Impedance remodeling method of grid-connected converter

Abstract

The invention discloses an impedance remodeling method for a grid-connected converter, and relates to the field of fire safety, and the method comprises the steps: respectively recording a virtual impedance transfer function and a virtual admittance transfer function into a current inner loop universal controller structure under a d / q coordinate system, and obtaining a series virtual impedance control structure and a parallel virtual admittance control structure; the series virtual impedance control structure and the parallel virtual admittance control structure are subjected to time domain and frequency domain conversion to obtain a series virtual impedance Norton equivalent circuit and a parallel virtual admittance Norton equivalent circuit respectively; based on the influence of virtual impedance and virtual admittance on the converter, multiple compensation links are added in a control framework of the grid-connected converter, so that the harmonic voltage and harmonic current of a grid-connected point are reduced, and the converter operates more stably.

Description

Technical Field

[0001] The present invention relates to the field of power supply control, and in particular to an impedance reshaping method for a grid-connected converter. Background Art

[0002] In the new power system dominated by renewable energy power generation, the stable transmission, safe grid connection and absorption capacity of large-scale onshore or offshore wind power generation face many difficulties and challenges, among which the power quality problem is the most prominent. Since the collection network of large offshore wind farms uses cable lines to collect electricity, the impedance network of the collection network is complex and changeable, and there is a risk of interaction with the impedance of wind turbines and thus high-frequency resonance. The harmonic currents generated by wind turbines are collected on the collection line and penetrate into the system. The inherent spectrum characteristics of the collection line will produce series / parallel resonance phenomena for specific harmonics, further amplifying the harmonic voltage / harmonic current, resulting in the harmonic voltage / harmonic current content rate exceeding the standard.

[0003] Harmonic problems are essentially caused by power network resonance. To suppress harmonics and improve power quality, the patent "A Control Method for Series Virtual Impedance in Grid-Connected Converters" (Patent No.: 201810801843.X) discloses a method for series virtual impedance in grid-connected converters for virtual inertia control. While this method achieves the control objectives of increasing system damping, suppressing DC voltage oscillations, and ensuring voltage quality during steady-state operation, the strategy ignores the impact of other links in the control loop on impedance. Furthermore, the circuit state and control framework are not perfect, resulting in low design accuracy for virtual impedance or virtual admittance, difficulty in parameter adjustment, and difficulty meeting practical application requirements. Summary of the Invention

[0004] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract of the specification and the title of the invention of this application to avoid blurring the purpose of this section, the abstract of the specification and the title of the invention, and such simplifications or omissions cannot be used to limit the scope of the invention.

[0005] In view of the fact that the above-mentioned and / or existing technologies exist in which the control objectives of increasing system damping, suppressing DC voltage oscillations and ensuring voltage quality during steady-state operation are used to offset the impact of harmonics on the converter, this strategy ignores the impact of other links in most control loops on impedance, and the circuit state and control framework are not perfect, resulting in low design accuracy of virtual impedance or virtual admittance, difficulty in parameter adjustment, and difficulty in meeting actual application requirements, the present invention is proposed.

[0006] Therefore, the technical problem to be solved by the present invention is to consider and add the influence of multiple unmentioned links on virtual impedance or virtual admittance in the entire power system converter control framework, thereby enhancing the measurement accuracy of the grid-connected converter, improving the operation stability, and reducing the difficulty of parameter adjustment.

[0007] To solve the above technical problems, the present invention provides the following technical solutions: a method for impedance reshaping of a grid-connected converter, comprising: respectively recording a virtual impedance transfer function and a virtual admittance transfer function into a current inner loop universal controller structure in a d / q coordinate system to derive a series virtual impedance control structure and a parallel virtual admittance control structure;

[0008] The series virtual impedance control structure and the parallel virtual admittance control structure are converted into time domain and frequency domain to obtain a series virtual impedance Norton equivalent circuit and a parallel virtual admittance Norton equivalent circuit respectively;

[0009] As a preferred solution of the impedance reshaping method of a grid-connected converter described in the present invention, wherein: the series virtual impedance Norton equivalent circuit indirectly adjusts the impedance characteristics of the power system by changing the internal impedance characteristics of the grid-connected converter, thereby improving the signal stability of the grid connection point;

[0010] The parallel virtual admittance Norton equivalent circuit directly adjusts the impedance characteristics of the power system by changing the impedance characteristics of the grid-connected converter port, thereby improving the signal stability of the grid-connected point.

[0011] As a preferred solution of the impedance reshaping method of a grid-connected converter described in the present invention, the virtual impedance transfer function is:

[0012]

[0013] The virtual impedance transfer function is composed of a virtual RLC parallel equivalent branch and a first compensation link;

[0014] The virtual impedance transfer function represents a virtual RLC parallel equivalent branch;

[0015] Wherein: Rv1, Lv1 and Cv1 represent the series virtual resistance, series virtual inductance and series virtual capacitance in the series virtual impedance Norton equivalent circuit respectively, and s is the independent variable.

[0016] As a preferred solution of the impedance reshaping method of a grid-connected converter described in the present invention, wherein: It represents the first compensation link, and its frequency domain expression is as follows:

[0017]

[0018] Among them: Gde (s) is the control link delay link.

[0019] As a preferred solution of the impedance reshaping method of a grid-connected converter described in the present invention, the virtual admittance transfer function is:

[0020]

[0021] The virtual admittance transfer function is composed of a virtual RLC series equivalent branch and a second compensation link;

[0022] The virtual admittance transfer function Represents a virtual RLC series equivalent branch;

[0023] Where: R v2 , L v2 and C v2 They represent the parallel virtual resistance, parallel virtual inductance, and parallel virtual capacitance in the parallel virtual admittance Norton equivalent circuit respectively.

[0024] As a preferred solution of the impedance reshaping method of a grid-connected converter described in the present invention, wherein: represents the second compensation link, and its frequency domain expression is as follows:

[0025]

[0026] Among them: G i (s) is the current control link, and L is the connection inductance between the grid-connected converter and the power system.

[0027] As a preferred solution of the impedance reshaping method of a grid-connected converter described in the present invention, wherein: the current inner loop universal controller structure in the d / q coordinate system includes:

[0028] d-axis current command value i d * , q-axis current command value i q * ;

[0029] d-axis current feedback value i d , q-axis current feedback value i q ;

[0030] d-axis control voltage v d , q-axis control voltage v q ;

[0031] Grid connection point d-axis voltage u sd , grid connection point q-axis voltage u sq ;

[0032] Feedforward link Gf (s), d-axis voltage feed-forward term u sdf ; q-axis voltage feed-forward term u sqf ;

[0033] d-axis current i d , q-axis current i q , decoupling coefficient X L ;

[0034] d-axis voltage command value v d * , q-axis voltage command value v q * .

[0035] As a preferred scheme of the impedance reshaping method of the grid-connected converter of the present application, wherein: the d-axis current command value i d * is subtracted by the d-axis current feedback value i d , and the difference is multiplied by the current control element to obtain the d-axis control voltage v d ;

[0036] the q-axis current command value i q * is subtracted by the d-axis current feedback value i q , and the difference is multiplied by the current control element to obtain the q-axis control voltage v q ;

[0037] the grid point d-axis voltage u sd is multiplied by the feed-forward element G f (s) to obtain the d-axis voltage feed-forward term u sdf ;

[0038] the grid point q-axis voltage u sq is multiplied by the feed-forward element G f (s) to obtain the q-axis voltage feed-forward term u sqf ;

[0039] the q-axis current i q is multiplied by the decoupling coefficient X L to obtain the d-axis current decoupling term;

[0040] the d-axis current i d is multiplied by the decoupling coefficient X L to obtain the q-axis current decoupling term.

[0041] As a preferred scheme of the impedance reshaping method of the grid-connected converter of the present application, wherein: the d-axis control voltage v d + the d-axis voltage feed-forward term u sdf - the d-axis virtual voltage u dv- The d-axis current decoupling term = d-axis voltage command value v d * ;

[0042] The q-axis control voltage v q + the q-axis voltage feedforward term u sqf - the q-axis virtual voltage u qv - The q-axis current decoupling term = q-axis voltage command value v q * .

[0043] As a preferred solution of the impedance reshaping method of the grid-connected converter described in the present invention, wherein: in the series virtual impedance Norton equivalent circuit, when L v1 →∞,C v1 =0, and satisfy R v1 When >0, the virtual impedance transfer function is:

[0044]

[0045] Substituting the above formula into the series virtual impedance control structure, the series virtual resistor Norton equivalent circuit is obtained.

[0046] As a preferred solution of the impedance reshaping method of the grid-connected converter described in the present invention, wherein: in the parallel virtual admittance Norton equivalent circuit, when L v2 =0, C v2 →∞, while satisfying R v1 When >0, the virtual admittance transfer function is:

[0047]

[0048] Substituting the above formula into the parallel virtual admittance control structure, a parallel virtual conductance Norton equivalent circuit is obtained.

[0049] The beneficial effects of the present invention are as follows: based on the influence of virtual impedance and virtual admittance on the converter, multiple compensation links are added to the control framework of the grid-connected converter, so that the harmonic voltage and harmonic current at the grid-connected point are reduced, and the converter operation is more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0051] Figure 1A schematic structural diagram of a series virtual impedance control block diagram of an impedance reshaping method for a grid-connected converter according to an embodiment of the present invention;

[0052] Figure 2 A schematic structural diagram of a parallel virtual admittance control block diagram of an impedance reshaping method for a grid-connected converter according to an embodiment of the present invention;

[0053] Figure 3 A schematic diagram of a series virtual impedance Norton equivalent circuit structure of an impedance reshaping method for a grid-connected converter according to an embodiment of the present invention;

[0054] Figure 4 A schematic diagram of a parallel virtual admittance Norton equivalent circuit structure of an impedance reshaping method for a grid-connected converter according to an embodiment of the present invention;

[0055] Figure 5 A schematic diagram of a Norton equivalent circuit structure of a series virtual resistor for an impedance reshaping method for a grid-connected converter according to an embodiment of the present invention;

[0056] Figure 6 A schematic diagram of a parallel virtual conductance Norton equivalent circuit structure of an impedance reshaping method for a grid-connected converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0058] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0059] Next, the present invention is described in detail with reference to schematic diagrams. For ease of illustration, when describing embodiments of the present invention, cross-sectional views illustrating device structures may be partially enlarged and not to scale. Furthermore, these schematic diagrams are merely illustrative and should not limit the scope of protection of the present invention. Furthermore, in actual production, three-dimensional dimensions, including length, width, and depth, should be included.

[0060] Furthermore, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0061] Example 1

[0062] Reference Figure 1 This embodiment provides an impedance reshaping method for a grid-connected converter, including incorporating a virtual impedance transfer function and a virtual admittance transfer function into a current inner-loop universal controller structure in a d / q coordinate system. The d / q coordinate system is a commonly used mathematical model for circuit calculations. Based on this model, a large number of complex calculations in power structures can be simplified. Based on the d / q coordinate system, a series virtual impedance control structure and a parallel virtual admittance control structure are derived.

[0063] Furthermore, the series virtual impedance control structure is to make the virtual impedance Z v A general control block diagram that takes into account each control link is added. In addition to the virtual impedance, multiple compensation links are added to neutralize the effects of other links in the control loop that are ignored in the existing technology, including the current decoupling term, the voltage feedforward term, and the control link demonstration link. These parts are combined into a transfer function through calculation and the virtual impedance Z is added. v The transfer function forms a virtual impedance Z v The reshape expression of Figure 1 Z in v (s);

[0064] The parallel virtual admittance control structure and the series virtual impedance control structure are similar. The compensation link calculation in the parallel state is combined into a transfer function, and then the virtual admittance Y is added. v The transfer function forms the reshaped expression of the virtual admittance Y v (s).

[0065] Furthermore, Z v (s) The series virtual impedance control structure formed after the addition of Y v (s) After the addition of the parallel virtual admittance control structure, the series virtual impedance Norton equivalent circuit and the parallel virtual admittance Norton equivalent circuit can be obtained through time-domain and frequency-domain conversion calculations respectively;

[0066] In detail, the series virtual impedance Norton equivalent circuit indirectly adjusts the power system impedance characteristics by changing the internal impedance characteristics of the grid-connected converter, because the series virtual impedance Norton equivalent short circuit obtained by the time domain and frequency domain conversion results shows that the position of the virtual impedance in the circuit diagram is consistent with Z o2 In series with the entire grid-connected converter, the principle port voltage u s That is to say, when the converter has internal problems, the virtual impedance will adjust the impedance characteristics of the converter, and then change the impedance characteristics of the entire power grid system through the output of the converter, thereby improving the signal stability of the grid connection point. This part can be based on Figure 3 or Figure 5a clearer understanding;

[0067] Furthermore, the parallel virtual admittance Norton equivalent circuit directly adjusts the power system impedance characteristics by changing the impedance characteristics of the grid-connected converter port, which is different from the virtual impedance in the series virtual impedance Norton equivalent circuit, thereby improving the signal stability of the grid connection point.

[0068] Example 2

[0069] Reference Figure 5 , which is the second embodiment of the present invention, is based on the previous embodiment, and differs from the previous embodiment in that the virtual impedance transfer function is:

[0070]

[0071] Furthermore, the virtual impedance transfer function consists of a virtual RLC parallel equivalent branch and the first compensation link. The combination of the two corrects the virtual impedance in the grid-connected converter. The former can be understood as the frequency domain expression of the virtual impedance in the uncorrected state. This value needs to be corrected by multiple compensation links to ignore the impact of harmonics and their derivatives. The latter is the time domain expression of the compensation link.

[0072] In detail, the virtual impedance transfer function Represents a virtual RLC parallel equivalent branch, that is, the RLC parallel equivalent branch can be understood as R v1 , L v1 and C v1 Frequency domain expression of ;

[0073] Where: R v1 , L v1 and C v1 They represent the series virtual resistance, series virtual inductance and series virtual capacitance in the series virtual impedance Norton equivalent circuit respectively. s is the independent variable. Resistance, inductance and capacitance are all constants under specific conditions. By adjusting these constants, the independent variable s can be changed, thereby determining the impedance.

[0074] Furthermore, in the virtual impedance transfer function It represents the first compensation link, and its frequency domain expression is as follows:

[0075]

[0076] Among them: G de(s) is the control link delay link, which is also a process of converting the compensation link from the time domain to the frequency domain, facilitating the correction of the RLC parallel equivalent branch in the frequency domain. At the same time, the control link delay link can be directly understood as the time transfer function of the time spent on the movement of the electrical signal in the frequency domain. This part has an interference effect on the virtual impedance. The expression that neutralizes this influence value is the above expression.

[0077] Example 3

[0078] Reference Figure 5 , which is the third embodiment of the present invention, is based on the previous embodiment, and differs from the previous embodiment in that the virtual admittance transfer function is:

[0079]

[0080] Furthermore, the virtual admittance transfer function is composed of a virtual RLC series equivalent branch and a second compensation link. Similar to the virtual impedance transfer function, the former is the frequency domain expression of the admittance before correction, and the latter is the time domain expression of the compensation link for the virtual admittance in the parallel state.

[0081] In detail, the virtual admittance transfer function Represents a virtual RLC series equivalent branch. Similarly, the RLC parallel equivalent branch can be understood as R v2 , L v2 and C v2 Frequency domain expression of ;

[0082] Where: R v2 , L v2 and C v2 They represent the parallel virtual resistance, parallel virtual inductance, and parallel virtual capacitance in the parallel virtual admittance Norton equivalent circuit respectively.

[0083] Virtual impedance transfer function It represents the second compensation link, and its frequency domain expression is as follows:

[0084]

[0085] Among them: G i (s) is the current control link, representing a current closed-loop control transfer function, and L is the connection inductance between the grid-connected converter and the power system.

[0086] Example 4

[0087] Reference Figure 5 , which is the third embodiment of the present invention. This embodiment is based on the previous embodiment and differs from the previous embodiment in that: the d-axis current command value i d *and q-axis current command value i q * Equivalent to the input current command, it serves as the starting point in the control structure;

[0088] Detailed, d-axis current feedback value i d , q-axis current feedback value i q Following the feedback values ​​of the d-axis and q-axis, the command value minus the feedback value multiplied by the current closed-loop control transfer function is used to obtain the control voltage of the d-axis and q-axis, i.e., v q and v d , v q and v d Equivalent to the lead of the voltage input without any adjustment.

[0089] Detailed, grid connection point d-axis voltage u sd , grid connection point q-axis voltage u sq , and the current command value is the same as the input command, in the frequency domain state through the G f (s), that is, multiplying the feedforward link transfer function to obtain the voltage feedforward term u of the d-axis and q-axis sdf and u sqf , a feedforward term needs to be added to the calculation to cancel the bias.

[0090] In detail, the d-axis current i d is the current advance occurring on the d-axis, and the q-axis current i q Similarly, it is the current advance occurring in the q axis, and the decoupling coefficient X L It can be understood as a conversion coefficient for the d-axis and q-axis currents. The d-axis current decoupling term and the q-axis current decoupling term formed by multiplying the two can be understood as a constant used to release the structural coupling of the d-axis and q-axis.

[0091] Furthermore, the d-axis voltage command value v d * , q-axis voltage command value v q * They are the accurate values ​​of the voltage control quantities occurring on the d-axis and q-axis respectively, and the two are formed by combining the above calculation results.

[0092] In detail, the d-axis control voltage v d +d-axis voltage feedforward term u sdf -d-axis virtual voltage u dv -d-axis current decoupling term = d-axis voltage command value v d * ;

[0093] In detail, the q-axis control voltage v q +q-axis voltage feedforward term u sqf -q-axis virtual voltage u qv-q-axis current decoupling term =q-axis voltage command value v q * ;

[0094] Furthermore, the voltage command values ​​of the two axes are respectively related to the control link delay link transfer function G de (s) are multiplied, and after passing through the modulation link, it acts on the actual circuit composed of the resistor R and the inductor L in series.

[0095] Example 6

[0096] Reference Figure 5 , which is the third embodiment of the present invention, is based on the previous embodiment and differs from the previous embodiment in that: in the series virtual impedance Norton equivalent circuit, when L v1 →∞,C v1 =0, and satisfy R v1 When θ > 0, in the series virtual impedance Norton equivalent circuit, the virtual impedance part becomes a pure resistor, which is the simplest form of the virtual impedance expression and also an optimal solution. In this state, the virtual impedance transfer function is:

[0097]

[0098] Substituting the above formula into the series virtual impedance control structure, we can obtain the Norton equivalent circuit of the series virtual resistor, which is the simplest model of the virtual resistor in the series state.

[0099] Example 7

[0100] Reference Figure 5 , which is the third embodiment of the present invention, is based on the previous embodiment and differs from the previous embodiment in that: in the parallel virtual admittance Norton equivalent circuit, when L v2 =0, C v2 →∞, while satisfying R v1 When >0, similarly, the virtual admittance forms the simplest model, and the virtual admittance transfer function is:

[0101]

[0102] Substituting the above formula into the parallel virtual admittance control structure, the parallel virtual conductance Norton equivalent circuit is obtained.

[0103] It is important to note that the construction and arrangement of the present application shown in a number of different exemplary embodiments are merely illustrative. Although only a few embodiments are described in detail in this disclosure, it should be readily understood by those who refer to this disclosure that many modifications are possible (e.g., the size, scale, structure, shape and proportion of various elements, as well as parameter values ​​(e.g., temperature, pressure, etc.), mounting arrangements, use of materials, color, directional changes, etc.) without departing substantially from the novel teachings and advantages of the subject matter described in this application. For example, an element shown as integrally formed may be composed of multiple parts or elements, the position of the element may be inverted or otherwise changed, and the nature or number or position of the discrete elements may be altered or changed. Therefore, all such modifications are intended to be included within the scope of the present invention. The order or sequence of any process or method steps may be changed or reordered according to alternative embodiments. In the claims, any "means plus function" clause is intended to cover the structure described herein that performs the function, and is not only structurally equivalent but also equivalent structures. Other replacements, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the exemplary embodiments without departing from the scope of the present invention. Therefore, the invention is not limited to the specific embodiments, but extends to various modifications that still fall within the scope of the appended claims.

[0104] Additionally, in order to provide a concise description of exemplary embodiments, all features of an actual embodiment (ie, those features that are not relevant to the best mode presently contemplated for carrying out the invention or those that are not relevant to implementing the invention) may not be described.

[0105] It will be appreciated that in the development of any actual embodiment, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but will, for those of ordinary skill having the benefit of this disclosure, be a routine undertaking of design, fabrication, and production without undue experimentation.

[0106] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for reshaping the impedance of a grid-connected converter, characterized by: include, The virtual impedance transfer function and the virtual admittance transfer function are recorded in the current inner loop universal controller structure in the d / q coordinate system, respectively, to obtain the series virtual impedance control structure and the parallel virtual admittance control structure; The series virtual impedance control structure and the parallel virtual admittance control structure respectively derive a series virtual impedance Norton equivalent circuit and a parallel virtual admittance Norton equivalent circuit through time domain and frequency domain conversion.

2. The impedance reshaping method of a grid-connected converter according to claim 1, characterized in that: The series virtual impedance Norton equivalent circuit indirectly adjusts the impedance characteristics of the power system by changing the internal impedance characteristics of the grid-connected converter, thereby improving the signal stability of the grid-connected point; The parallel virtual admittance Norton equivalent circuit directly adjusts the impedance characteristics of the power system by changing the impedance characteristics of the grid-connected converter port, thereby improving the signal stability of the grid-connected point.

3. The impedance reshaping method of a grid-connected converter according to claim 1, characterized in that: The virtual impedance transfer function is: The virtual impedance transfer function is composed of a virtual RLC parallel equivalent branch and a first compensation link; The virtual impedance transfer function represents a virtual RLC parallel equivalent branch; Where: Z v (s) is the virtual impedance, R v1 , L v1 and C v1 They represent the series virtual resistance, series virtual inductance and series virtual capacitance in the series virtual impedance Norton equivalent circuit respectively, and s is the independent variable.

4. The impedance reshaping method of a grid-connected converter according to claim 2, wherein: The virtual impedance transfer function The expression for the first compensation link, which transforms the time domain state into the frequency domain state, is as follows: Among them: G de (s) is the control link delay link, is the frequency domain expression of the control link delay link.

5. The impedance reshaping method of a grid-connected converter according to claim 1 or 3, characterized in that: The virtual admittance transfer function is: The virtual admittance transfer function is composed of a virtual RLC series equivalent branch and a second compensation link; The virtual admittance transfer function Represents a virtual RLC series equivalent branch; Where: R v2 , L v2 and C v2 They represent the parallel virtual resistance, parallel virtual inductance, and parallel virtual capacitance in the parallel virtual admittance Norton equivalent circuit respectively.

6. The impedance reshaping method of a grid-connected converter according to claim 4, characterized in that: The virtual impedance transfer function represents the second compensation link, and its frequency domain expression is as follows: Among them: G i (s) is the current control link, and L is the connection inductance between the grid-connected converter and the power system.

7. The impedance reshaping method of a grid-connected converter according to claim 5, characterized in that: The current inner loop universal controller structure in the d / q coordinate system includes: As input value: d-axis current command value i d * , q-axis current command value i q * ; As the tracking value: d-axis current feedback value i d , q-axis current feedback value i q ; As the advance amount: d-axis control voltage v d , q-axis control voltage v q ; As compensation advance: grid connection point d-axis voltage u sd , grid connection point q-axis voltage u sq ; Feedforward link G f (s) is the feedforward transfer function; As an additional value: d-axis voltage feedforward term u sdf ; q-axis voltage feedforward term u sqf ; d-axis current i d , q-axis current i q , decoupling coefficient X L is a constant; As an accurate value: d-axis voltage command value v d * , q-axis voltage command value v q * .

8. The impedance reshaping method of a grid-connected converter according to claim 5, characterized in that: The d-axis current command value i d * Subtract the d-axis current feedback value i d The difference is multiplied by the current control link to obtain the d-axis control voltage v d ; The q-axis current command value i q * Subtract the d-axis current feedback value i q The difference is multiplied by the current control link to obtain the q-axis control voltage v q ; The d-axis voltage u at the grid connection point sd With the feedforward link G f (s) is multiplied to obtain the d-axis voltage feedforward term u sdf ; The grid-connected point q-axis voltage u sq With the feedforward link G f (s) is multiplied to obtain the q-axis voltage feedforward term u sqf ; The q-axis current i q Multiply by the decoupling coefficient X L Get the d-axis current decoupling term; The d-axis current i d Multiply by the decoupling coefficient X L The q-axis current decoupling term is obtained.

9. The impedance reshaping method of a grid-connected converter according to claim 6, characterized in that: The d-axis control voltage v d + the d-axis voltage feedforward term u sdf - the d-axis virtual voltage u dv - The d-axis current decoupling term = d-axis voltage command value v d * ; The q-axis control voltage v q + the q-axis voltage feedforward term u sqf - the q-axis virtual voltage u qv - The q-axis current decoupling term = q-axis voltage command value v q * .

10. The impedance reshaping method of a grid-connected converter according to claim 7, characterized in that: In the series virtual impedance Norton equivalent circuit, when L v1 →∞,C v1 =0, and satisfy R v1 When >0, the virtual impedance transfer function is: Substituting the above formula into the series virtual impedance control structure, the series virtual resistor Norton equivalent circuit is obtained; In the parallel virtual admittance Norton equivalent circuit, when L v2 =0, C v2 →∞, while satisfying R v1 When >0, the virtual admittance transfer function is: Substituting the above formula into the parallel virtual admittance control structure, a parallel virtual conductance Norton equivalent circuit is obtained.

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