Integral feedforward decoupling method suitable for virtual synchronous generator

Abstract

The invention discloses an integral feed-forward decoupling method suitable for a virtual synchronous generator, and belongs to the technical field of power systems, and the method comprises the steps: enabling reactive power coupling to be independently equivalent to a parallel coupling admittance, and then enabling the two ends of the coupling admittance to be connected with a virtual P / omega admittance in parallel, so as to offset the influence of the coupling admittance. According to the method, under the condition of considering power coupling, a virtual P / omega admittance is introduced to counteract the influence of power coupling, dynamic and steady-state two-dimensional decoupling is realized, the decoupling efficiency and the decoupling accuracy are improved, the parameter complexity is reduced, the method has clear physical significance, engineering personnel can understand the working principle of the technology conveniently, and the method is suitable for popularization and application. And reliable technical support can be provided for application of the VSG in a complex power grid environment.

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 access of new energy to the power grid through power electronic converters, the inertia and damping of the power system have decreased, endangering the safe and stable operation of the system. For this reason, the virtual synchronous generator (VSG) technology has emerged. By mimicking the rotor motion equation and excitation equation of a traditional synchronous generator, the converter can have the ability to support frequency and voltage. In a power grid with a high resistance-to-inductance ratio (R / X), the VSG can achieve independent control of active power - frequency and reactive power - voltage.

[0003] However, in a low R / X power grid, there is a coupling phenomenon between active power and reactive power, and they cannot be independently controlled. This coupling will affect the steady-state accuracy, dynamic performance, and even stability of power control. The current power decoupling methods mainly focus on steady-state power decoupling and rarely consider the impact of power coupling on the dynamic performance of the 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 ability. Compared with the virtual impedance method, although the decoupling method based on relative gain theory or multivariable feedback theory can greatly improve the system decoupling performance, 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 view of the above deficiencies in the prior art, an integral feedforward decoupling method applicable to a virtual synchronous generator provided by the present application solves the problems that the existing power decoupling methods ignore the impact of power coupling on the dynamic performance of the VSG active power, the decoupling ability of the virtual impedance method decreases due to voltage drop, and the parameter design of the multivariable feedback method is complex and the physical meaning is ambiguous.

[0005] In order to achieve the above invention purpose, the technical solution adopted by the present application is as follows: An integral feedforward decoupling method applicable to a virtual synchronous generator provided by the present application includes: S1: Construct a power loop control model for the active power and reactive power of the VSG considering the influence of reactive power coupling; S2: According to the relationship between power and frequency characterized by the power loop control model, equivalent the power coupling to a coupling admittance, and construct a P / ω admittance model of the VSG considering power coupling; S3: Connect a virtual P / ω admittance in parallel at both ends of the coupling 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.

[0006] 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: 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.

[0007] 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: 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 considered, and the P / ω admittance model of VSG considering power coupling is constructed.

[0008] Furthermore, the first admittance Y a The second admittance Y b and the coupling admittance Y c They are:

[0009]

[0010]

[0011] 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 the VSG, respectively, is the rated angular frequency of the VSG, is the Laplace operator.

[0012] Furthermore, in the step S3, the virtual P / ω admittance Y d =-Y c .

[0013] Furthermore, in the step S4, according to the power decoupling strategy of the power decoupling P / ω admittance, the power loop control model is reconstructed, and decoupling is performed based on the reconstructed power loop control model, which specifically includes: S401: According to the power decoupling strategy of the power decoupling P / ω admittance, in the power loop control model, an additional feed-forward branch is connected in parallel to form an initial equivalent control model for power decoupling; S402: Move the phase addition point of the additional feed-forward branch from the output end to the input end to form a new equivalent control model; S403: Using the reactive power reference value plus as the simplification condition, simplify the new equivalent control model to obtain the reconstructed power loop control model; S404: Perform decoupling based on the reconstructed power loop control model.

[0014] The beneficial effects of this application are: A VSG power decoupling control method based on virtual P / ω admittance reshaping provided by this application. By separately equivalenting the reactive power coupling as a parallel-coupled admittance, and then connecting a virtual P / ω admittance in parallel at both ends of the coupled admittance to cancel the influence of the coupled admittance. Considering power coupling, this method introduces a virtual P / ω admittance to cancel the influence of power coupling, realizes decoupling in both dynamic and steady-state dimensions, improves the decoupling efficiency and decoupling accuracy, reduces parameter complexity, has a clear physical meaning, is convenient for engineers to understand the working principle of this technology, and can provide reliable technical support for the application of VSG in complex power grid environments. Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of this application. For those of ordinary skill in the art, other embodiments can also be obtained based on these drawings.

[0016] Figure 1 is a method flow chart of an integral feed-forward decoupling method applicable to a virtual synchronous generator provided by an embodiment of this application.

[0017] Figure 2 Schematic diagram of the initial VSG power loop control model considering the active and reactive power of VSG when reactive power control coupling is taken into account provided by the embodiment of the present application.

[0018] Figure 3 For the Figure 2 Schematic diagram of a power loop control model obtained by simplifying the initial VSG power loop control model provided by the embodiment of the present application.

[0019] Figure 4 Schematic diagram of the P / ω admittance model of VSG considering power coupling provided by the embodiment of the present application.

[0020] Figure 5 Schematic diagram of a power decoupling strategy based on virtual P / ω admittance provided by the embodiment of the present application.

[0021] Figure 6 Schematic diagram of the initial equivalent control model for realizing power decoupling based on virtual P / ω admittance provided by the embodiment of the present application.

[0022] Figure 7 Schematic diagram of another equivalent control model for realizing power decoupling based on virtual P / ω admittance provided by the embodiment of the present application.

[0023] Figure 8 For the Figure 7 Schematic diagram of the power loop control model obtained by simplifying the described equivalent control model provided by the embodiment of the present application. Detailed implementation manners

[0024] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art based on the present application belong to the scope of protection of the present application.

[0025] With a large number of new energy sources accessing the power grid through power electronic converters, the inertia and damping of the power system decrease, endangering the safe and stable operation of the system. For this reason, the virtual synchronous generator (VSG) technology has emerged. By mimicking the rotor motion equation and excitation equation of a traditional synchronous generator, the converter can have the ability to support frequency and voltage. In a power grid with a high resistance-to-inductance ratio (R / X), the VSG can achieve independent control of active power-frequency and reactive power-voltage. However, in a low R / X power grid, there is a coupling phenomenon between active and reactive power and they cannot be independently controlled, and this coupling will affect the steady-state accuracy, dynamic performance, and even stability of power control.

[0026] Regarding 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 influence of power coupling by reshaping the line impedance to be inductive. However, virtual impedance also brings voltage drop, which limits its decoupling ability, and the decoupling effect is not good under the condition of large power angle. 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, resulting in large power fluctuations during the dynamic process. In addition, there are also 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 applicable to dynamic power coupling problems.

[0027] In order to achieve dynamic decoupling, the existing technology designs a decoupling strategy based on multivariable feedback theory, using internal model control and H∞ control based on the Jacobian transfer matrix. This method can effectively suppress the interaction between active power and reactive power. However, it is difficult to design a high-order controller based on the prior knowledge of the entire system model. This method is feasible in theory but difficult to implement in practice. Another existing technology proposes a power decoupling method based on proportional cross-feedforward compensation, which shows that it can reduce oscillations, but the two proportional gains are adjusted by repeated trial and error, and the parameter tuning is relatively complex.

[0028] 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 seen in Figure 1 , Figure 1 The method flow chart of an integral feedforward decoupling method applicable to a virtual synchronous generator provided by the embodiment of the present application is shown in S1: Construct a power loop control model of the active power and reactive power of the VSG considering the influence of reactive power coupling.

[0029] Further, in the S1, constructing a power loop control model of the active power and reactive power of the VSG considering the influence of reactive power coupling specifically includes: S101: Construct an initial VSG power loop control model of the active power and reactive power of the VSG considering reactive power control coupling.

[0030] In an embodiment of the present application, according to the relationship between system control parameters and active power and reactive power, a VSG power loop control model is constructed. This model can be seen in Figure 2 。

[0031] Among them, Figure 2 shown in ,where and are the angular frequency of the VSG and its reference value respectively, is the angular frequency of the disturbance; is the reactive power-voltage controller, , where, is the reactive power droop coefficient, is the reactive power inertia coefficient, is the Laplace operator; and are the power angle coefficients of the active power and the reactive power respectively; and are the voltage amplitude coefficients of the active power and the reactive power respectively, is the active power reference, is the reactive power reference, is the virtual inertia, is the angular frequency of the VSG, is the frequency of the common connection point, is the active power droop coefficient, is the power angle, is the amplitude of the VSG output voltage.

[0032] In an embodiment of the present application, the power angle coefficients 、 of the active power and the reactive power and the voltage amplitude coefficients 、 are respectively:

[0033]

[0034]

[0035]

[0036] where the subscript "0" represents the initial steady-state operating point, is the voltage amplitude of the common connection point during the steady-state operation of the system, is the voltage amplitude of the common connection point, is the equivalent resistance of the transmission line, is the equivalent inductance of the transmission line, is the rated amplitude of the VSG output voltage, is the power angle of the VSG during steady-state operation, is the rated angular frequency of the VSG, is the sine function, is the cosine function.

[0037] S102: Simplify the VSG power loop control model with the condition that the reactive power reference change amount in the model is zero to obtain the power loop control model.

[0038] In one embodiment of the present application, by assuming that the reactive power reference change amount is zero, that is , the constructed model as Figure 2 shown can be simplified, such that the multi-input multi-output model as Figure 2 shown can be equivalent to the single-input single-output model as Figure 3 shown.

[0039] S2: According to the relationship between power and frequency characterized by the power loop control model, equivalently transform power coupling into coupling admittance, and construct a P / ω admittance model of the VSG considering power coupling.

[0040] Further, in S2, according to the relationship between power and frequency characterized by the power loop control model, equivalently transform power coupling into coupling admittance, and construct a P / ω admittance model of the VSG considering power coupling, which specifically includes: S201: According to the relationship between power and frequency characterized by the power loop control model, equivalently transform power coupling into coupling admittance Y c , and respectively determine the first admittance Y a , the second admittance Y b and the coupling admittance Y c ; S202: According to the relationship between the first admittance Y a , the second admittance Y b and the coupling admittance Y c with the VSG control parameters, the angular frequency of the VSG, and the system operating point, construct a P / ω admittance model of the VSG considering power coupling; Among them, the first admittance Y a , the second admittance Y b and the coupling admittance Y c are respectively:

[0041]

[0042]

[0043] Among them, and are the power angle coefficients of active power and reactive power, and are the voltage amplitude coefficients of active power and reactive power, is the reactive-voltage controller, and are the active power droop coefficient and virtual inertia of the VSG respectively, is the rated angular frequency of the VSG, is the Laplace operator.

[0044] In an embodiment of the present application, as can be seen from the above formula, the admittance Y a is only related to the VSG control parameters, and the admittance Y b is related to the line impedance and the system operating point. Y c is the admittance additionally introduced by power coupling. Therefore, through the admittance model of Figure 4 the influence of the active power loop, system operating point, and reactive power loop on the P / ω admittance characteristics can be characterized respectively.

[0045] In an embodiment of the present application, the VSG control parameters include: active power reference , reactive power reference , virtual inertia , the angular frequency of the VSG , the frequency of the common connection point , active power droop coefficient , power angle , the amplitude of the VSG output voltage , reactive power droop coefficient , reactive inertia coefficient , power angle coefficients of active power and reactive power and , voltage amplitude coefficients of active power and reactive power and .

[0046] S3: A virtual P / ω admittance is connected in parallel at both ends of the coupling admittance in the P / ω admittance model to form a power decoupling strategy based on the virtual P / ω admittance.

[0047] Wherein, the virtual P / ω admittance Y d =-Y c .

[0048] In an embodiment of the present application, reactive power coupling will change the original P / ω characteristics of the VSG, which is mainly related to the coupling admittance Y c . In order to eliminate the influence of the coupling admittance Y c , a virtual impedance 1 / Y c can be connected in parallel at both ends of the coupling impedance 1 / Y d , as shown in Figure 5 . The parallel connection of impedances is equivalent to adding their respective admittances, that is, Y d +Y c . If Y d =-Yc , then the influence of Y can be eliminated c .

[0049] S4: Reconstruct the power loop control model according to the power decoupling strategy of the power decoupling P / ω admittance, and perform decoupling based on the reconstructed power loop control model.

[0050] Furthermore, as Figures 6-8 shown, it specifically includes: S401: According to the power decoupling strategy of the power decoupling P / ω admittance, in the power loop control model, connect a parallel additional feedforward branch to form an initial equivalent control model for power decoupling; S402: Move the phase addition point of the additional feedforward branch from the output end to the input end to form a new equivalent control model; S403: Using the reactive power reference value plus as the simplification condition, simplify the new equivalent control model to obtain the reconstructed power loop control model; S404: Perform decoupling based on the reconstructed power loop control model.

[0051] In an embodiment of the present application, according to the power decoupling strategy of the power decoupling P / ω admittance, in the power loop control model, connecting a parallel additional feedforward branch can be equivalent to Figure 5 the parallel virtual P / ω admittance Y shown by the dotted line in d , to form an initial equivalent control model for power decoupling based on the virtual P / ω admittance Y d . It can be seen in Figure 6 that by moving the phase addition point of the Y Figure 6 branch in d to the left, it is transformed into a new equivalent control model as shown in Figure 7 ; using the reactive power reference value plus as the simplification condition, simplify the new equivalent control model to obtain the simplified power loop control model as shown in Figure 8 .

[0052] It can be seen that the power decoupling strategy based on the virtual P / ω admittance proposed in the present application is essentially frequency integral feedforward control.

[0053] In this application, the reactive power coupling is equivalently regarded as a parallel coupling admittance alone, and then a virtual P / ω admittance is connected in parallel across the coupling admittance to cancel the influence of the coupling admittance. Considering the power coupling, this method introduces a virtual P / ω admittance to cancel the influence of power coupling, realizes decoupling in both dynamic and steady-state dimensions, improves the decoupling efficiency and decoupling accuracy, reduces the parameter complexity, has a clear physical meaning, facilitates engineers to understand the working principle of this technology, and can provide reliable technical support for the application of VSG in a complex power grid environment.

[0054] It should be noted that those of ordinary skill in the art will realize that the embodiments described herein are for helping readers understand the principles of the present application, and it should be understood that the protection scope of the present application is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations without departing from the essence of the present application according to these technical revelations disclosed in the present application, and these deformations and combinations are still within the protection scope of the present application.

Claims

1. An integral feedforward decoupling method applicable to a virtual synchronous generator, characterized in that, Including: S1: Construct a power loop control model for the active power and reactive power of the VSG considering the influence of reactive power coupling; S2: According to the relationship between power and frequency characterized by the power loop control model, equivalent the power coupling to a coupling admittance, and construct a P / ω admittance model of the VSG considering power coupling; S3: Connect a virtual P / ω admittance in parallel at both ends of the coupling admittance in the P / ω admittance model to form a power decoupling strategy based on the virtual P / ω admittance; S4: Reconstruct the power loop control model according to the power decoupling strategy of the power decoupling P / ω admittance, and perform decoupling based on the reconstructed power loop control model.

2. The integral feedforward decoupling method applicable to a virtual synchronous generator according to claim 1, characterized in that In the above S1, constructing a power loop control model for the active power and reactive power of the VSG considering the influence of reactive power coupling specifically includes: S101: Construct an initial VSG power loop control model for the active power and reactive power of the VSG considering reactive power control coupling; S102: Take the zero reference change of reactive power in the initial VSG power loop control model as a simplification condition, and simplify the initial VSG power loop control model to obtain the power loop control model.

3. The integral feedforward decoupling method applicable to a virtual synchronous generator according to claim 1, wherein, In the above S2, according to the relationship between power and frequency characterized by the power loop control model, equivalent the power coupling to a coupling admittance, and construct a P / ω admittance model of the VSG considering power coupling, specifically including: S201: According to the relationship between power and frequency characterized by the power loop control model, the power coupling is equivalently represented as a coupling admittance Y c , and the first admittance Y a , the second admittance Y b and the coupling admittance Y c are determined respectively; S202: According to the first admittance Y a , the second admittance Y b and the coupling admittance Y c and their relationships with the VSG control parameters, the angular frequency of the VSG, and the system operating point, construct the P / ω admittance model of the VSG considering power coupling.

4. The integral feedforward decoupling method applicable to a virtual synchronous generator according to claim 3, characterized in that The first admittance Y a 、the second admittance Y b and the coupling admittance Y c are respectively: Among them, and are the power angle coefficients of active power and reactive power, and are the voltage amplitude coefficients of active power and reactive power, is the reactive power-voltage controller, and are the active droop coefficient and virtual inertia of the VSG respectively, is the rated angular frequency of the VSG, is the Laplace operator.

5. The integral feedforward decoupling method applicable to a virtual synchronous generator according to claim 1, wherein In S3, the virtual P / ω admittance Y d = -Y c .

6. The integral feedforward decoupling method applicable to a virtual synchronous generator according to claim 1, wherein In the above S4, reconstruct the power loop control model according to the power decoupling strategy of the power decoupling P / ω admittance, and perform 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, connect an additional feed-forward branch in parallel in the power loop control model to form an initial equivalent control model for power decoupling; S402: Move the phase addition point of the additional feed-forward branch from the output end to the input end to form a new equivalent control model; S403: Add the reactive power reference value to As a simplification condition, simplify the new equivalent control model to obtain the reconstructed power loop control model; S404: Perform decoupling based on the reconstructed power loop control model.

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