditional fossil energy reserves, renewable energy systems have become an alternative to traditional fossil energy systems due to their sustainability. Among various renewable energy systems, multi-source systems have become a solution to alleviate the intermittent problem in single energy systems because they can achieve the coordinated work of multiple energy sources.

[0003] The power conversion performance of a multi-source system is mainly determined by the topology of the multi-port power electronic interface. Among the existing multi-port power electronic interfaces, multi-port inverters have attracted widespread attention because they directly connect multiple energy sources without the need for an intermediate DC-DC converter, thus having the advanced advantages of low cost, high power density, and single-stage power conversion. However, as an emerging technology in recent years, multi-port inverters have the problem of a limited number of topological structures. Therefore, how to derive a variety of multi-port inverters has become an urgent problem to be solved.

[0004] Existing topology derivation methods can be divided into two categories: existing structure-based methods and model-based derivation methods. The existing structure-based method transforms the existing multilevel inverter topology through duality, combination, etc. to obtain the multi-port inverter topology. However, the existing multilevel structure is not specially designed for multi-port inverters. Some devices used for DC side voltage balance in multilevel inverters are not required in multi-port inverters, which will bring about problems such as device redundancy and cost increase. In addition, model-based derivation methods have attracted much attention in recent years because they use graphical languages ​​to intuitively and vividly represent topologies. Although these methods can intuitively analyze and derive topological structures, their application is limited as the number of DC power sources increases because they fix or do not take into account the connection relationship of multiple DC sources. In contrast, the dual graph has the advantage of conveniently determining adjacent relationships, which is conducive to the design and analysis of the connection relationship of DC sources. However, due to the lack of mapping rules and topology driving processes, topology derivation methods based on dual graphs have not yet been proposed. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for deriving a multi-port inverter topology based on a dual graph, which can derive a variety of multi-port inverters.

[0006] To achieve the above-mentioned object of the invention, the present invention provides a method for deriving a multi-port inverter topology based on a dual graph, characterized in that it comprises the following steps:

[0007] (1) Define mapping rules based on dual graphs;

[0008] (2) Based on the mapping rules of the dual graph, the circuit constraints of the multi-port inverter are converted into graph constraints;

[0009] (3) Derive the topology based on graph constraints;

[0010] (4) Expand the obtained topology;

[0011] (5) Convert the dual graph into a circuit diagram of a multi-port inverter.

[0012] The object of the invention of the present invention is achieved in this way:

[0013] The present invention discloses a method for deriving a topology of a multi-port inverter based on an even graph. First, a mapping rule based on the even graph is constructed to map components in the multi-port inverter to edges in the even graph, and to map circuit nodes, DC sources, and AC ports in the multi-port inverter to points in the even graph. Then, based on the mapping rule of the even graph, basic circuit constraints are converted into graph constraints, so as to obtain the minimum degree of each point. Then, the degree of each point is determined in combination with the handshake theorem, so as to derive an even graph that satisfies the graph constraints. In addition, the even graph can be expanded in terms of topological types and more sources, so as to obtain diversified effective even graphs. Finally, the diversified effective even graphs are converted into a topological graph of the multi-port inverter.

[0014] At the same time, the multi-port inverter topology derivation method based on the dual graph of the present invention also has the following beneficial effects:

[0015] (1) The present invention uses a method of constructing a dual graph to derive topology, without relying on an existing multi-port inverter;

[0016] (2) The present invention provides a mapping rule based on a dual graph, which maps a DC source to a point. Compared with the existing mapping method of mapping a DC source to an edge, the number of edges in the entire graph is reduced, thereby reducing the complexity of the entire graph;

[0017] (3) The present invention takes into account the diversity of DC source connection positions, and a new topology can be obtained by changing the labels of the points in the dual graph without having to derive from scratch;

[0018] (4) The present invention can quickly obtain the topology of more sources by simply adding points. Compared with the existing methods, it has good scalability and is more suitable for multi-source occasions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of a method for deriving a multi-port inverter topology based on a dual graph of the present invention;

[0020] Figure 2Schematic diagram of mapping various parts of a multi-port inverter into a dual graph, wherein (a) is a schematic diagram of mapping the entire inverter circuit topology into a dual graph, (b) is a schematic diagram of mapping circuit nodes into points in a dual graph, (c) is a schematic diagram of mapping inverter AC ports into points in a dual graph, and (d) is a schematic diagram of mapping different DC source connection modes into points in a dual graph;

[0021] Figure 3 is a schematic diagram of graph constraints, where (a) is a schematic diagram of the actual application requirements mapped to points in the even graph, (b) is a topological diagram that violates graph constraint 1, (c) is a topological diagram that violates graph constraint 2, (d) is a topological diagram that violates graph constraint 3-1, (e) is a topological diagram that violates graph constraint 3-2, and (f) is a topological diagram that satisfies all graph constraints;

[0022] Figure 4 is a topological diagram that violates graph constraint 4;

[0023] Figure 5 is a schematic diagram of constraint 5;

[0024] Figure 6 This is a flowchart for deriving topology based on a dual graph, where (a) is the actual application requirement, (b) is a schematic diagram for determining the points in the dual graph according to the requirement, (c) is a schematic diagram for the minimum degree of the points in the dual graph, (d) is a schematic diagram for the degree of the points in the graph after the degree is increased, and (e) is a schematic diagram for the feasible topology;

[0025] Figure 7 It is a schematic diagram of the process of obtaining an isomorphic graph of a dual graph by exchanging sticky notes;

[0026] Figure 8 Schematic diagrams of inverters with more ports are obtained by adding points, wherein (a) is a schematic diagram of a multi-source inverter topology with two DC sources, (b) is a schematic diagram of a multi-source inverter topology with three DC sources, (c) is a schematic diagram of a multi-source inverter topology with four DC sources, and (d) is a schematic diagram of a multi-source inverter circuit with four DC sources;

[0027] Fig. 9 is a schematic diagram of converting a dual graph into a multi-port inverter;

[0028] Fig.10 It is a schematic diagram of expanding the single-phase circuit topology into a three-phase circuit topology;

[0029] Fig.11 is a schematic diagram of the resulting multi-port inverter topology schematic with two DC sources. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0031] Example

[0032] In this embodiment, if Figure 1 As shown, the present invention provides a method for deriving a multi-port inverter topology based on a dual graph, comprising the following steps:

[0033] (1) Define mapping rules based on dual graphs;

[0034] (1.1) Map the components in the multi-port inverter to the edges in the even graph, and map the circuit nodes, AC ports, and DC sources in the multi-port inverter to the points in the even graph;

[0035] In this embodiment, Figure 2 (a) is a schematic diagram of mapping the entire inverter circuit topology into a bigraph, wherein the switch devices in the multi-port inverter are mapped into edges. Based on this, the number of edges is equal to the number of switch devices, which is convenient for reducing redundant devices in the subsequent process.

[0036] (1.2) Use different shapes to distinguish the points in the dual graph: use triangles to represent the points after the circuit nodes are mapped, use squares to represent the points after the AC ports are mapped, and use circles to represent the points after the DC power supply is mapped;

[0037] In this embodiment, if Figure 2 As shown in (b), the circuit nodes in the multi-port inverter are mapped to points in the dual graph and represented by triangles, and labeled as X, Y, etc.; Figure 2 As shown in (c), the AC ports in the multi-port inverter are mapped to points in the even graph and represented by squares and labeled A. Figure 2 As shown in (d), the DC source in the multi-port inverter is mapped to a point in the dual graph and represented by a circle;

[0038] (1.3) Set labels to distinguish the points in the even graph that represent DC sources: Set label E a + / - indicates the positive or negative pole of DC source a; set label E a / b Indicates DC power supply E a The negative electrode and E b positive connection; use label E a / b / c / - indicates DC power supply E a 、E b 、E c The negative connection of

[0039] In this embodiment, the multi-port inverter includes two DC sources, wherein the negative electrode of E1 and the negative electrode of E2 are connected together, and the DC sources are labeled as: E1+, E2+, E 1 / 2 -, and E1>E2, such as Figure 2 (d.1)

[0040] (2) Based on the mapping rules of the dual graph, the circuit constraints of the multi-port inverter are converted into graph constraints;

[0041] (2.1) Define the basic circuit constraints of the multi-port inverter;

[0042] (2.1.1) The AC port requires at least two power paths to connect to the positive and negative poles of the DC source respectively;

[0043] (2.1.2) Multi-port inverters cannot be open-circuited;

[0044] (2.1.3) Multi-port inverters cannot be short-circuited, which can be divided into the DC source itself cannot be short-circuited and multiple DC sources cannot be short-circuited with each other;

[0045] (2.1.4) The negative pole of the DC source is connected to the ground to avoid excessive common mode voltage;

[0046] (2.1.5) Two components connected in series are equivalent to one component;

[0047] (2.2), convert the circuit constraints of the multi-port inverter into graph constraints;

[0048] (2.2.1) According to step (2.1.1), we get AC port diagram constraint 1:

[0049] D min (A)≥2

[0050] Where D min (A) represents the minimum degree of point A of the AC port;

[0051] (2.2.2) According to step (2.1.2), the dual graph corresponding to the multi-port inverter is a connected graph, and the graph constraint 2 is:

[0052] ω(G)=1

[0053] Among them, ω(G) is the number of connected branches of the bipartite graph G; furthermore, there is the minimum degree of the DC source:

[0054] D min (E)≥1

[0055] Where D min (E) represents the minimum degree of the DC source E;

[0056] (2.2.3) According to step (2.1.3), we get graph constraint 3:

[0057] According to the short circuit of DC source, constraint 3 can be divided into two types:

[0058] Figure Constraint 3-1: In the case where the DC source itself cannot be short-circuited, the positive and negative nodes of the DC source cannot be adjacent in the even graph;

[0059] Figure constraint 3-2: Multiple DC sources cannot be short-circuited. If there is a common point in the connection of multiple DC sources, the positive nodes of the DC sources cannot be adjacent in the even graph;

[0060] In this embodiment, if Figure 3 As shown in (a), due to the lack of a connection path from the negative electrode of E2 to the AC port A, the graph constraint 1 is violated and is therefore invalid; Figure 3 As shown in (b), since there are two connected branches H1 and H2, graph constraint 2 is violated and is therefore invalid; Figure 3 In (c), when switch S1 is activated, E1 itself is short-circuited, violating the constraint 3-1 of the diagram, so it is invalid. Similarly, Figure 3 When switch S2 in (d) is activated, the topology is invalid because E1 and E2 are short-circuited, violating the graph constraint 3-2. In addition, Figure 3 The topology in (f) satisfies all graph constraints and is therefore valid;

[0061] (2.2.4) According to step (2.1.4), we obtain graph constraint 4: if there is no common point in the connection of multiple DC sources, the negative nodes of the DC sources must be adjacent;

[0062] In this embodiment, Figure 4 This is a diagram that violates constraint 4. In this diagram, since the cathodes of E1 and E2 are not adjacent, no matter how the components are operated, E1 and E2 cannot be grounded. Therefore, this topology is invalid due to the problem of excessive common-mode voltage.

[0063] (2.2.5) According to step (2.1.5), we get graph constraint 5:

[0064] D min (x)>2

[0065] Among them, D min (x) represents the minimum degree of circuit node x;

[0066] In this embodiment, Figure 5 FIG. 5 is a schematic diagram of reducing redundant devices according to constraint 5. In this figure, two switch devices connected in series can be simplified to one switch device, thereby reducing redundant devices;

[0067] (3) Derivation to obtain a valid even graph;

[0068] (3.1) According to the connection mode of the DC source of the multi-port inverter, the number of DC ports is determined; in addition, based on the voltage stress requirements of the components, whether circuit nodes are required is determined; according to the number of DC ports, AC ports and circuit nodes, the number of points in the dual graph is obtained;

[0069] In this embodiment, if Figure 6 As shown in (a) to (b), there is a common point between the two DC sources. The number of DC ports in the even graph is determined to be three, and there is no circuit node. Combined with an AC port, the number of points in the even graph is obtained, namely E1+, E2+, E 1 / 2 - and A four points;

[0070] (3.2), according to the graph constraints of the even graph, that is: To obtain the minimum degree of the four points in (3.1), such as Figure 6 (c) as shown.

[0071] Then use the graph theory handshake theorem to determine the degree of each point. The calculation formula is:

[0072]

[0073] Among them, E s Represents the total number of edges in the even graph, n represents the total number of points in the even graph, and D(i) represents the degree of each point. It is not difficult to see that the sum of the total degrees of the points in the even graph needs to be an even number. It should be noted that the mapping rule proposed in the present invention makes the number of devices the same as the number of edges in the even graph, and reducing redundant devices can be equivalent to reducing the number of edges in the even graph, and twice the number of edges in the even graph is equivalent to the sum of the degrees of the points in the even graph. Based on this, to reduce the redundant devices of the multi-port inverter, it is only necessary to reduce the degree of the points in the even graph.

[0074] In this embodiment, Figure 6 The minimum sum of the degrees of the four points in (c) is 5, which violates the handshake theorem. Based on this, we need to increase the degree of a certain point; finally, under the premise of meeting the graph constraints, such as Figure 6 As shown in (d), add 1 to the degree of point A, so that the degree of point A increases to 3, and the total degree increases to 6;

[0075] (3.3), based on steps (3.1) and (3.2), we can get Figure 6 (e) The effective dual graph shown;

[0076] (4) Expand the dual graph;

[0077] (4.1) When the graph constraints are satisfied, the structure of the dual graph is not changed. Only the labels of the points representing the DC source in the dual graph are swapped to derive the isomorphic graph of the dual graph. Different types of topologies can be obtained without starting from scratch.

[0078] In this embodiment, if Figure 7 As shown, label E1+ and label E 1 / 2 -by exchanging the positions of the two graphs, we can get the isomorphic graph of the dual graph. The dual graph and the isomorphic graph correspond to different types of circuit topologies.

[0079] (4.2) Under the condition that the graph constraints are satisfied, by adding points representing DC sources, the number of DC sources is expanded to obtain the extended graph of the even graph;

[0080] Among them, in the extended graph, if the added DC source has a common point with the existing DC source in the even graph, the labels of the added DC source and the existing DC source are merged; if the added DC source has no common point with the existing DC source in the even graph, a point representing the DC source is directly added to the even graph, and a label is added;

[0081] In this embodiment, when the graph constraints are satisfied, Figure 8 As shown in (a) to (b), when the extended DC source E3 is added to the existing dual graph, the negative electrode of E3 and the existing DC source E 1 / 2 - are connected together, then the label E3- is merged into E 1 / 2 -, the point label becomes E 1 / 2 / 3 -. If the positive electrode of E3 has no common point with the existing DC source, then add a point and label it E3+ while satisfying the graph constraints, and obtain Figure 8 (b) shows a multi-source inverter topology with three DC sources. Similarly, a fourth DC source E4 can be added to the existing dual graph to obtain Figure 8 (c) shows a multi-source inverter topology with four DC sources, and its corresponding circuit topology is as follows: Figure 8 (d)

[0082] (5) Convert the dual graph into a topological graph of a multi-port inverter;

[0083] (5.1) Based on the mapping rule of the even graph, the even graph or isomorphic graph or extended graph is converted into a topological graph of a multi-port inverter;

[0084] (5.2) Traverse each edge in the topology graph, determine the maximum potential of two points on the same edge, determine the direction of the components, and obtain the initial circuit topology;

[0085] (5.3) Fine-tune the initial circuit topology: replace the unidirectional components that cause the DC source to conduct directly in the initial circuit topology with bidirectional components, thereby obtaining a single-phase circuit topology. Then expand the single-phase circuit topology into a three-phase topology to obtain the final multi-source inverter topology.

[0086] In this embodiment, if Fig. 9 As shown in the figure, due to the presence of diode D1, E2 and the AC port are directly connected, causing E2 to be uncontrollable. Therefore, it is necessary to replace this unidirectional component with a bidirectional component to effectively obtain a single-phase circuit topology; then expand the single-phase circuit topology into a three-phase topology to obtain the final multi-port inverter topology, as shown in Fig.10 shown.

[0087] In this embodiment, the above steps can be used to obtain Fig.11 Ten multi-port inverter topologies with two DC sources are shown.

[0088] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A method for deriving a multi-port inverter topology based on a bigraph, characterized in that: The following steps are involved: (1) Define mapping rules based on dual graphs; (2) Based on the mapping rules of the dual graph, the circuit constraints of the multi-port inverter are converted into graph constraints; (3) Derive the multi-port inverter topology based on the graph constraints; (4) Expanding the obtained multi-port inverter topology; (5) Convert the dual graph into a circuit diagram of a multi-port inverter.

2. The method for deriving a multi-source inverter topology based on a dual graph according to claim 1, characterized in that: The mapping rule based on the dual graph in step (1) is: (2.1) Map the components in the multi-source inverter to the edges in the dual graph, and map the circuit nodes, AC ports, and DC sources in the multi-source inverter to the points in the dual graph; (2.2) Use different shapes to distinguish the points in the dual graph: use triangles to represent the points after the circuit nodes are mapped, use squares to represent the points after the AC ports are mapped, and use circles to represent the points after the DC power supply is mapped; (2.3) Set labels to distinguish the points in the dual graph that represent DC sources: Set label E a + / - indicates the positive or negative pole of DC source a; set label E a / b Indicates DC power supply E a The negative electrode and E b positive connection; use label E a / b / c / - indicates DC power supply E a 、E b 、E c negative connection.

3. The method for deriving a multi-source inverter topology based on a dual graph according to claim 1, characterized in that: The method for converting the circuit constraints of the multi-source inverter into graph constraints in step (2) is: (3.1) Define the basic circuit constraints of the multi-source inverter; (3.1.1) The AC port requires at least two power paths to connect to the positive and negative poles of the DC source respectively; (3.1.2) Multi-source inverters cannot be open-circuited; (3.1.3) Multi-source inverters cannot be short-circuited, which can be divided into the DC source itself cannot be short-circuited and multiple DC sources cannot be short-circuited with each other; (3.1.4) The negative pole of the DC source is connected to the ground to avoid excessive common mode voltage; (3.1.5) Two components connected in series are equivalent to one component; (3.2),Convert the circuit constraints of the multi-source inverter into graph constraints; (3.2.1), according to step (3.1.1), we get AC port diagram constraint 1: D min (A)≥2 Where D min (A) represents the minimum degree of point A of the AC port; (3.2.2) According to step (3.1.2), the dual graph corresponding to the multi-source inverter is a connected graph, and the graph constraint 2 is: ω(G)=1 Among them, ω(G) is the number of connected branches of the bipartite graph G; furthermore, there is the minimum degree of the DC source: D min (E)≥1 Where D min (E) represents the minimum degree of the DC source E; (3.2.3) According to step (3.1.3), we get graph constraint 3: According to the short circuit of DC source, the graph constraint 3 is divided into two types: Figure Constraint 3-1: In the case where the DC source itself cannot be short-circuited, the positive and negative nodes of the DC source cannot be adjacent in the even graph; Figure constraint 3-2: Multiple DC sources cannot be short-circuited. If there is a common point in the connection of multiple DC sources, the positive nodes of the DC sources cannot be adjacent in the even graph; (3.2.4) According to step (3.1.4), we obtain graph constraint 4: if there is no common point in the connection of multiple DC sources, the negative nodes of the DC sources must be adjacent; (3.2.5) According to step (3.1.5), we get graph constraint 5: D min (x)>2 Among them, D min (x) represents the minimum degree of circuit node x.

4. The method for deriving a multi-source inverter topology based on a dual graph according to claim 1, characterized in that: The method for deriving the multi-port inverter topology based on the graph constraint in step (3) is: (4.1) According to the connection mode of the DC source of the multi-source inverter, the number of DC ports is determined; in addition, based on the voltage stress requirements of the components, whether circuit nodes are required is determined; according to the number of DC ports, AC ports and circuit nodes, the number of points in the dual graph is obtained; (4.2) According to the minimum degree of each point in the even graph, the degree of each point is determined using the graph theory handshake theorem; (4.3), based on steps (4.1) and (4.2), a dual graph that satisfies the graph constraints is derived.

5. The method for deriving a multi-source inverter topology based on a dual graph according to claim 1, characterized in that: The method for expanding the multi-port inverter topology in step (4) is: (5.1) When the graph constraints are satisfied, the structure of the dual graph is not changed. Only the labels of the points representing the DC source in the dual graph are swapped to derive isomorphic graphs of the dual graph, thereby obtaining different types of topologies. (5.2) When the graph constraints are satisfied, add points representing DC sources to expand the number of DC sources and obtain the extended graph of the even graph; Among them, in the extended graph, if the added DC source has a common point with the existing DC source in the even graph, the labels of the added DC source and the existing DC source are merged; if the added DC source has no common point with the existing DC source in the even graph, a point representing the DC source is directly added to the even graph, and a label is added.

6. The method for deriving a multi-source inverter topology based on a dual graph according to claim 1, characterized in that: The method for converting the dual graph into a circuit diagram of a multi-port inverter in step (5) is: (6.1) Based on the mapping rules of the dual graph, the dual graph, isomorphic graph and extended graph are converted into the topological graph of the multi-source inverter; (6.2) Traverse each edge in the topology graph, determine the maximum potential of two points on the same edge, determine the current direction of the components, and obtain the initial circuit topology; (6.3) Fine-tune the initial circuit topology: replace the unidirectional components in the initial circuit topology that cause the DC source to conduct directly with bidirectional components to obtain a single-phase circuit topology; then expand the single-phase circuit topology into a three-phase topology to obtain the final multi-source inverter topology.

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