A five-level grid-connected inverter structure, inverter and photovoltaic power supply system

Abstract

The present invention discloses a five-level grid-connected inverter structure, an inverter and a photovoltaic power supply system, and belongs to the field of inverter circuit topology. The inverter circuit includes a DC source, an inverter network, an AC filter and an external AC source, the positive pole of the DC source is connected to the input end of the inverter network, the output end of the inverter network is connected to the input end of the AC filter, the output end of the AC filter is connected to one end of the external AC source, the other end of the external AC source is grounded, the negative pole of the DC source, the ground end of the inverter network and the ground end of the AC filter network are all grounded, and the driving signal of the power switch tube of the single-phase common ground type five-level inverter circuit is generated by comparing the modulation wave and the carrier. The inverter circuit of the present invention has the characteristics of low differential mode voltage harmonic content and complete elimination of leakage current, and is suitable for small and medium power non-isolated photovoltaic grid-connected inverter system applications.

Description

Technical Field

[0001] The invention relates to the field of inverter circuit topology, and in particular to a five-level grid-connected inverter structure, an inverter and a photovoltaic power supply system. Background Art

[0002] Solar energy is a very important component of clean and renewable energy, and distributed photovoltaic power generation is playing an increasingly important role as an important component of the power grid. However, there is a large parasitic capacitance between the photovoltaic panel and the ground, and the common-mode leakage current generated is large, which not only reduces the system efficiency, but also may affect the safety of personnel and equipment. The common ground structure that directly connects the neutral point of the grid to the positive or negative pole of the input voltage can short-circuit the parasitic capacitance and completely eliminate the leakage current. Since the output voltage of the photovoltaic panel needs to match the peak voltage of the grid through the inverter circuit; in addition, improving the power quality by increasing the number of output voltage levels has become another major measure for non-isolated inverter circuits, which helps to integrate smaller AC filters. Therefore, the step-down characteristics of the inverter circuit output voltage and the leakage current generated are the two main disadvantages of the current non-isolated inverter circuit. In addition, when the output voltage of the inverter circuit is three-level, a larger AC filter needs to be configured to improve the power quality of the injected grid current. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention proposes a five-level grid-connected inverter structure, an inverter and a photovoltaic power supply system.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A five-level grid-connected inverter structure, characterized by comprising: an inverter network and an AC filter;

[0006] The input end of the inverter network is connected to the positive pole of the DC source; the output end of the inverter network is connected to the input end of the AC filter; the output end of the AC filter is connected to one end of the external AC source, and the other end of the external AC source is grounded; the negative pole of the DC source, the ground end of the inverter network and the ground end of the AC filter are all grounded;

[0007] The inverter network includes a first power switch tube, a second power switch tube, a third power switch tube, a fourth power switch tube, a fifth power switch tube, a sixth power switch tube, a seventh power switch tube, an eighth power switch tube, a ninth power switch tube, a first capacitor and a second capacitor;

[0008] The drain of the first power switch tube is connected to the drain of the second power switch tube; the source of the first power switch tube and the drain of the fifth power switch tube are connected to the positive electrode of the first capacitor; the source of the second power switch tube, the drain of the third power switch tube, and the source of the fourth power switch tube are connected to the negative electrode of the first capacitor;

[0009] The source of the fifth power switch tube and the drain of the sixth power switch tube are connected to the drain of the seventh power switch tube; the drain of the fourth power switch tube is connected to the positive electrode of the second capacitor; the source of the eighth power switch tube and the ninth power switch tube are connected to the negative electrode of the second capacitor; the source of the sixth power switch tube is connected to the drain of the eighth power switch tube;

[0010] The drain of the first power switch tube is the input end of the inverter network and is connected to the positive electrode of the DC source; the source of the sixth power switch tube and the drain of the eighth power switch tube are both output ends of the inverter network; the source of the third power switch tube, the source of the seventh power switch tube and the drain of the ninth power switch tube are all the ground end of the inverter network and are connected to the negative electrode of the DC source.

[0011] Furthermore, the second power switch tube, the fourth power switch tube, the fifth power switch tube, the sixth power switch tube, the seventh power switch tube, the eighth power switch tube and the ninth power switch tube are all composed of a power transistor and an anti-parallel diode, the drain or collector of the power transistor is connected to the cathode of the anti-parallel diode to form the drain of the power switch tube, and the source or emitter of the power transistor is connected to the anode of the anti-parallel diode to form the source of the power switch tube.

[0012] Furthermore, the first power switch tube and the third power switch tube are a series structure in which a source of a power switch tube without an anti-parallel diode or a power switch tube with an anti-parallel diode is connected to an anode of the power switch tube.

[0013] Furthermore, the AC filter includes a filter inductor and a filter capacitor, one end of the filter inductor is the input end of the AC filter network, the other end of the filter inductor is connected to the positive electrode of the filter capacitor, the connection point between the filter inductor and the filter capacitor is the output end of the AC filter, and the negative electrode of the filter capacitor is the ground terminal of the AC filter.

[0014] Furthermore, the driving signal of the power switch tube of the inverter network is generated by modulation of a modulation wave and a high-frequency carrier, the modulation wave is an industrial frequency of 50 Hz, and the frequency of the carrier is 100 kHz.

[0015] Furthermore, the five-level grid-connected inverter structure includes the following working modes:

[0016] Mode 1: the output voltage of the inverter network is equal to the DC source, the first power switch tube, the third power switch tube, the fifth power switch tube and the sixth power switch tube are turned on; the second power switch tube, the fourth power switch tube, the seventh power switch tube, the eighth power switch tube and the ninth power switch tube are turned off;

[0017] Mode 2: the output voltage of the inverter network is equal to twice the DC source, the second power switch tube, the fourth power switch tube, the fifth power switch tube, the sixth power switch tube and the ninth power switch tube are turned on; the first power switch tube, the third power switch tube, the seventh power switch tube and the eighth power switch tube are turned off;

[0018] Mode three: the output voltage of the inverter network is equal to 0, the first power switch tube, the third power switch tube, the eighth power switch tube and the ninth power switch tube are turned on; the second power switch tube, the fourth power switch tube, the fifth power switch tube, the sixth power switch tube and the seventh power switch tube are turned off;

[0019] Mode 4: the output voltage of the inverter network is equal to 0; the second power switch tube, the fourth power switch tube, the eighth power switch tube and the ninth power switch tube are turned on; the first power switch tube, the third power switch tube, the fifth power switch tube, the sixth power switch tube and the seventh power switch tube are turned off;

[0020] Mode 5: the output voltage of the inverter network is equal to negative one times the DC source; the first power switch tube, the third power switch tube, the fourth power switch tube and the eighth power switch tube are turned on; the second power switch tube, the fifth power switch tube, the sixth power switch tube, the seventh power switch tube and the ninth power switch tube are turned off;

[0021] Mode six: the output voltage of the inverter network is equal to twice the DC source; the fourth power switch tube, the fifth power switch tube, the seventh power switch tube and the eighth power switch tube are turned on; the first power switch tube, the second power switch tube, the third power switch tube, the sixth power switch tube and the ninth power switch tube are disconnected.

[0022] The present invention also provides an inverter, comprising the five-level grid-connected inverter structure as described in any one of the above items.

[0023] The present invention also provides a photovoltaic power supply system, comprising:

[0024] A photoelectric device, the photoelectric device being used as a DC power source for outputting a DC voltage;

[0025] AC distribution network;

[0026] As for the inverter as described above, the input end of the inverter is connected to the photovoltaic device, the output end of the inverter is connected to the AC power distribution network, and the inverter is used to convert the DC voltage into AC voltage and output it to the AC power distribution network.

[0027] Beneficial effects of the present invention:

[0028] The inverter circuit of the present invention clamps the voltage on the parasitic capacitor between the photovoltaic panel and the ground at 0 through a common ground structure, which can completely eliminate the leakage current in the non-isolated grid-connected inverter system; the inverter circuit of the present invention can output a five-level voltage, reduce the volume of the AC filter, the grid-connected current harmonics, and realize the boost function; the inverter circuit of the present invention has the ability to transmit reactive power to the power grid, and is suitable for the application of small and medium power non-isolated photovoltaic grid-connected inverter systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] Figure 1 It is a structural schematic diagram of the inverter circuit of the present invention;

[0031] Figure 2 It is a schematic diagram of the power switch tube driving signal of the inverter circuit of the present invention;

[0032] Figure 3 It is a schematic diagram of the inverter circuit mode 1 of the present invention;

[0033] Figure 4 It is a schematic diagram of the second mode of the inverter circuit of the present invention;

[0034] Figure 5 It is a schematic diagram of the inverter circuit mode 3 of the present invention;

[0035] Figure 6 It is a schematic diagram of the fourth mode of the inverter circuit of the present invention;

[0036] Figure 7 It is a schematic diagram of the fifth mode of the inverter circuit of the present invention;

[0037] Figure 8 It is a schematic diagram of the inverter circuit mode 6 of the present invention;

[0038] Fig. 9 is the V of the inverter circuit of the present invention in With v ab Waveform diagram of

[0039] Fig.10 is the waveform of the capacitor voltage of the inverter circuit of the present invention;

[0040] Fig.11 is the operating waveform of the inverter circuit of the present invention under the unity power factor;

[0041] Fig.12 It is the operating waveform of the inverter circuit of the present invention when the grid current leads under the non-unity power factor;

[0042] Fig.13 It is the operating waveform of the inverter circuit of the present invention when the grid current lags under the non-unit power factor. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] In the description of the present invention, it should be understood that the terms "opening", "upper", "lower", "thickness", "top", "middle", "length", "inside", "all around" and the like indicating orientation or positional relationship are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0045] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0046] A single-phase common ground type five-level inverter circuit, the inverter circuit includes a DC source, an inverter network, an AC filter and an external AC source, such as Figure 1 As shown, the positive pole of the DC source is connected to the input end of the inverter network, the output end of the inverter network is connected to the input end of the AC filter, the output end of the AC filter is connected to one end of the external AC source, the other end of the external AC source is grounded, the negative pole of the DC source, the ground end of the inverter network and the ground end of the AC filter are all grounded, and the DC source is a voltage V in , the voltage across the external AC source is the grid voltage u g, the current on the external AC source is the grid current i g .

[0047] The inverter network includes a first power switch tube S1, a second power switch tube S2, a third power switch tube S3, a fourth power switch tube S4, a fifth power switch tube S5, a sixth power switch tube S6, a seventh power switch tube S7, an eighth power switch tube S8, a ninth power switch tube S9, a first capacitor C1, and a second capacitor C2.

[0048] The second power switch tube S2, the fourth power switch tube S4, the fifth power switch tube S5, the sixth power switch tube S6, the seventh power switch tube S7, the eighth power switch tube S8, and the ninth power switch tube S9 are all composed of power transistors and anti-parallel diodes. The drain or collector of the power transistor is connected to the cathode of the anti-parallel diode to form the drain of the power switch tube, and the source or emitter of the power transistor is connected to the anode of the anti-parallel diode to form the source of the power switch tube.

[0049] The first power switch tube S1 and the third power switch tube S3 are power switch tubes without anti-parallel diodes or a series structure in which the source of a power switch tube with an anti-parallel diode is connected to the anode of the power switch tube.

[0050] The drain of the first power switch tube S1 is connected to the drain of the second power switch tube S2, the source of the first power switch tube S1 and the drain of the fifth power switch tube S5 are connected to the positive electrode of the first capacitor C1, and the source of the second power switch tube S2, the drain of the third power switch tube S3, and the source of the fourth power switch tube S4 are connected to the negative electrode of the first capacitor C1;

[0051] The source of the fifth power switch tube S5 and the drain of the sixth power switch tube S6 are connected to the drain of the seventh power switch tube S7, the drain of the fourth power switch tube S4 is connected to the positive electrode of the second capacitor C2, the source of the eighth power switch tube S8 and the ninth power switch tube S9 are connected to the negative electrode of the second capacitor C2, and the source of the sixth power switch tube S6 is connected to the drain of the eighth power switch tube S8;

[0052] The drain of the first power switch tube S1 is the input end of the inverter network and the DC source V in The positive electrode is connected, the source of the sixth power switch tube S6 and the drain of the eighth power switch tube S8 are both output ends of the inverter network, the source of the third power switch tube S3, the source of the seventh power switch tube S7 and the drain of the ninth power switch tube S9 are both ground ends of the inverter network and connected to the DC source V in Negative pole connected.

[0053] The AC filter includes a filter inductor L f And filter capacitor C f , filter inductor Lf One end is the input end of the AC filter network, and the other end is connected to the filter capacitor C f The positive pole is connected to the filter inductor L f With filter capacitor C f The connected points are connected to the output end of the AC filter, the filter capacitor C f The negative pole of is the grounding terminal of the AC filter.

[0054] The power switch drive signal of the single-phase common ground type five-level inverter circuit is composed of the modulation wave u m and carrier v tri Compare the generated, modulated wave u m is the industrial frequency, the frequency is 50Hz; the carrier v tri The two frequencies are modulated to generate a driving signal to control the switching mode of the power switch tube, thereby completing the state switching of the inverter network and realizing the energy exchange between the DC source and the external AC source.

[0055] The working modes of the inverter circuit of the present invention at the switching frequency scale include mode 1, mode 2, mode 3, mode 4, mode 5 and mode 6. Figure 2 As shown, mode 1 is the working mode during the period of t3-t4, mode 2 is the working mode during the period of t4-t5, mode 3 is the working mode of unity power factor during the period of t1-t2, mode 4 is the working mode during the period of t6-t7, mode 5 is the working mode of unity power factor during the period of t8-t9, and mode 6 is the working mode of unity power factor during the period of t9-t 10 Unity power factor operating mode for the time period.

[0056] The output voltage of the inverter network in mode 1 is equal to the DC source V in ,like Figure 3 As shown, the first power switch tube S1, the third power switch tube S3, the fifth power switch tube S5 and the sixth power switch tube S6 are turned on, the second power switch tube S2, the fourth power switch tube S4, the seventh power switch tube S7, the eighth power switch tube S8 and the ninth power switch tube S9 are turned off, and the grid current i g Can flow in both directions.

[0057] The output voltage of the inverter network in mode 2 is equal to twice the DC source, which is 2V. in ,like Figure 4 As shown, the second power switch tube S2, the fourth power switch tube S4, the fifth power switch tube S5, the sixth power switch tube S6 and the ninth power switch tube S9 are turned on, the first power switch tube S1, the third power switch tube S3, the seventh power switch tube S7 and the eighth power switch tube S8 are turned off, and the grid current i g Can flow in both directions.

[0058] The output voltage of the inverter network in mode three is equal to 0, such as Figure 5 As shown, it is the freewheeling mode of the positive half cycle of the power grid. The first power switch tube S1, the third power switch tube S3, the eighth power switch tube S8 and the ninth power switch tube S9 are turned on, and the second power switch tube S2, 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 are turned off. The grid current i g Can flow in both directions.

[0059] The output voltage of the inverter network in mode 4 is equal to 0, such as Figure 6 As shown, it is the freewheeling mode of the negative half cycle of the power grid. The second power switch tube S2, the fourth power switch tube S4, the eighth power switch tube S8 and the ninth power switch tube S9 are turned on, the first power switch tube S1, the third power switch tube S3, the fifth power switch tube S5, the sixth power switch tube S6 and the seventh power switch tube S7 are turned off, and the grid current i g Can flow in both directions.

[0060] The output voltage of the inverter network in mode 5 is equal to negative one times the DC source, which is -V in ,like Figure 7 As shown, the first power switch tube S1, the third power switch tube S3, the fourth power switch tube S4 and the eighth power switch tube S8 are turned on, the second power switch tube S2, the fifth power switch tube S5, the sixth power switch tube S6, the seventh power switch tube S7 and the ninth power switch tube S9 are turned off, and the grid current i g Can flow in both directions;

[0061] The output voltage of the inverter network in mode 6 is equal to twice the DC source, which is -2V. in ,like Figure 8 As shown, the fourth power switch tube S4, the fifth power switch tube S5, the seventh power switch tube S7 and the eighth power switch tube S8 are turned on, the first power switch tube S1, the second power switch tube S2, the third power switch tube S3, the sixth power switch tube S6 and the ninth power switch tube S9 are turned off, and the grid current i g Can flow in both directions;

[0062] When all power switch tubes work according to the driving signal, the inverter network continuously switches between the five output levels mentioned above to realize energy exchange between the input DC voltage and the external AC power.

[0063] The operating waveform of the inverter circuit of the present invention when it is in five-level output is as follows: Fig. 9 Shown is V dc With v ab As shown in the waveform diagram, the input voltage (200V in the example) is lower than the peak value of the output five-level voltage (400V in the example), so the inverter circuit can achieve the boost function.

[0064] The waveform of the capacitor voltage when the inverter circuit of the present invention is in five-level output is as follows: Fig.10 As shown, it can be seen that the capacitor voltage (200V in the example) is equal to the input voltage.

[0065] The operating waveforms of the inverter circuit of the present invention when it is in the five-level output state with unity power factor, leading current into the grid, and lagging current into the grid are as follows: Fig.11 , Fig.12 and Fig.13 As shown, it can be seen that the single-phase five-level inverter circuit has the ability to transmit reactive power to the power grid.

[0066] In summary, the single-phase common ground type five-level inverter circuit and its switch control strategy of the present invention can completely eliminate the leakage current in the non-isolated grid-connected inverter system by clamping the voltage on the parasitic capacitor between the photovoltaic panel and the ground at 0V through the common ground type structure. The output five-level voltage can reduce the volume of the AC filter and the grid current harmonics, and realize the boost function. The inverter circuit has the ability to deliver reactive power to the grid, and is suitable for small and medium power non-isolated photovoltaic grid-connected inverter system applications.

[0067] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A five-level grid-connected inverter structure, characterized in that: include: Inverter network and AC filter; The input end of the inverter network is connected to the positive pole of the DC source; the output end of the inverter network is connected to the input end of the AC filter; the output end of the AC filter is connected to one end of the external AC source, and the other end of the external AC source is grounded; the negative pole of the DC source, the ground end of the inverter network and the ground end of the AC filter are all grounded; The inverter network includes a first power switch tube, a second power switch tube, a third power switch tube, a fourth power switch tube, a fifth power switch tube, a sixth power switch tube, a seventh power switch tube, an eighth power switch tube, a ninth power switch tube, a first capacitor and a second capacitor; The drain of the first power switch tube is connected to the drain of the second power switch tube; the source of the first power switch tube and the drain of the fifth power switch tube are connected to the positive electrode of the first capacitor; the source of the second power switch tube, the drain of the third power switch tube, and the source of the fourth power switch tube are connected to the negative electrode of the first capacitor; The source of the fifth power switch tube and the drain of the sixth power switch tube are connected to the drain of the seventh power switch tube; the drain of the fourth power switch tube is connected to the positive electrode of the second capacitor; the source of the eighth power switch tube and the ninth power switch tube are connected to the negative electrode of the second capacitor; the source of the sixth power switch tube is connected to the drain of the eighth power switch tube; The drain of the first power switch tube is the input end of the inverter network and is connected to the positive electrode of the DC source; the source of the sixth power switch tube and the drain of the eighth power switch tube are both the output ends of the inverter network; the source of the third power switch tube, the source of the seventh power switch tube and the drain of the ninth power switch tube are all the ground end of the inverter network and are connected to the negative electrode of the DC source; The second power switch tube, the fourth power switch tube, the fifth power switch tube, the sixth power switch tube, the seventh power switch tube, the eighth power switch tube and the ninth power switch tube are all composed of a power transistor and an anti-parallel diode, the drain or collector of the power transistor is connected to the cathode of the anti-parallel diode to form the drain of the power switch tube, and the source or emitter of the power transistor is connected to the anode of the anti-parallel diode to form the source of the power switch tube; The AC filter includes a filter inductor and a filter capacitor, one end of the filter inductor is the input end of the AC filter network, the other end of the filter inductor is connected to the positive electrode of the filter capacitor, the connection point between the filter inductor and the filter capacitor is the output end of the AC filter, and the negative electrode of the filter capacitor is the grounding end of the AC filter.

2. The five-level grid-connected inverter structure according to claim 1, characterized in that: The driving signal of the power switch tube of the inverter network is generated by modulation of a modulation wave and a high-frequency carrier wave, wherein the modulation wave is an industrial frequency of 50 Hz and the frequency of the carrier wave is 100 kHz.

3. The five-level grid-connected inverter structure according to claim 1, characterized in that: The five-level grid-connected inverter structure includes the following working modes: Mode 1: the output voltage of the inverter network is equal to the DC source, the first power switch tube, the third power switch tube, the fifth power switch tube and the sixth power switch tube are turned on; the second power switch tube, the fourth power switch tube, the seventh power switch tube, the eighth power switch tube and the ninth power switch tube are turned off; Mode 2: the output voltage of the inverter network is equal to twice the DC source, and the second power switch tube, the fourth power switch tube, the fifth power switch tube, the sixth power switch tube and the ninth power switch tube are turned on; The first power switch tube, the third power switch tube, the seventh power switch tube and the eighth power switch tube are disconnected; Mode three: the output voltage of the inverter network is equal to 0, the first power switch tube, the third power switch tube, the eighth power switch tube and the ninth power switch tube are turned on; the second power switch tube, the fourth power switch tube, the fifth power switch tube, the sixth power switch tube and the seventh power switch tube are turned off; Mode 4: the output voltage of the inverter network is equal to 0; the second power switch tube, the fourth power switch tube, the eighth power switch tube and the ninth power switch tube are turned on; the first power switch tube, the third power switch tube, the fifth power switch tube, the sixth power switch tube and the seventh power switch tube are turned off; Mode 5: the output voltage of the inverter network is equal to negative one times the DC source; the first power switch tube, the third power switch tube, the fourth power switch tube and the eighth power switch tube are turned on; the second power switch tube, the fifth power switch tube, the sixth power switch tube, the seventh power switch tube and the ninth power switch tube are turned off; Mode 6: the output voltage of the inverter network is equal to twice the DC source; the fourth power switch tube, the fifth power switch tube, the seventh power switch tube and the eighth power switch tube are turned on; The first power switch tube, the second power switch tube, the third power switch tube, the sixth power switch tube and the ninth power switch tube are disconnected.

4. An inverter, characterized in that: It comprises a five-level grid-connected inverter structure as described in any one of claims 1 to 3.

5. A photovoltaic power supply system, characterized in that: include: A photoelectric device, the photoelectric device being used as a DC power source for outputting a DC voltage; AC distribution network; The inverter according to claim 4, wherein the input end of the inverter is connected to the photovoltaic device, the output end of the inverter is connected to the AC power distribution network, and the inverter is used to convert the DC voltage into an AC voltage and output it to the AC power distribution network.

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