Sequence impedance modeling method and device for a network-forming converter

Abstract

The present invention discloses a method and device for sequence impedance modeling of a network-forming converter, belonging to the technical field of power system control. The method includes: adding voltage disturbances to the AC port and DC port in the equivalent two-port network of the network-forming converter to be analyzed and modeled; performing frequency coupling analysis on the non-linear circuit under the current response of the voltage disturbance to model the initial transfer function of the sequence impedance model corresponding to each frequency coupling component, fully considering the interaction between network-forming converters, revealing the frequency coupling law of the converter, and improving the accuracy of the sequence impedance model; using the control equation of the network-forming control loop model corresponding to the control loop sequence impedance to remove the zero-sequence component in the circuit equation of the non-linear circuit to obtain a modified sequence impedance circuit equation, which can reduce the complexity of modeling calculation; using the modified sequence impedance circuit equation to modify the initial transfer function of each sequence impedance model to accurately perform linearized modeling of the sequence impedance of the network-forming converter.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system control, and more specifically, relates to a method and device for sequence impedance modeling of a grid-forming converter. Background Art

[0002] At present, most of the new energy controls connected to the power grid adopt grid-following (GFL) control, which needs to rely on traditional synchronous generators to provide a stable voltage source and is difficult to adapt to the future power grid scenarios with a high proportion of new energy incorporated into the power grid. While using a grid-forming (GFM) converter for new energy control connected to the power grid can achieve the operation support of the power grid. That is, in the face of the trend of new energy grid connection, it is necessary to conduct a detailed frequency-domain modeling of the grid-forming converter, so as to realize the excavation of the characteristics of the grid-forming converter and help the stable operation of renewable energy in the full frequency band.

[0003] Existing modeling methods are divided into modeling methods under dq axes and sequence impedance modeling methods. The modeling method based on dq axes originates from the frequency-domain modeling of small-capacity systems, and the modeling accuracy is difficult to meet the requirements in the low-frequency band below 100 Hz in the frequency domain; furthermore, it is difficult to consider the influence of frequency coupling effect and the influence of DC-side coupling terms. In addition, in the stable analysis and control of large systems, it is very difficult to realize the stability analysis of multiple machines based on the modeling method under dq axes, and the phase angles under multiple machines are difficult to directly determine, which restricts the application scope of the modeling method under dq axes. The sequence impedance-based modeling method can be extended to more converter scenarios because of its modeling under the stationary coordinate system, and it has an important application scenario in the future stable analysis of large-scale new energy grid connection; however, the detailed modeling process of the grid-forming converter has not been considered at present, and more specifically, the small-signal modeling of the grid-forming converter has not been carried out from the perspective of considering frequency coupling and DC feedback. Moreover, the sequence impedance modeling does not consider the advantages of admittance, and it is difficult to directly characterize the equivalent circuit relationship of the converter, making the steps and processes in the stable analysis more complex.

[0004] In summary, traditional modeling methods are difficult to directly perform linearized modeling of grid-forming converters with low computational complexity and high accuracy. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement requirements of the prior art, the present invention provides a method and device for sequence impedance modeling of a grid-forming converter, and its purpose is to solve the technical problem that traditional modeling methods are difficult to directly perform linearized modeling of grid-forming converters with low computational complexity and high accuracy.

[0006] To achieve the above object, according to one aspect of the present invention, a method for sequence impedance modeling of a grid-forming converter is provided, including:

[0007] S1: Equivalent the network-forming converter to be analyzed and modeled at both ports to obtain the two-port network of the network-forming converter to be analyzed and modeled; the two-port network includes: a control loop, a non-linear circuit, an AC port, and a DC port; apply voltage perturbations to the AC port and the DC port;

[0008] S2: Perform sequence impedance modeling on the control loop under the current response of the voltage perturbation to obtain a network-forming control loop model;

[0009] S3: Conduct frequency coupling analysis on the non-linear circuit under the current response of the voltage perturbation to obtain multiple frequency coupling components; use the method of harmonic linearization to model the initial transfer function of the sequence impedance model corresponding to each frequency coupling component;

[0010] S4: Simultaneously solve the circuit equation of the non-linear circuit and the control equation of the network-forming control loop model to remove the zero-sequence component in the circuit equation of the non-linear circuit and obtain a modified sequence impedance circuit equation;

[0011] S5: Use the modified sequence impedance circuit equation to correct the initial transfer function of the sequence impedance model corresponding to each frequency coupling component to obtain the modified transfer function of the sequence impedance model corresponding to each frequency coupling component.

[0012] In one embodiment, the virtual synchronous control loop in the network-forming control loop model is expressed as:

[0013]

[0014] where, is the phase angle in the frequency domain, J is the inertia coefficient of the virtual synchronous control loop, D p is the damping coefficient of the virtual synchronous control loop, is the voltage perturbation applied to the AC port, is the current perturbation after the voltage perturbation applied to the AC port, ω0 is the initial rotational angular velocity, ω1 is the fundamental frequency, U1 * 、I1 * are the conjugates of the initial phasors of voltage and current respectively.

[0015] In one embodiment, the method of using harmonic linearization to model the initial transfer function of the sequence impedance model corresponding to each frequency coupling component includes:

[0016] Use the formula to model the initial transfer function of the sequence impedance model corresponding to each frequency coupling component;

[0017] where, x(t) is the time-domain value of the x variable, y(t) is the time-domain value of the y variable, is the steady-state value at the steady-state operating point of the x variable, is the superimposed small-signal value under a small perturbation of the x variable, is the steady-state value at the steady-state operating point of the y variable, is the superimposed small-signal value under a small perturbation of the y variable, is the small-signal value after harmonic linearization of Z(t), is the superimposed small-signal value under a small perturbation of the y variable, Y l is the steady-state value at the steady-state operating point of the y variable, where l is used to represent the number of components of the y variable itself X k is the steady-state value at the steady-state operating point of the variable, is the superimposed small-signal value under a small perturbation of the variable, where k is used to represent the number of components of the x variable itself; ω p is the perturbation frequency, ω1 is the fundamental frequency, X k is the k-th harmonic component of the x variable, Y k is the k-th harmonic component of Y.

[0018] In one embodiment, when a positive-sequence voltage perturbation is applied to the AC port, the initial transfer function of the sequence admittance model corresponding to each frequency coupling component is:

[0019]

[0020] where, Y pp (s) is the positive-sequence response self-admittance under positive-sequence voltage perturbation, Y pd (s) is the AC-DC coupling admittance of the DC response under positive-sequence voltage perturbation, Y pn (s) is the negative-sequence response AC transfer admittance under positive-sequence voltage perturbation; is the response current of the AC port, is the voltage perturbation of the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0021] In one embodiment, when a negative-sequence voltage perturbation is applied to the AC port, the initial transfer function of the sequence admittance model corresponding to each frequency coupling component is:

[0022]

[0023] where, Y nn (s) is the positive-sequence response self-admittance under negative-sequence voltage perturbation, Y nd (s) is the AC-DC coupling admittance of the DC response under negative-sequence voltage perturbation, Y np(s) is the negative-sequence response AC transfer admittance under negative-sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance of the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0024] In one embodiment, when a DC voltage disturbance is applied to the DC port, the initial transfer function of the sequence admittance model corresponding to each frequency coupling component is:

[0025]

[0026] where, Y dd (s) is the DC response self-admittance under DC disturbance, Y dp (s) is the AC-DC coupling admittance of the positive-sequence response of the AC under DC disturbance, Y pn (s) is the AC transfer admittance of the negative-sequence response of the AC under DC disturbance; is the response current of the AC port, is the voltage disturbance of the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0027] In one embodiment, the modified transfer function of the sequence admittance model corresponding to each frequency coupling component is expressed as:

[0028]

[0029] where, L is the AC inductor, K d is the feedback coefficient of the current inner loop, V dc is the DC voltage value, ω1 is the fundamental frequency, is the transfer function of the current inner loop, M(s - jω1) is the closed-loop transfer function of the virtual synchronous control loop, M 1 is the fundamental frequency parameter of the modulation signal, I 1 is the parameter of the current fundamental frequency, is I the conjugate of 1, is the fundamental voltage U the conjugate of 1, ω0 is the frequency base value, is the response current of the AC port, is the voltage disturbance of the AC port.

[0030] In one embodiment, after S5, it further includes: equivalenting the feedback loop of the DC port to the admittance of the DC port, and feeding back the admittance of the DC port to the correction transfer function of the sequence admittance model corresponding to each frequency coupling component to obtain the target transfer function of the sequence admittance model corresponding to each frequency coupling component.

[0031] In one embodiment, the target transfer function of the sequence admittance model corresponding to each frequency coupling component is expressed as:

[0032]

[0033] Y an (s) is the negative-sequence coupling response admittance under positive-sequence voltage perturbation, Y nn (s) is the positive-sequence response self-admittance under negative-sequence voltage perturbation, Y nd (s) is the AC-DC coupling admittance of the DC response under negative-sequence voltage perturbation, Y dn (s +1 ) is the negative-sequence AC-DC coupling admittance under DC voltage perturbation, Z dc (s +1 ) is the self-impedance after applying voltage perturbation to the DC port, Y dd (s +1 ) is the self-admittance after applying voltage perturbation to the DC port, Y cn (s) is the admittance at the coupling frequency under negative-sequence voltage perturbation, Y np (s) is the positive-sequence coupling admittance under negative-sequence voltage perturbation, Y dp (s +1 ) is the positive-sequence AC-DC coupling admittance under voltage perturbation applied to the DC port According to another aspect of the present invention, there is provided a sequence admittance modeling device for a network-forming converter, including:

[0034] A perturbation module, configured to equivalent the network-forming converter to be analyzed and modeled into a two-port network to obtain the two-port network of the network-forming converter to be analyzed and modeled; the two-port network includes: a control loop, a non-linear circuit, an AC port, and a DC port; voltage perturbations are added to the AC port and the DC port;

[0035] A first modeling module, configured to perform sequence admittance modeling on the control loop under the current response of the voltage perturbation to obtain a network-forming control loop model;

[0036] A second modeling module, configured to perform frequency coupling analysis on the non-linear circuit under the current response of the voltage perturbation to obtain a plurality of frequency coupling components; the initial transfer function of the sequence admittance model corresponding to each frequency coupling component is modeled by using the harmonic linearization method;

[0037] A first correction module is used to combine the circuit equation of the nonlinear circuit and the control equation of the meshed control loop model to remove the zero-sequence component in the circuit equation of the nonlinear circuit to obtain a corrected sequence impedance circuit equation;

[0038] The second correction module is used to correct the initial transfer function of the sequence immittance model corresponding to each frequency coupling component by using the corrected sequence immittance circuit equation to obtain the corrected transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0039] According to another aspect of the present invention, an electronic device is provided, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0040] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the above method are implemented.

[0041] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0042] (1) The present invention provides a method for modeling the sequence impedance of a grid-type converter, which comprises the following steps: performing two-port equivalent on the grid-type converter to be analyzed and modeled to obtain a two-port network, and adding voltage disturbance to the AC port and the DC port in the two-port network; performing sequence impedance modeling on the control loop under the current response of the voltage disturbance to obtain a grid-type control loop model; performing frequency coupling analysis on the nonlinear circuit under the current response of the voltage disturbance to model the initial transfer function of the sequence impedance model corresponding to each frequency coupling component, fully considering the interaction between the grid-type converters, revealing the frequency coupling law of the converter, and improving the accuracy of the sequence impedance model; using the control equation of the grid-type control loop model to remove the zero-sequence component in the circuit equation of the nonlinear circuit to obtain a modified sequence impedance circuit equation, thereby reducing the modeling calculation complexity; using the modified sequence impedance circuit equation to correct the initial transfer function of the sequence impedance model corresponding to each frequency coupling component, and accurately performing linear modeling on the sequence impedance of the grid-type converter.

[0043] (2) The virtual synchronous control loop in the frequency domain of the meshed control loop model described in this scheme is expressed as: It takes into account the effect of frequency domain phase angle under frequency coupling of meshed control, and solves it as the addition of disturbance voltage and response current. Compared with the existing modeling of meshed control, it can explain the effect of virtual synchronous control in sequence impedance, and model the frequency domain model of virtual synchronous control.

[0044] (3) In this solution, the harmonic linearization method is used to model the initial transfer function of the sequence impedance model corresponding to each frequency coupling component. It takes into account the feedback coupling of the converter DC system and the effect of frequency coupling. Compared with the existing sequence impedance modeling, this method defines the influence of multiple functions. Compared with the traditional two functions and four transfer functions, it can more comprehensively explain the influence mechanism of the transfer function of the sequence impedance of the network-forming control and explain the role of impedance modeling.

[0045] (4) In this solution, when a positive-sequence voltage disturbance is applied to the AC port, the initial transfer function of the sequence impedance model corresponding to each frequency coupling component is as follows: It takes into account the coupling feedback effect on the grid side and the feedback loop effect on the DC side. Compared with the existing sequence impedance modeling, it can more comprehensively reflect the interaction relationship between the control of the converter and the circuit, and improve the frequency-domain modeling accuracy of the positive-sequence impedance in the low-frequency band.

[0046] (5) In this solution, when a negative-sequence voltage disturbance is applied to the AC port, the initial transfer function of the sequence impedance model corresponding to each frequency coupling component is as follows: It takes into account the coupling feedback effect on the grid side and the feedback loop effect on the DC side. Compared with the existing sequence impedance modeling, it can more comprehensively reflect the interaction relationship between the control of the converter and the circuit, and improve the frequency-domain modeling accuracy of the negative-sequence impedance in the low-frequency band.

[0047] (6) In this solution, when a DC voltage disturbance is applied to the AC port, the initial transfer function of the sequence impedance model corresponding to each frequency coupling component is as follows: It takes into account the AC-DC coupling characteristics of the converter. Compared with the existing sequence impedance modeling, it can improve the modeling accuracy of the DC impedance.

[0048] (7) In this solution, the modified transfer function of the sequence impedance model corresponding to each frequency coupling component is expressed as: It takes into account the frequency-domain modeling of the virtual synchronous control loop and the AC-DC coupling effect. Compared with the existing sequence impedance modeling, it can accurately characterize the frequency-domain characteristics of the network-forming control.

[0049] (8) After S5 in this solution, it further includes: applying the impedance feedback of the DC port to the modified transfer function of the sequence impedance model corresponding to each frequency coupling component to obtain the target transfer function of the sequence impedance model corresponding to each frequency coupling component; it takes into account the coupling feedback effect of the DC port affected by the main circuit and can improve the accuracy of the frequency-domain model considering DC side disturbances.

[0050] (9) After S5 in this solution, it further includes: The target transfer function of the sequence impedance model corresponding to each frequency coupling component is expressed as: It takes into account the AC-DC coupling characteristics of the converter. Compared with the existing sequence impedance modeling, it can further improve the accuracy of the model. Description of the Drawings

[0051] Figure 1 It is a flowchart of a method for modeling the sequence impedance of a network-forming converter provided in Embodiment 1 of the present invention;

[0052] Figure 2 It is the control loop and main circuit diagram of the network-forming converter provided in Embodiment 1 of the present invention;

[0053] Figure 3a It is a positive sequence impedance amplitude-phase diagram of the impedance characteristics of a method for modeling the sequence impedance of a network-forming converter considering frequency coupling effects provided in Embodiment 1 of the present invention;

[0054] Figure 3b It is a negative sequence impedance amplitude-phase diagram of the impedance characteristics of a method for modeling the sequence impedance of a network-forming converter considering frequency coupling effects provided in Embodiment 1 of the present invention;

[0055] Figure 3c It is a DC self-impedance amplitude-phase diagram of the impedance characteristics of a method for modeling the sequence impedance of a network-forming converter considering frequency coupling effects provided in Embodiment 1 of the present invention;

[0056] Figure 4 It is an amplitude-phase diagram of the impedance characteristics of the frequency coupling term of a converter considering frequency domain coupling provided in Embodiment 1 of the present invention;

[0057] Figure 5 It is a comparison result diagram of the impedance characteristics and modeling comparison between a network-following type and a network-forming type converter considering frequency coupling effects and the equivalent impedance characteristics of the grid side provided in Embodiment 1 of the present invention. Detailed Embodiments

[0058] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0059] Embodiment 1

[0060] As Figure 1As shown, this embodiment provides a method for modeling the sequence impedance of a grid-type converter, including steps S1-S5. S1: Perform two-port equivalence on the grid-type converter to be analyzed and modeled to obtain a two-port network of the grid-type converter to be analyzed and modeled; the two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; a voltage disturbance is added to the AC port and the DC port to obtain a current response of the voltage disturbance. S2: Perform sequence impedance modeling on the control loop under the current response of the voltage disturbance to obtain a grid-type control loop model. S3: Perform frequency coupling analysis on the nonlinear circuit under the current response of the voltage disturbance to obtain multiple frequency coupling components; use the harmonic linearization method to model the initial transfer function of the sequence impedance model corresponding to each frequency coupling component. S4: Combine the circuit equation of the nonlinear circuit and the control equation of the grid-type control loop model to remove the zero-sequence component in the circuit equation of the nonlinear circuit to obtain a modified sequence impedance circuit equation. S5: using the modified sequence immittance circuit equation to modify the initial transfer function of the sequence immittance model corresponding to each frequency coupling component, to obtain the modified transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0061] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0062] Among them, the equivalent process of the two-port network is:

[0063]

[0064] s p The reference component representing the sequence is multiplied by the reference component matrix on the basis of phase a. The matrix defines the relationship between the sequences. By multiplying the reference component matrix, the complete components of the other three phases can be obtained.

[0065] Specifically, the meshed control loop model includes a current control loop, a voltage control loop, a PLL phase-locked loop, and a virtual synchronous control loop. Figure 2 It is a control loop and main circuit diagram of the grid-connected converter provided in Example 1 of the present invention.

[0066] The modeling process of the current control loop in step S2 is calculated as:

[0067]

[0068] Z c (s) represents the equivalent impedance of the grid-connected type, H c (s) is the gain of the loop, K d represents the feedback gain of the current loop, and L represents the grid-connected inductor of the converter.

[0069] The modeling process of the voltage control loop in step S2 is calculated as:

[0070]

[0071] Z v (s) represents the equivalent impedance of the grid-connected type, H va (s) is the gain of the voltage loop, V dc represents the DC bus voltage gain, and L represents the grid-connected inductor of the converter.

[0072] The modeling process of the PLL phase-locked loop in step S2 is calculated as:

[0073]

[0074] The phase angle in the frequency domain is expressed as H θ (s) is the open-loop gain of the PLL phase-locked PI, T θ (s) is the forward gain of the PLL phase-locked loop, G θ (s) is the closed-loop gain of the PLL phase-locked loop.

[0075] As a preferred implementation, the virtual synchronous control loop in the grid-forming control loop model is expressed as: Among them, is the phase angle in the frequency domain, J is the inertia coefficient of the virtual synchronous control loop, D p is the damping coefficient of the virtual synchronous control loop, is the voltage disturbance applied to the AC port, is the current disturbance after the voltage disturbance applied to the AC port, ω0 is the initial rotational angular velocity, ω1 is the fundamental frequency, U1 * 、I1 * are the conjugates of the initial phasors of voltage and current respectively.

[0076] As a preferred implementation, it should be noted that the frequency coupling comes from the nonlinearity of control: dq conversion and PLL, and the dq transformation will couple ω p -2ω1 and ω pFor the component of +2ω1, the PLL control causes control asymmetry on the q-axis, the DC voltage acts on the d-axis, and the frequency coupling also comes from the modulation effect in the main circuit. The initial transfer functions of the sequence impedance models corresponding to each frequency coupling component are modeled using the harmonic linearization method, including:

[0077] Using the formula to model the initial transfer functions of the sequence impedance models corresponding to each frequency coupling component; where x(t) is the time-domain value of the x variable, y(t) is the time-domain value of the y variable, is the steady-state value of the x variable at the steady-state operating point, is the superimposed small-signal value of the x variable under small perturbations, is the steady-state value of the y variable at the steady-state operating point, is the superimposed small-signal value of the y variable under small perturbations, is the small-signal value after harmonic linearization of Z(t), is the superimposed small-signal value of the y variable under small perturbations, Y l is the steady-state value of the y variable at the steady-state operating point, where l is used to represent the number of components of the y variable itself X k is the steady-state value of the variable at the steady-state operating point, is the superimposed small-signal value of the variable under small perturbations, where k is used to represent the number of components of the x variable itself; ω p is the perturbation frequency, ω1 is the fundamental frequency, X k is the k-th harmonic component of the x variable, Y k is the k-th harmonic component of Y.

[0078] As a preferred implementation, as Figure 3a shown, when a positive-sequence voltage perturbation is applied to the AC port, the initial transfer functions of the sequence impedance models corresponding to each frequency coupling component are:

[0079]

[0080] where, Y pp (s) is the positive-sequence response self-admittance under positive-sequence voltage perturbation, Y pd (s) is the AC-DC coupling admittance of the DC response under positive-sequence voltage perturbation, Y pn (s) is the negative-sequence response AC transfer admittance under positive-sequence voltage perturbation; is the response current of the AC port, is the voltage perturbation of the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0081] As a preferred embodiment, Figure 3b As shown in the figure, when a negative sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is:

[0082]

[0083] Among them, Y nn (s) is the positive sequence response self-admittance under negative sequence voltage disturbance, Y nd (s) is the AC-DC coupled admittance of the DC response under negative sequence voltage disturbance, Y np (s) is the negative sequence response AC transfer admittance under negative sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0084] As a preferred embodiment, Figure 3c As shown in the figure, when a DC voltage disturbance is added to the DC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is:

[0085]

[0086] Among them, Y dd (s) is the DC response self-admittance under DC disturbance, Y dp (s) is the AC-DC coupled admittance of the AC positive sequence response under DC disturbance, Y pn (s) is the AC transfer admittance of the AC negative sequence response under DC disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0087] The calculation process of solving the circuit equation of the main circuit and the control equation of the network control model is as follows:

[0088]

[0089] v m represents the average grid voltage in the grid-connected busbar, i0 represents the current flowing through the three-phase neutral point, d a d b d c Represents the duty cycle of phases a, b, and c, Y l represents the zero-sequence component elimination matrix, and C represents the DC capacitance value.

[0090] As a preferred embodiment, the modified transfer function of the sequence impedance model corresponding to each frequency coupling component is expressed as:

[0091] L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc is the DC voltage value, ω1 is the fundamental frequency, is the transfer function of the inner current loop, M(s - jω1) is the closed-loop transfer function of the virtual synchronous control loop, M 1 is the fundamental parameter of the modulation signal, I1 is the parameter of the fundamental current, is I the conjugate of 1, is the fundamental voltage U the conjugate of 1, ω0 is the frequency base value, is the response current of the AC port, is the voltage perturbation of the AC port. Z c (s) represents the equivalent impedance of the grid-connected type, H c (s) is the gain of the loop, K d represents the feedback gain of the current loop, s represents the time-domain variable of the control, J represents the inertia coefficient, D p represents the damping coefficient, represents the voltage and current components of the perturbation frequency. Among them, Figure 4 is the amplitude-phase diagram of the impedance characteristic of the frequency coupling term of the converter considering frequency-domain coupling.

[0092] As a preferred embodiment, after S5, it further includes: equivalent the feedback loop of the DC port to the impedance of the DC port, and feedback the impedance of the DC port to the modified transfer function of the sequence impedance model corresponding to each frequency coupling component to obtain the target transfer function of the sequence impedance model corresponding to each frequency coupling component.

[0093] As a preferred embodiment, the target transfer function of the sequence impedance model corresponding to each frequency coupling component is expressed as: Y an (s) is the negative-sequence coupling response admittance under positive-sequence voltage perturbation, Y nn (s) is the positive-sequence response self-admittance under negative-sequence voltage perturbation, Y nd (s) is the AC-DC coupling admittance of the DC response under negative-sequence voltage perturbation, Y dn (s +1 ) is the negative-sequence AC-DC coupling admittance under DC voltage perturbation, Z dc (s +1 ) is the self-impedance after applying voltage perturbation to the DC port, Y dd (s +1 ) is the self-admittance after applying voltage perturbation to the DC port, Y cn(s) is the admittance at the coupling frequency under the negative sequence voltage disturbance, Y np (s) is the positive sequence coupling admittance under the negative sequence voltage disturbance, Y dp (s +1 ) is the positive sequence AC-DC coupling admittance v under voltage disturbance applied to the DC port m represents the average grid voltage in the grid-connected busbar, i0 represents the current flowing through the three-phase neutral point, d a ,d b ,d c Represents the duty cycle of phases a, b, and c, Y l represents the zero-sequence component elimination matrix, and C represents the DC capacitance value. Figure 5 It is a comparison and modeling result diagram of the grid-following and grid-forming converters and the grid-side equivalent reactance characteristics taking into account the influence of frequency coupling.

[0094] Example 2

[0095] The present embodiment provides a sequence-immittance modeling device for a grid-type converter, comprising: a disturbance module, a first modeling module, a second modeling module, a first correction module, and a second correction module. The disturbance module is used to perform two-port equivalence on the grid-type converter to be analyzed and modeled, so as to obtain a two-port network of the grid-type converter to be analyzed and modeled; the two-port network comprises: a control loop, a nonlinear circuit, an AC port, and a DC port; a voltage disturbance is added to the AC port and the DC port to obtain a current response of the voltage disturbance. The first modeling module is used to perform sequence-immittance modeling on the control loop under the current response of the voltage disturbance, so as to obtain a grid-type control loop model. The second modeling module is used to perform frequency coupling analysis on the nonlinear circuit under the current response of the voltage disturbance, so as to obtain multiple frequency-coupled components; and the initial transfer function of the sequence-immittance model corresponding to each frequency-coupled component is modeled by using a harmonic linearization method. The first correction module is used to combine the circuit equation of the nonlinear circuit and the control equation of the grid-type control loop model to remove the zero-sequence component in the circuit equation of the nonlinear circuit, so as to obtain a corrected sequence-immittance circuit equation. The second correction module is used to correct the initial transfer function of the sequence immittance model corresponding to each frequency coupling component by using the corrected sequence immittance circuit equation to obtain the corrected transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0096] The division of each module in the above-mentioned sequence impedance modeling device of the grid-type converter is only for illustrative purposes. In other embodiments, the sequence impedance modeling device of the grid-type converter can be divided into different modules as needed to complete all or part of the functions of the sequence impedance modeling device of the grid-type converter.

[0097] For the specific limitations of the sequence impedance modeling device of the network-forming converter, reference can be made to the limitations of the sequence impedance modeling method of the network-forming converter in the above text, which will not be elaborated here. Each module in the above sequence impedance modeling device of the network-forming converter can be implemented in whole or in part by software, hardware, and their combination. The above modules can be embedded in the processor of the computer device in hardware form or independent of it, or stored in the memory of the computer device in software form, so as to facilitate the processor to call and execute the operations corresponding to each of the above modules.

[0098] Embodiment 3

[0099] This embodiment provides an electronic device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the above method are implemented.

[0100] Embodiment 4

[0101] This embodiment provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above method are implemented.

[0102] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for modeling sequence impedance of a grid-connected converter, characterized in that: include: S1: Perform two-port equivalence on the grid-type converter to be analyzed and modeled, so as to obtain a two-port network of the grid-type converter to be analyzed and modeled; The dual-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; voltage disturbances are added to the AC port and the DC port; S2: performing sequence impedance modeling on the control loop under the current response of the voltage disturbance to obtain a meshed control loop model; S3: performing frequency coupling analysis on the nonlinear circuit under the current response of the voltage disturbance to obtain a plurality of frequency coupling components; using a harmonic linearization method to model the initial transfer function of the sequence immittance model corresponding to each frequency coupling component; S4: combining the circuit equation of the nonlinear circuit and the control equation of the meshed control loop model to remove the zero-sequence component in the circuit equation of the nonlinear circuit and obtain a modified sequence immittance circuit equation; S5: using the modified sequence immittance circuit equation to modify the initial transfer function of the sequence immittance model corresponding to each frequency coupling component, to obtain a modified transfer function of the sequence immittance model corresponding to each frequency coupling component; The modified transfer function of the sequence immittance model corresponding to each frequency coupling component is expressed as: Where, L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc is the DC voltage value, ω1 is the fundamental frequency, is the transfer function of the current inner loop, M(s-jω1) is the closed-loop transfer function of the virtual synchronous control loop, M 1 is the base frequency parameter of the modulation signal, I 1 is the parameter of the current fundamental frequency, for I The conjugate of 1, is the fundamental voltage U 1 is the conjugate, ω0 is the base frequency value, is the response current of the AC port, is the voltage disturbance at the AC port.

2. The sequence immittance modeling method of a grid-connected converter according to claim 1, characterized in that: The virtual synchronous control loop in the meshed control loop model is expressed as: in, is the phase angle in the frequency domain, J is the inertia coefficient of the virtual synchronous control loop, D p is the damping coefficient of the virtual synchronous control loop, is the voltage disturbance applied to the AC port, is the current disturbance after the voltage disturbance added to the AC port, ω0 is the initial rotation angular velocity, ω1 is the fundamental frequency, U1 * 、I1 * are the conjugates of the initial phasors of voltage and current, respectively.

3. The sequence immittance modeling method of a grid-connected converter according to claim 1, characterized in that: The method of using harmonic linearization to model the initial transfer function of the sequence immittance model corresponding to each frequency coupling component includes: Using the formula Modeling the initial transfer function of the sequence immittance model corresponding to each frequency coupling component; Among them, x(t) is the time domain value of the x variable, y(t) is the time domain value of the y variable, is the steady-state value of the x variable at the steady-state operating point, is the superimposed small signal value under small perturbation of x variable, is the steady-state value of the y variable at the steady-state operating point, is the superimposed small signal value under small perturbation of the y variable, is the small signal value after the harmonic linearization of Z(t), is the superimposed small signal value under the small disturbance of the y variable, Y l is the steady-state value of the y variable at the steady-state operating point, where l is used to represent the number of components of the y variable itself, X k is the steady-state value of the variable at the steady-state operating point, is the superimposed small signal value under small perturbation of the variable, where k is used to represent the number of components of the x variable itself; ω p is the disturbance frequency, ω1 is the fundamental frequency, X k is the kth harmonic component of the x variable, Y k is the kth harmonic component of Y.

4. The sequence immittance modeling method of a grid-connected converter according to claim 3, characterized in that: When a positive sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: Among them, Y pp (s) is the positive sequence response self-admittance under positive sequence voltage disturbance, Y pd (s) is the AC-DC coupled admittance of the DC response under positive sequence voltage disturbance, Y pn (s) is the negative sequence response AC transfer admittance under positive sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port under the positive sequence voltage disturbance, is the coupling current of the AC port under the positive sequence voltage disturbance.

5. The sequence immittance modeling method of a grid-connected converter according to claim 3, characterized in that: When a negative sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: Among them, Y nn (s) is the positive sequence response self-admittance under negative sequence voltage disturbance, Y nd (s) is the AC-DC coupled admittance of the DC response under negative sequence voltage disturbance, Y np (s) is the negative sequence response AC transfer admittance under negative sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port under the negative sequence voltage disturbance, is the coupling current of the AC port under the negative sequence voltage disturbance.

6. The sequence immittance modeling method of a grid-connected converter according to claim 3, characterized in that: When a DC voltage disturbance is added to the DC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: Among them, Y dd (s) is the DC response self-admittance under DC disturbance, Y dp (s) is the AC-DC coupled admittance of the AC positive sequence response under DC disturbance, Y dn (s) is the AC transfer admittance of the AC negative sequence response under DC disturbance.

7. The sequence immittance modeling method of a grid-connected converter according to claim 1, characterized in that: The S5 also includes: The feedback loop of the DC port is equivalent to the immittance of the DC port, and the immittance of the DC port is fed back to act on the modified transfer function of the sequence immittance model corresponding to each frequency coupling component to obtain the target transfer function of the sequence immittance model corresponding to each frequency coupling component.

8. The sequence immittance modeling method of a grid-connected converter according to claim 7, characterized in that: The target transfer function of the sequence immittance model corresponding to each frequency coupling component is expressed as: Y an (s) is the negative sequence coupling response admittance under the positive sequence voltage disturbance, Y nn (s) is the positive sequence response self-admittance under negative sequence voltage disturbance, Y nd (s) is the AC-DC coupled admittance of the DC response under negative sequence voltage disturbance, Y dn (s +1 ) is the negative sequence AC / DC coupling admittance under DC voltage disturbance, Z dc (s +1 ) is the self-impedance after the voltage disturbance is applied to the DC port, Y dd (s +1 ) is the self-admittance after voltage disturbance is applied to the DC port, Y cn (s) is the admittance at the coupling frequency under the negative sequence voltage disturbance, Y np (s) is the positive sequence coupling admittance under the negative sequence voltage disturbance, Y dp (s +1 ) is the positive sequence AC / DC coupling admittance under voltage disturbance applied to the DC port.

9. A sequence impedance modeling device for a grid-type converter, characterized in that: include: A disturbance module is used to perform two-port equivalence on the grid-type converter to be analyzed and modeled, so as to obtain a two-port network of the grid-type converter to be analyzed and modeled; The dual-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; voltage disturbances are added to the AC port and the DC port; A first modeling module is used to perform sequence impedance modeling on the control loop under the current response of the voltage disturbance to obtain a meshed control loop model; The second modeling module is used to perform frequency coupling analysis on the nonlinear circuit under the current response of the voltage disturbance to obtain multiple frequency coupling components; and use a harmonic linearization method to model the initial transfer function of the sequence immittance model corresponding to each frequency coupling component; A first correction module is used to combine the circuit equation of the nonlinear circuit and the control equation of the meshed control loop model to remove the zero-sequence component in the circuit equation of the nonlinear circuit to obtain a corrected sequence impedance circuit equation; A second correction module is used to correct the initial transfer function of the sequence immittance model corresponding to each frequency coupling component by using the corrected sequence immittance circuit equation to obtain a corrected transfer function of the sequence immittance model corresponding to each frequency coupling component; The modified transfer function of the sequence immittance model corresponding to each frequency coupling component is expressed as: Where, L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc is the DC voltage value, ω1 is the fundamental frequency, is the transfer function of the current inner loop, M(s-jω1) is the closed-loop transfer function of the virtual synchronous control loop, M 1 is the base frequency parameter of the modulation signal, I 1 is the parameter of the current fundamental frequency, for I The conjugate of 1, is the fundamental voltage U 1 is the conjugate, ω0 is the base frequency value, is the response current of the AC port, is the voltage disturbance at the AC port.

Images