Topology Structure of Voltage-Source Multilevel Converter and Its Control Method

Abstract

The present invention relates to the technical field of power electronics and electrical energy conversion, and provides a topology structure of a voltage source multi-level converter and a control method thereof. It includes two sets of half-bridge circuits, two sets of flying capacitors, and a plurality of switches. Each set of half-bridge circuits has two DC connection terminals, and one switch is connected to the output of each of the two sets of half-bridge circuits, and two sets of flying capacitors connected in series are connected. The connection midpoint of the two sets of flying capacitors is connected to the AC terminal through two switches connected in reverse series, and the positive and negative poles of the entire two sets of flying capacitors connected in series are respectively connected to the AC terminal through switches. It has advantages such as a simple structure, easy control, low switch voltage stress, and small output harmonics.

Description

Technical Field

[0001] (Cross - reference to related applications) This invention claims the priority of a Chinese patent application with the application number 202310736660.5 and the invention title "Topology Structure of Voltage - Source Multi - Level Converter and Its Control Method", which was filed with the Chinese Patent Office on June 20, 2023, and all of its content is incorporated into this invention by reference.

[0002] This invention relates to the technical field of power electronics and electrical energy conversion, and particularly to the topology structure of a voltage - source multi - level converter and its control method.

Background Art

[0003] The description of this part only provides the background art related to this invention and does not necessarily constitute the prior art.

[0004] Power electronic converters can achieve flexible power conversion and active control of voltage, current, and power, so they are widely applied. The multi - level topology can reduce the voltage withstand requirements of internal power semiconductor devices through the design of the topology structure, and has advantages such as few output harmonics, low voltage change rate, and low common - mode voltage. Therefore, it is widely applied to medium - high voltage and large - power converters.

[0005] However, the topology structures of multilevel converters with a large number of output levels often have complex structures. Topology structures with modular characteristics such as cascade multilevel topology or modular multilevel topology rely on passive components such as transformers and capacitors, so they are often costly and large in volume. Practical non-modular topology structures are usually as follows. Concise topologies such as 3-level neutral point clamped topology and 5-level active neutral point clamped topology have a low number of output levels, mainly 3 levels and 5 levels. Topologies with a concise structure and a large number of output levels such as hybrid 7-level topology tend to have a narrow operating range and are difficult to operate with a wide power factor and a wide modulation depth.

[0006] Therefore, current topologies generally have difficulty in achieving a good balance among the number of output levels, the conciseness of the structure, and the operating range. There is an urgent need to propose a topology structure with more than five levels, a concise structure, and a wide operating range.

Summary of the Invention

[0007] In order to solve the deficiencies of the prior art, the present invention provides a topology structure of a voltage source type multilevel converter and its control method, which has a concise structure, simple control, and can be widely applied to the application scenarios of medium and low voltage AC-DC conversion.

[0008] To achieve the above object, the present invention adopts the following technical solutions.

[0009] In a first aspect, the present invention provides a topology structure of a voltage source type multilevel converter.

[0010] It includes two sets of half-bridge circuits, two sets of flying capacitors, and a plurality of switches. Each set of half-bridge circuits has two DC connection terminals, and two sets of serially connected flying capacitors are connected to the output of each of the two sets of half-bridge circuits through one switch. The midpoint of connection of two sets of flying capacitors is connected to the AC terminal via two switches connected in inverse series, and the positive and negative electrodes of the two sets of flying capacitors connected in series are respectively connected to the AC terminal via switches. This is the topology structure of a voltage source type multilevel converter.

[0011] Furthermore, a full-bridge inverter unit is not cascade-connected to the AC terminal.

[0012] Furthermore, one or more full-bridge inverter units are cascade-connected to the AC terminal.

[0013] Furthermore, when n full-bridge inverter units are cascade-connected to the AC terminal, (6 * 2 n + 1) levels are generated.

[0014] Furthermore, a single DC power supply and a three-divided DC capacitor are connected to the DC connection terminal.

[0015] Furthermore, three DC link capacitors are connected to four DC connection terminals, and after the entire DC link capacitors are connected in series, they are connected to the DC power supply.

[0016] Furthermore, a plurality of DC power supplies are connected to the DC connection terminal.

[0017] In a second aspect, the present invention provides a voltage source type multilevel converter that uses the topology structure of the voltage source type multilevel converter described in the first aspect as a single-phase bridge arm.

[0018] Furthermore, different bridge arms share the DC side.

[0019] In a third aspect, the present invention Provided is a control method for a topology structure of a voltage source type multilevel converter according to the first aspect, including a step of driving each switch to execute respective switching states, generating different current paths from a DC terminal to an AC terminal, and setting the voltage of the AC terminal to different levels.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows.

[0021] 1. In the topology structure of the voltage source type multilevel converter described in the present invention, each phase bridge arm consists of a switching tube and a flying capacitor. There are four connection terminals on the DC side, and three DC link capacitors are connected. The entire DC link capacitor may be connected to a DC power supply after being connected in series, or three independent DC power supplies may be connected. According to the application requirements, single-phase, three-phase, and multi-phase AC-DC converters can be constituted by half-bridges, full-bridges, three-phase bridges, and even more bridge arms. Therefore, the converter has advantages such as a simple structure, easy control, low switch voltage stress inherent in the multilevel converter, and small output harmonics.

[0022] 2. The topology structure of the voltage source type multilevel converter described in the present invention can be widely applied to the application scenarios of medium and low voltage AC-DC conversion.

[0023] The drawings in the specification constituting a part of the present invention are for providing a further understanding of the present invention. The exemplary embodiments and their descriptions of the present invention are for interpreting the present invention and are not intended to limit the present invention inappropriately.

Brief Description of the Drawings

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[0025] Hereinafter, the present invention will be further described with reference to the drawings and embodiments.

[0026] It should be noted that all of the following detailed descriptions are illustrative and are for further explaining the present invention. Unless otherwise specified, all technical terms and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art.

[0027] It should be noted that the terms used in this specification are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. When used in this specification, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. Also, when the terms "comprising" and / or "including" are used in this specification, it should be understood that the presence of features, steps, operations, devices, assemblies and / or combinations thereof is indicated.

[0028] In the present invention, the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "side", "bottom", etc. is based on the orientation or positional relationship shown in the drawings, and is merely a relational term defined for the purpose of facilitating the description of the relationship between each member or element structure of the present invention. It does not specifically refer to any member or element in the present invention and should not be understood as limiting the present invention.

[0029] In the present invention, terms such as "fixed connection", "connection", and "coupling" should be understood in a broad sense, indicating that they may be fixedly connected, integrally connected, removably connected, directly connected, or indirectly connected through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to specific situations and should not be understood as limiting the present invention.

[0030] Unless there is a contradiction, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0031] Embodiment 1 Embodiment 1 of the present invention provides a topology structure of a voltage-source multi-level converter.

[0032] The topology structure of the voltage-source multi-level converter provided in this embodiment can be widely applied to the application scenarios of medium and low voltage AC-DC conversion.

[0033] In the topology structure of the voltage-source multilevel converter provided in this embodiment, each phase's bridge arm consists of a switching tube and a flying capacitor. There are four connection terminals on the DC side, and three DC link capacitors are connected. The entire DC link capacitors may be connected in series and then connected to the DC power supply, or three independent DC power supplies may be connected. According to the application requirements, single-phase, three-phase, and multi-phase AC-DC converters can be constructed by half-bridge, full-bridge, three-phase bridge, and even more bridge arms. The converter has advantages such as a simple structure, easy control, low switch voltage stress, and small output harmonics. The present invention can be widely applied to the application scenarios of medium and low voltage AC-DC conversion.

[0034] The topology structure of the voltage-source multilevel converter provided in this embodiment includes a T-type structure and a multilevel circuit with three-segment DC, and a selective cascaded full-bridge inverter unit. The DC-side connection circuit includes a total of four DC connection terminals on the three-segment DC side. The four terminals are divided into two sets of connection half-bridge circuits. One series switch is connected to the output of each of the two half-bridge circuits, and the T-type structure is connected. The T-type structure includes two sets of flying capacitors connected in series. The connection midpoint of the capacitors is connected to the AC terminal through two switches connected in reverse series. The positive and negative poles of the entire series-connected capacitors are also connected to the AC terminal through switches respectively. Depending on the voltage on the DC side and the voltage on the flying capacitors of the T-type structure, the AC terminal can generate a multilevel output, and the current can flow bidirectionally.

[0035] Specifically, as shown in FIG. 1, the topology structure 100 of the voltage-source multilevel converter provided in this embodiment includes two sets of connection half-bridge circuits, namely the first connection half-bridge circuit 102 and the second connection half-bridge circuit 103. The first connection half-bridge circuit 102 includes two series switches S1 and

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[0036] As shown in FIGS. 4(a) and 4(b), the topology structure of the voltage source type multilevel converter provided in this embodiment is such that one or more full bridge inverter units 301 may or may not be cascade-connected to the AC terminal. The T-shaped multilevel circuit can generate seven levels. By cascade-connecting the full bridge conversion structures, each time a single-stage full bridge inverter unit is added, in combination with the T-shaped structure and the multilevel circuit having three-part DC, the overall structure can generate an additional six levels. A structure having n full bridge inverter units can generate (6*2 n +1) levels.

[0037] As shown in FIGS. 4(a) and 4(b), each full bridge inverter unit 301 includes switches S H1 ,

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[0038] The topology structure of the voltage source type multilevel converter provided in this embodiment can be used as a single-phase bridge arm of the converter, whereby a single-phase full bridge, a three-phase bridge, and a multiphase bridge system can be configured. Different numbers of bridge arms can share the DC side, and the DC side can be a power source, a capacitor, or a load. The power source and the load may be connected to the entire DC side, or may be divided into three groups and connected to four DC terminals respectively.

[0039] As shown in FIG. 2, in the multilevel topology structure using a single DC power source 120 and a three-divided DC capacitor 110, one capacitor is connected between every two adjacent DC connection terminals among the four DC connection terminals. Specifically, between the DC connection terminals to which the switch S1 and

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[0040] FIG. 5(a), FIG. 5(b), and FIG. 5(c) are respectively structural schematic diagrams of a single-phase H bridge, a three-phase converter, and an n-phase converter configured using the multilevel topology of the present invention.

[0041] As shown in Fig. 3, in the multi-level topology structure using three DC power supplies 201, one DC power supply is connected between every two adjacent DC connection terminals among the four DC connection terminals. Specifically, a DC power supply DC1 is connected between the DC connection terminals to which switch S1 and

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[0042] The topology structure of the voltage source type multi-level converter provided in this embodiment has a simple structure and can output multiple levels. Moreover, it has multiple DC link structure methods and can be applied to single-phase, three-phase, and multi-phase systems.

[0043] Example 2 Example 2 of the present invention provides a voltage source type multi-level converter that uses the topology structure of the voltage source type multi-level converter in Example 1 as a single-phase bridge arm.

[0044] Different bridge arms share the DC side.

[0045] Example 3 Example 3 of the present invention provides a control method for the topology structure of the voltage source type multi-level converter in Example 1, which drives each switch to execute its respective switching state, generates different current flow paths from the DC terminal to the AC terminal, and makes the voltage at the AC terminal different levels. Specifically, it includes the following steps.

[0046] (1) The control system generates a sine wave modulation reference signal by closed-loop control or open-loop modulation.

[0047] (2) The modulation reference signal generates an expected output voltage or directly generates the switching state of each switch by multi-level modulation strategies such as carrier stacking modulation and carrier phase shift modulation.

[0048] (3) Drive the switches in the topology to execute the generated switching state, and generate different current paths from the DC terminal to the AC terminal according to the switching state. Since the voltages of each DC terminal are different and the number of flying capacitors flowing through is different, the voltages of the AC terminals show different levels.

[0049] By outputting different levels according to a reasonable sequence, the fundamental wave component can be made equivalent to the expected sine wave modulation reference. The typical output is as shown in Figure 6, where W01 is the multi-level AC voltage output generated by the topology, and W02 is the expected voltage fundamental wave component, that is, the modulation reference waveform. Depending on the number of extended modules arranged, the generated multi-level voltage waveform has different numbers of levels, but the fundamental wave component must always be equivalent to the modulation reference.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various changes and modifications to the present invention. Changes, equivalent substitutions, improvements, etc. made without departing from the spirit and principle of the present invention are all included within the protection scope of the present invention.

Claims

1. comprising two sets of half - bridge circuits, two sets of flying capacitors, and a plurality of switches, each set of half - bridge circuits has two DC connection terminals, and two sets of flying capacitors connected in series are connected to the output of each of the two sets of half - bridge circuits via one switch, the connection mid - point of the two sets of flying capacitors is connected to the AC terminal via two switches connected in inverse series, and the positive and negative poles of the entire series - connected two sets of flying capacitors are respectively connected to the AC terminal via switches, characterized in that it is a topology structure of a voltage - source type multilevel converter.

2. The topology structure of the voltage - source type multilevel converter according to claim 1, characterized in that a full - bridge inverter unit is not cascade - connected to the AC terminal.

3. The topology structure of the voltage - source type multilevel converter according to claim 1, characterized in that one or more full - bridge inverter units are cascade - connected to the AC terminal.

4. When n full-bridge inverter units are cascade-connected to the AC terminal, (6 * 2 ｎ + 1) levels are generated, characterized in that it is the topology structure of the voltage source type multilevel converter according to claim 3.

5. The topology structure of the voltage - source type multilevel converter according to claim 1, characterized in that a single DC power source and a three - divided DC capacitor are connected to the DC connection terminals.

6. Three DC link capacitors are connected to four DC connection terminals, and the whole of the DC link capacitors is connected to the DC power source after being connected in series, characterized in that it is a topology structure of the voltage - source type multilevel converter according to claim 5.

7. The topology structure of the voltage - source type multilevel converter according to claim 1, characterized in that a plurality of DC power sources are connected to the DC connection terminals.

8. A voltage - source type multilevel converter, characterized by using the topology structure of the voltage - source type multilevel converter according to any one of claims 1 to 7 as a single - phase bridge arm.

9. The voltage - source type multilevel converter according to claim 8, characterized in that different bridge arms share the DC side.

10. The step of driving each switch to execute its respective switching state, generating different current flow paths from the DC terminal to the AC terminal, and making the voltage at the AC terminal different levels A control method for a topology structure of a voltage-source multi-level converter according to any one of claims 1 to 7, characterized by including

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