A reactive power compensation method for a three-phase inverter

Abstract

The present invention discloses a reactive power compensation method for a three-phase inverter, which can accurately control the reactive power compensation amount of each phase, reduce the power control cost. The output end of the three-phase inverter is connected to the power grid, and the three-phase inverter has a three-phase four-wire topology. The reactive power compensation method includes: collecting the output current, voltage and the reactive power of the first grid connection end of each phase of the three-phase inverter, setting a first reference value for the reactive power output of each phase of the three-phase inverter, calculating the reactive power output of each phase of the three-phase inverter, calculating the reactive power of each phase of the load, setting the expected reactive power value of the grid connection end, calculating the reactive power compensation amount to be compensated for each phase, calculating and obtaining a second reference value for the reactive power output of each phase of the three-phase inverter, obtaining the reactive power of the second grid connection end after the three-phase inverter runs stably again, and judging whether the reactive power of the second grid connection end reaches the expected reactive power of the grid connection end. If so, it indicates that the power factor of the grid connection end meets the requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and specifically to a reactive power compensation method for a three-phase inverter. Background Art

[0002] According to the "Technical Regulations for Grid Connection of Small Household Photovoltaic Power Generation Systems", the power factor of a photovoltaic power generation system should be adjustable within the range of leading 0.95 to lagging 0.95. However, the power factor directly output after the voltage generated by the photovoltaic is inverted by the inverter generally cannot meet the requirements of this standard. Therefore, reactive power compensation needs to be made for the power factor. Currently, there are various reactive power compensation methods for three-phase grid-connected inverters. For example, a reactive power compensation device is installed in the system. The reactive power compensation device mainly includes a mechanically switched capacitor, a magnetically controlled reactor, and a static var generator. This kind of reactive power compensation mainly relies on hardware to achieve. Although it can greatly improve the power supply environment, the investment cost of hardware equipment is high, it is not suitable for household photovoltaic inverters, the application flexibility is poor, and when installed, it occupies a large area of space. Another reactive power compensation method is software reactive power compensation, which is mainly realized through a control algorithm and can solve the problems of high hardware investment cost, poor application flexibility, and large occupied space area. However, the commonly used three-phase inverters currently are three-phase three-wire systems, and it is impossible to independently control the reactive power output of each phase of the inverter. Therefore, most are overall compensations, that is, the voltage and current quantities on the three-phase coordinate system are transformed to the dq coordinate axes of the two-phase rotating coordinate system through Park transformation, and the overall reactive power compensation of the three-phase inverter is realized by controlling the q-axis current component. This compensation method cannot accurately control the reactive power compensation amount of each phase, and there may be problems of reactive power compensation redundancy in a certain phase or lack of reactive power compensation in a certain phase. This not only increases the difficulty of power factor compensation but also increases the power control cost. Summary of the Invention

[0003] Aiming at the above problems existing in the prior art, the present invention provides a reactive power compensation method for a three-phase inverter, which can achieve three-phase unbalance compensation of a photovoltaic grid-connected inverter, can accurately control the reactive power compensation amount of each phase, and can reduce the power control cost.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A reactive power compensation method for a three-phase inverter, which is implemented based on a reactive power compensation system. The input ends of the three-phase inverter are respectively connected to a DC bus capacitor Cbus and a photovoltaic array. The output end of the three-phase inverter is connected to the power grid. A three-phase electric meter is connected between the output end of the three-phase inverter and the input end of the power grid. It is characterized in that the three-phase inverter has a three-phase four-wire topological structure. The three-phase four-wire topological structure means that the output end of the three-phase inverter includes phase A, phase B, phase C, and the N line, and the N line is the ground wire;

[0006] The reactive power compensation method includes: S1. Collect data, where the data includes the output current of each phase of the three-phase inverter, the output voltage of each phase of the three-phase inverter, and the reactive power of the first grid connection end of each phase. The reactive power of the first grid connection end of each phase is obtained by measuring with a three-phase electricity meter;

[0007] S2. Preset a first reference value for the reactive power output of each phase of the three-phase inverter;

[0008] S3. Calculate the reactive power output of each phase of the three-phase inverter, and calculate the reactive power of each phase of the load based on the reactive power output of each phase of the three-phase inverter and the reactive power of the first grid connection end of each phase;

[0009] S4. Preset the desired reactive power value of the grid connection end, and calculate the reactive power compensation amount to be compensated for each phase based on the reactive power value of the first grid connection end of each phase and the desired reactive power value of the grid connection end;

[0010] S5. Based on the first reference value and the reactive power compensation amount, recalculate to obtain a second reference value for the reactive power output of each phase of the three-phase inverter;

[0011] S6. After the three-phase inverter runs stably again, obtain the reactive power of the second grid connection end through a three-phase electricity meter;

[0012] S7. Judge whether the reactive power of the second grid connection end reaches the preset desired reactive power of the grid connection end. If so, it indicates that the power factor of the grid connection end meets the requirements and the reactive power output of each phase of the three-phase inverter is compensated. Otherwise, it indicates that the power factor of the grid connection end does not meet the requirements.

[0013] It is further characterized in that

[0014] The three-phase electricity meter is communicatively connected to the controller through an RS485 communication bus. The controller includes an ARM chip and a DSP chip, and the ARM chip is connected to the DSP chip through a UART port;

[0015] Further, in step S1, the reactive power value of each phase at the grid input end is collected in real time through a three-phase electricity meter, the reactive power of the first grid connection end of each phase is obtained and sent to the controller. The reactive power of the first grid connection end of each phase includes the reactive power of grid phase A, the reactive power of grid phase B, and the reactive power of grid phase C. The reactive power of the first grid connection end of each phase is equal to the sum of the reactive power output of the corresponding phase of the three-phase inverter and the reactive power of the corresponding phase of the load;

[0016] Further, in step S1, the sampled data further includes the DC bus voltage value;

[0017] Further, in step S2, the first reference value for the reactive power output of each phase of the three-phase inverter is obtained based on the rated power and power factor of the three-phase inverter;

[0018] Further, in step S3, the difference between the reactive power value of each phase collected by the three-phase electricity meter and the reactive power output of each phase of the three-phase inverter is the reactive power of each phase load. The reactive power output of each phase of the three-phase inverter is obtained based on the output current of each phase of the three-phase inverter and the output voltage of each phase of the three-phase inverter.

[0019] Further, in step S4, the difference between the expected reactive power value of the grid connection end and the reactive power value of the first grid connection end of this phase is used as the reactive power compensation amount of this phase.

[0020] Further, in step S5, the first reference value of the reactive power output of each phase of the three-phase inverter is summed with the reactive power compensation amount of the corresponding phase to obtain the second reference value of the reactive power output of each phase of the three-phase inverter.

[0021] In step S7, the current reactive power of the grid connection end collected by the three-phase electricity meter is the reactive power of the second grid connection end. It is judged whether the current reactive power of the grid connection end is consistent with the pre-set expected reactive power of the grid connection end. If they are consistent, it means that this reactive power compensation method is effective.

[0022] When the expected reactive power of the grid connection end is 0, the power factor is 1.

[0023] Adopting the above structure of the present invention can achieve the following beneficial effects: In the reactive power compensation method of this three-phase inverter, by collecting the current, voltage and the reactive power of the first grid connection end of each phase at the output end of the three-phase inverter, the reactive power compensation amount that needs to be compensated for each phase is calculated. Based on the first reference value and the reactive power compensation amount, the second reference value of the reactive power output of each phase of the three-phase inverter is recalculated. This second reference value is the value after the reactive power output of each phase of the three-phase inverter is compensated separately. By judging whether the current reactive power of the grid connection end is consistent with the pre-set expected reactive power of the grid connection end, the effectiveness of the reactive power compensation method is judged. Compared with other existing reactive power compensation methods, the reactive power compensation method of this application for the three-phase inverter has no additional device preparation cost, does not occupy volume, is flexible in application, and is suitable for household photovoltaic inverters. And through the reactive power compensation method of this application, the separate compensation of the reactive power output of each phase of the three-phase inverter can be realized, thus avoiding the problem of redundant reactive power compensation in a certain phase or lack of reactive power compensation in a certain phase, and reducing the power control cost. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. The following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 This is the structural block diagram of a three-phase photovoltaic grid-connected inverter with reactive power compensation control according to the present invention;

[0026] Figure 2 This is the flowchart of the reactive power compensation method for a three-phase photovoltaic grid-connected inverter according to the present invention;

[0027] Figure 3 This is the control block diagram of the reactive power compensation strategy for a three-phase photovoltaic grid-connected inverter according to the present invention. Detailed implementation manners

[0028] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusion. For example, a process, method, device, product or equipment including a series of steps or units does not necessarily limit to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products or equipment.

[0030] Aiming at the technical problem in the prior art that reactive power overall compensation is achieved by controlling the q-axis current component on the dq axis, and this compensation method cannot accurately control the reactive power compensation amount of each phase, there may be reactive power compensation redundancy in a certain phase or reactive power compensation shortage in a certain phase, increasing the power control cost. The present application provides a reactive power compensation method for a three-phase inverter, which is implemented based on a three-phase photovoltaic grid-connected inverter system with reactive power compensation control. Refer to Figure 1 , this system includes a three-phase electric meter 1 and a controller 2. The three-phase electric meter is communicatively connected to the controller through an RS485 communication bus. The controller includes an ARM chip and a DSP chip. The ARM chip is connected to the DSP chip through a UART port. The three-phase electric meter 1 is a three-phase intelligent electric meter with communication function, such as Ankerui ACR10R. The model of the ARM chip in the controller is GD32F404VET, and the DSP chip is of the TM320F2837xS series.

[0031] The three-phase electricity meter 2 is connected between the output terminal of the inverter 3 and the power grid 4, and the three-phase electricity meter 1 is connected to the controller 2; the input terminals of the three-phase inverter 3 are respectively connected to the capacitor Cbus and the photovoltaic array 5, and the output terminal of the three-phase inverter 3 is connected to the power grid 4. The three-phase inverter 3 has a three-phase four-wire topology structure. The three-phase four-wire topology structure means that the output terminal of the three-phase inverter 3 includes phase A, phase B, phase C, and the N line. Among them, the N line is the ground wire. The setting of the N line is beneficial to the independent control of the three phases of the inverter, so as to facilitate the realization of unbalanced reactive power compensation. The independent control of the three phases of the inverter means that the three phases of the inverter are controlled as three single-phase inverters. Each phase is transformed to the dq axis according to the Park transformation to represent the voltage and current on each single phase. Among them, the d axis is the double-loop control of the DC bus voltage outer loop and the d-axis current component inner loop, and the q axis is the double-loop control of the reactive power outer loop and the q-axis current component inner loop.

[0032] The Park transformation is usually used for three-phase electrical quantities, which refers to projecting electrical quantities such as voltage and current on the three-phase coordinate abc axis onto the two-phase rotating coordinate axes dq axis. Taking the three-phase currents i a 、i b 、i c as an example, through the Park transformation matrix, it can be transformed into two-phase currents i d 、i q on the dq axis, as shown below:

[0033]

[0034] Then in this application, because there is an N line at the output terminal of the three-phase inverter, the individual control of phases A, B, and C can be realized, that is, each phase is individually transformed to the dq axis using the Park transformation, with the aim of individually controlling the reactive power of each phase. For the case where there is only one voltage and current quantity for each phase, when using the Park transformation, a slight change is made, as shown below:

[0035]

[0036]

[0037]

[0038] Among them, θ A 、θ B 、θ C are the phase angles of phase A voltage, phase B, and phase C respectively, usually obtained by calculation using a phase-locked loop. i LA 、i LB 、i LC represent the output current of each phase of the three-phase inverter, and after the Park transformation, we get: i dA 、i qA 、i dB 、i qB 、idC , i qC , i dA represents the d-axis component of the output current of phase A of the three-phase inverter, and i qA represents the q-axis component of the output current of phase A of the three-phase inverter, and i dB represents the d-axis component of the output current of phase B of the three-phase inverter, and i qB represents the q-axis component of the output current of phase B of the three-phase inverter, and i dC represents the d-axis component of the output current of phase C of the three-phase inverter, and i qC represents the q-axis component of the output current of phase C of the three-phase inverter.

[0039] When the system is running, the reactive power compensation method of the present application is used to compensate the reactive power of the power grid in real time. During the compensation process, first, the reactive power of the first grid connection end collected by the three-phase electric meter is transmitted to the ARM chip in the controller through the RS485 communication bus, and then transmitted to the DSP chip for logical operation after being processed by the ARM chip. The specific steps of the reactive power compensation method include: S1, collecting data, the data includes: the DC bus voltage value, the output current of each phase of the three-phase inverter, the output voltage of each phase of the three-phase inverter, and the reactive power of the first grid connection end of each phase. The grid connection end refers to the input end of the power grid; the reactive power of the first grid connection end of each phase of the power grid is collected in real time through the three-phase electric meter 2 and sent to the controller 2.

[0040] The reactive power of the first grid connection end of each phase includes the reactive power of phase A of the power grid, the reactive power of phase B of the power grid, and the reactive power of phase C of the power grid, and are respectively represented by Q gA , Q gB , Q gC , and the reactive power of the first grid connection end of each phase is the sum of the reactive power output by the three-phase inverter of this phase and the reactive power of this phase of the load.

[0041] S2, preset the first reference value of the reactive power output by each phase of the three-phase inverter, which is obtained based on the rated power and power factor of the three-phase inverter. Taking the reference value of the total three-phase reactive power of the three-phase inverter as an example, the reference value of the total three-phase reactive power is the rated value Q N of the total three-phase reactive power. This rated value is generally not directly given, but depends on the rated power P N and power factor of the current design requirements of the three inverters, that is, first, according to the power factor to obtain the power factor angle and then there is: Before reactive power compensation is achieved, the first reference value of the reactive power output by each phase of the three-phase inverter is 1 / 3 of the reference value of the total three-phase reactive power. This value has been calculated during the design of the inverter. Here, the first reference value of the reactive power output by each phase of the three-phase inverter is respectively represented by Q *A1 , Q * B1 , Q * C1 is represented by

[0042] S3. Calculate the reactive power output of each phase of the three-phase inverter, and subtract the first grid-connected reactive power value of each phase collected by the three-phase electricity meter from the reactive power output of each phase of the three-phase inverter to obtain the reactive power of each phase of the load. The load reactive power includes the reactive power of phase A of the load, the reactive power of phase B of the load, and the reactive power of phase C of the load, and are represented by Q load_A , Q load_B , Q load_C is represented by

[0043] Among them, the reactive power output of each phase of the three-phase inverter is calculated from the output voltage and output current of each phase of the three-phase inverter, as shown below, where Q A , Q B , Q C represents the reactive power output of the three phases of the three-phase inverter:

[0044] Q A = u A i LA sinθ A , Q B = u B i LB sinθ B , Q C = u C i LC sinθ C ;

[0045] Among them, u A represents the output voltage of phase A of the three-phase inverter, i LA represents the output current of phase A of the three-phase inverter, u B represents the output voltage of phase B of the three-phase inverter, i LB represents the output current of phase B of the three-phase inverter, u C represents the output voltage of phase C of the three-phase inverter, i LC represents the output current of phase C of the three-phase inverter.

[0046] S4. Calculate the reactive power compensation amount required for each phase. Specifically, set the desired reactive power at the grid connection end. The desired reactive power includes the desired reactive power of phase A of the power grid, the desired reactive power of phase B of the power grid, and the desired reactive power of phase C of the power grid, and are represented by Q * gA , Q * gB , Q * gCIt is shown that the difference between the desired reactive power at the grid connection end and the reactive power output by each phase of the three-phase inverter is used as the reactive power compensation amount for the corresponding phase of the three-phase inverter. In this embodiment, the desired reactive power Q at the grid connection end is set * gA 、Q * gB 、Q * gC are all 0 var, so that the reactive power at the final grid connection end reaches 0, and the purpose is to make the power factor reach 1. The reactive power compensation amount output by each phase of the three-phase inverter includes the reactive power compensation amount ΔQ A output by phase A of the inverter, the reactive power compensation amount ΔQ B output by phase B of the inverter, and the reactive power compensation amount ΔQ C output by phase C of the inverter.

[0047] S5. The first reference value of the reactive power output by each phase of the three-phase inverter is summed with the reactive power compensation amount of the corresponding phase to obtain the second reference value of the reactive power output by each phase of the three-phase inverter. The second reference value of the reactive power output by each phase of the three-phase inverter includes: the second reference value of the reactive power of phase A, the second reference value of the reactive power of phase B, and the second reference value of the reactive power of phase C, and are respectively represented by Q * A2 、Q * B2 、Q * C2 .

[0048] S6. The three-phase reactive power compensation amount is used to compensate the reactive power output by each phase of the three-phase inverter. After the three-phase inverter runs stably again, the second grid connection end reactive power is obtained through the three-phase electric meter.

[0049] As Figure 3 shown, when the first reference value of the reactive power output by each phase of the three-phase inverter is compensated, the second reference value of the reactive power output by each phase of the three-phase inverter, then the output of the reactive power loop, that is, the inner loop reference value of the q-axis current component changes, and finally the drive signal of the three-phase inverter changes, thus changing the reactive power output by each phase of the three-phase inverter. When the load reactive power is certain, the grid connection end reactive power changes with the change of the reactive power output by the three-phase inverter. After reactive power compensation, the grid connection end reactive power becomes the second grid connection end reactive power.

[0050] S7. It is judged whether the second grid connection end reactive power collected by the three-phase electric meter reaches the pre-set desired reactive power at the grid connection end. If so, it indicates that the grid connection end power factor meets the requirements, and the reactive power output by each phase of the three-phase inverter is compensated. Otherwise, it indicates that the grid connection end power factor does not meet the requirements.

[0051] In step S7, the three-phase reactive power of the power grid after reactive power compensation is measured by a three-phase electricity meter (i.e., the reactive power of the second grid connection end). If the expected reactive power of the grid connection end is reached, it indicates that the reactive power compensation method of this application is effective, can improve the power factor, and enables the three-phase photovoltaic grid-connected inverter to reach the actual power factor of the user specified by the standard.

[0052] The following provides a specific embodiment for reactive power compensation of a three-phase photovoltaic grid-connected inverter, taking phase A as an example for illustration.

[0053] In the first case, the rated power of the three-phase inverter is P N = 3 kW, and the power factor is required to be between ±0.95. Here, the power factor is set Then, for the three-phase inverter, the power factor angle can be calculated At this time, the total rated value of the reactive power of the three-phase inverter is: Set the first reference value Q of the reactive power output per phase of the three-phase inverter * A1 = Q * B1 = Q * C1 = (1 / 3)×Q N = 0.81 kvar.

[0054] It is known that the reactive power Q of the first grid connection end of phase A is obtained by collecting through a three-phase electricity meter gA1 = 3 kvar, and the reactive power Q output by phase A of the current three-phase inverter is calculated according to the voltage of phase A and the inductor current of phase A of the three-phase inverter A = 0.809 kvar ≈ 0.8 kvar. According to the fact that the reactive power of each first grid connection end is the sum of the reactive power output by phase A of the three-phase inverter and the reactive power of phase A of the load, the reactive power of phase A of the load can be known:

[0055] Q load_A = Q gA1 -Q A = 3 kvar - 0.809 kvar = 2.191 kvar;

[0056] According to the reactive power compensation strategy proposed by the present invention, the expected power factor of the grid connection end is At this time, the expected reactive power of the grid connection end should be 0. Based on the reactive power of the first grid connection end of phase A, the reactive power compensation amount of phase A of the three-phase inverter is calculated and set as:

[0057] ΔQ A = Q * gA -Q gA = 0 - 3 kvar = -3 kvar;

[0058] And, the second reference value of phase A reactive power becomes:

[0059] Q * A2 =Q * A1 +ΔQ A =0.81-3=-2.19kvar;

[0060] After compensation, under stable operating conditions, the reactive power of the second grid-connected end of phase A obtained by the three-phase meter is: Q gA2 =0.001kvar (If the reactive power of the second grid-connected end of phase A is calculated based on the reactive compensation amount of phase A, it can be known that: Q gA2 =Q gA1 +ΔQ A =3-3=0 kvar). It can be seen that the reactive power Q of the second grid-connected end of phase A is gA2 ≈Q * gA , three-phase inverter A phase output reactive power Q A2 ≈Q * A2 After the three-phase inverter closed-loop regulation, the output reactive power of phase A of the three-phase inverter under stable operation is: Q A2 =Q A +ΔQ A

[0061] =0.809-3=-2.191, which is infinitely close to the second reference value of the inverter phase A reactive power. In actual situations, the reactive power output of each phase of the three-phase inverter will fluctuate to a certain extent. Therefore, at this time, the reactive power compensation is directly judged by observing the reactive power of phase A of the power grid measured by the current three-phase meter. The reactive power of phase A of the power grid measured by the current three-phase meter is Q gA =0.001kvar≈0kvar, which is close to the expected reactive power value at the grid-connected end. At this time, the power factor at the grid-connected end is 1, indicating that the reactive power compensation method of this statement is effective and can improve the power factor at the grid-connected end to reach the maximum power factor of 1 for user electricity consumption specified in the standard.

[0062] The above are only preferred embodiments of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the invention should be considered to be included in the scope of protection of the invention.

Claims

1. A reactive power compensation method for a three-phase inverter, which is implemented based on a reactive power compensation system. The input ends of the three-phase inverter are respectively connected to a DC bus capacitor Cbus and a photovoltaic array. The output end of the three-phase inverter is connected to the power grid. A three-phase electricity meter is connected between the output end of the three-phase inverter and the input end of the power grid. It is characterized in that, The three-phase inverter has a three-phase four-wire topology. The three-phase four-wire topology means that the output terminals of the three-phase inverter include phase A, phase B, phase C, and the N wire, and the N wire is the grounding wire; The reactive power compensation method includes: S1, collecting data, where the data includes the output current of each phase of the three-phase inverter, the output voltage of each phase of the three-phase inverter, and the reactive power of the first grid-connected terminal of each phase. The reactive power of the first grid-connected terminal of each phase is obtained by measuring with a three-phase electric meter; S2, presetting a first reference value for the reactive power output of each phase of the three-phase inverter; S3, presetting an expected reactive power value at the grid-connected terminal, and calculating the reactive power compensation amount to be compensated for each phase based on the reactive power value of the first grid-connected terminal of each phase and the expected reactive power value at the grid-connected terminal; taking the difference between the expected reactive power value at the grid-connected terminal and the reactive power value of the first grid-connected terminal of this phase as the reactive power compensation amount for this phase; S4, recalculating to obtain a second reference value for the reactive power output of each phase of the three-phase inverter based on the first reference value and the reactive power compensation amount. The second reference value is used to change the reactive power output of each phase of the three-phase inverter; adding the first reference value of the reactive power output of each phase of the three-phase inverter and the reactive power compensation amount of the corresponding phase to obtain the second reference value of the reactive power output of each phase of the three-phase inverter; S5, after the three-phase inverter runs stably again, obtaining the reactive power of the second grid-connected terminal through a three-phase electric meter; S6, judging whether the reactive power of the second grid-connected terminal reaches the preset expected reactive power at the grid-connected terminal. If so, it indicates that the power factor at the grid-connected terminal meets the requirements and the reactive power output of each phase of the three-phase inverter is compensated. Otherwise, it indicates that the power factor at the grid-connected terminal does not meet the requirements.

2. The reactive power compensation method for a three-phase inverter according to claim 1, characterized in that The three-phase electric meter is communicatively connected to the controller through an RS485 communication bus. The controller includes an ARM chip and a DSP chip, and the ARM chip is connected to the DSP chip through a UART port.

3. The reactive power compensation method for a three-phase inverter according to claim 2, characterized in that, In step S1, the reactive power value of each phase at the grid input end is collected in real time through a three-phase electric meter, the reactive power of the first grid-connected terminal of each phase is obtained, and sent to the controller. The reactive power of the first grid-connected terminal of each phase includes the reactive power of grid phase A, the reactive power of grid phase B, and the reactive power of grid phase C. The reactive power of the first grid-connected terminal of each phase is equal to the sum of the reactive power output of the corresponding phase of the three-phase inverter and the reactive power of the corresponding phase load.

4. The reactive power compensation method for a three-phase inverter according to claim 3, characterized in that, In step S2, the first reference value of the reactive power output of each phase of the three-phase inverter is obtained based on the rated power and power factor of the three-phase inverter.

5. The reactive power compensation method for a three-phase inverter according to claim 1, characterized in that, In step S6, the current reactive power at the grid-connected terminal collected by the three-phase electric meter is the reactive power of the second grid-connected terminal. Judge whether the current reactive power at the grid-connected terminal is consistent with the preset expected reactive power at the grid-connected terminal. If they are consistent, it means that this reactive power compensation method is effective.

6. The reactive power compensation method for a three-phase inverter according to claim 5, characterized in that, When the expected reactive power at the grid-connected terminal is 0, the power factor is 1.

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