Control method of inverter circuit and inverter

Abstract

The invention provides a control method of a three-phase four-wire system inverter circuit and an inverter, and the method comprises the steps: obtaining a real-time output current of the three-phase four-wire system inverter circuit, carrying out the coordinate transformation of the real-time output current, obtaining a direct-axis current, a quadrature-axis current and a zero-sequence component, and obtaining a first control quantity according to the direct-axis current, the quadrature-axis current and the zero-sequence component; and obtaining a current average value of the three-phase four-wire system inverter circuit, obtaining a second control quantity according to a difference between the current average value and the current reference value, superposing the second control quantity to the first control quantity to obtain a target control quantity, and generating a driving signal according to the target control quantity. Therefore, in the process of generating the driving signal, negative feedback regulation on the target control quantity is realized according to the current average value, so that the driving signal generated according to the target control quantity can suppress a direct current component output by the three-phase four-wire system inverter circuit, the output stability of the three-phase four-wire system inverter circuit is improved, and the stability of the three-phase four-wire system inverter circuit is improved. And the control is simple, and the cost and the size are reduced.

Description

Technical Field

[0001] The present application belongs to the technical field of inverters, and in particular relates to a control method of an inverter circuit and an inverter. Background Art

[0002] The DC component (DCI) refers to the DC component contained in the AC signal. In the photovoltaic grid-connected inverter, the DC component will be injected into the grid, causing the transformer operating point to shift and cause the transformer to saturate. It may also cause high current to burn out the fuse and cause power outage. The DC component will increase the harmonic component of the grid and affect the overall stability of the grid. Therefore, the grid-connected inverter needs to be able to suppress the DC component.

[0003] The DC component in the output current of the grid-connected inverter is caused by many factors. For example, there is an error in the sampling of the DC input voltage of the photovoltaic grid-connected inverter. The switching signal generated by modulating the input voltage with error will cause the inverter output current to contain a DC component. In order to suppress the DC component, the related technology uses a DC blocking capacitor in the inverter or an industrial frequency transformer at the output end of the inverter, but this requires additional devices, which will increase the cost and size of the inverter. Summary of the invention

[0004] The embodiment of the present application provides a control method and inverter for a three-phase four-wire inverter circuit, wherein the input end of the three-phase four-wire inverter circuit is connected to a positive and negative DC bus, two bus capacitors are connected in series between the positive and negative DC bus, the midpoint of the two bus capacitors is the neutral point of the three-phase four-wire inverter circuit, the output end of the inverter circuit is connected to a power grid through three phase lines, and the neutral point is connected to the zero point of the power grid through a neutral line, and the control method includes: obtaining a real-time output current of the three-phase four-wire inverter circuit; performing coordinate transformation on the real-time output current to obtain a direct-axis current, a quadrature-axis current and a zero-sequence component; obtaining a first control quantity according to the direct-axis current, the quadrature-axis current and the zero-sequence component; obtaining an average current of the three-phase four-wire inverter circuit; obtaining a second control quantity according to the difference between the average current and a current reference value; wherein the current reference value is zero; superimposing the second control quantity on the first control quantity to obtain a target control quantity; generating a drive signal according to the target control quantity, and controlling the three-phase four-wire inverter circuit according to the drive signal.

[0005] In the embodiment of the present application, by obtaining the real-time output current of the three-phase four-wire inverter circuit, the coordinate transformation of the real-time output current is performed to obtain the direct-axis current, the quadrature-axis current and the zero-sequence component, and the first control quantity is obtained according to the direct-axis current, the quadrature-axis current and the zero-sequence component. Then the current average value of the three-phase four-wire inverter circuit is obtained, the second control quantity is obtained according to the difference between the current average value and the current reference value, and the second control quantity is superimposed on the first control quantity to obtain the target control quantity, and the drive signal is generated according to the target control quantity. In this way, in the process of generating the drive signal, the negative feedback regulation of the target control quantity is realized according to the current average value, so that the drive signal generated according to the target control quantity can suppress the DC component output by the three-phase four-wire inverter circuit, and improve the stability of the output of the three-phase four-wire inverter circuit. In the embodiment of the present application, the DC component can be suppressed without adding additional devices, thereby reducing the cost and volume of the three-phase four-wire inverter circuit.

[0006] In one possible implementation, the real-time output current of the three-phase four-wire inverter circuit is obtained, including: in each power frequency cycle, the real-time output current of the three-phase four-wire inverter circuit is collected at a preset sampling frequency; the current average value of the three-phase four-wire inverter circuit is obtained, including: the current average value is calculated based on the real-time output current collected in n power frequency cycles; wherein n is a positive integer greater than or equal to 1.

[0007] In one possible implementation, the control method also includes: calculating the DC component based on the real-time output current collected during the current power frequency cycle; when the DC component is not within a preset range, updating n according to n=nm; wherein the preset range is the allowable range of the DC component of the three-phase four-wire inverter circuit, m is a positive integer greater than or equal to 0, and m is less than n; calculating the current average value based on the updated n until the DC component is within the preset range.

[0008] In a possible implementation, the control method further includes: when the DC component is within a preset range or the current average value has not yet been obtained, obtaining the target control amount according to the first control amount.

[0009] In a possible implementation, obtaining the second control amount according to the difference between the current average value and the current reference value includes: obtaining a current deviation value according to the difference between the current average value and the current reference value; and performing deviation adjustment on the current deviation value to obtain the second control amount.

[0010] In one possible implementation, a first control quantity is obtained based on the direct-axis current, the quadrature-axis current and the zero-sequence component, including: obtaining a first deviation value based on the difference between the direct-axis reference value and the direct-axis current; obtaining a second deviation value based on the difference between the quadrature-axis reference value and the quadrature-axis current; obtaining a third deviation value based on the difference between the zero-sequence reference value and the zero-sequence component; and obtaining the first control quantity based on the first deviation value, the second deviation value and the third deviation value.

[0011] In one possible implementation, the control method also includes: obtaining a real-time input voltage and a voltage reference value of a three-phase four-wire inverter circuit; obtaining a direct-axis reference value based on the real-time input voltage and the voltage reference value; wherein the quadrature-axis reference value and the zero-sequence reference value are zero.

[0012] In one possible implementation, the input end of the three-phase four-wire inverter circuit is connected to a photovoltaic module, and the real-time input voltage is the photovoltaic voltage output by the photovoltaic module; the real-time input voltage and voltage reference value of the three-phase four-wire inverter circuit are obtained, including: obtaining the real-time input voltage and real-time input current of the three-phase four-wire inverter circuit; wherein the real-time input current is the photovoltaic current output by the photovoltaic module; and performing maximum power point tracking on the real-time input voltage and real-time input current to obtain a voltage reference value.

[0013] In one possible implementation, coordinate transformation is performed on the real-time output current to obtain a direct-axis current, a quadrature-axis current and a zero-sequence component, including: obtaining a grid voltage output by the grid to each phase line, and obtaining a grid angle according to the grid voltage; coordinate transformation is performed on the real-time output current according to the grid angle to obtain a direct-axis current, a quadrature-axis current and a zero-sequence component; a first control quantity is obtained according to a first deviation value, a second deviation value and a third deviation value, including: deviation adjustment is performed on the first deviation value to obtain a direct-axis voltage compensation value, deviation adjustment is performed on the second deviation value to obtain a quadrature-axis voltage compensation value, and deviation adjustment is performed on the third deviation value to obtain a zero-sequence voltage compensation value; coordinate inverse transformation is performed on the direct-axis voltage compensation value, the quadrature-axis voltage compensation value and the zero-sequence voltage compensation value according to the grid angle to obtain a target output voltage of the three-phase four-wire inverter circuit; and the first control quantity is obtained according to the target output voltage.

[0014] In a second aspect, the present application provides an inverter, comprising: a three-phase four-wire inverter circuit, wherein the input end of the three-phase four-wire inverter circuit is connected to a positive and negative DC bus, two bus capacitors are connected in series between the positive and negative DC bus, the midpoint of the two bus capacitors is the neutral point of the three-phase four-wire inverter circuit, the output end of the inverter circuit is connected to a power grid through three phase lines, and the neutral point is connected to a zero point of the power grid through a neutral line; and a control circuit, the control circuit is used to: obtain the real-time output current of the three-phase four-wire inverter circuit; perform coordinate transformation on the real-time output current to obtain a direct-axis current, a quadrature-axis current and a zero-sequence component; obtain a first control quantity according to the direct-axis current, the quadrature-axis current and the zero-sequence component; obtain the current average value of the three-phase four-wire inverter circuit; obtain a second control quantity according to the difference between the current average value and a current reference value; wherein the current reference value is zero; superimpose the second control quantity on the first control quantity to obtain a target control quantity; generate a drive signal according to the target control quantity, and control the inverter circuit according to the drive signal.

[0015] In one possible implementation, the control circuit includes: a sampling unit, which is used to collect real-time output current; and a control unit, which is connected to the sampling unit and is used to receive the real-time output current and obtain a driving signal according to the real-time output current.

[0016] In one possible implementation, a three-phase four-wire inverter circuit includes a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a fifth bridge arm and a sixth bridge arm; the first bridge arm is connected between the positive and negative DC bus bars, and the first bridge arm includes a first switch tube and a second switch tube connected in series; the midpoint between the first switch tube and the second switch tube is connected to the first terminal of the power grid through a first phase line; the second bridge arm is connected between the midpoint and the neutral point of the first bridge arm; the third bridge arm is connected between the positive and negative DC bus bars, and the third bridge arm includes a third switch tube and a fourth switch tube connected in series; the midpoint between the third switch tube and the fourth switch tube is connected to the second terminal of the power grid through a second phase line; the fourth bridge arm is connected between the midpoint and the neutral point of the third bridge arm; the fifth bridge arm is connected between the positive and negative DC bus bars, and the fifth bridge arm includes a fifth switch tube and a sixth switch tube connected in series; the midpoint between the fifth switch tube and the sixth switch tube is connected to the third terminal of the power grid through a third phase line; the sixth bridge arm is connected between the midpoint and the neutral point of the first bridge arm. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a module schematic diagram of the inverter provided in an embodiment of the present application.

[0018] Figure 2 It is a module schematic diagram of an inverter provided in another embodiment of the present application.

[0019] Figure 3 It is a circuit structure diagram of a three-phase four-wire inverter circuit provided in an embodiment of the present application.

[0020] Figure 4 It is a flow chart of a control method for a three-phase four-wire inverter circuit provided in an embodiment of the present application.

[0021] Figure 5 It is a partial flow chart of a control method for a three-phase four-wire inverter circuit provided in another embodiment of the present application.

[0022] Figure 6 yes Figure 4 Detailed flowchart of step S500.

[0023] Figure 7 It is a partial flow chart of a control method of a three-phase four-wire inverter circuit provided in yet another embodiment of the present application.

[0024] Figure 8 yes Figure 7 Detailed flowchart of step S110 in FIG.

[0025] Fig. 9 yes Figure 4 Detailed flowchart of step S200.

[0026] Fig.10 yes Figure 4 Detailed flowchart of step S300.

[0027] Fig.11 yes Fig.10 Detailed flowchart of step S340 in FIG.

[0028] Fig.12 It is a specific flow chart of the control method of the three-phase four-wire inverter circuit provided in the embodiment of the present application.

[0029] Fig.13 It is a specific control block diagram of the control method of the three-phase four-wire inverter circuit in the embodiment of the present application. DETAILED DESCRIPTION

[0030] It should be noted that the terms "first" and "second" in the specification, claims and drawings of the present application are used to distinguish similar objects, rather than to describe a specific order or sequence. In the specification, claims and drawings of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the term "multiple" in the specification, claims and drawings of the present application refers to two or more than two.

[0031] It is understandable that the connection relationship described in the present application refers to direct or indirect connection. For example, A is connected to B or A is electrically connected to B, which can be either A and B are directly connected or A and B are indirectly connected through one or more other electrical components, for example, A and C are directly connected, and C and B are directly connected, so that A and B are connected through C.

[0032] It should also be noted that the method disclosed in the embodiments of the present application or the method shown in the flowchart includes one or more steps for implementing the method. Without departing from the scope of the claims, the execution order of multiple steps can be interchangeable with each other, and some of the steps can also be deleted.

[0033] Some embodiments will be described below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0034] See also Figure 1 , Figure 1A module schematic diagram of the inverter 10 provided in an embodiment of the present application is shown.

[0035] like Figure 1 As shown, the inverter 10 includes a three-phase four-wire inverter circuit 100 and a control circuit 200. The input end of the three-phase four-wire inverter circuit 100 is connected to the positive and negative DC bus bars (BUS+, BUS-), two bus capacitors (Ci1, Ci2) are connected in series between the positive and negative DC bus bars (BUS+, BUS-), the midpoint of the two bus capacitors is the neutral point of the three-phase four-wire inverter circuit 100, the output end of the three-phase four-wire inverter circuit 100 is connected to the power grid 20 through three phase lines (A, B, C), and the neutral point is connected to the zero point N of the power grid 20 through the neutral line.

[0036] The control circuit 200 is used to control the three-phase four-wire inverter circuit 100 to operate so that the three-phase four-wire inverter circuit 100 is connected to the power grid 20 .

[0037] It can be understood that the input end of the three-phase four-wire inverter circuit 100 can be connected to the photovoltaic assembly 30 through the positive and negative DC bus (BUS+, BUS-). At this time, the inverter 10 is a photovoltaic energy storage inverter. Of course, the inverter 10 of the embodiment of the present application is not limited to a photovoltaic energy storage inverter.

[0038] One end of the bus capacitor Ci1 is connected to the positive DC bus BUS+, the other end of the bus capacitor Ci1 is connected to one end of the bus capacitor Ci2, and the other end of the bus capacitor Ci2 is connected to the negative DC bus BUS-. The midpoint O of the two bus capacitors is the connection point between the two bus capacitors, and the potential of this point is the reference zero potential. The positive and negative DC bus (BUS+, BUS-) are used to connect the photovoltaic assembly 30 to transmit the DC power provided by the photovoltaic assembly 30 to the bus capacitor Ci1 and the bus capacitor Ci2, and store energy through the bus capacitor Ci1 and the bus capacitor Ci2. It can be understood that the voltage at the input end of the three-phase four-wire inverter circuit 100 is the photovoltaic voltage V PV The bus capacitor Ci1 and the bus capacitor Ci2 divide the input voltage of the three-phase four-wire inverter circuit 100 into three levels, namely V PV / 2, 0, -V PV / 2.

[0039] The control circuit 200 outputs a driving signal to the three-phase four-wire inverter circuit 100 to control the output current of the three-phase four-wire inverter circuit 100 .

[0040] If there is an error in the sampling of the input voltage at the input end of the three-phase four-wire inverter circuit 100 obtained by the control circuit 200, it will cause the drive signal generated by the control circuit 200 according to the sampled input voltage to change, resulting in a DC component in the voltage output by the three-phase four-wire inverter circuit 100, and then the current output by the three-phase four-wire inverter circuit 100 also has a DC component, affecting the stability of the output of the three-phase four-wire inverter circuit 100.

[0041] To this end, the control circuit 200 obtains the real-time output current of the three-phase four-wire inverter circuit 100, performs coordinate transformation on the real-time output current to obtain the direct-axis current, the quadrature-axis current and the zero-sequence component, and then obtains the first control amount according to the direct-axis current, the quadrature-axis current and the zero-sequence component. The control circuit 200 obtains the current average value of the three-phase four-wire inverter circuit 100, and then obtains the second control amount according to the difference between the current average value and the current reference value. Then, the control circuit 200 superimposes the second control amount on the first control amount to obtain the target control amount, generates a drive signal according to the target control amount, and controls the three-phase four-wire inverter circuit 100 according to the drive signal. Under ideal conditions, the DC component contained in the current output by the three-phase four-wire inverter circuit 100 is zero, so the current reference value is set to zero.

[0042] It should be noted that the three-phase four-wire inverter circuit 100 can be used to connect a symmetrically balanced three-phase load, or a single-phase load. When the three phase lines at the output end of the three-phase four-wire inverter circuit 100 are connected to an asymmetrical load, the output can be decomposed into positive sequence, negative sequence, and zero sequence components by using a symmetrical component method when analyzing the asymmetrical three-phase output. The zero sequence component belongs to three components of the same size and phase. By introducing the zero sequence component when generating the drive signal, the three-phase four-wire inverter circuit 100 can effectively power the asymmetrical load and provide a stable power output.

[0043] In the embodiment of the present application, the control circuit 200 obtains the second control amount by the difference between the current average value and the current reference value of zero, and then superimposes the second control amount on the first control amount to obtain the target control amount, and generates a drive signal according to the target control amount. In this way, the control circuit 200 implements negative feedback regulation of the target control amount according to the current average value in the process of generating the drive signal, and then the drive signal generated according to the target control amount can suppress the DC component output by the three-phase four-wire inverter circuit 100, thereby improving the stability of the output of the three-phase four-wire inverter circuit 100. Moreover, since the control circuit 200 of the embodiment of the present application only introduces negative feedback of the current average value in the process of generating the drive signal, the DC component is suppressed, and no additional devices are required, which has the advantages of simple control and reduced cost and volume of the inverter 10.

[0044] It can be understood that the real-time output current of the three-phase four-wire inverter circuit 100 includes the phase line currents output by the three-phase four-wire inverter circuit 100 to the three phase lines.

[0045] In some embodiments, the control circuit 200 can calculate the current average value based on the real-time output current collected from multiple power frequency cycles of the three-phase four-wire inverter circuit 100, for example, calculate the current average value based on the real-time output current collected from n power frequency cycles.

[0046] In order to obtain the average current value, when the three-phase four-wire inverter circuit 100 starts to be powered on, the control circuit 200 can collect the real-time output current of the three-phase four-wire inverter circuit 100 in each power frequency cycle at a preset sampling frequency. After current collection for n power frequency cycles, the control circuit 200 calculates the current average value based on the real-time output current collected in n power frequency cycles. Among them, the real-time output current includes the phase line current of each phase line connected to the three-phase four-wire inverter circuit 100.

[0047] It should be noted that the power frequency can represent the rated frequency used by the power generation, transmission, transformation and distribution equipment of the power system and industrial and civil electrical equipment, and the unit is Hertz (HZ). Under the standard power frequency of 50Hz, each power frequency cycle is 20 milliseconds (ms). When the power grid 20 is connected to the grid-connected output port of the inverter 10, the inverter 10 needs to be synchronized with the power grid 20, so the power frequency cycle of the inverter 10 is the power frequency cycle of the power grid 20.

[0048] It can be understood that the preset sampling frequency needs to be greater than the power frequency, and correspondingly, the sampling period is less than the power frequency period. For example, when the power frequency is 50 Hz and the power frequency period is 20 milliseconds (ms), the sampling frequency can be set to 50 kHz, and the sampling period is 20 microseconds (us), that is, within a power frequency period, the control circuit 200 samples the real-time output current of the three-phase four-wire inverter circuit 100 at 1000 sampling moments in each power frequency period. In the embodiment of the present application, the sampling frequency can be consistent with the frequency of the control signal of the switch tube in the three-phase four-wire inverter circuit 100 by the control circuit 200. Of course, the embodiment of the present application does not limit the specific value of the sampling frequency, and can be set according to actual application requirements.

[0049] like Figure 2 As shown, in some embodiments, the control circuit 200 may include a sampling unit 210 and a control unit 220. The sampling unit 210 is used to collect the real-time output current. The control unit 220 is connected to the sampling unit 210, and the control unit 220 is used to receive the real-time output current collected by the sampling unit 210, and obtain a driving signal according to the real-time output current.

[0050] The control unit 220 may include a central processing unit (CPU), other general-purpose processors, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, etc.

[0051] In the embodiment of the present application, the control circuit 200 can obtain a direct-axis reference value according to the real-time input voltage of the three-phase four-wire inverter circuit 100, and then obtain a first control amount according to the direct-axis current, the quadrature-axis current, the zero-sequence component and the direct-axis reference value. For example, the real-time input voltage can be input into the voltage control loop, and the output of the voltage control loop is used as the direct-axis reference value.

[0052] It can be understood that since the input end of the three-phase four-wire inverter circuit 100 is connected to the photovoltaic module 30, the real-time input voltage is the photovoltaic voltage output by the photovoltaic module 30. In some embodiments, in order to maximize the utilization rate of the photovoltaic module 30, the photovoltaic power can be obtained according to the photovoltaic voltage and photovoltaic current of the photovoltaic module 30, and the maximum power point tracking (MPPT) of the photovoltaic power is performed to obtain a voltage reference value, and then a direct axis reference value is obtained according to the voltage reference value. The driving signal generated based on this can control the input end of the three-phase four-wire inverter circuit 100 to obtain the maximum power of the photovoltaic module 30. Among them, the photovoltaic voltage is the real-time input voltage of the three-phase four-wire inverter circuit 100, and the photovoltaic current is the real-time input current of the three-phase four-wire inverter circuit 100.

[0053] Since the output end of the three-phase four-wire inverter circuit 100 is connected to the power grid 20, the control circuit 200 needs to control the output of the three-phase four-wire inverter circuit 100 to be synchronized with the power grid 20. Based on this, the control circuit 200 can obtain the power grid voltage of the power grid 20, and input the power grid voltage into a phase-locked loop to obtain the power grid angle. When the control circuit 200 obtains the first control amount according to the direct-axis current, the quadrature-axis current and the zero-sequence component, and generates a drive signal according to the target control amount, the power grid angle is introduced so that when the control circuit 200 controls the three-phase four-wire inverter circuit 100 according to the generated drive signal, the output of the three-phase four-wire inverter circuit 100 can be synchronized with the power grid 20.

[0054] Therefore, in some specific examples, such as Figure 3As shown, the sampling unit 210 may include a first sampling unit 211, a second sampling unit 212, a third sampling unit 213 and a fourth sampling unit 214. The first sampling unit 211 is connected to the output end of the three-phase four-wire inverter circuit 100, and the first sampling unit 211 is used to collect the real-time output current of the three-phase four-wire inverter circuit 100. The second sampling unit 212 and the third sampling unit 213 are connected to the input end of the three-phase four-wire inverter circuit 100, the second sampling unit 212 is used to collect the real-time input voltage of the three-phase four-wire inverter circuit 100, and the third sampling unit 213 is used to collect the real-time input current of the three-phase four-wire inverter circuit 100. The fourth sampling unit 214 is connected to the power grid 20, and the fourth sampling unit 214 is used to collect the power grid voltage.

[0055] The first sampling unit 211 and the third sampling unit 213 can be implemented by any one of a sampling resistor, a Hall element or a current transformer to respectively collect the real-time output current and the real-time input current of the three-phase four-wire inverter circuit 100. The second sampling unit 212 and the fourth sampling unit 214 can be implemented by any one of voltage divider resistor sampling, differential sampling, isolation sampling, etc. to respectively collect the real-time input voltage and grid voltage of the three-phase four-wire inverter circuit 100.

[0056] Specifically, Figure 3 As shown, the three-phase four-wire inverter circuit 100 may be a three-phase T-type three-level three-phase four-wire inverter circuit, wherein the three-phase four-wire inverter circuit 100 includes a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a fifth bridge arm and a sixth bridge arm.

[0057] The first bridge arm is connected between the positive and negative DC busbars (BUS+, BUS-), and the first bridge arm includes a first switch tube Q1 and a second switch tube Q2 connected in series. The midpoint between the first switch tube Q1 and the second switch tube Q2 is connected to the first terminal (not marked in the figure) of the power grid 20 through the first phase line A. Specifically, the first end of the first switch tube Q1 is connected to the positive DC busbar BUS+, the second end of the first switch tube Q1 is connected to the first end of the second switch tube Q2 (that is, the midpoint of the first bridge arm), and the second end of the second switch tube Q2 is connected to the negative DC busbar BUS-.

[0058] The second bridge arm is connected between the midpoint of the first bridge arm and the neutral point.

[0059] The third bridge arm is connected between the positive and negative DC busbars (BUS+, BUS-), and the third bridge arm includes a third switch tube Q3 and a fourth switch tube Q4 connected in series. The midpoint between the third switch tube Q3 and the fourth switch tube Q4 is connected to the second terminal (not marked in the figure) of the power grid 20 through the second phase line B. Specifically, the first end of the third switch tube Q3 is connected to the positive DC busbar BUS+, the second end of the third switch tube Q3 is connected to the first end of the fourth switch tube Q4 (that is, the midpoint of the third bridge arm), and the second end of the fourth switch tube Q4 is connected to the negative DC busbar BUS-.

[0060] The fourth bridge arm is connected between the midpoint of the third bridge arm and the midpoint of the neutral point.

[0061] The fifth bridge arm is connected between the positive and negative DC busbars (BUS+, BUS-), and the fifth bridge arm includes a fifth switch tube Q5 and a sixth switch tube Q6 connected in series. The midpoint between the fifth switch tube Q5 and the sixth switch tube Q6 is connected to the third terminal (not marked in the figure) of the power grid 20 through the third phase line C. Specifically, the first end of the fifth switch tube Q5 is connected to the positive DC busbar BUS+, the second end of the fifth switch tube Q5 is connected to the first end of the sixth switch tube Q6 (that is, the midpoint of the fifth bridge arm), and the second end of the sixth switch tube Q6 is connected to the negative DC busbar BUS-.

[0062] The sixth bridge arm is connected between the midpoint of the fifth bridge arm and the midpoint of the neutral point.

[0063] The second bridge arm includes a seventh switch tube Q7 and an eighth switch tube Q8 connected in reverse series, a first end of the seventh switch tube Q7 is connected to a first end of the eighth switch tube Q8, a second end of the seventh switch tube Q7 is connected to a neutral point, and a second end of the eighth switch tube Q8 is connected to a midpoint of the first bridge arm.

[0064] The fourth bridge arm includes a ninth switch tube Q9 and a tenth switch tube Q10 connected in reverse series, a first end of the ninth switch tube Q9 is connected to a first end of the tenth switch tube Q10, a second end of the ninth switch tube Q9 is connected to a neutral point, and a second end of the tenth switch tube Q10 is connected to a midpoint of the third bridge arm.

[0065] The sixth bridge arm includes an eleventh switch tube Q11 and a twelfth switch tube Q12 connected in reverse series, a first end of the eleventh switch tube Q11 is connected to a first end of the twelfth switch tube Q12, a second end of the eleventh switch tube Q11 is connected to a neutral point, and a second end of the twelfth switch tube Q12 is connected to a midpoint of the fifth bridge arm.

[0066] The midpoint of the first bridge arm is connected to the first terminal of the grid 20 through the first phase line A, the midpoint of the third bridge arm is connected to the second terminal of the grid 20 through the second phase line B, and the midpoint of the fifth bridge arm is connected to the third terminal of the grid 20 through the third phase line C.

[0067] The control unit 220 can be connected to the control end of each switch tube of each bridge arm, and send a control signal to each switch tube, so that each switch tube can be turned on or off under the drive of the control signal. The control signal is a pulse width modulation (PWM) signal.

[0068] In this way, when the three-phase four-wire inverter circuit 100 is inverting, the photovoltaic component 30 can input direct current through the positive and negative DC bus bars, and convert it into three-phase alternating current through the on and off of the switching tubes on the first bridge arm, the second bridge arm, the third bridge arm, the fourth bridge arm, the fifth bridge arm and the sixth bridge arm, and output it to the first phase line A, the second phase line B and the third phase line C respectively.

[0069] It can be understood that the present application does not specifically limit each switch tube, and each switch tube may include but is not limited to a triode, a silicon controlled rectifier (Silicon Controlled Rectifier, SCR), a metal oxide semiconductor field effect transistor (Metal Oxide Semiconductor Field Effect Transistor, MOSFET), an insulated gate bipolar transistor (Insulated Gate Bipolar Transistor, IGBT) or a gallium nitride high electron mobility transistor (GaN High Electron Mobility Transistor, GaN HEMT), or at least one of a triode, SCR, MOSFET, IGBT, and GaN HEMT connected in parallel with a reverse-connected diode. For example, when the switch tube is a triode, the base of the triode is the control terminal, the collector is the first terminal, and the emitter is the second terminal.

[0070] Correspondingly, the first sampling unit 211 can be connected to the first phase line A, the second phase line B and the third phase line C respectively to detect the phase line currents of the first phase line A, the second phase line B and the third phase line C respectively, and each phase line current corresponds to a current average value. The second sampling unit 212 and the third sampling unit 213 are respectively connected to the positive and negative DC bus (BUS+, BUS-) to detect the real-time input voltage and real-time input current of the three-phase four-wire inverter circuit 100. The fourth sampling unit 214213 is respectively connected to the three terminals of the power grid 20 to detect the terminal voltage of each terminal.

[0071] The control method of the three-phase four-wire inverter circuit provided by the embodiment of the present invention will be described in detail below through specific embodiments.

[0072] See also Figure 4, which shows a flow chart of a control method for a three-phase four-wire inverter circuit provided by an embodiment of the present invention, and the control method is applied to the inverter 10. In at least one embodiment, the control method for a three-phase four-wire inverter circuit can be executed by the control circuit 200 described above.

[0073] like Figure 4 As shown, the control method of the three-phase four-wire inverter circuit includes:

[0074] S100, obtaining the real-time output current of the three-phase four-wire inverter circuit.

[0075] The control circuit 200 samples the real-time output current of the three-phase four-wire inverter circuit 100 to obtain the real-time output current.

[0076] S200, performing coordinate transformation on the real-time output current to obtain a direct-axis current, a quadrature-axis current and a zero-sequence component.

[0077] In some embodiments, the control circuit 200 performs Clark transformation and Park transformation on the real-time output current to obtain the direct-axis current, quadrature-axis current and zero-sequence component.

[0078] S300, obtaining a first control variable according to the direct-axis current, the quadrature-axis current and the zero-sequence component.

[0079] The control circuit 200 can perform deviation adjustment on the direct-axis current, the quadrature-axis current and the zero-sequence component respectively, perform coordinate inverse transformation on the deviation-adjusted value, and then perform signal modulation on the coordinate inverse-transformed value to obtain the first control quantity. Among them, the deviation adjustment can be any one or more combinations of adjustment methods such as proportional adjustment, proportional integral (PI) adjustment, proportional integral differential (PID) adjustment, quasi-proportional resonance (QPR) adjustment, and proportional resonance (PR) adjustment. The embodiment of the present application does not limit the method of deviation adjustment.

[0080] It can be understood that the first control variable is a parameter related to the driving signal, such as a duty cycle, a pulse width modulation value, and the like.

[0081] S400, obtaining an average current of a three-phase four-wire inverter circuit.

[0082] The control circuit 200 can obtain the current average value according to the real-time output current obtained. For example, the control circuit 200 can determine the current average value according to the real-time output current of the three-phase four-wire inverter circuit 100 sampled in multiple power frequency cycles. For details, please refer to the description of the inverter 10 above, which will not be repeated here.

[0083] S500 , obtaining a second control variable according to a difference between a current average value and a current reference value.

[0084] The current reference value is zero. It can be understood that the control circuit 200 can obtain the second control amount after performing deviation adjustment on the difference between the current average value and the current reference value.

[0085] S600: Superimpose the second control amount on the first control amount to obtain a target control amount.

[0086] The control circuit 200 may add the second control amount to the first control amount to obtain the target control amount. Specifically, the second control amount and the first control amount may be input into an adder to obtain the target control amount.

[0087] S700: Generate a drive signal according to the target control amount, and control the three-phase four-wire inverter circuit according to the drive signal.

[0088] The control circuit 200 obtains the second control amount by the difference between the current average value and the current reference value of zero, and then superimposes the second control amount on the first control amount to obtain the target control amount, and generates a driving signal according to the target control amount. In this way, in the process of generating the driving signal, the control circuit 200 implements negative feedback regulation of the target control amount according to the current average value, so that the driving signal generated according to the target control amount can suppress the DC component output by the three-phase four-wire inverter circuit 100, reduce the DC component output by the three-phase four-wire inverter circuit 100, and improve the stability of the output of the three-phase four-wire inverter circuit 100.

[0089] In the embodiment of the present application, the control method applied to the inverter 10 may be executed by the control circuit 200 in the inverter 10, specifically, by the control unit 220. For example, by a microcontroller unit (MCU), a digital signal processor (DSP) or an energy management system (EMS) in the inverter 10. The control circuit 200 may include a plurality of controllers or control chips, such as a DSP chip and a RAM (Random Access Memory) chip.

[0090] It is understandable that in the embodiment of the present application, the control circuit 200 in the inverter 10 can repeatedly execute steps S100 to S700 during the entire operation process to achieve suppression of the DC component during the entire operation process of the three-phase four-wire inverter circuit 100.

[0091] Wherein, step S100 may include: in each power frequency cycle, collecting the real-time output current of the three-phase four-wire inverter circuit 100 at a preset sampling frequency. In other words, the control circuit 200 may collect the real-time output current of the three-phase four-wire inverter circuit 100 at a preset sampling frequency in each power frequency cycle.

[0092] For example, when the power frequency cycle is ms, the sampling frequency is 50 kHz, the number of samples is 1000, and the phase line currents of the first phase line A collected in one power frequency cycle are I A1 ,I A2 ,I A3 ,…,I A1000 The phase line currents of the second phase line B collected in one power frequency cycle are I B1 ,I B2 ,I B3 ,…,I B1000 The phase line currents of the third phase line C collected in one power frequency cycle are I C1 ,I C2 ,I C3 ,…,I C1000 .

[0093] Correspondingly, step S400 includes: calculating the current average value according to the real-time output current collected in n power frequency cycles.

[0094] Wherein, n is a positive integer greater than or equal to 1. At this time, the number of real-time output currents collected by the control circuit 200 in n power frequency cycles is n*1000. Specifically, the phase line currents of the first phase line A collected in n power frequency cycles are I A1 ,I A2 ,I A3 ,…,I A1000 ,…,I A(n*1000) The phase line currents of the second phase line B collected in n power frequency cycles are I B1 ,I B2 ,I B3 ,…,I B1000 ,…,I B(n*1000) The phase line currents of the third phase line C collected in n power frequency cycles are I C1 ,I C2 ,I C3 ,…,I C1000 ,…,I C(n*1000)Correspondingly, the average current value corresponding to the phase line current of the first phase line A is: I AV =(I A1 +I A2 +I A3 +…+I A1000 +…+I A(n*1000) ) / (n*1000), the average current value corresponding to the phase line current of the second phase line B is: I BV =(I B1 +I B2 +I B3 +…+I B1000 +…+I B(n*1000) ) / (n*1000), the average current value corresponding to the phase line current of the third phase line C is: I CV =(I C1 +I C2 +I C3 +…+I C1000 +…+I C(n*1000) ) / (n*1000).

[0095] See also Figure 5 In some embodiments, after step S700, the control method may further include:

[0096] S810. Calculate the DC component according to the real-time output current collected in the current power frequency cycle.

[0097] The DC component of the signal is the average value of the signal, so the control circuit 200 can add all the real-time output currents collected in the current power frequency cycle and then divide it by the number of samples to obtain the DC component. Of course, when the output end of the three-phase four-wire inverter circuit 100 is connected to multiple phase lines, the average value of the real-time output current of each phase line is calculated to obtain the DC component of each phase line.

[0098] Specifically, when the power frequency cycle is ms and the sampling frequency is 50 kHz, the number of samples in one power frequency cycle is 1000, and the DC component of the first phase line A is: I ADC =(I A1 +I A2 +I A3 +…+I A1000 ) / 1000, the DC component of the second phase line B is: I BDC =(I B1 +I B2 +I B3 +…+I B1000 ) / 1000, the DC component of the current in the third phase line C is: I CDC =(I C1 +I C2 +I C3+…+I C1000 ) / 1000.

[0099] S820: When the DC component is not within the preset range, update n according to n=nm.

[0100] Among them, the preset range is the allowable range of the DC component of the three-phase four-wire inverter circuit, m is a positive integer greater than or equal to 0, and m is less than n. For example, n can be set to 10, and m can be set to 1. Of course, the embodiment of the present application does not limit the specific values ​​of n and m, and can be set according to actual needs. For example, n can also be set to 5, 8, 12, 20, etc., and m can also be set to 2, 3, etc.

[0101] Under ideal conditions, the DC component contained in the current output by the three-phase four-wire inverter circuit 100 is zero, but in actual working conditions, it is difficult to adjust the DC component to zero, so a preset range is set to adjust the DC component of the three-phase four-wire inverter circuit 100 to within the preset range.

[0102] S830, calculating the current average value according to the updated n until the DC component is within a preset range.

[0103] It can be understood that after n is updated, the control circuit 200 calculates the current average value based on the real-time output current collected in the next n power frequency cycles, and obtains the second control quantity based on the current average value and the current reference value, and then superimposes the second control quantity on the first control quantity to obtain the target control quantity, generates a drive signal according to the target control quantity, and controls the three-phase four-wire inverter circuit 100 according to the newly generated drive signal.

[0104] Before the control circuit 200 collects the real-time output current of n power frequency cycles, the control circuit 200 continues to calculate the second control variable according to the current average value calculated last time.

[0105] It is understandable that the calculation of the DC component requires obtaining the real-time output current collected within one power frequency cycle. Therefore, after the control circuit 200 collects the real-time output current of n power frequency cycles and obtains the current average value according to the real-time output current of n power frequency cycles, the control circuit 200 first obtains the driving signal according to the first control quantity and the second control quantity generated by the current average value to control the three-phase four-wire inverter circuit 100 for one power frequency cycle, that is, in the n+1 power frequency cycle, the control circuit 200 first obtains the driving signal according to the first control quantity and the second control quantity generated by the current average value to control the three-phase four-wire inverter circuit 100. Then the control circuit 200 calculates the DC component according to the real-time output current collected in the n+1 power frequency cycle, and determines whether the DC component is within the preset range.

[0106] In some embodiments, when the DC component is within a preset range or the current average value has not yet been obtained, the target control amount is obtained according to the first control amount.

[0107] Among them, when the DC component is within the preset range, it means that the DC component meets the allowable range. At this time, there is no need to continue to suppress the DC component. Therefore, the control circuit 200 directly uses the first control amount as the target control amount to generate a drive signal to directly control the three-phase four-wire inverter circuit 100.

[0108] It should be noted that the control circuit 200 in the inverter 10 needs to provide a driving signal to the three-phase four-wire inverter circuit 100 from the time the inverter 10 is powered on. However, in the first n power frequency cycles, the control circuit 200 has not yet obtained the average current value, and thus cannot generate the second control amount according to the average current value. The first control amount can be directly used as the target control amount to generate a driving signal to directly control the three-phase four-wire inverter circuit 100. Alternatively, the control circuit 200 can perform steps S100 to S700 to generate a driving signal to control the three-phase four-wire inverter circuit 100 to work when the second control amount is zero.

[0109] In this way, the control circuit 200 calculates the current average value once every n power frequency cycles, and before the next calculation of the current average value, the second control amount is obtained with the current average value currently calculated, which can reduce the amount of calculation of the control circuit 200. After calculating the current average value once every n power frequency cycles, the DC component of the three-phase four-wire inverter circuit 100 is calculated in the next power frequency cycle after the current average value is calculated. If the DC component is not within the preset range, n is reduced, and the current average value is calculated with the real-time output current of the reduced n power frequency cycles, and the frequency of calculating the current average value by the control circuit 200 is increased, which is conducive to reducing the DC component more quickly.

[0110] See also Figure 6 , Figure 6 Shows Figure 4 Detailed flowchart of step S500 in FIG.

[0111] like Figure 6 As shown, in some embodiments, step S500 may include:

[0112] S510 , obtaining a current deviation value according to a difference between a current average value and a current reference value.

[0113] The control circuit 200 may subtract the current reference value from the current average value to obtain the current deviation value. Specifically, the current average value and the current reference value may be input into a subtractor to obtain the current deviation value.

[0114] S520, performing deviation adjustment on the current deviation value to obtain a second control amount.

[0115] Specifically, the control circuit 200 may input the current deviation value into a PI regulator, a PID regulator, a QPR regulator or a PR regulator to obtain the second control variable.

[0116] In some embodiments, Figure 7 As shown, the control method also includes:

[0117] S110, obtaining a real-time input voltage and a voltage reference value of a three-phase four-wire inverter circuit.

[0118] The control circuit 200 can obtain the real-time input voltage by detecting the voltage at the input end of the three-phase four-wire inverter circuit 100. Figure 3 In the example, the real-time input voltage of the three-phase four-wire inverter circuit 100 is collected by the second sampling unit 212 .

[0119] The voltage reference value is determined according to the required voltage of the three-phase four-wire inverter circuit 100. For example, the voltage reference value is a value preset according to the voltage value required to be output by the three-phase four-wire inverter circuit 100. For another example, the voltage reference value is a value determined according to the real-time input voltage of the three-phase four-wire inverter circuit 100. The embodiment of the present application does not limit the method for obtaining the voltage reference value.

[0120] S120: Obtain a direct-axis reference value according to the real-time input voltage and the voltage reference value.

[0121] Among them, the quadrature axis reference value and the zero sequence reference value are zero. Specifically, the control circuit 200 can subtract the real-time input voltage from the voltage reference value to obtain a voltage deviation value, and perform deviation adjustment on the voltage deviation value to obtain a direct axis reference value. It can be understood that the control circuit 200 can input the voltage reference value and the real-time input voltage into a subtractor to obtain a voltage deviation value, and then input the voltage deviation value into a PI regulator, a PID regulator, a QPR regulator or a PR regulator to obtain a direct axis reference value.

[0122] When the input end of the three-phase four-wire inverter circuit 100 is connected to the photovoltaic module 30, the real-time input voltage is the photovoltaic voltage output by the photovoltaic module 30. In order to maximize the utilization rate of the photovoltaic module 30, Figure 8 As shown, step S910 may include:

[0123] S111. Acquire the real-time input voltage and real-time input current of the three-phase four-wire inverter circuit.

[0124] The real-time input current is the photovoltaic current output by the photovoltaic module. The control circuit 200 obtains the real-time input voltage and the real-time input current by performing voltage detection and current detection on the input end of the three-phase four-wire inverter circuit 100. For example Figure 3In the example, the real-time input voltage of the three-phase four-wire inverter circuit 100 is collected by the second sampling unit 212, and the real-time input current of the three-phase four-wire inverter circuit 100 is collected by the third sampling unit 213.

[0125] S112, performing maximum power point tracking on the real-time input voltage and the real-time input current to obtain a voltage reference value.

[0126] The control circuit 200 can multiply the sampled real-time input voltage and real-time input current to obtain the real-time input power of the three-phase four-wire inverter circuit 100, obtain the P / U curve of the photovoltaic module 30 according to the real-time input voltage and the real-time input current, and determine the voltage reference value according to the real-time input voltage corresponding to the maximum power point in the P / U curve. Thus, the control circuit 200 performs negative feedback adjustment on the target control amount of the drive signal of the three-phase four-wire inverter circuit 100 through the current average value, changes the target control amount of the drive signal, and then compensates for the control amount error caused by the sampling error of the second sampling unit 212 on the real-time input voltage, so as to suppress the DC component.

[0127] It can be understood that those skilled in the art can clearly know the specific implementation method of the control circuit 200 to track the maximum power point of the real-time input voltage and the real-time input current based on the existing technology related to the maximum power point tracking method of the photovoltaic component 30, which is not elaborated here.

[0128] See also Fig. 9 , Fig. 9 Shows Figure 4 Detailed flowchart of step S200 in FIG.

[0129] like Fig. 9 As shown, step S200 includes:

[0130] S210: Obtain a grid voltage output by the grid to each phase line, and obtain a grid angle according to the grid voltage.

[0131] The control circuit 200 may input the grid voltage of each phase line into a phase-locked loop to obtain the grid angle.

[0132] S220, performing coordinate transformation on the real-time output current according to the grid angle to obtain a direct-axis current, a quadrature-axis current and a zero-sequence component.

[0133] The control circuit 200 can perform coordinate transformation on the three phase line currents according to the grid angle to obtain the direct axis current, the quadrature axis current and the zero sequence component. For example, the three phase line currents can be subjected to Clark transformation and Park transformation according to the grid angle to obtain the direct axis current, the quadrature axis current and the zero sequence component. Specifically, the three phase line currents and the grid angle can be input into a coordinate transformer to obtain the direct axis current, the quadrature axis current and the zero sequence component.

[0134] See also Fig.10 , Fig.10 Shows Figure 4 Detailed flowchart of step S300 in FIG.

[0135] like Fig.10 As shown, step S300 includes:

[0136] S310 , obtaining a first deviation value according to a difference between a direct-axis reference value and a direct-axis current.

[0137] The control circuit 200 may subtract the direct-axis current from the direct-axis reference value to obtain the first deviation value. Specifically, the direct-axis reference value and the direct-axis current may be input into a subtractor to obtain the first deviation value.

[0138] It can be understood that the direct-axis reference value can be obtained according to the real-time input voltage of the three-phase four-wire inverter circuit 100 .

[0139] S320: Obtain a second deviation value according to a difference between the quadrature-axis reference value and the quadrature-axis current.

[0140] The control circuit 200 may subtract the quadrature-axis current from the quadrature-axis reference value to obtain the second deviation value. Specifically, the quadrature-axis reference value and the quadrature-axis current may be input into a subtractor to obtain the second deviation value. The quadrature-axis reference value may be set to zero.

[0141] S330. Obtain a third deviation value according to a difference between a zero-sequence reference value and a zero-sequence component.

[0142] The control circuit 200 can subtract the zero-sequence component from the zero-sequence reference value to obtain a third deviation value. Specifically, the zero-sequence component can be input into a subtractor to obtain the third deviation value. The zero-sequence reference value can be set to zero.

[0143] S340. Obtain a first control amount according to the first deviation value, the second deviation value, and the third deviation value.

[0144] Furthermore, if Fig.11 As shown, step S340 includes:

[0145] S341, performing deviation adjustment on the first deviation value to obtain a direct-axis voltage compensation value, performing deviation adjustment on the second deviation value to obtain a quadrature-axis voltage compensation value, and performing deviation adjustment on the third deviation value to obtain a zero-sequence voltage compensation value.

[0146] The control circuit 200 may input the first deviation value into a PI regulator, a PID regulator, a QPR regulator or a PR regulator to obtain a direct-axis voltage compensation value. The control circuit 200 may input the second deviation value into a PI regulator, a PID regulator, a QPR regulator or a PR regulator to obtain a quadrature-axis voltage compensation value. The control circuit 200 may input the third deviation value into a PI regulator, a PID regulator, a QPR regulator or a PR regulator to obtain a zero-sequence voltage compensation value.

[0147] S342, performing inverse coordinate transformation on the direct-axis voltage compensation value, the quadrature-axis voltage compensation value, and the zero-sequence voltage compensation value according to the grid angle to obtain a target output voltage of the three-phase four-wire inverter circuit.

[0148] Among them, the control circuit 200 can perform inverse coordinate transformation on the direct-axis voltage compensation value, the quadrature-axis voltage compensation value, and the zero-sequence voltage compensation value according to the grid angle to obtain three target output voltages output to the three phase lines by the three-phase four-wire inverter circuit 100. For example, the direct-axis voltage compensation value, the quadrature-axis voltage compensation value, and the zero-sequence voltage compensation value can be inversely transformed by Park and inversely transformed by Clark according to the grid angle to obtain three target output voltages output to the three phase lines by the three-phase four-wire inverter circuit 100.

[0149] S343. Obtain a first control variable according to the target output voltage.

[0150] The control circuit may perform signal modulation on the obtained target output voltage to obtain the first control amount. For example, the obtained target output voltage may be subjected to space vector pulse width modulation (SVPWM) to obtain the first control amount.

[0151] See also Fig.12 , Fig.12 Shown is applied to Figure 3 A specific flow chart of the control method is shown in FIG.

[0152] like Fig.12 As shown, the control method includes:

[0153] S910, collect I A ,I B ,I C 、V pv ,I pv 、E A 、E B 、E C .

[0154] Among them, I A ,I B,I C are the real-time phase line currents of the three phase lines of the three-phase four-wire inverter circuit 100, V pv is the real-time input voltage of the three-phase four-wire inverter circuit 100, I pv is the real-time input current of the three-phase four-wire inverter circuit 100, E A 、E B 、E C They are grid voltages connected to three phase lines of the three-phase four-wire inverter circuit 100 .

[0155] S920, according to E A 、E B 、E C Obtain the grid angle θ, according to I A ,I B ,I C The direct axis current I is obtained by coordinate transformation with the grid angle θ d , quadrature axis current I q And zero sequence component I0.

[0156] The control circuit 200 can A 、E B 、E C Input a phase-locked loop to obtain the grid angle θ, and then the grid angle θ and I A ,I B ,I C are input into a coordinate converter to convert I A ,I B ,I C Perform Park transform and Clark transform to get the direct axis current I d , quadrature axis current I q And zero sequence component I0.

[0157] S930, V pv ,I pv Perform maximum power point tracking to obtain a voltage reference value, and perform deviation adjustment on the voltage reference value to obtain a direct axis reference value I* d .

[0158] S940, according to the direct axis reference value I* d and the direct axis current I d The difference between the first deviation value and the quadrature axis reference value I* q and the quadrature axis current I q The second deviation value is obtained according to the difference between the zero-sequence reference value I*0 and the zero-sequence component I0, and the third deviation value is obtained according to the difference between the zero-sequence reference value I*0 and the zero-sequence component I0.

[0159] The control circuit 200 can respectively set the direct axis reference value I* d and the direct axis current I dInput a subtractor to convert the quadrature axis reference value I* q and the quadrature axis current I q A subtractor is input to input the zero-sequence reference value I*0 and the zero-sequence component I0 into a subtractor to obtain a first deviation value, a second deviation value and a third deviation value.

[0160] S950, respectively perform deviation adjustment on the first deviation value, the second deviation value and the third deviation value to obtain a direct-axis voltage compensation value, a quadrature-axis voltage compensation value and a zero-sequence voltage compensation value, perform inverse coordinate transformation on the direct-axis voltage compensation value, the quadrature-axis voltage compensation value and the zero-sequence voltage compensation value according to the grid angle θ to obtain a target output voltage, and perform signal modulation on the target output voltage to obtain a first control quantity.

[0161] S960, based on the I collected from n power frequency cycles A ,I B ,I C Computation I AV ,I BV ,I CV , respectively I AV ,I BV ,I CV Subtracting the current reference value from the current deviation value yields three current deviation values, and performing proportional-integral adjustment on the three current deviation values ​​to obtain a second control variable.

[0162] S970, superimposing the second control amount on the first control amount to obtain a target control amount, and generating a drive signal according to the target control amount to control the three-phase four-wire inverter circuit.

[0163] S980, according to the current power frequency cycle I A ,I B ,I C Computation I ADC ,I BDC ,I CDC , and confirm I ADC ,I BDC ,I CDC Is it within the preset range?

[0164] S990, when I ADC ,I BDC ,I CDC When it is not within the preset range, n=n-1, and step S960 is executed again.

[0165] Among them, in the n power frequency cycles of the initial power-on operation, the control circuit 200 repeatedly executes steps S910-S950 and step S970, at which time, the second control amount is zero. Starting from the n+1th power frequency cycle, the control circuit 200 repeatedly executes steps S910-S970. At the last sampling moment of the n+1th power frequency cycle, the control circuit 200 also executes steps S980 and S990.

[0166] See also Fig.13 , Fig.13 The specific control block diagram of the control method of the three-phase four-wire inverter circuit in the embodiment of the present application is shown. Fig.13 As shown, the control circuit 200 controls the output of the three-phase four-wire inverter circuit 100 through a dual-loop control loop to suppress the DC component output by the three-phase four-wire inverter circuit 100. The dual-loop control loop includes a first calculator 221, an MPPT controller 222, a first subtractor 223, a first PI regulator 224, a coordinate converter 225, a phase-locked loop 226, a second subtractor 227, a third subtractor 228, a fourth subtractor 229, a second PI regulator 230, a third PI regulator 231, a fourth PI regulator 232, a coordinate inverse converter 233, an SVPWM modulator 234, a fifth subtractor 235, a fifth PI regulator 236, an adder 237, and a signal driver 238. It can be understood that the first calculator 221, the MPPT controller 222, the first subtractor 223, the first PI regulator 224, the coordinate transformer 225, the phase-locked loop 226, the second subtractor 227, the third subtractor 228, the fourth subtractor 229, the second PI regulator 230, the third PI regulator 231, the fourth PI regulator 232, the coordinate inverse transformer 233, the SVPWM modulator 234, the fifth subtractor 235, the fifth PI regulator 236, the adder 237, and the signal driver 238 can be integrated into the control unit 220 of the control circuit 200.

[0167] The following Figure 3 The three-phase T-type three-level three-phase four-wire inverter circuit shown is taken as an example and Fig.12 The specific control block diagram shown illustrates the specific workflow of the control method provided in the embodiment of the present application.

[0168] When the three-phase four-wire inverter circuit 100 starts to be powered on, the first sampling unit 211 respectively samples the phase line current I of the first phase line A, the second phase line B and the third phase line C at a preset sampling frequency. A ,I B ,I C The second sampling unit 212 and the third sampling unit 213 respectively collect the real-time input voltage V of the three-phase four-wire inverter circuit 100 at a preset sampling frequency. pvand real-time input current I pv The fourth sampling unit 214 respectively collects the terminal voltages E of the three terminals connected to the power grid and the first phase line A, the second phase line B and the third phase line C. A 、E B 、E C .

[0169] The first sampling unit 211 collects the phase line current I A ,I B ,I C The first calculator 221 inputs the first phase current I collected by the first sampling unit 211 in n power frequency cycles. A ,I B ,I C Calculate the average current I AV ,I BV ,I CV .

[0170] The second sampling unit 212 and the third sampling unit 213 collect the real-time input voltage V pv and real-time input current I pv Input to the MPPT controller 222 to output a voltage reference value V ref . Set the voltage reference value V ref and real-time input voltage V pv The first subtractor 223 converts the voltage reference value V ref Subtract the real input voltage V pv The voltage deviation value is input to the first PI regulator 224, and the first PI regulator 224 outputs the direct axis reference value I* d .

[0171] The first sampling unit 211 collects the phase line current I A ,I B ,I C The fourth sampling unit 214 collects the terminal voltage E A 、E B 、E C The grid voltage is input into the phase-locked loop 226 to obtain the grid angle θ, and the grid voltage is input into the coordinate transformer 225 and the inverse coordinate transformer 233 .

[0172] The coordinate converter 225 converts the phase line current I A ,I B ,I C Perform Clark and Park transformation to obtain the direct axis current I d , quadrature axis current I qAnd zero sequence component I0.

[0173] The direct axis current I d and direct axis reference value I* d The second subtractor 227 is used to input the direct axis reference value I* d Subtract the direct axis current I d , to obtain the first deviation value. q and quadrature axis reference value I* q The third subtractor 228 is input to the quadrature axis reference value I* q Subtract the quadrature axis current I q , to obtain the second deviation value. The zero-sequence component I0 and the zero-sequence reference value I*0 are input to the fourth subtractor 229, and the fourth subtractor 229 subtracts the zero-sequence component I0 from the zero-sequence reference value I*0 to obtain the third deviation value. q And the zero-sequence reference value I*0 is zero.

[0174] The first deviation value is input to the second PI regulator 230 to obtain the direct-axis voltage compensation value, the second deviation value is input to the third PI regulator 231 to obtain the quadrature-axis voltage compensation value, and the third deviation value is input to the fourth PI regulator 232 to obtain the zero-sequence voltage compensation value.

[0175] The direct-axis voltage compensation value, the quadrature-axis voltage compensation value and the zero-sequence voltage compensation value are input to the coordinate inverse transformer 233, and the coordinate inverse transformer 233 performs inverse Park transformation and inverse Clark transformation on the direct-axis voltage compensation value, the quadrature-axis voltage compensation value and the zero-sequence voltage compensation value according to the grid angle θ to obtain the target output voltage. The target output voltage is then input to the SVPWM modulator 234, and the SVPWM modulator 234 performs signal modulation according to the target output voltage to obtain the three first control quantities P of the switch tubes on the corresponding bridge arms of the three phase lines respectively. A1 , P B1 , P C1 The first control variable is the duty cycle of the driving signal.

[0176] The current reference value and the three current average values ​​I AV ,I BV ,I CV The three fifth subtractors 235 are respectively inputted, and the three fifth subtractors 235 respectively convert the three current average values ​​I AV ,I BV ,I CV The current reference values ​​are respectively subtracted to obtain three current deviation values, and the three current deviation values ​​are respectively input into three fifth PI regulators 236 to obtain three second control quantities P A2 , P B2 , P C2. Among them, the current reference value is zero.

[0177] The three first control quantities P A1 , P B1 , P C1 and three second control quantities P A2 , P B2 , P C2 are input into three adders 237 respectively to obtain three target control quantities P A , P B , P C The three target control quantities P A , P B , P C The signal is sent to the signal driver 238, and the signal driver 238 controls the three target quantities P A , P B , P C Generate a drive signal and send the drive signal to the control end of each switch tube of the three-phase four-wire inverter circuit 100 to control the on and off of each switch tube, thereby controlling the output of the three-phase four-wire inverter circuit 100 and suppressing the DC component output by the three-phase four-wire inverter circuit 100.

[0178] Then, the first calculator 221 can also calculate the real-time output current I collected in the next power frequency cycle in the next power frequency cycle after the current average value is calculated. A ,I B ,I C Calculate the DC component I ADC ,I BDC ,I CDC , confirm the DC component I ADC ,I BDC ,I CDC Is it within the preset range? ADC ,I BDC ,I CDC When it is not within the preset range, the first calculator 221 updates n according to n=nm, so as to obtain the real-time output current I according to the subsequent n power frequency cycles. A ,I B ,I C Calculate the average current I again AV ,I BV ,I CV , and then recalculate the second control quantity. After the current average value I is calculated again AV ,I BV ,I CV Before, the second control variable is still calculated based on the current average value calculated before.

[0179] Of course, in the embodiment of the present application, another calculator can also be used to calculate the real-time output current I collected in the next power frequency cycle in the next power frequency cycle after the current average value is calculated. A ,I B ,I C Calculate the DC component I ADC ,I BDC ,I CDC , confirm the DC component I ADC ,I BDC ,I CDC Is it within the preset range? ADC ,I BDC ,I CDC When it is not within the preset range, the calculator can send a trigger signal to the first calculator 221, so that the first calculator 221 updates n with n=nm according to the trigger signal, and then updates n according to the real-time output current I collected in the next n power frequency cycles. A ,I B ,I C Calculate the average current I again AV ,I BV ,I CV , and then recalculate the second control amount.

[0180] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit them. In the actual application process, the entire content of the technical solutions described in any embodiment of the present application can be implemented, or some content can be added, or some content can be deleted, or some content can be changed / replaced. Although the present application is described in detail with reference to the preferred embodiments, it should be understood by those of ordinary skill in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A control method for a three-phase four-wire inverter circuit, wherein the input end of the three-phase four-wire inverter circuit is connected to a positive and negative DC bus, two bus capacitors are connected in series between the positive and negative DC bus, the midpoint of the two bus capacitors is the neutral point of the three-phase four-wire inverter circuit, the output end of the inverter circuit is connected to a power grid through three phase lines, and the neutral point is connected to the zero point of the power grid through a neutral line, characterized in that: The control method comprises: Obtaining the real-time output current of the three-phase four-wire inverter circuit; Performing coordinate transformation on the real-time output current to obtain a direct-axis current, a quadrature-axis current and a zero-sequence component; Obtaining a first control variable according to the direct-axis current, the quadrature-axis current and the zero-sequence component; Obtaining an average current value of the three-phase four-wire inverter circuit; A second control value is obtained according to the difference between the current average value and the current reference value; wherein the current reference value is zero; Adding the second control amount to the first control amount to obtain a target control amount; A drive signal is generated according to the target control amount, and the three-phase four-wire inverter circuit is controlled according to the drive signal.

2. The control method according to claim 1, characterized in that: The step of obtaining the real-time output current of the three-phase four-wire inverter circuit comprises: In each power frequency cycle, the real-time output current of the three-phase four-wire inverter circuit is collected at a preset sampling frequency; The step of obtaining the current average value of the three-phase four-wire inverter circuit includes: The current average value is calculated based on the real-time output current collected in n power frequency cycles; wherein n is a positive integer greater than or equal to 1.

3. The control method according to claim 2, characterized in that: include: Calculating the DC component according to the real-time output current collected during the current power frequency cycle; When the DC component is not within the preset range, n is updated according to n=nm; wherein the preset range is the allowable range of the DC component of the three-phase four-wire inverter circuit, m is a positive integer greater than or equal to 0, and m is less than n; The current average value is calculated according to the updated n until the DC component is within the preset range.

4. The control method according to claim 3, characterized in that: Also includes: When the DC component is within the preset range or the current average value has not been obtained, the target control amount is obtained according to the first control amount.

5. The control method according to claim 1, characterized in that: The obtaining of the second control value according to the difference between the current average value and the current reference value comprises: Obtaining a current deviation value according to a difference between the current average value and the current reference value; The current deviation value is deviation-adjusted to obtain the second control amount.

6. The control method according to claim 1, characterized in that: The obtaining of the first control variable according to the direct-axis current, the quadrature-axis current and the zero-sequence component comprises: Obtaining the first deviation value according to a difference between a direct-axis reference value and the direct-axis current; Obtaining the second deviation value according to the difference between the quadrature-axis reference value and the quadrature-axis current; Obtaining a third deviation value according to a difference between a zero-sequence reference value and the zero-sequence component; The first control amount is obtained according to the first deviation value, the second deviation value and the third deviation value.

7. The control method according to claim 6, characterized in that: Also includes: Obtaining a real-time input voltage and a voltage reference value of the three-phase four-wire inverter circuit; The direct-axis reference value is obtained according to the real-time input voltage and the voltage reference value; wherein the quadrature-axis reference value and the zero-sequence reference value are zero.

8. The control method according to claim 7, characterized in that: The input end of the three-phase four-wire inverter circuit is connected to a photovoltaic module, and the real-time input voltage is a photovoltaic voltage output by the photovoltaic module; the real-time input voltage and voltage reference value of the three-phase four-wire inverter circuit are obtained, including: Acquire the real-time input voltage and real-time input current of the three-phase four-wire inverter circuit; wherein the real-time input current is the photovoltaic current output by the photovoltaic module; The voltage reference value is obtained by performing maximum power point tracking on the real-time input voltage and the real-time input current.

9. The control method according to claim 6, characterized in that: The coordinate transformation of the real-time output current to obtain the direct-axis current, the quadrature-axis current and the zero-sequence component includes: Acquire a grid voltage output by the grid to each of the phase lines, and obtain a grid angle according to the grid voltage; Performing coordinate transformation on the real-time output current according to the grid angle to obtain the direct-axis current, the quadrature-axis current and the zero-sequence component; The obtaining the first control amount according to the first deviation value, the second deviation value and the third deviation value includes: performing deviation adjustment on the first deviation value to obtain a direct-axis voltage compensation value, performing deviation adjustment on the second deviation value to obtain a quadrature-axis voltage compensation value, and performing deviation adjustment on the third deviation value to obtain a zero-sequence voltage compensation value; Performing inverse coordinate transformation on the direct-axis voltage compensation value, the quadrature-axis voltage compensation value, and the zero-sequence voltage compensation value according to the grid angle to obtain a target output voltage of the three-phase four-wire inverter circuit; The first control amount is obtained according to the target output voltage.

10. An inverter, characterized in that: include: A three-phase four-wire inverter circuit, wherein the input end of the three-phase four-wire inverter circuit is connected to a positive and negative DC bus, two bus capacitors are connected in series between the positive and negative DC bus, the midpoint of the two bus capacitors is the neutral point of the three-phase four-wire inverter circuit, the output end of the inverter circuit is connected to a power grid through three phase lines, and the neutral point is connected to a zero point of the power grid through a neutral line; as well as A control circuit, the control circuit being used for: Obtaining the real-time output current of the three-phase four-wire inverter circuit; Performing coordinate transformation on the real-time output current to obtain a direct-axis current, a quadrature-axis current and a zero-sequence component; Obtaining a first control variable according to the direct-axis current, the quadrature-axis current and the zero-sequence component; Obtaining an average current value of the three-phase four-wire inverter circuit; A second control value is obtained according to the difference between the current average value and the current reference value; wherein the current reference value is zero; Adding the second control amount to the first control amount to obtain a target control amount; A drive signal is generated according to the target control amount, and the three-phase four-wire inverter circuit is controlled according to the drive signal.

11. The inverter according to claim 10, characterized in that: The control circuit comprises: a sampling unit, the sampling unit being used to collect the real-time output current; and A control unit is connected to the sampling unit, and is used to receive the real-time output current and obtain the driving signal according to the real-time output current.

12. The inverter according to claim 10 or 11, characterized in that: The three-phase four-wire inverter circuit comprises a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a fifth bridge arm and a sixth bridge arm; The first bridge arm is connected between the positive and negative DC busbars, and the first bridge arm includes a first switch tube and a second switch tube connected in series; a midpoint between the first switch tube and the second switch tube is connected to a first terminal of the power grid through a first phase line; The second bridge arm is connected between the midpoint of the first bridge arm and the neutral point; The third bridge arm is connected between the positive and negative DC busbars, and the third bridge arm includes a third switch tube and a fourth switch tube connected in series; the midpoint between the third switch tube and the fourth switch tube is connected to the second terminal of the power grid through a second phase line; The fourth bridge arm is connected between the midpoint of the third bridge arm and the neutral point; The fifth bridge arm is connected between the positive and negative DC busbars, and the fifth bridge arm includes a fifth switch tube and a sixth switch tube connected in series; a midpoint between the fifth switch tube and the sixth switch tube is connected to a third terminal of the power grid through a third phase line; The sixth bridge arm is connected between the midpoint of the fifth bridge arm and the neutral point.

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