Reactive branch control link construction method and device based on improved GFM system

Abstract

The invention discloses a reactive branch control link construction method and device based on an improved GFM system, and relates to the technical field of power system dynamic balance control. The reactive branch improvement method based on PI control is provided for solving the problem of steady-state errors existing in a reactive control branch of a traditional GFM system, indifference adjustment of reactive power is achieved by introducing an integration link, the problem that the voltage control precision is insufficient due to parameter changes and disturbance in a new energy grid-connected system can be solved, and the stability of the system is improved. And an innovative solution is provided for voltage stabilization of a high-proportion new energy power grid.

Description

TECHNICAL FIELD

[0001] The application discloses a reactive branch control link construction method and device based on an improved GFM system, and relates to the technical field of power system dynamic balance control. BACKGROUND

[0002] With high proportion of new energy access to the power grid, the dynamic characteristics of the power system have undergone profound changes, the rapid regulation capacity of traditional synchronous power sources has gradually weakened, and the voltage stability of the power grid is facing severe challenges. Especially under weak grid conditions, the line impedance increases and the short-circuit capacity decreases, making the voltage fluctuation problem more prominent. The existing grid-forming (GFM) converters generally adopt a reactive-voltage regulation strategy based on droop control or virtual synchronous machine (VSG), and the control performance has obvious deficiencies in actual operation.

[0003] Firstly, the traditional reactive control adopts proportional regulation or open-loop strategy, which cannot eliminate the steady-state error, resulting in limited voltage regulation accuracy. Especially when the new energy output fluctuates or the load suddenly changes, the voltage deviation may persist, affecting the power quality. Secondly, the fixed parameter reactive control is difficult to adapt to the change of grid impedance, and may easily cause resonance or stability problems in weak grid scenarios. The measured data shows that the traditional control strategy is slow in regulating when the voltage deviation is small, but may over-regulate under large disturbance, and the dynamic response and steady-state accuracy are difficult to balance.

[0004] In addition, with the increase of the penetration rate of distributed power sources, when multiple GFM converters are operated in parallel, the traditional control strategy may cause reactive circulating current problems due to the lack of accurate zero-error regulation capability, and aggravate system loss. Especially in micro-grid or island operation mode, the voltage control accuracy is directly related to the power supply reliability, and the performance bottleneck of the existing method is increasingly prominent. Therefore, it is urgent to improve the reactive control strategy of the GFM converter to realize high-precision, zero-error voltage regulation in complex grid environment, while ensuring the stability and reliability of the dynamic process. SUMMARY

[0005] The application provides a reactive branch control link construction method and device based on an improved GFM system to solve the problems in the prior art.

[0006] In a first aspect, a reactive branch control link construction method based on an improved GFM system comprises the following steps:

[0007] According to the line power transmission principle and the small-signal linearization processing method, a small-signal model based on the traditional reactive control branch is established, and the steady-state error is verified through step response simulation according to the small-signal model.

[0008] When the steady-state error exists, a PI controller is introduced into the conventional reactive power control circuit as an improved reactive power control circuit; the steady-state error is eliminated by the improved reactive power control circuit.

[0009] Based on the traditional function model under step input, the steady-state error expression is obtained through the improved reactive power control circuit; based on the steady-state error expression, the traditional reactive power control branch is improved through the small-signal model.

[0010] Based on the improved reactive power control circuit, the consistency between the transfer function and the actual simulated waveform is verified through small disturbance testing.

[0011] Some implementations include:

[0012] Based on the small-signal model of the traditional reactive power control branch, the reactive power control equation is improved as shown in formula (2):

[0013]

[0014] In the formula, K q K i These are the proportional and integral coefficients of the reactive power control branch in the GFM system, respectively; Q ref Q and are the reference value and actual output power of the GFM system, respectively; u and u ref These are the actual output voltage and voltage reference value at the grid connection point of the GFM system, respectively.

[0015] In some implementations, when the steady-state error exists, a PI controller is introduced into the conventional reactive power control circuit as an improved reactive power control circuit; the improved reactive power control circuit eliminates the steady-state error, including:

[0016] The effectiveness of the PI controller is verified by comparing the steady-state error before and after elimination.

[0017] Based on the steady-state error, the output deviation is corrected by the error accumulation characteristic of the integral element, thereby eliminating the steady-state error.

[0018] In some implementations, a steady-state error expression is obtained through the improved reactive power control circuit based on a traditional function model under a step input; based on the steady-state error expression, the traditional reactive power control branch is improved through the small-signal model, including:

[0019] Based on the reactive power compensation coefficient, the voltage at the network point is adjusted for transient stability using the reactive power control equation.

[0020] In some implementations, in S3, according to the reactive power compensation coefficient, the net point voltage is adjusted for transient stability by the reactive power control equation.

[0021] In a second aspect, the embodiment of the present application provides a reactive branch control link construction device based on an improved GFM system, comprising:

[0022] A model establishing module is configured to establish a small signal model based on a traditional reactive control branch according to a line power transmission principle and a small signal linearization processing method, and verify a steady-state error by step response simulation according to the small signal model.

[0023] An error elimination module is configured to introduce a PI controller into the traditional reactive control circuit as an improved reactive control circuit when the steady-state error exists, and eliminate the steady-state error by the improved reactive control circuit.

[0024] A branch optimization module is configured to obtain a steady-state error expression by the improved reactive control circuit according to a traditional function model under step input, and improve the traditional reactive control branch by the small signal model according to the steady-state error expression.

[0025] A control verification module is configured to verify consistency of a transfer function and an actual simulation waveform by small disturbance test according to the improved reactive control circuit.

[0026] In some implementations, the model establishing module is configured to improve the small signal model of the traditional reactive control branch by a reactive power control equation, as shown in formula (2):

[0027]

[0028] In the formula, K q , K i are coefficients of proportional and integral links of a reactive power control branch of a GFM system; Q ref , Q are a reference value and an actual output power of reactive power of the GFM system; u, u ref are an actual output voltage and a voltage reference value of a grid connection point of the GFM system.

[0029] In some implementations, the error elimination module comprises:

[0030] An elimination verification unit is configured to verify effectiveness of the PI controller by comparison according to steady-state errors before and after elimination of the PI controller.

[0031] An elimination processing unit is configured to correct output deviation by an error accumulation characteristic of the integral link according to the steady-state error, so as to eliminate the steady-state error.

[0032] In some implementations, in the branch optimization module, according to a reactive power compensation coefficient, the net point voltage is adjusted for transient stability by the reactive power control equation.

[0033] In a third aspect, an embodiment of the present application provides an electronic device, comprising a memory and a processor, the memory being used to store one or more computer instructions, wherein the one or more computer instructions are executed by the processor to implement the method in the first aspect.

[0034] In a fourth aspect, an embodiment of the present application provides a computer storage medium, the computer readable storage medium storing a computer program, the computer program being executed by a processor to implement the method in the first aspect.

[0035] One or more embodiments of the present application can bring at least the following beneficial effects:

[0036] The method of the present application proposes an improved reactive power branch method based on PI control to solve the steady-state error problem of the traditional GFM system reactive power control branch, realizes errorless adjustment of reactive power by introducing an integral element, and can solve the problem of insufficient voltage control accuracy caused by parameter changes and disturbances in a new energy grid-connected system, thereby providing an innovative solution for voltage stability of a high-proportion new energy grid.

[0037] The method of the present application has more accurate steady-state regulation characteristics and stronger anti-interference ability compared with the traditional proportional control method by constructing an improved small-signal model of the reactive power control branch, and can effectively improve the voltage support performance of the GFM system under weak grid conditions, and enhance the power angle stability of the system by optimizing the reactive power compensation coefficient.

[0038] The method of the present application only needs to add a PI adjustment element in the existing control architecture without changing the hardware structure or introducing complex control algorithms, and has the advantages of simple implementation, low modification cost, high reliability, etc., and can provide a more efficient and stable control scheme for grid voltage quality control, and has significant engineering application value. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0040] Figure 1 is a structure comparison diagram of the traditional reactive power control branch and the improved reactive power control branch provided by the embodiment of the present application.

[0041] Figure 2 is a small signal model structure schematic diagram of a traditional reactive control branch provided by the embodiment of the present application;

[0042] Figure 3 is a small signal model structure schematic diagram of an improved reactive control branch provided by the embodiment of the present application;

[0043] Figure 4 is a U pcc and K q curve relationship schematic diagram provided by the embodiment of the present application;

[0044] Figure 5 is a K q and δ' curve relationship schematic diagram provided by the embodiment of the present application. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the 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 of the present application. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0046] Embodiment one:

[0047] The embodiment provides a reactive branch control link construction method based on an improved GFM system, which comprises the following steps:

[0048] S1, according to the line power transmission principle and the small signal linearization processing method, a small signal model based on a traditional reactive control branch is established; according to the small signal model, the steady-state error is verified through step response simulation;

[0049] S2, when the steady-state error exists, a PI controller is introduced into the traditional reactive control circuit as an improved reactive control circuit; according to the steady-state error, the improved reactive control circuit is used for eliminating the steady-state error;

[0050] S3, according to the traditional function model under step input, a steady-state error expression is obtained through the improved reactive control circuit; according to the steady-state error expression, the traditional reactive control branch is improved through a small signal model.

[0051] S4, according to the improved reactive power control circuit, the consistency of the transfer function and the actual simulation waveform is verified by small disturbance test.

[0052] First, according to S1, the control link of the improved GFM system reactive power control branch is built. The mathematical model of the "stimulus-response" relationship model of the traditional Q-V control branch is as follows:

[0053] E = U n +k q (Q ref -Q)(1)

[0054] In order to ensure the stability of the GFM system under the condition such as fault period under the step input response of reactive power and improve its response speed, the mathematical model of the improved reactive power control branch can be improved to improve the dynamic response performance and stability of the system, and the reactive power control equation of the VSG under fault condition is as follows:

[0055]

[0056] According to formula (1) and formula (2), the control block diagram of the strategy of the two kinds of reactive power control links is as shown in Figure 1 , wherein K q , K i are the coefficients of the proportional and integral links of the reactive power control branch of the GFM system respectively; Q ref , Q are the reference value and actual output power of the reactive power of the GFM system respectively; u, u ref are the actual output voltage and voltage reference value of the GFM system grid connection point respectively.

[0057] Next, according to S2, the steady-state error of the two control modes under step response is compared. Based on formula (1), the traditional reactive power control branch is linearized by approximately processing the output reactive power Q and voltage E according to the coefficient K, and the "stimulus-response" relationship small signal model of the traditional reactive power control branch shown in figure (2) can be derived;

[0058] Among them, based on its transfer function model, the steady-state error expression of the output reactive power under step input can be derived, which is as follows:

[0059]

[0060] As can be seen from formula (3), there is a large steady-state deviation of the output reactive power under step input in the traditional control model, which cannot completely eliminate the voltage deviation. This difference is particularly significant in the scene of large grid voltage fluctuation or frequent load change. Therefore, in actual application, the "stimulus-response" relationship model of the traditional reactive power control branch needs to be improved, as shown in formula (2), to improve the dynamic response performance and stability of the system.

[0061] Based on equation (2) and using the same linearization method described above, the improved small-signal model of the excitation-response relationship of the QV control branch can be derived, as follows: Figure 3 As shown;

[0062] Also based on its Figure 3 Based on the transfer function model shown, the steady-state error expression of the output reactive power of the improved model under step input is derived:

[0063]

[0064] The improved reactive power control branch's excitation-response relationship model exhibits zero steady-state error under step input, significantly enhancing control accuracy and better meeting the needs of practical engineering applications. By introducing a PI regulator into the reactive power control loop and utilizing the error accumulation characteristics of the integral element, output deviations can be gradually corrected, ultimately achieving precise and error-free reactive power control. The integral action automatically compensates for the effects of system parameter changes, measurement errors, and external disturbances, ensuring that the reactive power output strictly tracks the reference value in steady state. Simultaneously, reasonable design of PI parameters (such as the integral coefficient and limiting strategy) can avoid integral saturation, guaranteeing dynamic response speed and stability. This improvement not only enhances the voltage support capability of grid-connected inverters but also strengthens their adaptability in weak grids or environments with a high proportion of renewable energy integration, making system operation more reliable.

[0065] Next, according to S3, consider the reactive power compensation factor K. q Impact on power angle stability. According to the principle of line power transmission, the power delivered by the GFM system to the grid is:

[0066]

[0067] Because the lines often Therefore, the resistance R is ignored. g Equation (5) can then be further derived as follows:

[0068]

[0069] Taking a grid voltage drop to 0.5 pu as an example, the transient stability of the system was analyzed. When the fault occurs, the system's power characteristics switch from normal operating conditions to voltage sag conditions, where the active power command value P... ref It remains unchanged. During the fault, due to P... ref >P, under the influence of excess torque, its dynamic behavior corresponds to the region of power angle change, defined as the acceleration area. After the fault is cleared, the electromagnetic power P returns to its normal level, at which point P... refWhen the generator is subjected to the reverse torque, the corresponding power angle variation area of the dynamic behavior is defined as the deceleration area. According to the equal-area criterion, the condition for the system to restore the power angle stability is that the acceleration area is less than the deceleration area, that is, the energy consumed by the system in the deceleration process is sufficient to offset the energy accumulated in the acceleration process, so as to make the power angle finally converge to the stable equilibrium point.

[0070] In the transient stability analysis of the power system, the reactive power compensation coefficient k q has a significant influence on the grid-connected point voltage U pcc . To quantitatively analyze the relationship between k q and U pcc , modeling and solving can be performed through power flow calculation.

[0071] Next, according to S4, the error of the reactive power control link and the power angle stability are verified through simulation. Based on the Matlab / Simulink platform, a model of the GFM system is constructed to simulate the case where the grid voltage drops to 0.5 p.u. at the third second, and the response characteristics of the grid-connected point voltage under different values of k q are observed. Meanwhile, the dynamic response characteristics of δ' under different values of k q are analyzed, and the response curves of the system frequency deviation Δω about the power angle δ' under different values of k q are plotted, as shown in FIG. 3. With the increase of the reactive power compensation coefficient k q , the power angle stability of the GFM system during the fault is significantly improved. In particular, when k q _3 = 500, Δω returns to 0, and δ' can quickly converge and return to the stable equilibrium point. This result shows that the reactive power compensation coefficient k q can effectively enhance the power angle stability of the GFM system under the voltage drop fault, thereby improving the dynamic response performance of the system.

[0072] Embodiment Two:

[0073] In a second aspect, an apparatus for constructing a reactive power branch control link based on an improved GFM system is provided, comprising:

[0074] A model establishing module is configured to establish a small-signal model based on a traditional reactive power control branch according to a line power transmission principle and a small-signal linearization processing method, and verify a steady-state error through step response simulation according to the small-signal model.

[0075] An error elimination module is configured to introduce a PI controller into the traditional reactive power control circuit as an improved reactive power control circuit when the steady-state error exists, and eliminate the steady-state error through the improved reactive power control circuit.

[0076] The branch optimization module is configured to obtain a steady-state error expression by the improved reactive power control circuit according to a traditional function model under a step input; and improve the traditional reactive power control branch by the small-signal model according to the steady-state error expression.

[0077] The control verification module is configured to perform consistency verification of a transfer function and an actual simulation waveform by small disturbance test according to the improved reactive power control circuit.

[0078] Further, the model establishment module is configured to improve the reactive power control equation according to the small-signal model of the traditional reactive power control branch, as shown in equation (2):

[0079]

[0080] wherein K q , K i are coefficients of proportional and integral links of a reactive power control branch of the GFM system respectively; Q ref , Q are a reference value and an actual output power of the reactive power of the GFM system respectively; u, u ref are an actual output voltage and a voltage reference value of a grid-connected point of the GFM system respectively.

[0081] Further, the error elimination module comprises:

[0082] The elimination verification unit is configured to verify effectiveness of the PI controller by comparison according to the steady-state error before and after elimination of the PI controller.

[0083] The elimination processing unit is configured to correct output deviation by error accumulation characteristics of the integral link according to the steady-state error, so as to eliminate the steady-state error.

[0084] Further, in the branch optimization module, the grid point voltage is adjusted for transient stability by the reactive power control equation according to a reactive power compensation coefficient.

[0085] Embodiment three:

[0086] The embodiment also provides an electronic device comprising a memory and a processor, wherein the memory is configured to store one or more computer instructions, and the one or more computer instructions are configured to implement the method of embodiment one when executed by the processor.

[0087] In practical applications, the processor can be an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP), a Digital Signal Processing Device (DSPD), a Programmable Logic Device (PLD), a Field Programmable Gate Array (FPGA), a controller, a microcontroller (MCU), a microprocessor, or other electronic elements, which are used to execute the methods in the above embodiments.

[0088] The method implemented by the embodiment is as shown in the content of Embodiment One.

[0089] Embodiment Four

[0090] The embodiment also provides a computer readable storage medium, and the computer readable storage medium stores a computer program. When the computer program is executed by one or more processors, the method of Embodiment One is implemented.

[0091] The computer readable storage medium can be implemented by any type of volatile or nonvolatile storage devices or a combination thereof, such as a Static Random Access Memory (SRAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), an Erasable Programmable Read-Only Memory (EPROM), a Programmable Read-Only Memory (PROM), a Read-Only Memory (ROM), a magnetic storage, a flash memory, a magnetic disk or an optical disk.

[0092] The method implemented by the embodiment is as shown in the content of Embodiment One.

[0093] In several embodiments provided by the present application, it should be understood that the disclosed system and method can also be implemented in other ways. The system and method embodiments described above are only illustrative.

[0094] It should be noted that, in the present document, the terms "first", "second", and the like, in the description and in the claims of the present application and in the above-described drawings, are intended to distinguish similar objects and not necessarily to describe a particular chronological or sequential order. The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by an indefinite article "a" does not exclude the existence, under the same conditions, of two or more identical elements.

[0095] Although the embodiments of the present application have been disclosed as above, the above-described content is only for the purpose of facilitating the understanding of the present application, and is not intended to limit the present application. Any person skilled in the art of the present application can make any modification and change in the form of implementation and details without departing from the spirit and scope of the present application, but the patent protection scope of the present application shall be subject to the scope defined by the appended claims.

Claims

1. A construction method of a reactive branch control link based on an improved GFM system, characterized in that, Comprising: According to the line power transmission principle and the small signal linearization processing method, a small signal model based on the traditional reactive power control branch is established; According to the small signal model, the steady-state error is verified by step response simulation; According to the existence of the steady-state error, a PI controller is introduced into the traditional reactive power control circuit as an improved reactive power control circuit; According to the steady-state error, the improved reactive power control circuit is used to eliminate the steady-state error; According to the traditional function model under step input, the steady-state error expression is obtained through the improved reactive power control circuit; According to the steady-state error expression, the traditional reactive power control branch is improved through the small signal model; According to the improved reactive power control circuit, the consistency of the transfer function and the actual simulation waveform is verified by small disturbance test.

2. The method of claim 1, wherein, Comprising: According to the small signal model of the traditional reactive power control branch, the reactive power control equation is improved, as shown in formula (2): In the formula, K q , K i are the coefficients of the proportional and integral links of the reactive power control branch of the GFM system; Q ref , Q are the reference value and the actual output power of the reactive power of the GFM system; u, u ref are the actual output voltage and the voltage reference value of the grid-connected point of the GFM system.

3. The method of claim 2, wherein, According to the existence of the steady-state error, a PI controller is introduced into the traditional reactive power control circuit as an improved reactive power control circuit; According to the steady-state error, the improved reactive power control circuit is used to eliminate the steady-state error, including: According to the steady-state error before and after the PI controller, the effectiveness of the PI controller is verified by comparison; According to the steady-state error, the output deviation correction is realized by the error accumulation characteristic of the integral element, so as to eliminate the steady-state error.

4. The method of claim 1, wherein, According to the traditional function model under step input, the steady-state error expression is obtained through the improved reactive power control circuit; According to the steady-state error expression, the traditional reactive power control branch is improved through the small signal model, including: According to the reactive power compensation coefficient, the transient stability of the network point voltage is adjusted through the reactive power control equation.

5. A device for constructing a control link of a reactive branch based on an improved GFM system, characterized in that, Comprising: The model establishing module is used for establishing a small signal model based on a traditional reactive power control branch according to the line power transmission principle and the small signal linearization processing method; According to the small signal model, the steady-state error is verified by step response simulation; The error elimination module is used for introducing a PI controller into the traditional reactive power control circuit as an improved reactive power control circuit according to the existence of the steady-state error; According to the steady-state error, the improved reactive power control circuit is used to eliminate the steady-state error; The branch optimization module is used for obtaining a steady-state error expression through the improved reactive power control circuit according to the traditional function model under step input; According to the steady-state error expression, the traditional reactive power control branch is improved through the small signal model; The control verification module is used for verifying the consistency of the transfer function and the actual simulation waveform by small disturbance test according to the improved reactive power control circuit.

6. The apparatus of claim 5, wherein, The model establishing module is used for improving the reactive power control equation according to the small signal model of the traditional reactive power control branch, as shown in formula (2): In the formula, K q , K i are the coefficients of the proportional and integral links of the reactive power control branch of the GFM system respectively; Q ref , Q are the reference value and actual output power of the reactive power of the GFM system respectively; u, u ref are the actual output voltage and voltage reference value of the grid-connected point of the GFM system respectively.

7. The apparatus of claim 6, wherein, The error elimination module includes: The elimination verification unit is used for verifying the effectiveness of the PI controller by comparison according to the steady-state error before and after the PI controller; The elimination processing unit is used for eliminating the steady-state error by output deviation correction through the error accumulation characteristic of the integral link according to the steady-state error.

8. The apparatus of claim 5, wherein, In the branch optimization module, the net point voltage is adjusted for transient stability according to a reactive compensation coefficient through the reactive control equation.

9. An electronic device, comprising: The computer readable storage medium stores a computer program, and the computer program is executed by the processor to implement the method in any one of claims 1-4.

10. A computer-readable storage medium, characterized in that, The computer readable storage medium stores a computer program, and the computer program is executed by the processor to implement the method in any one of claims 1-4.

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