A method for setting virtual internal potential control parameters of a network-forming converter

Abstract

The application provides a grid-forming converter virtual internal voltage control parameter setting method, relates to the technical field of grid-forming converters, and comprises the following steps: S1, determining a grid-forming converter virtual internal voltage control parameter; S2, generating an equivalent circuit of the grid-forming converter by using an equivalent circuit method; constructing an equivalent voltage source model of the grid-forming converter by using the virtual internal voltage control parameter and the equivalent circuit; S3, according to a constraint condition one of grid-connected operation of the converter, calculating a constraint condition two of the control parameter in different operating states; S4, based on the constraint condition two, performing parameter scanning on the value range of the control parameter to generate a solution space satisfying the constraint condition two; and S5, according to the functional characteristics of the converter, obtaining an optimal parameter combination of the virtual internal voltage control parameter in the solution space. The application further optimizes the virtual internal voltage control algorithm, improves the adaptability and safety of the virtual internal voltage control algorithm under various power grid fault conditions, and improves the stability and reliability of the new energy grid-connected system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of grid-forming converter, and particularly relates to a grid-forming converter virtual internal potential control parameter setting method. BACKGROUND

[0002] In order to meet the demand of long-distance power transmission of Shagehuang new energy base, the ultra-high voltage direct current transmission system has become the strategic choice of China due to its low loss and long-distance transmission capability. However, the Shagehuang new energy base lacks synchronous power support, and when the receiving end occurs commutation failure, DC lockout and other faults, it is easy to cause the sending end grid transient overvoltage problem, and higher requirements are put forward for the reactive power response characteristics of new energy. The grid-forming converter has good reactive power response characteristics due to its voltage source characteristics, and is considered to be an effective solution to improve the reactive power support capability of new energy. In order to obtain better reactive power response characteristics, the grid-forming converter adopts virtual internal potential control. Compared with the traditional power outer ring and voltage and current double closed loop control structure, the control mode based on virtual internal impedance converts the voltage ring into an open loop control structure according to Ohm's law, avoiding the delay effect of the integral element in the traditional closed loop control voltage ring on the voltage response, thereby improving the reactive power response effect of the grid-forming converter.

[0003] However, the introduction of virtual internal impedance in virtual internal potential control also brings some risks, such as converter overcurrent problem. How to ensure the safe operation of the converter under the premise of maximizing the reactive power support effect of the grid-forming converter, maintain the safety of the internal power electronic elements of the converter and the fault ride-through capability of the new energy grid-connected system are all difficult problems faced by the application of the converter. The current main research lacks understanding of the response capability of the grid-forming converter under complex fault conditions, and often ignores the influence of phase jump on the size of short-circuit current when the converter is connected to the grid and a short-circuit fault occurs, and lacks in-depth research on the performance of virtual internal potential control and the selection of virtual internal potential control parameters under extreme conditions. SUMMARY

[0004] The present application provides a grid-forming converter virtual internal potential control parameter setting method to solve the problem of selecting appropriate grid-forming converter virtual internal potential control parameters under extreme conditions.

[0005] The present application provides a grid-forming converter virtual internal potential control parameter setting method, comprising:

[0006] S1: determining the virtual internal potential control parameter of the grid-forming converter for limiting the amplitude control of the virtual internal potential;

[0007] S2: generating an equivalent circuit of the grid-forming converter based on virtual internal impedance control using the equivalent circuit method; constructing an equivalent voltage source model of the grid-forming converter through the virtual internal potential control parameter and the equivalent circuit;

[0008] S3: According to the constraint condition one when the grid-connected converter is in grid-connected operation, calculate the constraint condition two of the virtual internal potential control parameter of the equivalent voltage source model of the grid-connected converter in different operating states;

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

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

[0011] According to the grid-connected converter virtual internal potential control parameter setting method provided by the application, in step S1, the control parameters of the virtual internal potential of the grid-connected converter include: the virtual internal potential E v of the converter, the virtual internal potential resistance X v of the converter, the maximum modulation voltage E max of the converter, and the maximum output current I max of the converter.

[0012] According to the grid-connected converter virtual internal potential control parameter setting method provided by the application, in step S2, the equivalent circuit method replaces the internal modulation voltage and filter impedance of the grid-connected converter with a Thevenin network using a virtual internal potential in series with a virtual internal impedance to construct an equivalent circuit of the grid-connected converter. The external parameters of the equivalent circuit include: the converter modulation voltage E, the converter terminal voltage V, the grid bus voltage U g , the converter filter resistance X L , and the grid resistance X g ; the equivalent circuit behaves as a voltage source in external connection.

[0013] According to the grid-connected converter virtual internal potential control parameter setting method provided by the application, in step S3, the constraint conditions when the grid-connected converter is in grid-connected operation include:

[0014] Under normal operating conditions, the grid-connected converter can output rated active power under unity power factor when the terminal voltage is rated voltage, and can realize the common output of rated active power and rated reactive power, that is, it meets the maximum operating state;

[0015] The grid-connected converter does not have over-modulation phenomenon:

[0016] The grid-connected converter does not have over-current phenomenon.

[0017] According to the grid-connected converter virtual internal potential control parameter setting method provided by the application, in step S3, the calculation method of the constraint condition two includes:

[0018] S31: determining grid resistance X of the grid type converter equivalent voltage source model g , converter rated output active power P n , converter rated output reactive power Q n , converter rated power factor and converter internal resistance X c ;

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

[0020] S33: adjusting the maximum output current I cmax of the grid type converter by phase jump; estimating the most serious short-circuit fault of the system where the grid type converter is located, and determining the electrical distance X k between the fault point and the grid type converter;

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

[0022] According to the grid type converter virtual internal potential control parameter setting method provided by the application, in step S33, the phase jump includes:

[0023] A single machine infinite system of the grid type converter is constructed, the relationship between the converter terminal voltage and the infinite grid is found by the method of Thevenin equivalence, and the grid equivalent voltage amplitude change coupling phase jump analysis is realized.

[0024] According to the grid type converter virtual internal potential control parameter setting method provided by the application, after the short-circuit fault of the grid occurs, the expression of the output current I of the grid type converter is:

[0025]

[0026] In the formula, E0 and θ E0 respectively represent the steady-state amplitude and phase of the virtual internal potential E of the converter, U g0 and θ g0 represent the steady-state amplitude and phase of the infinite grid bus voltage U g , X1 represents the equivalent resistance of the infinite grid, X2 represents the electrical distance between the short-circuit fault point and the outlet of the converter, X3 represents the filter resistance of the grid type converter, and R f represents the grounding resistance of the short-circuit fault point.

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

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

[0029] wherein, X g represents the equivalent reactance of the system grid, X k represents the electrical distance between the short-circuit fault point and the outlet of the converter, X L represents the filter reactance of the grid-forming converter, R f represents the grounding resistance of the fault point.

[0030] According to the grid-forming converter virtual internal voltage control parameter setting method provided by the application, in step S33, the maximum output current I cmax needs to satisfy the following constraints:

[0031] I cmax < I max

[0032] wherein, I max represents the maximum output current of the converter.

[0033] According to the grid-forming converter virtual internal voltage control parameter setting method provided by the application, in step S34, the expression of the second constraint condition includes:

[0034] The value range of the upper limit E vmax of the virtual internal voltage of the grid-forming converter is:

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

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

[0037] The value range of the lower limit E vmin of the virtual internal voltage of the grid-forming converter is:

[0038]

[0039] wherein, V n represents the rated voltage of the converter terminal voltage, I cmax represents the maximum output current of the converter considering phase jump, V max represents the maximum voltage of the converter terminal voltage, represents the power factor corresponding to the maximum power angle between the virtual internal voltage and the terminal voltage of the grid-forming converter, I max represents the maximum output current of the converter.

[0040] According to the grid-connected converter virtual internal voltage control parameter setting method provided by the application, in step S34, the maximum modulation voltage E of the converter is calculated according to the following formula: max The calculation formula is:

[0041]

[0042] In the formula, V n The rated voltage of the converter terminal voltage is represented.

[0043] The grid-connected converter virtual internal voltage control parameter setting method provided by the application considers that when the grid-connected converter is connected to the power grid and a short-circuit fault occurs, the phase jump may affect the size of the short-circuit current, and then the selection of the virtual internal voltage control parameter is restricted, thereby solving the overcurrent risk when the grid-connected converter is connected to the grid, maximizing the maximum reactive power support effect of the grid-connected converter under the premise of ensuring the safe operation of the converter, and being beneficial to the safety of the power electronic elements in the converter and the fault ride-through capability of the new energy grid-connected system, and further optimizing the virtual internal voltage control algorithm, improving the adaptability and safety of the virtual internal voltage control algorithm under various power grid fault conditions, and promoting the stability and reliability of the new energy grid-connected system. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0045] Figure 1 is a flowchart of a grid-connected converter virtual internal voltage control parameter setting method provided by an embodiment of the application;

[0046] Figure 2 is a grid-connected converter virtual internal voltage control structure diagram provided by an embodiment of the application;

[0047] Figure 3 is an equivalent circuit diagram of a grid-connected converter provided by an embodiment of the application;

[0048] Figure 4 is a single-machine infinite system diagram of a grid-connected converter provided by an embodiment of the application;

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

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

[0051] Figure 7 The virtual internal potential control parameter E provided in this simulation verification v With X v A schematic diagram of the feasible region. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0053] Example 1

[0054] The following is combined with Figures 1-7 This invention describes a method for tuning virtual internal potential control parameters of a grid-type converter.

[0055] Figure 1 This is a flowchart illustrating a method for tuning virtual internal potential control parameters of a grid-type converter according to Embodiment 1 of the present invention.

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

[0057] S1: Determine the virtual internal potential control parameters for the grid-type converter to limit the virtual internal potential.

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

[0059] S2: Use the equivalent circuit method to generate the equivalent circuit of the grid-type converter based on virtual internal impedance control; construct the equivalent voltage source model of the grid-type converter through virtual internal potential control parameters and the equivalent circuit.

[0060] like Figure 3As shown, the equivalent circuit method replaces the internal voltage and filter impedance of the network-connected converter by using a Thevenin network of virtual internal voltage in series with virtual internal impedance to construct an equivalent circuit of the network-connected 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 connection.

[0061] S3: According to the constraint condition one of the network-connected converter during grid-connected operation, calculate the constraint condition two of the virtual internal voltage control parameters of the equivalent voltage source model of the network-connected converter under different operating states.

[0062] Wherein, the constraint condition one of the network-connected converter during grid-connected operation includes:

[0063] Under normal operating conditions, the network-connected converter can output rated active power under unit power factor when the terminal voltage is rated voltage, and can realize the common output of rated active power and rated reactive power, that is, meet the maximum operating state.

[0064] When the three-level converter based on PWM control technology occurs over-modulation, it will cause the output voltage waveform to deviate significantly from the sinusoidal waveform, and a nonlinear voltage waveform will appear. This waveform distortion will increase the harmonic content of the output voltage, which will adversely affect the 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 easily oscillate and become unstable. Therefore, it is necessary to ensure that the network-connected converter does not occur over-modulation phenomenon.

[0065] The converter contains a large number of power electronic components such as thyristors, IGBTs, etc. Overcurrent will directly act on the internal components of the converter, interfere with the safe and stable operation of the converter, cause the output waveform of the system to distort, and thus affect the stability of the entire system. Therefore, it is necessary to ensure that the network-connected converter does not occur overcurrent phenomenon.

[0066] The steps of calculating the constraint condition two of the virtual internal voltage control parameters of the equivalent voltage source model of the network-connected converter under different operating states are as follows:

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

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

[0069] S33: Adjust the maximum output current I cmax of the grid-forming converter by phase jump, and estimate the most serious short-circuit fault of the system where the grid-forming converter is located to determine the electrical distance X k between the fault point and the grid-forming converter.

[0070] Considering phase jump, the method for adjusting the maximum output current I cmax of the grid-forming converter is as follows:

[0071] As shown in Figures 4-5 , a single grid-forming converter infinite system is constructed, the relationship between the voltage at the converter end and the infinite grid is found by the method of Thevenin equivalence, and the analysis of the change of the equivalent voltage amplitude of the grid coupled with phase jump is realized. As shown in Figure 5 , u s is the voltage at the converter end, e is the equivalent voltage of the grid, i is the output current of the converter, Z1 is the equivalent impedance between the infinite grid and the fault point, Z2 is the impedance between the outlet of the converter and the fault point, and Z f is the grounding impedance of the fault point, wherein Z1=R1+jX1, Z2=R2+jX2. E 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 the Thevenin equivalent voltage and the equivalent impedance are as follows:

[0073]

[0074] Where t r and t f are the times of fault occurrence and circuit recovery, respectively.

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

[0076]

[0077] The phase jump amount of the grid voltage phase at the time of short-circuit fault occurrence is :

[0078]

[0079] As can be seen from the above formula, when the impedance angle of the grounding impedance Z f and the system impedance Z1 is different, the phase of the voltage at the converter end will jump at the time of grid fault, and the jump amount is related to the fault point location, fault type, etc.

[0080] In the actual operation of the power grid, the topology and system parameters are diverse, which results in a variety of phase jumps of the converter terminal voltage after the short-circuit fault of the power grid. Here, the most serious case of phase jump is studied, i.e., the system impedance Z1 is considered as a pure inductive reactance, and the grounding impedance Z f of the fault point is considered as a pure resistance, i.e., R1 = 0 and X f = 0. Substituting the above into the formula, we can obtain:

[0081]

[0082] The grid-forming converter can have reactive power support capability because when the power grid is disturbed by voltage fluctuation, the grid-forming converter can be equivalent to a controllable voltage source, which maintains the internal potential E of the converter constant, i.e., it behaves as a constant voltage source when the grid voltage drops or rises. As shown in FIG. 1, when the power grid is short-circuited, the grid-forming converter responds to the voltage fluctuation of the power grid. Figure 6

[0083] After the short-circuit fault of the power grid, the expression of the output current I of the grid-forming converter is:

[0084]

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

[0086] According to the expression of the output current I of the grid-forming converter, the smaller the electrical distance X2 between the fault point and the outlet of the converter, the larger the current amplitude after the fault occurs, i.e., the amplitude of the output current I of the converter is the largest when the short-circuit fault occurs at the outlet of the converter. When the short-circuit fault occurs at the port of the grid-forming converter, the expression of the maximum output current I cmax of the grid-forming converter is as follows:

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

[0088] where X g represents the equivalent reactance of the system grid, X k represents the electrical distance between the short-circuit fault point and the outlet of the converter, X L represents the filter resistance of the grid-forming converter, R f represents the grounding resistance of the fault point.

[0089] In summary, first, according to the estimation of the severity of the short-circuit fault, the electrical distance X k between the fault point and the converter is set. Then, under the condition of determining the design parameters of the grid-forming converter and the equivalent impedance of the grid, the maximum output current I cmax of the grid-forming converter is obtained by traversing the possible short-circuit fault types, the modulation voltage size and the phase angle of the converter.

[0090] The maximum output current I cmax of the grid-forming converter needs to meet the following constraints:

[0091] I cmax <I max

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

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

[0094] For the low-voltage fault ride-through working condition of the grid, the voltage at the converter end is suddenly reduced due to short-circuit fault, and without considering the phase jump of the voltage, 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 , and the main constraint for the converter during three-phase short-circuit fault is to avoid overcurrent. The expression of the output current I of the converter is as follows:

[0095]

[0096] In the formula, X k is the equivalent short-circuit resistance between the short-circuit fault point and the outlet voltage of the grid-forming converter during three-phase short-circuit, I max is the maximum output current allowed by the design of the converter.

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

[0098]

[0099] Considering the phase jump, the maximum output current I cmaxThe following constraints must be met to make the adjustment:

[0100] I cmax max

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

[0102]

[0103] In summary, considering the impact of phase transitions 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 range of values ​​for:

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

[0105] For high-voltage fault ride-through conditions, considering that when AC power at the renewable energy sending end fails to commutate or DC power is blocked at the DC receiving end, a large amount of reactive power will be fed in, causing transient overvoltage problems at the converter terminals. In the event of the most severe overvoltage problem, the converter's virtual internal potential will reach its minimum value E under the proportional droop control. vmin First, the converter must prevent overcurrent. Considering normal steady-state operation, 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, as shown in the following expression:

[0106]

[0107] Under the constraint of the maximum power angle, and assuming that the converter terminal voltage points in the d-axis direction in the dq coordinate system, the following constraint can be derived to prevent overcurrent in the converter:

[0108]

[0109] Meanwhile, considering that the virtual internal potential amplitude and terminal voltage maximum value 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 its maximum value. At this time, the converter does not experience overmodulation due to the constraint condition:

[0110]

[0111] This allows us to obtain the minimum virtual internal potential E of the converter. vmin Constraints:

[0112]

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

[0114]

[0115] where V n represents the rated voltage of the converter terminal voltage, I cmax represents the maximum output current of the converter considering phase jump, V max represents the maximum voltage of the converter terminal voltage, 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 represents the maximum output current of the converter.

[0116] S4: Based on the constraint condition of the virtual internal potential control parameter, the value range of the virtual internal potential control parameter is scanned by Matlab software, and the solution space satisfying the above constraint condition is generated.

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

[0118] The embodiment proposes a grid-connected converter virtual internal potential control parameter setting method. This method aims to deal with the short-circuit fault that the grid-connected converter may encounter when connected to the grid. Phase jump may cause a sharp change in short-circuit current, which may pose a risk to the power system. Therefore, in the process of parameter selection, special consideration is given to the impact of such phase jump on the size of short-circuit current. By reasonably constraining the virtual internal potential control parameter, the overcurrent risk of the converter when connected to the grid can be effectively reduced, and the safe operation of the converter when facing grid faults can be ensured. At the same time, this method can also maximize the reactive power support capability of the grid-connected converter, supporting the stability of the grid. For the power electronic elements inside the converter, optimizing the parameter configuration not only helps to improve its tolerance, but also provides 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 under various grid fault conditions. This improvement will significantly promote the development of new energy grid-connected systems towards higher stability and reliability, providing necessary technical support for the construction of smart grids. In summary, this method not only solves the technical bottleneck faced by the current grid-connected converter when connected to the grid, but also contributes to enhancing the overall resilience of the power system.

[0120] Simulation verification:

[0121] The following will be combined Figure 7 ​The description provides a setting example of a network configuration type converter virtual internal potential control parameter setting method.

[0122] Firstly, according to the minimum short-circuit ratio required by the network configuration type converter to support the weak power grid, the converter system impedance demand X g = 1.0 p.u., the converter output rated active power P n = 1.0 p.u., the converter rated power factor The voltage limit value of the terminal voltage of the converter during the high-voltage and low-voltage fault crossing is set as V max = 1.3 p.u., V min = 0.3 p.u. X k of the most severe short-circuit fault is selected. k The larger X k , the more optimistic the estimation of the most severe short-circuit fault condition is, and X f = 0.15 p.u. is selected.

[0123] Considering the influence of phase jump on the converter output current demand, different short-circuit fault grounding resistances R cmax are traversed to obtain the maximum output current demand I v of the converter. As shown in FIG. 6, according to the operation constraint condition of the network configuration type converter, the value range of the virtual internal impedance X v and the virtual internal potential E v is scanned by using Matlab, and the feasible domain of the virtual internal potential control parameter E v and X v can be obtained as shown in FIG. 6. The network configuration type converter needs to have strong reactive power support capability in this embodiment 2, that is, when the virtual internal impedance X v takes the minimum value 0.215 p.u. in the feasible domain, according to the feasible domain, the value of the virtual internal potential E is 1.153 p.u.. In other embodiments, different functional characteristics of the network configuration type converter include power flow control capability, short-circuit fault crossing capability and dynamic response capability, and the optimal parameter combination of the virtual internal potential control parameter is obtained in the solution space according to different specific conditions.

[0124] The device embodiments described above are only schematic, wherein the units described as separate components can or can not be physically separate, and the components displayed as units can or can not be physical units, that is, they can be located in one place, or can be distributed on multiple network units. Part or all of the modules can be selected to achieve the purpose of the embodiment scheme according to actual needs. Those skilled in the art can understand and implement it without creative labor.

[0125] Those skilled in the art can clearly understand the technical solutions of the various embodiments from the above description of the embodiments, and the various embodiments can be implemented by means of software with the necessary general hardware platforms, and of course, can also be implemented by hardware. Based on such understanding, the above technical solutions, essentially or in other words, the part of the prior art that makes a contribution, can be embodied in the form of a software product, which can be stored in a computer readable storage medium, such as a ROM / RAM, a magnetic disk, an optical disk, and the like, and includes a number of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in the various embodiments 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 application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for some technical features therein; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for setting a virtual inner potential control parameter of a grid-forming converter, characterized in that, The method comprises the following steps: S1: determining a virtual internal voltage control parameter of the network-forming converter for amplitude control of a virtual internal voltage, the virtual internal voltage control parameter comprising a converter virtual internal voltage E v , a converter virtual internal voltage reactance X v , a converter maximum modulation voltage E max , and a converter maximum output current I max ; S2: generating an equivalent circuit of the grid-connected converter based on a virtual internal impedance control by using an equivalent circuit method; and constructing an equivalent voltage source model of the grid-connected converter by using the virtual internal potential control parameter and the equivalent circuit; S3: calculating constraint condition two of the virtual internal potential control parameter of the equivalent voltage source model of the grid-connected converter in different operating states according to constraint condition one of the grid-connected converter in a grid-connected operation; The constraint condition one comprises: (1) in a normal operating condition, the grid-connected converter can output a rated active power in a unit power factor when an end voltage is a rated voltage, and can realize a common output of the rated active power and a rated reactive power, i.e., satisfies a maximum operating state; (2) the grid-connected converter does not have an over-modulation phenomenon; and (3) the grid-connected converter does not have an over-current phenomenon; The calculation method of the constraint condition two comprises: S31: determining grid reactance X of the equivalent voltage source model of the network-type converter g , converter rated output active power P n , converter rated output reactive power Q n , converter rated power factor and converter internal reactance X c ; S32: setting a voltage limit value of the grid-connected converter according to an operating grid condition of the grid-connected converter; S33: using phase jump to adjust the maximum output current I of the network-forming converter cmax adjusting; estimating the most serious short-circuit fault of the system where the network-forming converter is located, and determining the electrical distance X between the fault point and the network-forming converter k ; S34: generating the constraint condition two according to a maximum modulation voltage of the converter; S4: performing parameter scanning on a value range of the virtual internal potential control parameter based on the constraint condition two, and generating a solution space satisfying the constraint condition two; S5: obtaining an optimal parameter combination of the virtual internal potential control parameter in the solution space according to different functional characteristics of the grid-connected converter.

2. The method of claim 1, wherein the method is a method of setting a virtual internal potential control parameter of a network-forming converter, characterized by, In step S2, the equivalent circuit method replaces the modulated voltage and filter impedance in the network type converter by using a virtual internal potential series virtual internal impedance Davine network to construct the equivalent circuit of the network type converter; the external parameters of the equivalent circuit include: converter modulated voltage E, transformer terminal voltage V, grid bus voltage U g , converter filter resistance X L and grid resistance X g ; the equivalent circuit behaves as a voltage source in external connection.

3. The method of claim 1, wherein the method is a method of setting a virtual internal potential control parameter of a networked converter, characterized in that, In step S33, the phase jump comprises: A single-machine infinite system of the grid-connected converter is constructed, a relationship between a converter end voltage and an infinite grid is found by using a Thevenin equivalent method, and a change coupling phase jump analysis of an equivalent voltage amplitude of the grid is realized.

4. The method of claim 1, wherein the method is a method of setting a virtual internal potential control parameter of a networked converter, characterized in that, In step S33, after a short-circuit fault occurs in the grid, an expression of an output current I of the grid-connected converter is: where E0and θ E0 respectively represent the steady-state amplitude and phase of the virtual internal potential E of the converter, U g0 and θ g0 represent the steady-state amplitude and phase of the bus voltage U g of the infinite grid, X1represents the equivalent reactance of the infinite grid, X2represents the electrical distance between the short-circuit fault point and the converter outlet, and X3represents the filter reactance of the grid-forming converter, R f represents the grounding resistance of the short-circuit fault point; When a short circuit fault occurs at the network-forming converter port, the maximum output current I of the network-forming converter cmax The expression of I is: I cmax = f(X g , X k , X L , R f ) where X g represents the system grid equivalent reactance, X k represents the electrical distance between the short-circuit fault point and the converter outlet, X L represents the filter resistance of the grid-forming converter, R f represents the grounding resistance of the fault point.

5. The method of claim 1, wherein the method is a method of setting a virtual internal potential control parameter of a networked converter, and the method further comprises: determining a virtual internal potential control parameter of the networked converter based on the voltage difference between the first voltage and the second voltage. In step S33, the network-forming converter maximum output current I cmax The following constraints need to be satisfied: I cmax <I max In the formula, I max represents the maximum output current of the converter.

6. The method of claim 4, wherein the method further comprises: In step S34, the expression of the constraint condition two comprises: Upper limit E of virtual internal potential of network-constituting converter vmax The value range of E is: E max ≤E vmax ≤(X k +X v )I cmax In the formula, E max is the maximum modulation voltage of the converter; Lower limit of virtual internal potential of network-forming converter E vmin The value range of E is: where I cmax denotes the maximum output current of the phase jump converter, V max denotes the maximum voltage of the transformer terminal voltage, denotes the power factor corresponding to the maximum power angle between the virtual internal potential and the terminal voltage of the network-forming converter, I max denotes the maximum output current of the converter.

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