A nine-level converter topology with four dc input and its control method

Abstract

The application provides a four-way direct current input nine-level converter topology and a control method thereof, which comprises a four-split direct current side and an alternating current end; the four-split direct current side has five direct current connection ends, each two adjacent ends are connected into a half-bridge circuit, and the five direct current connection ends are divided into four groups of half-bridge circuits; the outputs of the four groups of half-bridge circuits are connected with one series switch respectively, and there are four series switches in total, wherein the first flying capacitor is connected between the first two series switches, and the second flying capacitor is connected between the last two series switches; the positive electrode and the negative electrode of the first flying capacitor are connected with the first group of half-bridge circuits respectively, the positive electrode and the negative electrode of the second flying capacitor are connected with the second group of half-bridge circuits respectively, the outputs of the first group of half-bridge circuits and the second group of half-bridge circuits are connected with the third group of half-bridge circuits respectively, and the output of the third group of half-bridge circuits is connected to the alternating current end; and the alternating current end generates a nine-level output based on the voltage of the four-split direct current side, the voltage on the first flying capacitor and the voltage on the second flying capacitor.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronic power conversion, and particularly relates to a four-way direct-current input nine-level converter topology and a control method thereof. BACKGROUND

[0002] The statements in this section merely provide background information related to the application and do not necessarily constitute prior art.

[0003] Under the background of rapid development of new energy power generation, energy storage technology with high reliability, high efficiency and high performance has become the focus and dominant development direction of current research. As the core component of energy exchange between "source-grid-load-storage", the topology structure and control method of power converter have always been concerned.

[0004] The common two-level converter has high output voltage waveform harmonics, and is limited by the requirement of device insulation voltage resistance, so that the switching device voltage stress is high, which limits the direct-current voltage level and leads to relatively low capacity. In medium and high voltage application occasions, a step-up transformer needs to be connected to meet the requirements, which introduces additional energy loss. The multi-level converter improves the output voltage level by connecting multiple power supplies, so that it can meet the medium and high voltage application requirements without the help of a transformer, and has the advantages of large capacity, small output harmonics, small switching device voltage stress, etc. Therefore, it is widely used in medium and high voltage large power microgrid systems.

[0005] With the increasing proportion of renewable energy (such as solar and wind energy) in energy production, its weather dependence and volatility also significantly increase. Multiple energy storage systems can balance these fluctuations, store excess energy for release when needed, and thus improve the availability and stability of renewable energy. In addition, the mainstream 1500V energy storage system plays an important role in large-scale energy storage applications, and its grouping balancing problem needs to be carefully handled. The multi-level converter with multiple power supply inputs can flexibly manage energy from different sources, effectively coordinate and manage multiple energy storage systems, and ensure the balance during charging and discharging.

[0006] The practical multi-level topology structure generally has the problems of few input power supplies, few fundamental frequency switches, and many capacitors.

[0007] Therefore, under the background of the increasing application of current microgrid and large-scale energy storage systems, it is urgent to propose a multi-level converter topology structure that can meet the requirements of multiple energy storage systems with multiple power supply inputs and has simple structure and efficient operation. SUMMARY

[0008] In order to overcome the above-mentioned deficiencies of the prior art, the application provides a four-way direct current input nine-level converter topology, which is a multi-level converter topology structure capable of meeting the multi-group energy storage demand of multi-group power supply access and having simple structure and high efficiency.

[0009] In order to achieve the above-mentioned purpose, one or more embodiments of the application provide the following technical solutions:

[0010] In a first aspect, a four-way direct current input nine-level converter topology is disclosed, comprising:

[0011] 4 split direct current sides, multi-group half-bridge structures, a first flying capacitor and a second flying capacitor;

[0012] The 4 split direct current sides have 5 direct current connection ends, each adjacent 2 ends are connected to form a half-bridge circuit, and the 5 direct current connection ends are divided into 4 groups of half-bridge circuits, thereby forming a multi-group half-bridge structure;

[0013] The outputs of the 4 groups of half-bridge circuits are respectively connected to 1 series switch, and there are 4 series switches in total, wherein the first 2 series switches are connected to the first flying capacitor, and the last 2 series switches are connected to the second flying capacitor;

[0014] The positive and negative poles of the first flying capacitor are respectively connected to the first group of half-bridge circuits, the positive and negative poles of the second flying capacitor are respectively connected to the second group of half-bridge circuits, and the outputs of the first group of half-bridge circuits and the second group of half-bridge circuits are respectively connected to the third group of half-bridge circuits, and the output of the third group of half-bridge circuits is connected to an alternating current end;

[0015] Based on the voltage of the 4 split direct current sides, the voltage on the first flying capacitor and the second flying capacitor, the alternating current end generates a nine-level output.

[0016] As a further technical solution, the four-way direct current input nine-level converter topology is used as a phase bridge arm of a converter, thereby forming a single-phase full-bridge, three-phase bridge or multi-phase bridge system.

[0017] As a further technical solution, the 4 split direct current sides are power supplies, capacitors or loads.

[0018] As a further technical solution, the power supplies and loads are connected to the entire direct current side or divided into four groups and connected to the 5 direct current ends.

[0019] As a further technical solution, the alternating current end is not cascaded or is cascaded with 1 to multiple full-bridge inverter units.

[0020] In a second aspect, a control method of a four-way direct current input nine-level converter topology is disclosed, comprising:

[0021] Generating a sinusoidal modulation reference signal;

[0022] For the sinusoidal modulation reference signal, the expected output voltage is generated by the multi-level modulation strategy or the switch state of each switch is directly generated;

[0023] The switch state generated is executed by the switch in the output instruction driving topology based on the multi-level modulation strategy, wherein different switch states will generate different flow paths from the DC end to the AC end, and due to the different voltages of each DC end, the number of flying capacitors flowing through is different, and different levels are output at the AC end.

[0024] The above one or more technical solutions have the following beneficial effects:

[0025] The four-way DC input nine-level converter topology of the embodiment of the application is composed of a switch tube and a flying capacitor. The DC side has five connection ends, connects four DC link capacitors, and connects the DC link capacitors in series after the whole series connection to connect the DC power supply. According to the application needs, a single-phase, three-phase, or multi-phase AC-DC converter can be formed by a half-bridge, a full-bridge, a three-phase bridge, or even more bridge arms. The converter has the advantages of multiple power supply access, multiple output levels, and simple structure. The application can be widely applied to AC-DC conversion application occasions with multiple power supply access and low output harmonic requirements, and is especially suitable for energy storage converters and other applications.

[0026] The advantages of the additional aspects of the application will be partially given in the following description, partially will become obvious from the following description, or will be known by the practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0027] The drawings accompanying the specification of the application form part of the specification and serve to further understand the application. The schematic embodiments of the application and the description thereof serve to explain the application and do not constitute an improper limitation of the application.

[0028] Figure 1 A schematic diagram of the multi-level circuit topology of the application;

[0029] Figure 2 A schematic diagram of the multi-level topology using a single DC power supply and four split DC capacitors according to the application;

[0030] Figure 3 A schematic diagram of the multi-level topology using four DC power supplies according to the embodiment 1 of the application;

[0031] Fig. 4(a) is a schematic diagram of the multi-level topology structure expanded to more levels using the application;

[0032] Fig. 4(b) is a structure diagram of the multi-level topology expansion module according to the embodiment 1 of the application;

[0033] Fig. 5(a) is a schematic diagram of the multi-level topology structure of a single-phase H-bridge according to the embodiment 1 of the application;

[0034] Fig. 5(b) is a schematic diagram of a structure of a three-phase converter constructed by a multi-level topology of Embodiment 1 of the present application;

[0035] Fig. 5(c) is a schematic diagram of a structure of an n-phase converter constructed by a multi-level topology of Embodiment 1 of the present application;

[0036] Figure 6 Fig. 6 is a schematic diagram of a conduction path when a multi-level topology of Embodiment 3 of the present application outputs different levels;

[0037] Fig. 7(a) is a waveform simulation diagram of a nine-level alternating voltage output by a multi-level circuit of Embodiment 4 of the present application;

[0038] Fig. 7(b) is a waveform simulation diagram of a current output by a multi-level circuit of Embodiment 4 of the present application;

[0039] Fig. 7(c) is a waveform simulation diagram of voltages on flying capacitors C1 and C2 in a multi-level circuit of Embodiment 4 of the present application. DETAILED DESCRIPTION

[0040] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0041] It should be noted that the terms used herein are only intended to describe specific embodiments and are not intended to limit exemplary embodiments according to the present application.

[0042] In the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0043] Embodiment One

[0044] The present embodiment discloses a four-way direct current input nine-level converter topology, which is connected with multiple groups of power supply and can output nine levels with a simple structure. The topology has multiple direct current chain construction methods and can be applied to single-phase, three-phase, and multi-phase systems and can be widely applied to medium and low voltage AC-DC conversion application occasions. The topology structure solves the problem of few direct current inputs of existing nine-level topologies with a simple structure, which helps to optimize the balance of multiple energy storage systems and the system cost of new energy collection.

[0045] In the present embodiment, the nine-level converter topology with four DC inputs includes a multi-level circuit with multi-stage half-bridge structure and 4 split DC and optional cascaded full-bridge inverter unit. The 4 split DC side has 5 DC terminals, each adjacent 2 terminals form a half-bridge circuit, and the 5 terminals are divided into 4 groups to connect the half-bridge circuits. The outputs of the 4 half-bridge circuits are connected to 1 series switch respectively, and then the first 2 and the last 2 series switches are connected to 2 groups of flying capacitors respectively. The positive and negative poles of each group of flying capacitors are connected to 1 group of half-bridge circuits respectively. The outputs of the 2 groups of half-bridge circuits are connected to 1 group of half-bridge circuits, and the outputs of the half-bridge circuits are connected to the AC terminals. With the DC side voltage and the voltage on the flying capacitors, the AC terminals can generate multi-level output, and the current can flow in both directions.

[0046] The multi-stage half-bridge structure is composed of cascaded multiple half-bridge structures to generate different levels. The multi-level circuit with 4 split DC is composed of DC connection terminals with 5 terminals to balance the DC voltage. The optional cascaded full-bridge inverter unit is used to generate additional levels.

[0047] Specifically, as shown in Figure 1 The voltage source multi-level converter topology structure 100 provided by the present embodiment includes a first group of connected half-bridge circuits 101, a second group of connected half-bridge circuits 102, a third group of connected half-bridge circuits 103, and a fourth group of connected half-bridge circuits 104. The first group of connected half-bridge circuits is composed of two series switches S1 and S2, both of which have one DC connection terminal, and the midpoints of the two series switches S1 and S2 are connected to one series switch (S9) 105. The second group of connected half-bridge circuits is composed of two series switches S3 and S4, both of which have one DC connection terminal, and the midpoints of the two series switches S3 and S4 are connected to one series switch (S10) 106. The third group of connected half-bridge circuits is composed of two series switches S5 and S6, both of which have one DC connection terminal, and the midpoints of the two series switches S5 and S6 are connected to one series switch (S11) 107. The fourth group of connected half-bridge circuits is composed of two series switches S7 and S8, both of which have one DC connection terminal, and the midpoints of the two series switches S7 and S8 are connected to one series switch (S12) 108. The first two series switches S9 and S10 are connected to the half-bridge circuit 111 through one flying capacitor (C1) 109. The last two series switches S11 and S12 are connected to the half-bridge circuit 112 through one flying capacitor (C2) 110. The midpoints of the two series switches S13 and S14 of the half-bridge circuit 111 and the midpoints of the two series switches S15 and S16 of the half-bridge circuit 112 are connected to one half-bridge circuit 113. The midpoints of the two series switches S17 and S18 of the half-bridge circuit 113 are connected to the AC terminals.

[0048] This embodiment provides a voltage source type multilevel converter topology, as shown in Figure 4, which can be either not cascaded or can be cascaded with one or more full-bridge inverter units at the AC end.

[0049] If one or more full-bridge inverter units are cascaded in a voltage source multilevel converter topology, as shown in Figures 4(a) and 4(b), each full-bridge inverter unit 301 includes a switch SH1. SH2, Among them, SH1 and They are connected in series to form a half-bridge structure, with the central connection terminal T1, used to connect the midpoint of the two series switches S17 and S18 of the half-bridge circuit 113 or the connection terminal T2 of the previous full-bridge inverter unit 301; SH2 and It is also connected as a half-bridge structure, with the central connection terminal T2, which is used to connect to the connection terminal T1 of the next full-bridge inverter unit; the floating capacitor CH is connected in parallel with the two half-bridges mentioned above.

[0050] It should be noted that cascading full-bridge inverter units in this topology increases the number of voltage levels generated. Each additional full-bridge inverter unit adds 8 voltage levels to the entire structure. A structure cascading n full-bridge inverter units can generate a total of (8*2) voltage levels. n +1) level.

[0051] The above topology can be used as one phase arm of a converter, thus enabling the construction of single-phase full-bridge, three-phase bridge, and multi-phase bridge systems. Different numbers of arms can share the DC side, which can be a power source, capacitor, or load. The power source can be connected to the entire DC side or divided into four groups connected to five DC terminals respectively.

[0052] like Figure 2 As shown, a multi-level topology using a single DC power supply 130 and four split DC capacitors 120 is employed, meaning that a capacitor is connected between every two adjacent DC connection terminals in the five DC connection terminals. Specifically, capacitor C is connected between the DC connection terminals connected by switches S1 and S2. DC1 A capacitor C is connected between the DC terminals of switches S3 and S4. DC2 A capacitor C is connected between the DC connection terminals of switches S5 and S6. DC3 A capacitor C is connected between the DC terminals of switches S7 and S8. DC4 Capacitor C DC1 and capacitor C DC4 Connect the positive and negative terminals of the DC power supply 130 respectively.

[0053] like Figure 3As shown, four DC power sources 201 are used in the multi-level topology, that is, one DC power source is connected between every two adjacent DC connection terminals of the five DC connection terminals, specifically, the DC connection terminals connected by switches S1 and S2 are connected by capacitor DC1, the DC connection terminals connected by switches S3 and S4 are connected by capacitor DC2, the DC connection terminals connected by switches S5 and S6 are connected by capacitor DC3, and the DC connection terminals connected by switches S7 and S8 are connected by capacitor DC4.

[0054] The voltage source multi-level converter topology provided by the embodiment can output multiple levels with a simple structure, has multiple DC link construction modes, and can be applied to single-phase, three-phase, and multi-phase systems.

[0055] Embodiment 2

[0056] The voltage source multi-level converter provided by the embodiment 2 adopts the voltage source multi-level converter topology as a phase bridge arm, as in the embodiment 1. Different bridge arms share a DC side. As shown in FIG. 5(a), FIG. 5(b), and FIG. 5(c), they are structure diagrams of a single-phase H-bridge, a three-phase converter, and an n-phase converter using the multi-level topology of the application, respectively.

[0057] Embodiment 3

[0058] The control method of the voltage source multi-level converter topology as in the embodiment 1 is provided in the embodiment 3, which drives each switch to execute a respective switching state, generates different flow paths from the DC end to the AC end, and makes the voltage at the AC end present different levels, and specifically includes the following steps:

[0059] (1) The control system samples the grid voltage and the grid-connected current through closed-loop control, and generates a sinusoidal modulation reference signal after phase-locked loop, coordinate transformation, and PI control; or directly provides a given sinusoidal modulation reference signal through open-loop modulation.

[0060] (2) The modulation reference signal is modulated by a multi-level modulation strategy, such as carrier superimposed modulation, carrier phase-shifted modulation, etc., to generate an expected output voltage, thereby determining the switching state of each switch in the topology. The carrier superimposed modulation, carrier phase-shifted modulation, etc., are common knowledge.

[0061] (3) The switch in the driving topology executes the generated switch state, and different switch states will generate different flow paths from the DC end to the AC end. Due to the different voltages of each DC end, the number of flying capacitors flowing through is different, and the voltage of the AC end presents different levels. When there are several different switch state combinations for outputting the same kind of level, the switch state combination is determined according to the voltage value on the flying capacitor, such as when the flying capacitor voltage is lower than the set value, the switch state combination for charging the flying capacitor is used; when the flying capacitor voltage is higher than the set value, the switch state combination for discharging the flying capacitor is used. Thus, the voltage on the flying capacitor is kept stable, while meeting the requirement of the output level.

[0062] The effective working state of each switch tube, the output level, and the charging and discharging state of the flying capacitor are shown in Table 1. The conduction path when outputting different levels is shown in Table 2. Figure 6

[0063] Table 1 Switch state table of nine-level converter with four DC inputs

[0064]

[0065]

[0066] According to the expected output voltage generated by the control link according to the comparison of the modulation wave and the carrier wave and the different levels output by the switch state, the fundamental component can be equivalent to the expected sinusoidal modulation reference. According to the different number of configuration expansion modules, the generated multi-level voltage waveform will have different number of levels, but the fundamental component should always be equivalent to the modulation reference.

[0067] Example 4

[0068] Referring to FIG. 7, this embodiment discloses the simulation waveforms of the AC voltage and current output by the nine-level converter topology with four DC inputs and the voltage simulation waveforms of the flying capacitors in the topology. When the modulation wave frequency decreases from 60 Hz to 0 and then increases to 60 Hz, the nine-level AC voltage waveform output, the load current waveform, and the voltage waveforms on the flying capacitors C1 and C2 are shown in FIG. 7(a), FIG. 7(b), and FIG. 7(c), respectively.

[0069] Multi-level converter topology. The converter topology includes the multi-level circuit with the multi-stage half-bridge structure described above, and can not be cascaded or be cascaded with one to multiple full-bridge inverter units at the AC end. The multi-level circuit with the multi-stage half-bridge structure can generate nine levels.

[0070] ​The voltage source type multi-level converter topology of the embodiment has five connection terminals at the DC side, can connect four DC link capacitors, and connects the DC link capacitors in series as a whole to connect the DC power supply. According to application requirements, the converter can be configured as a single-phase, three-phase or multi-phase AC-DC converter with half-bridge, full-bridge, three-phase bridge or even more bridge arms. The converter has the advantages of simple structure, simple control, low switching voltage stress and small output harmonic.

[0071] Those skilled in the art should understand that the modules or steps of the present application described above can be realized by a general computer device, or alternatively, they can be realized by program codes executable by a computing device, so that they can be stored in a storage device and executed by a computing device, or they can be respectively manufactured into individual integrated circuit modules, or a plurality of modules or steps among them can be manufactured into a single integrated circuit module. The present application is not limited to any specific combination of hardware and software.

[0072] Although the specific embodiments of the present application are described above in combination with the drawings, the description is not a limitation on the scope of protection of the present application, and those skilled in the art should understand that various modifications or changes made on the basis of the technical solutions of the present application without creative labor are still within the scope of protection of the present application.

Claims

1. A nine-level converter topology with four dc inputs, characterized by, The application relates to a four-split direct-current side, a multi-group half-bridge structure, a first flying capacitor and a second flying capacitor. The four-split direct-current side has five direct-current connection ends, two adjacent ends of which are connected to form a half-bridge circuit, and the five direct-current connection ends are divided into four groups of half-bridge circuits to form a multi-group half-bridge structure. The outputs of the four groups of half-bridge circuits are respectively connected to one of four series switches, wherein the first two series switches are connected to the first flying capacitor, and the last two series switches are connected to the second flying capacitor. The positive and negative poles of the first flying capacitor are respectively connected to the first group of half-bridge circuits, the positive and negative poles of the second flying capacitor are respectively connected to the second group of half-bridge circuits, and the outputs of the first group of half-bridge circuits and the second group of half-bridge circuits are respectively connected to the third group of half-bridge circuits, and the output of the third group of half-bridge circuits is connected to an alternating-current end. Based on the voltage of the four-split direct-current side, the voltage on the first flying capacitor and the voltage on the second flying capacitor, the alternating-current end generates a nine-level output. The nine-level converter topology of the four-way direct-current input is used as a bridge arm of a phase of a converter to form a single-phase full-bridge, a three-phase bridge or a multi-phase bridge system.

2. A nine-level converter topology with four dc inputs as claimed in claim 1 characterized by, The four-split direct-current side is a power supply, a capacitor or a load.

3. A nine-level converter topology with four dc inputs as claimed in claim 1 characterized by, The power supply or the load is connected to the whole direct-current side or is divided into four groups and connected to the five direct-current ends.

4. A nine-level converter topology with four dc inputs as claimed in claim 3, characterized in that, The alternating-current end is not cascaded or is cascaded with one to multiple full-bridge inverter units.

5. A nine-level converter topology with four dc inputs as claimed in claim 1 characterized in that, The four groups of half-bridge circuits form a multi-level half-bridge structure to generate different levels.

6. A nine-level converter topology with four dc inputs as claimed in claim 1 characterized by, The five direct-current connection ends form a multi-level circuit of the four-split direct-current to balance the direct-current voltage.

7. A nine-level converter topology with four dc inputs as claimed in claim 1 characterized by, The full-bridge inverter unit is used to generate additional levels.

8. A nine-level converter topology with four dc inputs as claimed in claim 5 characterized by, The application further relates to a method for generating a nine-level output from a four-split direct-current side. The structure of cascading n full-bridge inverter units can generate (8*2 n +1) levels in total.

9. A control method for a nine-level converter topology with four dc inputs according to any of claims 1-8, characterized by, A sinusoidal modulation reference signal is generated. For the sinusoidal modulation reference signal, an expected output voltage is generated through a multi-level modulation strategy or the switching states of each switch are directly generated. The switching states are executed by driving the switches in the topology based on the output instructions of the multi-level modulation strategy, wherein different switching states will generate different flow paths from the direct-current end to the alternating-current end, the number of flying capacitors flowing through is different due to the different voltages of the direct-current ends, and different levels are output at the alternating-current end. When there are several different switching state combinations for outputting the same level, the switching state combination is determined according to the voltage value on the flying capacitor.

10. A control method of a nine-level converter topology with four dc inputs as claimed in claim 9, characterized by, When the voltage on the flying capacitor is lower than a set value, a switching state combination for charging the flying capacitor is used; when the voltage on the flying capacitor is higher than the set value, a switching state combination for discharging the flying capacitor is used; thereby the voltage on the flying capacitor is kept stable while meeting the requirement of the output level. ​

Images