A common ground type ten-switch voltage-doubled five-level single-phase photovoltaic inverter topology

Abstract

The application provides a common ground type ten-switch voltage-doubled five-level single-phase photovoltaic inverter topology, which comprises a photovoltaic cell, a common ground type ten-switch voltage-doubled five-level single-phase inverter circuit, a single-phase LC output filter circuit and a single-phase load; the photovoltaic cell is PV; the common ground type ten-switch voltage-doubled five-level single-phase inverter circuit comprises an input filter capacitor Cdc, two flying capacitors C1 and C2 and ten switch tubes S1-S10, wherein S1, S2 and S9 are IGBTs without freewheeling diodes, S3-S8 and S10 are IGBT modules with freewheeling diodes; the single-phase LC output filter circuit and the single-phase load comprise a filter inductor Lf, a filter capacitor Cf and a load Ro. The common ground type ten-switch voltage-doubled five-level single-phase photovoltaic inverter topology can improve the utilization rate of the direct current voltage of the inverter, improve the quality of the output voltage waveform and reduce the common mode current of the inverter.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronic DC-AC conversion, and particularly relates to a common-ground type ten-switch five-level voltage-boosting single-phase photovoltaic inverter topology. BACKGROUND

[0002] With the consumption of fossil energy and the deterioration of the ecological environment of the earth, the advantages of solar energy are increasingly prominent. Photovoltaic power generation, as a major form of using solar energy, is particularly focused on. Data released by the National Energy Administration shows that in the first half of 2022, the renewable energy power generation in China reached 1.25 trillion kilowatt-hours, of which the solar power generation increased by 13.5%. According to the International Energy Agency (IEA), by 2030, global renewable energy power demand will account for 80% of the global power demand growth, of which wind power and photovoltaic power will account for nearly 30%, up from 8% in 2019. With the development of photovoltaic power generation, non-isolated photovoltaic grid-connected inverters are widely used in solar power generation at home and abroad due to their low cost and high efficiency.

[0003] The non-isolated photovoltaic grid-connected system has no effective electrical isolation with the power grid. When the power switch tube is switched at high frequency, a common-mode voltage is generated. The parasitic capacitance between the solar photovoltaic panel, the inverter equipment and the ground forms a loop with the non-isolated photovoltaic grid-connected system, thereby forming a common-mode current. The common-mode current, also known as the leakage current, not only causes distortion of the grid-connected current, but more importantly, it poses a risk of electric shock to relevant personnel and a safety hazard to equipment with high reliability. In order to suppress the adverse effects of leakage current and common-mode voltage on equipment and personal safety, the non-isolated photovoltaic grid-connected inverter generally uses a method of changing the topology structure and the corresponding switch control logic to make the common-mode voltage constant or reduce the fluctuation range of the common-mode voltage, but it cannot completely suppress the generation of leakage current and common-mode voltage.

[0004] Therefore, it is necessary to design a new common-ground photovoltaic inverter topology to solve the above problems. SUMMARY

[0005] The main purpose of the application is to provide a common-ground single-phase photovoltaic inverter topology with good output voltage waveform quality.

[0006] In order to achieve the above object, the present application provides a common ground type ten-switch voltage-doubled five-level single-phase photovoltaic inverter topology, comprising: a photovoltaic cell, a common ground type ten-switch voltage-doubled five-level single-phase inverter circuit, a single-phase output LC filter circuit and a single-phase load; the photovoltaic cell is PV; the common ground type ten-switch voltage-doubled five-level single-phase inverter circuit comprises an input filter capacitor Cdc, two flying capacitors C1 and C2 and ten switch tubes S1-S10, wherein S1, S2 and S9 are IGBTs without freewheeling diodes, S3-S8 and S10 are IGBT modules with freewheeling diodes; the single-phase output LC filter circuit and the single-phase load comprise a filter inductor Lf, a filter capacitor Cf and a load Ro.

[0007] Further improvement of the present application is that the positive electrode of the photovoltaic cell PV is connected with the collector of the switch tube S1, the collector of the switch tube S4 and the positive electrode of the input filter capacitor Cdc; the emitter of the switch tube S1 is connected with the collector of the switch tube S2, the collector of the switch tube S3 and the positive electrode of the flying capacitor C1; the emitter of the switch tube S3 is connected with the collector of the switch tube S7, the collector of the switch tube S9 and one end of the filter inductor Lf; the emitter of the switch tube S4 is connected with the collector of the switch tube S5 and the positive electrode of the flying capacitor C2; the negative electrode of the flying capacitor C2 is connected with the collector of the switch tube S10 and the emitter of the switch tube S8; the emitter of the switch tube S10 is connected with the emitter of the switch tube S7; the negative electrode of the flying capacitor C1 is connected with the emitter of the switch tube S5, the collector of the switch tube S6 and the emitter of the switch tube S9; the other end of the filter inductor Lf is connected with the positive electrode of the filter capacitor Cf and one end of the load Ro; the emitter of the switch tube S2, the emitter of the switch tube S6, the collector of the switch tube S8, the input filter capacitor Cdc, the negative electrode of the filter capacitor Cf and the other end of the load Ro are connected with the negative electrode of the photovoltaic cell PV.

[0008] Further improvement of the present application is that the switch tube S10 and the switch tube S7 in the common ground type ten-switch voltage-doubled five-level single-phase inverter circuit form a pair of reverse series switch tubes, so as to ensure that the current flowing direction of the branch is controlled.

[0009] Further improvement of the present application is that the independent charging path and the independent discharging path of the flying capacitors C1 and C2 are respectively constructed, so that the two flying capacitors do not affect each other when they are alternately charged and discharged; since the flying capacitors C1 and C2 are alternately charged and discharged, the situation that only the flying capacitor C2 is always in the discharging state and the output waveform fluctuates greatly does not occur, the two flying capacitors can maintain a stable voltage Upv, and the inverter can output a more stable voltage waveform.

[0010] The further improvement of the present application is that the working modes of the inverter are defined as [M1, M2, M3, M4, M5, M6]; wherein the working mode M1 represents that the inverter outputs 2Upv; the working mode M2 represents that the inverter outputs Upv; the working mode M3 represents that the inverter outputs 0; the working mode M4 represents that the inverter outputs -Upv, at this time, the flying capacitor C2 is in the discharging state; the working mode M5 represents that the inverter outputs -2Upv, at this time, the flying capacitor C1 is in the discharging state; and the working mode M6 represents that the inverter outputs -2Upv.

[0011] The further improvement of the present application is that the states of the ten switch tubes IGBT corresponding to the six working modes of the inverter are respectively: mode M1 [0, 0, 1, 0, 1, 0, 0, 1, 0, 0], mode M2 [1, 0, 1, 1, 0, 1, 0, 1, 0, 0], mode M3 [1, 0, 0, 1, 0, 1, 1, 1, 0, 1], mode M4 [1, 0, 0, 0, 1, 1, 1, 0, 0, 1], mode M5 [0, 1, 0, 1, 0, 0, 0, 1, 1, 0], mode M6 [0, 1, 0, 0, 1, 0, 1, 0, 0, 1].

[0012] The present application has the following beneficial effects: the proposed common ground type ten-switch voltage-doubled five-level single-phase photovoltaic inverter topology can eliminate the influence of the leakage current caused by the parasitic capacitance of the photovoltaic cell to the ground; during the whole working period of the inverter, the output voltage of the common ground type ten-switch voltage-doubled five-level inverter circuit is the five-level voltage-doubled voltage, which ranges from 0 to ±Upv and ±2Upv. The five-level voltage-doubled voltage improves the amplitude of the output voltage, improves the utilization rate of the direct-current voltage, and reduces the generation of harmonics, thereby reducing the size of the filter; the common ground type ten-switch voltage-doubled five-level single-phase inverter circuit constructs independent charging paths and independent discharging paths for the flying capacitors C1 and C2, respectively, so that the two flying capacitors are not affected when they are alternately charged and discharged, the purpose of stabilizing the voltages of the two flying capacitors is achieved, and the state that only the flying capacitor C2 is always in the discharging state during the working stages of -Upv and -2Upv is avoided, thereby improving the quality of the output voltage waveform of the inverter. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is the main circuit structure diagram of the present application.

[0014] Figure 2 It is the schematic diagram of mode one of the present application.

[0015] Figure 3 It is the schematic diagram of mode two of the present application.

[0016] Figure 4 It is the schematic diagram of mode three of the present application.

[0017] Figure 5 A schematic diagram of a mode four of the present application.

[0018] Figure 6 A schematic diagram of a mode five of the present application.

[0019] Figure 7 A schematic diagram of a mode six of the present application.

[0020] Figure 8 A schematic diagram of an inverter output SPWM waveform of the present application. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described in detail below in combination with the drawings and specific embodiments.

[0022] It is emphasized that in the description of the present application, various formulas and constraints are respectively distinguished by consistent labels before and after, but different labels are not excluded to mark the same formula and / or constraint, and the purpose of such setting is to make the features of the present application clearer.

[0023] As shown in Figure 1 The present application proposes a common ground type ten-switch voltage-doubled five-level single-phase photovoltaic inverter topology, which comprises a photovoltaic cell, a common ground type ten-switch voltage-doubled five-level single-phase inverter circuit, a single-phase output LC filter circuit and a single-phase load; the photovoltaic cell is PV; the common ground type ten-switch voltage-doubled five-level single-phase inverter circuit comprises an input filter capacitor Cdc, two flying capacitors C1 and C2 and ten switch tubes S1-S10, wherein S1, S2 and S9 are IGBTs without freewheeling diodes, S3-S8 and S10 are IGBT modules with freewheeling diodes; the single-phase output LC filter circuit and the single-phase load comprise a filter inductor Lf, a filter capacitor Cf and a load Ro.

[0024] The positive pole of the photovoltaic cell PV is connected with the collector of the switch tube S1, the collector of the switch tube S4 and the positive pole of the input filter capacitor Cdc in the common ground type ten switch voltage five level single phase photovoltaic inverter topology; the emitter of the switch tube S1 is connected with the collector of the switch tube S2, the collector of the switch tube S3 and the positive pole of the flying capacitor C1; the emitter of the switch tube S3 is connected with the collector of the switch tube S7, the collector of the switch tube S9 and one end of the filter inductor Lf; the emitter of the switch tube S4 is connected with the collector of the switch tube S5 and the positive pole of the flying capacitor C2; the negative pole of the flying capacitor C2 is connected with the collector of the switch tube S10 and the emitter of the switch tube S8; the emitter of the switch tube S10 is connected with the emitter of the switch tube S7; the negative pole of the flying capacitor C1 is connected with the emitter of the switch tube S5, the collector of the switch tube S6 and the emitter of the switch tube S9; the other end of the filter inductor Lf is connected with the positive pole of the filter capacitor Cf and one end of the load Ro; the emitter of the switch tube S2, the emitter of the switch tube S6, the collector of the switch tube S8, the input filter capacitor Cdc, the negative pole of the filter capacitor Cf and the other end of the load Ro are connected with the negative pole of the photovoltaic cell PV.

[0025] The switch tube S10 is added in the common ground type ten switch voltage five level single phase inverter circuit, and forms a pair of reverse series switch tubes with the switch tube S7. The reverse series switch tubes of the switch tube S7 and the switch tube S10 are used to ensure the current flowing direction of the branch to be controlled. If only the switch tube S7 is used, the current will flow out through the body diode of the switch tube S7 in the mode five, which will cause short circuit to the flying capacitor C1.

[0026] The common ground type ten switch voltage five level single phase inverter circuit respectively constructs the independent charging path and the independent discharging path of the flying capacitors C1 and C2, so that the two flying capacitors do not affect each other when they are alternately charged and discharged. Since the flying capacitors C1 and C2 are alternately charged and discharged, the output waveform will not fluctuate greatly due to the fact that only the flying capacitor C2 is always in the discharging state, and the two flying capacitors can maintain a stable voltage Upv, and the inverter can output a more stable waveform.

[0027] The working modes of the inverter are defined as [M1, M2, M3, M4, M5, M6]; wherein the working mode M1 represents that the inverter outputs 2Upv; the working mode M2 represents that the inverter outputs Upv; the working mode M3 represents that the inverter outputs 0; the working mode M4 represents that the inverter outputs -Upv, and the flying capacitor C2 is in the discharging state; the working mode M5 represents that the inverter outputs -Upv, and the flying capacitor C1 is in the discharging state; and the working mode M6 represents that the inverter outputs -2Upv.

[0028] Through the above analysis of the inverter, the corresponding working modes can be obtained as follows:

[0029] Mode one: asFigure 2 As shown, the inverter switching states are [0, 0, 1, 0, 1, 0, 0, 1, 0, 0], with switches S3, S5, and S8 in the on state and switches S1, S2, S4, S6, S7, S9, and S10 in the off state. Flying capacitors C1 and C2 are connected via switch S5, with a voltage of 2Upv across them. Current flows from the positive electrode of the flying capacitor, through S3-Lf-Ro-S8, and back to the negative electrode of flying capacitor C2. At this point, both flying capacitors are discharged, and the output voltage of the common-ground, ten-switch, voltage-doubling, five-level single-phase inverter circuit is 2Upv, with zero leakage current.

[0030] Mode 2: If Figure 3 As shown, the inverter switching states are [1, 0, 1, 1, 0, 1, 0, 1, 0, 0]. Switches S1, S3, S4, S6, and S8 are on; switches S2, S5, S7, S9, and S10 are off. Current flows from the positive electrode of the photovoltaic cell PV, through S1-S3-Lf-Ro, S1-C1-S6, and S4-C2-S8, before returning to the negative electrode of the photovoltaic cell PV. At this point, flying capacitors C1 and C2 are charging. The output voltage of the common-ground, ten-switch, voltage-doubling, five-level single-phase inverter circuit is Upv, and the leakage current is zero.

[0031] Mode 3: If Figure 4 As shown, the inverter switching states are [1, 0, 0, 1, 0, 1, 1, 1, 0, 1]. Switches S1, S4, S6, S7, S8, and S10 are on; switches S2, S3, S5, and S9 are off. Current flows from the positive terminal of the photovoltaic cell (PV), through S1-C1-S6 and S4-C2-S8, respectively, before returning to the negative terminal of the photovoltaic cell (PV). Simultaneously, the current in the filter circuit and the load continues to flow through the path of S7-S10-S8. At this point, flying capacitors C1 and C2 are charged, the output voltage of the common-ground, ten-switch voltage-doubling, five-level single-phase inverter circuit is zero, and the leakage current is zero.

[0032] Mode 4: If Figure 5As shown, if the flying capacitor C2 has sufficient energy, the capacitor voltage is higher, and the inverter switch state is [1, 0, 0, 0, 1, 1, 1, 0, 0, 1], the switch tubes S1, S5, S6, S7 and S10 are in the on state; the switch tubes S2, S3, S4, S8 and S9 are in the off state. The current flows out from the positive electrode of the photovoltaic cell PV, flows through S1-C1-S6, and then flows back to the negative electrode of the photovoltaic cell PV. At the same time, the current flows out from the positive electrode of the flying capacitor C2, flows through S5-S6-Ro-Lf-S7-S10, and then flows back to the negative electrode of the flying capacitor C2. At this time, the flying capacitor C1 is in the charging state, the flying capacitor C2 is in the discharging state, and the output voltage of the common ground type ten-switch voltage-doubled five-level single-phase inverter circuit is -Upv, and the leakage current is 0.

[0033] Mode five: as shown in Figure 6 If the flying capacitor C2 has insufficient energy, the capacitor voltage is lower, and the inverter switch state is [0, 1, 0, 1, 0, 0, 0, 1, 1, 0], the switch tubes S2, S4, S8 and S9 are in the on state; the switch tubes S1, S3, S5, S6, S7 and S10 are in the off state. The current flows out from the positive electrode of the photovoltaic cell PV, flows through S4-C2-S8, and then flows back to the negative electrode of the photovoltaic cell PV. At the same time, the current flows out from the positive electrode of the flying capacitor C1, flows through S2-Ro-Lf-S9, and then flows back to the negative electrode of the flying capacitor C1. At this time, the flying capacitor C1 is in the discharging state, the flying capacitor C2 is in the charging state, and the output voltage of the common ground type ten-switch voltage-doubled five-level single-phase inverter circuit is -Upv, and the leakage current is 0.

[0034] Mode six: as shown in Figure 7 The inverter switch state is [0, 1, 0, 0, 1, 0, 1, 0, 0, 1], the switch tubes S2, S5, S7 and S10 are in the on state; the switch tubes S1, S3, S4, S6, S8 and S9 are in the off state. The flying capacitors C1 and C2 are connected through the switch tube S5, and the voltage across the two ends is 2Upv. The current flows out from the positive electrode of the flying capacitor C1, flows through S2-Ro-Lf-S7-S10, and then flows back to the negative electrode of the flying capacitor C2. At this time, the flying capacitors C1 and C2 are in the discharging state, and the output voltage of the common ground type ten-switch voltage-doubled five-level single-phase inverter circuit is -2Upv, and the leakage current is 0.

[0035] Table 1 shows the correspondence between the inverter working state, the switch tube state and the SPWM output voltage.

[0036] Table 1 Inverter working mode, switch tube state and SPWM output voltage

[0037]

[0038] The six working modes are switched regularly and alternately in the whole inverter cycle, and the SPWM waveform of the inverter is shown in Figure 8 It can be seen that the maximum level of the inverter output is 2Upv, the voltage multiplication function of the photovoltaic cell is realized, there are totally 5 levels in the whole inverter cycle, the harmonic content is small compared with the 3-level inverter, and the ideal sine wave output waveform can be obtained after the high-order harmonics are filtered by the LC output filter.

[0039] From the above analysis, the common ground type ten-switch voltage multiplication five-level single-phase photovoltaic inverter topology can eliminate the influence of the leakage current caused by the parasitic capacitance of the photovoltaic cell to the ground; during the whole working period of the inverter, the common ground type ten-switch voltage multiplication five-level inverter circuit output voltage is five-level voltage multiplication, and the range is 0, ±Upv, ±2Upv. The five-level voltage multiplication improves the amplitude of the output voltage, improves the utilization rate of the direct current voltage, and can also reduce the generation of harmonics, thereby reducing the size of the filter; the common ground type ten-switch voltage multiplication five-level single-phase inverter circuit constructs independent charging paths and independent discharging paths for the flying capacitors C1 and C2, so that the two flying capacitors are not affected when they are alternately charged and discharged, the purpose of stabilizing the voltages of the two flying capacitors is achieved, the situation that the output voltage decreases and generates large fluctuations due to the fact that only the flying capacitor C2 is always in the discharging state during the working stage of the inverter at -Upv and -2Upv is reduced, and the inverter can output more stable waveforms.

[0040] In summary, the common ground type ten-switch voltage multiplication five-level single-phase photovoltaic inverter topology of the present application not only can eliminate the leakage current, but also can improve the utilization rate of the direct current voltage, and by using the five-level technology, the generation of harmonic voltage is reduced, and the present application has good engineering application value.

[0041] The above examples are only used to illustrate the technical solutions of the present application and not to limit the present application, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A common ground type ten-switch voltage-doubling five-level single-phase photovoltaic inverter topology, characterized in that: include: A photovoltaic cell, a common ground type ten-switch voltage doubling five-level single-phase inverter circuit, a single-phase output LC filter circuit and a single-phase load; the photovoltaic cell is PV; the common ground type ten-switch voltage doubling five-level single-phase inverter circuit includes an input filter capacitor Cdc, two flying capacitors C1 and C2 and ten switching tubes S1 to S10, wherein S1, S2 and S9 are IGBTs without freewheeling diodes, and S3 to S8 and S10 are IGBT modules with freewheeling diodes; the single-phase output LC filter circuit and the single-phase load include a filter inductor Lf, a filter capacitor Cf and a load Ro; the positive electrode of the photovoltaic cell PV is connected to the collector of the switching tube S1, the collector of the switching tube S4, and the positive electrode of the input filter capacitor Cdc; the emitter of the switching tube S1 is connected to the collector of the switching tube S2, the collector of the switching tube S3, and the positive electrode of the flying capacitor C1 The emitter of the switching tube S3 is connected to the collector of the switching tube S7, the collector of the switching tube S9, and one end of the filter inductor Lf; the emitter of the switching tube S4 is connected to the collector of the switching tube S5 and the positive electrode of the flying capacitor C2; the negative electrode of the flying capacitor C2 is connected to the collector of the switching tube S10 and the emitter of the switching tube S8; the emitter of the switching tube S10 is connected to the emitter of the switching tube S7; the negative electrode of the flying capacitor C1 is connected to the emitter of the switching tube S5, the collector of the switching tube S6, and the emitter of the switching tube S9; the other end of the filter inductor Lf is connected to the positive electrode of the filter capacitor Cf and one end of the load Ro; the emitter of the switching tube S2, the emitter of the switching tube S6, the collector of the switching tube S8, the input filter capacitor Cdc, the negative electrode of the filter capacitor Cf, and the other end of the load Ro are connected to the negative electrode of the photovoltaic cell PV.

2. The common ground type ten-switch voltage-doubling five-level single-phase photovoltaic inverter topology according to claim 1, characterized in that: In the common ground type ten-switch voltage doubling five-level single-phase inverter circuit, the switch tube S10 and the switch tube S7 form a pair of switch tubes connected in reverse series, thereby ensuring that the current flow direction of the pair of switch tube branches connected in reverse series is controlled.

3. The common ground type ten-switch voltage-doubling five-level single-phase photovoltaic inverter topology according to claim 1, characterized in that: Independent charging and discharging paths are constructed for the flying capacitors C1 and C2, respectively, so that the two flying capacitors do not affect each other when they are alternately charged and discharged. Since the flying capacitors C1 and C2 are alternately charged and discharged, there will not be a situation where only the flying capacitor C2 is always in a discharging state, resulting in large fluctuations in the output waveform. The two flying capacitors can maintain a stable voltage Upv, and the inverter can output a more stable voltage waveform.

4. The common ground type ten-switch voltage-doubling five-level single-phase photovoltaic inverter topology according to claim 1, characterized in that: The working modes of the inverter are defined as [M1, M2, M3, M4, M5, M6]; among them, the working mode M1 represents the inverter output 2Upv; the working mode M2 ​​represents the inverter output Upv; the working mode M3 represents the inverter output 0; the working mode M4 represents the inverter output -Upv, at which time the flying capacitor C2 is in the discharged state; the working mode M5 represents the inverter output -Upv, at which time the flying capacitor C1 is in the discharged state; the working mode M6 represents the inverter output -2Upv.

5. The common ground type ten-switch voltage-doubling five-level single-phase photovoltaic inverter topology according to claim 4, characterized in that: The states of the ten switching tubes IGBTs corresponding to the six working modes of the inverter are: mode M1[0,0,1,0,1,0,0,1,0,0], mode M2[1,0,1,1,0,1,0,1,0,0], mode M3[1,0,0,1,0,1,1,1,0,1], mode M4[1,0,0,0,1,1,1,0,0,1], mode M5[0,1,0,1,0,0,0,1,1,0], mode M6[0,1,0,0,1,0,1,0,0,1], where 0 indicates that the IGBT is turned off and 1 indicates that the IGBT is turned on.

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