Method for setting virtual internal potential control parameters of network construction type converter

Abstract

The invention provides a method for setting virtual internal potential control parameters of a network-building type converter, and relates to the technical field of network-building type converters, and the method comprises the steps: S1, determining the virtual internal potential control parameters of the network-building type converter; s2, using an equivalent circuit method to generate a network-forming converter equivalent circuit; constructing an equivalent voltage source model of the network-forming converter through the virtual internal potential control parameters and the equivalent circuit; s3, calculating a constraint condition II of control parameters of the model in different operation states according to a constraint condition I of grid-connected operation of the converter; s4, performing parameter scanning on the value range of the control parameters based on a constraint condition II, and generating a solution space meeting the constraint condition II; and S5, according to the functional characteristics of the converter, obtaining the optimal parameter combination of the virtual internal potential control parameters in the solution space. The method further optimizes the virtual internal potential control algorithm, improves the adaptability and safety of the virtual internal potential control algorithm under various power grid fault conditions, and improves the stability and reliability of a new energy grid-connected system.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-type converters, and in particular to a method for setting virtual internal potential control parameters of a grid-type converter. Background Art

[0002] In order to meet the needs of long-distance power transmission of the Shagohuang New Energy Base, the UHV DC transmission system has become a strategic choice for my country due to its low loss and long-distance transmission capacity. However, the Shagohuang New Energy Base lacks synchronous power support, which easily causes transient overvoltage problems in the sending-end power grid when commutation failure, DC locking and other faults occur at the receiving end, and puts forward higher requirements on the reactive response characteristics of new energy. The grid-type converter has good reactive response characteristics due to its voltage source characteristics, and is considered to be an effective solution to improve the reactive support capacity of new energy. In order to obtain better reactive response characteristics, the grid-type converter adopts virtual internal potential control. Compared with the traditional power outer loop and voltage and current double closed-loop control structure, the control method based on virtual internal impedance proposes that the voltage loop is transformed into an open-loop control structure through Ohm's law, avoiding the delay effect of the integral link in the traditional closed-loop control voltage loop on the voltage response, thereby improving the reactive response effect of the grid-type converter.

[0003] However, the introduction of virtual internal impedance in virtual internal potential control also brings some risks, such as converter overcurrent problems. How to maximize the reactive power support effect of the grid-connected converter under the premise of ensuring the safe operation of the converter, maintain the safety of the power electronic components inside the converter and the fault ride-through capability of the new energy grid-connected system are all difficult problems faced by converter applications. The current main research lacks understanding of the response capability of the grid-connected converter under complex fault conditions. When a short-circuit fault occurs when the converter is connected to the grid, the effect of phase jump on the short-circuit current is often ignored. There is a lack of in-depth research on the performance of virtual internal potential control under extreme conditions and the selection of virtual internal potential control parameters. Summary of the invention

[0004] The present invention provides a method for setting virtual internal potential control parameters of a grid-type converter, which is used to solve the problem of selecting appropriate virtual internal potential control parameters of the grid-type converter under extreme conditions.

[0005] The present invention provides a method for setting virtual internal potential control parameters of a grid-connected converter, comprising:

[0006] S1: Determine a virtual internal potential control parameter for limiting the virtual internal potential of the grid-connected converter;

[0007] S2: Generate an equivalent circuit of a grid-type converter based on virtual internal impedance control using the equivalent circuit method; construct an equivalent voltage source model of a grid-type converter through virtual internal potential control parameters and equivalent circuits;

[0008] S3: According to the constraint condition 1 when the grid-connected converter is in grid-connected operation, the constraint condition 2 of the virtual internal potential control parameters of the equivalent voltage source model of the grid-connected converter under different operating states is calculated;

[0009] S4: Based on constraint condition 2, perform parameter scanning on the value range of the virtual internal potential control parameter to generate a solution space that satisfies constraint condition 2;

[0010] S5: According to the different functional characteristics of the grid-connected converter, the optimal parameter combination of the virtual internal potential control parameters is obtained in the solution space.

[0011] According to a method for setting control parameters of a virtual internal potential of a grid-type converter provided by the present invention, in step S1, the control parameters of the virtual internal potential of the grid-type converter include: the converter virtual internal potential E v , converter virtual internal potential impedance X v , the maximum modulation voltage of the converter E max and the maximum output current of the converter I max .

[0012] According to a method for setting virtual internal potential control parameters of a grid-type converter provided by the present invention, in step S2, an equivalent circuit method replaces the modulation voltage and filter impedance of the grid-type converter by using a Thevenin network with a virtual internal potential in series with a virtual internal impedance to construct an equivalent circuit of the grid-type converter; the external parameters of the equivalent circuit include: converter modulation voltage E, converter terminal voltage V, grid bus voltage U g 、Converter filter impedance X L and grid impedance X g ; The equivalent circuit exhibits voltage source characteristics in external connections.

[0013] According to a method for setting virtual internal potential control parameters of a grid-connected converter provided by the present invention, in step S3, the constraints of the grid-connected converter during grid-connected operation include:

[0014] Under normal operating conditions, the grid-type converter can output the rated active power at unity power factor when the terminal voltage is the rated voltage, and can achieve the common output of the rated active power and the rated reactive power, that is, meet the maximum operating state;

[0015] The grid-type converter does not have overmodulation phenomenon:

[0016] The grid-type converter does not experience overcurrent.

[0017] According to a method for setting virtual internal potential control parameters of a grid-connected converter provided by the present invention, in step S3, a calculation method of constraint condition 2 includes:

[0018] S31: Determine the grid impedance X of the equivalent voltage source model of the grid-connected converter g , Rated output active power P of converter n , Rated output reactive power of converter Q n , Rated power factor of converter and the internal impedance X of the converter c ;

[0019] S32: setting a voltage limit of the grid-forming converter according to the operating grid condition of the grid-forming converter;

[0020] S33: Use phase jump to construct the maximum output current I of the grid-type converter cmax Make adjustments; estimate the most serious short-circuit fault of the system where the grid-type converter is located, and determine the electrical distance X between the fault point and the grid-type converter k ;

[0021] S34: Generate constraint condition 2 according to the maximum modulation voltage of the converter.

[0022] According to a method for setting virtual internal potential control parameters of a grid-connected converter provided by the present invention, in step S33, the phase jump includes:

[0023] A single-machine infinite grid system of grid-connected converter is constructed, and the relationship between the converter terminal voltage and the infinite grid is found through the Thevenin equivalent method, realizing the coupled phase jump analysis of the grid equivalent voltage amplitude change.

[0024] According to a method for setting virtual internal potential control parameters of a grid-connected converter provided by the present invention, in step S33, the expression of the output current I of the grid-connected converter after a short-circuit fault occurs in the power grid is obtained as follows:

[0025]

[0026] In the formula, E0 and θ E0 They represent the steady-state amplitude and phase of the virtual internal potential E of the converter, U g0 and θ g0 Indicates the infinite power grid bus voltage U g The steady-state amplitude and phase of X1 represents the equivalent impedance of the infinite power grid, X2 represents the electrical distance from the short-circuit fault point to the converter outlet, X3 represents the filter impedance of the grid-type converter, R f Indicates the grounding resistance at the short-circuit fault point;

[0027] When a short circuit occurs at the port of the grid-connected converter, the maximum output current I cmax The expression is:

[0028] I cmax=f(X g ,X k ,X L ,R f )

[0029] Among them, X g Represents the equivalent reactance of the system grid, X k Indicates the electrical distance from the short-circuit fault point to the converter outlet, X L Represents the filter impedance of the grid-type converter, R f Indicates the grounding resistance at the fault point.

[0030] According to a method for setting virtual internal potential control parameters of a grid-type converter provided by the present invention, in step S33, the maximum output current I cmax The following constraints need to be met:

[0031] I cmax max

[0032] In the formula, I max Indicates the maximum output current of the converter.

[0033] According to a method for setting virtual internal potential control parameters of a grid-connected converter provided by the present invention, in step S34, the expression of constraint condition 2 includes:

[0034] The upper limit of virtual internal potential E of grid-connected converter vmax The value range of is:

[0035] E max ≤E vmax ≤(X k +X v )I cmax

[0036] In the formula, E max is the maximum modulation voltage of the converter;

[0037] Virtual internal potential lower limit E of grid-connected converter vmin The value range of is:

[0038]

[0039] Where V n Indicates the rated voltage of the converter terminal voltage, I cmax Indicates the maximum output current of the phase-jump converter, V max Indicates the maximum voltage of the converter terminal voltage, It represents the power factor corresponding to the maximum power angle between the virtual internal potential and the terminal voltage of the grid-connected converter, I max Indicates the maximum output current of the converter. ​

[0040] According to a method for setting virtual internal potential control parameters of a grid-connected converter provided by the present invention, in step S34, the converter maximum modulation voltage E max The calculation formula is:

[0041]

[0042] Where V n Indicates the rated voltage of the converter terminal voltage.

[0043] The present invention provides a method for setting virtual internal potential control parameters of a grid-connected converter. By considering that when a short-circuit fault occurs when the grid-connected converter is connected to the power grid, phase jumps may affect the size of the short-circuit current, thereby constraining the selection of virtual internal potential control parameters, thereby solving the risk of overcurrent when the grid-connected converter is connected to the grid, and maximizing the reactive power support effect of the grid-connected converter while ensuring the safe operation of the converter. It is beneficial to the safety of power electronic components inside the converter and the fault-crossing capability of the new energy grid-connected system, and further optimizes the virtual internal potential control algorithm, improves its adaptability and safety in various power grid fault conditions, and promotes the stability and reliability of the new energy grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0045] Figure 1 It is a flow chart of a method for setting virtual internal potential control parameters of a grid-connected converter provided by an embodiment of the present invention;

[0046] Figure 2 1 is a schematic diagram of a virtual internal potential control structure of a grid-connected converter provided in an embodiment of the present invention;

[0047] Figure 3 is an equivalent circuit diagram of a grid-type converter provided in an embodiment of the present invention;

[0048] Figure 4 Schematic diagram of a grid-type converter single machine infinite system provided by an embodiment of the present invention;

[0049] Figure 5 is a Thevenin equivalent circuit diagram of a grid-connected grid-connected converter provided by an embodiment of the present invention;

[0050] Figure 6is a phasor diagram of a grid-type converter response during a short-circuit fault provided by an embodiment of the present invention;

[0051] Figure 7 is the virtual internal potential control parameter E provided by this simulation verification v With X v Schematic diagram of the feasible domain. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings 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 are within the scope of protection of the present invention.

[0053] Example 1

[0054] Combine the following Figure 1-Figure 7 A method for setting virtual internal potential control parameters of a grid-connected converter according to the present invention is described.

[0055] Figure 1 It is a flow chart of a method for setting virtual internal potential control parameters of a grid-connected converter provided in Example 1 of the present invention.

[0056] like Figure 1 As shown, a method for setting virtual internal potential control parameters of a grid-connected converter provided in Embodiment 1 of the present invention mainly comprises the following steps:

[0057] S1: Determine the virtual internal potential control parameters for the grid-connected converter to perform limiting control on the virtual internal potential.

[0058] like Figure 2 As shown in the figure, the virtual internal potential control structure of the grid-type converter uses proportional droop control to control the virtual internal potential. The control parameters of the virtual internal potential of the grid-type converter include: the converter virtual internal potential E v 、Converter virtual internal potential impedance X v , the maximum modulation voltage of the converter E max and the maximum output current of the converter I max .

[0059] S2: Generate an equivalent circuit of a grid-type converter based on virtual internal impedance control using the equivalent circuit method; construct an equivalent voltage source model of the grid-type converter through virtual internal potential control parameters and equivalent circuits.

[0060] like Figure 3As shown in the figure, the equivalent circuit method uses a Thevenin network with virtual internal potential in series with virtual internal impedance to replace the modulation voltage and filter impedance in the grid-type converter to construct an equivalent circuit of the grid-type converter based on virtual internal impedance control. The external parameters of the equivalent circuit include: converter modulation voltage E, converter terminal voltage V, grid bus voltage U g 、Converter filter impedance X L and grid impedance X g The equivalent circuit behaves as a voltage source in external connections.

[0061] S3: According to constraint condition 1 of the grid-connected converter during grid-connected operation, constraint condition 2 of the virtual internal potential control parameters of the equivalent voltage source model of the grid-connected converter under different operating states is calculated.

[0062] Among them, the first constraint condition of the grid-connected converter includes:

[0063] Under normal operating conditions, the grid-type converter can output the rated active power at unity power factor when the terminal voltage is the rated voltage, and can achieve the common output of the rated active power and the rated reactive power, that is, meet the maximum operating state.

[0064] When overmodulation occurs in a three-level converter based on PWM control technology, the output voltage waveform will significantly deviate from the sinusoidal waveform, resulting in a nonlinear voltage waveform. This waveform distortion will increase the harmonic content of the output voltage, which will have an adverse effect on the power grid and load equipment. At the same time, the nonlinear voltage waveform will introduce more current harmonics, affecting the stability of the system, causing the system to oscillate and become unstable. Therefore, it is necessary to ensure that the grid-type converter does not overmodulate.

[0065] The converter contains a large number of power electronic components such as thyristors and IGBTs. Overcurrent will directly affect the components inside the converter, interfere with the safe and stable operation of the converter, cause system output waveform distortion, and further affect the stability of the entire system. Therefore, it is necessary to ensure that the grid-type converter does not have overcurrent.

[0066] The steps for calculating the constraint condition 2 of the virtual internal potential control parameters of the equivalent voltage source model of the grid-connected converter under different operating conditions are as follows:

[0067] S31: Determine the grid impedance X of the equivalent voltage source model of the grid-connected converter g , Rated output active power of converter P n , Rated output reactive power of converter Q n , inverter rated power factor and the internal impedance X of the converter c ;

[0068] S32: setting a voltage limit of the grid-forming converter according to the operating grid condition of the grid-forming converter;

[0069] S33: Use phase jump to construct the maximum output current I of the grid-type converter cmax Make adjustments; estimate the most serious short-circuit fault of the system where the grid-type converter is located, and determine the electrical distance X between the fault point and the grid-type converter k ;

[0070] Considering the phase jump, the maximum output current I cmax Here’s how to make the adjustment:

[0071] like Figure 4-Figure 5 As shown in the figure, a grid-type converter single-machine infinite system is constructed, and the relationship between the converter terminal voltage and the infinite grid is found through the Thevenin equivalent method, realizing the grid equivalent voltage amplitude change coupled phase jump analysis. Figure 5 As shown, u s is the voltage at the converter terminal, e is the equivalent voltage of the power grid, i is the output current of the converter, Z1 is the equivalent impedance between the infinite power grid and the fault point, Z2 is the impedance between the converter outlet and the fault point, and Z f is the grounding impedance of the fault point, where Z1=R1+jX1, Z2=R2+jX2. eq is the Thevenin equivalent voltage source, Z eq =R eq +jX eq is the Thevenin equivalent impedance.

[0072] According to the Thevenin equivalent circuit, the expressions of Thevenin equivalent voltage and equivalent impedance are:

[0073]

[0074] Among them, t r ,t f are the fault occurrence and circuit recovery moments respectively.

[0075] The equivalent voltage phase of the power grid is obtained as:

[0076]

[0077] The phase jump value of the grid voltage phase when a short circuit fault occurs for:

[0078]

[0079] From the above formula, we can know that when the ground impedance Z f When the impedance angle of the system impedance Z1 is different, the voltage phase at the converter end will jump when the grid fails, and the jump amount It is related to the location of the fault point, the type of fault, etc.

[0080] In the actual operation of the power grid, the power grid topology and system parameters are diverse, which results in various voltage phase jumps at the converter end after a short circuit occurs in the power grid. Here we study the most serious phase jump, that is, assuming that the system impedance Z1 is a pure inductive reactance and the ground impedance Z f It is purely resistive, that is, R1 = 0, X f =0, substituting into the above formula we can get:

[0081]

[0082] The reason why the grid-type converter can have reactive power support capability is that when the grid experiences voltage fluctuations and other disturbances, the grid-type converter can be equivalent to a controllable voltage source. When the grid voltage drops or rises, the potential E in the converter is kept constant, that is, it shows a constant voltage source characteristic to the outside. Figure 6 As shown in FIG. 1 , when a short circuit occurs in the power grid, the phasor diagram of the response of the grid-connected converter to the voltage fluctuation of the power grid is shown.

[0083] After a short circuit occurs in the power grid, the expression of the output current I of the grid-connected converter is:

[0084]

[0085] In the formula, the voltage at the converter terminal points to the d-axis of the dq coordinate system, and E0 and θ E0 They represent the steady-state amplitude and phase of the virtual internal potential E of the converter, U g0 and θ g0 Indicates the infinite power grid bus voltage U g The steady-state amplitude and phase of X1 represents the equivalent impedance of the infinite power grid, X2 represents the electrical distance from the short-circuit fault point to the converter outlet, X3 represents the filter impedance of the grid-type converter, R f Indicates the grounding resistance at the short-circuit fault point.

[0086] It can be deduced from the expression of the output current I of the grid-type converter that as the electrical distance X2 between the fault point and the converter outlet decreases, the current amplitude increases after the fault occurs, that is, when a short-circuit fault occurs at the converter outlet, the converter output current I has the maximum amplitude. When a short-circuit fault occurs at the port of the grid-type converter, the maximum output current I of the grid-type converter is cmax The expression is as follows:

[0087] I cmax =f(X g ,X k ,X L ,R f )

[0088] Among them, X g Represents the equivalent reactance of the system grid, X k Indicates the electrical distance from the short-circuit fault point to the converter outlet, X L Represents the filter impedance of the grid-type converter, R f Indicates the grounding resistance at the fault point.

[0089] In summary, firstly, according to the estimation of the severity of the short-circuit fault, the electrical distance X between the fault point and the converter is set. k Then, when the design parameters of the grid-type converter and the equivalent impedance of the power grid are determined, the maximum output current I of the grid-type converter is obtained by traversing possible short-circuit fault types, converter modulation voltage magnitudes, and phase angles. cmax .

[0090] Maximum output current of grid-type converter I cmax The following constraints need to be met:

[0091] I cmax max

[0092] In the formula, I max Indicates the maximum output current allowed by the converter design.

[0093] S34: Generate constraint condition 2 according to the maximum modulation voltage of the converter.

[0094] For the low-voltage fault ride-through condition of the power grid, short-circuit fault usually causes the voltage at the converter terminal to drop suddenly. Without considering the voltage phase jump, it can be considered that the three-phase short-circuit fault is the most serious. The most serious fault is selected for analysis. At this time, the virtual internal potential of the converter reaches the maximum value E vmax During a three-phase short-circuit fault, the main constraint for the converter is that no overcurrent occurs. The expression of the converter output current I is as follows:

[0095]

[0096] Where, X k is the equivalent short-circuit impedance from the short-circuit fault point to the terminal voltage of the grid-connected converter during a three-phase short circuit, I max Design the converter for the maximum output current allowed.

[0097] The maximum value of the virtual internal potential E of the converter is derived from the above formula: vmax The value range of is as follows:

[0098]

[0099] Considering the phase jump, the maximum output current I cmax ​To make adjustments, the following constraints need to be met:

[0100] I cmax max

[0101] Converter maximum modulation voltage E max Calculation formula:

[0102]

[0103] In summary, after considering the influence of phase jump on the maximum output current of the converter, the upper limit of the virtual internal potential E of the grid-type converter is vmax The value range of is:

[0104] E max ≤E vmax ≤(X k +X v )I cmax

[0105] For the high-voltage fault ride-through condition of the power grid, considering that the commutation failure and DC blocking of the AC at the DC receiving end of the new energy sending end occur, a large amount of reactive power will be fed in, which will cause transient overvoltage problems at the converter end voltage. When the most serious overvoltage problem occurs, the virtual internal potential of the converter will reach the minimum value E under the action of proportional droop control. vmin First, the converter needs to ensure that no overcurrent occurs. Considering the normal steady-state operating conditions, the maximum power angle between the virtual internal potential and the terminal voltage of the grid-type converter can be determined by the known rated active power and rated terminal voltage. The expression is as follows:

[0106]

[0107] Under the constraint of the maximum power angle, the voltage at the converter terminal is specified to point to the d-axis direction in the dq coordinate system. The following constraints can be derived if the converter does not have overcurrent:

[0108]

[0109] At the same time, considering that the virtual internal potential amplitude and the maximum terminal voltage of the converter are determined at this time, when the two are in the same direction, the modulation voltage of the grid-type converter reaches the maximum value. At this time, the constraint condition that the converter does not over-modulate is:

[0110]

[0111] Then we can get the minimum value of the virtual internal potential E of the converter: vmin Constraints:

[0112]

[0113] ​In summary, the virtual internal potential lower limit E of the grid-connected converter is vmin The value range of is:

[0114]

[0115] Where V n Indicates the rated voltage of the converter terminal voltage, I cmax Indicates the maximum output current of the phase-jump converter, V max Indicates the maximum voltage of the converter terminal voltage, It represents the power factor corresponding to the maximum power angle between the virtual internal potential and the terminal voltage of the grid-connected converter, I max Indicates the maximum output current of the converter.

[0116] S4: Based on the constraints of the virtual internal potential control parameters, the value range of the virtual internal potential control parameters is scanned by Matlab software to generate a solution space that meets the above constraints.

[0117] S5: According to the different functional characteristics of the grid-type converter, the optimal parameter combination of the virtual internal potential control parameters is obtained in the solution space.

[0118] This embodiment proposes a method for setting the virtual internal potential control parameters of a grid-type converter. The method is intended to deal with short-circuit faults that may be encountered when the grid-type converter is connected to the power grid. Phase jumps may cause drastic changes in short-circuit current, thereby posing risks to the power system. Therefore, in the process of parameter selection, special consideration is given to the impact of this phase jump on the magnitude of the short-circuit current. By reasonably constraining the virtual internal potential control parameters, the overcurrent risk of the converter when connected to the grid can be effectively reduced, ensuring the safe operation of the converter when facing a grid failure. At the same time, the method can also maximize the reactive support capability of the grid-type converter and support the stability of the power grid. For the power electronic components inside the converter, optimizing the parameter configuration not only helps to improve its tolerance, but also provides a stronger fault ride-through capability for the new energy grid-connected system.

[0119] This embodiment further optimizes the virtual internal potential control algorithm to improve its adaptability and safety in various power grid fault conditions. This improvement will significantly promote the development of new energy grid-connected systems towards higher stability and reliability, and provide the necessary technical guarantee for building smart grids. In summary, this method not only solves the technical bottlenecks faced by current grid-connected converters when connected to the grid, but also contributes to enhancing the overall resilience of the power system.

[0120] Simulation verification:

[0121] Combine the following Figure 7A setting example of a method for setting virtual internal potential control parameters of a grid-connected converter provided by the present invention is described.

[0122] First, according to the minimum short-circuit ratio of the grid-forming converter required to support the weak grid, the converter system impedance requirement X is determined. g =1.0pu, inverter output rated active power P n =1.0pu, rated power factor of converter Set the voltage limit of the terminal voltage during high voltage and low voltage ride through faults, V max =1.3pu,V min =0.3pu. Select the X with the worst expected short-circuit fault k , X k The larger the value, the more optimistic the prediction of the worst short-circuit fault condition is. k =0.15pu.

[0123] Considering the impact of phase jump on the output current demand of the converter, traverse different short-circuit fault grounding resistances R f , get the maximum output current requirement of the converter I cmax .like Figure 5 As shown in the figure, according to the operating constraints of the grid-type converter, the virtual internal impedance X is calculated using Matlab. v and virtual internal potential E v By scanning the value range of , we can get the virtual internal potential control parameter E as shown in v With X v This embodiment 2 requires the converter to have a strong reactive power support capability, that is, the virtual internal impedance X v When the minimum value of 0.215pu in the feasible region is taken, according to the feasible region, the virtual internal potential E v The value of is 1.153 pu. In other embodiments, different functional characteristics of the grid-connected converter also include: power flow control capability, short-circuit fault ride-through capability and dynamic response capability, and the best parameter combination of the virtual internal potential control parameters is obtained in the solution space according to different specific conditions.

[0124] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0125] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for setting virtual internal potential control parameters of a grid-connected converter, characterized in that: include: S1: Determine a virtual internal potential control parameter for limiting the virtual internal potential of the grid-connected converter; S2: Generate an equivalent circuit of a grid-type converter based on virtual internal impedance control using an equivalent circuit method; construct an equivalent voltage source model of the grid-type converter through the virtual internal potential control parameters and the equivalent circuit; S3: according to the first constraint condition when the grid-connected converter is in grid-connected operation, calculating the second constraint condition of the virtual internal potential control parameter of the grid-connected converter equivalent voltage source model under different operating states; S4: Based on the second constraint condition, performing parameter scanning on the value range of the virtual internal potential control parameter to generate a solution space that satisfies the second constraint condition; S5: According to different functional characteristics of the grid-connected converter, an optimal parameter combination of the virtual internal potential control parameters is obtained in the solution space.

2. A method for setting virtual internal potential control parameters of a grid-connected converter according to claim 1, characterized in that: In step S1, the control parameters of the virtual internal potential of the grid-connected converter include: the virtual internal potential E v 、Converter virtual internal potential impedance X v , the maximum modulation voltage of the converter E max and the maximum output current of the converter I max .

3. A method for setting virtual internal potential control parameters of a grid-connected converter according to claim 1, characterized in that: In step S2, the equivalent circuit method uses a Thevenin network with a virtual internal potential in series with a virtual internal impedance to replace the modulation voltage and filter impedance in the grid-type converter to construct the equivalent circuit of the grid-type converter; the external parameters of the equivalent circuit include: converter modulation voltage E, converter terminal voltage X, grid bus voltage U g , converter filter impedance x L and grid impedance X g ; The equivalent circuit exhibits voltage source characteristics in external connection.

4. A method for setting virtual internal potential control parameters of a grid-connected converter according to claim 1, characterized in that: In step S3, the constraints of the grid-connected converter during grid-connected operation include: Under normal operating conditions, the grid-type converter can output rated active power at unity power factor when the terminal voltage is rated voltage, and can achieve the common output of rated active power and rated reactive power, that is, meet the maximum operating state; The grid-type converter does not have overmodulation phenomenon: The grid-type converter does not have an overcurrent phenomenon.

5. A method for setting virtual internal potential control parameters of a grid-connected converter according to claim 1, characterized in that: In step S3, the calculation method of the second constraint condition includes: S31: Determine the grid impedance X of the equivalent voltage source model of the grid-connected converter g , Rated output active power of converter P n , Rated output reactive power of converter Q n , inverter rated power factor and the internal impedance X of the converter c ; S32: setting a voltage limit of the grid-forming converter according to the operating grid condition of the grid-forming converter; S33: Using phase jump to adjust the maximum output current I of the grid-type converter cmax Adjustment; estimate the most serious short-circuit fault of the system in which the grid-type converter is located, and determine the electrical distance X between the fault point and the grid-type converter k ; S34: Generate the second constraint condition according to the maximum modulation voltage of the converter.

6. A method for setting virtual internal potential control parameters of a grid-connected converter according to claim 5, characterized in that: In step S33, the phase jump includes: A single-machine infinite grid system of grid-connected converter is constructed, and the relationship between the converter terminal voltage and the infinite grid is found through the Thevenin equivalent method, realizing the coupled phase jump analysis of the grid equivalent voltage amplitude change.

7. A method for setting virtual internal potential control parameters of a grid-connected converter according to claim 6, characterized in that: In step S33, the expression of the output current I of the grid-connected converter after a short-circuit fault occurs in the grid is obtained as follows: In the formula, E0 and θ E0 They represent the steady-state amplitude and phase of the virtual internal potential E of the converter, U g0 and θ g0 Indicates the infinite power grid bus voltage U g The steady-state amplitude and phase of X1 represents the equivalent impedance of the infinite power grid, X2 represents the electrical distance from the short-circuit fault point to the converter outlet, X3 represents the filter impedance of the grid-type converter, R f Indicates the grounding resistance at the short-circuit fault point; When a short circuit occurs at the port of the grid-type converter, the maximum output current I cmax The expression is: I cmax =f(X g ,X k ,X L ,R f ) Among them, X g Represents the equivalent reactance of the system grid, X k Indicates the electrical distance from the short-circuit fault point to the converter outlet, X L Represents the filter impedance of the grid-type converter, R f Indicates the grounding resistance at the fault point.

8. A method for setting virtual internal potential control parameters of a grid-connected converter according to claim 6, characterized in that: In step S33, the maximum output current I cmax The following constraints need to be met: I cmax <I max In the formula, I max Indicates the maximum output current of the converter.

9. A method for setting virtual internal potential control parameters of a grid-connected converter according to claim 5, characterized in that: In step S34, the expression of the second constraint condition includes: The upper limit of virtual internal potential E of grid-connected converter vmax The value range of is: E max ≤E vmax ≤(X k +X v )I cmax In the formula, E max is the maximum modulation voltage of the converter; Virtual internal potential lower limit E of grid-connected converter vmin The value range of is: Where V n Indicates the rated voltage of the converter terminal voltage, I cmax Indicates the maximum output current of the phase-jump converter, V max Indicates the maximum voltage of the converter terminal voltage, It represents the power factor corresponding to the maximum power angle between the virtual internal potential and the terminal voltage of the grid-connected converter, I max Indicates the maximum output current of the converter.

10. A method for setting virtual internal potential control parameters of a grid-connected converter according to claim 9, characterized in that: In step S34, the maximum modulation voltage E of the converter is max The calculation formula is: Where V n Indicates the rated voltage of the converter terminal voltage.

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