An integral feedforward decoupling method for virtual synchronous generators

Abstract

The present application discloses an integral feedforward decoupling method for a virtual synchronous generator, belonging to the field of power system technology, comprising: equating reactive power coupling to a parallel coupled admittance alone, and then connecting a virtual P / ω admittance in parallel at both ends of the coupled admittance to offset the influence of the coupled admittance. While considering power coupling, this method introduces a virtual P / ω admittance to offset the influence of power coupling, achieving dynamic and steady-state dual-dimensional decoupling, improving decoupling efficiency and decoupling accuracy, reducing parameter complexity, having clear physical meaning, facilitating engineers' understanding of the working principle of the technology, and providing reliable technical support for the application of VSG in complex power grid environments.

Description

Technical Field

[0001] The present application relates to the technical field of power systems, and in particular to an integral feedforward decoupling method applicable to a virtual synchronous generator. Background Art

[0002] With the large-scale integration of renewable energy into the power grid via power electronic converters, the inertia and damping of power systems are decreasing, jeopardizing the safe and stable operation of the system. To address this issue, virtual synchronous generator (VSG) technology has emerged. By mimicking the rotor motion equations and excitation equations of traditional synchronous generators, VSGs can provide converters with frequency and voltage support capabilities. In power grids with high resistance-to-inductance (R / X) ratios, VSGs can achieve independent control of active power-frequency and reactive power-voltage.

[0003] However, in low R / X power grids, active and reactive power are coupled and cannot be controlled independently. This coupling affects the steady-state accuracy, dynamic performance, and even stability of power control. Current power decoupling methods mainly focus on steady-state power decoupling, and rarely consider the impact of power coupling on the dynamic performance of VSG active power. Although the decoupling method based on virtual impedance has a clear physical meaning, the voltage drop on the virtual impedance limits its decoupling capability. Compared with the virtual impedance method, the decoupling method based on relative gain theory or multivariable feedback theory can greatly improve the system decoupling performance, but the parameter design of this method is relatively complex and does not have a clear physical meaning, which is not convenient for engineering implementation. Summary of the Invention

[0004] In response to the above-mentioned deficiencies in the prior art, the present application provides an integral feedforward decoupling method suitable for a virtual synchronous generator, which solves the problems that the existing power decoupling method ignores the influence of power coupling on the dynamic performance of the active power of the VSG, and the virtual impedance method has a reduced decoupling capability due to voltage drop, while the multivariable feedback method has complex parameter design and ambiguous physical meaning.

[0005] In order to achieve the above-mentioned invention objectives, the technical solutions adopted in this application are:

[0006] The present application provides an integral feedforward decoupling method applicable to a virtual synchronous generator, comprising:

[0007] S1: Construct a power loop control model for active power and reactive power of VSG considering the influence of reactive power coupling;

[0008] S2: Based on the relationship between power and frequency represented by the power loop control model, power coupling is equivalent to coupling admittance, and a P / ω admittance model of the VSG considering power coupling is constructed;

[0009] S3: connecting a virtual P / ω admittance in parallel at both ends of the coupled admittance in the P / ω admittance model to form a power decoupling strategy based on the virtual P / ω admittance;

[0010] S4: reconstructing the power loop control model according to the power decoupling strategy of the power decoupling P / ω admittance, and performing decoupling based on the reconstructed power loop control model.

[0011] Furthermore, the power loop control model of the active power and reactive power of the VSG is constructed in S1 considering the influence of reactive power coupling, specifically including:

[0012] S101: Constructing an initial VSG power loop control model considering active power and reactive power of the VSG when reactive power control is coupled;

[0013] S102: Taking the reactive power reference variation in the initial VSG power loop control model as zero as a simplification condition, simplify the initial VSG power loop control model to obtain the power loop control model.

[0014] Furthermore, in S2, based on the relationship between power and frequency represented by the power loop control model, power coupling is equivalent to coupling admittance, and a P / ω admittance model of the VSG after considering power coupling is constructed, which specifically includes:

[0015] S201: According to the relationship between power and frequency represented by the power loop control model, the power coupling is equivalent to the coupling admittance Y c , respectively determine the first admittance Y a , the second admittance Y b and the coupling admittance Y c ;

[0016] S202: According to the first admittance Y a The second admittance Y b and the coupling admittance Y c The relationship between VSG control parameters, VSG angular frequency and system operating point is considered, and the P / ω admittance model of VSG considering power coupling is constructed.

[0017] Furthermore, the first admittance Y a The second admittance Y b and the coupling admittance Y c They are:

[0018]

[0019]

[0020]

[0021] in, and is the power angle coefficient of active power and reactive power, and is the voltage amplitude coefficient of active power and reactive power, is a reactive-voltage controller, and are the active droop coefficient and virtual inertia of VSG respectively, is the rated angular frequency of VSG, is the Laplace operator.

[0022] Furthermore, in S3, the virtual P / ω admittance Y d =-Y c .

[0023] Furthermore, in S4, reconstructing the power loop control model according to the power decoupling strategy of the power decoupling P / ω admittance, and performing decoupling based on the reconstructed power loop control model specifically include:

[0024] S401: According to the power decoupling strategy of the power decoupling P / ω admittance, an additional feedforward branch is connected in parallel in the power loop control model to form an initial equivalent control model of power decoupling;

[0025] S402: Shift the addition point of the additional feedforward branch from the output end to the input end to form a new equivalent control model;

[0026] S403: Add reactive power reference value As a simplification condition, simplifying the new equivalent control model to obtain the reconstructed power loop control model;

[0027] S404: Decoupling is performed based on the reconstructed power loop control model.

[0028] The beneficial effects of this application are:

[0029] This application provides a VSG power decoupling control method based on virtual P / ω admittance reconstruction, which is achieved by equating reactive power coupling to a parallel coupled admittance alone, and then connecting a virtual P / ω admittance in parallel at both ends of the coupled admittance to offset the influence of the coupled admittance. While considering power coupling, this method introduces a virtual P / ω admittance to offset the influence of power coupling, achieves dynamic and steady-state dual-dimensional decoupling, improves decoupling efficiency and decoupling accuracy, reduces parameter complexity, has clear physical meaning, facilitates engineers to understand the working principle of the technology, and can provide reliable technical support for the application of VSG in complex power grid environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0031] Figure 1 A method flow chart of an integral feedforward decoupling method applicable to a virtual synchronous generator provided in an embodiment of the present application.

[0032] Figure 2 A schematic diagram of an initial VSG power loop control model that considers active power and reactive power of VSG when reactive power control coupling is provided in an embodiment of the present application.

[0033] Figure 3 The embodiment of this application provides Figure 2 A schematic diagram of a power loop control model that simplifies the initial VSG power loop control model.

[0034] Figure 4 A schematic diagram of a P / ω admittance model of a VSG after power coupling is provided in an embodiment of the present application.

[0035] Figure 5 A schematic diagram of a power decoupling strategy based on virtual P / ω admittance provided in an embodiment of the present application.

[0036] Figure 6 A schematic diagram of an initial equivalent control model for achieving power decoupling based on virtual P / ω admittance provided in an embodiment of the present application.

[0037] Figure 7 A schematic diagram of another equivalent control model for achieving power decoupling based on virtual P / ω admittance provided in an embodiment of the present application.

[0038] Figure 8 The embodiment of this application provides Figure 7 Schematic diagram of the power loop control model obtained by simplifying the equivalent control model. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field based on this application are within the scope of protection of this application.

[0040] With the large-scale integration of renewable energy into the power grid via power electronic converters, the inertia and damping of power systems are decreasing, jeopardizing the safe and stable operation of the system. To address this issue, virtual synchronous generator (VSG) technology has emerged. By mimicking the rotor motion equations and excitation equations of traditional synchronous generators, VSGs can provide converters with frequency and voltage support capabilities. In power grids with high resistance-to-inductance ratios (R / X), VSGs can achieve independent control of active power versus frequency and reactive power versus voltage. However, in power grids with low R / X, active and reactive power are coupled and cannot be controlled independently. This coupling can affect the steady-state accuracy, dynamic performance, and even stability of power control.

[0041] In response to the power coupling problem of VSG, scholars at home and abroad have proposed many decoupling strategies, which are mainly divided into steady-state decoupling strategies and dynamic decoupling strategies. The decoupling strategy based on virtual impedance is the most common steady-state decoupling method, which reduces the impact of power coupling by reshaping the line impedance to inductive. However, virtual impedance will also cause voltage drops, which in turn limits its decoupling ability, and the decoupling effect is not good under large power angles. The decoupling strategy based on q-axis voltage compensation improves the decoupling ability of the traditional virtual impedance method, but this method only compensates for the q-axis voltage, which will cause large power fluctuations in the dynamic process. In addition, there are methods such as introducing feedforward compensation based on relative gain theory and virtual current feedforward to reduce coupling. However, the aforementioned methods can only achieve static power decoupling and are not suitable for dynamic power coupling problems.

[0042] To achieve dynamic decoupling, existing technologies use internal model control and H∞ control based on the Jacobian transfer matrix to design decoupling strategies based on multivariable feedback theory. This approach can effectively suppress the interaction between active and reactive power. However, designing high-order controllers based on prior knowledge of the entire system model is difficult. While this approach is theoretically feasible, it is difficult to implement in practice. Another existing technology proposes a power decoupling method based on proportional cross-feedforward compensation. This method has been shown to mitigate oscillations, but the two proportional gains are adjusted through trial and error, making parameter tuning complex.

[0043] Based on this, the embodiment of the present application provides an integral feedforward decoupling method applicable to a virtual synchronous generator. The method can be found in Figure 1 , Figure 1 FIG. 1 is a flow chart of an integral feedforward decoupling method for a virtual synchronous generator provided in an embodiment of the present application, comprising:

[0044] S1: Construct a power loop control model for active power and reactive power of VSG considering the influence of reactive power coupling.

[0045] Furthermore, the power loop control model of the active power and reactive power of the VSG is constructed in S1 considering the influence of reactive power coupling, specifically including:

[0046] S101: Construct an initial VSG power loop control model considering active power and reactive power of the VSG when reactive power control coupling is considered.

[0047] In one embodiment of the present application, a VSG power loop control model is constructed based on the relationship between system control parameters and active power and reactive power. The model can be found in Figure 2 .

[0048] in, Figure 2 As shown in ,in and are the angular frequency of VSG and its reference value, is the angular frequency of the disturbance; is a reactive-voltage controller, ,in, is the reactive droop coefficient, is the reactive inertia coefficient, is the Laplace operator; and are the power angle coefficients of active power and reactive power respectively; and are the voltage amplitude coefficients of active power and reactive power, is the active power reference, is the reactive power reference, is the virtual inertia, is the angular frequency of VSG, The frequency of the public grid connection point, is the active power droop coefficient, For the power angle, is the VSG output voltage amplitude.

[0049] In one embodiment of the present application, the power angle coefficients of the active power and the reactive power are 、 and voltage amplitude coefficient 、 They are:

[0050]

[0051]

[0052]

[0053]

[0054] Among them, the subscript "0" represents the initial steady-state operating point, is the voltage amplitude of the public grid connection point when the system is in steady state operation, is the voltage amplitude of the public grid connection point, is the equivalent resistance of the transmission line, is the equivalent inductance of the transmission line, is the rated amplitude of VSG output voltage, is the VSG steady-state operating power angle, is the rated angular frequency of VSG, is a sine function, is the cosine function.

[0055] S102: Taking the reactive power reference variation in the VSG power loop control model as zero as a simplification condition, simplify the VSG power loop control model to obtain the power loop control model.

[0056] In one embodiment of the present application, it is assumed that the reactive power reference variation is zero, that is, , you can build Figure 2 The model shown is simplified so that Figure 2 The multi-input multi-output model shown can be equivalent to Figure 3 The single-input single-output model shown.

[0057] S2: Based on the relationship between power and frequency represented by the power loop control model, power coupling is equivalent to coupling admittance, and a P / ω admittance model of the VSG after considering power coupling is constructed.

[0058] Furthermore, in S2, based on the relationship between power and frequency represented by the power loop control model, power coupling is equivalent to coupling admittance, and a P / ω admittance model of the VSG after considering power coupling is constructed, which specifically includes:

[0059] S201: According to the relationship between power and frequency represented by the power loop control model, the power coupling is equivalent to the coupling admittance Y c , respectively determine the first admittance Y a , the second admittance Y b and the coupling admittance Y c ;

[0060] S202: According to the first admittance Y a The second admittance Y b and the coupling admittance Y c The relationship between VSG control parameters, VSG angular frequency and system operating point is established to construct the P / ω admittance model of VSG after considering power coupling;

[0061] Wherein, the first admittance Ya The second admittance Y b and the coupling admittance Y c They are:

[0062]

[0063]

[0064]

[0065] in, and is the power angle coefficient of active power and reactive power, and is the voltage amplitude coefficient of active power and reactive power, is a reactive-voltage controller, and are the active droop coefficient and virtual inertia of VSG respectively, is the rated angular frequency of VSG, is the Laplace operator.

[0066] In one embodiment of the present application, as can be seen from the above formula, the admittance Y a Only related to VSG control parameters, admittance Y b Related to line impedance and system operating point, Y c is the additional admittance introduced by power coupling. Figure 4 The admittance model can respectively characterize the influence of the active loop, system operating point and reactive loop on the P / ω admittance characteristics.

[0067] In one embodiment of the present application, the VSG control parameters include: active power reference , reactive power reference , virtual inertia , angular frequency of VSG , the frequency of the public grid connection point , Active power droop coefficient , power angle , VSG output voltage amplitude , reactive power droop coefficient , reactive inertia coefficient , active power and reactive power power angle coefficient and , voltage amplitude coefficient of active power and reactive power and .

[0068] S3: A virtual P / ω admittance is connected in parallel at both ends of the coupled admittance in the P / ω admittance model to form a power decoupling strategy based on the virtual P / ω admittance.

[0069] Wherein, the virtual P / ω admittance Y d =-Y c .

[0070] In one embodiment of the present application, reactive coupling will change the original P / ω characteristic of the VSG, which is mainly related to the coupling admittance Y c In order to eliminate the coupling admittance Y c The effect of the coupling impedance 1 / Y c A virtual impedance 1 / Y is connected in parallel at both ends d ,like Figure 5 As shown, the impedances in parallel are equivalent to the addition of their respective admittances, that is, Y d +Y c , if Y d =-Y c , then we can eliminate Y c impact.

[0071] S4: reconstructing the power loop control model according to the power decoupling strategy of the power decoupling P / ω admittance, and performing decoupling based on the reconstructed power loop control model.

[0072] Further, if Figure 6-8 As shown, specifically including:

[0073] S401: According to the power decoupling strategy of the power decoupling P / ω admittance, an additional feedforward branch is connected in parallel in the power loop control model to form an initial equivalent control model of power decoupling;

[0074] S402: Shift the addition point of the additional feedforward branch from the output end to the input end to form a new equivalent control model;

[0075] S403: Add reactive power reference value As a simplification condition, simplifying the new equivalent control model to obtain the reconstructed power loop control model;

[0076] S404: Decoupling is performed based on the reconstructed power loop control model.

[0077] In one embodiment of the present application, according to the power decoupling strategy of the power decoupling P / ω admittance, in the power loop control model, an additional feedforward branch is connected in parallel, which can be equivalent to Figure 5 The parallel virtual P / ω admittance Y shown by the dashed line d , forming a virtual P / ω admittance Y d The initial equivalent control model for power decoupling can be found in Figure 6 ,Will Figure 6 Y in dThe addition point of the branch is shifted to the left, and transformed into Figure 7 The new equivalent control model shown is based on the reactive power reference plus As a simplified condition, the new equivalent control model is simplified to obtain Figure 8 The simplified power loop control model is shown.

[0078] It can be seen that the power decoupling strategy based on virtual P / ω admittance proposed in this application is essentially frequency integral feedforward control.

[0079] This application treats reactive power coupling as equivalent to a parallel coupled admittance, and then connects a virtual P / ω admittance in parallel at both ends of the coupled admittance to offset the influence of the coupled admittance. This method introduces a virtual P / ω admittance to offset the influence of power coupling while considering power coupling, achieving dynamic and steady-state dual-dimensional decoupling, improving decoupling efficiency and accuracy, reducing parameter complexity, and having clear physical meaning, making it easier for engineers to understand the working principle of the technology, and providing reliable technical support for the application of VSG in complex power grid environments.

[0080] It should be noted that those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of this application, and it should be understood that the scope of protection of this application is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in this application without departing from the essence of this application, and such variations and combinations are still within the scope of protection of this application.

Claims

1. An integral feedforward decoupling method for a virtual synchronous generator, characterized in that: include: S1: Construct a power loop control model for active power and reactive power of VSG considering the influence of reactive power coupling; S2: Based on the relationship between power and frequency represented by the power loop control model, power coupling is equivalent to coupling admittance, and a P / ω admittance model of the VSG considering power coupling is constructed; S3: connecting a virtual P / ω admittance in parallel at both ends of the coupled admittance in the P / ω admittance model to form a power decoupling strategy based on the virtual P / ω admittance; S4: reconstructing the power loop control model according to the power decoupling strategy of the power decoupling P / ω admittance, and performing decoupling based on the reconstructed power loop control model; In S2, based on the relationship between power and frequency represented by the power loop control model, power coupling is equivalent to coupling admittance, and a P / ω admittance model of the VSG after considering power coupling is constructed, which specifically includes: S201: According to the relationship between power and frequency represented by the power loop control model, the power coupling is equivalent to the coupling admittance Y c , respectively determine the first admittance Y a , the second admittance Y b and the coupling admittance Y c ; S202: According to the first admittance Y a The second admittance Y b and the coupling admittance Y c The relationship between VSG control parameters, VSG angular frequency and system operating point is established to construct the P / ω admittance model of VSG after considering power coupling; The first admittance Y a The second admittance Y b and the coupling admittance Y c They are: in, and is the power angle coefficient of active power and reactive power, and is the voltage amplitude coefficient of active power and reactive power, is a reactive-voltage controller, and are the active droop coefficient and virtual inertia of VSG respectively, is the rated angular frequency of VSG, is the Laplace operator; In S3, the virtual P / ω admittance Y d =-Y c .

2. The integral feedforward decoupling method for a virtual synchronous generator according to claim 1, characterized in that: The power loop control model of the active power and reactive power of the VSG is constructed in S1 considering the influence of reactive power coupling, specifically including: S101: Constructing an initial VSG power loop control model considering active power and reactive power of the VSG when reactive power control is coupled; S102: Taking the reactive power reference variation in the initial VSG power loop control model as zero as a simplification condition, simplify the initial VSG power loop control model to obtain the power loop control model.

3. The integral feedforward decoupling method for a virtual synchronous generator according to claim 1, characterized in that: The step S4 reconstructs the power loop control model according to the power decoupling strategy of the power decoupling P / ω admittance, and performs decoupling based on the reconstructed power loop control model, specifically including: S401: According to the power decoupling strategy of the power decoupling P / ω admittance, an additional feedforward branch is connected in parallel in the power loop control model to form an initial equivalent control model of power decoupling; S402: Move the addition point of the additional feedforward branch from the output end of the power loop control model to the left. The output end of forms a new equivalent control model; S403: Add reactive power reference value As a simplification condition, simplifying the new equivalent control model to obtain the reconstructed power loop control model; S404: Decoupling is performed based on the reconstructed power loop control model.

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