A five-level photovoltaic grid-connected inverter and system

Abstract

The present application provides a five-level photovoltaic grid-connected inverter and system, the inverter comprising a first half-bridge inverter, a second half-bridge inverter, a third half-bridge inverter, and a controller. The first half-bridge inverter, the second half-bridge inverter, and the third half-bridge inverter have the same structure, each consisting of two power switches and a capacitor. The first half-bridge inverter is connected in series with the second half-bridge inverter. The third half-bridge inverter is connected in series with the seventh power switch. The third half-bridge inverter and the seventh power switch are connected in parallel with the first half-bridge inverter and the second half-bridge inverter. The capacitor is used for voltage division, and the controller controls the turning on and off of the power switches to generate multiple output voltages. The inverter adopts the circuit structure of a series half-bridge inverter and achieves five output voltage levels through seven power switches and three capacitors, reducing the harmonic distortion of the output voltage and improving the power conversion efficiency and output voltage quality.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a five-level photovoltaic grid-connected inverter and system. Background Art

[0002] Photovoltaic systems are a crucial component of distributed power generation in the field of decentralized renewable energy production. A photovoltaic system is a system that utilizes solar energy for power generation, consisting of photovoltaic modules (PV), inverters, grid-connected cabinets, and other electrical equipment. PV modules convert light energy directly into electrical energy through the photovoltaic effect, while inverters convert the direct current (DC) generated by the PV modules into alternating current (AC) for integration into the power grid.

[0003] However, the single-phase inverter structure used in photovoltaic systems leads to low system safety and efficiency. Furthermore, the inverter requires a transformer, which increases its size and weight and introduces energy losses. Furthermore, some inverter structures require complex control systems to achieve stable operation and efficient power conversion. The use of a transformerless H-bridge inverter can cause harmonic distortion in the output voltage, disrupting the power grid and other equipment. It also suffers from low energy conversion efficiency, leading to energy loss and system heat generation. Summary of the Invention

[0004] The present application provides a five-level photovoltaic grid-connected inverter and system to solve the problems of low power conversion efficiency and high harmonic content of the output voltage.

[0005] In a first aspect, the present application provides a five-level photovoltaic grid-connected inverter, comprising a first half-bridge inverter, a second half-bridge inverter, a third half-bridge inverter, and a controller, wherein:

[0006] The first half-bridge inverter includes a first power switch tube, a second power switch tube and a first capacitor; the collector of the first power switch tube is connected to the emitter of the second power switch tube; the collector of the second power switch tube is connected to the positive electrode of the first capacitor; and the negative electrode of the first capacitor is connected to the emitter of the first power switch tube;

[0007] The second half-bridge inverter includes a third power switch tube, a fourth power switch tube and a second capacitor; the collector of the third power switch tube is connected to the positive electrode of the second capacitor; the negative electrode of the second capacitor is connected to the emitter of the fourth power switch tube; the collector of the fourth power switch tube is connected to the emitter of the third power switch tube;

[0008] The third half-bridge inverter includes a fifth power switch tube, a sixth power switch tube, and a third capacitor; the collector of the fifth power switch tube is connected to the positive electrode of the third capacitor; the negative electrode of the third capacitor is connected to the emitter of the sixth power switch tube; and the collector of the sixth power switch tube is connected to the emitter of the fifth power switch tube.

[0009] The first half-bridge inverter and the second half-bridge inverter are connected in series; the third half-bridge inverter and the seventh power switch tube are connected in series; the third half-bridge inverter and the seventh power switch tube are connected in parallel with the first half-bridge inverter and the second half-bridge inverter;

[0010] The first capacitor, the second capacitor and the third capacitor are used for voltage division; the controller is configured to control the opening and closing of the first power switch tube, the second power switch tube, the third power switch tube, the fourth power switch tube, the fifth power switch tube, the sixth power switch tube and the seventh power switch tube to generate multiple output voltages.

[0011] In combination with the first aspect, in an implementable manner, a resistor is further included; a first end of the resistor is connected to the emitter of the fifth power switch tube and the collector of the sixth power switch tube.

[0012] In combination with the first aspect, in one practicable manner, an inductor is further included, wherein a first end of the inductor is connected to a second end of the resistor.

[0013] In combination with the first aspect, in an implementable manner, the collector of the second power switch tube, the positive electrode of the first capacitor, the emitter of the fourth power switch tube, and the negative electrode of the second capacitor are connected;

[0014] The negative electrode of the third capacitor, the emitter of the sixth power switch tube and the emitter of the seventh power switch tube are connected;

[0015] The emitter of the third power switch tube, the collector of the fourth power switch tube, and the collector of the fifth power switch tube are connected to the positive electrode of the third capacitor;

[0016] The collector of the first power switch tube, the emitter of the second power switch tube and the collector of the seventh power switch tube are connected.

[0017] In conjunction with the first aspect, in one practicable manner, the controller is configured to:

[0018] Sending an activation instruction to the first power switch tube, the third power switch tube, the fifth power switch tube, and the seventh power switch tube;

[0019] Sending a shutdown instruction to the second power switch tube, the fourth power switch tube, and the sixth power switch tube so that the five-level photovoltaic grid-connected inverter generates a first output voltage; the first output voltage is equal to the input voltage of the five-level photovoltaic grid-connected inverter.

[0020] In conjunction with the first aspect, in one practicable manner, the controller is configured to:

[0021] Sending an activation instruction to the first power switch tube, the fourth power switch tube, the fifth power switch tube, and the seventh power switch tube;

[0022] Sending a shutdown instruction to the second power switch tube, the third power switch tube, and the sixth power switch tube to enable the five-level photovoltaic grid-connected inverter to generate a second output voltage; the second output voltage is 1 / 2 of the first output voltage;

[0023] or sending an activation instruction to the second power switch tube, the third power switch tube, the fifth power switch tube, and the seventh power switch tube;

[0024] A shutdown instruction is sent to the first power switch tube, the fourth power switch tube, and the sixth power switch tube, so that the five-level photovoltaic grid-connected inverter generates a second output voltage.

[0025] In conjunction with the first aspect, in one practicable manner, the controller is configured to:

[0026] Sending an activation instruction to the second power switch tube, the fourth power switch tube, and the fifth power switch tube;

[0027] Sending a shutdown instruction to the first power switch tube, the third power switch tube, the sixth power switch tube, and the seventh power switch tube, so that the five-level photovoltaic grid-connected inverter generates a third output voltage; the third output voltage is a reference zero level;

[0028] or sending an activation instruction to the first power switch tube, the third power switch tube, and the sixth power switch tube;

[0029] Sending a shutdown instruction to the second power switch tube, the fourth power switch tube, the fifth power switch tube, and the seventh power switch tube, so that the five-level photovoltaic grid-connected inverter generates a third output voltage.

[0030] In conjunction with the first aspect, in one practicable manner, the controller is configured to:

[0031] Sending an activation instruction to the first power switch tube, the fourth power switch tube, and the sixth power switch tube;

[0032] Sending a shutdown instruction to the second power switch tube, the third power switch tube, the fifth power switch tube, and the seventh power switch tube, so that the five-level photovoltaic grid-connected inverter generates a fourth output voltage; the fourth output voltage is the inverse of the second output voltage;

[0033] or sending an activation instruction to the second power switch tube, the third power switch tube, and the sixth power switch tube;

[0034] Sending a shutdown instruction to the first power switch tube, the fourth power switch tube, the fifth power switch tube, and the seventh power switch tube, so that the five-level photovoltaic grid-connected inverter generates a fourth output voltage.

[0035] In conjunction with the first aspect, in one practicable manner, the controller is configured to:

[0036] Sending an activation instruction to the second power switch tube, the fourth power switch tube, and the sixth power switch tube;

[0037] Sending a shutdown instruction to the first power switch tube, the third power switch tube, the fifth power switch tube, and the seventh power switch tube so that the five-level photovoltaic grid-connected inverter generates a fifth output voltage; the fifth output voltage is the inverse of the first output voltage.

[0038] In a second aspect, the present application provides a five-level photovoltaic grid-connected system, comprising an input voltage source, a power grid, and the above-mentioned five-level photovoltaic grid-connected inverter, wherein the input voltage source and the power grid are connected to the five-level photovoltaic grid-connected inverter.

[0039] As can be seen from the above technical solutions, some embodiments of the present application provide a five-level photovoltaic grid-connected inverter and system, wherein the inverter includes a first half-bridge inverter, a second half-bridge inverter, a third half-bridge inverter, and a controller. The first half-bridge inverter, the second half-bridge inverter, and the third half-bridge inverter have the same structure, each consisting of two power switches and a capacitor. The first half-bridge inverter is connected in series with the second half-bridge inverter. The third half-bridge inverter is connected in series with the seventh power switch. The third half-bridge inverter and the seventh power switch are connected in parallel with the first half-bridge inverter and the second half-bridge inverter. The capacitor is used for voltage division, and the controller controls the turning on and off of the power switches to generate multiple output voltages. The inverter adopts the circuit structure of a series half-bridge inverter and achieves five output voltage levels through seven power switches and three capacitors, reducing the harmonic distortion of the output voltage and improving the power conversion efficiency and output voltage quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0041] Figure 1 A schematic diagram of the topology of a five-level photovoltaic grid-connected inverter provided in an embodiment of the present application;

[0042] Figure 2 A circuit diagram of a first voltage output mode provided in an embodiment of the present application;

[0043] Figure 3 A circuit diagram of the second voltage output mode provided in an embodiment of the present application;

[0044] Figure 4 A circuit diagram of the third voltage output mode provided in an embodiment of the present application;

[0045] Figure 5 A circuit diagram of a fourth voltage output mode provided in an embodiment of the present application;

[0046] Figure 6 A circuit diagram of a fifth voltage output mode provided in an embodiment of the present application;

[0047] Figure 7 A circuit diagram of a sixth voltage output mode provided in an embodiment of the present application;

[0048] Figure 8 A circuit diagram of the seventh voltage output mode provided in an embodiment of the present application;

[0049] Figure 9 This is a circuit diagram of the eighth voltage output mode provided in an embodiment of the present application. DETAILED DESCRIPTION

[0050] In order to make the purpose and implementation of this application clearer, the exemplary implementation of this application will be clearly and completely described below in conjunction with the drawings in the exemplary embodiments of this application. Obviously, the described exemplary embodiments are only part of the embodiments of this application, not all of the embodiments.

[0051] It should be noted that the brief descriptions of terms in this application are only for the purpose of facilitating the understanding of the embodiments described below, and are not intended to limit the embodiments of this application. Unless otherwise specified, these terms should be understood according to their ordinary and usual meanings.

[0052] In the specification and claims of this application and the accompanying drawings, the terms "first," "second," "third," etc. are used to distinguish similar or similar objects or entities, and are not necessarily intended to limit a particular order or sequence, unless otherwise noted. It should be understood that the terms used in this manner are interchangeable under appropriate circumstances.

[0053] Photovoltaic systems are a crucial component of distributed power generation in the field of decentralized renewable energy production. A photovoltaic system is a system that utilizes solar energy for power generation, consisting of photovoltaic modules (PV), inverters, grid-connected cabinets, and other electrical equipment. PV modules convert light energy directly into electrical energy through the photovoltaic effect, while inverters convert the direct current (DC) generated by the PV modules into alternating current (AC) for integration into the power grid.

[0054] Photovoltaic systems are categorized as standalone and grid-connected. The core component of a grid-connected system is the inverter, which serves as the interface between the PV panels and the grid. Inverters are categorized as either isolated or non-isolated. Isolation inverters utilize a low-frequency transformer on the AC side or a high-frequency transformer on the DC side. However, isolation transformers negatively impact the efficiency of the DC-to-AC conversion process in grid-connected systems.

[0055] In some embodiments, to address these issues, a transformerless inverter with lower cost, smaller size, lighter weight, and higher efficiency is introduced. The transformerless inverter can be an H-bridge inverter (a two-level inverter). However, the H-bridge inverter topology is less efficient at high power conversion and high frequency operation, and the output voltage has high harmonic content, which limits the inverter's efficiency and power quality.

[0056] In some embodiments, to overcome the limitations of the aforementioned inverters, a multi-level inverter topology may be employed. Multi-level inverters can achieve more efficient power conversion and lower harmonic content by increasing voltage levels and changing switching methods.

[0057] Based on the above embodiments, it can be seen that a single-phase inverter structure will lead to low system safety and efficiency. In addition, the inverter requires the use of a transformer, which increases the size and weight of the inverter and introduces energy loss. In addition, some inverter structures require complex control systems to achieve stable operation and efficient power conversion. The use of a transformerless H-bridge inverter may cause harmonic distortion of the output voltage, causing interference to the power grid and other equipment, and there is a problem of low energy conversion efficiency, resulting in energy loss and heat generation in the system. This limits the performance and reliability of inverter technology.

[0058] In order to solve the limitations of the inverter topology and improve the efficiency and quality of power conversion, some embodiments of the present application provide a five-level photovoltaic grid-connected inverter, which improves the efficiency of the grid-connected system by reducing the stress voltage and number of components of the switch. By connecting the half-bridge inverter in series, the input capacitance is halved to limit the stress voltage of the power switch to half of the input voltage. The use of multi-level output can effectively reduce harmonic distortion and improve the quality of the output current. And because it is a transformerless design, it can reduce leakage current problems, improve the safety and stability of the system, and the overall design is more compact, reducing the size and weight of the inverter.

[0059] like Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of a five-level photovoltaic grid-connected inverter provided in an embodiment of the present application. The inverter includes a first half-bridge inverter, a second half-bridge inverter, a third half-bridge inverter, and a controller. The first, second, and third half-bridge inverters have identical structures, each consisting of two power switches and a capacitor.

[0060] like Figure 1 As shown, the first half-bridge inverter includes a first power switch S1, a second power switch S2, and a first capacitor C1. The collector of the first power switch S1 is connected to the emitter of the second power switch S2. The collector of the second power switch S2 is connected to the positive electrode of the first capacitor C1. The negative electrode of the first capacitor C1 is connected to the emitter of the first power switch S1.

[0061] The second half-bridge inverter includes a third power switch S3, a fourth power switch S4, and a second capacitor C2. The collector of the third power switch S3 is connected to the positive electrode of the second capacitor C2. The negative electrode of the second capacitor C2 is connected to the emitter of the fourth power switch S4. The collector of the fourth power switch S4 is connected to the emitter of the third power switch S3.

[0062] The third half-bridge inverter includes a fifth power switch S5, a sixth power switch S6, and a third capacitor C3. The collector of the fifth power switch S5 is connected to the positive electrode of the third capacitor C3. The negative electrode of the third capacitor C3 is connected to the emitter of the sixth power switch S6. The collector of the sixth power switch S6 is connected to the emitter of the fifth power switch S5.

[0063] The first half-bridge inverter is connected in series with the second half-bridge inverter. The third half-bridge inverter is connected in series with the seventh power switch tube S7. The third half-bridge inverter and the seventh power switch tube S7 are connected in parallel with the first half-bridge inverter and the second half-bridge inverter. Figure 1As shown, the collector of the second power switch tube S2, the positive electrode of the first capacitor C1, and the emitter of the fourth power switch tube S4 are connected to the negative electrode of the second capacitor C2. The negative electrode of the third capacitor C3, the emitter of the sixth power switch tube S6, and the emitter of the seventh power switch tube S7 are connected. The emitter of the third power switch tube S3, the collector of the fourth power switch tube S4, and the collector of the fifth power switch tube S5 are connected to the positive electrode of the third capacitor C3. The collector of the first power switch tube S1, the emitter of the second power switch tube S2, and the collector of the seventh power switch tube S7 are connected.

[0064] In the inverter topology, capacitors are used for voltage division, and the half-bridge inverter structure enables the inverter to generate multiple different voltage levels, thereby reducing the pressure and power consumption of the switching devices, reducing the harmonic content of the output voltage, improving the power quality, and increasing the service life of the inverter.

[0065] Based on the inverter topology, the five-level photovoltaic grid-connected inverter includes eight voltage output modes: the first voltage output mode, the second voltage output mode, the third voltage output mode, the fourth voltage output mode, the fifth voltage output mode, the sixth voltage output mode, the seventh voltage output mode, and the eighth voltage output mode. The following table shows the corresponding relationship between the on / off state of each power switch and the voltage output mode:

[0066]

[0067] In the table above, the five-level photovoltaic grid-connected inverter includes 8 voltage output modes and can generate five output levels, namely the first output voltage: +V dc , Second output voltage: The third output voltage: 0, the fourth output voltage: Fifth output voltage: -V dc Among them, "1" indicates that the power switch tube Sx is turned on, and "0" indicates that the power switch tube Sx is turned off. Among them, x = 1, 2, 3, 4, 5, 6, 7, respectively represent seven power switch tubes. V dc is the input voltage of the five-level photovoltaic grid-connected inverter, V out is the output voltage generated by the five-level photovoltaic grid-connected inverter.

[0068] In the first voltage output mode, the first power switch tube S1, the third power switch tube S3, the fifth power switch tube S5 and the seventh power switch tube S7 are turned on; the second power switch tube S2, the fourth power switch tube S4 and the sixth power switch tube S6 are turned off, and the five-level photovoltaic grid-connected inverter generates a first output voltage, i.e., V out +V dc The circuit diagram in the first voltage output mode is as follows: Figure 2 shown.

[0069] In the first voltage output mode, the first power switch tube S1, the fourth power switch tube S4, the fifth power switch tube S5 and the seventh power switch tube S7 are turned on; the second power switch tube S2, the third power switch tube S3 and the sixth power switch tube S6 are turned off, and the five-level photovoltaic grid-connected inverter generates a second output voltage, namely V out for The circuit diagram in the second voltage output mode is as follows Figure 3 shown.

[0070] In the third voltage output mode, the second power switch tube S2, the third power switch tube S3, the fifth power switch tube S5 and the seventh power switch tube S7 are turned on; the first power switch tube S1, the fourth power switch tube S4 and the sixth power switch tube S6 are turned off, and the five-level photovoltaic grid-connected inverter generates a second output voltage, namely V out for The circuit diagram in the third voltage output mode is as follows Figure 4 shown.

[0071] In the fourth voltage output mode, the second power switch tube S2, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on; the first power switch tube S1, the third power switch tube S3, the sixth power switch tube S6 and the seventh power switch tube S7 are turned off, and the five-level photovoltaic grid-connected inverter generates a third output voltage, namely V out =0, the circuit diagram in the fourth voltage output mode is as follows Figure 5 shown.

[0072] In the fifth voltage output mode, the first power switch tube S1, the third power switch tube S3, and the sixth power switch tube S6 are turned on; the second power switch tube S2, the fourth power switch tube S4, the fifth power switch tube S5, and the seventh power switch tube S7 are turned off, and the five-level photovoltaic grid-connected inverter generates a third output voltage, namely V out is 0, the circuit diagram in the fifth voltage output mode is as follows Figure 6 shown.

[0073] In the sixth voltage output mode, the first power switch tube S1, the fourth power switch tube S4, and the sixth power switch tube S6 are turned on; the second power switch tube S2, the third power switch tube S3, the fifth power switch tube S5, and the seventh power switch tube S7 are turned off, and the five-level photovoltaic grid-connected inverter generates a fourth output voltage, namely V out for The circuit diagram in the sixth voltage output mode is as follows Figure 7 shown.

[0074] In the seventh voltage output mode, the second power switch tube S2, the third power switch tube S3 and the sixth power switch tube S6 are turned on; the first power switch tube S1, the fourth power switch tube S4, the fifth power switch tube S5 and the seventh power switch tube S7 are turned off, and the five-level photovoltaic grid-connected inverter generates a fourth output voltage, namely V out for The circuit diagram in the seventh voltage output mode is as follows Figure 8 shown.

[0075] In the eighth voltage output mode, the second power switch tube S2, the fourth power switch tube S4, and the sixth power switch tube S6 are turned on; the first power switch tube S1, the third power switch tube S3, the fifth power switch tube S5, and the seventh power switch tube S7 are turned off, and the five-level photovoltaic grid-connected inverter generates a fifth output voltage, namely V out -V dc The circuit diagram in the eighth voltage output mode is as follows: Figure 9 shown.

[0076] It should be noted that Figure 2-Figure 9 The circuit diagrams respectively represent 8 voltage output modes. The circuit in the dotted part indicates that when the power switch tube located in the dotted part of the circuit is turned off, the dotted part of the circuit forms an open circuit and current cannot flow through the dotted part of the circuit.

[0077] Thus, the controller can control the opening and closing of the first power switch tube S1, the second power switch tube S2, the third power switch tube S3, the fourth power switch tube S4, the fifth power switch tube S5, the sixth power switch tube S6, and the seventh power switch tube S7 to generate multiple output voltages. The controller can be configured as follows:

[0078] An on instruction is sent to the first power switch tube S1, the third power switch tube S3, the fifth power switch tube S5, and the seventh power switch tube S7; and a off instruction is sent to the second power switch tube S2, the fourth power switch tube S4, and the sixth power switch tube S6, so that the five-level photovoltaic grid-connected inverter generates a first output voltage.

[0079] Or send an opening instruction to the first power switch tube S1, the fourth power switch tube S4, the fifth power switch tube S5 and the seventh power switch tube S7; send a closing instruction to the second power switch tube S2, the third power switch tube S3 and the sixth power switch tube S6, so that the five-level photovoltaic grid-connected inverter generates a second output voltage.

[0080] Or send an opening instruction to the second power switch tube S2, the third power switch tube S3, the fifth power switch tube S5 and the seventh power switch tube S7; send a closing instruction to the first power switch tube S1, the fourth power switch tube S4 and the sixth power switch tube S6, so that the five-level photovoltaic grid-connected inverter generates a second output voltage.

[0081] Or send an opening instruction to the second power switch tube S2, the fourth power switch tube S4 and the fifth power switch tube S5; send a closing instruction to the first power switch tube S1, the third power switch tube S3, the sixth power switch tube S6 and the seventh power switch tube S7, so that the five-level photovoltaic grid-connected inverter generates a third output voltage.

[0082] Or send an opening instruction to the first power switch tube S1, the third power switch tube S3 and the sixth power switch tube S6; send a closing instruction to the second power switch tube S2, the fourth power switch tube S4, the fifth power switch tube S5 and the seventh power switch tube S7, so that the five-level photovoltaic grid-connected inverter generates a third output voltage.

[0083] Or send an opening instruction to the first power switch tube S1, the fourth power switch tube S4 and the sixth power switch tube S6; send a closing instruction to the second power switch tube S2, the third power switch tube S3, the fifth power switch tube S5 and the seventh power switch tube S7, so that the five-level photovoltaic grid-connected inverter generates a fourth output voltage.

[0084] Or send an opening instruction to the second power switch tube S2, the third power switch tube S3 and the sixth power switch tube S6; send a closing instruction to the first power switch tube S1, the fourth power switch tube S4, the fifth power switch tube S5 and the seventh power switch tube S7, so that the five-level photovoltaic grid-connected inverter generates a fourth output voltage.

[0085] Or send an opening instruction to the second power switch tube S2, the fourth power switch tube S4 and the sixth power switch tube S6; send a shutdown instruction to the first power switch tube S1, the third power switch tube S3, the fifth power switch tube S5 and the seventh power switch tube S7, so that the five-level photovoltaic grid-connected inverter generates a fifth output voltage.

[0086] In some embodiments, the five-level photovoltaic grid-connected inverter further includes a resistor R, a first end of which is connected to the emitter of the fifth power switch S5 and the collector of the sixth power switch S6. The resistor R can be used to limit the flow of current in the circuit.

[0087] In some embodiments, the five-level photovoltaic grid-connected inverter further includes an inductor L, wherein a first end of the inductor L is connected to a second end of the resistor R. The inductor L is a component that stores energy in a magnetic field and is used for filtering and tuning of the circuit.

[0088] The topological circuit structure of the five-level photovoltaic grid-connected inverter provided in the embodiment of the present application connects capacitors for voltage division. By using two half-bridge inverters in series, the input capacitance is halved, limiting the stress voltage of the power switch to half of the input voltage. This means that low input voltage can be used while maintaining high conversion efficiency. Five output voltage levels are achieved by using seven power switches and three capacitors, and fewer power switches and capacitors are used to achieve a five-level output, thereby reducing the complexity and cost of the system and enabling the system to have higher output voltage quality and lower harmonic distortion.

[0089] This inverter topology evenly distributes voltage stress across the power switches, reducing switching losses and improving system efficiency and reliability. Furthermore, the transformerless design reduces leakage current and associated losses, reducing the size and weight of the inverter and ultimately improving DC-to-AC conversion efficiency.

[0090] In addition, it should be noted that the power switching tubes described in the embodiments of the present application are all power electronic switching tubes, and the different characteristic names are only used for differentiation. Moreover, the embodiments of the present application do not limit the specific implementation of the power electronic switching tube. For example, the power electronic switching tube can be an insulated gate bipolar transistor (IGBT).

[0091] Based on the above-mentioned five-level photovoltaic grid-connected inverter, some embodiments of the present application further provide a five-level photovoltaic grid-connected system, comprising an input voltage source, a power grid, and the five-level photovoltaic grid-connected inverter described in the above-mentioned embodiment. The input voltage source and the power grid are connected to the five-level photovoltaic grid-connected inverter.

[0092] In a photovoltaic system, the input voltage source is the photovoltaic module (PV) used to convert light energy into electrical energy in the photovoltaic system. Figure 1 in,i pv and i g is the current identifier in the circuit, i pv Indicates the current generated by the photovoltaic module. g Indicates the current after passing through the five-level photovoltaic grid-connected inverter.

[0093] like Figure 1As shown, the five-level photovoltaic grid-connected inverter includes a first half-bridge inverter, a second half-bridge inverter, a third half-bridge inverter, a resistor R, an inductor L, and a controller. The first half-bridge inverter includes a first power switch S1, a second power switch S2, and a first capacitor C1. The collector of the first power switch S1 is connected to the emitter of the second power switch S2. The collector of the second power switch S2 is connected to the positive electrode of the first capacitor C1. The negative electrode of the first capacitor C1 is connected to the emitter of the first power switch S1.

[0094] The second half-bridge inverter includes a third power switch S3, a fourth power switch S4, and a second capacitor C2. The collector of the third power switch S3 is connected to the positive electrode of the second capacitor C2. The negative electrode of the second capacitor C2 is connected to the emitter of the fourth power switch S4. The collector of the fourth power switch S4 is connected to the emitter of the third power switch S3.

[0095] The third half-bridge inverter includes a fifth power switch S5, a sixth power switch S6, and a third capacitor C3. The collector of the fifth power switch S5 is connected to the positive electrode of the third capacitor C3. The negative electrode of the third capacitor C3 is connected to the emitter of the sixth power switch S6. The collector of the sixth power switch S6 is connected to the emitter of the fifth power switch S5.

[0096] The collector of the second power switch tube S2, the positive electrode of the first capacitor C1, and the emitter of the fourth power switch tube S4 are connected to the negative electrode of the second capacitor C2. The negative electrode of the third capacitor C3, the emitter of the sixth power switch tube S6, and the emitter of the seventh power switch tube S7 are connected. The emitter of the third power switch tube S3, the collector of the fourth power switch tube S4, and the collector of the fifth power switch tube S5 are connected to the positive electrode of the third capacitor C3. The collector of the first power switch tube S1, the emitter S2 of the second power switch tube, and the collector of the seventh power switch tube S7 are connected.

[0097] The first end of resistor R is connected to the emitter of the fifth power switch S5 and the collector of the sixth power switch S6. The second end of resistor R is connected to the first end of inductor L. The second end of inductor L is connected to the first port of power grid Vg. The collector of first power switch S1, the emitter of second power switch S2, and the collector of seventh power switch S7 are connected to the second port of power grid Vg. The negative electrode of first capacitor C1 is connected to the negative electrode of input voltage source. The positive electrode of second capacitor C2 is connected to the positive electrode of input voltage source.

[0098] As can be seen from the above technical solutions, some embodiments of the present application provide a five-level photovoltaic grid-connected inverter and system, wherein the inverter includes a first half-bridge inverter, a second half-bridge inverter, a third half-bridge inverter, and a controller. The first half-bridge inverter, the second half-bridge inverter, and the third half-bridge inverter have the same structure, each consisting of two power switches and a capacitor. The first half-bridge inverter is connected in series with the second half-bridge inverter. The third half-bridge inverter is connected in series with the seventh power switch. The third half-bridge inverter and the seventh power switch are connected in parallel with the first half-bridge inverter and the second half-bridge inverter. The capacitor is used for voltage division, and the controller controls the turning on and off of the power switches to generate multiple output voltages. The inverter adopts the circuit structure of a series half-bridge inverter and achieves five output voltage levels through seven power switches and three capacitors, reducing the harmonic distortion of the output voltage and improving the power conversion efficiency and output voltage quality.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0100] For ease of explanation, the above description has been made with reference to specific embodiments. However, the above exemplary discussion is not intended to be exhaustive or to limit the embodiments to the specific forms disclosed above. Based on the above teachings, various modifications and variations are possible. The above embodiments are selected and described to better explain the principles and practical applications, so that those skilled in the art can better utilize the embodiments and various different variations of the embodiments suitable for specific use considerations.

Claims

1. A five-level photovoltaic grid-connected inverter, characterized in that: The invention comprises a first half-bridge inverter, a second half-bridge inverter, a third half-bridge inverter and a controller, wherein: The first half-bridge inverter includes a first power switch tube, a second power switch tube and a first capacitor; the collector of the first power switch tube is connected to the emitter of the second power switch tube; the collector of the second power switch tube is connected to the positive electrode of the first capacitor; and the negative electrode of the first capacitor is connected to the emitter of the first power switch tube; The second half-bridge inverter includes a third power switch tube, a fourth power switch tube and a second capacitor; the collector of the third power switch tube is connected to the positive electrode of the second capacitor; the negative electrode of the second capacitor is connected to the emitter of the fourth power switch tube; the collector of the fourth power switch tube is connected to the emitter of the third power switch tube; The third half-bridge inverter includes a fifth power switch tube, a sixth power switch tube, and a third capacitor; the collector of the fifth power switch tube is connected to the positive electrode of the third capacitor; the negative electrode of the third capacitor is connected to the emitter of the sixth power switch tube; and the collector of the sixth power switch tube is connected to the emitter of the fifth power switch tube. The first half-bridge inverter and the second half-bridge inverter are connected in series; the third half-bridge inverter and the seventh power switch tube are connected in series; the third half-bridge inverter and the seventh power switch tube are connected in parallel with the first half-bridge inverter and the second half-bridge inverter; The collector of the first power switch tube, the emitter of the second power switch tube and the collector of the seventh power switch tube are connected; The emitter of the fifth power switch tube and the collector of the sixth power switch tube are connected to the first port of the power grid; the collector of the first power switch tube, the emitter of the second power switch tube, and the collector of the seventh power switch tube are connected to the second port of the power grid; The first capacitor, the second capacitor and the third capacitor are used for voltage division; the controller is configured to control the opening and closing of the first power switch tube, the second power switch tube, the third power switch tube, the fourth power switch tube, the fifth power switch tube, the sixth power switch tube and the seventh power switch tube to generate multiple output voltages.

2. The five-level photovoltaic grid-connected inverter according to claim 1, characterized in that: It also includes a resistor; a first end of the resistor is connected to the emitter of the fifth power switch tube and the collector of the sixth power switch tube.

3. The five-level photovoltaic grid-connected inverter according to claim 2, characterized in that: An inductor is also included, wherein a first end of the inductor is connected to the second end of the resistor.

4. The five-level photovoltaic grid-connected inverter according to claim 1, characterized in that: The collector of the second power switch tube, the positive electrode of the first capacitor, the emitter of the fourth power switch tube and the negative electrode of the second capacitor are connected; The negative electrode of the third capacitor, the emitter of the sixth power switch tube and the emitter of the seventh power switch tube are connected; The emitter of the third power switch tube, the collector of the fourth power switch tube, and the collector of the fifth power switch tube are connected to the positive electrode of the third capacitor.

5. The five-level photovoltaic grid-connected inverter according to claim 1, characterized in that: The controller is configured to: Sending an activation instruction to the first power switch tube, the third power switch tube, the fifth power switch tube, and the seventh power switch tube; Sending a shutdown instruction to the second power switch tube, the fourth power switch tube, and the sixth power switch tube so that the five-level photovoltaic grid-connected inverter generates a first output voltage; the first output voltage is equal to the input voltage of the five-level photovoltaic grid-connected inverter.

6. The five-level photovoltaic grid-connected inverter according to claim 5, characterized in that: The controller is configured to: Sending an activation instruction to the first power switch tube, the fourth power switch tube, the fifth power switch tube, and the seventh power switch tube; Sending a shutdown instruction to the second power switch tube, the third power switch tube, and the sixth power switch tube to enable the five-level photovoltaic grid-connected inverter to generate a second output voltage; the second output voltage is 1 / 2 of the first output voltage; or sending an activation instruction to the second power switch tube, the third power switch tube, the fifth power switch tube, and the seventh power switch tube; A shutdown instruction is sent to the first power switch tube, the fourth power switch tube, and the sixth power switch tube, so that the five-level photovoltaic grid-connected inverter generates a second output voltage.

7. The five-level photovoltaic grid-connected inverter according to claim 5, characterized in that: The controller is configured to: Sending an activation instruction to the second power switch tube, the fourth power switch tube, and the fifth power switch tube; Sending a shutdown instruction to the first power switch tube, the third power switch tube, the sixth power switch tube, and the seventh power switch tube, so that the five-level photovoltaic grid-connected inverter generates a third output voltage; the third output voltage is a reference zero level; or sending an activation instruction to the first power switch tube, the third power switch tube, and the sixth power switch tube; Sending a shutdown instruction to the second power switch tube, the fourth power switch tube, the fifth power switch tube, and the seventh power switch tube, so that the five-level photovoltaic grid-connected inverter generates a third output voltage.

8. The five-level photovoltaic grid-connected inverter according to claim 6, characterized in that: The controller is configured to: Sending an activation instruction to the first power switch tube, the fourth power switch tube, and the sixth power switch tube; Sending a shutdown instruction to the second power switch tube, the third power switch tube, the fifth power switch tube, and the seventh power switch tube, so that the five-level photovoltaic grid-connected inverter generates a fourth output voltage; the fourth output voltage is the inverse of the second output voltage; or sending an activation instruction to the second power switch tube, the third power switch tube, and the sixth power switch tube; Sending a shutdown instruction to the first power switch tube, the fourth power switch tube, the fifth power switch tube, and the seventh power switch tube, so that the five-level photovoltaic grid-connected inverter generates a fourth output voltage.

9. The five-level photovoltaic grid-connected inverter according to claim 5, characterized in that: The controller is configured to: Sending an activation instruction to the second power switch tube, the fourth power switch tube, and the sixth power switch tube; Sending a shutdown instruction to the first power switch tube, the third power switch tube, the fifth power switch tube, and the seventh power switch tube so that the five-level photovoltaic grid-connected inverter generates a fifth output voltage; the fifth output voltage is the inverse of the first output voltage.

10. A five-level photovoltaic grid-connected system, characterized in that: The system comprises an input voltage source, a power grid and the five-level photovoltaic grid-connected inverter according to any one of claims 1 to 9, wherein the input voltage source and the power grid are connected to the five-level photovoltaic grid-connected inverter.

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