Inductor boost type common-ground single-phase photovoltaic inverter

Abstract

The invention discloses an inductance boosting type common-ground single-phase photovoltaic inverter which comprises a photovoltaic cell, an inductance boosting type common-ground single-phase inverter circuit, a single-phase output LC filter circuit and a single-phase load. Wherein the inductor boost type common-ground single-phase inverter circuit is composed of a boost inductor L1, a switched capacitor C1 and switching tubes S1 to S7, S1 and S3 are switching tubes without fly-wheel diodes, and others are switching tubes with fly-wheel diodes. The control method of the inverter comprises the following steps of: comparing a single-phase sinusoidal modulation wave with a two-phase laminated triangular carrier wave to obtain two paths of pre-processing signals, and performing logical operation on the two paths of pre-processing signals to obtain control signals of the eight switch tubes according to a switch tube conduction relation in six working modes. The inductance boost type common-ground single-phase photovoltaic inverter topology not only can eliminate leakage current, but also has the advantage of switched capacitor soft charging and dynamic boost capability, and the reliability of the inverter and the utilization rate of direct-current voltage are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic DC-AC conversion, and is applicable to photovoltaic off-grid inverters whose loads are AC loads and whose power sources are DC power sources. If the AC loads and filter capacitors are replaced with grid power sources, the present invention can also be applicable to photovoltaic grid-connected inverters, and specifically relates to an inductive boost type common ground single-phase photovoltaic inverter. Background Art

[0002] With the leapfrog development of the photovoltaic industry, non-isolated photovoltaic grid-connected inverters have become an extremely important development direction in the photovoltaic field due to their advantages of small size, low cost and higher efficiency. However, there is parasitic capacitance between the photovoltaic panel and the earth, and there is a direct electrical connection between the non-isolated photovoltaic inverter and the power grid. A loop will be formed between the solar panel, the inverter, and the parasitic capacitance of the photovoltaic panel to the ground and the power grid. When the switch tube works at a high frequency, it will inevitably generate a common-mode voltage, and then generate a common-mode current, that is, leakage current. The existence of leakage current will not only increase system losses and generate electromagnetic interference, but also cause distortion of the grid current. More importantly, it will bring great safety hazards to grid workers. In order to reduce the series of adverse effects caused by the above leakage current, the common-mode voltage is generally maintained at a constant value or the fluctuation range of the common-mode voltage is reduced by changing the inverter topology and optimizing the control strategy, but this cannot completely suppress the generation of leakage current and common-mode voltage. The emergence of common-ground structure inverters provides another direction to eliminate common-mode current and common-mode voltage. In the common ground inverter topology, the grid or load neutral point is directly connected to the negative pole of the DC bus, so that the voltage on the parasitic capacitor is constant at zero, thereby completely eliminating leakage current. However, the common ground single-phase photovoltaic inverter without inductor has the problem of direct charging of the capacitor by the power supply, and the charging current is too large instantaneously, and if you want to get a higher voltage gain, you can only do so by increasing the number of switching capacitors.

[0003] The inductive boost type common ground inverter effectively avoids the problem of instantaneous excessive current caused by direct charging of the capacitor by the power supply, and has soft charging capability. At the same time, by adjusting the inductive energy storage time, the circuit can obtain different voltage gains and achieve the effect of dynamic boost.

[0004] In view of this, it is indeed necessary to invent an inductive boost type common ground single-phase photovoltaic inverter to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide an inductive boost type common ground single-phase photovoltaic inverter to effectively solve the problem of direct charging of the capacitor by the power supply and the instantaneous excessive charging current in the common ground single-phase photovoltaic inverter without inductor, and to overcome the defect that a higher voltage gain can only be obtained by increasing the number of switching capacitors, so as to achieve the effect of dynamic boost.

[0006] The present invention provides an inductive boost type common ground single-phase photovoltaic inverter, comprising a photovoltaic cell PV, an inductive boost type common ground single-phase photovoltaic inverter circuit, a single-phase output LC filter circuit and a single-phase load. The inductive boost type common ground single-phase photovoltaic inverter circuit comprises: a DC input filter capacitor Cdc, a boost inductor L1, a switch capacitor C1, and switch tubes S1 to S7, wherein the switch tubes S1 and S3 are switch tubes without freewheeling diodes, and the other switch tubes are switch tubes 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 R.

[0007] A further improvement of the present invention is that the positive electrode of the photovoltaic cell PV is connected to the anode of the DC input filter capacitor Cdc and the collector of the switch tube S1; the emitter of the switch tube S1 is connected to the emitter of the switch tube S3 and one end of the boost inductor L1; the collector of the switch tube S3 is connected to the emitter of the switch tube S5, the collector of the switch tube S6, and one end of the filter inductor Lf; the other end of the filter inductor Lf is connected to the anode of the filter capacitor Cf and one end of the load R; the other end of the boost inductor L1 is connected to the collector of the switch tube S2 and the emitter of the switch tube S4; the collector of the switch tube S4 is connected to the collector of the switch tube S5 and the anode of the switch capacitor C1; the cathode of the switch capacitor C1 is connected to the emitters of the switch tubes S6 and S7; the cathode of the DC input filter capacitor Cdc, the emitter of the switch tube S2, the collector of the switch tube S7, the cathode of the filter capacitor Cf, and the other end of the load R are connected to the negative electrode of the photovoltaic cell PV.

[0008] A further improvement of the present invention is that a switched capacitor soft charging working mode is constructed. This mode includes two working processes: 1. Inductor energy storage process. The photovoltaic cell PV, the boost inductor L1, the switch tubes S1 and S2 constitute the inductor charging circuit, and the power supply charges the inductor; 2. Capacitor soft charging process. The boost inductor L1, the switch capacitor C1 and the switch tubes S3, S4, S6 constitute the capacitor soft charging circuit, which transfers the energy on the inductor to the capacitor to prevent the power supply from directly charging the capacitor. During the energy transfer process, since the current on the inductor cannot change suddenly, the switch tube is prevented from breaking down due to the instantaneous excessive current, so the safety and reliability of the circuit are effectively improved.

[0009] A further improvement of the present invention is that by adjusting the duty cycle of the switch tubes S1 and S2 and adjusting the energy storage time of the inductor, voltage gains of different sizes are obtained, so that the circuit has a dynamic boost function.

[0010] A further improvement of the present invention 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 power supply charges the boost inductor L1, and the switch capacitor C1 provides a positive voltage to the load R; the working mode M2 ​​represents that the boost inductor L1 softly charges the switch capacitor C1, and the current in the filter inductor Lf flows clockwise through the load R, the switch tube S7 and the freewheeling diode of the switch tube S6, and the inverter outputs zero voltage; the working mode M3 represents that all the energy on the inductor L1 is transferred to the capacitor C1, and the current in the filter inductor Lf is The current continues to flow in the clockwise direction, and the inverter continues to output zero voltage; the working mode M4 represents that the power supply charges the boost inductor L1, and the switch capacitor C1 provides a negative voltage to the load R; the working mode M5 represents that the boost inductor L1 softly charges the switch capacitor C1, and the current in the filter inductor Lf flows counterclockwise through the switch tube S6, the freewheeling diode of the switch tube S7 and the load R, and the inverter outputs zero voltage; the working mode M6 represents that all the energy on the inductor L1 is transferred to the capacitor C1, the current in the filter inductor Lf continues to flow counterclockwise, and the inverter continues to output zero voltage.

[0011] The present invention also provides a control method for an inductive boost type common ground single-phase inverter, which is used to control the above-mentioned inductive boost type common ground single-phase photovoltaic inverter, and specifically comprises the following steps:

[0012] The first step: intercept the sinusoidal modulated wave ut with the stacked triangular carriers uc1 and uc2 respectively, and obtain two pre-processed signals A and B through the comparator, and then invert them to obtain a and b respectively.

[0013] Step 2: Perform an OR operation on signal A and the inverted signal b of signal B to obtain the drive signals ug1 and ug2 of switch tubes S1 and S2; perform an AND operation on the inverted signal a of signal A and signal B to obtain the drive signal ug3 of switch tube S3; perform an AND operation on the inverted signal a of signal A and signal B, and then perform an OR operation on the result of the AND operation and the inverted signal b of signal B to obtain the drive signals ug4 and ug6 of switch tubes S4 and S6; use signal A as the drive signal ug5 of switch tube S5; perform an AND operation on the inverted signal a of signal A and signal B, and then perform an OR operation on the result of the AND operation and signal A to obtain the drive signal ug7 of switch tube S7.

[0014] A further improvement of the present invention is that the states of the switching tubes corresponding to the six working modes of the inverter are: mode M1 [1,1,0,0,1,0,1], mode M2 ​​[0,0,1,1,0,1,1], mode M3 [0,0,0,0,0,1,1], mode M4 [1,1,0,1,0,1,0], mode M5 [0,0,1,1,0,1,1], mode M6 [0,0,0,0,0,1,1], where 0 is a low level indicating that the switching tube is turned off, and 1 is a high level indicating that the switching tube is turned on.

[0015] The beneficial effects of the present invention are as follows: the present invention adopts an inductive boost type common ground single-phase photovoltaic inverter topology to eliminate the influence of leakage current caused by the parasitic capacitance of the photovoltaic cell to the ground; the present invention uses an inductor to soft-charge the capacitor. Since the current on the inductor cannot change suddenly, the instantaneous excessive current caused by the direct charging of the capacitor by the power supply is effectively avoided, so that the reliability of the inverter is effectively improved; at the same time, the present invention obtains different voltage gains by adjusting the circuit boost ratio by adjusting the duty cycle of the switch tube, provides dynamic boost capability, and improves the utilization rate of the DC voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the main circuit structure diagram of the present invention.

[0017] Figure 2 It is a schematic diagram of the logic control of the present invention.

[0018] Figure 3 It is a schematic diagram of Mode 1 of the present invention.

[0019] Figure 4 It is a schematic diagram of Mode 2 of the present invention.

[0020] Figure 5 It is a schematic diagram of Mode 3 of the present invention.

[0021] Figure 6 It is a schematic diagram of Mode 4 of the present invention.

[0022] Figure 7 It is a schematic diagram of Mode 5 of the present invention.

[0023] Figure 8 It is a schematic diagram of Mode 6 of the present invention.

[0024] Fig. 9 It is a schematic diagram of the driving signal timing diagram, the current value of the boost inductor L1, the voltage value of the switch capacitor C1 and the voltage value of the inverter output terminal of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] It should be emphasized that in the process of describing the present invention, various formulas and constraints are distinguished by consistent labels, but the use of different labels to mark the same formula and / or constraints is not excluded. The purpose of this setting is to more clearly illustrate the characteristics of the present invention.

[0027] like Figure 1 As shown, this implementation case proposes that the present invention provides an inductive boost type common ground single-phase photovoltaic inverter, the inverter includes a photovoltaic cell PV, an inductive boost type common ground single-phase photovoltaic inverter circuit, a single-phase output LC filter circuit and a single-phase load. The inductive boost type common ground single-phase photovoltaic inverter circuit includes: a DC input filter capacitor Cdc, a boost inductor L1, a switch capacitor C1, and switch tubes S1 to S7, wherein the switch tubes S1 and S3 are switch tubes without freewheeling diodes, and the other switch tubes are switch tubes 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 R.

[0028] The positive electrode of the photovoltaic cell PV of the common-ground single-phase photovoltaic inverter topology of the inductive boost type is connected to the anode of the DC input filter capacitor Cdc and the collector of the switch tube S1; the emitter of the switch tube S1 is connected to the emitter of the switch tube S3 and one end of the boost inductor L1; the collector of the switch tube S3 is connected to the emitter of the switch tube S5, the collector of the switch tube S6, and one end of the filter inductor Lf; the other end of the filter inductor Lf is connected to the anode of the filter capacitor Cf and one end of the load R; the other end of the boost inductor L1 is connected to the collector of the switch tube S2 and the emitter of the switch tube S4; the collector of the switch tube S4 is connected to the collector of the switch tube S5 and the anode of the switch capacitor C1; the cathode of the switch capacitor C1 is connected to the emitters of the switch tubes S6 and S7; the cathode of the DC input filter capacitor Cdc, the emitter of the switch tube S2, the collector of the switch tube S7, the cathode of the filter capacitor Cf, and the other end of the load R are connected to the negative electrode of the photovoltaic cell PV.

[0029] A switched capacitor soft charging working mode is constructed. This mode includes two working processes: ① Inductor energy storage process. The photovoltaic cell PV, boost inductor L1, switch tubes S1 and S2 form an inductor charging circuit, and the power supply charges the inductor; ② Capacitor soft charging process. The boost inductor L1, switch capacitor C1 and switch tubes S3, S4, S6 form a capacitor soft charging circuit, which transfers the energy on the inductor to the capacitor to prevent the power supply from directly charging the capacitor. During the energy transfer process, since the current on the inductor cannot change suddenly, the switch tube is prevented from breaking down due to the instantaneous excessive current, so the circuit has soft charging capability.

[0030] By adjusting the duty cycle of the switch tubes S1 and S2 and the energy storage time of the inductor, different voltage gains can be obtained, so that the circuit has a dynamic boost function.

[0031] The present invention also provides a control method for an inductive boost type common ground single-phase inverter, which is used to control the above-mentioned inductive boost type common ground single-phase photovoltaic inverter. Figure 2 and Fig. 9 As shown, the specific steps include:

[0032] The first step: intercept the sinusoidal modulated wave ut with the stacked triangular carriers uc1 and uc2 respectively, and obtain two pre-processed signals A and B through the comparator, and then invert them to obtain a and b respectively.

[0033] Step 2: Perform an OR operation on signal A and the inverted signal b of signal B to obtain the drive signals ug1 and ug2 of switch tubes S1 and S2; perform an AND operation on the inverted signal a of signal A and signal B to obtain the drive signal ug3 of switch tube S3; perform an AND operation on the inverted signal a of signal A and signal B, and then perform an OR operation on the result of the AND operation and the inverted signal b of signal B to obtain the drive signals ug4 and ug6 of switch tubes S4 and S6; use signal A as the drive signal ug5 of switch tube S5; perform an AND operation on the inverted signal a of signal A and signal B, and then perform an OR operation on the result of the AND operation and signal A to obtain the drive signal ug7 of switch tube S7.

[0034] Therefore, through the above control method, the working mode of the inverter can be defined as [M1, M2, M3, M4, M5, M6]; wherein the working mode M1 represents that the power supply charges the boost inductor L1, and the switch capacitor C1 provides a positive voltage to the load R; the working mode M2 ​​represents that the boost inductor L1 softly charges the switch capacitor C1, and the current in the filter inductor Lf flows clockwise through the load, the switch tube S7 and the freewheeling diode of the switch tube S6, and the inverter outputs zero voltage; the working mode M3 represents that all the energy on the inductor L1 is transferred to the capacitor C1, and the current in the filter inductor Lf is The current continues to flow in a clockwise direction, and the inverter continues to output zero voltage; the working mode M4 represents that the power supply charges the boost inductor L1, and the switch capacitor C1 provides a negative voltage to the load R; the working mode M5 represents that the boost inductor L1 softly charges the switch capacitor C1, and the current in the filter inductor Lf flows counterclockwise through the freewheeling diodes of the switch tubes S6 and S7 and the load, and the inverter outputs zero voltage; the working mode M6 represents that all the energy on the inductor L1 is transferred to the capacitor C1, the current in the filter inductor Lf continues to flow counterclockwise, and the inverter continues to output zero voltage.

[0035] The above modes are as follows Figures 3 to 8 As shown, the working principle of each mode of the inverter is briefly analyzed as follows:

[0036] Mode 1: If Figure 3 As shown, the inverter switching state is [1,1,0,0,1,0,1], the voltage between the gate and emitter of the switch tubes S1, S2, S5, and S7 is high, and they are in the on state; the voltage between the gate and emitter of the switch tubes S3, S4, and S6 is low, and they are in the off state. The current flows out from the positive electrode of the photovoltaic cell PV, flows through S1-L1-S2 respectively, and then returns to the negative electrode of the photovoltaic cell PV. The current on the capacitor flows out from the positive electrode of the switch capacitor C1, flows through S5-Lf-R-S7, and then returns to the negative electrode of the switch capacitor C1. At this time, the boost inductor L1 is in the charging state, the switch capacitor C1 is in the discharging state, the output voltage of the inductor boost type common ground single-phase photovoltaic inverter circuit is positive, and the leakage current is zero.

[0037] Mode 2: If Figure 4 As shown, the inverter switch state is [0,0,1,1,0,1,1], the voltage between the gate and emitter of the switch tubes S3, S4, S6, and S7 is high, and they are in the on state; the voltage between the gate and emitter of the switch tubes S1, S2, and S5 is low, and they are in the off state. The current on the inductor L1 flows through the freewheeling diode-C1 of S4-the freewheeling diode-S3 of S6, and the energy is transferred from L1 to C1. The current on the filter inductor Lf flows clockwise through the freewheeling diode of R-S7-S6. At this time, the switch capacitor C1 is in the charging state, the boost inductor L1 is in the discharging state, the output voltage of the common ground single-phase inverter circuit of the inductor boost type is zero, and the leakage current is zero.

[0038] Mode 3: If Figure 5 As shown, the inverter switch state is [0,0,0,0,0,1,1], the voltage between the gate and emitter of the switch tubes S6 and S7 is high, and they are in the on state; the voltage between the gate and emitter of the switch tubes S1, S2, S3, S4, and S5 is low, and they are in the off state. All the energy on the boost inductor L1 is transferred to the switch capacitor C1, and the current on the filter inductor Lf continues to flow clockwise through the freewheeling diode of R-S7-S6. At this time, the output voltage of the common ground single-phase inverter circuit of the inductor boost type is zero, and the leakage current is zero.

[0039] Mode 4: If Figure 6As shown, the inverter switching state is [1,1,0,1,0,1,0], the voltage between the gate and emitter of the switch tubes S1, S2, S4, and S6 is high, and they are in the on state; the voltage between the gate and emitter of the switch tubes S3, S5, and S7 is low, and they are in the off state. The current flows out from the positive electrode of the photovoltaic cell PV, flows through S1-L1-S2, and then returns to the negative electrode of the photovoltaic cell PV. At the same time, the current flows out from the positive electrode of the switch capacitor C2, flows through S4-S2-R-Lf-S6, and then returns to the negative electrode of the switch capacitor C2. At this time, the boost inductor L1 is in the charging state, the switch capacitor C1 is in the discharging state, the output voltage of the inductor boost type common ground single-phase inverter circuit is negative, and the leakage current is zero.

[0040] Mode 5: If Figure 7 As shown, the inverter switch state is [0,0,1,1,0,1,1], the voltage between the gate and emitter of the switch tubes S3, S4, S6, and S7 is high, and they are in the on state; the voltage between the gate and emitter of the switch tubes S1, S2, and S5 is low, and they are in the off state. The current on the inductor L1 flows through the freewheeling diode-C1 of S4-the freewheeling diode-S3 of S6, and the energy is transferred from L1 to C1. The current on the filter inductor Lf flows counterclockwise through the freewheeling diode-NR of S6-S7. At this time, the switch capacitor C1 is in the charging state, the boost inductor L1 is in the discharging state, the output voltage of the common ground single-phase inverter circuit of the inductor boost type is zero, and the leakage current is zero.

[0041] Mode 6: If Figure 8 As shown, the switching state of the inverter is [0,0,0,0,0,1,1], the voltage between the gate and the emitter of the switch tubes S7 and S8 is high, and they are in the on state; the voltage between the gate and the emitter of the switch tubes S1, S2, S3, S4, and S5 is low, and they are in the off state. All the energy on the boost inductor L1 is transferred to the switch capacitor C1. At the same time, the current on the filter circuit and the load continues to flow counterclockwise through the freewheeling diode -NR of S6-S7. At this time, the output voltage of the common ground single-phase inverter circuit of the inductor boost type is zero, and the leakage current is zero.

[0042] Fig. 9The driving signal timing diagram of the inverter, the current value of the boost inductor L1, the voltage value of the switch capacitor C1 and the schematic diagram of the voltage value at the inverter output are given. The waveforms in the figure are from top to bottom: the voltage waveforms ug1 and ug2 between the gate and emitter of the switch tubes S1 and S2; the voltage waveform ug3 between the gate and emitter of the switch tube S3; the voltage waveforms ug4 and ug6 between the gate and emitter of the switch tubes S4 and S6; the voltage waveform ug5 between the gate and emitter of the switch tube S5; the voltage waveform ug7 between the gate and emitter of the switch tube S7; the current value iL1 on the boost inductor L1; the voltage value ufc1 of the switch capacitor C1; the voltage value uo at the inverter output. Taking the positive half cycle as an example, assuming that the photovoltaic cell voltage is Upv, the duty cycle of the switch tubes S1 and S2 is D, the voltage value uo at the inverter output is

[0043]

[0044] From the above analysis, it can be seen that the inductor boost type common ground single-phase photovoltaic inverter topology can eliminate the influence of leakage current caused by the parasitic capacitance of photovoltaic cells to the ground; the inductor is used to softly charge the capacitor. Since the current on the inductor cannot change suddenly, it effectively avoids the instantaneous excessive current caused by the direct charging of the capacitor by the power supply, so that the reliability of the inverter is effectively improved; when the switch duty cycle D is greater than 0.5, the circuit has a boost function. At the same time, by adjusting the switch duty cycle to adjust the circuit boost ratio, different voltage gains are obtained, providing dynamic boost capability, and greatly improving the utilization rate of DC voltage.

[0045] In summary, the inductive boost type common ground single-phase photovoltaic inverter topology of the present invention can not only eliminate leakage current, but also utilize soft charging technology to effectively avoid the instantaneous excessive current caused by direct charging of the capacitor by the power supply. At the same time, it has a dynamic boost function, which can improve the utilization rate of the DC voltage and has good engineering application value.

[0046] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. An inductive boost type common ground single-phase photovoltaic inverter, characterized in that: It includes a photovoltaic cell PV, an inductive boost type common ground single-phase photovoltaic inverter circuit, a single-phase output LC filter circuit and a single-phase load; the inductive boost type common ground single-phase photovoltaic inverter circuit includes a DC input filter capacitor Cdc, a boost inductor L1, a switch capacitor C1, and switch tubes S1 to S7, wherein the switch tubes S1 and S3 are switch tubes without freewheeling diodes, and the other switch tubes are switch tubes 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 R.

2. The inductive boost type common ground single-phase photovoltaic inverter according to claim 1, characterized in that: The positive electrode of the photovoltaic cell PV is connected to the anode of the DC input filter capacitor Cdc and the collector of the switch tube S1; the emitter of the switch tube S1 is connected to the emitter of the switch tube S3 and one end of the boost inductor L1; the collector of the switch tube S3 is connected to the emitter of the switch tube S5, the collector of the switch tube S6, and one end of the filter inductor Lf; the other end of the filter inductor Lf is connected to the anode of the filter capacitor Cf and one end of the load R; the other end of the boost inductor L1 is connected to the collector of the switch tube S2 and the emitter of the switch tube S4; the collector of the switch tube S4 is connected to the collector of the switch tube S5 and the anode of the switch capacitor C1; the cathode of the switch capacitor C1 is connected to the emitters of the switch tubes S6 and S7; the cathode of the DC input filter capacitor Cdc, the emitter of the switch tube S2, the collector of the switch tube S7, the cathode of the filter capacitor Cf, and the other end of the load R are connected to the negative electrode of the photovoltaic cell PV.

3. The inductive boost type common ground single-phase photovoltaic inverter according to claim 1, characterized in that: A switched capacitor soft charging working mode is constructed, which includes two working processes: ① Inductor energy storage process, in which the photovoltaic cell PV, boost inductor L1, switch tubes S1 and S2 form an inductor charging circuit, and the power supply charges the inductor; ② Capacitor soft charging process, in which the boost inductor L1, switch capacitor C1 and switch tubes S3, S4, S6 form a capacitor soft charging circuit, which transfers the energy on the inductor to the capacitor to prevent the power supply from directly charging the capacitor.

4. The inductive boost type common ground single-phase photovoltaic inverter according to claim 1, characterized in that: By adjusting the duty cycle of the switch tubes S1 and S2 and the energy storage time of the inductor, different voltage gains can be obtained, so that the circuit has a dynamic boost function.

5. The inductive boost type common ground single-phase photovoltaic inverter according to claim 1, characterized in that: The working modes of the inverter are defined as [M1, M2, M3, M4, M5, M6]; the working mode M1 represents that the power supply charges the boost inductor L1, and the switch capacitor C1 provides a positive voltage to the load R; the working mode M2 ​​represents that the boost inductor L1 softly charges the switch capacitor C1, and the current in the filter inductor Lf flows clockwise through the load R, the switch tube S7 and the freewheeling diode of the switch tube S6, and the inverter outputs zero voltage; the working mode M3 represents that all the energy on the inductor L1 is transferred to the capacitor C1, and the current in the filter inductor Lf continues to flow clockwise. The working mode M4 represents that the power supply charges the boost inductor L1, and the switch capacitor C1 provides a negative voltage to the load R; the working mode M5 represents that the boost inductor L1 softly charges the switch capacitor C1, and the current in the filter inductor Lf flows counterclockwise through the switch tube S6, the freewheeling diode of the switch tube S7 and the load R, and the inverter outputs zero voltage; the working mode M6 represents that all the energy on the inductor L1 is transferred to the capacitor C1, the current in the filter inductor Lf continues to flow counterclockwise, and the inverter continues to output zero voltage.

6. The inductive boost type common ground single-phase photovoltaic inverter according to claim 1, characterized in that: The control method of the inverter comprises the following steps: Step 1: Intersect the sinusoidal modulated wave ut with the stacked triangular carriers uc1 and uc2 respectively, and obtain two pre-processed signals A and B through the comparator, and then invert them to obtain a and b respectively; Step 2: Perform an OR operation on signal A and the inverted signal b of signal B to obtain the drive signals ug1 and ug2 of switch tubes S1 and S2; perform an AND operation on the inverted signal a of signal A and signal B to obtain the drive signal ug3 of switch tube S3; perform an AND operation on the inverted signal a of signal A and signal B, and then perform an OR operation on the result of the AND operation and the inverted signal b of signal B to obtain the drive signals ug4 and ug6 of switch tubes S4 and S6; use signal A as the drive signal ug5 of switch tube S5; perform an AND operation on the inverted signal a of signal A and signal B, and then perform an OR operation on the result of the AND operation and signal A to obtain the drive signal ug7 of switch tube S7.

7. The inductive boost type common ground single-phase photovoltaic inverter according to claim 5, characterized in that: The switching states of the switching tubes corresponding to the six working modes of the inverter are: mode M1 [1,1,0,0,1,0,1], mode M2 ​​[0,0,1,1,0,1,1], mode M3 [0,0,0,0,0,1,1], mode M4 [1,1,0,1,0,1,0], mode M5 [0,0,1,1,0,1,1], mode M6 [0,0,0,0,0,1,1], where 0 is a low level indicating that the switch tube is turned off, and 1 is a high level indicating that the switch tube is turned on.

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