CN115589170A

CN115589170A - Two-phase inverter system and two-phase inverter control method

Info

Publication number: CN115589170A
Application number: CN202211595678.XA
Authority: CN
Inventors: 朱京成
Original assignee: Foxess Co Ltd
Current assignee: Foxess Co ltd
Priority date: 2022-12-13
Filing date: 2022-12-13
Publication date: 2023-01-10
Anticipated expiration: 2042-12-13
Also published as: CN115589170B

Abstract

The invention discloses a two-phase inverter system and a two-phase inverter control method, relates to the field of power supplies, and aims to offset the influence of direct current modulation quantity on one side modulation degree by correspondingly increasing fundamental wave triple frequency component of corresponding amplitude based on the direct current modulation quantity or the fundamental wave modulation component, judge whether harmonic component of alternating current end current exceeds a preset value, and give up adding the fundamental wave triple frequency component if the harmonic component exceeds the preset value, so that the system efficiency can be optimized on the premise of not influencing the current characteristics of a power grid or an alternating load, and the technical problem that the inverter cannot be compatible with the system efficiency and reliability in the related technology is solved.

Description

Two-phase inverter system and two-phase inverter control method

Technical Field

The invention relates to the field of power supplies, in particular to a two-phase inverter system and a two-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 solutions of the light storage system, fig. 1 shows an alternative light storage integrated inverter in the prior art, which is the solution with the lowest cost 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 photovoltaic-storage inverter, and the same applies to other inverters, except that the input terminal is connected to a different power source, 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 two-phase inverter system and a two-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 two-phase inverter system including: the two-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 middle line, and the middle line is connected with the bus midpoint, a neutral line end of a grid-connected port and a neutral line end of an important load port; 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: the output fundamental frequency triple frequency component adding mark value n2 is 1, and the starting mark value n1 of the bus voltage control module is 0; detecting harmonic components of alternating-current end current, and judging whether the harmonic components of the alternating-current end current exceed a preset value, if so, outputting n2 as 0, n1 as1, if not, continuously outputting n2 as1, and n1 as 0; the second operation procedure includes: the output n2 is 0, and n1 is 1; the output n2 is 1, and n1 is still 1, detecting harmonic components of the alternating-current end current, and judging whether the harmonic components of the alternating-current end current exceed a preset value, if so, the output n2 is 0, n1 is 1, if not, the output n2 is 1, and n1 is 11; 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 two-phase inverter, where a neutral line of the inverter connects a bus midpoint, a neutral line endpoint of a grid-connected port, and a neutral line endpoint of an important load port, the method including: receiving a modulation degree M of a fundamental wave modulation component, an A-phase direct current modulation amount and a B-phase direct current modulation amount, selecting the direct current modulation amount with a larger amplitude in the A-phase direct current modulation amount and the B-phase direct current modulation amount, judging whether overmodulation risks exist according to the sum of the modulation degree M and the direct current modulation amount with the larger amplitude, if yes, executing a first operation or a second operation, and if not, executing a third operation, wherein the first operation comprises S11, superposing the fundamental wave modulation component, the A-phase direct current modulation amount and a fundamental wave frequency tripling component to obtain an A-phase second total modulation instruction, and superposing a negative fundamental wave modulation component, the B-phase direct current modulation amount and a fundamental wave frequency tripling component to obtain a B-phase second total modulation instruction; s12, detecting harmonic components of alternating-current end current, judging whether the harmonic components of the alternating-current end current exceed a preset value or not, if so, performing superposition of the fundamental wave modulation components and the A-phase direct-current modulation quantity to obtain an A-phase first total modulation instruction, performing superposition of the negative fundamental wave modulation components and the B-phase direct-current modulation quantity to obtain a B-phase first total modulation instruction, starting a bus voltage control module to increase bus voltage, and if not, continuing to perform the step S11; 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, superposing the negative fundamental wave modulation component and the B-phase direct current modulation quantity to obtain a B-phase first total modulation instruction, and starting the bus voltage control module to increase the bus voltage from a first bus voltage to a second bus voltage; s22, 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; s23, keeping starting the bus voltage control module to increase the bus voltage; s24, detecting harmonic components of the alternating-current end current, judging whether the harmonic components of the alternating-current end current exceed a preset value or not, if so, executing a step S21, otherwise, continuing to execute a step S22; and keeping starting the bus voltage control module to reduce 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 on which the computer-readable storage medium is located is controlled to execute any one of the above-mentioned two-phase inverter control methods.

In the method, the fundamental wave triple frequency component of the corresponding amplitude is correspondingly added based on the direct current modulation quantity or the fundamental wave modulation component, so that the influence of the direct current modulation quantity on the modulation degree on one side can be counteracted, whether the harmonic component of the alternating current side exceeds a preset value or not is judged, and if the harmonic component of the alternating current side exceeds the preset value, the fundamental wave triple frequency component is abandoned, so that the system efficiency can be optimized on the premise of not influencing the current characteristics of a power grid or an alternating load, and the technical problem that an inverter cannot be compatible with the system efficiency and reliability in the related technology is solved.

In the application, because the neutral line of the two-phase inverter is connected with the neutral point of the bus, the neutral line end point of the grid-connected port and the neutral line end point of the important load port, and because of the parallel load and the equivalent inductance capacitance of the line on the alternating current side, part of triple frequency current flows into the alternating current side (such as a power grid, an important load or a common load), the triple frequency current content of the current on the alternating current side needs to be detected after fundamental wave triple frequency components are added, if the triple frequency content does not exceed the requirement, the fundamental wave triple frequency components can be increased to inhibit overmodulation, the direct current bus voltage of the inverter can not be lifted, and the system efficiency is optimal. On the contrary, if the triple frequency content exceeds the requirement, the fundamental triple frequency component is abandoned to be added, and the voltage of the direct current bus is increased, so that the performance meets the requirement, and the reliability of the system is improved. Therefore, the system efficiency can be optimized on the premise of improving the system reliability.

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 and do not constitute a limitation of 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 two-phase inverter according to an embodiment of the present invention;

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

FIG. 4 is a waveform diagram of a fundamental modulation component;

fig. 5 is a waveform diagram of a direct current modulation amount and a fundamental triple frequency component;

fig. 6 is a waveform diagram after superimposing a dc modulation amount on the fundamental wave modulation component;

fig. 7 is a waveform diagram after superimposing the dc modulation amount and the fundamental frequency tripling component on the fundamental modulation component;

fig. 8 is a waveform of a two-bridge arm modulated wave and a waveform of an overall voltage modulated wave after superimposing a direct-current modulation amount and a fundamental triple-frequency component on a fundamental modulated component;

fig. 9 is a schematic diagram of a two-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 obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, 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 two-phase inverter according to an embodiment of the present invention.

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

Referring to fig. 2, a schematic diagram of a two-phase inverter circuit according to an embodiment and a schematic diagram of a two-phase inverter circuit according to another embodiment are shown in fig. 3, where the two-phase inverter includes a bus capacitor unit 110 and an inverter switch unit 130 connected in sequence.

The bus capacitor unit (a dc bus capacitor unit) 110 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) for receiving a dc power output from a photovoltaic cell or a household energy storage battery is provided 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 a bus midpoint DN, a neutral line point N-Grid of the Grid-connected port 161 and a neutral line point N-Load of the important Load port 162, 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, a bus split capacitor-based H5 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 of the A phase can be called as a bridge arm A, and the four switching tubes of the B phase can be called as a bridge arm B.

As shown in fig. 2, the inverter circuit further includes: the filtering unit 140 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 neutral line N.

As shown in fig. 2, the inverter circuit further includes a first grid-connection/disconnection switching unit 151 connected between the filtering unit 140 and the grid-connection port 161 and the important load port 162, and configured to switch the ac-side output of the inverter switching unit 130 between the grid-connection port 161 and the important load port 162 or simultaneously connect the grid-connection port 161 and the important load port 162, where neutral terminals of the grid-connection port 161 and the important load port 162 are connected to a neutral line N through the first grid-connection/disconnection switching unit 151. 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 selection switch CS1 connected between the first end of the second filter capacitor C22 and the first node d1, a selection switch CS2 connected between the first end of the first filter capacitor C11 and the second node d2, a selection switch CS3 connected between the neutral line N and the third node d3, a selection switch DS1 connected between the first node d1 and the first phase end point L1-Load of the important Load port 162, a selection switch DS2 connected between the second node d2 and the second phase end point L2-Load of the important Load port 162, a selection switch DS3 connected between the third node d3 and the neutral line end point N-Load of the important Load port 162, a selection switch ES1 connected between the first node d1 and the first phase end point L1-Grid of the Grid-connected port 161, a selection switch ES2 connected between the second node d2 and the second phase end point L2-Grid of the Grid-connected port 161, and a selection switch ES3 connected between the third node d3 and the neutral line end point N-Grid of the Grid-connected phase end point L2-connected to the Grid port 161. When the selection switch CS1, the selection switch CS2, the selection switch CS3, the selection switch DS1, the selection switch DS2, and the selection switch DS3 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 CS3, the selection switch ES1, the selection switch ES2, and the selection switch ES3 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. In this way, the grid neutral line and the important load neutral line are connected to the bus midpoint DN and the neutral line N of the inverter 100 through the first shunt network switching unit 151.

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 end point L1-Load, a second phase end point L2-Load, and a neutral end point N-Load. The present application does not limit the specific structure of the second grid-connected and off-grid switching unit 152 as long as it can achieve the above-described functions. The second on-off-grid switching unit 152 shown in fig. 3 is an embodiment and includes a select switch CS1 connected between the first end of the second filter capacitor C22 and the first phase end point L1-Load of the important Load port 162, a select switch CS2 connected between the first end of the first filter capacitor C11 and the second phase end point L2-Load of the important Load port 162, and a select switch CS3 connected between the N line and the neutral line end point N-Load. When the select switch CS1, the select switch CS2, and the select switch CS3 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, the select switch CS2, and the select switch CS3 are turned off, the ac side output of the inverting switch 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-connected port 161 is connected to an ac two-phase three-wire grid, and the two-phase grids are opposite in phase. In practical application, important loads can be connected between L1-Load and N-Load or L2-Load and N-Load, and ordinary loads can be connected between L1-Grid and N-Grid or L2-Grid and N-Grid. Because the phases of the two phases of power grids are opposite, the amplitude values of the modulation waves adopted by the inverter are the same, the phases are opposite, and the total output L1-Grid and L2-Grid or L1-Load and L2-Load are equivalent to a single phase, the utilization rate of the direct-current bus voltage cannot be improved by adding a frequency tripling component on the two-phase modulation waves with opposite positive and negative polarities like a three-phase inverter.

In practical applications, the average voltages of the upper and lower bus capacitors (the upper bus capacitor C1 and the lower bus capacitor C2) are often different, and therefore, the average voltages of the upper and lower bus capacitors need 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

Via an addition unit 541 willDirect current modulation quantity for inhibiting average voltage difference of upper and lower bus capacitors or direct current component of alternating current side

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）；

Where ω is the grid fundamental angular frequency, t is time, and M represents the fundamental modulation component

Normalizing the modulation degree; and 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, even over-modulation occurs beyond a threshold (the threshold 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 as it is, 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, with 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 accordance with an embodiment of the present invention, there is provided a two-phase inverter control method embodiment, it is noted that the steps illustrated in the flowchart of the drawings may be performed in a computer system such as a set of computer executable instructions, and that while a logical order is illustrated in the flowchart, in some cases the steps illustrated or described may be performed in an order different than here.

In an embodiment of the present application, a method for controlling a two-phase inverter is provided to improve the efficiency and reliability of the two-phase inverter shown in fig. 2 and 3, where a neutral line N of the two-phase inverter connects a bus midpoint DN, a neutral line end N-Grid of a Grid-connected port 161, and a neutral line end N-Load of an important Load port 162. 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 quantity with a medium amplitude is large; and 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

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

B phase DC modulation

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; s12, detecting harmonic component of alternating current end current, judging whether the harmonic component of the alternating current end current exceeds a preset value or not, if so, executing fundamental wave modulation component

And A phase DC modulation amount

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

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

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 generate the first total modulation command in accordance with the B-phase

) Outputting a switch control signal of a B-phase switch tube in the inversion switch unit 130, starting a bus voltage control module to increase the bus voltage, and if not, continuing to execute the step S11;

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

And A phase DC modulation amount

Adding to obtain A phase first total modulation command

And B phase DC modulation amount

Adding to obtain B phase first total modulation command

Outputting a switch control signal of a B-phase switch tube in the inversion switch unit 130, and starting a bus voltage control module to raise the bus voltage from a first bus voltage Vbus1 to a second bus voltage Vbus2; s22, modulating the fundamental wave component

A phase DC modulation amount

Sum fundamental frequency tripled component

Adding to obtain A phase second total modulation instruction

B phase DC modulation amount

Sum fundamental frequency tripled component

Adding to obtain B phase second total modulation instruction

Outputting a switch control signal of a B-phase switch tube in the inversion switch unit 130; s23, keeping starting the bus voltage control module to increase the bus voltage; s24, detecting harmonic components of the alternating-current end current, judging whether the harmonic components of the alternating-current end current exceed a preset value or not, if so, executing a step S21, otherwise, continuing to execute a step S22; and keep activating the bus voltage control module to reduce the bus voltage from the first bus voltage Vbus1 to the second bus voltage Vbus2;

the third operation includes: modulating the fundamental wave component

And A phase DC modulation amount

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

Negative fundamental modulation component

And B phase DC modulation amount

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

。

Since the neutral line N of the two-phase inverter is connected to the bus midpoint DN, the neutral line end N-Grid of the Grid-connected port 161 and the neutral line end N-Load of the important Load port 162, and since the Load and the line equivalent inductance capacitance connected in parallel on the ac side, a part of triple frequency current flows into the ac side (such as the power Grid, the important Load or the common Load), it is necessary to add the fundamental wave triple frequency division currentQuantity of

Then detecting the triple frequency current content of the AC side current, if the triple frequency current content does not exceed the requirement, the fundamental triple frequency component can be increased

By suppressing the overmodulation, the inverter dc bus voltage is not raised, and the system efficiency is optimized. Otherwise, if the triple frequency current content exceeds the requirement, the fundamental triple frequency component is abandoned to be added

And the voltage of the direct current bus is regulated, so that the performance meets the requirement, and the reliability of the system is improved. Therefore, the system efficiency can be optimized on the premise of improving the system reliability.

In particular, according to the modulation component at the fundamental wave

And negative fundamental modulation component

Upper superimposing A phase DC modulation quantity

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 harmonic component of the alternating current end current exceeds a preset value, if so, raising the bus voltage to avoid overmodulation, and if not, continuing to add the fundamental frequency tripling component

That is, then over-modulation is avoided by not having to raise the bus voltage, which can optimize efficiency; or raising the bus voltage to avoid over-modulation, raising the system reliability, and adding fundamental frequency tripling component

Judging whether the harmonic component of the alternating current end current exceeds a preset value, if so, abandoning the addition of the fundamental frequency tripling component

If not, continuing to add the fundamental frequency tripling component

The bus voltage is reduced, 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 separated between step S11 and step S12 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 S22 and step S24 in the second operation. Wherein the first time is, for example, 5 to 8 power frequency cycles.

Wherein, in some applications, the A phase DC modulation amount

Equal to B phase DC modulation amount

Such as for suppressing the difference in average voltage of the upper and lower bus capacitance. In another 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 three times the power frequency. In the first embodiment, the amount of A-phase DC modulation is based

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 the content of the first and second substances,

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 triple frequency 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 the formula (3)

（3）；

Wherein, omega is the angular frequency of the fundamental wave of the power grid; m is the fundamental modulation component

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

referring to fundamental wave period of power network, n is natural number, sgn is symbol, and DC modulation amount

Modulating the A-phase direct current

And B phase DC modulation amount

The direct current modulation amount with a medium amplitude is large. 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 frequency tripling component

Is a component of three times the power frequency. Please refer to the modulation component at the fundamental shown in fig. 6

Upper superimposed DC modulation

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 in order to not overmodulation. Please refer to fig. 7 for the fundamental modulation component

Upper superimposed DC modulation

Sum fundamental frequency tripled component

In the waveform diagram, the solid line still represents the bridge arm A, and the dotted line still represents the bridge arm B, so that the fundamental triple frequency component is shown

So that the peak of the waveform shown in fig. 6 is lowered and both sides of the peak are raised upward to form a saddle-like waveform shown in fig. 7, thereby avoiding the fundamental modulation component

Overmodulation by upward deflection, i.e. without raising the motherLine voltage can also avoid over-modulation and can be seen in the fundamental modulation component shown in FIG. 8

Upper superposed DC modulation quantity

Sum fundamental frequency tripled component

The solid line represents the bridge arm A, the dotted line represents the bridge arm B, and the dotted line represents the integral voltage modulated wave obtained by subtracting the bridge arm B from the bridge arm A

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 an alternating current end, zero-sequence current corresponding to a specific zero-sequence component does not flow into a power grid or an alternating current load.

According to modulation degree M and A phase direct current modulation quantity

And B phase DC modulation amount

And if the sum of the medium-amplitude large direct current modulation amount judges whether the risk of overmodulation exists, executing a first operation or a second operation, and comprising the following steps of: receiving fundamental modulated components

Modulation degree M, A phase DC modulation amount

And B phase DC modulation amount

If the sum of the modulation M and the dc modulation amount having the large amplitude is equal to or greater than the first modulation limit threshold value, it is considered that there is a risk of overmodulation, and the first operation or the second operation is executed.

In an embodiment, performing the first operation or the second operation includes: either one of the two is selected; or judging the A-phase direct current modulation quantity

And B phase DC modulation amount

Medium-amplitude large 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%.

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 add to 1, greater than 0.99, there is a risk of overmodulation and the first operation or the 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.

Another embodimentIn the method, according to the modulation degree M and the A-phase direct current 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: if the modulation degree M and the A phase direct current modulation quantity

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 a second modulation degree limiting threshold value and is smaller than a third modulation degree limiting threshold value, executing the first operation, and if the sum of the direct current modulation amounts with the medium amplitude value 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 frequency tripling operation is performed), the fundamental frequency modulation component is selected

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

And the sum of the voltage and the frequency is 0.05, the sum of the voltage and the frequency is 0.98, less than 0.99 and more than 0.95, the condition of long-term operation is not met, the first operation can be executed, the fundamental wave triple frequency component is firstly added for probing, if the harmonic component of the alternating current end current is in an acceptable range, the fundamental wave triple frequency component is continuously added, and if the harmonic component of the alternating current end current is not in the acceptable range, the fundamental wave triple frequency component is abandoned, and the direct current bus voltage is selected to be increased. If fundamental wave modulation component

Modulation degree M ofIs 0.94, DC modulation amount

And 0.055, the sum of the two is 0.995 and is more than 0.99, the fundamental wave frequency tripling component cannot be directly added for probing, and then the second operation can be executed, wherein the direct current bus voltage is firstly increased, overmodulation is quickly avoided, and the fundamental wave frequency tripling component is added for probing.

As described above, based on the a-phase dc modulation amount

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. And judging whether harmonic component of AC end current exceeds preset value, if so, abandoning to add fundamental wave triple frequency component

. Therefore, the method can optimize the system efficiency without influencing the current characteristics of the power grid or the alternating load.

Wherein 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.

The triple frequency current content of the alternating-current side current is detected by a current sensor disposed between the filtering unit 140 and the grid-connected and off-grid switching unit (such as the first grid-connected and off-grid switching unit 151 or the second grid-connected and off-grid switching unit 152).

In an embodiment of the present application, a two-phase inverter system is further provided, please refer to a schematic diagram of the two-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

According to the fundamental modulation component

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; wherein, the A phase DC modulation amount

And B phase DC modulation amount

To suppress the DC component of the AC side current or the average voltage difference between the upper and lower bus capacitors, the fundamental modulation component is required

The modulation amount superposed on the above;

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, in the process,

the first operation procedure includes: the output fundamental frequency triple frequency component adding mark value n2 is 1, and the starting mark value n1 of the bus voltage control module is 0; detecting harmonic components of alternating-current-end current, judging whether the harmonic components of the alternating-current-end current exceed a preset value or not, if so, outputting a fundamental frequency tripling component adding mark value n2 as 0, and a bus voltage control module starting mark value n1 as1, otherwise, continuously outputting the fundamental frequency tripling component adding mark value n2 as1, and the bus voltage control module starting mark value n1 as 0;

the second operation procedure includes: the output fundamental frequency triple frequency component adding mark value n2 is 0, and the starting mark value n1 of the bus voltage control module is 1; outputting a fundamental wave frequency tripling component addition marking value n2 to be 1, and still setting a bus voltage control module starting marking value n1 to be 1, detecting an alternating current end current harmonic component, and judging whether the alternating current end current harmonic component exceeds a preset value, if so, outputting a fundamental wave frequency tripling component addition marking value n2 to be 0, setting a bus voltage control module starting marking value n1 to be 1, if not, outputting a fundamental wave frequency tripling component addition marking value n2 to be 1, and setting a bus voltage control module starting marking value n1 to be 11;

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 two-phase inverter system further includes a bus voltage control module 540 that receives a bus voltage control module activation flag value n1, wherein the bus voltage control module is activated to raise the bus voltage from the second bus voltage Vbus2 to the first bus voltage Vbus1 when the bus voltage control module activation flag value n1 is 1, the bus voltage control module is not operated when 0, and the bus voltage control module is activated to lower the bus voltage from the first bus voltage Vbus1 to the second bus voltage Vbus2 when 11.

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

A phase 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 inversion switching unit (see fig. 2); a second addition unit 542 receiving the negative-going fundamental modulation component

B phase DC modulation

And baseAddition amount of wave triple frequency

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

^* 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).

The method comprises the steps of outputting a fundamental wave frequency tripling component adding mark value n2 as1, starting the mark value n1 of a bus voltage control module as 0, detecting an alternating current harmonic component, and judging whether the alternating current harmonic component exceeds a preset value or not at a first interval. Wherein the first time is, for example, 5 to 8 power frequency cycles.

And the step in the second operation program outputs a fundamental frequency tripling component adding mark value n2 of 1, and the bus voltage control module starts the mark value n1 to be still 1, detects the harmonic component of the alternating current end, and judges whether the harmonic component of the alternating current end exceeds a preset value or not at a first 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. As shown in fig. 9, the first phase current I1 is detected by a current sensor connected between the first filter inductor L1 and the first end of the second filter capacitor C22, and the second phase current I2 is detected by a current sensor connected between the second filter inductor L2 and the first end of the first filter capacitor C11.

Optionally, as shown in fig. 9, current sensors are disposed between the first end of the second filter capacitor C22 and the grid-connected and off-grid switching unit (such as the first grid-connected and off-grid switching unit 151 or the second grid-connected and off-grid switching unit 152), the first end of the first filter capacitor C11 and the grid-connected and off-grid switching unit, and the N line and grid-connected and off-grid switching unit, so as to detect triple-frequency current content, that is, harmonic component, of the alternating-current side current. The three current sensors form a current sensor unit 120.

In an alternative embodiment, as shown in fig. 9, a fundamental triple-frequency component generating module 530 is further included, which receives the a-phase dc modulation amount

And B phase DC modulation amount

Medium and large amplitude DC modulation

Obtaining fundamental frequency tripler component according to formula (2)

，

（2）；

Wherein the content of the first and second substances,

referring to the period of the fundamental wave 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, a fundamental triple frequency component generation module 530 is further included, which receives a fundamental modulation component

Obtaining fundamental frequency tripling component according to formula (3)

，

（3）；

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

The direct current modulation amount with a medium amplitude is large. 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

Medium amplitude valueIf the sum of the larger dc modulation amounts 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 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 direct current modulation amounts with the medium amplitude value is greater than or equal to the first modulation degree limiting threshold value, the modulation instruction generation module 520 is instructed to execute the first operation program or the second operation program by considering that the risk of overmodulation exists, and if the sum is less than the first modulation degree limiting threshold value, the modulation instruction generation module 520 is instructed to execute the third operation program by considering that the risk of overmodulation does not exist.

More specifically, the operation command dr instructs the modulation command generating module 520 to execute the first operation procedure or the second operation procedure, which includes: either one of the two is selected; alternatively, the determining module 510 further determines the a-phase dc modulation amount

And B phase DC modulation amount

Medium-amplitude large 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 and DC modulation amount

If the sum of the two is greater than or equal to the second modulation degree limiting threshold and less than the third modulation degree limiting threshold, the operation command dr instructs the modulation command generation module 520 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, the operation command dr instructs the modulation command generation module 520 to execute the second operation.

The two-phase inverter system is compatible with the two-phase inverter control method, and has the same principle of high efficiency and high reliability, which is not described herein again.

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, a device in which the computer-readable storage medium is located is controlled to execute any one of the above-mentioned two-phase inverter control methods.

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 technology can be implemented in other ways. The above-described apparatus embodiments 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 may be integrated into another system, or some features may be omitted, or may not be executed. In addition, the shown or discussed coupling or direct coupling or communication connection between each other may be an indirect coupling or communication connection through some interfaces, units or modules, and may be electrical or in other forms.

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 may be embodied in the form of 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 execute 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 two-phase inverter system, comprising:

the two-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 central line, and the central line is connected with the bus midpoint, a neutral line end of a grid-connected port and a neutral line end of an important load port;

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: the output fundamental frequency triple frequency component adding mark value n2 is 1, and the starting mark value n1 of the bus voltage control module is 0; detecting harmonic components of alternating-current end current, and judging whether the harmonic components of the alternating-current end current exceed a preset value, if so, outputting n2 to be 0, and n1 to be 1, otherwise, continuously outputting n2 to be 1, and n1 to be 0; the second operation procedure includes: the output n2 is 0, and n1 is 1; the output n2 is 1, and n1 is still 1, detecting the harmonic component of the alternating-current end current, and judging whether the harmonic component of the alternating-current end current exceeds a preset value, if so, the output n2 is 0, n1 is 1, if not, the output n2 is 1, and n1 is 11; 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.

2. The two-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 two-phase inverter system according to 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 does not work when the starting mark value n1 is 0, and the bus voltage control module is started to reduce the bus voltage when the starting mark value n1 is 11.

4. The two-phase inverter system according to claim 1, further comprising:

the first addition operation unit receives the fundamental wave modulation component, the A-phase direct current modulation quantity and the fundamental wave frequency tripling addition quantity, performs addition operation on 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, and the A-phase PWM signal generation 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;

and the second addition operation unit is used for receiving the negative fundamental wave modulation component, the B-phase direct current modulation quantity and the fundamental wave frequency tripling addition quantity, performing addition operation on the negative fundamental wave modulation component, the B-phase direct current modulation quantity and the fundamental wave frequency tripling addition quantity, outputting a B-phase total modulation instruction, and outputting a switch control signal of a B-phase switch tube of the inverter switch unit by the B-phase PWM signal generation circuit according to the B-phase total modulation instruction.

5. The two-phase inverter system according to claim 1, further comprising:

the filter unit comprises a first filter inductor, a second filter inductor, a first filter capacitor and a second filter capacitor, wherein the first filter inductor is connected between the first phase output end and the first end of the second filter capacitor, the second filter inductor is connected between the second phase output end and the first end of the first filter capacitor, and the second end of the first filter capacitor and the second end of the second filter capacitor are connected with a central line.

6. The two-phase inverter system according to claim 5, wherein current sensors are respectively disposed between the first end of the second filter capacitor, the first end of the first filter capacitor, and the on-grid and off-grid switching unit and between the N line and the on-grid and off-grid switching unit.

7. The two-phase inverter system according to 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, the first and the second end of the pipe are connected with each other,

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 triple frequency component.

8. The two-phase inverter system according to 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:

，

where ω is the angular frequency of the fundamental wave of the power grid, t is time, and M is the modulation component of the fundamental wave

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 of the a-phase dc modulation amount and the B-phase dc modulation amount,

is a fundamental triple frequency component.

9. The two-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 dc modulation amount with the larger amplitude, and the operation command instructs the modulation command generation module to execute the third operation routine.

10. The two-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.

11. The two-phase inverter system according to claim 10, wherein the operating commands instruct a modulation command generation module to perform the first operating procedure or the second operating procedure, comprising:

either of the first operating procedure and the second operating procedure is optional; alternatively, the first and second electrodes may be,

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 the operation instruction indicates the modulation instruction generation module to execute the second operation program, otherwise, the operation instruction indicates the modulation instruction generation module to execute the first operation program.

12. The two-phase inverter system according to claim 1, wherein the determination module receives 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; 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 a first operation program; and if the sum of the two is greater than or equal to a third modulation degree limiting threshold value, the operation instruction instructs the modulation instruction generation module to execute a second operation.

13. A control method of a two-phase inverter is characterized in that a neutral line of the inverter is connected with a bus midpoint, a neutral line terminal of a grid-connected port and a neutral line terminal of an important load port, and the method comprises the following steps:

receiving the modulation degree M of a fundamental wave modulation component, an A-phase direct current modulation quantity and a B-phase direct current modulation quantity, selecting the direct current modulation quantity with larger amplitude in the A-phase direct current modulation quantity and the B-phase direct current modulation quantity, judging whether the over-modulation risk exists according to the sum of the modulation degree M and the direct current modulation quantity with larger amplitude, if so, executing a first operation or a second operation, and if not, executing a third operation,

the first operation comprises S11, 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; s12, detecting harmonic components of alternating-current end current, judging whether the harmonic components of the alternating-current end current exceed a preset value or not, if so, performing superposition on the fundamental wave modulation component and the A-phase direct-current modulation quantity to obtain an A-phase first total modulation instruction, performing superposition on the negative fundamental wave modulation component and the B-phase direct-current modulation quantity to obtain a B-phase first total modulation instruction, starting a bus voltage control module to increase bus voltage, and if not, continuing to perform the step S11;

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, superposing the negative fundamental wave modulation component and the B-phase direct current modulation quantity to obtain a B-phase first total modulation instruction, and starting the bus voltage control module to increase the bus voltage from a first bus voltage to a second bus voltage; s22, 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; s23, keeping starting the bus voltage control module to increase the bus voltage; s24, detecting harmonic components of the alternating-current end current, judging whether the harmonic components of the alternating-current end current exceed a preset value or not, if so, executing a step S21, otherwise, continuing to execute a step S22; and keeping starting the bus voltage control module to reduce 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.

14. The two-phase inverter control method according to claim 13, wherein the fundamental frequency tripling component is obtained according to the following formula:

，

modulating the A-phase direct current

And the B-phase direct current modulation amount

The direct current modulation quantity with a medium amplitude value is large,

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

is a fundamental frequency tripling component.

15. The two-phase inverter control method according to claim 13, wherein the fundamental frequency tripling component is obtained according to the following formula:

，

the direct current modulation quantity with a larger amplitude value in the A-phase direct current modulation quantity and the B-phase direct current modulation quantity is obtained, omega is the fundamental wave angular frequency of the power grid, and t is time; m is the fundamental modulation component

is a fundamental frequency tripling component.

16. The two-phase inverter control method according to claim 13, wherein the step of determining whether or not 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 sum of the modulation M and the direct current modulation amount with the larger amplitude is greater than or equal to a first modulation limit threshold value, the first operation or the second operation is executed, and if the sum is smaller than the first modulation limit threshold value, the risk of overmodulation is determined not to exist.

17. The two-phase inverter control method according to claim 16, wherein the performing the first operation or the second operation includes:

either one of the first operation and the second operation is optional; alternatively, the first and second electrodes may be,

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 threshold value, if so, executing the second operation, and otherwise, executing the first operation.

18. The two-phase inverter control method according to claim 13, wherein determining whether there is a risk of overmodulation based on a sum of a modulation degree M and the dc modulation amount having the larger amplitude, and if the first operation or the second operation is performed, the method includes:

if the sum of the modulation degree M and the larger-amplitude direct-current modulation quantity of the A-phase direct-current modulation quantity and the B-phase direct-current modulation quantity 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 larger-amplitude direct-current modulation amount of the A-phase direct-current modulation amount and the B-phase direct-current modulation amount is greater 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 when the computer program is run, the computer-readable storage medium is controlled to execute the two-phase inverter control method according to any one of claims 13 to 18.