Switched capacitor type five-level inverter applied to photovoltaic grid connection

Abstract

The invention discloses a switched capacitor type five-level inverter applied to photovoltaic grid connection, and relates to the technical field of power electronic converters. The inverter comprises a direct-current voltage source Vdc, eight power switch tubes, a diode D1, a diode D2, a switched capacitor C1, a switched capacitor C2, an inductor L and a load. Wherein the eight power switch tubes are respectively marked as a switch tube S1, a switch tube S2, a switch tube S3, a switch tube S4, a switch tube S5, a switch tube S6, a switch tube S7 and a switch tube S8. According to the switch capacitance type high-frequency five-level inverter, the switch capacitance unit converts constant direct-current voltage into multi-level direct-current voltage through different switch state combinations of the eight switch tubes in the control circuit, the inverter generates five-level output with the voltage gains of + / -2Vdc, + / -Vdc and 0, the circuit structure of the switch capacitance type high-frequency five-level inverter is simpler, and the cost is lower. The boost function can be realized by using fewer switch tube devices, and capacitor voltage regulation is not needed.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and in particular to a switched capacitor five-level inverter applied to photovoltaic grid connection. Background Art

[0002] With the growth of global energy demand and the improvement of environmental protection awareness, new energy technologies, especially photovoltaic power generation technology, have received extensive attention and application. As a form of clean and renewable energy, photovoltaic power generation has the advantages of being pollution-free, rich in resources, and widely distributed, and has gradually become an important part of the global energy structure transformation.

[0003] In photovoltaic power generation systems, an inverter is usually required to effectively connect the DC power generated by the photovoltaic array to the AC power grid. The inverter can convert DC power into AC power while ensuring the waveform quality and voltage stability of the output current to ensure the safety and stability of grid-connected power generation. Traditional photovoltaic inverters usually adopt a two-level structure, and their output waveform contains more harmonic components, causing grid pollution and affecting the life of the equipment. In order to improve these shortcomings, multi-level inverter technology has gradually been widely used. Multi-level inverters increase the number of output voltage levels to make the output voltage waveform closer to the ideal sine wave, thereby significantly reducing the harmonic content and improving system efficiency. However, traditional multi-level inverters based on midpoint clamping, cascaded H-bridges and flying capacitors require a large number of semiconductor devices and DC power supplies, which increases the complexity of the circuit and the difficulty of control.

[0004] In recent years, switched capacitor technology has attracted widespread attention due to its advantages such as simple circuit, high efficiency and high power density. The switched capacitor multi-level inverter realizes voltage conversion and level boosting by switching the switch tube and the switched capacitor, which can not only simplify the circuit structure but also improve the efficiency and reliability of the system. However, the current switched capacitor multi-level inverter still requires a large number of DC power supplies and switching devices, which seriously limits the application scenarios of this type of inverter. Therefore, it is particularly important to further study a switched capacitor multi-level inverter circuit with fewer switching devices, simple control and high efficiency. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above problems existing in the existing switched capacitor type five-level inverter applied to photovoltaic grid connection, the present invention is proposed.

[0007] Therefore, the object of the present invention is to provide a switched capacitor type five-level inverter applied to photovoltaic grid-connected power generation, in order to provide a switched capacitor type multi-level inverter circuit with fewer switching devices, simpler control and higher efficiency.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] A switched capacitor five-level inverter for photovoltaic grid connection includes: a DC voltage source V d c , eight power switch tubes, diode D 1 With diode D 2 , switch capacitor C 1 With the switch capacitor C 2 , an inductor L and a load; the eight power switch tubes are respectively denoted as switch tubes S 1 , switch tube S 2 , switch tube S 3 , switch tube S 4 , switch tube S 5 , switch tube S 6 , switch tube S 7 And switch tube S 8 ; The AC output voltage of the inverter is recorded as the load voltage V o ;

[0010] The switch capacitor C 1 One end of each is connected to the switch tube S 3 The emitter and switch tube S 4 The emitter and switch tube S 1 The collector of the diode D 1 The cathode and switch tube S 2 The collector of the switch capacitor C 2 One end of each is connected to the switch tube S 7 The emitter and switch tube S 8 The emitter and switch tube S 5 The collector of the diode D 2 The cathode and switch tube S 6 The collector of the inductor L is connected to the diode D 1 The anode and diode D 2 The anode of the switch tube S 4 The collector of the switch tube S 8 The collector and DC voltage source V d cThe positive electrode of the load; one end of the load is connected to the emitter of the switch tube S2 and the collector of the switch tube S3, and the other end of the load is connected to the emitter of the switch tube S6 and the collector of the switch tube S7; the DC voltage source V d c The negative electrode is connected to the emitter of the switch tube S1 and the emitter of the switch tube S5.

[0011] As a preferred solution of the switched capacitor five-level inverter applied to photovoltaic grid-connected power system described in the present invention, the switch tube S1, switch tube S2, switch tube S3, switch tube S4, switch tube S5, switch tube S6, switch tube S7 and switch tube S8 are all switch tubes with anti-parallel diodes.

[0012] As a preferred solution of a switched capacitor type five-level inverter applied to photovoltaic grid connection described in the present invention, when the switch tube S1, the switch tube S3, the switch tube S5 and the switch tube S7 are all turned on, the switch tube S2, the switch tube S4, the switch tube S6 and the switch tube S8 are all turned off and the load current is positive, the switch capacitor C1 is connected to the DC voltage source V through the inductor L, the diode D1, the switch tube S3, the load, the switch tube S7, and the DC voltage source V d c The circuit is charged to V d c , the switch capacitor C2 is connected to the DC voltage source V through the switch tube S5, the inductor L, the diode D2 d c The circuit is charged to V d c In this state, both ends of the load are short-circuited and the load output voltage is zero.

[0013] As a preferred solution of the switched capacitor type five-level inverter applied to photovoltaic grid connection described in the present invention, when the switch tube S1, the switch tube S2, the switch tube S5 and the switch tube S7 are all turned on, the switch tube S 3 , switch tube S 4 Shut down S 6 And switch tube S 8 When both are turned off and the load current is positive, the switch capacitor C 1 Through the switch tube S 1 , inductor L, diode D 1 With DC voltage source V d c The circuit is charged to V d c , the switching capacitor C 2 Through the switch tube S 5 , inductor L, diode D 2 With DC voltage source V d c The circuit is charged to Vd c In this state, the load output voltage is +V d c .

[0014] As a preferred solution of the switched capacitor type five-level inverter applied to photovoltaic grid connection described in the present invention, when the switch tube S 2 , switch tube S 4 , switch tube S 5 And switch tube S 7 Both are turned on, the switch tube S 1 , switch tube S 3 Shut down S 6 And switch tube S 8 When both are turned off and the load current is positive, the switch capacitor C 2 Through the switch tube S 5 , inductor L, diode D 2 With DC voltage source V d c The circuit is charged to V d c In this state, the load output voltage is +2V d c .

[0015] As a preferred solution of the switched capacitor type five-level inverter applied to photovoltaic grid connection described in the present invention, when the switch tube S 1 , switch tube S 3 , switch tube S 5 And switch tube S 7 Both are turned on, the switch tube S 2 , switch tube S 4 Shut down S 6 And switch tube S 8 When both are turned off and the load current is negative, the switch capacitor C 1 Through the switch tube S 1 , inductor L, diode D 1 With DC voltage source V d c The circuit is charged to V d c , the switching capacitor C 2 Through the inductor L, diode D 2 , switch tube S 3 , load, switch tube S 7 With DC voltage source V d c The circuit is charged to V d c In this state, both ends of the load are short-circuited and the load output voltage is zero.

[0016] As a preferred solution of a switched capacitor type five-level inverter applied to photovoltaic grid connection described in the present invention, wherein: when the switch tube S1, the switch tube S3, the switch tube S5 and the switch tube S6 are all turned on, the switch tube S2, the switch tube S4, the switch tube S7 and the switch tube S8 are all turned off and the load current is negative, the switch capacitor C1 is connected to the DC voltage source V through the switch tube S1, the inductor L, the diode D1 d c The circuit is charged to V d c , the switch capacitor C2 is connected to the DC voltage source V through the switch tube S5, the inductor L, the diode D2 d c The circuit is charged to V d c In this state, the load output voltage is -V d c .

[0017] As a preferred solution of a switched capacitor type five-level inverter applied to photovoltaic grid connection described in the present invention, wherein: when the switch tube S1, the switch tube S3, the switch tube S6 and the switch tube S8 are all turned on, the switch tube S2, the switch tube S4, the switch tube S5 and the switch tube S7 are all turned off and the load current is negative, the switch capacitor C1 is connected to the DC voltage source V through the switch tube S1, the inductor L, the diode D1 d c The circuit is charged to V d c In this state, the load output voltage is -2V d c .

[0018] Beneficial effects of the present invention:

[0019] 1. The present invention controls the different switch state combinations of eight power switch tubes in the circuit, and the switch capacitor unit converts the constant DC voltage into a five-level DC voltage, which significantly reduces the harmonic content and improves the operating efficiency of the system;

[0020] 2. The present invention only needs a single DC voltage source to generate the required multi-level output, realize the double boost function, and does not require capacitor voltage regulation. Therefore, the present invention has a simple structure, flexible control, and is conducive to improving power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0022] Figure 1 A topological structure diagram of a switched capacitor five-level inverter for photovoltaic grid connection disclosed in an embodiment of the present invention.

[0023] Figure 2 The present invention discloses a schematic diagram of the working mode 1 of a switched capacitor five-level inverter applied to photovoltaic grid connection.

[0024] Figure 3 The present invention discloses a schematic diagram of the working mode 2 of a switched capacitor five-level inverter applied to photovoltaic grid connection.

[0025] Figure 4 The present invention discloses a schematic diagram of the working mode 3 of a switched capacitor five-level inverter applied to photovoltaic grid connection.

[0026] Figure 5 The present invention discloses a schematic diagram of the operation of mode 4 of a switched capacitor five-level inverter for photovoltaic grid connection.

[0027] Figure 6 The present invention discloses a schematic diagram of the working mode 5 of a switched capacitor five-level inverter applied to photovoltaic grid connection.

[0028] Figure 7 The present invention discloses a schematic diagram of the operation of mode 6 of a switched capacitor five-level inverter for photovoltaic grid connection. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0032] Reference Figure 1-Figure 7, is an embodiment of the present invention, providing a switched capacitor type five-level inverter for photovoltaic grid connection, the inverter comprising: a DC voltage source V d c , eight power switch tubes, diode D 1 With diode D 2 , switch capacitor C 1 With the switch capacitor C 2 , an inductor L and a load; the eight power switch tubes are respectively denoted as switch tubes S 1 , switch tube S 2 , switch tube S 3 , switch tube S 4 , switch tube S 5 , switch tube S 6 , switch tube S 7 And switch tube S 8 ; The AC output voltage of the inverter is recorded as the load voltage V o .

[0033] Specifically, the switch capacitor C 1 One end of each is connected to the switch tube S 3 The emitter and switch tube S 4 The emitter and switch tube S 1 The collector of the diode D 1 The cathode and switch tube S 2 The collector of the switch capacitor C 2 One end of each is connected to the switch tube S 7 The emitter and switch tube S 8 The emitter and switch tube S 5 The collector of the diode D 2 The cathode and switch tube S 6 The collector of the inductor L is connected to the diode D 1 The anode and diode D 2 The anode of the switch tube S 4 The collector of the switch tube S 8 The collector and DC voltage source V d c The positive electrode of the load; one end of the load is connected to the emitter of the switch tube S2 and the collector of the switch tube S3, and the other end of the load is connected to the emitter of the switch tube S6 and the collector of the switch tube S7; the DC voltage source V d c The negative electrode is connected to the emitter of the switch tube S1 and the emitter of the switch tube S5.

[0034] Furthermore, the switch tube S1 , the switch tube S2 , the switch tube S3 , the switch tube S4 , the switch tube S5 , the switch tube S6 , the switch tube S7 and the switch tube S8 are all switch tubes with anti-parallel diodes.

[0035] The working mode of the switched capacitor high frequency five-level inverter as described above is as follows:

[0036] Mode 1: When the switch tubes S1, S3, S5 and S7 are all turned on, the switch tubes S2, S4, S6 and S8 are all turned off and the load current is positive, the switch capacitor C1 is connected to the DC voltage source V through the inductor L, the diode D1, the switch tube S3, the load, the switch tube S7 and the DC voltage source V d c The circuit is charged to V d c , the switch capacitor C2 is connected to the DC voltage source V through the switch tube S5, the inductor L, the diode D2 d c The circuit is charged to V d c In this state, the two ends of the load are short-circuited and the load output voltage is zero, that is, V o =0.

[0037] Mode 2: When the switch tubes S1, S2, S5 and S7 are all turned on, the switch tubes S3, S4, S6 and S8 are all turned off and the load current is positive, such as Figure 3 As shown; the switch capacitor C1 is connected to the DC voltage source V through the switch tube S1, the inductor L, the diode D1 dc The circuit is charged to V d c , the switching capacitor C 2 Through the switch tube S 5 , inductor L, diode D 2 With DC voltage source V d c The circuit is charged to V d c In this mode, the load output voltage is equal to the DC voltage source voltage, that is, V o =+V d c .

[0038] Mode 3: When the switch tube S 2 , switch tube S 4 , switch tube S 5 And switch tube S 7 Both are turned on, the switch tube S 1 , switch tube S 3 Shut down S 6 And switch tube S8 When both are off and the load current is positive, such as Figure 4 As shown; switch capacitor C 2 Through the switch tube S 5 , inductor L, diode D 2 With DC voltage source V d c The circuit is charged to V d c In this mode, the load output voltage is twice the DC voltage source voltage, that is, V o =+2V d c .

[0039] Mode 4: When the switch tube S 1 , switch tube S 3 , switch tube S 5 And switch tube S 7 Both are turned on, the switch tube S 2 , switch tube S 4 Shut down S 6 And switch tube S 8 When both are off and the load current is negative, Figure 5 As shown; switch capacitor C 1 Through the switch tube S1, inductor L, diode D 1 With DC voltage source V d c The circuit is charged to V d c , the switching capacitor C 2 Through the inductor L, diode D 2 , switch tube S3, load, switch tube S7 and DC voltage source V d c The circuit is charged to V d c In this mode, the load is short-circuited and the load output voltage is zero, that is, V o =0

[0040] Mode 5: When the switch tube S 1 , switch tube S 3 , switch tube S 5 And switch tube S 6 Both are turned on, the switch tube S 2 , switch tube S 4 Shut down S 7 And switch tube S 8 When both are off and the load current is negative, Figure 6 As shown; the switch capacitor C1 is connected to the DC voltage source V through the switch tube S1, the inductor L, the diode D1 d c The circuit is charged to V dc , the switch capacitor C2 is connected to the DC voltage source V through the switch tube S5, the inductor L, the diode D2 d c The circuit is charged to V d c In this mode, the load output voltage is negative one times the DC voltage source voltage, that is, V o = -V d c

[0041] Mode 6: When the switch tubes S1, S3, S6 and S8 are all turned on, the switch tubes S2, S4, S5 and S7 are all turned off and the load current is negative, such as Figure 7 As shown; the switch capacitor C1 is charged to V through the switch tube S1, inductor L, diode D1 and DC voltage source Vdc to form a loop. d c In this mode, the load output voltage is negative twice the DC voltage source voltage, that is, V o = -2V d c .

[0042] In summary, the present invention controls the different switch state combinations of the eight power switch tubes in the circuit, and the switch capacitor unit converts the constant DC voltage into a five-level DC voltage, which significantly reduces the harmonic content and improves the operating efficiency of the system. Only a single DC voltage source is needed to generate the required multi-level output, realize the double boost function, and no capacitor voltage adjustment is required. Therefore, the invention has a simple structure, flexible control, and is conducive to improving power density.

[0043] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A switched capacitor five-level inverter for photovoltaic grid connection, characterized in that: include: A DC voltage source V d c , eight power switch tubes, diode D 1 With diode D 2 , switch capacitor C 1 With the switch capacitor C 2 , an inductor L and a load; the eight power switch tubes are respectively denoted as switch tubes S 1 , switch tube S 2 , switch tube S 3 , switch tube S 4 , switch tube S 5 , switch tube S 6 , switch tube S 7 And switch tube S 8 ; The AC output voltage of the inverter is recorded as the load voltage V o ; The switch capacitor C 1 One end of each is connected to the switch tube S 3 The emitter and switch tube S 4 The emitter and switch tube S 1 The collector of the diode D 1 The cathode and switch tube S 2 The collector of the switch capacitor C 2 One end of each is connected to the switch tube S 7 The emitter and switch tube S 8 The emitter and switch tube S 5 The collector of the diode D 2 The cathode and switch tube S 6 The collector of the inductor L is connected to the diode D 1 The anode and diode D 2 The anode of the switch tube S 4 The collector of the switch tube S 8 The collector and DC voltage source V d c One end of the load is connected to the switch tube S 2 The emitter and switch tube S 3 The collector of the load is connected to the switch tube S 6 The emitter and switch tube S 7 The collector of the DC voltage source V d c The negative pole of the switch tube S 1 The emitter and switch tube S 5 of the emitter.

2. A switched capacitor five-level inverter for photovoltaic grid connection according to claim 1, characterized in that: The switch tube S1 , switch tube S2 , switch tube S3 , switch tube S4 , switch tube S5 , switch tube S6 , switch tube S7 and switch tube S8 are all switch tubes with anti-parallel diodes.

3. The switched capacitor five-level inverter for photovoltaic grid connection according to claim 1, characterized in that: When the switch tubes S1, S3, S5 and S7 are all turned on, the switch tubes S2, S4, S6 and S8 are all turned off and the load current is positive, the switch capacitor C1 is connected to the DC voltage source V through the inductor L, the diode D1, the switch tube S3, the load, the switch tube S7, and the DC voltage source V d c The circuit is charged to V d c , the switch capacitor C2 is connected to the DC voltage source V through the switch tube S5, the inductor L, the diode D2 d c The circuit is charged to V d c In this state, both ends of the load are short-circuited and the load output voltage is zero.

4. The switched capacitor five-level inverter for photovoltaic grid connection according to claim 1, characterized in that: When the switch tubes S1, S2, S5 and S7 are all turned on, the switch tubes S3, S4, S6 and S8 are all turned off and the load current is positive, the switch capacitor C1 is connected to the DC voltage source V through the switch tube S1, the inductor L and the diode D1. d c The circuit is charged to V d c , the switch capacitor C2 is connected to the DC voltage source V through the switch tube S5, the inductor L, the diode D2 d c The circuit is charged to V d c In this state, the load output voltage is +V d c .

5. The switched capacitor five-level inverter for photovoltaic grid connection according to claim 1, characterized in that: When the switch tube S 2 , switch tube S 4 , switch tube S 5 And switch tube S 7 Both are turned on, the switch tube S 1 , switch tube S 3 Shut down S 6 And switch tube S 8 When both are turned off and the load current is positive, the switch capacitor C 2 Through the switch tube S 5 , inductor L, diode D 2 With DC voltage source V d c The circuit is charged to V d c In this state, the load output voltage is +2V d c .

6. The switched capacitor five-level inverter for photovoltaic grid connection according to claim 1, characterized in that: When the switch tube S 1 , switch tube S 3 , switch tube S 5 And switch tube S 7 Both are turned on, the switch tube S 2 , switch tube S 4 Shut down S 6 And switch tube S 8 When both are turned off and the load current is negative, the switch capacitor C 1 Through the switch tube S 1 , inductor L, diode D 1 With DC voltage source V d c The circuit is charged to V d c , the switching capacitor C 2 Through the inductor L, diode D 2 , switch tube S 3 , load, switch tube S 7 With DC voltage source V d c The circuit is charged to V d c In this state, both ends of the load are short-circuited and the load output voltage is zero.

7. The switched capacitor five-level inverter for photovoltaic grid connection according to claim 1, characterized in that: When the switch tube S 1 , switch tube S 3 , switch tube S 5 And switch tube S 6 Both are turned on, the switch tube S 2 , switch tube S 4 Shut down S 7 And switch tube S 8 When both are turned off and the load current is negative, the switch capacitor C 1 Through the switch tube S 1 , inductor L, diode D 1 With DC voltage source V d c The circuit is charged to V d c , the switching capacitor C 2 Through the switch tube S 5 , inductor L, diode D 2 With DC voltage source V d c The circuit is charged to V d c In this state, the load output voltage is -V d c .

8. The switched capacitor five-level inverter for photovoltaic grid connection according to claim 1, characterized in that: When the switch tubes S1, S3, S6 and S8 are all turned on, the switch tubes S2, S4, S5 and S7 are all turned off and the load current is negative, the switch capacitor C1 is connected to the DC voltage source V through the switch tube S1, the inductor L and the diode D1. d c The circuit is charged to V d c In this state, the load output voltage is -2V dc .

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