Enhanced power decoupling control method for virtual synchronous generator

Abstract

The invention discloses an enhanced power decoupling control method for a virtual synchronous generator, relates to the technical field of virtual synchronous generators, and solves the problems that a systematic analysis method for a resistance-inductance line power coupling mechanism is lacked and a collaborative design framework of a dynamic power decoupling condition and a steady-state power transmission requirement cannot be established in the prior art. According to the method, firstly, a dynamic coupling coefficient is accurately quantified through small signal modeling, then a voltage amplitude compensation mechanism based on virtual impedance is established, steady-state power transmission constraints are embedded into dynamic decoupling conditions, and virtual impedance parameters have the dual functions of eliminating dynamic coupling and guaranteeing steady-state tracking. The method does not depend on ideal working condition assumption, can calculate the optimal virtual resistance and virtual reactance on line according to real-time line parameters and operation working conditions, improves the adaptability of the VSG to a weak power grid resistance-inductance line, effectively inhibits dynamic cross coupling between power, and enhances the frequency support and voltage support capability of the VSG under a complex power grid condition.

Description

Technical Field

[0001] This invention relates to the field of virtual synchronous generator technology, and in particular to a method for enhancing power decoupling control of a virtual synchronous generator. Background Technology

[0002] With the large-scale integration of distributed renewable energy into distribution networks, Virtual Synchronous Generator (VSG) technology effectively enhances the grid support capability of power electronic interfaces by simulating the rotor inertia and damping characteristics of synchronous generators. This technology provides frequency regulation and voltage support to the grid through active power-frequency control and reactive power-voltage control, and has become one of the key technologies for building high-proportion renewable energy power systems. However, in weak grid scenarios such as medium- and low-voltage distribution networks, transmission lines generally exhibit significant inductive and resistive characteristics, with generally high line impedance ratios, posing a severe challenge to traditional VSG control strategies based on purely inductive assumptions.

[0003] Existing VSG control technology suffers from fundamental shortcomings under weak grid conditions with resistive-inductive lines: It lacks a systematic analysis method for the power coupling mechanism of resistive-inductive lines, and cannot establish a collaborative design framework for dynamic power decoupling conditions and steady-state power transmission requirements. Traditional decoupling methods are mostly based on simplification assumptions, ignoring the coupling effect of power angle on reactive power. Their control parameters are only applicable to specific operating conditions. When line impedance characteristics or operating points change, the power coupling suppression effect deteriorates significantly, causing mutual interference between the dynamic responses of active and reactive power, leading to power output deviations and transient oscillations. This severely restricts the power transmission capacity and dynamic support performance of VSGs in weak grids.

[0004] Therefore, a virtual synchronous generator is needed to enhance power decoupling control. Summary of the Invention

[0005] To address the lack of a systematic analysis method for the power coupling mechanism of resistive-inductive lines in existing technologies, and the inability to establish a collaborative design framework for dynamic power decoupling conditions and steady-state power transmission requirements, this invention provides a virtual synchronous generator-enhanced power decoupling control method. By constructing a complete theoretical model of power coupling under resistive-inductive line conditions, it achieves an organic unity between dynamic decoupling and steady-state accuracy, fundamentally solving the deficiency of collaborative design in existing technologies. The specific technical solution is as follows: A method for enhancing power decoupling control using a virtual synchronous generator includes the following steps: Establish active power-frequency control model and reactive power-voltage control model of virtual synchronous generator; and analyze the power transmission characteristics of virtual synchronous generator when connected to weak power grid through resistive-inductive line, and construct coupled equations including active power, reactive power, output voltage amplitude, power angle and line impedance parameters. A power coupling matrix is ​​established through small-signal linearization processing to identify dynamic coupling coefficients; a virtual impedance is connected in series at the output of the virtual synchronous generator, and the virtual voltage is defined as the vector sum of the output voltage of the virtual synchronous generator and the voltage drop of the virtual impedance. Establish the steady-state power transfer equations with virtual impedance and set steady-state power tracking constraints; The output voltage amplitude compensation is calculated based on the change in the active power reference value, and a linear relationship between the voltage change coefficient and the active power disturbance is established; the output current change is calculated based on the change in the active power reference value, and a linear relationship between the current change coefficient and the active power disturbance is established. The steady-state power transfer equation is linearized at the initial steady-state operating point. After substituting the voltage amplitude compensation and output current change, it is decomposed into steady-state components and small-signal components. The virtual resistance and virtual reactance parameters that satisfy the dynamic decoupling conditions and steady-state transmission requirements are solved. The calculated virtual impedance parameters are applied to the virtual synchronous generator control system to achieve dynamic decoupling of active power and reactive power and accurate steady-state tracking.

[0006] Preferably, the establishment of the active power-frequency control model and reactive power-voltage control model of the virtual synchronous generator specifically includes: The active power control adopts a virtual rotor motion equation, which includes active power reference value, output power, rated angular velocity, actual angular velocity, virtual inertia and damping coefficient; Reactive power control adopts the QU droop characteristic equation, which includes reactive power reference value, output power, rated voltage amplitude, and voltage amplitude reference value.

[0007] Preferably, the analysis of the power transmission characteristics of the virtual synchronous generator when connected to a weak power grid via an inductive line specifically includes: Establish active and reactive power transmission equations between two voltage sources in an AC system. The equations are functions of output voltage amplitude, grid voltage amplitude, power angle, line resistance, and line reactance. The coupling equations verify that there is an inherent coupling path between active power and reactive power caused by the impedance of the resistive-inductive line.

[0008] Preferably, the step of establishing the power coupling matrix through small-signal linearization specifically includes: By performing partial differential linearization on the active and reactive power transmission equations at the operating equilibrium point, four coupling coefficients in the small-signal model are obtained. Among them, the coupling coefficients characterizing the influence of voltage amplitude on active power and the coupling coefficients characterizing the influence of power angle on reactive power are not zero under the condition of resistive-inductive circuit, resulting in power coupling.

[0009] Preferably, establishing the steady-state power transfer equations containing virtual impedance specifically includes: Based on the law of cosines, a steady-state vector equation is constructed between virtual voltage, grid voltage, output current, line impedance, and virtual impedance; With the reactive power reference value at zero, the virtual voltage amplitude is set to be equal to the rated voltage amplitude as the steady-state power tracking target.

[0010] Preferably, the calculation of the output voltage amplitude compensation based on the change in the active power reference value specifically includes: The voltage variation coefficient is calculated at the initial steady-state operating point, and the coefficient is equal to the partial derivative of the output voltage amplitude with respect to the active power. The product of the voltage variation coefficient and the active power disturbance is used as the output voltage amplitude compensation.

[0011] Preferably, the solution for the virtual resistance and virtual reactance parameters specifically includes: The virtual resistance value is taken as the negative of the line resistance to achieve complete cancellation. The virtual reactance value is calculated based on the line reactance, steady-state output current amplitude, grid voltage, virtual voltage, and power reference value. The calculation formula is as follows: in, K PI E0 represents the current variation coefficient caused by active power disturbance, and E0 represents the steady-state output voltage amplitude. K PE I represents the voltage change coefficient caused by active power disturbance, and I0 represents the steady-state output current amplitude.

[0012] A computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device where the computer-readable storage medium is located to perform the virtual synchronous generator enhanced power decoupling control method as described above.

[0013] A processor for running a program, wherein the program executes the virtual synchronous generator enhanced power decoupling control method as described above.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The enhanced power decoupling control method proposed in this invention achieves an organic unity of dynamic decoupling and steady-state accuracy by constructing a complete theoretical model of power coupling under resistive-inductive line conditions, fundamentally solving the deficiency of collaborative design in existing technologies. This method first precisely quantifies the dynamic coupling coefficient through small-signal modeling, revealing the key coupling effect of the power angle in weak power grids. Then, it establishes a voltage amplitude compensation mechanism based on virtual impedance, embedding steady-state power transmission constraints into the dynamic decoupling conditions, enabling the virtual impedance parameter to have the dual function of eliminating dynamic coupling and ensuring steady-state tracking. Compared to traditional methods, this invention does not rely on ideal operating condition assumptions and can calculate the optimal virtual resistance and virtual reactance online based on real-time line parameters and operating conditions. This significantly improves the adaptability of VSG to resistive-inductive lines in weak power grids, effectively suppresses dynamic cross-coupling between power sources, and ensures accurate steady-state power tracking of the reference value, significantly enhancing the frequency and voltage support capabilities of VSG under complex power grid conditions. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0016] Figure 1 This is a flowchart of the decoupling control method of the present invention; Figure 2 This refers to the general topology and control structure of the virtual synchronous generator in this invention; Figure 3 This is a simplified circuit diagram and a phasor diagram containing virtual impedance in this invention; Figure 4 This is a result diagram of the VSG output power in Embodiment 1 of the present invention; Figure 5 This is a diagram showing the results of virtual resistance and virtual inductance under different circuit conditions in Embodiment 1 of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0019] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0020] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0021] like Figures 1-5 As shown, in one embodiment of the present invention, an enhanced power decoupling control method is provided, comprising two aspects: 1) based on the analysis of the power coupling mechanism under resistive-inductive line conditions, the intrinsic causes of dynamic power coupling and steady-state power delivery deviations are revealed; 2) an improved virtual impedance power decoupling method is proposed to eliminate coupling between power loops while simultaneously satisfying the conditions for dynamic power decoupling and power delivery requirements. The proposed method can effectively improve the dynamic and steady-state power response of the VSG. Simulation tests have verified the proposed method.

[0022] The basic principle of the virtual synchronous generator (VSG) is analyzed, considering the impedance characteristics of the inductive line. The VSG is connected to the power grid through the inductive line, and the active power control output of the VSG is modeled as follows: (1) (2) In the formula, P ref and P e These are the active power reference value and the output power, respectively. ω n and ω These are the rated angular velocity and the actual angular velocity, respectively. J For virtual inertia, D This refers to the damping coefficient. In reactive power control, the voltage amplitude reference value... E ref Depend on QU The drooping characteristic is determined by the following expression: (3) In the formula, E n This is the rated voltage amplitude. Q e and Q ref These are reactive power output and power reference, respectively.

[0023] Based on the analysis of the active power control output and reactive power control output of the virtual synchronous generator (VSG), P can be independently adjusted by controlling the frequency and amplitude of the VSG output voltage. e and Q e Since the power transmission characteristics of a power system are mainly determined by line impedance, it is necessary to construct the active and reactive power flowing between two voltage sources in an AC system, as expressed below: (4) (5) In the formula, the power angle δ yes E and U g The phase difference between them P e and Q e All δ and E The function, according to P e and Q e and δ and E The relationship between them verified P e and Q e There are inherent coupling paths between them, which can be used to establish... VSG The small-signal model of is expressed as follows: (6) In the formula, constant λ 11 , λ 12 , λ 21 and λ 22 belong E These are related to the operating point and line impedance.

[0024] when λ 12 and λ 21When they are not both zero, active and reactive power are coupled rather than independent. Under ideal assumptions, the line impedance is mainly inductive, and the power angle is very small. λ 12 and λ 21 Almost zero. In reality, virtual synchronous generators (VSGs) are typically connected to weak grids at medium / low voltage levels, where their impedance ratios and values ​​are usually high, and the power angle's effect on coupling cannot be ignored. Meanwhile, λ 12 much smaller λ 21 The effect of its output voltage on active power is negligible compared to the effect of the power angle on reactive power.

[0025] A simplified circuit and phasor diagram of a grid-connected VSG with VI were drawn. The output voltage of the RPC is defined as a virtual voltage, and its expression is as follows: (7) In the formula, E v This represents the amplitude of the virtual voltage. When using... VI hour, VSG The voltage amplitude will be optimized through necessary voltage compensation. Assuming the reactive power reference is zero, there exists a steady-state equation that satisfies the cosine theorem, expressed as follows: (8) In this formula, if the amplitude of the virtual voltage equals the rated voltage, the target of tracking the power reference value can be guaranteed. However, the coupling problem is not only a steady-state power transfer problem, but also involves the key process of dynamic power response. Therefore, a decoupling method should be designed by combining voltage amplitude compensation with dynamic small-signal decoupling conditions, and its expression is as follows: (9) Assuming steady-state power transmission capability is guaranteed, fluctuations in active power will not affect reactive power output. Based on the design principles of decoupling methods, the expression for ΔE can be derived as follows: (10) (11) In the formula, K PE This represents the voltage change coefficient caused by active power disturbances. P e Disturbances will also cause changes in the output current, which can be derived as follows: (12) In the formula, I0, E0, and P0 represent the steady-state output current amplitude, voltage amplitude, and active power, respectively. The expression for ΔI can be derived as follows: (13) (14) In the formula, K PI The coefficient of current change caused by active power disturbance is represented by equation (8). By linearizing equation (8) at the initial steady-state point, the small-signal expression can be obtained: (15) Substituting equations (10), (11), (13), and (14) into equation (15), and ignoring the quadratic terms of the small signal, equation (15) can be decomposed into a steady-state part and a small-signal part, as shown in the following expression: (15) (16) By solving equations (15) and (16), the value of VI can be calculated. This value is related to the operating conditions and grid parameters. The derivation results are as follows: (17) (18) (19) In the formula, by adding VI Power coupling will be effectively eliminated.

[0026] The following is combined Figures 4-5 The technical solution of the present invention will be further illustrated through specific embodiments.

[0027] Example 1: To verify the effectiveness of the proposed method, tests were conducted in MATLAB / Simulink. A virtual synchronous generator (VSG) was connected to a 10 kV medium-voltage power grid, where the line impedance was represented by resistance and inductance. Figure 4 P in Embodiment 1 of the present invention ref The result graph of VSG output power during the change process, at 5 seconds, P ref From 0.5 to 1.0 pu, Q ref Keep it at zero, then obtain the power response curve. According to... Figure 4 When using ordinary VSG control, the output power cannot completely track the reference value due to coupling. For example... Figure 4 As shown in (a), when P refWhen the value changes, the reactive power deviation changes from -0.165 pu to -0.295 pu, indicating a significant deviation in reactive power under different power reference values. According to... Figure 4 (b) When the proposed method is used, the reference values ​​of both active power and reactive power can be well tracked, and the dynamic power response is satisfactory.

[0028] Figure 5 This paper demonstrates the virtual resistance and virtual inductance under different line conditions. Different voltage and current (VI) are required to satisfy the power decoupling condition under different line impedances and power demands. The power reference value changes at t=5 seconds. The results show that ideal power decoupling can only be guaranteed when the virtual resistance completely cancels out the actual resistance component and the virtual inductance is set to the desired value to provide sufficient voltage compensation. When the power reference value changes, the required virtual resistance hardly changes because the line impedance does not change significantly with power fluctuations. However, the ideal virtual inductance changes due to the additional voltage compensation requirement. Even so, the expected virtual inductance does not change significantly. Therefore, a constant VI is applicable without strict power decoupling constraints.

[0029] The enhanced power decoupling control method proposed in this invention achieves an organic unity of dynamic decoupling and steady-state accuracy by constructing a complete theoretical model of power coupling under resistive-inductive line conditions, fundamentally solving the deficiency of collaborative design in existing technologies. This method first precisely quantifies the dynamic coupling coefficient through small-signal modeling, revealing the key coupling effect of the power angle in weak power grids. Then, it establishes a voltage amplitude compensation mechanism based on virtual impedance, embedding steady-state power transmission constraints into the dynamic decoupling conditions, enabling the virtual impedance parameter to have the dual function of eliminating dynamic coupling and ensuring steady-state tracking. Compared to traditional methods, this invention does not rely on ideal operating condition assumptions and can calculate the optimal virtual resistance and virtual reactance online based on real-time line parameters and operating conditions. This significantly improves the adaptability of VSG to resistive-inductive lines in weak power grids, effectively suppresses dynamic cross-coupling between power sources, and ensures accurate steady-state power tracking of the reference value, significantly enhancing the frequency and voltage support capabilities of VSG under complex power grid conditions.

[0030] Those skilled in the art will recognize that the units of the various examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the invention.

[0031] In the embodiments provided by the present invention, it should be understood that the division of units is only a logical functional division. In actual implementation, there may be other division methods, such as multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored.

[0032] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0033] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for enhancing power decoupling control using a virtual synchronous generator, characterized in that, Includes the following steps: Establish active power-frequency control model and reactive power-voltage control model of virtual synchronous generator; and analyze the power transmission characteristics of virtual synchronous generator when connected to weak power grid through resistive-inductive line, and construct coupled equations including active power, reactive power, output voltage amplitude, power angle and line impedance parameters. A power coupling matrix is ​​established through small-signal linearization processing to identify dynamic coupling coefficients; a virtual impedance is connected in series at the output of the virtual synchronous generator, and the virtual voltage is defined as the vector sum of the output voltage of the virtual synchronous generator and the voltage drop of the virtual impedance. Establish the steady-state power transfer equations with virtual impedance and set steady-state power tracking constraints; The output voltage amplitude compensation is calculated based on the change in the active power reference value, and a linear relationship between the voltage change coefficient and the active power disturbance is established. The change in output current is calculated based on the change in active power reference value, and a linear relationship between the current change coefficient and active power disturbance is established. The steady-state power transfer equation is linearized at the initial steady-state operating point. After substituting the voltage amplitude compensation and output current change, it is decomposed into steady-state components and small-signal components. The virtual resistance and virtual reactance parameters that satisfy the dynamic decoupling conditions and steady-state transmission requirements are solved. The calculated virtual impedance parameters are applied to the virtual synchronous generator control system to achieve dynamic decoupling of active power and reactive power and accurate steady-state tracking.

2. The virtual synchronous generator enhanced power decoupling control method according to claim 1, characterized in that, The establishment of the active power-frequency control model and reactive power-voltage control model of the virtual synchronous generator specifically includes: The active power control adopts a virtual rotor motion equation, which includes active power reference value, output power, rated angular velocity, actual angular velocity, virtual inertia and damping coefficient; Reactive power control adopts the QU droop characteristic equation, which includes reactive power reference value, output power, rated voltage amplitude, and voltage amplitude reference value.

3. The virtual synchronous generator enhanced power decoupling control method according to claim 1, characterized in that, The analysis of the power transmission characteristics of the virtual synchronous generator when connected to a weak power grid via an inductive line specifically includes: Construct the active and reactive power transmission equations between two voltage sources in an AC system. The equations are functions of the output voltage amplitude, the grid voltage amplitude, the power angle, the line resistance, and the line reactance. The coupling equations verify that there is an inherent coupling path between active power and reactive power caused by the impedance of the resistive-inductive line.

4. The virtual synchronous generator enhanced power decoupling control method according to claim 1, characterized in that, The establishment of the power coupling matrix through small-signal linearization specifically includes: By performing partial differential linearization on the active and reactive power transmission equations at the operating equilibrium point, four coupling coefficients in the small-signal model are obtained. Among them, the coupling coefficients characterizing the influence of voltage amplitude on active power and the coupling coefficients characterizing the influence of power angle on reactive power are not zero under the condition of resistive-inductive circuit, resulting in power coupling.

5. The virtual synchronous generator enhanced power decoupling control method according to claim 1, characterized in that, The establishment of the steady-state power transfer equations containing virtual impedance specifically includes: Based on the law of cosines, a steady-state vector equation is constructed between virtual voltage, grid voltage, output current, line impedance, and virtual impedance; With the reactive power reference value at zero, the virtual voltage amplitude is set to be equal to the rated voltage amplitude as the steady-state power tracking target.

6. The virtual synchronous generator enhanced power decoupling control method according to claim 1, characterized in that, The calculation of the output voltage amplitude compensation based on the change in the active power reference value specifically includes: The voltage variation coefficient is calculated at the initial steady-state operating point, and the coefficient is equal to the partial derivative of the output voltage amplitude with respect to the active power. The product of the voltage variation coefficient and the active power disturbance is used as the output voltage amplitude compensation.

7. The virtual synchronous generator enhanced power decoupling control method according to claim 1, characterized in that, The specific steps for solving the virtual resistance and virtual reactance parameters include: The virtual resistance value is taken as the negative of the line resistance to achieve complete cancellation. The virtual reactance value is calculated based on the line reactance, steady-state output current amplitude, grid voltage, virtual voltage, and power reference value. The calculation formula is as follows: in, K PI E0 represents the current variation coefficient caused by active power disturbance, and E0 represents the steady-state output voltage amplitude. K PE I represents the voltage change coefficient caused by active power disturbance, and I0 represents the steady-state output current amplitude.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device containing the computer-readable storage medium to perform the virtual synchronous generator enhanced power decoupling control method according to any one of claims 1 to 7.

9. A processor, characterized in that, The processor is used to run a program, wherein the program executes the virtual synchronous generator enhanced power decoupling control method according to any one of claims 1 to 7.

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