Photovoltaic grid-connected inverter and modulation method, device, medium, equipment and product thereof

Abstract

This invention discloses a photovoltaic grid-connected inverter and its modulation method, apparatus, medium, equipment, and products. The inverter includes a DC source, an inverter network, a filter inductor, and a power grid. The inverter network includes a flying capacitor, a first power switch, a second power switch, a third power switch, a fourth power switch, and a fifth power switch. The positive terminal of the DC source is connected to the collectors of the first and third power switches, and the negative terminal is connected to the emitter of the second power switch, the collector of the fifth power switch, and the power grid. The positive terminal of the flying capacitor is connected to the emitter of the first power switch and the collector of the second power switch, and the negative terminal is connected to the emitter of the third power switch, the collector of the fourth power switch, and the filter inductor. By inserting the fifth power switch and the flying capacitor, the photovoltaic grid-connected inverter decouples the DC source from the AC power grid in freewheeling mode, maintaining a constant common-mode voltage to suppress leakage current.

Description

Technical Field

[0001] This invention relates to photovoltaic grid-connected inverters and their modulation methods, devices, media, equipment, and products, belonging to the technical field of photovoltaic grid-connected inverters. Background Technology

[0002] In distributed photovoltaic (PV) power generation systems, non-isolated grid-connected inverters (TLI) offer advantages such as small size, low cost, and high efficiency. However, due to the lack of effective electrical isolation between the TLI topology and the grid, common-mode voltage generates common-mode leakage current through the parasitic capacitance of the PV array to ground, increasing grid-connected current harmonics, affecting the quality of the incoming current, and potentially causing safety issues. Half-bridge TLI topologies directly connect the grid neutral point to the DC bus midpoint, clamping the voltage across the parasitic capacitance and suppressing leakage current. However, half-bridge TLI topologies exhibit significant voltage drop, requiring twice the input voltage of full-bridge TLI topologies, making them unsuitable for low-power applications. Full-bridge TLI topologies employing unipolar sinusoidal pulse width modulation also suppress leakage current, but generate high-frequency common-mode voltage, resulting in larger grid-connected current harmonics, and require two filter inductors, increasing cost. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a photovoltaic grid-connected inverter and its modulation method, device, medium, equipment and products. By inserting the fifth power switch S5 and the flying capacitor C1, the photovoltaic grid-connected inverter decouples the DC source from the AC grid in freewheeling mode, keeping the common mode voltage unchanged to suppress leakage current.

[0004] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0005] In a first aspect, this invention discloses a photovoltaic grid-connected inverter, comprising a DC source, an inverter network, and a filter inductor L. f and power grid,

[0006] The inverter network includes a flying capacitor C1, a first power switch S1, a second power switch S2, a third power switch S3, a fourth power switch S4, and a fifth power switch S5.

[0007] The positive terminal of the DC source is connected to the collector of the first power switch S1 and the collector of the third power switch S3, respectively; the negative terminal of the DC source is connected to the emitter of the second power switch S2, the collector of the fifth power switch S5, and one end of the power grid, respectively; the other end of the power grid is connected to the filter inductor L. f One end;

[0008] The positive terminal of the flying capacitor C1 is connected to the emitter of the first power switch S1 and the collector of the second power switch S2, respectively; the negative terminal of the flying capacitor C1 is connected to the emitter of the third power switch S3, the collector of the fourth power switch S4, and the filter inductor L, respectively. f The other end; the emitter of the fourth power switch S4 is connected to the emitter of the fifth power switch S5.

[0009] Furthermore, the inverter network also includes a parasitic capacitance to ground C. pv The parasitic capacitance to ground C pv One end is connected to the negative terminal of the DC source, and the parasitic capacitance to ground C pv The other end is grounded and connected to one end of the power grid; the negative terminal of the DC source is directly connected to one end of the power grid to form a common-ground topology, thereby reducing the parasitic capacitance C to ground. pv Short circuit, thereby eliminating common-mode leakage current.

[0010] Furthermore, the first power switch S1, the second power switch S2, the third power switch S3, the fourth power switch S4, and the fifth power switch S5 are all switching devices with symmetrical parasitic parameters.

[0011] Furthermore, the DC source includes a photovoltaic cell (PV) and a DC voltage regulator capacitor (C). dc ,

[0012] The positive terminal of the photovoltaic cell PV is connected to a DC voltage regulator capacitor C. dc The positive terminal of the photovoltaic cell PV is connected to the negative terminal of the DC voltage regulator capacitor C. dc The negative electrode.

[0013] Secondly, this invention discloses a modulation method for the aforementioned photovoltaic grid-connected inverter, wherein the current flowing through the power grid is the grid-connected current i. g The voltage across the power grid is the grid voltage v. g Its characteristic is that it includes the following steps:

[0014] Obtain and determine the grid-connected current i g and grid voltage v g The direction; where, from the filter inductor L f Grid-connected current i flowing to the power grid g Positive direction;

[0015] If the grid current i g and grid voltage v g When both directions are positive, the photovoltaic grid-connected inverter is in the working range I and switches between M1 mode and M2 mode;

[0016] If the grid current i gIn the positive direction, the grid voltage v g When the direction is negative, the photovoltaic grid-connected inverter is in the operating range II and switches between M3 mode and M4 mode;

[0017] If the grid current i g and grid voltage v g When both directions are negative, the photovoltaic grid-connected inverter is in operating range III, switching between M5 mode and M6 mode;

[0018] If the grid current i g In the negative direction, the grid voltage v g When the direction is positive, the photovoltaic grid-connected inverter is in the working range IV and switches between M7 mode and M8 mode.

[0019] Furthermore, when the photovoltaic grid-connected inverter is in M1 mode, the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the DC source supplies power to the filter inductor L through the third power switch S3. f Charge;

[0020] When the photovoltaic grid-connected inverter is in M2 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off. This allows the DC source to charge the flying capacitor C1 through the first power switch S1, and the filter inductor L... f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5.

[0021] Furthermore, when the photovoltaic grid-connected inverter is in M3 mode, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned off, so that the grid supplies power to the flying capacitor C1 and the filter inductor L through the second power switch S2. f Charge;

[0022] When the photovoltaic grid-connected inverter is in M4 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that current flows through the fourth power switch S4, the fifth power switch S5, and the filter inductor L. f And power grid.

[0023] Furthermore, when the photovoltaic grid-connected inverter is in M5 mode, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3 and the fifth power switch S5 are turned off, so that the flying capacitor C1 supplies power to the grid through the second power switch S2.

[0024] When the photovoltaic grid-connected inverter is in M6 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off. This allows the DC source to charge the flying capacitor C1 through the first power switch S1, the fourth power switch S4, and the fifth power switch S5, and the filter inductor L... f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5.

[0025] Furthermore, when the photovoltaic grid-connected inverter is in M7 mode, the first power switch S1, the third power switch S3 and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the grid supplies power to the DC source.

[0026] When the photovoltaic grid-connected inverter is in M8 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch S1, the fourth power switch S4, and the fifth power switch S5.

[0027] Thirdly, the present invention discloses a modulation device for a photovoltaic grid-connected inverter, applicable to the photovoltaic grid-connected inverter of the first aspect, wherein the current flowing through the grid is the grid-connected current i. g The voltage across the power grid is the grid voltage v. g Its characteristic is that it includes the following steps:

[0028] The current and voltage module is used to acquire and determine the grid-connected current i. g and grid voltage v g The direction; where, from the filter inductor L f Grid-connected current i flowing to the power grid g Positive direction;

[0029] The working interval I module is used to determine if the grid-connected current i g and grid voltage v g When both directions are positive, the photovoltaic grid-connected inverter is in the working range I and switches between M1 mode and M2 mode;

[0030] The working interval II module is used to handle the grid-connected current i g In the positive direction, the grid voltage vg When the direction is negative, the photovoltaic grid-connected inverter is in the operating range II and switches between M3 mode and M4 mode;

[0031] The working interval III module is used to address the grid-connected current i g and grid voltage v g When both directions are negative, the photovoltaic grid-connected inverter is in operating range III, switching between M5 mode and M6 mode;

[0032] The IV module for the working interval is used to determine if the grid-connected current i g In the negative direction, the grid voltage v g When the direction is positive, the photovoltaic grid-connected inverter is in the working range IV and switches between M7 mode and M8 mode.

[0033] Furthermore, when the photovoltaic grid-connected inverter is in M1 mode, the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the DC source supplies power to the filter inductor L through the third power switch S3. f Charge;

[0034] When the photovoltaic grid-connected inverter is in M2 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off. This allows the DC source to charge the flying capacitor C1 through the first power switch S1, and the filter inductor L... f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5.

[0035] Fourthly, the present invention discloses a computer-readable storage medium storing a computer program / instructions thereon, which, when executed by a processor, implements the steps of the modulation method for a photovoltaic grid-connected inverter of the second aspect.

[0036] Fifthly, the present invention discloses a computer device, comprising:

[0037] Memory, used to store computer programs / instructions;

[0038] A processor for executing the computer program / instructions to implement the modulation method of the photovoltaic grid-connected inverter in the second aspect.

[0039] In a sixth aspect, the present invention discloses a computer program product, including a computer program / instructions, which, when executed by a processor, implement the steps of the modulation method for a photovoltaic grid-connected inverter of the second aspect.

[0040] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0041] The photovoltaic grid-connected inverter of the present invention, through the insertion of the fifth power switch S5 and the flying capacitor C1, decouples the DC source from the AC grid in the freewheeling mode, and keeps the common-mode voltage unchanged to suppress leakage current.

[0042] The negative terminal of the DC source of this invention is directly connected to one end of the power grid to form a common-ground topology, thereby reducing the parasitic capacitance C to ground. pv Short circuit, thus completely eliminating common-mode leakage current.

[0043] The modulation method of the photovoltaic grid-connected inverter of this invention adopts a unipolar PWM modulation strategy. First, it selects the DC source to directly transfer energy to the grid as much as possible to reduce energy loss. Second, it controls the number of switching transistors to a minimum to reduce conduction losses. Finally, it reduces switching losses by reducing the frequency of switching transistor operation. This reduces the harmonic distortion rate of the grid-connected current and improves the grid-connected power quality, demonstrating significant application value and promising prospects. Attached Figure Description

[0044] Figure 1 This is the topology diagram of the photovoltaic grid-connected inverter provided in Example 1;

[0045] Figure 2 This is the switching transistor drive signal diagram provided in Embodiment 1;

[0046] Figure 3 This is a schematic diagram of the M1 mode provided in Embodiment 1;

[0047] Figure 4 This is a schematic diagram of the M2 mode provided in Embodiment 1;

[0048] Figure 5 This is a schematic diagram of the M3 mode provided in Embodiment 1;

[0049] Figure 6 This is a schematic diagram of the M4 mode provided in Embodiment 1;

[0050] Figure 7 This is a schematic diagram of the M5 mode provided in Embodiment 1;

[0051] Figure 8 This is a schematic diagram of the M6 ​​mode provided in Embodiment 1;

[0052] Figure 9 This is a schematic diagram of the M7 mode provided in Embodiment 1;

[0053] Figure 10 This is a schematic diagram of the M8 mode provided in Embodiment 1. Detailed Implementation

[0054] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0055] Example 1

[0056] This embodiment 1 provides a photovoltaic grid-connected inverter, such as Figure 1 As shown, it includes a DC source, an inverter network, and a filter inductor L. f and power grid,

[0057] The inverter network includes a flying capacitor C1, a first power switch S1, a second power switch S2, a third power switch S3, a fourth power switch S4, and a fifth power switch S5;

[0058] The positive terminal of the DC source is connected to the collectors of the first power switch S1 and the third power switch S3, respectively; the negative terminal of the DC source is connected to the emitter of the second power switch S2, the collector of the fifth power switch S5, and one end of the power grid, respectively; the other end of the power grid is connected to the filter inductor L. f One end;

[0059] The positive terminal of the flying capacitor C1 is connected to the emitter of the first power switch S1 and the collector of the second power switch S2, respectively; the negative terminal of the flying capacitor C1 is connected to the emitter of the third power switch S3, the collector of the fourth power switch S4, and the filter inductor L, respectively. f At the other end; the emitter of the fourth power switch S4 is connected to the emitter of the fifth power switch S5.

[0060] The technical concept of this invention is as follows: By inserting the fifth power switch S5 and the flying capacitor C1, the photovoltaic grid-connected inverter of this invention decouples the DC source from the AC grid in freewheeling mode, keeping the common-mode voltage unchanged to suppress leakage current.

[0061] like Figure 1 As shown, the inverter network also includes a parasitic capacitance to ground, C. pv Parasitic capacitance to ground C pv One end is connected to the negative terminal of the DC source, and the parasitic capacitance to ground is C. pv The other end is grounded and connected to one end of the power grid; the negative terminal of the DC source is directly connected to one end of the power grid to form a common-ground topology, thereby generating a parasitic capacitance C to ground. pv Short circuit, thereby eliminating common-mode leakage current.

[0062] DC sources include photovoltaic cells (PV) and DC voltage regulator capacitors (C). dc The positive terminal of the photovoltaic cell PV is connected to a DC voltage regulator capacitor C. dcThe positive terminal of the photovoltaic cell (PV) is connected to the negative terminal of the DC voltage regulator capacitor (C). dc The negative electrode.

[0063] In this embodiment, the first power switch S1, the second power switch S2, the third power switch S3, the fourth power switch S4, and the fifth power switch S5 are all switching devices with symmetrical parasitic parameters.

[0064] The photovoltaic grid-connected inverter in this embodiment operates in two phases: an energy transfer phase and a freewheeling phase. During the negative half-cycle of the grid voltage, energy is provided by the flying capacitor C1.

[0065] Specifically, the design steps for the modulation method of a photovoltaic grid-connected inverter are as follows:

[0066] Step 1: Determine the operating mode selection principles. Based on the unipolar PWM modulation strategy, the operating mode selection principles are determined as follows: 1) Select photovoltaic cells that directly transfer energy to the grid whenever possible to reduce energy loss. 2) Select the minimum number of power switching transistors involved to reduce conduction losses. 3) Reduce the operating frequency of the power switching transistors to reduce switching losses.

[0067] Step Two: Analyze the common-mode characteristics of the photovoltaic grid-connected inverter. By simplifying the equivalent circuit of the photovoltaic grid-connected inverter, the equivalent common-mode voltage is obtained. The equivalent common-mode voltage v tCM The expression is as follows:

[0068]

[0069] In the formula, v AN This represents the potential difference between the AC output point A and the negative DC input point N; v BN This represents the potential difference between the AC output point B and the negative DC input point N.

[0070] like Figure 1 As shown, AC output point A is located at the filter inductor L. f Between the third power switch S3 and the fifth power switch S5, the AC output point B is located between the power grid and the fifth power switch S5, and the negative DC input point N is located between the DC source and the second power switch S2.

[0071] This photovoltaic grid-connected inverter inserts an additional fifth power switch S5 and a flying capacitor C1 into a traditional single-phase bridge inverter to decouple the DC side from the AC side during the inverter's freewheeling phase, maintain the common-mode voltage, and suppress leakage current.

[0072] Step 3: Divide the working area. The current flowing through the power grid is the grid-connected current i. g The voltage across the power grid is the grid voltage v. g Assuming from the filter inductor L fGrid-connected current i flowing to the power grid g The positive direction. Based on the grid-connected current i g and grid voltage v g Based on the direction, photovoltaic grid-connected inverters can be divided into four operating ranges I-IV, such as... Figure 2 As shown. Based on the energy transfer direction, each operating range has two operating stages, I-II: the energy transfer stage and the freewheeling stage. According to the relationship between the common-mode characteristics and the switching state in each operating range, and combined with the operating mode selection principle in step one, the operating stage can be changed by controlling the inverter's switching.

[0073] The following are the specific design steps for each work area:

[0074] Interval I: Grid-connected current i at this time g and grid voltage v g Both are in the positive direction, and the power grid absorbs power. During the energy transfer phase, to reduce energy loss, the DC bus voltage U... dc Energy is directly transferred to the grid, and the third power switch S3 is turned on; during the freewheeling phase, the photovoltaic cells charge the flying capacitor C1, and the filter inductor L... f During freewheeling, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on. Considering the switching states of Stage I and Stage II, and without affecting normal operation, to reduce the frequency of switching actions, the first power switch S1 and the fifth power switch S5 are kept constantly on within interval I.

[0075] Interval II: At this time, the grid-connected current i g In the positive direction, the grid voltage v g In the negative direction, the power grid generates power. During the energy transfer phase, according to principle 2, the power grid directly replenishes energy to the flying capacitor C1, and the second power switch S2 is turned on. Since the conduction of the fourth power switch S4 does not affect the normal operation of the energy transfer phase, and at the same time, it is necessary to provide a loop for the inductor freewheeling current, according to principle 3, the fourth power switch S4 is kept on throughout interval II. During the freewheeling phase, combined with the interval I modulation strategy, according to principle 3, the first power switch S1 and the fifth power switch S5 are turned on.

[0076] Interval III: At this time, the grid-connected current i g and grid voltage v g Both directions are negative, and the grid absorbs power. During the energy transfer phase, according to principle 2, the flying capacitor C1 directly transmits energy to the grid, and the second power switch S2 is turned on; during the freewheeling phase, the photovoltaic cell PV charges the flying capacitor C1, and the filter inductor L... fDuring freewheeling, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on. Considering the switching states in stages I and II, and to reduce the frequency of switching operations without affecting normal operation, the fourth power switch S4 is kept constantly on in interval III.

[0077] Interval IV: At this time, the grid-connected current i g In the negative direction, the grid voltage v g In the positive direction, the grid generates power. During the energy transfer phase, according to principle 1, the grid directly transfers energy to the photovoltaic cell PV, and the third power switch S3 is turned on; during the freewheeling phase, the photovoltaic cell PV charges the flying capacitor C1, and the filter inductor L... f During freewheeling, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on. Considering the switching states of Stage I and Stage II, and to reduce the frequency of switching operations without affecting normal operation, the first power switch S1 and the fifth power switch S5 are kept constantly on within interval IV.

[0078] Based on the modulation method described above, the photovoltaic grid-connected inverter has four operating zones I-IV. Within each operating zone, two operating stages are switched by a switch: a power transmission stage and a freewheeling stage. This results in a total of eight operating modes M1-M8 for the photovoltaic grid-connected inverter, as detailed below:

[0079] M1 mode: such as Figure 3 As shown, the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the DC source supplies power to the filter inductor L through the third power switch S3. f Charge.

[0080] M2 mode: such as Figure 4 As shown, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch S1, and the filter inductor L... f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5.

[0081] M3 mode: such as Figure 5 As shown, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned off, so that the power grid supplies power to the flying capacitor C1 and the filter inductor L through the second power switch S2. f Charge.

[0082] M4 mode: such as Figure 6As shown, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that current flows through the fourth power switch S4, the fifth power switch S5, and the filter inductor L. f And power grid.

[0083] M5 mode: such as Figure 7 As shown, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3 and the fifth power switch S5 are turned off, so that the flying capacitor C1 supplies power to the grid through the second power switch S2.

[0084] M6 mode: such as Figure 8 As shown, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch S1, the fourth power switch S4, and the fifth power switch S5. The filter inductor L... f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5.

[0085] M7 mode: such as Figure 9 As shown, when the photovoltaic grid-connected inverter is in M7 mode, the first power switch S1, the third power switch S3 and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the grid can supply power to the DC source.

[0086] M8 mode: such as Figure 10 As shown, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch S1, the fourth power switch S4, and the fifth power switch S5.

[0087] In summary, this photovoltaic grid-connected inverter, through the insertion of the fifth power switch S5 and the flying capacitor C1, decouples the DC source from the AC grid in freewheeling mode, maintaining the common-mode voltage constant to suppress leakage current.

[0088] The negative terminal of the DC source is directly connected to one end of the power grid to form a common-ground topology, thereby generating a parasitic capacitance C to ground. pv Short circuit, thus completely eliminating common-mode leakage current.

[0089] The modulation method of the photovoltaic grid-connected inverter adopts a unipolar PWM modulation strategy. First, it selects the DC source to directly transfer energy to the grid as much as possible to reduce energy loss. Second, it controls the number of switching transistors to a minimum to reduce conduction losses. Finally, it reduces switching losses by decreasing the frequency of switching transistor operation. This reduces the harmonic distortion rate of the grid-connected current and improves the grid-connected power quality, demonstrating significant application value and promising prospects.

[0090] Example 2

[0091] This embodiment 2 provides a modulation method for a photovoltaic grid-connected inverter based on embodiment 1, wherein the current flowing through the grid is the grid-connected current i. g The voltage across the power grid is the grid voltage v. g Its characteristic is that it includes the following steps:

[0092] Obtain and determine the grid-connected current i g and grid voltage v g The direction; where, from the filter inductor L f Grid-connected current i flowing to the power grid g Positive direction;

[0093] If the grid current i g and grid voltage v g When both directions are positive, the photovoltaic grid-connected inverter is in operating range I, switching between M1 mode and M2 mode;

[0094] If the grid current i g In the positive direction, the grid voltage v g When the direction is negative, the photovoltaic grid-connected inverter is in operating range II, switching between M3 mode and M4 mode;

[0095] If the grid current i g and grid voltage v g When both directions are negative, the photovoltaic grid-connected inverter is in operating range III, switching between M5 mode and M6 mode;

[0096] If the grid current i g In the negative direction, the grid voltage v g When the direction is positive, the photovoltaic grid-connected inverter is in the working range IV, switching between M7 mode and M8 mode.

[0097] Furthermore, when the photovoltaic grid-connected inverter is in M1 mode, the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the DC source supplies power to the filter inductor L through the third power switch S3. f Charge;

[0098] When the photovoltaic grid-connected inverter is in M2 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off. This allows the DC source to charge the flying capacitor C1 through the first power switch S1, and the filter inductor L... f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5.

[0099] Furthermore, when the photovoltaic grid-connected inverter is in M3 mode, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned off, so that the grid supplies power to the flying capacitor C1 and the filter inductor L through the second power switch S2. f Charge;

[0100] When the photovoltaic grid-connected inverter is in M4 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, allowing current to flow through the fourth power switch S4, the fifth power switch S5, and the filter inductor L. f And power grid.

[0101] Furthermore, when the photovoltaic grid-connected inverter is in M5 mode, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3 and the fifth power switch S5 are turned off, so that the flying capacitor C1 supplies power to the grid through the second power switch S2.

[0102] When the photovoltaic grid-connected inverter is in M6 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off. This allows the DC source to charge the flying capacitor C1 through the first power switch S1, the fourth power switch S4, and the fifth power switch S5. The filter inductor L... f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5.

[0103] Furthermore, when the photovoltaic grid-connected inverter is in M7 mode, the first power switch S1, the third power switch S3 and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the grid can supply power to the DC source.

[0104] When the photovoltaic grid-connected inverter is in M8 mode, the first power switch S1, the fourth power switch S4 and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch S1, the fourth power switch S4 and the fifth power switch S5.

[0105] Example 3

[0106] This embodiment 3 provides a modulation device for a photovoltaic grid-connected inverter, applicable to the photovoltaic grid-connected inverter of embodiment 1, wherein the current flowing through the grid is the grid-connected current i. g The voltage across the power grid is the grid voltage v. g Its characteristic is that it includes the following steps:

[0107] The current and voltage module is used to acquire and determine the grid-connected current i. g and grid voltage v g The direction; where, from the filter inductor L f Grid-connected current i flowing to the power grid g Positive direction;

[0108] The working interval I module is used to handle grid-connected current i g and grid voltage v g When both directions are positive, the photovoltaic grid-connected inverter is in operating range I, switching between M1 mode and M2 mode;

[0109] Working area II module, used if the grid-connected current i g In the positive direction, the grid voltage v g When the direction is negative, the photovoltaic grid-connected inverter is in operating range II, switching between M3 mode and M4 mode;

[0110] Working section III module, used if the grid-connected current i g and grid voltage v g When both directions are negative, the photovoltaic grid-connected inverter is in operating range III, switching between M5 mode and M6 mode;

[0111] The IV module for the working interval is used when the grid-connected current i g In the negative direction, the grid voltage v g When the direction is positive, the photovoltaic grid-connected inverter is in the working range IV, switching between M7 mode and M8 mode.

[0112] Furthermore, when the photovoltaic grid-connected inverter is in M1 mode, the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the DC source supplies power to the filter inductor L through the third power switch S3. f Charge;

[0113] When the photovoltaic grid-connected inverter is in M2 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off. This allows the DC source to charge the flying capacitor C1 through the first power switch S1, and the filter inductor L... f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5.

[0114] Example 4

[0115] This embodiment 4 provides a computer-readable storage medium storing a computer program / instruction, which, when executed by a processor, implements the steps of the modulation method for the photovoltaic grid-connected inverter in embodiment 2.

[0116] Example 5

[0117] This embodiment 5 provides a computer device, including:

[0118] Memory, used to store computer programs / instructions;

[0119] A processor for executing computer programs / instructions to implement the steps of the modulation method for the photovoltaic grid-connected inverter of Embodiment 2.

[0120] Example 6

[0121] This embodiment 6 provides a computer program product, including a computer program / instruction, which, when executed by a processor, implements the steps of the modulation method for the photovoltaic grid-connected inverter in embodiment 2.

[0122] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0123] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0124] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0125] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0126] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A modulation method for a photovoltaic grid-connected inverter, characterized in that, The photovoltaic grid-connected inverter includes a DC source, an inverter network, and a filter inductor. L f and power grid, The inverter network includes a flying capacitor. C 1. First power switch S1, second power switch S2, third power switch S3, fourth power switch S4 and fifth power switch S5; The positive terminal of the DC source is connected to the collector of the first power switch S1 and the collector of the third power switch S3, respectively; the negative terminal of the DC source is connected to the emitter of the second power switch S2, the collector of the fifth power switch S5, and one end of the power grid, respectively; the other end of the power grid is connected to a filter inductor. L f One end; The flying capacitor C The positive terminal of 1 is connected to the emitter of the first power switch S1 and the collector of the second power switch S2, respectively; the flying capacitor C The negative terminal of 1 is connected to the emitter of the third power switch S3, the collector of the fourth power switch S4, and the filter inductor, respectively. L f At the other end; the emitter of the fourth power switch S4 is connected to the emitter of the fifth power switch S5; The current flowing through the power grid is the grid-connected current. i g The voltage across the power grid is the grid voltage. v g The modulation method of the photovoltaic grid-connected inverter includes the following steps: Obtain and determine the grid-connected current i g and grid voltage v g The direction; where, from the filter inductor L f Grid-connected current flowing to the power grid i g Positive direction; If the grid-connected current i g and grid voltage v g When both directions are positive, the photovoltaic grid-connected inverter is in the working range I and switches between M1 mode and M2 mode; If the grid-connected current i g In the positive direction, the grid voltage v g When the direction is negative, the photovoltaic grid-connected inverter is in the operating range II and switches between M3 mode and M4 mode; If the grid-connected current i g and grid voltage v g When both directions are negative, the photovoltaic grid-connected inverter is in operating range III, switching between M5 mode and M6 mode; If the grid-connected current i g In the negative direction, the grid voltage v g When the direction is positive, the photovoltaic grid-connected inverter is in the working range IV and switches between M7 mode and M8 mode; When the photovoltaic grid-connected inverter is in M1 mode, the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the DC source supplies power to the filter inductor through the third power switch S3. L f Charge; When the photovoltaic grid-connected inverter is in M2 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source supplies power to the flying capacitor through the first power switch S1. C 1. Charging and filtering inductors L f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5. When the photovoltaic grid-connected inverter is in M3 mode, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned off, so that the grid supplies power to the flying capacitor through the second power switch S2. C 1 and filter inductor L f Charge; When the photovoltaic grid-connected inverter is in M4 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that current flows through the fourth power switch S4, the fifth power switch S5, and the filter inductor. L f and power grid; When the photovoltaic grid-connected inverter is in M5 mode, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned off, so that the flying capacitor... C 1. Power is supplied to the grid through the second power switch S2; When the photovoltaic grid-connected inverter is in M6 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source supplies power to the flying capacitor through the first power switch S1, the fourth power switch S4, and the fifth power switch S5. C 1. Charging and filtering inductors L f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5. When the photovoltaic grid-connected inverter is in M7 mode, the first power switch S1, the third power switch S3 and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the grid can supply power to the DC source. When the photovoltaic grid-connected inverter is in M8 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source supplies power to the flying capacitor through the first power switch S1, the fourth power switch S4, and the fifth power switch S5. C 1. Charge.

2. The modulation method for a photovoltaic grid-connected inverter according to claim 1, characterized in that, The inverter network also includes parasitic capacitance to ground. C pv The parasitic capacitance to ground C pv One end is connected to the negative terminal of the DC source, and the parasitic capacitance to ground... C pv The other end is grounded and connected to one end of the power grid; the negative terminal of the DC source is directly connected to one end of the power grid to form a common-ground topology, thereby generating parasitic capacitance to ground. C pv Short circuit, thereby eliminating common-mode leakage current.

3. The modulation method for a photovoltaic grid-connected inverter according to claim 1, characterized in that, The first power switch S1, the second power switch S2, the third power switch S3, the fourth power switch S4, and the fifth power switch S5 are all switching devices with symmetrical parasitic parameters.

4. The modulation method for a photovoltaic grid-connected inverter according to claim 1, characterized in that, The DC source includes photovoltaic cells (PV) and a DC voltage regulator capacitor. C dc , The positive terminal of the photovoltaic cell PV is connected to a DC voltage regulator capacitor. C dc The positive terminal of the photovoltaic cell (PV) is connected to a DC voltage regulator capacitor, and the negative terminal of the photovoltaic cell (PV) is connected to a DC voltage regulator capacitor. C dc The negative electrode.

5. A modulation device for a photovoltaic grid-connected inverter, characterized in that, The photovoltaic grid-connected inverter includes a DC source, an inverter network, and a filter inductor. L f and power grid, The inverter network includes a flying capacitor. C 1. First power switch S1, second power switch S2, third power switch S3, fourth power switch S4 and fifth power switch S5; The positive terminal of the DC source is connected to the collector of the first power switch S1 and the collector of the third power switch S3, respectively; the negative terminal of the DC source is connected to the emitter of the second power switch S2, the collector of the fifth power switch S5, and one end of the power grid, respectively; the other end of the power grid is connected to a filter inductor. L f One end; The flying capacitor C The positive terminal of 1 is connected to the emitter of the first power switch S1 and the collector of the second power switch S2, respectively; the flying capacitor C The negative terminal of 1 is connected to the emitter of the third power switch S3, the collector of the fourth power switch S4, and the filter inductor, respectively. L f At the other end; the emitter of the fourth power switch S4 is connected to the emitter of the fifth power switch S5; The current flowing through the power grid is the grid-connected current. i g The voltage across the power grid is the grid voltage. v g The modulation device includes the following modules: The current and voltage module is used to acquire and determine the grid-connected current. i g and grid voltage v g The direction; where, from the filter inductor L f Grid-connected current flowing to the power grid i g Positive direction; Working section I module, used if the grid-connected current i g and grid voltage v g When both directions are positive, the photovoltaic grid-connected inverter is in the working range I and switches between M1 mode and M2 mode; Working section II module, used if the grid-connected current i g When it is in the positive direction, the grid voltage v g When the direction is negative, the photovoltaic grid-connected inverter is in the operating range II and switches between M3 mode and M4 mode; Working section III module, used if the grid-connected current i g and grid voltage v g When both directions are negative, the photovoltaic grid-connected inverter is in operating range III, switching between M5 mode and M6 mode; The IV module for the working interval is used to determine if the grid-connected current... i g In the negative direction, the grid voltage v g When the direction is positive, the photovoltaic grid-connected inverter is in the working range IV and switches between M7 mode and M8 mode; When the photovoltaic grid-connected inverter is in M1 mode, the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the DC source supplies power to the filter inductor through the third power switch S3. L f Charge; When the photovoltaic grid-connected inverter is in M2 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source supplies power to the flying capacitor through the first power switch S1. C 1. Charging and filtering inductors L f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5. When the photovoltaic grid-connected inverter is in M3 mode, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned off, so that the grid supplies power to the flying capacitor through the second power switch S2. C 1 and filter inductor L f Charge; When the photovoltaic grid-connected inverter is in M4 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that current flows through the fourth power switch S4, the fifth power switch S5, and the filter inductor. L f and power grid; When the photovoltaic grid-connected inverter is in M5 mode, the second power switch S2 and the fourth power switch S4 are turned on, while the first power switch S1, the third power switch S3, and the fifth power switch S5 are turned off, so that the flying capacitor... C 1. Power is supplied to the grid through the second power switch S2; When the photovoltaic grid-connected inverter is in M6 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source supplies power to the flying capacitor through the first power switch S1, the fourth power switch S4, and the fifth power switch S5. C 1. Charging and filtering inductors L f Discharge is achieved through the fourth power switch S4 and the fifth power switch S5. When the photovoltaic grid-connected inverter is in M7 mode, the first power switch S1, the third power switch S3 and the fifth power switch S5 are turned on, while the second power switch S2 and the fourth power switch S4 are turned off, so that the grid can supply power to the DC source. When the photovoltaic grid-connected inverter is in M8 mode, the first power switch S1, the fourth power switch S4, and the fifth power switch S5 are turned on, while the second power switch S2 and the third power switch S3 are turned off, so that the DC source supplies power to the flying capacitor through the first power switch S1, the fourth power switch S4, and the fifth power switch S5. C 1. Charge.

6. A computer-readable storage medium having a computer program / instructions stored thereon, characterized in that, When the computer program / instruction is executed by the processor, it implements the steps of the modulation method for the photovoltaic grid-connected inverter as described in any one of claims 1-4.

7. A computer device, characterized in that it comprises: Memory, used to store computer programs / instructions; A processor for executing the computer program / instructions to implement the steps of the modulation method for the photovoltaic grid-connected inverter according to any one of claims 1-4.

8. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the modulation method for the photovoltaic grid-connected inverter as described in any one of claims 1-4.

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