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

Abstract

The invention discloses a photovoltaic grid-connected inverter and a modulation method and device thereof, a medium, equipment and a product, the inverter comprises a direct current source, an inverter network, a filter inductor and a power grid, and the inverter network comprises a flying capacitor, a first power switch tube, a second power switch tube, a third power switch tube, a fourth power switch tube and a fifth power switch tube; the positive electrode of the DC source is connected with the collectors of the first power switch tube and the third power switch tube, and the negative electrode is connected with the emitter of the second power switch tube, the collector of the fifth power switch tube and the power grid. The positive electrode of the flying capacitor is connected with the emitter of the first power switch tube and the collector of the second power switch tube, and the negative electrode is connected with the emitter of the third power switch tube, the collector of the fourth power switch tube and the filter inductor. Through insertion of a fifth power switch tube and a flying capacitor, when the photovoltaic grid-connected inverter is in a follow current mode, a direct current source and an alternating current power grid are decoupled, and common-mode voltage is kept unchanged to suppress leakage current.

Description

Technical Field

[0001] The invention relates to a photovoltaic grid-connected inverter and a modulation method, device, medium, equipment and product thereof, belonging to the technical field of photovoltaic grid-connected inverters. Background Art

[0002] In distributed photovoltaic power generation systems, non-isolated photovoltaic grid-connected inverters (Transformerless Grid-connected Inverter, TLI) have the advantages of small size, low cost, and high efficiency. However, since there is no effective electrical isolation between the TLI topology and the grid, the common-mode voltage generates common-mode leakage current through the parasitic capacitance of the photovoltaic array to the ground, increases the grid-connected current harmonics, affects the quality of the grid-connected current, and also causes safety problems. The half-bridge TLI topology directly connects the neutral point of the grid to the midpoint of the DC bus, clamps the voltage on the parasitic capacitor, and can suppress leakage current. However, the half-bridge TLI topology has obvious step-down characteristics, and the input voltage requirement is twice that of the full-bridge TLI topology, which is not suitable for low-power scenarios. The full-bridge TLI topology using unipolar sinusoidal pulse width modulation also has the ability to suppress leakage current, but it will generate high-frequency common-mode voltage, the grid-connected current harmonics are large, and two filter inductors are required, which increases the cost. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a photovoltaic grid-connected inverter and a modulation method, device, medium, equipment and product thereof. By inserting a fifth power switch tube S5 and a flying capacitor C1, the photovoltaic grid-connected inverter decouples the DC source from the AC power grid in the freewheeling mode, keeps the common mode voltage unchanged and suppresses the leakage current.

[0004] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

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

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

[0007] The positive electrode of the DC source is connected to the collector of the first power switch tube S1 and the collector of the third power switch tube S3 respectively; the negative electrode of the DC source is connected to the emitter of the second power switch tube S2, the collector of the fifth power switch tube 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 of

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

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

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

[0011] Furthermore, the DC source includes a photovoltaic cell PV and a DC stabilizing capacitor C dc ,

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

[0013] In a second aspect, the present invention discloses a modulation method for the photovoltaic grid-connected inverter, wherein the current flowing through the grid is the grid-connected current i g , the voltage across the grid is the grid voltage v g , which is characterized by comprising the following steps:

[0014] Obtain and determine the grid-connected current i g and grid voltage v g direction; among them, from the filter inductor L f The grid-connected current i flowing to the grid g is the positive direction;

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

[0016] If the grid-connected current i gis in the positive direction, the grid voltage v g When it is in the negative direction, the photovoltaic grid-connected inverter is in the working range II, and the M3 mode and the M4 mode are switched;

[0017] If the grid-connected current i g and grid voltage v g When both are in the negative direction, the photovoltaic grid-connected inverter is in the working range III, and the M5 mode and the M6 ​​mode are switched;

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

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

[0020] When the photovoltaic grid-connected inverter is in the M2 mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, and the filter inductor L f The discharge is carried out through the fourth power switch tube S4 and the fifth power switch tube S5.

[0021] Furthermore, when the photovoltaic grid-connected inverter is in the M3 mode, the second power switch tube S2 and the fourth power switch tube S4 are turned on, and the first power switch tube S1, the third power switch tube S3 and the fifth power switch tube S5 are turned off, so that the grid supplies the flying capacitor C1 and the filter inductor L1 to the flying capacitor C1 through the second power switch tube S2. f Charge;

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

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

[0024] When the photovoltaic grid-connected inverter is in the M6 ​​mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5, and the filter inductor L f The discharge is carried out through the fourth power switch tube S4 and the fifth power switch tube S5.

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

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

[0027] In a third aspect, the present invention discloses a modulation device for a photovoltaic grid-connected inverter, which is 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 grid is the grid voltage v g , which is characterized by comprising the following steps:

[0028] The current and voltage module is used to obtain and determine the grid-connected current i g and grid voltage v g direction; among them, from the filter inductor L f The grid-connected current i flowing to the grid g is the positive direction;

[0029] Working interval I module, used if the grid-connected current i g and grid voltage v g When both are in the positive direction, the photovoltaic grid-connected inverter is in the working range I, and the switching between the M1 mode and the M2 mode is performed;

[0030] Working range II module, used if the grid current i g is in the positive direction, the grid voltage vg When it is in the negative direction, the photovoltaic grid-connected inverter is in the working range II, and the M3 mode and the M4 mode are switched;

[0031] Working range III module, used if the grid-connected current i g and grid voltage v g When both are in the negative direction, the photovoltaic grid-connected inverter is in the working range III, and the M5 mode and the M6 ​​mode are switched;

[0032] Working interval IV module, used if the grid current i g In the negative direction, the grid voltage v g When it is in the positive direction, the photovoltaic grid-connected inverter is in the working range IV, and the switching between the M7 mode and the M8 mode is performed.

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

[0034] When the photovoltaic grid-connected inverter is in the M2 mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, and the filter inductor L f The discharge is carried out through the fourth power switch tube S4 and the fifth power switch tube S5.

[0035] In a fourth aspect, the present invention discloses a computer-readable storage medium having a computer program / instruction stored thereon, which, when executed by a processor, implements the steps of the modulation method of the photovoltaic grid-connected inverter of the second aspect.

[0036] In a fifth aspect, the present invention discloses a computer device, comprising:

[0037] Memory, for storing computer programs / instructions;

[0038] A processor is used to execute the computer program / instructions to implement the steps of the modulation method of the photovoltaic grid-connected inverter of the second aspect.

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

[0040] Compared with the prior art, the present invention has the following beneficial effects:

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

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

[0043] The modulation method of the photovoltaic grid-connected inverter of the present invention adopts a unipolar PWM modulation strategy. First, a DC source is selected as much as possible to directly transfer energy with the power grid to reduce energy loss. Secondly, the number of switch tubes involved is controlled to be the minimum to reduce conduction loss. Finally, the switching loss is reduced by reducing the frequency of switch tube action. The harmonic distortion rate of the grid-connected current is reduced, and the quality of grid-connected power is improved. The application value and prospects are huge. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a topology diagram of a photovoltaic grid-connected inverter provided in this embodiment 1;

[0045] Figure 2 is a switch tube driving signal diagram provided in this embodiment 1;

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

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

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

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

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

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

[0052] Fig. 9 is a schematic diagram of the M7 mode provided in this embodiment 1;

[0053] Fig.10 It is a schematic diagram of the M8 mode provided in this embodiment 1. DETAILED DESCRIPTION

[0054] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope 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 DC source, inverter network, filter inductor L f and the power grid,

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

[0058] The positive electrode of the DC source is connected to the collector of the first power switch tube S1 and the collector of the third power switch tube S3 respectively; the negative electrode of the DC source is connected to the emitter of the second power switch tube S2, the collector of the fifth power switch tube 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 of

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

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

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

[0062] The DC source includes photovoltaic cells PV and DC stabilizing capacitors C dc , the positive pole of the photovoltaic cell PV is connected to the DC voltage stabilizing capacitor C dcThe positive pole of the photovoltaic cell PV is connected to the DC stabilizing capacitor C dc of the negative electrode.

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

[0064] The working phases of the photovoltaic grid-connected inverter of this embodiment include an energy transfer phase and a freewheeling phase. In the negative half cycle of the grid voltage, the flying capacitor C1 provides energy.

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

[0066] Step 1: Determine the working mode selection principle. First, based on the unipolar PWM modulation strategy, determine the working mode selection principle: 1) Try to select photovoltaic cells to directly transfer energy with the power grid to reduce energy loss. 2) Select the minimum number of power switch tubes to reduce conduction loss. 3) Reduce the action frequency of the power switch tube to reduce switching loss.

[0067] Step 2: 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 v tCM The expression is as follows:

[0068]

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

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

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

[0072] Step 3: Divide the working area. The current flowing through the grid is the grid-connected current i g , the voltage across the grid is the grid voltage v g , assuming that the filter inductor L fThe grid-connected current i flowing to the grid g is the positive direction. According to the grid-connected current i g and grid voltage v g The photovoltaic grid-connected inverter can be divided into four working ranges I-IV, such as Figure 2 As shown. According to the direction of energy transfer, each working range has two working stages I-II, namely the energy transfer stage and the freewheeling stage. According to the relationship between the common mode characteristics and the switch state in each working range, combined with the working mode selection principle in step 1, the working stage can be changed by controlling the switch of the inverter.

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

[0074] Interval I: grid-connected current i g and grid voltage v g In the energy transfer stage, in order to reduce energy loss, the DC bus voltage U dc The third power switch tube S3 is turned on to transfer energy directly with the power grid. In the freewheeling stage, the photovoltaic cell charges the flying capacitor C1 and the filter inductor L f In the continuous flow, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on. In combination with the switching states of stage I and stage II, the first power switch tube S1 and the fifth power switch tube S5 are always turned on in interval I to reduce the switching action frequency without affecting normal operation.

[0075] Interval II: At this time, the grid-connected current i g is in the positive direction, the grid voltage v g In the negative direction, the power grid emits power. In the energy transfer stage, according to Principle 2, the power grid directly replenishes energy for the flying capacitor C1, and the second power switch tube S2 is turned on; since the fourth power switch tube S4 is turned on and does not affect the normal operation of the energy transfer stage, and at the same time it is necessary to provide a loop for the inductor to continue the flow, according to Principle 3, the fourth power S4 is always turned on in interval II. In the continuous flow stage, combined with the interval I modulation strategy, according to Principle 3, the first power switch tube S1 and the fifth power switch tube S5 are turned on.

[0076] Interval III: At this time, the grid-connected current i g and grid voltage v g In the energy transfer stage, according to Principle 2, the flying capacitor C1 directly transmits energy to the grid, and the second power switch tube S2 is turned on; in the freewheeling stage, the photovoltaic cell PV charges the flying capacitor C1, and the filter inductor L fIn the continuous flow, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on. Combining the switching states of stage I and stage II, without affecting normal operation, in order to reduce the switching action frequency, the fourth power switch tube S4 is always turned 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 emits power. In the energy transfer stage, according to principle 1, the grid directly transfers energy to the photovoltaic cell PV, and the third power switch tube S3 is turned on; in the freewheeling stage, the photovoltaic cell PV charges the flying capacitor C1, and the filter inductor L f In the continuous flow, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on. In combination with the switching states of stage I and stage II, without affecting normal operation, in order to reduce the switching action frequency, the first power switch tube S1 and the fifth power switch tube S5 are always turned on in interval IV.

[0078] According to the above modulation method, the photovoltaic grid-connected inverter has 4 working intervals I-IV. In each working area, the switch switches between 2 working stages, namely the power transmission stage and the freewheeling stage. The photovoltaic grid-connected inverter finally has 8 working modes M1-M8, as follows:

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

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

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

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

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

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

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

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

[0087] In summary, by inserting the fifth power switch tube S5 and the flying capacitor C1, the photovoltaic grid-connected inverter decouples the DC source from the AC grid in the freewheeling mode, keeps the common mode voltage unchanged and suppresses the leakage current.

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

[0089] The modulation method of photovoltaic grid-connected inverter adopts unipolar PWM modulation strategy. First, DC source is selected as much as possible to directly transfer energy with the grid to reduce energy loss. Secondly, the number of switch tubes is controlled to be the minimum to reduce conduction loss. Finally, the switching loss is reduced by reducing the frequency of switch tube action. The harmonic distortion rate of grid-connected current is reduced and the quality of grid-connected power is improved. The application value and prospects are huge.

[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 grid is the grid voltage v g , which is characterized by comprising the following steps:

[0092] Obtain and determine the grid-connected current i g and grid voltage v g direction; among them, from the filter inductor L f The grid-connected current i flowing to the grid g is the positive direction;

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

[0094] If the grid current i g is in the positive direction, the grid voltage v g When it is in the negative direction, the photovoltaic grid-connected inverter is in the working range II, and the M3 mode and the M4 mode are switched;

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

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

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

[0098] When the photovoltaic grid-connected inverter is in the M2 mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, and the filter inductor L f The discharge is carried out through the fourth power switch tube S4 and the fifth power switch tube S5.

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

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

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

[0102] When the photovoltaic grid-connected inverter is in the M6 ​​mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5, and the filter inductor L f The discharge is carried out through the fourth power switch tube S4 and the fifth power switch tube S5.

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

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

[0105] Example 3

[0106] This embodiment 3 provides a modulation device for a photovoltaic grid-connected inverter, which is applicable to the photovoltaic grid-connected inverter of embodiment 1. The current flowing through the grid is the grid-connected current i g , the voltage across the grid is the grid voltage v g , which is characterized by comprising the following steps:

[0107] Current and voltage module, used to obtain and determine the grid-connected current i g and grid voltage v g direction; among them, from the filter inductor L f The grid-connected current i flowing to the grid g is the positive direction;

[0108] Working range I module, used if the grid current i g and grid voltage v g When both are in the positive direction, the photovoltaic grid-connected inverter is in the working range I, and the switching between the M1 mode and the M2 mode is performed;

[0109] Working range II module, used if the grid current i g is in the positive direction, the grid voltage v g When it is in the negative direction, the photovoltaic grid-connected inverter is in the working range II, and the M3 mode and the M4 mode are switched;

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

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

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

[0113] When the photovoltaic grid-connected inverter is in the M2 mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, and the filter inductor L f The discharge is carried out through the fourth power switch tube S4 and the fifth power switch tube S5.

[0114] Example 4

[0115] This embodiment 4 provides a computer-readable storage medium on which a computer program / instruction is stored. When the computer program / instruction is executed by a processor, the steps of the modulation method of the photovoltaic grid-connected inverter of embodiment 2 are implemented.

[0116] Example 5

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

[0118] Memory, for storing computer programs / instructions;

[0119] A processor is used to execute computer programs / instructions to implement the steps of the modulation method of 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 implements the steps of the modulation method of the photovoltaic grid-connected inverter of embodiment 2 when executed by a processor.

[0122] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0123] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0124] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0125] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0126] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. Photovoltaic grid-connected inverter, characterized by: Including DC source, inverter network, filter inductor L f and the power grid, The inverter network includes a flying capacitor C1, a first power switch tube S1, a second power switch tube S2, a third power switch tube S3, a fourth power switch tube S4 and a fifth power switch tube S5; The positive electrode of the DC source is connected to the collector of the first power switch tube S1 and the collector of the third power switch tube S3 respectively; the negative electrode of the DC source is connected to the emitter of the second power switch tube S2, the collector of the fifth power switch tube 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 of The positive electrode of the flying capacitor C1 is respectively connected to the emitter of the first power switch tube S1 and the collector of the second power switch tube S2; the negative electrode of the flying capacitor C1 is respectively connected to the emitter of the third power switch tube S3, the collector of the fourth power switch tube S4 and the filter inductor L f the emitter of the fourth power switch tube S4 is connected to the emitter of the fifth power switch tube S5.

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

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

4. The photovoltaic grid-connected inverter according to claim 1, characterized in that: The DC source includes a photovoltaic cell PV and a DC stabilizing capacitor C dc , The positive electrode of the photovoltaic cell PV is connected to a DC voltage stabilizing capacitor C dc The positive electrode of the photovoltaic cell PV is connected to the DC stabilizing capacitor C dc of the negative electrode.

5. A modulation method for a photovoltaic grid-connected inverter according to any one of claims 1 to 4, wherein the current flowing through the grid is the grid-connected current i g , the voltage across the grid is the grid voltage v g , which is characterized by, The steps include: Obtain and determine the grid-connected current i g and grid voltage v g direction; among them, from the filter inductor L f The grid-connected current i flowing to the grid g is the positive direction; If the grid-connected current i g and grid voltage v g When both are in the positive direction, the photovoltaic grid-connected inverter is in the working range I, and the switching between the M1 mode and the M2 mode is performed; If the grid-connected current i g is in the positive direction, the grid voltage v g When it is in the negative direction, the photovoltaic grid-connected inverter is in the working range II, and the M3 mode and the M4 mode are switched; If the grid-connected current i g and grid voltage v g When both are in the negative direction, the photovoltaic grid-connected inverter is in the working range III, and the M5 mode and the M6 ​​mode are switched; If the grid-connected current i g In the negative direction, the grid voltage v g When it is in the positive direction, the photovoltaic grid-connected inverter is in the working range IV, and the switching between the M7 mode and the M8 mode is performed.

6. The modulation method of photovoltaic grid-connected inverter according to claim 5, characterized in that: When the photovoltaic grid-connected inverter is in the M1 mode, the first power switch tube S1, the third power switch tube S3 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the fourth power switch tube S4 are turned off, so that the DC source supplies the filter inductor L through the third power switch tube S3. f Charge; When the photovoltaic grid-connected inverter is in the M2 mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, and the filter inductor L f The discharge is carried out through the fourth power switch tube S4 and the fifth power switch tube S5.

7. The modulation method of photovoltaic grid-connected inverter according to claim 5, characterized in that: When the photovoltaic grid-connected inverter is in the M3 mode, the second power switch tube S2 and the fourth power switch tube S4 are turned on, and the first power switch tube S1, the third power switch tube S3 and the fifth power switch tube S5 are turned off, so that the grid supplies the flying capacitor C1 and the filter inductor L through the second power switch tube S2. f Charge; When the photovoltaic grid-connected inverter is in the M4 mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the current flows through the fourth power switch tube S4, the fifth power switch tube S5, the filter inductor L f and power grid.

8. The modulation method of photovoltaic grid-connected inverter according to claim 5, characterized in that: When the photovoltaic grid-connected inverter is in the M5 mode, the second power switch tube S2 and the fourth power switch tube S4 are turned on, and the first power switch tube S1, the third power switch tube S3 and the fifth power switch tube S5 are turned off, so that the flying capacitor C1 supplies power to the grid through the second power switch tube S2; When the photovoltaic grid-connected inverter is in the M6 ​​mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5, and the filter inductor L f The discharge is carried out through the fourth power switch tube S4 and the fifth power switch tube S5.

9. The modulation method of photovoltaic grid-connected inverter according to claim 5, characterized in that: When the photovoltaic grid-connected inverter is in the M7 mode, the first power switch tube S1, the third power switch tube S3 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the fourth power switch tube S4 are turned off, so that the power grid supplies power to the DC source; When the photovoltaic grid-connected inverter is in the M8 mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5.

10. A modulation device for a photovoltaic grid-connected inverter, characterized in that: The steps include: The current and voltage module is used to obtain and determine the grid-connected current i g and grid voltage v g direction; among them, from the filter inductor L f The grid-connected current i flowing to the grid g is the positive direction; Working interval I module, used if the grid-connected current i g and grid voltage v g When both are in the positive direction, the photovoltaic grid-connected inverter is in the working range I, and the switching between the M1 mode and the M2 mode is performed; Working range II module, used if the grid current i g When the grid voltage v is in the positive direction, g When it is in the negative direction, the photovoltaic grid-connected inverter is in the working range II, and the M3 mode and the M4 mode are switched; Working range III module, used if the grid-connected current i g and grid voltage v g When both are in the negative direction, the photovoltaic grid-connected inverter is in the working range III, and the M5 mode and the M6 ​​mode are switched; Working interval IV module, used if the grid current i g In the negative direction, the grid voltage v g When it is in the positive direction, the photovoltaic grid-connected inverter is in the working range IV, and the switching between the M7 mode and the M8 mode is performed.

11. The modulation device of photovoltaic grid-connected inverter according to claim 10, characterized in that: When the photovoltaic grid-connected inverter is in the M1 mode, the first power switch tube S1, the third power switch tube S3 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the fourth power switch tube S4 are turned off, so that the DC source supplies the filter inductor L through the third power switch tube S3. f Charge; When the photovoltaic grid-connected inverter is in the M2 mode, the first power switch tube S1, the fourth power switch tube S4 and the fifth power switch tube S5 are turned on, and the second power switch tube S2 and the third power switch tube S3 are turned off, so that the DC source charges the flying capacitor C1 through the first power switch tube S1, and the filter inductor L f The discharge is carried out through the fourth power switch tube S4 and the fifth power switch tube S5.

12. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instruction is executed by a processor, the steps of the modulation method of the photovoltaic grid-connected inverter described in any one of claims 5-9 are implemented.

13. A computer device, comprising: Memory, for storing computer programs / instructions; A processor, configured to execute the computer program / instructions to implement the steps of the modulation method for the photovoltaic grid-connected inverter according to any one of claims 5 to 9.

14. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the steps of the modulation method of the photovoltaic grid-connected inverter described in any one of claims 5-9 are implemented.

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