A switched-capacitor type five-level inverter applied to photovoltaic grid connection

Abstract

The present invention discloses a switched-capacitor type five-level inverter applied to photovoltaic grid connection, which relates to the technical field of power electronic converters. The inverter includes a DC voltage source V d c , eight power switching tubes, diode D 1 and diode D 2 , switched capacitor C 1 and switched capacitor C 2 , an inductor L and a load; among them, the eight power switching tubes are respectively denoted as switching tube S 1 , switching tube S 2 , switching tube S 3 , switching tube S 4 , switching tube S 5 , switching tube S 6 , switching tube S 7 and switching tube S 8 . By controlling different switching state combinations of the eight switching tubes in the circuit, the switched-capacitor unit converts the constant DC voltage into a multi-level DC voltage, enabling the inverter to generate a five-level output with voltage gains of ±2V d c , ±V d c and 0. The proposed switched-capacitor type high-frequency five-level inverter circuit structure is simpler, and the boost function can be realized with fewer switching tube devices without the need for capacitor voltage regulation.

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 connection, in order to provide a switched-capacitor type multilevel inverter circuit with fewer switching devices, simple control and high efficiency.

[0008] To solve the above technical problems, the present invention provides the following technical solutions:

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

[0010] One end of the switched capacitor C 1 is respectively connected to the emitter of switching tube S 3 , the emitter of switching tube S 4 and the collector of switching tube S 1 , and the other end is connected to the cathode of diode D 1 and the collector of switching tube S 2 ; One end of the switched capacitor C 2 is respectively connected to the emitter of switching tube S 7 , the emitter of switching tube S 8 and the collector of switching tube S 5 , and the other end is connected to the cathode of diode D 2 and the collector of switching tube S 6 ; One end of the inductor L is respectively connected to the anode of diode D 1 and the anode of diode D 2 , and the other end is respectively connected to the collector of switching tube S 4 , the collector of switching tube S 8 and the positive pole of the DC voltage source V d c ; One end of the load is connected to the emitter of switching tube S 2 and the emitter of switching tube S 3collector, and the other end of the load is connected to the switching transistor S 6 emitter of and the switching transistor S 7 collector; the DC voltage source V d c negative electrode is connected to the switching transistor S 1 emitter of and the switching transistor S 5 emitter.

[0011] As a preferred embodiment of the switched-capacitor type five-level inverter applied to photovoltaic grid connection according to the present invention, wherein: the switching transistor S 1 , switching transistor S 2 , switching transistor S 3 , switching transistor S 4 , switching transistor S 5 , switching transistor S 6 , switching transistor S 7 and switching transistor S 8 are all switching transistors with anti-parallel diodes.

[0012] As a preferred embodiment of the switched-capacitor type five-level inverter applied to photovoltaic grid connection according to the present invention, wherein: when the switching transistors S 1 , switching transistors S 3 , switching transistors S 5 and switching transistor S 7 are all conducting, and the switching transistors S 2 , switching transistors S 4 switching transistor S 6 and switching transistor S 8 are all turned off and the load current is positive, the switching capacitor C 1 is charged to V 1 through the inductor L, diode D 3 , switching transistor S 7 , load, switching transistor S d c to form a loop with the DC voltage source V d c , and the switching capacitor C 2 is charged to V 5 through the switching transistor S 2 , inductor L, diode D d c to form a loop with the DC voltage source V d c , and the load is short-circuited at both ends in this state, and the load output voltage is zero.

[0013] As a preferred embodiment of the switched-capacitor type five-level inverter applied to photovoltaic grid connection according to the present invention, wherein: when the switching transistors S 1 , switching transistors S 2 , switching transistors S5 and switch S 7 are both conducting, and switch S 3 , switch S 4 switch S 6 and switch S 8 are both turned off and the load current is positive, the switched capacitor C 1 is charged to V 1 , inductor L, diode D 1 forming a loop with the DC voltage source V d c , and the load output voltage in this state is +V d c . 2 is charged to V 5 , inductor L, diode D 2 forming a loop with the DC voltage source V d c , and the load output voltage in this state is +V d c , and the load output voltage in this state is +V d c .

[0014] As a preferred embodiment of the switched-capacitor type five-level inverter applied to photovoltaic grid connection according to the present invention, wherein: when the switch S 2 , switch S 4 , switch S 5 and switch S 7 are both conducting, and switch S 1 , switch S 3 switch S 6 and switch S 8 are both turned off and the load current is positive, the switched capacitor C 2 is charged to 2V 5 , inductor L, diode D 2 forming a loop with the DC voltage source V d c , and the load output voltage in this state is +2V d c . d c .

[0015] As a preferred embodiment of the switched-capacitor type five-level inverter applied to photovoltaic grid connection according to the present invention, wherein: when the switch S 1 , switch S 3 , switch S 5 and switch S 7 are both conducting, and switch S 2 , switch S 4 switch S 6and the switching transistor S 8 When both are turned off and the load current is negative, the switched capacitor C 1 passes through the switching transistor S 1 , the inductor L, the diode D 1 and the DC voltage source V d c to form a loop and is charged to V d c , the switched capacitor C 2 passes through the inductor L, the diode D 2 , the switching transistor S 3 , the load, the switching transistor S 7 and the DC voltage source V d c to form a loop and 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 according to the present invention, wherein: when the switching transistor S 1 , the switching transistor S 3 , the switching transistor S 5 and the switching transistor S 6 are all turned on, the switching transistor S 2 , the switching transistor S 4 the switching transistor S 7 and the switching transistor S 8 are all turned off and the load current is negative, the switched capacitor C 1 passes through the switching transistor S 1 , the inductor L, the diode D 1 and the DC voltage source V d c to form a loop and is charged to V d c , the switched capacitor C 2 passes through the switching transistor S 5 , the inductor L, the diode D 2 and the DC voltage source V d c to form a loop and 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 according to the present invention, wherein: when the switching transistor S 1 , the switching transistor S 3 , the switching transistor S 6 and the switching transistor S 8 are all turned on, the switching transistor S2 and switch tube S 4 switch tube S 5 and the switch tube S 7 When all are turned off and the load current is negative, the switched capacitor C 1 passes through the switch tube S 1 , inductor L, and diode D 1 and the DC voltage source V d c to form a loop and is charged to V d c , and the load output voltage in this state is -2V d c .

[0018] Advantages of the present invention:

[0019] 1. By controlling different switching state combinations of eight power switch tubes in the circuit, the switched capacitor unit converts a constant DC voltage into a five-level DC voltage, significantly reducing the harmonic content and improving the operating efficiency of the system;

[0020] 2. The present invention only requires a single DC voltage source to generate the required multi-level output, realizes a two-fold boost function, and does not require capacitor voltage regulation. Therefore, the invention has a simple structure and flexible control, which is beneficial to improving the power density. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only 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. Among them:

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

[0023] Figure 2 is a working schematic diagram of Mode 1 of a switched capacitor type five-level inverter applied to photovoltaic grid connection disclosed in an embodiment of the present invention.

[0024] Figure 3 is a working schematic diagram of Mode 2 of a switched capacitor type five-level inverter applied to photovoltaic grid connection disclosed in an embodiment of the present invention.

[0025] Figure 4 is a working schematic diagram of Mode 3 of a switched capacitor type five-level inverter applied to photovoltaic grid connection disclosed in an embodiment of the present invention.

[0026] Figure 5Schematic diagram of the operation of Mode 4 of a switched-capacitor type five-level inverter applied to photovoltaic grid connection disclosed in an embodiment of the present invention.

[0027] Figure 6 Schematic diagram of the operation of Mode 5 of a switched-capacitor type five-level inverter applied to photovoltaic grid connection disclosed in an embodiment of the present invention.

[0028] Figure 7 Schematic diagram of the operation of Mode 6 of a switched-capacitor type five-level inverter applied to photovoltaic grid connection disclosed in an embodiment of the present invention. Detailed implementation manners

[0029] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific implementation manners of the present invention will be given in conjunction with the accompanying drawings of the specification.

[0030] In the following description, many specific details are set forth to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0031] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that mutually excludes other embodiments.

[0032] Refer to Figures 1-7 , which is an embodiment of the present invention, and provides a switched-capacitor type five-level inverter applied to photovoltaic grid connection. This inverter includes: a DC voltage source V d c , eight power switching tubes, diodes D 1 and diode D 2 , switched capacitors C 1 and switched capacitor C 2 , an inductor L, and a load; among them, the eight power switching tubes are respectively denoted as switching tube S 1 , switching tube S 2 , switching tube S 3 , switching tube S 4 , switching tube S 5 , switching tube S 6 , switching tube S 7 and switching tube S 8 ; the AC output voltage of the inverter is denoted as the load voltage V o .

[0033] Specifically, one end of the switching capacitor C 1 is respectively connected to the emitter of the switching transistor S 3 , the emitter of the switching transistor S 4 , and the collector of the switching transistor S 1 , and the other end is connected to the cathode of the diode D 1 and the collector of the switching transistor S 2 ; one end of the switching capacitor C 2 is respectively connected to the emitter of the switching transistor S 7 , the emitter of the switching transistor S 8 , and the collector of the switching transistor S 5 , and the other end is connected to the cathode of the diode D 2 and the collector of the switching transistor S 6 ; one end of the inductor L is respectively connected to the anode of the diode D 1 and the anode of the diode D 2 , and the other end is respectively connected to the collector of the switching transistor S 4 , the collector of the switching transistor S 8 , and the positive electrode of the DC voltage source V d c ; one end of the load is connected to the emitter of the switching transistor S 2 and the collector of the switching transistor S 3 , and the other end of the load is connected to the emitter of the switching transistor S 6 and the collector of the switching transistor S 7 ; the negative electrode of the DC voltage source V d c is connected to the emitter of the switching transistor S 1 and the emitter of the switching transistor S 5 .

[0034] Furthermore, the switching transistors S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 and S 8 are all switching transistors with anti-parallel diodes.

[0035] The operating modes of the switching capacitor type high-frequency five-level inverter are as follows:

[0036] Mode 1: When the switching transistors S 1 , S 3 , S 5 and S 7 are all conducting, and the switching transistors S 2 ​4 Switching tube S 6 and switching tube S 8 are both turned off and when the load current is positive, the switching capacitor C 1 is charged to V through the inductor L, diode D 1 , switching tube S 3 , load, switching tube S 7 and the DC voltage source V d c to form a loop and is charged to V d c . At this state, both ends of the load are short - circuited and the load output voltage is zero, that is, V 2 = 0. 5 2 d c d c o 1 2 5 7 3

[0037] Mode 2: When switching tube S 1 , switching tube S 2 , switching tube S 5 and switching tube S 7 are all turned on, switching tube S 3 , switching tube S 4 switching tube S 6 and switching tube S 8 are both turned off and when the load current is positive, as shown in Figure 3 ; the switching capacitor C 1 is charged to V through the switching tube S 1 , inductor L, diode D 1 and the DC voltage source V dc to form a loop and is charged to V d c . The switching capacitor C 2 is charged to V through the switching tube S 5 , inductor L, diode D 2 and the DC voltage source V d c to form a loop and is charged to V d c . In this mode, the load output voltage is equal to the DC voltage source voltage value, that is, V o = +V d c .

[0038] Mode 3: When switching tube S 2 , switching tube S 4 , switching tube S 5 and switching tube S 7 are all turned on, switching tube S1 、Switching transistor S 3 Switching transistor S 6 and switching transistor S 8 are all turned off and the load current is positive, as shown in Figure 4 ; The switching capacitor C 2 is charged to V 5 through the switching transistor S 2 , inductor L, and diode D d c to form a loop and is charged to V d c . In this mode, the load output voltage is twice the value of the DC voltage source voltage, i.e., V o = +2V d c .

[0039] Mode Four: When the switching transistors S 1 , S 3 , S 5 and S 7 are all turned on, and the switching transistors S 2 , S 4 Switching transistor S 6 and S 8 are all turned off and the load current is negative, as shown in Figure 5 ; The switching capacitor C 1 is charged to V 1 through the switching transistor S1, inductor L, and diode D d c to form a loop and is charged to V d c , and the switching capacitor C 2 is charged to V 2 through the inductor L, diode D d c , switching transistor S3, load, switching transistor S7 and the DC voltage source V d c . In this mode, the two ends of the load are short-circuited, and the load output voltage is zero, i.e., V o = 0

[0040] Mode Five: When the switching transistors S 1 , S 3 , S 5 and S 6 are all turned on, and the switching transistors S 2 , S 4 Switching transistor S 7 and S 8 are all turned off and the load current is negative, as shown in Figure 6 ; The switching capacitor C 1 is charged through the switching transistor S1 , the inductor L and the diode D 1 form a loop with the DC voltage source V d c and are charged to V d c , the switched capacitor C 2 is connected through the switching transistor S 5 , the inductor L and the diode D 2 to form a loop with the DC voltage source V d c and are charged to V d c . In this mode, the load output voltage is negative one times the DC voltage source voltage value, i.e., V o = -V d c

[0041] Mode six: When the switching transistors S 1 , S 3 , S 6 and S 8 are all conducting, and the switching transistors S 2 , S 4 and S 5 and S 7 are all turned off and the load current is negative, as shown in Figure 7 ; the switched capacitor C 1 is connected through the switching transistor S 1 , the inductor L, the diode D1 and the DC voltage source Vdc to form a loop and is charged to V d c . In this mode, the load output voltage is negative two times the DC voltage source voltage value, i.e., V o = -2V d c .

[0042] In summary, the present invention controls different switching state combinations of eight power switching transistors in the circuit, and the switched capacitor unit converts a constant DC voltage into a five-level DC voltage, significantly reducing the harmonic content, improving the operating efficiency of the system, and only requiring a single DC voltage source to generate the required multi-level output, achieving a two-fold boost function and not requiring capacitor voltage regulation. Therefore, the invention has a simple structure, flexible control, and is beneficial to improving the power density

[0043] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within 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 Vdc, eight power switch tubes, diodes D1 and D2, switch capacitors C1 and C2, an inductor L and a load; the eight power switch tubes are respectively denoted as 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; the AC output voltage of the inverter is denoted as the load voltage Vo; One end of the switch capacitor C1 is respectively connected to the emitter of the switch tube S3, the emitter of the switch tube S4 and the collector of the switch tube S1, and the other end is connected to the cathode of the diode D1 and the collector of the switch tube S2; one end of the switch capacitor C2 is respectively connected to the emitter of the switch tube S7, the emitter of the switch tube S8 and the collector of the switch tube S5, and the other end is connected to the cathode of the diode D2 and the collector of the switch tube S6; one end of the inductor L is respectively connected to the anode of the diode D1 and the anode of the diode D2, and the other end is respectively connected to the collector of the switch tube S4, the collector of the switch tube S8 and the positive electrode of the DC voltage source Vdc; 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 negative electrode of the DC voltage source Vdc is connected to the emitter of the switch tube S1 and the emitter of the switch tube S5.

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 charged to Vdc through a loop formed by the inductor L, the diode D1, the switch tube S3, the load, the switch tube S7 and the DC voltage source Vdc, and the switch capacitor C2 is charged to Vdc through a loop formed by the switch tube S5, the inductor L, the diode D2 and the DC voltage source Vdc. 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 charged to Vdc through a loop formed by the switch tube S1, the inductor L, the diode D1 and the DC voltage source Vdc, and the switch capacitor C2 is charged to Vdc through a loop formed by the switch tube S5, the inductor L, the diode D2 and the DC voltage source Vdc. In this state, the load output voltage is +Vdc.

5. The switched capacitor five-level inverter for photovoltaic grid connection according to claim 1, characterized in that: When the switch tubes S2, S4, S5 and S7 are all turned on, the switch tubes S1, S3, S6 and S8 are all turned off and the load current is positive, the switch capacitor C2 is charged to Vdc through the switch tube S5, the inductor L, the diode D2 and the DC voltage source Vdc to form a loop. In this state, the load output voltage is +2Vdc.

6. 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 negative, the switch capacitor C1 is charged to Vdc through a loop formed by the switch tube S1, the inductor L, the diode D1 and the DC voltage source Vdc, and the switch capacitor C2 is charged to Vdc through a loop formed by the inductor L, the diode D2, the switch tube S3, the load, the switch tube S7 and the DC voltage source Vdc. 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 tubes S1, S3, S5 and S6 are all turned on, the switch tubes S2, S4, S7 and S8 are all turned off and the load current is negative, the switch capacitor C1 is charged to Vdc through a loop formed by the switch tube S1, the inductor L, the diode D1 and the DC voltage source Vdc, and the switch capacitor C2 is charged to Vdc through a loop formed by the switch tube S5, the inductor L, the diode D2 and the DC voltage source Vdc. In this state, the load output voltage is -Vdc.

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 charged to Vdc through the switch tube S1, the inductor L, the diode D1 and the DC voltage source Vdc to form a loop. In this state, the load output voltage is -2Vdc.

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