CN115664237A

CN115664237A - Single-phase inverter system and single-phase inverter control method

Info

Publication number: CN115664237A
Application number: CN202211595674.1A
Authority: CN
Inventors: 王盼盼
Original assignee: Foxess Co Ltd
Current assignee: Foxess Co ltd
Priority date: 2022-12-13
Filing date: 2022-12-13
Publication date: 2023-01-31
Anticipated expiration: 2042-12-13
Also published as: CN115664237B

Abstract

The invention discloses a single-phase inverter system and a single-phase inverter control method, which relate to the field of power supplies, and are characterized in that a fundamental wave triple frequency component of a corresponding amplitude value is correspondingly added based on a direct current modulation amount or a fundamental wave modulation component, so that the influence of the direct current modulation amount on the modulation degree of one side can be counteracted, wherein the added fundamental wave triple frequency component is a common mode component of modulation waves of an A-phase bridge arm and a B-phase bridge arm, so that no triple frequency component flows into an alternating current end, and the fundamental wave triple frequency component current only flows into the midpoint of a bus, so that the system efficiency is optimal on the premise of not influencing the current characteristics of a power grid or an alternating current load, and the technical problem that an inverter cannot be compatible with the system efficiency and reliability in the related technology is solved.

Description

Single-phase inverter system and single-phase inverter control method

Technical Field

The invention relates to the field of power supplies, in particular to a single-phase inverter system and a single-phase inverter control method.

Background

With the cost greatly reduced due to the progress of the light storage technology, more and more family users around the world install the light storage system.

Among the various schemes of the light storage system, fig. 1 shows an alternative light storage integrated inverter in the prior art, which is the lowest cost scheme at present. As shown in fig. 1, two dc input ports of a typical hybrid optical storage inverter 100 are respectively connected to a photovoltaic cell 210 and a household energy storage cell 220, one ac output port (grid-connected port) is connected to a power grid 300, and the other ac output port (off-grid port) is connected to a critical load 410. The grid connection port connected to the grid 300 is also connected to other common loads 420 connected to the grid. When the power grid is powered off, the hybrid optical storage inverter 100 supplies power to the important load 410 at the off-grid port and does not supply power to the common load 420 at the grid-connected port any more.

Fig. 1 illustrates a hybrid light storage inverter, and the other inverters are the same, except that the type of power source connected to the input terminal is different, such as a photovoltaic cell 210 or a household energy storage battery 220. In the light storage system, the photovoltaic cell and the inverter determine the performance of the light storage system and are core devices in the system.

In the prior art, the system efficiency is low due to a mode of preventing overmodulation, and if the bus voltage is not increased, the system reliability is poor, namely, the system efficiency and reliability cannot be compatible. Therefore, how to optimize the efficiency and improve the reliability of the inverter becomes an important direction for the research in the industry.

In view of the above problems, no effective solution has been proposed.

Disclosure of Invention

The embodiment of the invention provides a single-phase inverter system and a single-phase inverter control method, which at least solve the technical problem that an inverter cannot be compatible with system efficiency and reliability in the related technology.

According to an aspect of an embodiment of the present invention, there is provided a single-phase inverter system including: the single-phase inverter comprises a bus capacitor unit and an inversion switch unit which are sequentially connected, wherein the bus capacitor unit comprises an upper bus capacitor and a lower bus capacitor which are connected in series, a common node of the upper bus capacitor and the lower bus capacitor forms a bus midpoint, the inversion switch unit comprises a plurality of switch tubes, a direct current side is connected with two ends of the bus capacitor unit, an alternating current side comprises a first phase output end for outputting first phase alternating current, a second phase output end for outputting second phase alternating current and a neutral line, and the neutral line is connected with the bus midpoint; the judgment module is used for selecting the direct current modulation quantity with larger amplitude from the A-phase direct current modulation quantity and the B-phase direct current modulation quantity after receiving the fundamental wave modulation component, the A-phase direct current modulation quantity and the B-phase direct current modulation quantity, and outputting an operation instruction for executing a first operation program, a second operation program or a third operation program according to the sum of the modulation degree M of the fundamental wave modulation component and the direct current modulation quantity with larger amplitude; a modulation instruction generation module, which stores the first operation program, the second operation program and the third operation program, executes one of the operation programs according to the operation instruction, and receives the fundamental wave modulation component, wherein the first operation program comprises: recording the initial modulation degree M1 of the current fundamental wave modulation component; outputting a fundamental frequency triple frequency component adding mark value n2 as1, recording the modulation degree M2 of the current modulated fundamental frequency component, judging whether the modulated modulation degree M2 is smaller than the initial modulation degree M1, if so, keeping n2 as1, if not, outputting n2 as 0, and starting the mark value n1 as1 by an output bus voltage control module; the second operation procedure includes: recording the initial modulation degree M1 of the current fundamental wave modulation component and the current first bus voltage, and then outputting n1 as 1; the output n2 is 1, and n1 is still 1, recording the current modulation degree M3 after modulation, judging whether the modulation degree M3 after modulation is less than the initial modulation degree M1, if yes, executing: keeping n2 as1, and outputting n1 as 11, if not: the output n2 is 0 and n1 is still 1; the third operating procedure includes: the output n2 is 0 and n1 is 0; and the multiplier receives the fundamental frequency tripling component addition mark value n2 and the fundamental frequency tripling component, performs multiplication operation on the fundamental frequency tripling component addition mark value and the fundamental frequency tripling component, and outputs the fundamental frequency tripling addition amount.

According to another aspect of the embodiments of the present invention, there is also provided a method for controlling a single-phase inverter, where a neutral line of the inverter is connected to a midpoint of a bus, the method including: receiving a modulation degree M, A phase direct current modulation quantity and a B phase direct current modulation quantity of a fundamental wave modulation component, and selecting the direct current modulation quantity with a larger amplitude from the A phase direct current modulation quantity and the B phase direct current modulation quantity; judging whether the over-modulation risk exists or not according to the sum of the modulation degree M and the direct current modulation quantity with the larger amplitude, and if so, executing a first operation or a second operation; if not, executing a third operation, wherein the first operation comprises the following steps: s11, superposing the fundamental wave modulation component and the phase A direct current modulation quantity to obtain a phase A first total modulation instruction, and superposing the negative fundamental wave modulation component and the phase B direct current modulation quantity to obtain a phase B first total modulation instruction; s12, recording the initial modulation degree M1 of the current fundamental wave modulation component; s13, superposing the fundamental wave modulation component, the A-phase direct current modulation quantity and the fundamental wave frequency tripling component to obtain an A-phase second total modulation instruction, and superposing the negative fundamental wave modulation component, the B-phase direct current modulation quantity and the fundamental wave frequency tripling component to obtain a B-phase second total modulation instruction; s14, recording the current modulation degree M2 after modulation; s15, judging whether the modulation degree M2 after modulation is smaller than the initial modulation degree M1, if so, continuing to execute the step S13, otherwise, executing the step S11, and starting a bus voltage control module to increase the bus voltage; the second operation includes: s21, superposing the fundamental wave modulation component and the A-phase direct current modulation quantity to obtain an A-phase first total modulation instruction, and superposing the negative fundamental wave modulation component and the B-phase direct current modulation quantity to obtain a B-phase first total modulation instruction; s22, recording the initial modulation degree M1 of the current fundamental wave modulation component and the current first bus voltage; s23, starting the bus voltage control module to increase the bus voltage; s24, superposing the fundamental wave modulation component, the A-phase direct current modulation quantity and the fundamental wave triple frequency component to obtain an A-phase second total modulation instruction, and superposing the negative fundamental wave modulation component, the B-phase direct current modulation quantity and the fundamental wave triple frequency component to obtain a B-phase second total modulation instruction; s25, continuing to start the bus voltage control module to increase the bus voltage and recording the current modulation degree M3 after modulation; s26, judging whether the modulation degree M3 after modulation is smaller than the initial modulation degree M1, if so, executing the step S24, starting the bus voltage control module to reduce the bus voltage to a first bus voltage, otherwise, executing the step S21, and continuing to start the bus voltage control module to increase the bus voltage; the third operation includes: and superposing the fundamental wave modulation component and the A-phase direct current modulation quantity to obtain an A-phase first total modulation instruction, and superposing the negative fundamental wave modulation component and the B-phase direct current modulation quantity to obtain a B-phase first total modulation instruction.

According to another aspect of the embodiments of the present invention, there is also provided a computer-readable storage medium, which includes a stored computer program, wherein when the computer program runs, the apparatus where the computer-readable storage medium is located is controlled to execute any one of the above-mentioned single-phase inverter control methods.

In the application, the fundamental wave triple frequency component of the corresponding amplitude is correspondingly increased based on the direct current modulation amount or the fundamental wave modulation component, so that the influence of the direct current modulation amount on the one-side modulation degree can be offset. The added fundamental wave triple frequency component is a common mode component of modulation waves of an A-phase bridge arm and a B-phase bridge arm, so that no triple frequency component flows into an alternating current end, the fundamental wave triple frequency component current only flows into the middle point of a bus, the system efficiency is optimal on the premise of not influencing the current characteristics of a power grid or an alternating current load, and the technical problem of [ key words ] is solved.

According to the method, the fundamental wave triple frequency component is added firstly according to the modulation degree after the direct current modulation quantity with larger amplitude in the A-phase direct current modulation quantity and the B-phase direct current modulation quantity is superposed on the fundamental wave modulation component and the negative fundamental wave modulation component, then whether the current modulation degree is reduced to a proper range is judged, if yes, the fundamental wave triple frequency component is continuously added, overmodulation is avoided without raising the bus voltage, and if not, overmodulation can be avoided only by raising the bus voltage, so that the efficiency can be optimized; or raising the bus voltage to quickly avoid overmodulation and improve the system reliability, then adding a fundamental wave triple frequency component, judging whether the modulation degree is reduced after adding the fundamental wave triple frequency component, if so, continuing to keep adding the fundamental wave triple frequency component, reducing the bus voltage, namely, avoiding overmodulation by adding the fundamental wave triple frequency component, and if not, removing the fundamental wave triple frequency component, and only raising the bus voltage to avoid overmodulation, so that the system efficiency can be optimized on the premise of ensuring the system reliability; if the risk of overmodulation does not exist, the fundamental frequency tripling component does not need to be added, and the bus voltage does not need to be raised.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:

FIG. 1 is a schematic diagram of an alternative light-storing integrated inverter of the prior art;

FIG. 2 is a circuit schematic of an alternative inverter according to an embodiment of the present invention;

FIG. 3 is a circuit schematic of an alternative inverter according to an embodiment of the present invention;

fig. 4 is a waveform diagram of a fundamental modulation component according to an embodiment of the present invention;

fig. 5 is a waveform diagram of a dc modulation amount and a fundamental triple frequency component according to an embodiment of the present invention;

fig. 6 is a waveform diagram after superimposing a dc modulation amount on a fundamental modulation component according to an embodiment of the present invention;

fig. 7 is a waveform diagram after superimposing a dc modulation amount and a fundamental frequency tripling component on a fundamental modulation component according to an embodiment of the present invention;

fig. 8 is a two-leg modulated waveform and an overall voltage modulated waveform after superimposing a dc modulation amount and a fundamental triple frequency component on a fundamental modulated component according to an embodiment of the present invention;

fig. 9 is a schematic diagram of a single-phase inverter system according to an embodiment of the present application.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Fig. 2 is a circuit schematic of an alternative inverter according to an embodiment of the present invention.

Fig. 3 is a circuit schematic of an alternative inverter according to an embodiment of the present invention.

Please refer to fig. 2 for a schematic diagram of an inverter circuit according to an embodiment and fig. 3 for a schematic diagram of an inverter circuit according to another embodiment. The inverters thereof each include a bus capacitor unit 110 and an inverter switch unit 130 connected in sequence.

The bus capacitor unit 110 (a dc bus capacitor unit) includes an upper bus capacitor C1 and a lower bus capacitor C2 connected in series between a positive dc bus and a negative dc bus, a common node of the upper bus capacitor C1 and the lower bus capacitor C2 forms a bus midpoint DN, and a dc power Udc (or called a bus voltage Udc) output from a photovoltaic cell or a household energy storage cell is received between the positive dc bus and the negative dc bus.

The inversion switch unit 130 includes a plurality of switching tubes, the dc side is connected between the positive dc bus and the negative dc bus for receiving the bus voltage Udc, the ac side includes a first phase output end a, a second phase output end B and a neutral line N, the first phase output end a is used for outputting a first phase alternating current I1, the second phase output end B is used for outputting a second phase alternating current I2, the neutral line N is connected to the bus midpoint DN, and the inversion switch unit 130 is used for inverting the bus voltage Udc received by the dc side into an alternating current of the ac side. The inversion switch unit 130 may be any switch unit capable of inverting a direct current into an alternating current, such as a T-type three-level topology, an I-type three-level topology, a flying capacitor three-level topology, a bus split capacitor-based HERIC topology, or a bus split capacitor-based H4 topology, and the specific structure of the inversion switch unit 130 is not limited in the present application. Fig. 2 and 3 take a T-type three-level topology AS an example, which includes a first switch leg formed by a first switch AS1 of a phase and a fourth switch AS4 of a phase connected in series between a positive dc bus and a negative dc bus, a second switch leg formed by a first switch BS1 of B phase and a fourth switch BS4 of B phase connected in series between the positive dc bus and the negative dc bus, a connection point of the first switch AS1 of a phase and the fourth switch AS4 of a phase being a first phase output end a, a connection point of the first switch BS1 of B phase and the fourth switch BS4 of B phase being a second phase output end B, and a first series switch unit formed by connecting the second switch AS2 of a phase and the third switch AS3 of a phase in series, a second series switch unit formed by connecting the second switch BS2 of B phase and the third switch BS3 of B phase in series, the first series switch unit being connected between the first phase output end a and a neutral line N of the inverter 100, the second series switch unit being connected between the second output end B and the neutral line N of the inverter 100, and a midpoint of the neutral line N of the inverter 100 being connected. Because the two-phase voltage of the inverter is in opposite phase, the driving waveform of the corresponding switch tube is corresponding to a half period difference. Specifically, the a-phase first switch AS1 and the B-phase fourth switch BS4 are driven the same, the a-phase third switch AS3 and the B-phase second switch BS2 are driven the same, the a-phase second switch AS2 and the B-phase third switch BS3 are driven the same, the a-phase fourth switch AS4 and the B-phase first switch BS1 are driven the same, and the phase difference is half a cycle. The four switching tubes in the A phase can be called as a bridge arm A, and the four switching tubes in the B phase can be called as a bridge arm B.

As shown in fig. 2, the inverter circuit further includes a filtering unit 140, which includes a first filtering inductor L1, a second filtering inductor L2, a first filtering capacitor C11, and a second filtering capacitor C22, where the first filtering inductor L1 is connected between the first phase output end a and the first end of the second filtering capacitor C22, the second filtering inductor L2 is connected between the second phase output end B and the first end of the first filtering capacitor C11, and the second end of the first filtering capacitor C11 and the second end of the second filtering capacitor C22 are connected to the central line N.

As shown in fig. 2, the inverter circuit further includes a first grid-connected/disconnected switching unit 151 connected between the filtering unit 140 and the grid-connected port 161 and the important load port 162, and configured to switch the ac side output of the inverting switching unit 130 between the grid-connected port 161 and the important load port 162 or simultaneously connect the grid-connected port 161 and the important load port 162, where the grid-connected port 161 and the important load port 162 both include a first phase end point and a second phase end point. The present application does not limit the specific structure of the first offline switching unit 151 as long as it can implement the above-described functions. The first Grid-connected switching unit 151 shown in fig. 2 is an embodiment and includes a selector switch CS1 connected between the first end of the second filter capacitor C22 and the first node d1, a selector switch CS2 connected between the first end of the first filter capacitor C11 and the second node d2, a selector switch DS1 connected between the first node d1 and the first phase end L1-Load of the important Load port 162, a selector switch DS2 connected between the second node d2 and the second phase end L2-Load of the important Load port 162, a selector switch ES1 connected between the first node d1 and the first phase end L1-Grid of the Grid-connected port 161, and a selector switch ES2 connected between the second node d2 and the second phase end L2-Grid of the Grid-connected port 161. When the select switch CS1, the select switch CS2, the select switch DS1, and the select switch DS2 are turned on, the ac side output of the inverter switch unit 130 is switched to the important load port 162. When the selection switch CS1, the selection switch CS2, the selection switch ES1, and the selection switch ES2 are turned on, the ac side output of the inverter switching unit 130 is switched to the grid-connected port 161. When the selection switches are all turned on, the ac side output of the inverter switch unit 130 is switched to the important load port 162 and the grid connection port 161 at the same time. That is, one ac output port (grid-connected port 161) is connected to the grid, and the other ac output port (off-grid port or important load port 162) is connected to the important load, wherein the output port connected to the grid is also connected to other common loads connected to the grid.

As shown in fig. 3, the inverter circuit further includes a second grid-connected/disconnected switching unit 152 connected between the filtering unit 140 and the important load port 162, for switching the ac side output of the inverting switching unit 130 between supplying power to the important load port 162 or not supplying power to the important load port 162, where the important load port 162 includes a first phase terminal and a second phase terminal. The present application does not limit the specific structure of the second on-grid/off-grid switching unit 152 as long as it can implement the above-described functions. The second grid-connected/off-grid switching unit 152 shown in fig. 3 is an embodiment and includes a selection switch CS1 connected between the first end of the second filter capacitor C22 and the first phase terminal L1-Load of the important Load port 162, and a selection switch CS2 connected between the first end of the first filter capacitor C11 and the second phase terminal L2-Load of the important Load port 162. When the select switch CS1 and the select switch CS2 are turned on, the ac side output of the inverter switching unit 130 supplies power to the important load port 162. When the select switch CS1 and the select switch CS2 are turned off, the ac side output of the inverter switching unit 130 does not supply power to the important load port 162. I.e. only one ac output port (off-grid or important load port 162) is connected to the important load.

As shown in fig. 2, the grid connection port 161 is connected to an ac two-phase grid, and the phases of the two-phase grid are opposite. And the inverters shown in fig. 2 and 3 are single-phase inverters.

In practical applications, the average voltage of the upper and lower bus capacitors (the upper bus capacitor C1 and the lower bus capacitor C2) often has a deviation, and the average voltage of the upper and lower bus capacitors needs to be balanced. The ac side current of the inverter switch unit 130 also often includes a dc component, and the dc component needs to be suppressed. For the suppression of the direct current component of the alternating current side or the suppression of the average voltage of the upper and lower bus capacitors, the existing scheme adds the corresponding direct current modulation component on the basis of the normal sinusoidal modulation wave to suppress the average voltage difference of the upper and lower bus capacitors or the direct current component of the alternating current side. As shown in FIG. 2, the current control loop 550 outputs a fundamental modulation component

The addition unit 541 suppresses the average voltage difference between the upper and lower bus capacitors or the DC modulation amount of the AC side DC component

Superimposed on the fundamental modulation component

Get the total modulation instruction

Then the PWM signal generating circuit 560 generates a PWM signal according to the total modulation command

Outputting the switch control signal of the A-phase switch tube and the switch control signal of the B-phase switch tube, wherein the fundamental wave modulation component

Including A-phase fundamental modulation component

And B-phase fundamental wave modulation component

The expression is formula (1):

（1）；

wherein, omega is the fundamental wave angular frequency of the power grid, and t is time; m is the fundamental modulation component

Normalizing the modulation degree; theta is the initial phase angle.

It is known that the amount of added DC modulation

So that the fundamental wave modulates the component

Increasing the amount of DC modulation up or down

The offset will inevitably increase the modulation degree in one direction, and even over-modulation occurs beyond the threshold (which is set by itself, for example, to 1), which affects the normal operation of the system. In order to make the system work normally, the bus voltage Udc needs to be increased in the prior art, so that the modulation degree is controlled within the threshold value. For example, if the inverter bus voltage Udc is 360Vdc and the ac side voltage is plus or minus 120Vac, the fundamental wave modulation component

If the modulation degree of (2) is about 0.95, the DC modulation amount is set at that time

0.06 and is shifted upward by 0.06, then under the condition that the bus voltage Udc is unchanged, the modulation degree of the modulation wave in the upper half cycle will be 0.95+0.06=1.01, and the modulation degree of the lower half cycle will be 0.95-0.06=0.89, and overmodulation obviously occurs. In order to make the system work normally, the amplitude of the bus voltage Udc needs to be increased. For example, in order to make the modulation degree to be 0.95, the bus voltage Udc needs to be raised to ((0.95 + 0.06)/0.95) × 360vdc=383vdc. It is well known in the industry that the higher the bus voltage Udc, the lower the system efficiency at constant output power (constant grid voltage and constant ac side current). Therefore, the mode of preventing overmodulation in the prior art causes low system efficiency, and if the bus voltage is not increased, poor system reliability is caused, namely, the system efficiency and reliability cannot be compatible.

In the following, according to an embodiment of the present invention, there is provided an embodiment of a method for controlling a single-phase inverter, it is noted that the steps illustrated in the flowchart of the drawings may be executed in a computer system such as a set of computer executable instructions, and that although a logical order is illustrated in the flowchart, in some cases, the steps illustrated or described may be executed in an order different from that herein.

In another embodiment of the present application, it is an object to provide a method for controlling a single-phase inverter, in which a neutral line of the inverter is connected to a midpoint of a bus, so as to improve efficiency and reliability of the single-phase inverter shown in fig. 2 and 3. The method comprises the following steps:

receiving fundamental modulated component

Modulation degree M, A phase DC modulation amount

And B phase DC modulation amount

Selecting A-phase DC modulation amount

And B phase DC modulation amount

The direct current modulation amount with a medium amplitude is large; judging whether the risk of overmodulation exists according to the sum of the modulation degree M and the direct current modulation quantity with larger amplitude, if so, executing the first operation or the second operation, and if not, executing the third operation, wherein,

the first operation includes: s11, modulating the fundamental wave component

And A phase DC modulation amount

Adding to obtain A phase first total modulation command

For causing the PWM signal generating circuit to generate the first total modulation command in accordance with the A-phase

Outputting switch control signal of A-phase switch tube in the inversion switch unit 130 to modulate the negative fundamental wave component

And B phase DC modulation amount

The first total modulation command of the B phase is obtained by superposition

For causing the PWM signal generating circuit to respond to the B-phase first total modulation command

Outputting a switch control signal of a B-phase switch tube in the inversion switch unit 130; s12, recording the current fundamental wave modulation component

The initial modulation degree M1; s13, modulating the fundamental wave component

phase-A DC modulation amount

Sum fundamental frequency tripled component

Adding to obtain A phase second total modulation instruction

For causing the PWM signal generating circuit to respond to the A-phase second total modulation command

Outputting a switch control signal of an A-phase switch tube in the inversion switch unit 130, and modulating a negative fundamental wave component

B phase DC modulation amount

Sum fundamental frequency tripled component

Adding to obtain B phase second total modulation instruction

For causing the PWM signal generating circuit to generate the second total modulation command according to the B-phase

Outputting a switch control signal of a B-phase switch tube in the inversion switch unit 130; s14, recording the current modulation degree M2 after modulation; s15, judging whether the modulation degree M2 after modulation is smaller than the initial modulation degree M1, if so, continuing to execute the step S13, if not, executing the step S11, and starting the bus voltage control module to increase the bus voltage;

the second operation includes: s21, modulating the fundamental wave component

And A phase DC modulation amount

The first total modulation command of the phase A is obtained by superposition

To modulate the negative fundamental wave component

And B phase DC modulation amount

Adding to obtain B phase first total modulation command

(ii) a S22, recording the initial modulation degree M1 of the current fundamental wave modulation component and the current first bus voltage Vust 1; s23, starting the bus voltage control module to raise the busA voltage; s24, modulating the fundamental wave component

phase-A DC modulation amount

Sum fundamental frequency tripled component

Adding to obtain A-phase second total modulation instruction

To modulate the negative fundamental wave component

B phase DC modulation amount

Sum fundamental frequency tripled component

Adding to obtain B-phase second total modulation instruction

(ii) a S25, continuing to start the bus voltage control module to increase the bus voltage and recording the current modulation degree M3 after modulation; s26, judging whether the modulation degree M3 after modulation is smaller than the initial modulation degree M1, if so, executing the step S24, starting the bus voltage control module to reduce the bus voltage to a first bus voltage Vjust 1, otherwise, executing the step S21, and continuing to start the bus voltage control module to increase the bus voltage;

the third operation includes: modulating the fundamental wave component

And A phase DC modulation amount

SuperpositionObtaining A-phase first total modulation command

To modulate the negative fundamental wave component

And B phase DC modulation amount

Adding to obtain B phase first total modulation command

。

Thus, based on the modulation component at the fundamental wave

And negative fundamental modulation component

Upper-superposed A-phase DC modulation

And B phase DC modulation amount

Adding the fundamental wave triple frequency component into the modulation degree after the medium-amplitude large direct current modulation quantity

Then judging whether the current modulation degree is reduced to a proper range, if so, continuing to add the fundamental frequency tripling component

That is, overmodulation is avoided without raising the bus voltage, and if not, overmodulation can only be avoided by raising the bus voltage, thus optimizing efficiency; or raising the bus voltage to quickly avoid over-modulation, improving the system reliability, and addingFundamental triple frequency component

Then judging to add fundamental wave triple frequency component

If the post-modulation degree is decreased, if so, continuing to add the fundamental frequency tripling component

And lowering the bus voltage, i.e. by adding a fundamental frequency-tripling component

Avoiding overmodulation, if not, removing the fundamental frequency tripling component

Overmodulation can only be avoided by raising the bus voltage, so that the system efficiency can be optimized on the premise of ensuring the system reliability; if there is no risk of overmodulation, there is no need to add a fundamental triple frequency component

And the bus voltage does not need to be raised.

Wherein, a first time is spaced between step S13 and step S15 in the first operation. Wherein the first time is, for example, 5 to 8 power frequency cycles.

Wherein a first time is spaced between step S24 and step S26 in the second operation. Wherein the first time is, for example, 5 to 8 power frequency cycles.

The A-phase direct current modulation amount and the B-phase direct current modulation amount are modulation amounts which are required to be superposed on the fundamental wave modulation component for suppressing the alternating current side direct current component and/or suppressing the average voltage difference of the upper bus capacitor and the lower bus capacitor. Wherein, in some applications, the A phase DC modulation amount

Equal to B phase is straightFlow modulation amount

For example, to suppress the difference in average voltage between the upper and lower bus capacitors. In one embodiment, the A-phase DC modulation amount

DC modulation amount not equal to B phase

For example, the method is used for simultaneously suppressing the average voltage difference of the upper bus capacitor and the lower bus capacitor and suppressing the direct current component of the alternating current side current.

Fundamental triple frequency component

Refers to the component of triple power frequency. In one embodiment, the amount of A-phase DC modulation is based on

And B phase DC modulation amount

Medium and large amplitude DC modulation

(when the A phase DC modulation amount

Equal to B phase DC modulation amount

Any one of the values) to obtain fundamental frequency-tripling component

The expression is as formula (2):

（2）；

wherein,

referring to the fundamental wave period of the power grid, n is a natural number, omega is the angular frequency of the fundamental wave of the power grid, t is time, theta is an initial phase angle,

is a fundamental frequency tripling component. It can be understood that 3 frequency doubling components with opposite phases are respectively added according to positive and negative half waves of the power grid, namely, three frequency doubling components inverted according to the fundamental half wave.

In the second embodiment, the modulation component is based on the fundamental wave

Obtaining fundamental frequency triple frequency component

The expression is as formula (3):

（3）；

Normalizing the modulation degree; theta is the initial phase angle and theta is the initial phase angle,

referring to the fundamental wave period of the power grid, n is a natural number, sgn is a symbol, and the DC modulation quantity M _dc Modulating the A-phase direct current

And B phase DC modulation amount

Direct current with large medium amplitudeAnd (4) modulating the quantity. It can be understood that 3 frequency doubling components with opposite phases are respectively added according to positive and negative half waves of the power grid, namely, three frequency doubling components inverted according to the fundamental half wave.

Specifically, please refer to the fundamental modulation component shown in fig. 4

The horizontal axis is time t, the vertical axis is the adjustment component value, wherein the solid line is the A-phase fundamental wave modulation component of the bridge arm A

The dotted line represents the B-phase fundamental modulation component of the bridge arm B

The expression is shown in formula (1), which is a sine wave. Please refer to fig. 5 for the dc modulation amount

Sum fundamental frequency tripled component

Wherein the solid line is the DC modulation amount

The dotted line is the fundamental frequency tripler component

Fundamental triple frequency component

The expression is shown in formula (2) or formula (3), wherein the DC modulation amount

Is a direct current component, a fundamental triple frequency component

At a frequency of three times the power frequencyThe component of the rate. Please refer to fig. 6 for the fundamental modulation component

Upper superposed DC modulation quantity

In the waveform diagram, the solid line still represents the bridge arm A, the dotted line still represents the bridge arm B, and the DC modulation amount can be seen

Resulting in a fundamental modulation component

Shifted upwards if the amount of dc modulation is increased

Too large will cause the fundamental modulation component

One-sided overmodulation occurs, and the bus voltage must be increased in the prior art to avoid overmodulation. Please refer to fig. 7 for the fundamental modulation component

Upper superposed DC modulation quantity

Sum fundamental frequency tripled component

The waveform diagram after the above, in which the solid line still represents the arm A and the broken line still represents the arm B, can be seen due to the fundamental triple frequency component

So that the peak of the waveform shown in fig. 6 is lowered and both sides of the peak are raised upward, resulting in a saddle wave-like waveform shown in fig. 7Wave form, so that fundamental modulation components can be avoided

Overmodulation due to upward shift, i.e. it can be avoided without raising the bus voltage, and see the modulation component at the fundamental as shown in fig. 8

Upper superposed DC modulation quantity

Sum fundamental frequency tripled component

The solid line still represents the bridge arm A, the dotted line still represents the bridge arm B, and the dotted line is the integral voltage modulation wave obtained by subtracting the bridge arm B from the bridge arm A, so that the integral voltage modulation wave is still a sine wave, namely the added fundamental wave triple frequency component

The whole voltage modulation wave is changed, the total voltage is not influenced, and the normal work of the system is not influenced. And because the bus midpoint DN is not connected with the alternating current end, zero-sequence current corresponding to the specific zero-sequence component does not flow into the power grid or the alternating current load.

Specifically, in one embodiment, the step receives a fundamental modulation component

Modulation degree M, A phase DC modulation amount

And B phase DC modulation amount

According to the modulation degree M and the A phase DC modulation amount

And B phase DC modulation amount

And judging whether the overmodulation risk exists or not by the sum of the medium direct current modulation amount with larger amplitude, and if so, executing a first operation or a second operation, wherein the steps comprise:

if based on fundamental modulation component

Modulation degree M and A phase DC modulation amount

And B phase DC modulation amount

The sum of the medium-amplitude DC modulation amount is confirmed to have the risk of overmodulation, and the A-phase DC modulation amount is judged

And B phase DC modulation amount

Medium and large amplitude DC modulation and fundamental wave modulation

If the ratio of the modulation degree M is larger than the preset ratio threshold, executing the second operation if the ratio is larger than the preset ratio threshold, otherwise executing the first operation. In particular, the preset ratio threshold may be set by itself, for example, set between 1% and 3%. I.e. if the amount of added dc modulation

If the voltage is larger, the bus voltage needs to be increased firstly to quickly avoid overmodulation, and then the fundamental wave triple frequency component is added in a trial mode under a steady state

Whether the modulation degree can be lowered. If the amount of DC modulation is added

If smaller, the fundamental frequency tripling component can be added first

And if the modulation degree can be reduced, the problem of low system efficiency caused by increasing the bus voltage can be avoided, and if the modulation degree can not be reduced, the bus voltage is increased.

Step C, according to modulation degree M and A phase DC modulation quantity

And B phase DC modulation amount

The step of judging whether the overmodulation risk exists or not by the sum of the medium-amplitude large direct current modulation quantities comprises the following steps: if the modulation degree M and the A phase DC modulation quantity

And B phase DC modulation amount

If the sum of the medium-amplitude direct-current modulation amounts is greater than or equal to the first modulation degree limiting threshold, the first operation or the second operation is executed if the risk of overmodulation exists, and if the sum is less than the first modulation degree limiting threshold, the risk of overmodulation does not exist.

In one embodiment, the step of performing the first operation or the second operation comprises: either one of them is selected or the A-phase DC modulation amount is judged

And B phase DC modulation amount

Medium and large amplitude DC modulation and baseWave modulation component

If the ratio of the modulation degree M is larger than the preset ratio threshold, executing the second operation if the ratio is larger than the preset ratio threshold, otherwise executing the first operation. If the first modulation degree defines a threshold of 0.99, the condition to be satisfied under any operation is satisfied if the fundamental wave modulation component

Modulation degree M of (1) is 0.95, and DC modulation amount

0.05, which adds to 1, greater than 0.99, there is a risk of overmodulation and the first or second operation is performed. If the direct current modulation amount

0.02, 0.97, less than 0.99, the risk of overmodulation is deemed to be absent, and the third operation may be performed at this time as described above.

In another embodiment, after selecting the dc modulation amount with a larger amplitude from the a-phase dc modulation amount and the B-phase dc modulation amount, the method further includes: according to modulation degree M and A phase DC modulation quantity

And B phase DC modulation amount

And judging whether the overmodulation risk exists or not by the sum of the medium direct current modulation amount with larger amplitude, and if so, executing a first operation or a second operation, wherein the steps comprise: receiving fundamental modulated component

Modulation degree M, A phase DC modulation amount

And B phase DC modulation amount

If the modulation degree M and the A phase DC modulation amount

And B phase DC modulation amount

And if the sum of the direct current modulation amounts with the medium amplitude value is larger than or equal to the second modulation degree limiting threshold value and is smaller than the third modulation degree limiting threshold value, executing the first operation, and if the sum is larger than or equal to the third modulation degree limiting threshold value, executing the second operation. If the second modulation degree defines a threshold value of 0.95 (a condition to be satisfied for a long time operation under normal conditions), and the third modulation degree defines a threshold value of 0.99 (a condition to be satisfied for a short time when a fundamental wave triple frequency component trial operation is performed), if the fundamental wave modulated component is present

Modulation degree M of (1) is 0.93, direct current modulation amount

And 0.05, adding the two to be 0.98, less than 0.99 and more than 0.95, and not meeting the long-term operation condition, performing a first operation, adding the fundamental frequency tripling component for probing, if the modulation degree is reduced, continuing to add the fundamental frequency tripling component, and if the modulation degree is not reduced, abandoning to add the fundamental frequency tripling component, and selecting to increase the direct-current bus voltage. If fundamental wave modulation component

Modulation degree M of (1) is 0.94, direct current modulation amount

0.055, which is 0.995 and more than 0.99, and the fundamental wave triple frequency component can not be directly added for probing, the second operation can be executed, the direct current bus voltage is firstly increased, overmodulation is quickly avoided, and the fundamental wave triple frequency component is addedThe frequency multiplication component is probed.

As described above, the amount of DC modulation is based on the A phase

And B phase DC modulation amount

Medium-amplitude large DC modulation quantity or fundamental wave modulation component

Corresponding increase of fundamental frequency tripling component of corresponding amplitude

Thereby, the DC modulation amount can be offset

Influence on one-sided modulation. In which the added fundamental frequency tripling component

The common-mode components of the modulation waves of the A-phase bridge arm and the B-phase bridge arm are common-mode components, so that no triple frequency component flows into an alternating current end, and the fundamental wave triple frequency component current only flows into the middle point of a bus. Therefore, the method can optimize the system efficiency under the premise of not influencing the current characteristics of the power grid or the alternating load.

In which the fundamental wave modulation component

The current control loop 550 for the inverter is based on the difference between the first phase current I1 and the second phase current I2 and the grid-connected current command value IL ^* Thus obtaining the product.

In an embodiment of the present application, a single-phase inverter system is further provided, please refer to a schematic diagram of the single-phase inverter system in the embodiment of the present application shown in fig. 9, which further includes, on the basis of the inverter shown in fig. 2 or fig. 3:

a decision block 510 for receiving the fundamental modulation component

phase-A DC modulation amount

And B phase DC modulation amount

Then, the DC modulation quantity with larger amplitude value in the A-phase DC modulation quantity and the B-phase DC modulation quantity is selected, wherein the A-phase DC modulation quantity

And B phase DC modulation amount

In order to inhibit the direct current component of the alternating current side current and/or the average voltage difference of the upper and lower bus capacitors, the fundamental wave modulation component is required

An upper-superimposed modulation amount for modulating the component according to the fundamental wave

Modulation degree M and A phase DC modulation amount

And B phase DC modulation amount

The sum of the medium-amplitude large direct current modulation quantity outputs an operation instruction dr for executing a first operation program, a second operation program or a third operation program;

a modulation command generation module 520 for storing the first operation program, the second operation program and the third operation program, executing one of them according to the operation command dr, and receiving the fundamental wave modulation component

Wherein

the first operation procedure includes: recording the current fundamental modulation component

The initial modulation degree M1; outputting a fundamental frequency triple frequency component adding mark value n2 as1, recording the modulation degree M2 of the current modulated fundamental frequency component, and judging whether the modulated modulation degree M2 is smaller than the initial modulation degree M1, if so, keeping the fundamental frequency triple frequency component adding mark value n2 as1, if not, outputting the fundamental frequency triple frequency component adding mark value n2 as 0, and outputting a bus voltage control module to start the mark value n1 as 1;

the second operation procedure includes: recording the initial modulation degree M1 of the current fundamental wave modulation component and the current first bus voltage Vjust 1, and then outputting a starting mark value n1 of a bus voltage control module to be 1; outputting a fundamental frequency triple frequency component adding mark value n2 as1, starting the mark value n1 by a bus voltage control module to be still 1, recording a current modulation degree M3 after modulation, judging whether the modulation degree M3 after modulation is smaller than an initial modulation degree M1, if so, executing: keeping the adding mark value n2 of the fundamental frequency tripling component as1, starting the mark value n1 of the bus voltage control module as 11, and if not: outputting a fundamental frequency triple frequency component adding mark value n2 as 0, and starting a mark value n1 of a bus voltage control module to be still 1;

the third operation procedure includes: outputting a fundamental frequency triple frequency component adding mark value n2 as 0, and starting a mark value n1 of a bus voltage control module as 0;

a multiplier for receiving the fundamental frequency-tripled component and adding a mark value n2 and the fundamental frequency-tripled component

The two are multiplied to output the fundamental frequency tripling addition

^* 。

As shown in fig. 9, the single-phase inverter system further includes a bus voltage control module 540 that receives a start flag value n1 of the bus voltage control module, wherein the bus voltage control module is started to increase the bus voltage when the start flag value n1 is 1, the bus voltage control module is not operated when it is 0, and the bus voltage control module is started to decrease the bus voltage to a first bus voltage Vbust1 when it is 11.

As shown in fig. 9, the single-phase inverter system further includes: a first addition unit 541 receiving the fundamental wave modulation component

phase-A DC modulation amount

And fundamental frequency tripling addition

^* The three are added and operated to output the A phase total modulation instruction

^* The A-phase PWM signal generating circuit 561 generates a total A-phase modulation command

^* Outputting a switching control signal of an a-phase switching tube of the inverter switching unit (see fig. 2); a second addition unit 542 receiving the negative fundamental modulation component

B phase DC modulation amount

And fundamental frequency tripling addition

^* The three are added and operated to output B phase total modulation instruction

^* (ii) a The B-phase PWM signal generating circuit 562 generates a B-phase total modulation command according to the B-phase total modulation command

^* And outputting a switching control signal of the B-phase switching tube of the inversion switching unit (see fig. 2).

Wherein, the step in the first operation program outputs the fundamental frequency tripling component adding mark value n2 as1 to the step of judging whether the modulated modulation degree M2 is smaller than the initial modulation degree M1 or not with a first time interval. Wherein the first time is, for example, 5 to 8 power frequency cycles.

Wherein, the step in the second operation program outputs the fundamental frequency tripling component adding mark value n2 as1 to the step of judging whether the modulated modulation degree M3 is smaller than the initial modulation degree M1 or not with a first time interval. Wherein the first time is, for example, 5 to 8 power frequency cycles.

Wherein the fundamental wave modulation component

In order to obtain the current control loop 550 according to the first phase current I1 and the second phase current I2, the current control loop 550 is a prior art, and is not limited herein.

In the first embodiment, as shown in fig. 9, the single-phase inverter system further includes a fundamental triple-frequency component generation module 530 that receives the a-phase dc modulation amount

And B phase DC modulation amount

Medium and large amplitude DC modulation

Obtaining fundamental frequency tripling component according to formula (2)

（2）；

Wherein,

referring to the fundamental wave period of the power grid, n is a natural number, omega is the angular frequency of the fundamental wave of the power grid, theta is an initial phase angle,

is a fundamental frequency tripling component. It can be understood that the inverted 3-times frequency component is added according to the positive and negative half waves of the power grid respectively.

In the first embodiment, as shown in fig. 9, the single-phase inverter system further includes a fundamental triple-frequency component generation module 530 that receives a fundamental modulation component

Obtaining fundamental frequency tripling component according to formula (3)

:

(3) (ii) a Wherein, omega is the fundamental wave angular frequency of the power grid; m is the fundamental modulation component

referring to the fundamental wave period of the power grid, n is a natural number, sgn is a symbol, wherein

For A phase DC modulation

And B phase DC modulation amount

Direct current with medium amplitudeThe modulation amount. It can be understood that the inverted 3-times frequency component is added according to the positive and negative half waves of the power grid respectively.

Wherein the determining module 510 modulates the component according to the fundamental wave

Modulation degree M and A phase DC modulation amount

And B phase DC modulation amount

If the sum of the medium-amplitude DC modulation amounts is judged to have the risk of overmodulation, the A-phase DC modulation amount is judged

And B phase DC modulation amount

Medium and large amplitude DC modulation and fundamental wave modulation

If the ratio of the modulation degree M is greater than the threshold value, the operation command dr instructs the modulation command generating module 520 to execute the second operation procedure, otherwise, the operation command dr instructs the modulation command generating module 520 to execute the first operation. Specifically, the partial threshold may be set to be between 1% and 3%.

Modulation degree M and A phase DC modulation amount

And B phase DC modulation amount

Medium and large amplitude DC modulationIf the sum is determined that there is no risk of overmodulation, the operation command dr instructs the modulation command generation module 520 to execute a third operation procedure.

Wherein the determining module 510 performs receiving the fundamental modulation component

Modulation degree M, A phase DC modulation amount

And B phase DC modulation amount

If the modulation degree M and the A phase DC modulation amount

And B phase DC modulation amount

If the sum of the medium-amplitude direct-current modulation amounts is greater than or equal to the first modulation degree limiting threshold value, it is determined that there is a risk of overmodulation, the operation command dr instructs the modulation command generation module 520 to execute the first operation program or the second operation program, and if the sum is less than the first modulation degree limiting threshold value, it is determined that there is no risk of overmodulation, the operation command dr instructs the modulation command generation module 520 to execute the third operation program.

In an alternative embodiment, the operation command dr instructs the modulation command generation module 520 to execute the first operation procedure or the second operation procedure, which includes: either one of them is selected, or the judgment module 510 also judges the A-phase DC modulation amount

And B phase DC modulation amount

Medium and large amplitude DC modulation and fundamental wave modulation

If the ratio of the modulation degree M is greater than the preset ratio threshold, the operation command dr instructs the modulation command generation module 520 to execute the second operation procedure, otherwise, the operation command dr instructs the modulation command generation module 520 to execute the first operation procedure.

Modulation degree M, A phase DC modulation amount

And B phase DC modulation amount

(ii) a If the modulation degree M and the A phase DC modulation quantity

And B phase DC modulation amount

If the sum of the medium-amplitude direct-current modulation amounts is greater than or equal to the second modulation degree limiting threshold and smaller than the third modulation degree limiting threshold, the operation instruction dr instructs the modulation instruction generation module 520 to execute the first operation program; if the sum of the two is greater than or equal to the third modulation degree limiting threshold, the operation command dr instructs the modulation command generation module 520 to execute the second operation.

The principle of realizing compatibility of the single-phase inverter system and the single-phase inverter control method is the same as that of realizing compatibility of high efficiency and high reliability, and details are not repeated herein.

The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.

In the above embodiments of the present invention, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

In the embodiments provided in the present application, it should be understood that the disclosed technical content can be implemented in other manners. The above-described embodiments of the apparatus are merely illustrative, and for example, the division of the units may be a logical division, and in actual implementation, there may be another division, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, units or modules, and may be in an electrical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention, which is substantially or partly contributed by the prior art, or all or part of the technical solution may be embodied in a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to perform all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic or optical disk, and other various media capable of storing program codes.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A single-phase inverter system, comprising:

the single-phase inverter comprises a bus capacitor unit and an inversion switch unit which are sequentially connected, wherein the bus capacitor unit comprises an upper bus capacitor and a lower bus capacitor which are connected in series, a common node of the upper bus capacitor and the lower bus capacitor forms a bus midpoint, the inversion switch unit comprises a plurality of switch tubes, a direct current side is connected with two ends of the bus capacitor unit, an alternating current side comprises a first phase output end for outputting first phase alternating current, a second phase output end for outputting second phase alternating current and a neutral line, and the neutral line is connected with the bus midpoint;

the judgment module is used for selecting the direct current modulation quantity with larger amplitude from the A-phase direct current modulation quantity and the B-phase direct current modulation quantity after receiving the fundamental wave modulation component, the A-phase direct current modulation quantity and the B-phase direct current modulation quantity, and outputting an operation instruction for executing a first operation program, a second operation program or a third operation program according to the sum of the modulation degree M of the fundamental wave modulation component and the direct current modulation quantity with larger amplitude;

a modulation instruction generation module, which stores the first operation program, the second operation program and the third operation program, executes one of the operation programs according to the operation instruction, and receives the fundamental wave modulation component, wherein the first operation program comprises: recording the initial modulation degree M1 of the current fundamental wave modulation component; outputting a fundamental frequency triple frequency component adding marking value n2 as1, recording the modulation degree M2 of the current modulated fundamental frequency component, judging whether the modulated modulation degree M2 is smaller than the initial modulation degree M1, if so, keeping n2 as1, if not, outputting n2 as 0, and starting the marking value n1 as1 by an output bus voltage control module; the second operation procedure includes: recording the initial modulation degree M1 of the current fundamental wave modulation component and the current first bus voltage, and then outputting n1 as 1; the output n2 is 1, and n1 is still 1, recording the current modulation degree M3 after modulation, judging whether the modulation degree M3 after modulation is less than the initial modulation degree M1, if yes, executing: keeping n2 as1, and outputting n1 as 11, if not: the output n2 is 0 and n1 is still 1; the third operating procedure includes: the output n2 is 0, and n1 is 0;

and the multiplier receives the fundamental frequency tripling component addition mark value n2 and the fundamental frequency tripling component, and performs multiplication operation on the fundamental frequency tripling component addition mark value and the fundamental frequency tripling component to output fundamental frequency tripling addition quantity.

2. The single-phase inverter system according to claim 1, wherein the a-phase dc modulation amount and the B-phase dc modulation amount are modulation amounts that are added to the fundamental wave modulation component in order to suppress an ac-side dc component and/or suppress a difference in average voltage between upper and lower bus capacitors.

3. The single-phase inverter system of claim 1, further comprising: the bus voltage control module receives a starting mark value n1 of the bus voltage control module, wherein the bus voltage control module is started to increase the bus voltage when the starting mark value n1 is 1, the bus voltage control module is controlled not to work when the starting mark value n1 is 0, and the bus voltage control module is started to reduce the bus voltage to a first bus voltage when the starting mark value n1 is 11.

4. The single-phase inverter system of claim 1, further comprising:

a first addition operation unit which receives the fundamental wave modulation component, the A phase direct current modulation quantity and the fundamental wave frequency tripling addition quantity, adds the fundamental wave modulation component, the A phase direct current modulation quantity and the fundamental wave frequency tripling addition quantity, and outputs an A phase total modulation instruction; the A-phase PWM signal generating circuit outputs a switch control signal of an A-phase switch tube of the inverter switch unit according to the A-phase total modulation instruction;

the second addition operation unit receives a negative fundamental wave modulation component, the B-phase direct current modulation quantity and the fundamental wave frequency tripling addition quantity, performs addition operation on the negative fundamental wave modulation component, the B-phase direct current modulation quantity and the fundamental wave frequency tripling addition quantity and outputs a B-phase total modulation instruction; and the B-phase PWM signal generating circuit outputs a switch control signal of a B-phase switch tube of the inverter switch unit according to the B-phase total modulation instruction.

5. The single-phase inverter system of claim 1, further comprising:

a fundamental wave frequency tripling component generation module for receiving the DC modulation quantity with larger amplitude in the A phase DC modulation quantity and the B phase DC modulation quantity

Obtaining a fundamental frequency tripling component according to the following formula:

，

wherein,

referring to the fundamental wave period of the power grid, n is a natural number, t is time, omega is the angular frequency of the fundamental wave of the power grid, theta is an initial phase angle,

is a fundamental frequency tripling component.

6. The single-phase inverter system of claim 1, further comprising:

the fundamental frequency tripling component generating module receives the fundamental wave modulation component and obtains a fundamental frequency tripling component according to the following formula:

，

referring to the fundamental wave period of the power grid, n is a natural number, sgn represents a symbol,

the dc modulation amount with a larger amplitude is the dc modulation amount with the larger amplitude in the a-phase dc modulation amount and the B-phase dc modulation amount,

is a fundamental frequency tripling component.

7. The single-phase inverter system according to claim 1, wherein the determination module determines whether or not a ratio of the larger-amplitude dc modulation amount to the modulation degree M of the fundamental modulation component is greater than a threshold value, if it is determined that there is a risk of overmodulation based on a sum of the modulation degree M of the fundamental modulation component and the larger-amplitude dc modulation amount; if yes, the operation instruction instructs the modulation instruction generation module to execute a second operation program; if not, the operation instruction instructs the modulation instruction generation module to execute a first operation.

8. The single-phase inverter system according to claim 1, wherein the determination module determines that there is no risk of overmodulation based on a sum of the modulation degree M of the fundamental wave modulation component and the large-amplitude direct-current modulation amount, and the operation command instructs the modulation command generation module to execute a third operation routine.

9. The single-phase inverter system according to claim 1, wherein the determination module executes reception of a modulation degree M of the fundamental wave modulation component, the a-phase direct-current modulation amount, and the B-phase direct-current modulation amount, and if a sum of the modulation degree M and the large-amplitude direct-current modulation amount is equal to or greater than a first modulation degree limit threshold value, it is confirmed that there is a risk of overmodulation, and the operation command instructs the modulation command generation module to execute the first operation routine or the second operation routine.

10. The single-phase inverter system of claim 9, wherein the operating instructions instruct the modulation instruction generation module to perform a first operating procedure or a second operating procedure comprising:

either of the first operating procedure and the second operating procedure is optional; or,

the judgment module judges whether the ratio of the direct current modulation quantity with the larger amplitude to the modulation degree M of the fundamental wave modulation component is larger than a preset ratio threshold value or not; if yes, the operation instruction instructs the modulation instruction generation module to execute a second operation program, and if not, the operation instruction instructs the modulation instruction generation module to execute a first operation program.

11. The single-phase inverter system of claim 1, further comprising:

the judgment module executes receiving of the modulation degree M of the fundamental wave modulation component, the A-phase direct current modulation quantity and the B-phase direct current modulation quantity;

if the sum of the modulation degree M and the direct current modulation quantity with the larger amplitude is greater than or equal to a second modulation degree limiting threshold value and smaller than a third modulation degree limiting threshold value, the operation instruction instructs the modulation instruction generation module to execute the first operation program;

and if the sum of the two is greater than or equal to the third modulation degree limiting threshold value, the operation instruction instructs the modulation instruction generation module to execute a second operation.

12. A control method of a single-phase inverter is characterized in that a neutral line of the inverter is connected with a midpoint of a bus, and the control method comprises the following steps:

receiving a modulation degree M, A phase direct current modulation quantity and a B phase direct current modulation quantity of a fundamental wave modulation component, and selecting the direct current modulation quantity with a larger amplitude from the A phase direct current modulation quantity and the B phase direct current modulation quantity; judging whether overmodulation risks exist or not according to the sum of the modulation degree M and the direct current modulation amount with the larger amplitude, and if yes, executing a first operation or a second operation; if not, executing a third operation,

wherein the first operation comprises: s11, superposing the fundamental wave modulation component and the phase A direct current modulation quantity to obtain a phase A first total modulation instruction, and superposing the negative fundamental wave modulation component and the phase B direct current modulation quantity to obtain a phase B first total modulation instruction; s12, recording the initial modulation degree M1 of the current fundamental wave modulation component; s13, superposing the fundamental wave modulation component, the A-phase direct current modulation quantity and the fundamental wave frequency tripling component to obtain an A-phase second total modulation instruction, and superposing the negative fundamental wave modulation component, the B-phase direct current modulation quantity and the fundamental wave frequency tripling component to obtain a B-phase second total modulation instruction; s14, recording the current modulation degree M2 after modulation; s15, judging whether the modulation degree M2 after modulation is smaller than the initial modulation degree M1, if so, continuing to execute the step S13, if not, executing the step S11, and starting the bus voltage control module to increase the bus voltage;

the second operation includes: s21, superposing the fundamental wave modulation component and the A-phase direct current modulation quantity to obtain an A-phase first total modulation instruction, and superposing the negative fundamental wave modulation component and the B-phase direct current modulation quantity to obtain a B-phase first total modulation instruction; s22, recording the initial modulation degree M1 of the current fundamental wave modulation component and the current first bus voltage; s23, starting the bus voltage control module to increase the bus voltage; s24, superposing the fundamental wave modulation component, the A-phase direct current modulation quantity and the fundamental wave triple frequency component to obtain an A-phase second total modulation instruction, and superposing the negative fundamental wave modulation component, the B-phase direct current modulation quantity and the fundamental wave triple frequency component to obtain a B-phase second total modulation instruction; s25, continuing to start the bus voltage control module to increase the bus voltage and recording the current modulation degree M3 after modulation; s26, judging whether the modulation degree M3 after modulation is smaller than the initial modulation degree M1, if so, executing a step S24, starting the bus voltage control module to reduce the bus voltage to a first bus voltage, otherwise, executing a step S21, and continuing to start the bus voltage control module to increase the bus voltage;

the third operation includes: and superposing the fundamental wave modulation component and the A-phase direct current modulation quantity to obtain an A-phase first total modulation instruction, and superposing the negative fundamental wave modulation component and the B-phase direct current modulation quantity to obtain a B-phase first total modulation instruction.

13. The single-phase inverter control method according to claim 12, further comprising:

receiving the DC modulation quantity with larger amplitude in the A-phase DC modulation quantity and the B-phase DC modulation quantity

；

，

wherein,

is the fundamental frequency triplingAnd (4) components.

14. The single-phase inverter control method according to claim 12, further comprising:

receiving the fundamental modulation component;

，

wherein,

for the direct current modulation quantity with larger amplitude in the A-phase direct current modulation quantity and the B-phase direct current modulation quantity, omega is the fundamental wave angular frequency of the power grid, t is time, and M is the fundamental wave modulation component

t denotes the fundamental wave period of the power network, n is a natural number, sgn represents the symbol taking,

is a fundamental frequency tripling component.

15. The single-phase inverter control method according to claim 12, wherein the step of determining whether there is a risk of overmodulation based on a sum of the modulation degree M and the dc modulation amount having the larger amplitude, and if so, performing the first operation or the second operation includes:

and if the existence of the over-modulation risk is confirmed according to the sum of the modulation degree M of the fundamental wave modulation component and the modulation degree M of the direct current modulation component with the larger amplitude, judging whether the ratio of the direct current modulation component with the larger amplitude to the modulation degree M of the fundamental wave modulation component is larger than a preset ratio threshold value, if so, executing the second operation, and if not, executing the first operation.

16. The single-phase inverter control method according to claim 12, wherein the step of determining whether or not there is a risk of overmodulation based on a sum of a modulation degree M and the dc modulation amount having the large amplitude includes:

if the sum of the modulation M and the dc modulation amount with the large amplitude is equal to or greater than a first modulation limit threshold, it is determined that there is a risk of overmodulation, and if the sum is less than the first modulation limit threshold, it is determined that there is no risk of overmodulation.

17. The single-phase inverter control method according to claim 12, wherein the step of performing the first operation or the second operation includes:

either one of the first operation and the second operation is optional; or,

and judging whether the ratio of the direct current modulation quantity with the larger amplitude to the modulation degree M of the fundamental wave modulation component is larger than a preset ratio threshold value, if so, executing the second operation, and if not, executing the first operation.

18. The single-phase inverter control method according to claim 12, further comprising, after selecting a dc modulation amount having a larger amplitude of the a-phase dc modulation amount and the B-phase dc modulation amount:

if the sum of the modulation degree M and the direct current modulation quantity with the larger amplitude is greater than or equal to a second modulation degree limiting threshold value and smaller than a third modulation degree limiting threshold value, executing the first operation;

and if the sum of the modulation degree M and the direct current modulation quantity with the larger amplitude is larger than or equal to the third modulation degree limiting threshold value, executing the second operation.

19. A computer-readable storage medium, characterized in that the computer-readable storage medium comprises a stored computer program, wherein the computer program, when running, controls an apparatus in which the computer-readable storage medium is located to perform the single-phase inverter control method according to any one of claims 12 to 18.