A Three-Dimensional Space Vector Modulation Method and System for Inverters

Abstract

The present invention discloses a three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation method and system. The method includes: analyzing and determining an equivalent switching model of the topology of the three-level three-phase four-wire four-leg inverter, and mapping the three-phase voltage corresponding vectors of the three-level three-phase four-wire four-leg inverter to the α-β-γ three-dimensional coordinate system; according to the distribution characteristics of all switching three-dimensional space vectors in the α-β-γ coordinate system, rotating or symmetrically mapping the vectors in each main region to the three-dimensional space corresponding to the first major sector on the plane; determining the vector synthesis method for each tetrahedral block, and for irregular tetrahedrons that do not conform to the vector sequence generation principle, using the vector replacement and virtual vector synthesis methods; according to the vector synthesis method, giving the block division method for the three-dimensional space corresponding to the first major sector, and the corresponding duty cycle calculation method. The present invention analyzes the equivalent switching model of the topology structure, and maps it to the three-dimensional space through α-β-γ coordinate transformation to determine the vector synthesis method for any tetrahedral block.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and particularly relates to a three-dimensional space vector modulation method for a three-level three-phase four-wire four-leg inverter with a two-level fourth leg. Background Art

[0002] Three-level inverters have advantages such as low switching losses and low output harmonics, and have been widely used in industrial production in the past few decades. A three-phase four-wire four-leg (3P4W4L) inverter can effectively handle unbalanced or nonlinear AC loads. In addition, compared with a three-phase three-wire (3P3W) inverter, the capacitors supporting the DC bus in a 3P4W inverter group are significantly reduced. The fourth leg of the inverter can have different configurations, and a two-level leg composed of two switching devices can reduce the power loss of the N phase, thus bringing cost benefits.

[0003] However, with the increase in the number of legs and related requirements, such as the reduction of switching losses and the reduction of THD, etc., the complexity of its modulation algorithm has also increased greatly. At present, the research on the modulation algorithm of this topological structure is limited.

[0004] From an implementation perspective, for a three-level three-phase four-leg inverter, there are mainly two current modulation schemes. One is to use the traditional three-level modulation method to process positive and negative sequence components, and use the fourth leg to process zero sequence components alone; the other is to use the three-dimensional space vector method, consider the zero sequence component, map the vector into the three-dimensional space for equivalent synthesis, so as to achieve tracking of a continuously rotating space vector.

[0005] The document K. Li, M. Wei, C. Xie, F. Deng, J. M. Guerrero, and J. C. Vasquez, “Triangle Carrier-Based DPWM for Three-Level NPC Inverters,” IEEE J. Emerge. Sel. Topics Power Electron., vol. 6, no. 4, pp. 1966–1978, Dec. 2018 introduced an implementation method of triangle carrier-based discontinuous pulse width modulation (TCB-DPWM) for three-level inverters. The results show that the proposed TCB-DPWM can effectively simplify the implementation of modulation, reduce switching losses, and improve system efficiency. However, this method is difficult to apply to the modulation of four-leg inverters.

[0006] The literature "Decoupled Modulation With Common-Mode Load-Voltage Control for Three-Phase Four-Leg Three-Level Inverter" by L. Zhang, H. Yang, Y. Tang, J. Pou, and L. M. Tolbert, IEEE Trans. Ind. Electron., vol. 69, no. 8, pp. 8594–8598, Aug. 2022 proposed a decoupled modulation method, in which the three-phase bridge arm modulation realizes VBC and closed-loop DM load voltage control, while the fourth leg is modulated separately to realize closed-loop CM load voltage control. The proposed method has been experimentally verified. However, this method ignores the change of the voltage vector introduced by the fourth bridge arm, introduces redundant voltage vectors during the modulation process, and increases the switching loss.

[0007] The literature "3D-SVPWM modulation strategy for four-leg three-level inverter" by Siyuan Ren, Xiao Zhu, and Hu Bo, Journal of Power Systems and Automation 31.10 (2019) proposed a 3P4L4W-3L inverter with the fourth bridge arm configured as three levels, decomposed the αβγ coordinates into two two-level structures for modulation. The proposed modulation strategy greatly simplifies the operation process and realizes the balance of the upper and lower capacitor voltages on the DC side. This method provides a reference for the present invention. However, this method cannot be completely equivalently applied to a three-level three-phase four-leg inverter with a two-level fourth bridge arm. Summary of the Invention

[0008] Based on the previous overmodulation scheme, the present invention aims to realize the operation target of a three-level three-phase four-wire four-leg inverter (3P4W4L-3L) with a two-level fourth bridge arm under unbalanced or nonlinear loads. Analyze the equivalent switching model of the topology structure, and map it to three-dimensional space through α-β-γ coordinate transformation to determine the vector synthesis method of any tetrahedral block.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a three-dimensional space vector modulation method for a three-level three-phase four-wire four-leg inverter, including:

[0011] Analyze and determine the equivalent switch model of the three-level three-phase four-wire four-leg inverter topology, and map the three-phase voltage corresponding vectors of the three-level three-phase four-wire four-leg inverter to the α-β-γ three-dimensional coordinate system;

[0012] According to the distribution characteristics of all switch three-dimensional space vectors in the α-β-γ coordinate system, rotate or symmetrically map the vectors in each main area to the three-dimensional space corresponding to the first large sector on the plane;

[0013] Determine the vector synthesis method for each tetrahedron block. For irregular tetrahedrons that do not conform to the vector sequence generation principle, use the vector replacement and virtual vector synthesis methods;

[0014] According to the vector synthesis method, give the block division method for the three-dimensional space corresponding to the first large sector, and the corresponding duty cycle calculation method.

[0015] As a further improvement of the present invention, the three-level three-phase four-wire four-leg inverter is a 3P4L4W 3L T-type inverter.

[0016] As a further improvement of the present invention, the mapping of the three-phase voltage corresponding vectors of the three-level three-phase four-wire four-leg inverter to the α-β-γ three-dimensional coordinate system includes:

[0017] Each phase of the ABC three-phase bridge arm of the three-level three-phase four-wire four-leg inverter has three switching devices, and each switching device has two working states of on and off, which are combined into three different output states, defined as the switching function S j ={1, 0, -1}, j = {a, b, c}, corresponding to the symbols 'p', 'o', 'n'; the switching function S of the fourth leg n has two possible values {1, -1}, corresponding to the symbols 'p', 'n'; the three-phase output voltages v an 、v bn 、v cn are given by the following formula:

[0018]

[0019] where the switching function S of the ABC three phases with respect to the n point jn is defined by the following formula:

[0020]

[0021] The transformation from the abc coordinate system to the α-β-γ coordinate system is obtained by the following equation transformation

[0022]

[0023] In the formula, v α 、vβ , v γ are the corresponding coordinates of the α-axis, β-axis, and γ-axis respectively.

[0024] As a further improvement of the present invention, according to the distribution characteristics of all switch three-dimensional space vectors in the α-β-γ coordinate system, rotating or symmetrically mapping the vectors in each main region to the three-dimensional space corresponding to the first large sector on the plane includes:

[0025] For different switch states, calculate all switch states and their corresponding voltage vectors.

[0026] Plotting the voltage vectors on the α-β-γ coordinate system obtains the switch vector distribution diagram; obtaining the output distribution of all switch vectors in the three-dimensional α-β-γ coordinate system and their corresponding feasible regions;

[0027] The projection of the switch state corresponding to each specific vector on the α-β plane, where each main region is divided into 4 smaller sectors;

[0028] Showing the symmetric switch vector distribution of the feasible regions corresponding to adjacent main regions in the three-dimensional space, directly rotating to the position corresponding to the first sector for modulation calculation.

[0029] As a further improvement of the present invention, for the feasible regions showing a symmetric switch vector distribution, after rotating to the position corresponding to the first sector, the rotated α-β coordinates need to be symmetrically transformed with respect to the equation and then further modulation calculation is performed.

[0030] As a further improvement of the present invention, determining the vector synthesis method for each tetrahedron block, and proposing a vector replacement and virtual vector synthesis method for irregular tetrahedrons that do not conform to the vector sequence generation principle; including:

[0031] In the first main region, it is divided into upper, middle, and lower three regions by two yellow-filled planes. In the upper region, the switch vector Sn is always 'n', and in the lower region, the switch vector Sn is always 'p'; in these two regions, the state of the fourth bridge arm remains unchanged; for the target reference vectors in these two regions:

[0032] Based on the α-β projection, determine which one of the four small triangular regions it belongs to;

[0033] Based on the α-β-γ coordinates, find the smallest tetrahedron block containing the vector and use the four vectors at its vertices for synthesis;

[0034] Directly determine which tetrahedron block a vector belongs to by judging the a-b-c coordinates. After determining that it belongs to the small triangular region of the α-β projection, according to 1 < van <2,1<v bn <2,1<v cn <2 Determine its spatial position;

[0035] For the central region, which involves the switching action of the fourth bridge arm Sn, due to the insufficient number of switching vectors, the plane set v cannot be used jn =-2,-1,...,2, j={a,b,c} divides it into the aforementioned smallest tetrahedrons.

[0036] As a further improvement of the present invention, for the irregular tetrahedrons that do not conform to the vector sequence generation principle, a vector replacement and virtual vector synthesis method is adopted, including:

[0037] Adopt the vector replacement method, in which another vector with the same α-β coordinates but different γ coordinates is used to replace one of the vectors, ensuring that the newly constructed tetrahedron block contains the original block.

[0038] Adopt the virtual vector synthesis method, in which two vectors satisfying a specific duty cycle relationship are used to synthesize the vertex vector of the original tetrahedron that does not satisfy the vector generation principle.

[0039] As a further improvement of the present invention, according to the vector synthesis method, the block division method of the three-dimensional space corresponding to the first large sector and the corresponding duty cycle calculation method are given, including:

[0040] For the block modulated by 4 vectors, that is, SVM 7 modulation:

[0041] v0 - v1 - v2 - v3 - v2 - v1 - v0(4)

[0042] The action time or duty cycle of each vector satisfies the equation:

[0043]

[0044] For the special case corresponding to the first small triangular region, that is, SVM 9 modulation:

[0045] v0 - v1 - v2 - v3 - v4 - v3 - v2 - v1 - v0(6)

[0046] Among them, 5 vectors are used for modulation, and the action time or duty cycle of each vector satisfies the equation:

[0047]

[0048] Among them, v nm , n={0,1,2,3,4}, m={α,β,γ}, represents the coordinate value of the vector v n projected on the axis m.

[0049] In a second aspect, the present invention provides a three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation system, including:

[0050] A first mapping module, configured to analyze and determine an equivalent switching model of the topology of the three-level three-phase four-wire four-leg inverter, and map the three-phase voltage corresponding vectors of the three-level three-phase four-wire four-leg inverter to the α-β-γ three-dimensional coordinate system;

[0051] A second mapping module, configured to rotate or symmetrically map the vectors in each main region to the three-dimensional space corresponding to the first large sector on the plane according to the distribution characteristics of all the switching three-dimensional space vectors in the α-β-γ coordinate system;

[0052] A vector synthesis module, which determines the vector synthesis method for each tetrahedral block, and for irregular tetrahedrons that do not conform to the vector sequence generation principle, adopts vector replacement and virtual vector synthesis methods;

[0053] A division calculation module, which gives the block division method of the three-dimensional space corresponding to the first large sector and the corresponding duty ratio calculation method according to the vector synthesis method.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The steps of determining the equivalent switching model, three-dimensional coordinate system mapping, block division, and duty ratio calculation of the topology of the three-level three-phase four-wire four-leg inverter in the present invention are of great significance for improving the performance of the inverter and optimizing the quality of the output voltage and current. This method demonstrates the comprehensive application of power electronics, control theory, and mathematical tools in the design and analysis of power electronic systems. Description of the Drawings

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0057] Figure 1 It is the topology structure diagram of the 3P4L4W 3L T-type inverter adopted by the present invention.

[0058] Figure 2 It is the equivalent switching model diagram of the 3P4L4W 3L T-type inverter adopted by the present invention.

[0059] Figure 3It is the three-dimensional space switching vector distribution characteristic diagram adopted for the analysis of the present invention. Among them, Fig. (a) is a schematic diagram of the feasible region, Fig. (b) is a vector correspondence diagram, and Fig. (c) is a vector projection diagram on the α-β plane.

[0060] Figure 4 It is a schematic diagram of the spatial region division corresponding to the first major sector adopted for the analysis of the present invention. Among them, Fig. (a) is a three-division diagram of upper, middle, and lower parts, Fig. (b) is a division diagram on the v an plane, Fig. (c) is a division diagram on the v bn plane, and Fig. (d) is a division diagram on the v cn plane.

[0061] Figure 5 It is an example diagram of the smallest tetrahedron block adopted for the analysis of the present invention.

[0062] Figure 6 It is a schematic diagram of the vector synthesis of the first small triangular area adopted for the analysis of the present invention. Among them, Fig. (a) is a vector substitution scheme, and Fig. (b) is a virtual vector scheme.

[0063] Figure 7 It is a schematic diagram of the vector synthesis of the second small triangular area adopted for the analysis of the present invention.

[0064] Figure 8 It is a schematic diagram of the vector synthesis of the third small triangular area adopted for the analysis of the present invention.

[0065] Figure 9 It is a schematic diagram of the vector synthesis of the fourth small triangular area adopted for the analysis of the present invention.

[0066] Figure 10 It is a flow chart of the 3D-SVPWM modulation technology algorithm adopted by the present invention.

[0067] Figure 11 It is a simulation result diagram verified by the present invention under operating conditions 1&2. Among them, Fig. (a) is a schematic diagram of the power supply side output level and the filtered load side voltage, and Fig. (b) is the reference and modulation output vector trajectories.

[0068] Figure 12 It is a simulation result diagram verified by the present invention under operating conditions 3&4. Among them, Fig. (a) is a schematic diagram of the power supply side output level and the filtered load side voltage, and Fig. (b) is the reference and modulation output vector trajectories.

[0069] Figure 13 It is a simulation result diagram verified by the present invention under operating conditions 5&6. Among them, Fig. (a) is a schematic diagram of the power supply side output level and the filtered load side voltage, and Fig. (b) is the reference and modulation output vector trajectories. Detailed implementation manners

[0070] To make the objectives and technical solutions of the present invention clearer and easier to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0071] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order different from those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0072] Based on the previous overmodulation scheme, the present invention aims to achieve the operation objectives of a three-level three-phase four-wire four-leg inverter (3P4W4L-3L) with a two-level fourth leg under unbalanced or nonlinear loads. The equivalent switching model of the topology is analyzed, and it is mapped into a three-dimensional space through α-β-γ coordinate transformation to determine the vector synthesis method for any tetrahedral block. The present invention is applicable to fields such as motor drive, new energy power generation, and rail transit.

[0073] First, analyze and determine the equivalent switching model of the topology, and map the corresponding vectors of the three-phase voltages into the α-β-γ three-dimensional coordinate system. According to the distribution characteristics of all the switching three-dimensional space vectors in the α-β-γ coordinate system, the vectors in each main region are rotationally or symmetrically mapped to the three-dimensional space corresponding to the first major sector on the plane.

[0074] Determine the vector synthesis method for each tetrahedral block. For irregular tetrahedrons that do not conform to the vector sequence generation principle, two methods, namely vector replacement and virtual vector synthesis, are proposed.

[0075] According to the vector synthesis method in the previous step, propose the block division method for the three-dimensional space corresponding to the first major sector and the corresponding duty cycle calculation method.

[0076] The equivalent switching model proposed by the present invention is a key step in simplifying the complex behavior of the inverter. For a three-level three-phase four-wire four-leg inverter, each leg can be regarded as an independent switching unit, and each unit can generate three levels (positive, zero, negative). By controlling the states of these switching units, precise control of the output voltage and current can be achieved. The complexity of the inverter is reduced through the equivalent switching model, making the analysis and design more intuitive and convenient.

[0077] By independently controlling each switching unit, precise control of the output voltage and current can be achieved, improving the performance of the system.

[0078] Mapping the three-phase voltage corresponding vectors into the α-β-γ three-dimensional coordinate system can facilitate the understanding and analysis of the inverter's behavior. In this coordinate system, each phase voltage can be represented as a three-dimensional vector. The three-dimensional coordinate system provides an intuitive understanding of the inverter's behavior, which is helpful for analysis and design. In the three-dimensional coordinate system, vector operations can be used to simplify the calculation process and improve the calculation efficiency.

[0079] In the α-β-γ coordinate system, according to the distribution characteristics of all the switching three-dimensional space vectors, the vectors in each main region are rotated or symmetrically mapped to the three-dimensional space corresponding to the first major sector on the plane. Then, the vector synthesis method for each tetrahedral block is determined. For irregular tetrahedrons that do not conform to the vector sequence generation principle, vector replacement and virtual vector synthesis methods are adopted.

[0080] Through reasonable block division and vector synthesis methods, the performance of the inverter can be optimized, and the quality of the output voltage and current can be improved. The vector replacement and virtual vector synthesis methods can reduce unnecessary switching operations, reduce switching losses, and improve the efficiency of the inverter.

[0081] Optionally, according to the vector synthesis method, determine the block division method for the three-dimensional space corresponding to the first major sector, and calculate the corresponding duty cycle. The duty cycle is a key parameter for controlling the output voltage and current of the inverter. By adjusting the duty cycle, precise control of the output voltage and current can be achieved.

[0082] By precisely calculating the duty cycle, precise control of the output voltage and current can be achieved, improving the performance of the system. The duty cycle can be adjusted as needed to adapt to different application scenarios and requirements.

[0083] The mapping method based on the switching three-dimensional space vector characteristics proposed by the present invention maps the space vector, rotates or symmetrically maps it to the corresponding space in the first large sector, simplifying the calculation. The vector synthesis method of the tetrahedron block proposed by the present invention ensures that one of the four bridge arms is clamped within one switching period under specific working conditions, thereby reducing the switching loss. The block division and judgment method in the three-dimensional space proposed by the present invention does not require complex calculations in the α-β-γ coordinate system, and can judge the block position by analyzing the a-b-c coordinates, simplifying the judgment calculation.

[0084] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0085] 1. Three-dimensional space vector feature analysis

[0086] The topological structure of the 3P4L4W 3L T-type inverter studied in the present invention is as Figure 1 shown. To construct an equivalent switch model of the circuit, as Figure 2 shown, the output states of the three-phase bridge arms are represented as Sa, Sb, and Sc.

[0087] Each phase of the three-phase bridge arm has three switching devices, and each switching device has two working states of on and off, combined into three different output states {1, 0, -1}, corresponding to the symbols 'p', 'o', 'n'. The connection of the fourth bridge arm Sn has two possible values {1, -1}, corresponding to the symbols 'p', 'n'. Therefore, the three-phase output voltages v an 、v bn 、v cn are given by the following formula:

[0088]

[0089] where the value of S jn is given by the following formula:

[0090]

[0091] The transformation from the abc coordinate system to the α-β-γ coordinate system can be obtained by the following equation transformation

[0092]

[0093] For this inverter topology, there are a total of 2×3 3 , that is, 54 different switching states. The calculation results of all switching states and their corresponding voltage vectors are shown in Table 1.

[0094] Table 1 Three-dimensional space vector table

[0095]

[0096]

[0097] Plotting the vectors in Table 1 on the Α - Β - Γ coordinate system yields the switching vector distribution diagram, as Figure 3 shown. Figure 3 (A) shows the output distribution of all switching vectors in the three - dimensional Α - Β - Γ coordinate system and their corresponding feasible regions. Figure 3 (B) provides the switching states corresponding to each specific vector.

[0098] The projection of this feasible region on the Α - Β plane is as Figure 3 (C) shown, where each main region can be further divided into 4 smaller sectors.

[0099] It can be observed that in three - dimensional space, the feasible regions corresponding to adjacent main regions exhibit symmetric switching vector distributions. Therefore, for the vectors in the main regions labeled I, III, V, they can be directly rotated to the position corresponding to the first sector for modulation calculation. However, for the vectors in the main regions labeled II, IV, VI, after rotating them to the position corresponding to the first sector, the rotated α - β coordinates need to be symmetrically transformed with respect to the equation before further modulation calculation.

[0100] 2. Three - dimensional space division and reference vector synthesis

[0101] In the first main region, as Figure 4 (a) shown, it is divided into upper, middle, and lower three regions by two yellow - filled planes. In the upper region, the switching vector Sn is always 'n', and in the lower region, the switching vector Sn is always 'p'. Therefore, in these two regions, the state of the fourth bridge arm remains unchanged. Thus, for the target reference vectors in these two regions, first, based on the α - β projection, determine which of the four small triangular regions in Figure 3 (c) it belongs to. Then, based on the α - β - γ coordinates, find the smallest tetrahedron block that contains the vector and use the four vectors at its vertices to synthesize it. In fact, the tetrahedron block can be divided by the plane set v jn =-2,-1,...,2, j = {a,b,c}, as Figure 4 (b)(c)(d) shown.

[0102] Therefore, it is possible to directly determine which tetrahedron block a vector belongs to by judging the a - b - c coordinates, as Figure 5 shown. For the block marked in red, after determining that it belongs to the small triangular region 1 of the α - β projection, it can be directly based on 1 < v an <2, 1 < v bn <2, 1 < vcn <2 Determine its spatial position.

[0103] For the central region, involving the switching action of the fourth bridge arm Sn, due to insufficient switching vectors, the plane set v cannot be used. jn = -2, -1,..., 2, j = {a, b, c} divides it into the aforementioned smallest tetrahedrons. For irregular tetrahedrons, their four vertex vectors do not necessarily conform to the principle of vector sequence generation, which means that in each conversion, only one bridge arm should act and it should only change the state of one level. There are two solutions:

[0104] Solution 1 is vector replacement, where another vector with the same α-β coordinates but different γ coordinates is used to replace one of the vectors, ensuring that the newly constructed tetrahedron block contains the original block.

[0105] Solution 2 is virtual vector synthesis, where two vectors satisfying specific duty ratio relationships are used to synthesize the vertex vectors of the original tetrahedron that do not satisfy the vector generation principle.

[0106] These solutions are discussed separately for each small triangular region. For small triangular region 1, as Figure 6 (a) shows, Sol.1 causes multiple bridge arms to change their switching states simultaneously when the reference vector is converted in these two intervals, resulting in problems such as increased harmonics. Therefore, Solution 2 is selected, as Figure 6 (b) shows, where vectors V28 - ooon and V1 - ooop are used to synthesize the virtual vector V27(41)(000). By ensuring the equivalent action time of V28 - ooon and V1 - ooop, modulation can generate the vector corresponding to this block. For small triangular regions 2, 3, and 4, as Figure 7 、 8 、9 show, the corresponding regions are divided into three tetrahedron blocks by two planes. If the blocks obtained by division do not meet the conditions for generating the modulation vector sequence, Solution 2 can be used. This solution causes one bridge arm to keep its switching state unchanged within one switching period, thus reducing the switching loss. In region 2, the plane V19 - 29 - 47 and V19 - 20 - 29 are used to divide the block into three regular tetrahedrons. The block containing vectors V29 - oonn, V47 - ponn, V20 - ponp, and V19 - poop meets the switching conditions. However, for the block containing vectors V19, V29, V47, and V32 - onnn, the switching conditions cannot be met. If vector V46 - poon is used to replace V32, then vectors V19 - poop and V46 - poon can meet the switching conditions.

[0107] In region 3, the block is divided into three regular tetrahedrons using planes V32-47-50 and V19-20-50. The blocks containing vectors V19-poop, V32-onnn, V47-ponn, and V50-pnnn do not meet the switching conditions.

[0108] Using the method described above, V46-poon can replace V32-onnn to meet the switching conditions with V19-.

[0109] In region 4, the block is divided into three regular tetrahedrons using planes V26-29-47 and V20-26-29. The blocks containing vectors V20-ponp, V25-ppop, V26-ppnp, and V29-oonn do not meet the switching conditions. Using the method described above, V2-oonp can replace V25-ppop to meet the switching conditions with V29-oonn, forming a new tetrahedron containing the original block.

[0110] Therefore, for the space corresponding to the first major sector, the vector switching sequence and its region division basis are shown in Table 2.

[0111] Table 2 Vector sequence and region division basis table for the space corresponding to the first major sector

[0112]

[0113] For the block modulated by 4 vectors, i.e., SVM 7 modulation:

[0114] v0-v1-v2-v3-v2-v1-v0(4)

[0115] The action time or duty cycle of each vector satisfies the equation:

[0116]

[0117] For the special case corresponding to the first small triangle region, i.e., SVM 9 modulation:

[0118] v0-v1-v2-v3-v4-v3-v2-v1-v0(6)

[0119] Among them, 5 vectors are used for modulation, and the action time or duty cycle of each vector satisfies the equation:

[0120]

[0121] Among them, v nm , n = {0, 1, 2, 3, 4}, m = {α, β, γ}, representing the coordinate value of the projection of vector v n on axis m.

[0122] The flowchart of the 3D SVPWM modulation technology for the 3P4L4W 3L T-type inverter studied in this invention is as Figure 10 shown.

[0123] An open-loop simulation system was built using Simulink for testing. The detailed simulation parameters are given in Table 3, and six simulation conditions are listed in Table 4.

[0124] Table 3 Simulation Parameters

[0125]

[0126] Table 4 Simulation Conditions

[0127]

[0128] Figures 11 - 13 (a) shows the phase voltage at the power supply end and the phase voltage at the load end, while Figures 11 - 13 (b) shows the vector trajectory in three-dimensional space. The red trajectory represents the expected path, the green trajectory represents the trajectory of modulation tracking, and the area surrounded by the blue dotted line represents the area passed through. It can be seen from the simulation results that this modulation scheme effectively tracks the desired reference vector trajectory. Within a certain time range, Figure 11 and Figure 12 Case 2-4 in show that under significant modulation conditions, the output voltage at the power supply end can be clamped. Figure 13 It shows that under the condition of significant imbalance of the zero-sequence component, the midpoint voltage of the fourth bridge arm is clamped. Therefore, under specific working conditions, this modulation method ensures that one of the four bridge arms remains inactive within one switching cycle, achieving the goal of reducing switching losses.

[0129] This invention also provides a three-level three-phase four-wire four-bridge-arm inverter three-dimensional space vector modulation system, including:

[0130] A first mapping module, used to analyze and determine the equivalent switching model of the three-level three-phase four-wire four-bridge-arm inverter topology, and map the three-phase voltage corresponding vectors of the three-level three-phase four-wire four-bridge-arm inverter to the α-β-γ three-dimensional coordinate system;

[0131] A second mapping module, used to rotate or symmetrically map the vectors in each main area to the three-dimensional space corresponding to the first large sector on the plane according to the distribution characteristics of all switch three-dimensional space vectors in the α-β-γ coordinate system;

[0132] A vector synthesis module, which determines the vector synthesis method for each tetrahedral block, and uses the vector replacement and virtual vector synthesis methods for irregular tetrahedrons that do not conform to the vector sequence generation principle;

[0133] A partitioning calculation module, according to the vector synthesis method, gives the partitioning method of the three-dimensional space corresponding to the first major sector and the corresponding duty cycle calculation method.

[0134] The third aspect of the present invention is to provide an electronic device, which is characterized by including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the adaptive virtual impedance current limiting method applicable to a network-forming converter are implemented.

[0135] The fourth aspect of the present invention is to provide a computer-readable storage medium, which is characterized in that the computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the steps of the adaptive virtual impedance current limiting method applicable to a network-forming converter are implemented.

[0136] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0137] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the functions specified in Figure One one process or multiple processes and / or blocks Figure One one block or multiple blocks.

[0138] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device implements the functions specified in Figure One one process or multiple processes and / or blocks Figure One one block or multiple blocks.

[0139] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions for implementing the steps specified in one process or a plurality of processes and / or boxes Figure One one process or a plurality of processes and / or boxes Figure One steps for the functions specified in one box or a plurality of boxes.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation method, characterized in that, Including: Analyze and determine the equivalent switch model of the three-level three-phase four-wire four-leg inverter topology, and map the three-phase voltage corresponding vectors of the three-level three-phase four-wire four-leg inverter to the α-β-γ three-dimensional coordinate system; According to the distribution characteristics of all switch three-dimensional space vectors in the α-β-γ coordinate system, rotate or symmetrically map the vectors in each main area to the three-dimensional space corresponding to the first major sector on the plane; Determine the vector synthesis method for each tetrahedron block. For irregular tetrahedrons that do not conform to the vector sequence generation principle, use vector replacement and virtual vector synthesis methods; According to the vector synthesis method, give the block division method of the three-dimensional space corresponding to the first major sector and the corresponding duty cycle calculation method; The method of using vector replacement and virtual vector synthesis for irregular tetrahedrons that do not conform to the vector sequence generation principle includes: Adopt the vector replacement method, in which another vector with the same α-β coordinates but different γ coordinates is used to replace one of the vectors to ensure that the newly constructed tetrahedron block contains the original block; Adopt the virtual vector synthesis method, in which two vectors satisfying a specific duty cycle relationship are used to synthesize the vertex vector of the original tetrahedron that does not satisfy the vector generation principle; The method of giving the block division method of the three-dimensional space corresponding to the first major sector and the corresponding duty cycle calculation method according to the vector synthesis method includes: For the block modulated by 4 vectors, i.e., SVM 7 modulation: (4) The action time or duty cycle of each vector satisfies the equation: (5) For the special case corresponding to the first small triangle area, i.e., SVM 9 modulation: (6) Where 5 vectors are used for modulation, and the action time or duty cycle of each vector satisfies the equation: (7) Among them, v nm , n = {0, 1, 2, 3, 4}, m = {α, β, γ}, representing the vector v n The coordinate value of the projection on the axis m.

2. A three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation method according to claim 1, characterized in that The three-level three-phase four-wire four-leg inverter is a 3P4L4W 3L T-type inverter.

3. A three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation method according to claim 1, characterized in that The mapping of the three-phase voltage corresponding vectors of the three-level three-phase four-wire four-leg inverter to the α-β-γ three-dimensional coordinate system includes: Each of the three-phase arms of the three-level three-phase four-wire four-leg inverter has three switching devices, and each switching device has two operating states: on and off. These states combine to form three different output states, which are defined as switching functions. S j ={1, 0, -1}, j = {a, b, c}, corresponding to the symbols 'p', 'o', 'n'; the switching function of the fourth leg S n has two possible values {1, -1}, corresponding to the symbols 'p', 'n'; the three-phase output voltages v an 、 v bn 、 v cn are given by the following formula: (1) Among them, the switching functions of the three phases A, B, and C with respect to point n S jn are defined by the following formula: (2) The transformation from the abc coordinate system to the α-β-γ coordinate system is obtained by the following equation transformation (3) In the formula, v α , v β , v γ are the corresponding coordinates of the α-axis, β-axis, and γ-axis respectively.

4. A three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation method according to claim 1, characterized in that The method of rotating or symmetrically mapping the vectors in each main area to the three-dimensional space corresponding to the first major sector on the plane according to the distribution characteristics of all switch three-dimensional space vectors in the α-β-γ coordinate system includes: For different switch states, calculate all switch states and their corresponding voltage vectors; Plotting the voltage vectors on the α-β-γ coordinate system gives the switch vector distribution diagram; obtaining the output distribution of all switch vectors in the three-dimensional α-β-γ coordinate system and their corresponding feasible regions; The projection of the switch state corresponding to each specific vector on the α-β plane, where each main area is divided into 4 smaller sectors; Show the symmetric switch vector distribution of the feasible regions corresponding to adjacent main areas in the three-dimensional space, and directly rotate them to the position corresponding to the first sector for modulation calculation.

5. A three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation method according to claim 4, characterized in that The feasible region exhibits a symmetric switching vector distribution. After rotating to the position corresponding to the first sector, the rotated α-β coordinates need to be symmetrically transformed with respect to the equation and then further modulation calculations are performed.

6. A three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation method according to claim 1, characterized in that The method of determining the vector synthesis method for each tetrahedron block includes: In the first main region, it is divided into upper, middle, and lower regions by two filling planes; in the upper region, the switching vector Sn is always 'n', while in the lower region, the switching vector Sn is always 'p'; in these two regions, the state of the fourth bridge arm remains unchanged; for the target reference vectors in these two regions: Based on the α-β projection, determine which of the four small triangular regions it belongs to; Based on the α-β-γ coordinates, find the smallest tetrahedron block that contains this vector and use the four vectors of its vertices for synthesis; Directly determine which tetrahedron block a vector belongs to by judging the a-b-c coordinates. After determining that it belongs to the small triangular region of the α-β projection, judge its spatial position according to 1 < v an <2, 1 < v bn <2, 1 < v cn <2 For the central region, regarding the switching operation of the fourth bridge arm Sn, due to the insufficient number of switching vectors, the plane set cannot be used. v jn i = -2, -1,..., 2, j = {a, b, c}, and it is divided into the aforementioned minimum tetrahedrons.

7. A three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation system, based on the three-level three-phase four-wire four-leg inverter three-dimensional space vector modulation method according to any one of claims 1 to 6, characterized in that Including: The first mapping module is used to analyze and determine the equivalent switching model of the three-level three-phase four-wire four-bridge-arm inverter topology, and map the three-phase voltage corresponding vectors of the three-level three-phase four-wire four-bridge-arm inverter to the α-β-γ three-dimensional coordinate system; The second mapping module is used to rotate or symmetrically map the vectors in each main region to the three-dimensional space corresponding to the first large sector on the plane according to the distribution characteristics of all switching three-dimensional space vectors in the α-β-γ coordinate system; The vector synthesis module determines the vector synthesis method for each tetrahedron block, and for irregular tetrahedrons that do not conform to the vector sequence generation principle, uses the vector replacement and virtual vector synthesis methods; The division calculation module gives the block division method of the three-dimensional space corresponding to the first large sector and the corresponding duty ratio calculation method according to the vector synthesis method.

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