A method for deriving multi-port inverter topologies based on bipartite graphs

Abstract

The application discloses a kind of based on bipartite graph's multi-port inverter topological derivation method, first, based on the mapping rule of bipartite graph, the component in multi-port inverter is mapped as the edge in bipartite graph, the circuit node in multi-port inverter, DC source, AC port are all mapped as the point in bipartite graph;Then based on the mapping rule of bipartite graph, basic circuit constraint is converted into graph constraint, so that the minimum degree of each point is obtained;Then, the degree of each point is determined in combination with handshake theorem, and then a bipartite graph satisfying graph constraint is derived;In addition, the topology type and more source of bipartite graph can be expanded, so that diversified effective bipartite graph is obtained;Finally, the diversified effective bipartite graph is converted into the topological graph of multi-port inverter.

Description

Technical Field

[0001] This invention belongs to the field of power electronics topology technology, and more specifically, relates to a method for topology derivation of multi-port inverters based on dipole graphs. Background Technology

[0002] With increasing environmental awareness and the depletion of traditional fossil fuel reserves, renewable energy systems have become an alternative to traditional fossil fuel systems due to their sustainability. Among various renewable energy systems, multi-source systems, which enable multiple energy sources to work together, have become a solution to alleviate the intermittency problems of single-energy systems.

[0003] The power conversion performance of a multi-source system is primarily determined by the topology of the multi-port power electronic interface. Among existing multi-port power electronic interfaces, multi-port inverters have attracted widespread attention due to their advantages of low cost, high power density, and single-stage power conversion, as they directly connect to multiple energy sources without the need for an intermediate DC-DC converter. However, as an emerging technology in recent years, multi-port inverters suffer from a limited variety of topologies. Therefore, developing diverse multi-port inverters has become an urgent problem to be solved.

[0004] Existing topology derivation methods can be broadly categorized into two types: methods based on existing structures and model-based derivation methods. Methods based on existing structures modify existing multilevel inverter topologies through duality, combination, and other means to obtain multiport inverter topologies. However, existing multilevel structures are not specifically designed for multiport inverters; some devices used for DC-side voltage balancing in multilevel inverters are not needed in multiport inverters, leading to redundancy and increased costs. Furthermore, model-based derivation methods have gained significant attention in recent years due to their use of graphical representations to intuitively and vividly represent topologies. While these methods can intuitively analyze and derive topologies, their application is limited as the number of DC power sources increases because they fix or fail to consider the connection relationships of multiple DC sources. In contrast, dual graphs offer the advantage of easily determining adjacency relationships, which is beneficial for designing and analyzing DC source connections. However, due to the lack of mapping rules and topology-driving processes, dual graph-based topology derivation methods have not yet been proposed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for topology derivation of multiport inverters based on dipole graphs, which can generate a variety of multiport inverters.

[0006] To achieve the above-mentioned objectives, the present invention provides a method for topology derivation of multi-port inverters based on dipole graphs, characterized by comprising the following steps:

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

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

[0009] (3) The topology is derived based on graph constraints;

[0010] (4) Extend the obtained topology;

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

[0012] The objective of this invention is achieved as follows:

[0013] This invention presents a multi-port inverter topology derivation method based on a bipartite graph. First, it constructs a mapping rule based on the bipartite graph, mapping the components in the multi-port inverter to edges in the bipartite graph, and mapping the circuit nodes, DC sources, and AC ports in the multi-port inverter to points in the bipartite graph. Then, based on the bipartite graph mapping rule, it converts basic circuit constraints into graph constraints, thereby obtaining the minimum degree of each point. Next, it combines the handshake theorem to determine the degree of each point, thus deriving a bipartite graph that satisfies the graph constraints. Furthermore, it can expand the bipartite graph with topology types and more sources, thereby obtaining diverse effective bipartite graphs. Finally, it converts the diverse effective bipartite graphs into the topology graph of the multi-port inverter.

[0014] Meanwhile, the multi-port inverter topology derivation method based on even graphs of the present invention also has the following beneficial effects:

[0015] (1) The present invention performs topology derivation by constructing a dipole graph, without relying on existing multi-port inverters;

[0016] (2) This invention provides a mapping rule based on a bipartite graph, which maps DC sources to points. Compared with the existing mapping method that maps DC sources to edges, this reduces the number of edges in the entire graph and lowers the complexity of the entire graph.

[0017] (3) The present invention takes into account the diversity of DC source connection positions. A new topology can be obtained by changing the labels of points in the even 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 situations. Attached Figure Description

[0019] Figure 1 This is a flowchart of the multi-port inverter topology derivation method based on dipole graphs according to the present invention;

[0020] Figure 2This is a schematic diagram of the mapping of each part of a multi-port inverter to a dipole graph. Among them, (a) is a schematic diagram of the mapping of the entire inverter circuit topology to a dipole graph, (b) is a schematic diagram of the mapping of circuit nodes to points in the dipole graph, (c) is a schematic diagram of the mapping of the inverter AC port to points in the dipole graph, and (d) is a schematic diagram of the mapping of different DC source connection methods to points in the dipole graph.

[0021] Figure 3 Here are schematic diagrams of graph constraints, where (a) is a schematic diagram of the actual application requirements mapped to points in the bipartite graph, (b) is a topological schematic diagram of violating graph constraint 1, (c) is a topological schematic diagram of violating graph constraint 2, (d) is a topological schematic diagram of violating graph constraint 3-1, (e) is a topological schematic diagram of violating graph constraint 3-2, and (f) is a topological schematic diagram of satisfying all graph constraints.

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

[0023] Figure 5 This is a schematic diagram of constraint 5 in the figure;

[0024] Figure 6 This is a flowchart of deriving topology based on the bipartite graph, where (a) represents the actual application requirements, (b) is a schematic diagram of determining the points in the bipartite graph according to the requirements, (c) is a schematic diagram of the minimum degree of the points in the bipartite graph, (d) is a schematic diagram of the degree of the points in the graph after increasing the degree, and (e) is a schematic diagram of the feasible topology.

[0025] Figure 7 This is a flowchart illustrating the process of obtaining isomorphic graphs of dipole graphs through the exchange of notes;

[0026] Figure 8 The diagrams show how to obtain more ports by adding points. (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] Figure 9 This is a schematic diagram of converting a dipole diagram into a multi-port inverter;

[0028] Figure 10 This is a schematic diagram of extending a single-phase circuit topology to a three-phase circuit topology;

[0029] Figure 11 This is a schematic diagram of the obtained multi-port inverter topology with two DC sources. Detailed Implementation

[0030] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0031] Example

[0032] In this embodiment, as Figure 1 As shown, the present invention provides a method for topology derivation of multi-port inverters based on dipole graphs, comprising the following steps:

[0033] (1) Define mapping rules based on bipartite 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 to a bipartite graph, in which the switching devices in the multi-port inverter are mapped as edges. Based on this, the number of edges is equal to the number of switching devices, which facilitates the reduction of redundant devices in the future.

[0036] (1.2) Use different shapes to distinguish points in the bipartite diagram: use triangles to represent points mapped from circuit nodes, use squares to represent points mapped from AC ports, and use circles to represent points mapped from DC power supplies.

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

[0038] (1.3) Set labels to distinguish points representing DC sources in the dipole diagram: Set label E a + / - indicates the positive or negative terminal of DC source a; set label E a / b Indicates DC power supply E a 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 terminal connection;

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

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

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

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

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

[0044] (2.1.3) Multi-port inverters cannot be short-circuited, which is further divided into DC sources that cannot be short-circuited themselves and multiple DC sources that cannot be short-circuited with each other;

[0045] (2.1.4) The negative terminal of the DC source is grounded 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), the AC port diagram constraint 1 is obtained:

[0049] D min (A)≥2

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

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

[0052] ω(G)=1

[0053] Where ω(G) is the number of connected components in the even graph G; further, the minimum degree of the DC source is:

[0054] D min (E)≥1

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

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

[0057] Based on the short-circuit condition of the DC source, constraint 3 in Figure 3 can be divided into two types:

[0058] Figure constraint 3-1: For 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: For multiple DC sources that cannot be short-circuited, if there is a common point in the connection of multiple DC sources, the positive poles of the DC sources cannot be adjacent in the even graph.

[0060] In this embodiment, as Figure 3 As shown in (a), the lack of a connection path from the negative terminal of E2 to AC port A violates constraint 1 and is therefore invalid; Figure 3 As shown in (b), since there are two connected components H1 and H2, the graph constraint 2 is violated, and therefore the graph is invalid. Figure 3 In (c), when switch S1 is activated, E1 itself short-circuits, violating constraint 3-1 in Figure 3-1, and is therefore invalid; similarly... Figure 3 When switch S2 in (d) operates, the topology becomes invalid due to a short circuit between E1 and E2, violating constraint 3-2 of the diagram; furthermore... Figure 3 The topology in (f) satisfies all graph constraints, therefore it is valid;

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

[0062] In this embodiment, Figure 4 This is a schematic diagram violating constraint 4 in Figure 4. In this diagram, since the negative terminals of E1 and E2 are not adjacent, no matter how the components are operated, E1 and E2 cannot share a common ground. 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 obtain 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 This is a schematic diagram illustrating constraint 5 to reduce redundant devices. In this diagram, two switching devices connected in series can be simplified into one switching device, thereby reducing redundant devices;

[0067] (3) A valid bipartite graph is derived;

[0068] (3.1) Determine the number of DC ports based on the connection method of the DC source of the multi-port inverter; in addition, determine whether circuit nodes are needed based on the voltage stress requirements of the components; obtain the number of points in the even diagram based on the number of DC ports, AC ports and circuit nodes.

[0069] In this embodiment, as Figure 6 As shown in (a) to (b), there is a common point between the two DC sources, determining that the number of DC ports in the even-number diagram is three. There are no circuit nodes. Combining this with an AC port, the number of points in the even-number diagram is obtained, namely E1+, E2+, and E... 1 / 2 - and four points A;

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

[0071] Then, the degree of each vertex is determined using the handshake theorem in graph theory. The calculation formula is as follows:

[0072]

[0073] Among them, E s Let represent the total number of edges in the even graph, n represent the total number of vertices in the even graph, and D(i) represent the degree of each vertex. It is easy to see that the sum of the total degrees of the vertices in the even graph must be an even number. It should be noted that the mapping rule proposed in this invention ensures that the number of devices is the same as the number of edges in the even graph. Reducing redundant devices is 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 vertices in the even graph. Based on this, to reduce redundant devices in a multi-port inverter, it is only necessary to reduce the degree of the vertices in the even graph.

[0074] In this embodiment, Figure 6 The sum of the minimum degrees of the four vertices in (c) is 5, which violates the handshake theorem. Therefore, the degree of one of the vertices needs to be increased; finally, while satisfying the graph constraints, such as... Figure 6 As shown in (d), the degree of point A is increased by 1, so that the degree of point A increases to 3, and the total degree sum increases to 6;

[0075] (3.3) Based on steps (3.1) and (3.2), the following is obtained: Figure 6 The effective biplot shown in (e);

[0076] (4) Extend the dual graph;

[0077] (4.1) Under the condition of satisfying the graph constraints, without changing the structure of the even graph, only changing the labels of the points representing DC sources in the even graph, the isomorphic graph of the even graph is derived, and different kinds of topologies can be obtained without starting from scratch.

[0078] In this embodiment, as Figure 7 As shown, label E1+ and label E 1 / 2 By swapping the positions of -, we can obtain the isomorphic graph of the dipole graph. The dipole graph and the isomorphic graph correspond to different types of circuit topologies.

[0079] (4.2) Under the condition of satisfying the graph constraints, by adding points representing DC sources, the number of DC sources is expanded, and an extended graph of the even graph is obtained.

[0080] In the extended graph, if the added DC source has a common point with an 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 does not have a common point with an 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, under the condition that the graph constraints are satisfied, such as Figure 8 As shown in (a) to (b), when the extended DC source E3 is added to the existing dipole diagram, the negative terminal of E3 and the existing DC source E 1 / 2 - If connected together, the tag E3- will be merged into E 1 / 2 - Above, the label at that point becomes E. 1 / 2 / 3 Since E3's positive terminal and the existing DC source have no common point, under the condition of satisfying the graph constraints, add a point and add the label E3+ to obtain the following result: 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 dipole diagram to obtain the following topology: Figure 8 (c) shows a multi-source inverter topology with four DC sources, and its corresponding circuit topology is as follows: Figure 8 As shown in (d);

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

[0083] (5.1) Based on the mapping rules of the even graph, convert the even graph, isomorphic graph or extended graph into the topology graph of the 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-tuning the initial circuit topology: Replace the unidirectional components in the initial circuit topology that would 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.

[0086] In this embodiment, as Figure 9 As shown, the presence of diode D1 causes direct conduction between E2 and the AC port, resulting in uncontrollable E2. Therefore, this unidirectional component needs to be replaced with a bidirectional component to achieve an effective single-phase circuit topology; then, the single-phase circuit topology is expanded into a three-phase topology to obtain the final multi-port inverter topology, as shown. Figure 10 As shown.

[0087] In this embodiment, the above steps can yield the following result: Figure 11 The 10 multi-port inverter topologies with two DC sources are shown.

[0088] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A method for topology derivation of multi-port inverters based on dipole graphs, characterized in that, Includes the following steps: (1) Define mapping rules based on bipartite graphs; (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. (1.2) Different shapes are used to distinguish the points in the bipartite diagram: triangles are used to represent the points after the circuit nodes are mapped, squares are used to represent the points after the AC ports are mapped, and circles are used to represent the points after the DC power supply is mapped. (1.3) Set labels to distinguish points representing DC sources in the dipole diagram: Set label E a + / - indicates the positive or negative terminal of DC source a; set label E a / b Indicates DC power supply E a 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 terminal connection; (2) Based on the mapping rules of the bipartite graph, the circuit constraints of the multi-port inverter are converted into graph constraints; (3) The multi-port inverter topology is derived based on graph constraints; (4) Expand the obtained multi-port inverter topology; (4.1) Under the condition of satisfying the graph constraints, without changing the structure of the dual graph, only changing the labels of the points representing DC sources in the dual graph, a homogeneous graph of the dual graph is derived, thus obtaining different kinds of topologies; (4.2) Under the condition of satisfying the graph constraints, add points representing DC sources to expand the number of DC sources and obtain an extended graph of the bipartite graph; In the extended graph, if the added DC source has a common point with an 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 does not have a common point with an 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. (5) Convert the even diagram into a circuit diagram of a multi-port inverter.

2. The multi-port inverter topology derivation method based on dipole graphs according to claim 1, characterized in that, The method for converting the circuit constraints of the multi-port inverter into graph constraints in step (2) is as follows: (2.1) Define the basic circuit constraints of a multi-port inverter; (2.1.1) The AC port requires at least two power paths to connect to the positive and negative terminals of the DC source, respectively; (2.1.2) Multi-port inverters must not be open-circuited; (2.1.3) Multi-port inverters cannot be short-circuited, which is further divided into DC sources that cannot be short-circuited themselves and multiple DC sources that cannot be short-circuited with each other; (2.1.4) The negative terminal of the DC source should be grounded to avoid excessive common-mode voltage; (2.1.5) Two components connected in series are equivalent to one component; (2.2) Convert the circuit constraints of the multi-port inverter into graph constraints; (2.2.1) According to step (2.1.1), the AC port diagram constraint 1 is obtained: ； in This represents the minimum degree of AC port A. (2.2.2) According to step (2.1.2), the bipartite graph corresponding to the multi-port inverter is a connected graph, and graph constraint 2 is: ； in, The number of connected components in an even graph G; further, the minimum degree of a DC source: ； in Indicates the minimum degree of DC source E; (2.2.3) According to step (2.1.3), we obtain graph constraint 3: Based on the short-circuit condition of the DC source, constraint 3 in Figure 3 is divided into two types: Figure constraint 3-1: For 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: For multiple DC sources that cannot be short-circuited, if there is a common point in the connection of multiple DC sources, the positive poles of the DC sources cannot be adjacent in the even graph. (2.2.4) According to step (2.1.4), we obtain Figure constraint 4: If there is no common point in the connection of multiple DC sources, the negative pole nodes of the DC sources must be adjacent; (2.2.5) According to step (2.1.5), we obtain graph constraint 5: ； in, This represents the minimum degree of circuit node x.

3. The multi-port inverter topology derivation method based on dipole graphs according to claim 1, characterized in that, The method for deriving the multi-port inverter topology based on graph constraints in step (3) is as follows: (3.1) Determine the number of DC ports based on the connection method of the DC source of the multi-port inverter; in addition, determine whether circuit nodes are needed based on the voltage stress requirements of the components; obtain the number of points in the even diagram based on the number of DC ports, AC ports and circuit nodes. (3.2) Based on the minimum degree of each vertex in the bipartite graph, use the handshake theorem in graph theory to determine the degree of each vertex; (3.3) Based on steps (3.1) and (3.2), a bipartite graph that satisfies the graph constraints is derived.

4. The multi-port inverter topology derivation method based on dipole graphs according to claim 1, characterized in that, The method for converting the dipole diagram into a circuit diagram of a multi-port inverter in step (5) is as follows: (5.1) Based on the mapping rules of the even graph, convert the even graph, isomorphic graph and extended graph into the topology graph of the multi-port inverter; (5.2) 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. (5.3) Fine-tune the initial circuit topology: Replace the unidirectional components in the initial circuit topology that would 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-port inverter topology.

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