Sequence immittance modeling method and device for network construction type converter

Abstract

The invention discloses a sequence immittance modeling method and device for a network-building converter, and belongs to the technical field of power system control, and the method comprises the steps: adding voltage disturbance to an AC port and a DC port in an equivalent dual-port network of the network-building converter to be analyzed and modeled; frequency coupling analysis is carried out on a nonlinear circuit under current response of voltage disturbance to model an initial transfer function of a sequence immittance model corresponding to each frequency coupling component, interaction between network-forming converters is fully considered, the frequency coupling rule of the converters is disclosed, and the accuracy of the sequence immittance model is improved; a zero-sequence component in a circuit equation of a nonlinear circuit is removed by using a control equation of a network-forming control loop model corresponding to control loop sequence immittance to obtain a corrected sequence immittance circuit equation, so that the modeling calculation complexity can be reduced; and correcting the initial transfer function of each sequence immittance model by using the corrected sequence immittance circuit equation, and accurately carrying out linear modeling on the sequence immittance of the grid-forming converter.

Description

Technical Field

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

[0002] At present, most of the new energy control connected to the power grid adopts grid following (GFL) control, which needs to rely on traditional synchronous generators to provide a stable voltage source. It is difficult to adapt to the future power grid scenario with a high proportion of new energy connected to the power grid. The use of grid forming (GFM) converters to control the new energy connected to the power grid can achieve the operation support of the power grid. In other words, in the face of the trend of new energy grid connection, it is necessary to carry out detailed frequency domain modeling of grid forming converters, so as to realize the mining of grid forming converter characteristics and help the stable operation of renewable energy in the full frequency band.

[0003] The existing modeling methods are divided into modeling methods using dq axes and sequence impedance modeling methods. The modeling method based on dq axes originates from the frequency domain modeling of small-capacity systems. The modeling accuracy is difficult to meet the requirements in the low frequency band below 100Hz in the frequency domain; it is further difficult to consider the influence of frequency coupling effects and the influence of DC side coupling terms. In addition, in the stability analysis and control of large systems, it is difficult to achieve stability analysis of multiple machines based on the modeling method based on dq axes, and the phase angle under multiple machines is difficult to determine directly, which restricts the scope of use of the modeling method under dq axes. The modeling method based on sequence impedance can be extended to more scenarios under converters because it is based on modeling in a stationary coordinate system. It has important application scenarios in the future large-scale grid-connected stability analysis of new energy; however, the detailed modeling process of grid-type converters has not been considered yet, and more specifically, small signal modeling of grid-type converters has not been performed from the perspective of frequency coupling and DC feedback. Moreover, sequence impedance modeling does not take into account the advantages of impedance, and it is difficult to directly characterize the equivalent circuit relationship of the converter, making the steps and processes in stability analysis more complicated.

[0004] In summary, it is difficult for traditional modeling methods to directly perform linear modeling of grid-connected converters with low computational complexity and high accuracy. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a method and device for sequence impedance modeling of a grid-type converter, which aims to solve the technical problem that traditional modeling methods are difficult to directly perform linear modeling of the grid-type converter with low computational complexity and high accuracy.

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

[0007] 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; and voltage disturbances are added to the AC port and the DC port;

[0008] S2: performing sequence immittance modeling on the control loop under the current response of the voltage disturbance to obtain a meshed control loop model;

[0009] 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;

[0010] 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;

[0011] 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.

[0012] In one embodiment, the virtual synchronous control loop in the meshed control loop model is represented as:

[0013]

[0014] 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, ω 0 is the initial rotation angular velocity, ω 1 is the fundamental frequency, U 1 * ,I 1 * are the conjugates of the initial phasors of voltage and current, respectively.

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

[0016] Using the formula Modeling the initial transfer function of the sequence immittance model corresponding to each frequency coupling component;

[0017] 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, ω 1 is the fundamental frequency, X k is the kth harmonic component of the x variable, Y k is the kth harmonic component of Y.

[0018] In one embodiment, 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:

[0019]

[0020] 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, is the coupling current of the AC port.

[0021] In one embodiment, 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:

[0022]

[0023] Among them, Y nn (s) is the positive sequence response self-admittance under negative sequence voltage disturbance, Ynd (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.

[0024] In one embodiment, 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:

[0025]

[0026] 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.

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

[0028]

[0029] Where, L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc is the DC voltage value, ω 1 is the fundamental frequency, is the transfer function of the inner current loop, M(s-jω 1 ) 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 fundamental frequency of current, for I 1 The conjugate of is the fundamental voltage U 1 The conjugate of 0 is the base frequency value, is the response current of the AC port, is the voltage disturbance at the AC port.

[0030] In one of the embodiments, after S5, it also includes: equating the feedback loop of the DC port to the immittance of the DC port, and feeding back the immittance of the DC port to act on the modified transfer function of the sequence immittance model corresponding to each frequency coupling component, so as to obtain the target transfer function of the sequence immittance model corresponding to each frequency coupling component.

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

[0032]

[0033] 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 the voltage disturbance applied to the DC port. According to another aspect of the present invention, a sequence impedance modeling device for a grid-type converter is provided, comprising:

[0034] 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 two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; and voltage disturbances are added to the AC port and the DC port;

[0035] 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;

[0036] 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;

[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 scheme, 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 transfer function influence mechanism of the sequence impedance of the grid-type control and explain the role of impedance modeling.

[0045] (4) In this scheme, when the 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: 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 interactive influence relationship between the converter control and the circuit, and improve the frequency domain modeling accuracy of the positive-sequence impedance in the low-frequency band.

[0046] (5) In this scheme, 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: 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 interactive influence relationship between the converter control and the circuit, and improve the frequency domain modeling accuracy of negative sequence impedance in the low frequency band.

[0047] (6) In this scheme, when a DC voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: It takes into account the AC / DC coupling characteristics of the converter and can improve the modeling accuracy of DC impedance compared with the existing sequence impedance modeling.

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

[0049] (8) The step S5 in this scheme also 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; this 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 under the DC side disturbance.

[0050] (9) In this solution, after S5, the target transfer function of the sequence immittance model corresponding to each frequency coupling component is expressed as: It takes into account the AC and DC coupling characteristics of the converter and can further improve the accuracy of the model compared with the existing sequence impedance modeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a flow chart of a sequence impedance modeling method for a grid-connected converter provided in Embodiment 1 of the present invention;

[0052] Figure 2 It is a control loop and main circuit diagram of the grid-connected 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 sequence impedance of a grid-type converter taking into account the influence of frequency coupling provided in Example 1 of the present invention;

[0054] Figure 3b is a negative-sequence impedance amplitude phase diagram of the impedance characteristics of the sequence impedance modeling method of the grid-type converter taking into account the frequency coupling effect provided in Example 1 of the present invention;

[0055] Figure 3c It is a DC self-impedance amplitude phase diagram of the impedance characteristics of a sequence impedance modeling method for a grid-type converter taking into account the influence of frequency coupling provided in Example 1 of the present invention;

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

[0057] Figure 5 This is a comparison and modeling result diagram of the grid-following type and grid-forming type converters and the grid-side equivalent reactance characteristics taking into account the frequency coupling effect provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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 intended 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] Example 1

[0060] like Figure 1 As 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 pThe 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 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 inductance 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 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 inductance 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 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, ω 0 is the initial rotation angular velocity, ω 1 is the fundamental frequency, U 1 * ,I 1 * are the conjugates of the initial phasors of voltage and current, respectively.

[0076] As a preferred embodiment, it should be noted that the frequency coupling comes from the nonlinearity of the control: dq conversion and PLL, dq conversion will couple out ω p -2ω 1 With ω p +2ω 1 The PLL control acts on the q-axis, causing control asymmetry. The DC voltage acts on the d-axis. The frequency coupling also comes from the modulation in the main circuit. The initial transfer function of the sequence immittance model corresponding to each frequency coupling component is modeled using the harmonic linearization method, including:

[0077] Using the formula Model the initial transfer function of the sequence immittance model 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 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, ω 1 is the fundamental frequency, X k is the kth harmonic component of the x variable, Y k is the kth harmonic component of Y.

[0078] As a preferred embodiment, Figure 3a As shown in the figure, when the 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:

[0079]

[0080] 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, 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 bus, i 0 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 implementation, the modified transfer function of the sequence immittance model corresponding to each frequency coupling component is expressed as:

[0091] L is AC inductance, K d is the feedback coefficient of the inner current loop, V dc is the DC voltage value, ω 1 is the fundamental frequency, is the transfer function of the inner current loop, M(s-jω 1 ) 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 fundamental frequency of current, for I 1 The conjugate of is the fundamental voltage U 1 The conjugate of 0 is the base frequency value, is the response current of the AC port, is the voltage disturbance at the AC port. c (s) represents the equivalent impedance of the network 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, and D p represents the damping coefficient, Represents the voltage and current components of the disturbance frequency. Among them, Figure 4 The magnitude-phase diagram of the impedance characteristics of the frequency coupling term of the converter considering frequency domain coupling.

[0092] As a preferred implementation, after S5 it also includes: equating the feedback loop of the DC port to the immittance of the DC port, and feeding back the immittance of the DC port to act on the corrected transfer function of the sequence immittance model corresponding to each frequency coupling component, so as to obtain the target transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0093] As a preferred implementation, 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 v under voltage disturbance applied to the DC port m Represents the average grid voltage in the grid-connected bus, i 0 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] The specific definition of the sequence-conductance modeling device of the grid-type converter can be found in the definition of the sequence-conductance modeling method of the grid-type converter mentioned above, which will not be repeated here. Each module in the sequence-conductance modeling device of the grid-type converter can be implemented in whole or in part by software, hardware and a combination thereof. The above modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules.

[0098] Example 3

[0099] This embodiment provides an electronic device, including 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.

[0100] Example 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] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should 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 the modified transfer function of the sequence immittance model corresponding to each frequency coupling component.

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, is the coupling current of the AC port.

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, is the coupling current of the AC port.

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 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.

7. The sequence immittance modeling method of a grid-connected converter according to claim 1, characterized in that: 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.

8. 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.

9. The sequence immittance modeling method of a grid-connected converter according to claim 8, 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.

10. A sequence impedance modeling device for a grid-connected 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; 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.

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