Grid connection and harmonic suppression integrated control method of inverter and electronic equipment

Abstract

The invention relates to a grid-connected and harmonic suppression integrated control method of an inverter and electronic equipment. The method comprises the following steps: collecting real-time grid-connected current and common connection point current harmonic data; determining the lowest current required for grid connection, judging whether the current capacity of the inverter is greater than or equal to the sum of the lowest current required for grid connection of the inverter and a set current capacity redundancy value, and if not, only performing grid connection operation on the current output by the inverter; otherwise, according to an external harmonic suppression instruction input to the inverter, determining a current harmonic frequency set which is preferentially considered for suppression, and combining the current harmonic condition of the common connection point, if the current redundancy capacity is sufficient, performing suppression on all harmonic waves; and otherwise, carrying out amplitude limiting processing on the current for harmonic suppression and then governing part of harmonic waves. Compared with the prior art, the method has the advantages of realizing effective comprehensive control of grid connection and harmonic treatment under various conditions, preventing harmonic pollution and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of harmonic control, and in particular to a method and electronic equipment for integrated control of grid connection and harmonic management of an inverter. Background Art

[0002] With the rapid development of new energy technologies, the power system is facing many new challenges. Harmonic problems, as an important criterion for evaluating power quality, are becoming more and more serious.

[0003] The mainstream solution to the harmonic problem is to install harmonic elimination devices, which mainly include two categories: passive filters (Power Filter, PF) and active filters (Active Power Filter, APF). Among them, passive filters mainly use the resonance characteristics of passive devices such as capacitors and inductors to construct low-impedance branches for specific harmonics, thereby reducing the harmonics that ultimately reach the power grid. However, this resonance characteristic may cause the passive components to resonate with the system, causing the harmonics to be amplified in certain situations.

[0004] Another active filter solution is to extract the harmonic characteristics of the grid current through a harmonic detection module, and control the inverter to output opposite harmonics through a controller, so that the grid harmonics are eventually offset, thereby eliminating the grid harmonic components. In the prior art, a study has proposed an event-triggered switching control for an active power filter, which can reduce the number of switch tube actions while ensuring control accuracy after reaching a steady state. In response to the harmonic problem, traditional active harmonic control methods often use the method of adding an active power filter, but the following issues need to be considered: 1) The problem of installation space for the filter equipment; 2) The problem of increased costs; 3) The problem of resonance between the filter and the power system and other equipment in the system; 4) The problem of compensation accuracy, etc.

[0005] How to achieve effective inverter grid connection and harmonic control has become a technical problem that needs to be solved. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a comprehensive control method and electronic equipment for grid connection and harmonic control of inverters.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] According to one aspect of the present invention, a method for integrated control of grid connection and harmonic control of an inverter is provided, comprising the following steps:

[0009] Step 1: Collect real-time grid-connected current and common connection point current harmonic data;

[0010] Step 2: Determine the minimum current required for grid connection, and judge whether the inverter current capacity is greater than or equal to the sum of the minimum current required for grid connection of the inverter and the set current capacity redundancy value. If not, execute step 3; otherwise, execute step 4;

[0011] Step 3: The current output by the inverter is only connected to the grid, and the process returns to step 1;

[0012] Step 4: According to the external harmonic control instruction input to the inverter, determine the harmonic frequency set that is currently given priority for control, and combine the common connection point current harmonic data to determine whether the current redundancy capacity is sufficient. If so, combine the collected real-time grid-connected current to control all harmonics; otherwise, limit the current used for harmonic control and control some harmonics, and return to step 1. If the power is off or shut down, end the control;

[0013] The condition for sufficient current redundancy capacity is specifically: after removing the minimum current required for grid connection, if the effective value of the remaining current redundancy capacity still has a set redundancy compared to the total harmonic current of the actual common connection point, then the current redundancy capacity is considered to be sufficient and complete harmonic control is performed.

[0014] Preferably, the process of determining the minimum current required for grid connection includes: obtaining the lower limit of the inverter grid-connected current according to the collected inverter-related data as the instruction input, and finally determining the minimum current required for grid connection; wherein the lower limit of the inverter grid-connected current is obtained by internal calculation of the inverter controller, or is set by the user in combination with the current and power loss of the load operation;

[0015] The inverter related data includes the rated output capacity of the inverter, the inverter switching frequency, voltage, current, grid frequency and power.

[0016] Preferably, if it is detected that the voltage harmonic distortion rate at the common connection point exceeds the set threshold and the effective value of the current harmonic is greater than the set ratio of the fundamental wave, the minimum grid-connected current capacity i 1min The remaining capacity is used for harmonic control. At this time, the effective value of the current used for harmonic control is i r for:

[0017]

[0018] Among them, i m It is the upper limit of the effective value of the inverter current capacity.

[0019] Preferably, complete harmonic control is performed only when both the effective value and the peak value of the inverter current meet the conditions for complete harmonic control.

[0020] More preferably, the current redundancy capacity is sufficient in that, after removing the minimum current required for grid connection, if the effective value of the remaining current redundancy capacity still has a set redundancy compared to the total harmonic current of the actual common connection point, complete harmonic control is performed.

[0021] More preferably, the set redundancy is 10% to 20%.

[0022] Preferably, the control of all harmonics is specifically as follows: a part of the current capacity of the inverter is used for grid connection, and the other part is used for harmonic control, wherein the current i used for grid connection and harmonic control is oabc Specifically:

[0023]

[0024] Among them, i pabc is the grid-connected current, n is the upper limit of the maximum harmonic order that the system can detect, i hi is the i-th harmonic current, f1 is the fundamental frequency, θ i is the initial phase angle corresponding to the i-th harmonic, and t is the time variable.

[0025] Preferably, the controlling part of the harmonics after limiting the current for harmonic control includes setting a limiting gain k so that the system can control the harmonics to the maximum extent while satisfying the current constraint, wherein the limiting gain k is calculated as follows:

[0026]

[0027] Where, t x is the moment when the inverter output current reaches its peak value if the harmonics are completely controlled; i pabc is the grid-connected current; n is the upper limit of the maximum harmonic order that the system can detect; i hi is the i-th harmonic current; f1 is the fundamental frequency; θ i is the initial phase angle corresponding to the i-th harmonic; i max The maximum current output by the inverter.

[0028] Preferably, after the current for harmonic control is limited, the inverter outputs the current i for both grid connection and harmonic control. oabc The calculation formula is:

[0029]

[0030] In the formula, i pabc is the grid-connected current, k is the limiting gain, i pabc is the grid-connected current, n is the upper limit of the maximum harmonic order that the system can detect, i hi is the i-th harmonic current, f1 is the fundamental frequency, θi is the initial phase angle corresponding to the i-th harmonic, and t is the time variable.

[0031] According to another aspect of the present invention, an electronic device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the method described above is implemented when the processor executes the program.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1) The present invention calculates the current capacity according to the inverter current capacity and the minimum current required for grid connection, and determines the harmonic control mode according to the current capacity. If the grid-connected current is less than the sum of the minimum current required for the inverter grid connection and the set current capacity redundancy value, the current output by the inverter is only grid-connected. Otherwise, depending on whether the current redundancy capacity is sufficient, it is decided whether all harmonics are controlled or part of the harmonics are controlled after limiting processing, thereby achieving effective comprehensive control of grid connection and harmonic control in various situations.

[0034] 2) When the current harmonics at the common connection point are serious, the present invention uses the minimum grid-connected current capacity for grid connection to make more room for harmonic control, thereby ensuring the grid-connected power while maximizing harmonic control.

[0035] 3) The integrated control of grid connection and harmonic control of the present invention can be realized by relying on the existing grid-connected inverter, without the need to install additional harmonic control devices, thus saving space and usage and maintenance costs.

[0036] 4) In the case where the redundant capacity of the grid-connected inverter is limited, the present invention sets the limiting gain. Since clipping is not adopted, new harmonics will not be introduced into the system, thus preventing harmonic pollution and solving the harmonic introduction problem of the traditional limiting module (by setting the current peak upper limit).

[0037] 5) The simulation analysis results of the present invention show that this method can be applied to actual projects to improve the power quality to the greatest extent and effectively reduce the cost of harmonic control. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of the inverter grid-connected harmonic control comprehensive control method of the present invention;

[0039] Figure 2 A schematic diagram of switching the inverter grid-connected harmonic control mode in the present invention;

[0040] Figure 3 It is a schematic diagram of the principle of the harmonic control system in the present invention;

[0041] Figure 4 It is a structural schematic diagram of the harmonic control system in the present invention;

[0042] Figure 5 It is a structural schematic diagram of the harmonic extraction module in the present invention;

[0043] Figure 6(a) is a comparison of the output current of the traditional limiting method

[0044] FIG6( b ) is a comparison diagram of the output current using limiting gain;

[0045] Figure 7 When the inverter is only connected to the grid in the present invention pcc Schematic diagram of FFT analysis;

[0046] Figure 8 The inverter in the present invention is used before and after harmonic control. pcc Schematic diagram;

[0047] Fig. 9 This is a schematic diagram of FFT analysis before and after the inverter is involved in harmonic control in the present invention;

[0048] Figure 10(a) is a comparison diagram of the inverter output current under the limiting condition;

[0049] Figure 10(b) is a comparison diagram of the inverter output current under traditional clipping and limiting;

[0050] FIG10( c ) is a comparison diagram of the inverter output current using limiting gain according to the present invention;

[0051] Fig.11 This is the FFT analysis of the inverter output current comparison chart. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0053] As an important interface between renewable energy power generation and the power grid, the inverter also has the ability to control harmonics in addition to the grid-connected function. Therefore, the present invention proposes a comprehensive control method for grid-connected and harmonic control based on the current capacity of the grid-connected inverter, so that the user can set the current ratio for grid-connected / harmonic control, and perform partial harmonic control under the condition of limited current capacity. In addition, in view of the situation where the sum of the grid-connected and harmonic control currents that may be output exceeds the upper limit of the inverter, the amplitude gain is used to limit the current. Compared with the traditional method of setting the upper limit of the current (clipping), the amplitude gain method proposed in the present invention can prevent harmonic pollution, thereby further ensuring the quality of the system current.

[0054] This embodiment relates to a method for integrated control of grid connection and harmonic control of an inverter. Figure 1 , including the following steps:

[0055] Step 301: Collect real-time data, namely, the grid-connected current and the current harmonics of the Point of Common Coupling (PCC) at the current moment.

[0056] Step 302: Use the external data collected such as the rated output capacity of the inverter, the inverter switching frequency, voltage, current, grid frequency and power as command input, perform internal calculations in the controller or let the user set the lower limit of the inverter grid-connected current based on the current and power loss of the load operation, and finally determine the minimum current required for grid connection. Determine whether the inverter current capacity can control harmonics. The conditions for controlling harmonics are: the inverter current capacity is not less than the minimum current required for the inverter to be connected to the grid, and there is a certain current capacity redundancy δ, that is, the inverter current capacity is greater than or equal to the sum of the minimum current required for the inverter to be connected to the grid and the set current capacity redundancy value δ. If it is determined that the conditions for controlling harmonics are not met, execute step 303; otherwise, execute step 304;

[0057] Step 303: the current output by the inverter is only connected to the grid and does not participate in harmonic control, and the process returns to step 301;

[0058] Step 304: external harmonic control instructions are input to determine the harmonic frequency set F that is currently given priority for control.

[0059] Step 305: Based on the actual harmonic situation of the common connection point and the harmonic frequency set F constructed by external instructions, it is determined whether complete harmonic control can be performed. If the conditions are met, part of the current capacity of the grid-connected inverter is used for grid connection, and the other part is used for harmonic control. Determine whether the conditions for complete harmonic control are met: after removing the lower limit of the minimum grid-connected current capacity, if the effective value of the remaining current redundancy capacity has a redundancy of 10% to 20% compared to the total harmonic current of the actual common connection point calculated by external collection, complete harmonic control can be performed. If yes, execute step 306; otherwise, execute step 307;

[0060] Step 306: If the current redundancy capacity is sufficient, all harmonics are controlled. The current capacity that can be used for harmonic control is calculated based on the inverter current capacity (effective value and peak value) and the minimum current required for grid connection.

[0061] Step 307: If the current redundancy capacity is insufficient, the current used for harmonic control is limited, and the compensation current limiting gain k is set to ensure that the output total current effective value and peak value do not exceed the inverter capacity limit, and then proceed to step 308;

[0062] Step 308: Control some harmonics and return to step 301 to continue grid-connected harmonic control. If the power is off or the machine is shut down, the control ends.

[0063] In step 303, when harmonics are not controlled, the current output by the inverter is only connected to the grid.

[0064] like Figure 2 , assuming that the upper limit of the effective value of the inverter current capacity is i m , the effective value of the grid-connected current under normal conditions is i1, and the effective value of the current that can be used to control harmonics is i r for:

[0065]

[0066] like Figure 2 If the harmonic distortion rate of the voltage at the common connection point exceeds 5% and the effective value of the current harmonic is large, the harmonics are serious. In order to avoid damage to the inverter and load electrical equipment, the minimum grid-connected current capacity i is used. 1min The remaining capacity is used for harmonic control. Similarly, the effective value of the current that can be used to control harmonics is i r for:

[0067]

[0068] Regarding the harmonic control function of the inverter, the inverter topology used in the inverter grid-connected harmonic control comprehensive control method of the present invention is consistent with that of the common three-phase grid-connected inverter. Taking the three-phase PI-controlled grid-connected inverter as an example, the overall structure of the system is as follows: Figure 3 shown.

[0069] like Figure 3 and Figure 4 The system uses nonlinear load equivalent to the grid harmonic source. labc is the load current, including the fundamental component and harmonic component i habc ;i abc is the PCC current; i oabc is the output current of the grid-connected inverter. Under the condition of harmonic control, its expression can be written as:

[0070] i abc =i oabc -i labc (3)

[0071]

[0072] In the formula, i pabc is the grid-connected current; i habc' is the current output by the inverter for harmonic control. Therefore, the harmonic components in the nonlinear load and part of the current output by the inverter offset each other, thereby achieving the purpose of harmonic control. This harmonic control method is similar to the APF active power filter, but does not require additional harmonic control equipment.

[0073] The harmonic extraction structure of the system consists of several Figure 5 The structure shown is connected in parallel. Among them, the frequency-multiplying phase-locked loop can extract the harmonic components of a specific frequency, and then output the current command reference value with the same frequency as the extracted harmonic frequency through the subsequent structure, which is used as part of the inverter output current to offset the harmonic components in the grid current, thereby achieving the purpose of harmonic control.

[0074] exist Figure 5 In the harmonic extraction module structure diagram, C is the coordinate transformation matrix, and C -1 = C, which can transform the input signal into the synchronous rotating coordinate system for the next step of operation. LPF is a low pass filter (Low Pass Filter, LPF). The sin_cos module will generate corresponding sine and cosine waveforms according to the input phase angle. C 32 and C 23 For 32 and 23 transformation matrices, the matrix expressions are as follows:

[0075]

[0076]

[0077] Where ω and t are angular frequency and time variable respectively.

[0078] Through the harmonic extraction module, each harmonic current i can be extracted h2 ,i h3 …i hn , then the total effective value of the current harmonics that need to be controlled is i hsum for:

[0079]

[0080] Where n is the upper limit of the maximum harmonic order that the system can detect, and the frequency corresponding to the n-fold harmonic is f=n*50Hz.

[0081] By setting Figure 5 By adjusting the parameters of the frequency-multiplier phase-locked loop, we can obtain the harmonic extraction module for different frequencies. Taking the frequency-multiplier phase-locked loop output frequency of 150Hz as an example, the i containing harmonic components at this time abc After the calculation of the C matrix, the output signal contains two signals: DC and AC. The DC signal is generated by i abcThe original AC signal at 150Hz frequency is obtained after coordinate transformation, and i abc The remaining frequency components in the input signal become new AC components after being shifted by one time the phase-locked frequency. At this time, the parameters of the low-pass filter LPF can be set to retain only the DC component in the input signal. The cutoff frequency is selected as 10*πrad / s. At this time, only i abc The 150Hz harmonic component can pass through the low-pass filter LPF, that is, the effect of extracting harmonics of a specific order is achieved.

[0082] In step 306, if the current redundancy capacity is sufficient, all detected harmonics can be controlled by connecting several Figure 5 The harmonic extraction module shown can achieve the extraction and control functions for multiple harmonics. When the system current capacity is sufficient, the inverter outputs the current i for both grid connection and harmonic control. oabc It is shown in the following formula (8).

[0083]

[0084] Among them, θ i is the initial phase angle corresponding to the i-th harmonic, i pabc is the current required for grid connection, n is the upper limit of the maximum harmonic order that the system can detect, i hi is the ith harmonic current, and f1 is the fundamental frequency.

[0085] In step 307, when the current redundancy capacity is insufficient, a limiting scheme is adopted to determine a limiting gain value k.

[0086] When the grid-connected inverter is already operating at the minimum current required for grid connection, if the remaining current capacity is still insufficient to control all harmonic currents, partial harmonic control is required. In this case, if the controller still uses equation (8) to output current in order to control all harmonics, it will exceed the inverter's current tolerance limit and cause damage to the device. Therefore, it is necessary to limit the output current used to control harmonics. However, the traditional method of simply setting the current peak upper limit will cause new harmonic components to be generated in the system, as shown in Figure 6(a). This section sets the limiting gain k so that the system can control harmonics to the greatest extent while satisfying the current constraints, and because clipping is not used, new harmonics will not be introduced into the system, as shown in Figure 6(b).

[0087] The calculation method of the limiting gain k is as follows:

[0088]

[0089] In the formula, i max is the maximum current output by the inverter; tx If the harmonics are completely controlled, the inverter output current reaches its peak value. At this time, the inverter outputs the current i for both grid connection and harmonic control. oabc The calculation formula is:

[0090]

[0091] In the formula, i pabc is the current required for grid connection, k is the limiting gain, θ i is the initial phase angle corresponding to the i-th harmonic.

[0092] In order to verify the accuracy of the grid-connected and harmonic control integrated control method of the inverter proposed in the present invention and the established inverter model, a relevant model was built in MATLAB / SIMULINK simulation software for verification based on the above theoretical analysis. Its main parameters are shown in Table 1:

[0093] Table 1

[0094]

[0095] When the inverter is only connected to the grid and no harmonic control is performed, the current i at the PCC pcc The FFT analysis is as follows Figure 7 As shown in the figure, it can be seen that the current at the PCC contains 5th, 7th, and 11th harmonics, whose effective values ​​are about 10% of the fundamental wave, and the current distortion rate is 16.15%.

[0096] Complete harmonic control when the current capacity is sufficient: When the current capacity is sufficient, the inverter current i oabc Both the effective value and the peak value meet the requirements for controlling all harmonics. At this time, complete harmonic control can be performed. The i before and after control pcc Waveform and after treatment pcc The FFT analysis is as follows: Figure 8 and Fig. 9 As shown. pcc From the waveform, we can see that the inverter starts harmonic control after 0.15s. After the inverter intervenes in harmonic control, the current distortion rate (THD) is reduced to 3.12%, and the 5th, 7th, and 11th harmonics are almost completely eliminated.

[0097] Partial harmonic control when current capacity is insufficient: If the inverter current capacity upper limit (peak value) is reduced to 7A, harmonics cannot be completely controlled. If the grid-connected current is guaranteed to remain unchanged and all harmonics are controlled, the inverter needs to output a current with a maximum amplitude of 9.45A, which exceeds the inverter current capacity upper limit. Therefore, partial harmonic control should be selected.

[0098] As can be seen from Figure 10(a), the red curve represents the total output current of the inverter, the green line is the current output by the inverter for harmonic control, the blue line is the grid-connected current output by the inverter, and the red line is the sum of the amplitudes of the blue and green lines. x Moment, i o The peak value is 9.45A, which exceeds the maximum current peak of 7A by 2.45A, and the sum of harmonic amplitude is 6.13A.

[0099] If the traditional amplitude limiting method is used, the waveform after clipping is shown in Figure 10(b). If the limiting gain is used, k is (7-3.35) / 6.13A≈0.595. The output current waveform after limiting is shown in Figure 10(c).

[0100] Perform FFT analysis on the inverter output current under clipping limiting and gain limiting methods, and the results are as follows: Fig.11 As shown. Obviously, in addition to outputting 5th, 7th, and 11th harmonics for harmonic control, the clipping and limiting method will also output harmonics of other frequencies, thereby polluting the grid current and having a negative effect. Gain limiting will only control existing harmonics and will not introduce additional harmonic components. Therefore, compared with the traditional limiting scheme, the gain limiting method proposed in the present invention has advantages.

[0101] The electronic device of the present invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) or loaded from a storage unit into a random access memory (RAM). In the RAM, various programs and data required for device operation can also be stored. The CPU, ROM and RAM are connected to each other via a bus. An input / output (I / O) interface is also connected to the bus.

[0102] Multiple components in the device are connected to the I / O interface, including: input units, such as keyboards, mice, etc.; output units, such as various types of displays, speakers, etc.; storage units, such as disks, optical disks, etc.; and communication units, such as network cards, modems, wireless communication transceivers, etc. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunication networks.

[0103] The processing unit performs the various methods and processes described above. For example, in some embodiments, the method can be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program can be loaded and / or installed on the device via a ROM and / or a communication unit. When the computer program is loaded into RAM and executed by the CPU, one or more steps of the method described above can be performed. Alternatively, in other embodiments, the CPU can be configured to perform the method in any other appropriate manner (e.g., by means of firmware).

[0104] The functions described above herein may be performed at least in part by one or more hardware logic components. For example, without limitation, exemplary types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), complex programmable logic devices (CPLDs), and the like.

[0105] The program code for implementing the method of the present invention can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code can be executed entirely on the machine, partially on the machine, partially on the machine as a stand-alone software package and partially on a remote machine, or entirely on a remote machine or server.

[0106] In the context of the present invention, a machine-readable medium may be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, device, or equipment. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0107] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for integrated control of grid connection and harmonic control of inverters, characterized in that: The following steps are involved: Step 1: Collect real-time grid-connected current and common connection point current harmonic data; Step 2: Determine the minimum current required for grid connection, and judge whether the inverter current capacity is greater than or equal to the sum of the minimum current required for grid connection of the inverter and the set current capacity redundancy value. If not, execute step 3; Otherwise, proceed to step 4; Step 3: The current output by the inverter is only connected to the grid, and the process returns to step 1; Step 4: According to the external harmonic control instruction input to the inverter, determine the harmonic frequency set that is currently given priority for control, and combine the common connection point current harmonic data to determine whether the current redundancy capacity is sufficient. If so, combine the collected real-time grid-connected current to control all harmonics; otherwise, limit the current used for harmonic control and control some harmonics, and return to step 1. If the power is off or shut down, end the control; The condition for sufficient current redundancy capacity is specifically: after removing the minimum current required for grid connection, if the effective value of the remaining current redundancy capacity still has a set redundancy compared to the total harmonic current of the actual common connection point, then the current redundancy capacity is considered to be sufficient and complete harmonic control is performed.

2. The method for integrated control of grid connection and harmonic control of inverter according to claim 1, characterized in that: The process of determining the minimum current required for grid connection includes: obtaining the lower limit of the inverter grid-connected current according to the collected inverter related data as the instruction input, and finally determining the minimum current required for grid connection; wherein the lower limit of the inverter grid-connected current is obtained by internal calculation of the inverter controller, or is set by the user in combination with the current and power loss of the load operation; The inverter related data includes the rated output capacity of the inverter, the inverter switching frequency, voltage, current, grid frequency and power.

3. The method for integrated control of grid connection and harmonic control of inverter according to claim 1, characterized in that: If the voltage harmonic distortion rate at the common connection point exceeds the set threshold and the effective value of the current harmonic is greater than the set ratio of the fundamental wave, the minimum grid-connected current capacity i is used. 1min The remaining capacity is used for harmonic control. At this time, the effective value of the current used for harmonic control is i r for: Among them, i m It is the upper limit of the effective value of the inverter current capacity.

4. The method for integrated control of grid connection and harmonic control of inverter according to claim 1, characterized in that: Complete harmonic control can only be carried out when both the effective value and peak value of the inverter current meet the conditions for complete harmonic control.

5. The method for integrated control of grid connection and harmonic control of an inverter according to claim 1 or 4, characterized in that: The sufficient current redundancy capacity specifically means that after removing the minimum current required for grid connection, if the effective value of the remaining current redundancy capacity still has a set redundancy compared to the total harmonic current of the actual common connection point, complete harmonic control is performed.

6. The method for integrated control of grid connection and harmonic control of inverter according to claim 5, characterized in that: The set redundancy is 10% to 20%.

7. The method for integrated control of grid connection and harmonic control of inverter according to claim 1, characterized in that: The specific method of controlling all harmonics is as follows: a part of the current capacity of the inverter is used for grid connection, and the other part is used for controlling harmonics, wherein the current i used for grid connection and controlling harmonics is oabc Specifically: Among them, i pabc is the grid-connected current, n is the upper limit of the maximum harmonic order that the system can detect, i hi is the i-th harmonic current, f1 is the fundamental frequency, θ i is the initial phase angle corresponding to the i-th harmonic, and t is the time variable.

8. The method for integrated control of grid connection and harmonic control of inverter according to claim 1, characterized in that: The controlling of some harmonics after limiting the current for harmonic control includes setting a limiting gain k so that the system can control harmonics to the maximum extent while satisfying the current constraint, wherein the limiting gain k is calculated as follows: Where, t x is the moment when the inverter output current reaches its peak value if the harmonics are completely controlled; i pabc is the grid-connected current; n is the upper limit of the maximum harmonic order that the system can detect; i hi is the i-th harmonic current; f1 is the fundamental frequency; θ i is the initial phase angle corresponding to the i-th harmonic; i max The maximum current output by the inverter.

9. The method for integrated control of grid connection and harmonic control of inverter according to claim 1, characterized in that: After the current used for harmonic control is limited, the inverter outputs the current i used for grid connection and harmonic control at the same time. oabc The calculation formula is: In the formula, i pabc is the grid-connected current, k is the limiting gain, i pabc is the grid-connected current, n is the upper limit of the maximum harmonic order that the system can detect, i hi is the i-th harmonic current, f1 is the fundamental frequency, θ i is the initial phase angle corresponding to the i-th harmonic, and t is the time variable.

10. An electronic device comprising a memory and a processor, wherein a computer program is stored in the memory, wherein: When the processor executes the program, the method according to any one of claims 1 to 9 is implemented.

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