Transient stability improvement method for virtual synchronous generator based on power outer loop collaborative optimization

Abstract

The invention relates to a power outer loop collaborative optimization virtual synchronous generator transient stability improvement method, and belongs to the technical field of virtual synchronous generator transient stability, and the method comprises the following steps: S1, building a virtual synchronous generator small signal power angle model; s2, performing active transient compensation and capacity constraint of power angle-frequency difference cooperative state feedback; s3, voltage deviation driven adaptive reactive power coefficient and active-reactive power combined current limiting are carried out; and S4, fault current impact suppression of the current-driven virtual impedance. The method can effectively reduce peak values and oscillation time of a power angle and a frequency difference, limit a fault current not to exceed a set upper limit, consider voltage support and active support capabilities, has good stability and robustness, and is suitable for controlling the grid-connected virtual synchronous generator under different short-circuit ratios and various fault working conditions.

Description

Technical Field

[0001] This invention belongs to the field of transient stability technology of virtual synchronous generators, and relates to a method for improving the transient stability of virtual synchronous generators through power outer loop collaborative optimization. Background Technology

[0002] With the increasing integration of renewable energy sources, the proportion of grid-connected power sources based on power electronic converters in the power system is constantly rising, and the rotational inertia, voltage, and frequency support provided by traditional synchronous generators is gradually weakening. Virtual Synchronous Generators (VSGs) mimic the torque equations and excitation characteristics of synchronous machines at the control layer, enabling grid-connected inverters to possess active-frequency and reactive-voltage characteristics similar to synchronous machines. They are considered one of the important implementation forms of grid-connected control.

[0003] When the power grid experiences large disturbances such as short-circuit faults or sudden voltage drops, the VSG will exhibit transient power angle instability similar to that of a synchronous machine. If the electrical output power during the fault... P e The power supply is below the command level for an extended period of time. P ref As the power angle continues to accelerate, it eventually exceeds the critical power angle, leading to instability. Simultaneously, short-circuit current exceeding limits may occur during the fault, threatening grid-connected equipment and grid safety. Therefore, how to simultaneously ensure transient power angle stability and fault current limiting during a fault has become a key issue in VSG control research.

[0004] Existing research typically improves VSGs in two directions: one type introduces dynamic power angle compensation or virtual power angle in the active-frequency path to change the transient power angle trajectory and improve power angle stability margin; the other type focuses on current limiting and virtual impedance to suppress fault current by reducing active power, increasing reactive power, or lowering output voltage. However, most solutions either prioritize transient power angle stability without systematically considering fault current limiting, or significantly worsen power angle stability while implementing strong current limiting. Similar problems have been widely discussed in droop-controlled inverters.

[0005] Designing a transient stability method for a virtual synchronous generator that comprehensively considers transient power angle stability and fault current limiting is a pressing problem in the field of transient stability of virtual synchronous generators. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization includes the following steps: S1: Establish a small-signal power angle model for a virtual synchronous generator; S2: Active transient compensation and capacity constraint of power angle-frequency difference coordinated state feedback; S3: Voltage deviation driven adaptive reactive power coefficient and active-reactive combined current limiting; S4: Fault current surge suppression of current-driven virtual impedance.

[0008] Furthermore, step S1, establishing the small-signal power angle model of the virtual synchronous generator, involves establishing the swing equations and active and reactive power equations of the virtual synchronous generator (VSG) in a synchronous rotating coordinate system, forming a second-order small-signal model with power angle deviation and frequency difference as state variables. Specifically, this includes: Based on the oscillation equation:

[0009] Let the output voltage of the VSG be... E The grid voltage is U g During steady-state operation, the VSG voltage phasor is U 0 Assuming the impedance between the inverter and the grid is purely inductive, the active and reactive power transferred between the VSG and the grid are as follows:

[0010] In the formula E The equivalent internal potential amplitude of the stator. U g This refers to the phase voltage amplitude of the power grid. X g This is the equivalent reactance between the generator terminal and the power grid; Let the active power of the VSG at the steady-state operating point be... P 0, corresponding to the angle of attack is d 0. Perform a first-order Taylor expansion on the operating point and define the active power output increment as Δ. P e = P e - P 0, the power angle deviation is Δ d = d - d 0, then:

[0011] in K s This is called the synchronous torque coefficient; Let the power reduction command be Δ P m Substituting into the VSG oscillation equation, we get:

[0012] Define state variables:

[0013] Classic VSG model Δ P m When the power angle is 0, the dynamics of the power angle is a standard second-order system, and its characteristic equation is:

[0014] Therefore, the equivalent natural frequency and damping ratio of the classical VSG power angle dynamic system can be obtained as follows:

[0015] Without additional state feedback, the natural frequency and damping ratio of the classic VSG power angle dynamic system are determined by... J , D q , K s Decide.

[0016] Furthermore, the active power transient compensation and capacity constraint of the power angle-frequency difference coordinated state feedback described in step S2 is based on the target damping ratio and natural frequency. The state feedback gain of the power angle deviation and frequency difference is designed through pole configuration to achieve transient compensation of the active power channel during a fault. Simultaneously, combined with the capacity circle, upper and lower limits of active power are given, and the active power reference is limited. Specifically, this includes: When the angle deviation Δ d or frequency difference Δ oh When the power increases, the active power is reduced. P m The method to increase the transient stability of the system is as follows: The specific active power reduction value is:

[0017] In the formula k δ For power angle feedback gain, k ω For frequency difference feedback gain; At this point, a closed-loop system is obtained:

[0018] The closed-loop characteristic equation is:

[0019] Introducing frequency difference feedback gain kω Equivalent to controlling transient damping D q Introducing power angle feedback gain k δ Equivalent to control synchronous torque coefficient K s; By comparing the closed-loop characteristic equation with the standard form of a second-order linear system, we obtain:

[0020]

[0021] Specify the desired target natural frequency of the second-order linear system oh n Damping ratio with target g Calculate the corresponding k δ , k ω By reconfiguring the characteristic equation through an additional power angle state feedback channel, the VSG can maintain the desired dynamic characteristics of a second-order system under a wide range of operating conditions, including during fault periods. Introducing a capacity circle constraint, let the maximum allowable line current of the device in the VSG be... I max = k I I N ,in I N Rated current, k I If is a coefficient, then the voltage at the grid connection point is U PCC At that time, the upper limit of three-phase capacity is:

[0022] Given a reactive power instruction Q cmd The maximum allowed active power is as follows:

[0023] Set active power lower limit P min = c P N This allows setting upper and lower limits for the active power commands output by the status feedback to meet current limiting and active power support requirements.

[0024] Furthermore, in step S2, the target damping ratio and the target natural frequency are used to set the power angle feedback gain and the frequency difference feedback gain, wherein the target damping ratio... g The value range is 0.6 to 0.9, the target's natural frequency. oh n The value range is 20–40 rad / s to balance the power angle response speed and overshoot.

[0025] Furthermore, in step S3, an adaptive reactive power coefficient is constructed using voltage deviation as input. This coefficient maintains its original droop characteristics during minor voltage disturbances and automatically amplifies reactive power support during deep voltage drops. Combining capacity circle constraints, the allowable range of the reactive power coefficient is calculated from the upper limit of current and the minimum active power output, thus limiting the reactive power command. Specifically, this includes: First, define the normalized voltage deviation. s To characterize the significance of voltage dips, s The expression is:

[0026] when hour, s ≈ 0, when U 0- U n Approaching or exceeding the threshold Δ U th hour, s →1; The adaptive reactive power coefficient driven by the reconfigured voltage deviation is:

[0027]

[0028] For a given U PCC and the lower limit of merit P min From the capacity circle:

[0029] The upper limit of reactive power amplitude is obtained:

[0030] To ensure that reactive power commands do not exceed this limit at any time, the following must be satisfied:

[0031] Therefore, the upper bound of the adaptive reactive power coefficient is:

[0032] Ultimately, the reactive power coefficient is limited to: .

[0033] Furthermore, in the adaptive reactive power coefficient described in step S3, α The value range is 1 to 5, and the index is...p The value range is 2 to 4, so as to quickly enhance reactive power support when the voltage drops sharply and maintain the original reactive power droop characteristics when there is slight disturbance.

[0034] Furthermore, the fault current surge suppression using current-driven virtual impedance described in step S4 includes real-time monitoring of the current amplitude, increasing the equivalent line reactance to suppress the short-circuit surge current in the early stages of the fault, and gradually reducing the virtual inductance in the later stages of the fault, thereby achieving transient current suppression and power angle stabilization control in coordination with active and reactive power channels; specifically including: remember I rms Set two thresholds for the three-phase current RMS. I th1 < I th2 ,definition:

[0035] in L 1 represents the virtual inductance during normal operation. L 2 represents the large virtual inductance during fault suppression current surges.

[0036] The beneficial effects of this invention are as follows: 1. By establishing a small-signal model of the VSG power angle and introducing power angle state feedback, the transient power angle-frequency dynamic of the VSG is dynamically equivalent to a tuned second-order system, which significantly improves transient damping and convergence speed, and enhances the power angle stability margin during faults.

[0037] 2. By adopting an adaptive reactive power coefficient driven by voltage deviation and combining it with the upper limit of reactive power coefficient calculated by capacity circle, the original reactive power droop characteristics can be maintained under slight disturbances. During deep voltage drops, voltage support is enhanced without exceeding the current upper limit, thereby improving transient voltage quality and power angle stability.

[0038] 3. By combining active and reactive power limiting and capacity-based power allocation, the active power reduction is closely linked to the real-time voltage level and reactive power output. Under the premise of ensuring that the current does not exceed the limit, the active power support capacity is preserved as much as possible, taking into account both transient stability and power utilization efficiency, and meeting the dual requirements of safety and economy for engineering operation.

[0039] 4. The introduction of current-driven virtual impedance dynamically suppresses the initial current surge during a fault and automatically adjusts the equivalent reactance after the fault is restored, reducing the adverse effects on the power angle. Together with active and reactive power control, it forms a unified control framework that takes into account both transient power angle stability and fault current limiting. It is applicable to different short-circuit ratios and various fault scenarios and has good engineering promotion value.

[0040] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0041] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a framework diagram of a method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization; Figure 2 This is a diagram of the active transient compensation structure based on the power angle-frequency difference coordinated state feedback. Figure 3 This is a diagram of the adaptive reactive power coefficient structure driven by voltage deviation; Figure 4 This is the system main circuit and VSG control structure diagram; Figure 5 This is the fault phase plane diagram after introducing active transient compensation; Figure 6 This is the fault frequency response diagram after introducing active transient compensation; Figure 7 This is the fault phase plane diagram after introducing the adaptive reactive power coefficient; Figure 8 This is the fault frequency response diagram after introducing an adaptive reactive power coefficient; Figure 9 This method is compared with the transient output of the traditional VSG during a fault. Detailed Implementation

[0042] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0043] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0044] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0045] Example 1: This invention provides a method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization, such as... Figure 1 As shown, this method mainly includes the following four steps: Step 1: Establish a small-signal power angle model for a virtual synchronous generator. In a synchronous rotating coordinate system, establish the voltage, current, active, and reactive power equations for the VSG. Based on the oscillation equation, extract parameters such as virtual moment of inertia and equivalent damping to form a second-order small-signal model with power angle deviation and frequency difference as state variables, providing a basis for quantitative tuning of control parameters.

[0046] Step 2: Active transient compensation and capacity constraint based on power angle-frequency difference coordinated state feedback. Based on the target damping ratio and natural frequency, the state feedback gain for power angle deviation and frequency difference is designed through pole configuration. The compensation is superimposed on the active power reference value to achieve adaptive reduction of active power input during faults. Simultaneously, the capacity circle is calculated by combining real-time grid connection point voltage and reactive power command to provide upper and lower limits for active power, limiting the active power reference and balancing power angle stability with current upper limit constraints.

[0047] Step 3: Adaptive reactive power coefficient driven by voltage deviation and combined active and reactive power current limiting. An adaptive reactive power coefficient is constructed using voltage deviation as input, so that the original droop characteristics are maintained during slight voltage disturbances, and reactive power support is automatically amplified during deep voltage drops. Combined with capacity circle constraints, the allowable range of the reactive power coefficient is calculated from the upper limit of current and the minimum active power output, and the reactive power command is limited to achieve coordinated control of voltage support enhancement and fault current limiting.

[0048] Step 4: Fault current surge suppression using current-driven virtual impedance. The current amplitude is monitored in real time, and the virtual inductance is adjusted online according to a set threshold. In the early stages of a fault, the equivalent line reactance is increased to suppress the short-circuit surge current; in the later stages of a fault, the virtual inductance is gradually reduced, achieving transient current suppression and power angle stabilization control in coordination with active and reactive power channels.

[0049] In this embodiment, a second-order small-signal VSG model with power angle deviation and frequency difference as state variables is constructed. State feedback gain is introduced into the active-frequency loop through pole placement. An adaptive reactive power coefficient driven by voltage deviation and joint active-reactive current limiting are constructed. A current-driven virtual impedance is designed. The steps are as follows: Figure 1 As shown: Step 1: Establish a small-signal power angle model for a virtual synchronous generator.

[0050] Based on the oscillation equation:

[0051] Let the output voltage of the VSG be... E The grid voltage is U g During steady-state operation, the VSG voltage phasor is U 0 Assuming the impedance between the inverter and the grid is purely inductive, the active and reactive power transferred between the VSG and the grid are as follows:

[0052] In the formula: E The equivalent internal potential amplitude of the stator. U g This refers to the phase voltage amplitude of the power grid. X g This is the equivalent reactance between the generator terminal and the power grid.

[0053] Let the active power of the VSG at the steady-state operating point be... P 0, corresponding to the angle of attack is d 0. Perform a first-order Taylor expansion on the operating point and define the active power output increment as Δ. P e = P e - P 0, the power angle deviation is Δ d = d - d 0, then:

[0054] in K s This is called the synchronous torque coefficient.

[0055] Let the power reduction command be Δ P m Substituting into the VSG oscillation equation, we get:

[0056] Define state variables:

[0057] Classic VSG model Δ P m When the power angle is 0, the dynamics of the power angle is a standard second-order system, and its characteristic equation is:

[0058] Therefore, the equivalent natural frequency and damping ratio of the classical VSG power angle dynamic system can be obtained as follows:

[0059] Without additional state feedback, the natural frequency and damping ratio of the classic VSG power angle dynamic system are entirely determined by... J , D q , K s Decide.

[0060] Step 2: Active transient compensation and capacity constraint based on power angle-frequency difference coordinated state feedback.

[0061] Based on the classic VSG active-frequency loop, active transient compensation with power angle-frequency difference coordinated state feedback is introduced. This method reconstructs its equivalent second-order characteristics through state feedback, ensuring that the closed-loop natural frequency and damping ratio meet preset expected targets. Theoretically, this guarantees that the power angle oscillation has sufficient damping and decays rapidly, improving the stability margin of the power angle during fault transients while enabling rapid stabilization of the power angle oscillation.

[0062] like Figure 2 The specific principle is as follows: when the power angle deviation Δ d or frequency difference Δ oh When the power increases, the active power is reduced. P m The method to increase the transient stability of the system is as follows: The specific active power reduction value is:

[0063] In the formula: k δ The power angle feedback gain coefficient is... k ω This is the frequency difference feedback gain coefficient; At this point, a closed-loop system is obtained:

[0064] Its closed-loop characteristic equation is:

[0065] Introducing frequency difference feedback gaink ω Equivalent to controlling transient damping D q Introducing power angle feedback gain k δ Equivalent to control synchronous torque coefficient K s.

[0066] By comparing it with the standard form of a second-order linear system, we can obtain:

[0067]

[0068] Unlike traditional VSG which does not perform active power command reduction and other invention patents which specify active power command reduction values ​​using empirical coefficients, this method can change the natural frequency and damping ratio of the dynamic second-order linear system by configuring the power angle and frequency difference feedback gain coefficients, thereby enhancing the controllability of the dynamic power angle.

[0069] The target damping ratio and target natural frequency are used to set the power angle feedback gain and frequency difference feedback gain, where the target damping ratio is... g The value range is 0.6 to 0.9, the target's natural frequency. oh n The value range is 20–40 rad / s to balance the power angle response speed and overshoot.

[0070] In this embodiment, the desired target natural frequency of the second-order linear system with specified power angle is . oh n = 30rad / s, target damping ratio g = 0.7, calculate the corresponding k δ , k ω Then, the characteristic equation is reconfigured through an additional power angle state feedback channel, so that the VSG can maintain the desired dynamic characteristics of a second-order power angle system under a wide range of operating conditions, including during faults.

[0071] The above state feedback assumption P m It can be adjusted arbitrarily, but in actual VSG control, its active / reactive output is constrained by the upper limit of current, so a capacity circle limit needs to be introduced.

[0072] Let the maximum allowable line current of the device in the VSG be... I max = k I I N ( I NRated current, k I (Generally, 1.3~1.5 is taken), then the voltage at the grid connection point is... U PCC At that time, its three-phase capacity limit is:

[0073] Given a reactive power instruction Q cmd The maximum allowed active power is as follows:

[0074] Meanwhile, considering that excessive reduction in active power may affect the system's active power support, a lower limit for active power is set. P min γP N In this embodiment c = 0.2. Therefore, the active power command output by the state feedback is saturated.

[0075] Under small disturbances or shallow voltage drops, the capacity circle constraint generally does not take effect, and the system dynamics are completely consistent with the ideal second-order design. However, under deep faults or without significant reactive power support, the capacity circle automatically tightens, limiting further decreases in active power and thus ensuring that the current does not exceed [the limit]. I max This achieves consistency between power angle stability and current limiting.

[0076] Step 3: Adaptive reactive power coefficient driven by voltage deviation and combined active and reactive power current limiting.

[0077] To prevent excessive reactive power fluctuations in VSG during slight voltage fluctuations and to rapidly improve reactive power support during deep voltage drops, this paper proposes a voltage deviation-driven adaptive reactive power coefficient.

[0078] First, define the normalized voltage deviation. s To characterize the significance of voltage dips, s The expression is:

[0079] when hour, s ≈ 0, when U 0- U n Approaching or exceeding the threshold Δ U th hour, s →1.

[0080] like Figure 3 Reconstructing the adaptive reactive power coefficient driven by voltage deviation:

[0081]

[0082] in α The value range is 1 to 5, and the index is... p The value range is 2 to 4, which is used to quickly enhance reactive power support during deep voltage drops while maintaining the original reactive power droop characteristics during slight disturbances. In this embodiment... α =2, p= 2.

[0083] Unlike linear deviation gain, this adaptive reactive power coefficient has a smaller gain under slight voltage disturbances and amplifies the gain under deep voltage drops, thus improving reactive power support and maintaining transient stability under both minor and deep faults.

[0084] However, voltage support capability is ultimately limited by current capacity, for a given... U PCC and the lower limit of merit P min From the capacity circle:

[0085] The upper limit of reactive power amplitude can be obtained:

[0086] To ensure that reactive power commands do not exceed this limit at any time, the following must be satisfied:

[0087] Therefore, the upper bound of the adaptive reactive power coefficient can be obtained:

[0088] Ultimately, the reactive power coefficient is limited to:

[0089] When the voltage drop is shallow K lim Usually much larger K q (s), capacity constraints K q The impact is almost negligible; however, under deep faults, when K q (s) When attempting to further increase reactive power, the capacity circle will tighten in a timely manner, K q Limit it to a range that will not cause the current to exceed the limit.

[0090] Step 4: Fault current surge suppression using current-driven virtual impedance.

[0091] This invention designs an adaptive regulation law based on the virtual inductance of the current amplitude. I rms Set two thresholds for the three-phase current RMS. I th1 < I th2 ,definition:

[0092] in L 1 represents the virtual inductance during normal operation (which can be zero or very small). L 2 represents the larger virtual inductance during fault suppression current surges. It can be seen that when the current is within the normal range, L virt ≈ L 1. It has minimal impact on the system power angle and voltage; when a fault causes the current to rise close to the threshold, L virt exist[ L 1, L 2] The interval increases smoothly, which is equivalent to temporarily increasing the reactance and suppressing current overshoot; when the current gradually decreases in the later stage... I th1 When it is nearby, the virtual inductance naturally decreases.

[0093] By co-optimizing the active-frequency loop, reactive-voltage loop, and virtual impedance, the transient power angle stability of the virtual synchronous generator is significantly improved while meeting the fault current limiting requirements.

[0094] To verify the effectiveness and superiority of the virtual synchronous generator transient stability improvement method based on power outer loop collaborative optimization described in this invention, a verification example using a VSG simulation model in Matlab / Simulink is provided, such as... Figure 4 Establish the system main circuit and VSG control structure.

[0095] After adding active power transient compensation and capacity constraints with power angle-frequency difference coordinated state feedback, the grid fault depths are set as follows: K u = 0.7, 0.5, such as Figure 5 , Figure 6 Phase plane diagrams and frequency response diagrams of the traditional VSG and the improved active loop control VSG of this patent were plotted under two different grid fault depths. The phase plane diagrams show that... K u When the angle is 0.7, compared to the classic VSG control, the transient stable power angle of this method is higher. d 2 is less than the transient stable power angle of the classic VSG. d 1. Simultaneously, the power angle overshoot is smaller, and stability is reached more quickly. The frequency response diagram shows that the frequency change rate ROCOF and frequency deviation Δ of the improved active power loop control VSG in this patented method are significantly improved. oh All values ​​were significantly reduced, indicating that the improved active power loop control VSG in this patent enhances the frequency stability of the VSG; similarly, in K u When the angle is 0.5, the power angle of the classic VSG continues to accelerate, resulting in transient instability. However, the improved active power loop control VSG in this patent increases the power angle stability margin and maintains transient stability.

[0096] After setting the adaptive reactive power coefficient driven by voltage deviation and the combined active and reactive power current limiting, the grid fault depth is: K u When =0.5, such as Figure 7 , Figure 8 The classic VSG and initial values ​​of different reactive power coefficients were plotted. K q0 At (400°, 600°, 800°), the phase plane diagram and frequency response diagram of the VSG show that the classic VSG experiences transient instability due to continuous acceleration of the power angle. After setting the adaptive reactive power coefficient of this patent, the system remains stable, and the stable power angle increases as the initial value of the reactive power coefficient increases. d Gradually decrease, while ROCOF and Δ oh Both are significantly reduced, and the transient stability and frequency stability of the system are improved. However, due to the increase in reactive power coefficient, the fault current is also further increased. Therefore, it is necessary to set virtual impedance to limit the fault current.

[0097] After completing the above two steps, add a fault current surge suppression module with current-driven virtual impedance. And at a grid fault depth of... K u When = 0.3, such as Figure 9 The active power output, reactive power output, and power angle of the traditional VSG and the virtual synchronous generator transient stability improvement method of the power outer loop co-optimization proposed in this patent are plotted. d、 Δ oh The voltage and current comparison chart shows that when the voltage drops to 0.3 pu, the classic VSG experiences transient instability, with its power angle continuously diverging and oscillating, resulting in instability in active power, reactive power, and voltage. Simultaneously, the fault current exceeds the limit, severely impacting the safety of electronic components. The method proposed in this invention, however, maintains transient stability, preserving active power output while improving the output voltage and ensuring sufficient reactive power support, and also maintaining the power angle... d It stabilizes quickly while limiting fault current to below 1.3 pu.

[0098] Example 2: An electronic device, comprising a memory and a processor; The memory is used to store computer programs; The processor is configured to implement the method described in Embodiment 1 when executing the computer program.

[0099] Example 3: A computer-readable storage medium storing a computer program that, when executed by a processor, implements the method described in Embodiment 1.

[0100] Example 4: A computer program product includes a computer program that, when executed by a processor, implements the method described in Example 1.

[0101] In the above embodiments, the reference to "this embodiment" in the specification indicates that a specific feature, structure, or characteristic described in connection with the embodiment is included in at least some embodiments, but not necessarily all embodiments. Multiple appearances of "this embodiment" do not necessarily refer to the same embodiment.

[0102] In the above embodiments, although the invention has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory structures (e.g., dynamic RAM (DRAM)) may be used with the embodiments discussed. The embodiments of the invention are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims.

[0103] As will be understood by those skilled in the art, the computer-readable storage medium described in this embodiment allows for the implementation of all or part of the steps in the above method embodiments by computer program-related hardware. The aforementioned computer program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0104] The electronic terminal provided in this embodiment includes a processor, a memory, a transceiver, and a communication interface. The memory and the communication interface are connected to the processor and the transceiver and complete communication between them. The memory is used to store computer programs, the communication interface is used to perform communication, and the processor and the transceiver are used to run the computer programs, so that the electronic terminal performs the steps of the above method.

[0105] In this embodiment, the memory may include random access memory (RAM) and may also include non-volatile memory, such as at least one disk storage device.

[0106] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0107] This invention can be used in a wide range of general-purpose or special-purpose computing system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices, etc.

[0108] This invention can be described in the general context of computer-executable instructions, such as program modules, that are executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform a specific task or implement a specific abstract data type. This invention can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization, characterized in that: Includes the following steps: S1: Establish a small-signal power angle model for a virtual synchronous generator; S2: Active transient compensation and capacity constraint of power angle-frequency difference coordinated state feedback; S3: Voltage deviation driven adaptive reactive power coefficient and active-reactive combined current limiting; S4: Fault current surge suppression of current-driven virtual impedance.

2. The method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization according to claim 1, characterized in that: Step S1, establishing the small-signal power angle model of the virtual synchronous generator, involves establishing the swing equations and active and reactive power equations of the virtual synchronous generator (VSG) in a synchronous rotating coordinate system, forming a second-order small-signal model with power angle deviation and frequency difference as state variables. Specifically, this includes: Based on the oscillation equation: Let the output voltage of the VSG be... E The grid voltage is U g During steady-state operation, the VSG voltage phasor is U 0 Assuming the impedance between the inverter and the grid is purely inductive, the active and reactive power transferred between the VSG and the grid are as follows: In the formula E The equivalent internal potential amplitude of the stator. U g This refers to the phase voltage amplitude of the power grid. X g This is the equivalent reactance between the generator terminal and the power grid; Let the active power of the VSG at the steady-state operating point be... P 0, corresponding to the angle of attack is δ 0. Perform a first-order Taylor expansion on the operating point and define the active power output increment as Δ. P e = P e - P 0, the power angle deviation is Δ δ = δ - δ 0, then: in K s This is called the synchronous torque coefficient; Let the power reduction command be Δ P m Substituting into the VSG oscillation equation, we get: Define state variables: Classic VSG model Δ P m When the power angle is 0, the dynamics of the power angle is a standard second-order system, and its characteristic equation is: Therefore, the equivalent natural frequency and damping ratio of the classical VSG power angle dynamic system are obtained as follows: Without additional state feedback, the natural frequency and damping ratio of the classic VSG power angle dynamic system are determined by... J , D q , K s Decide.

3. The method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization according to claim 1, characterized in that: The active transient compensation and capacity constraint of the power angle-frequency difference coordinated state feedback described in step S2 is based on the target damping ratio and natural frequency. The state feedback gain of power angle deviation and frequency difference is designed through pole configuration to realize the active channel transient compensation during the fault. Simultaneously, in conjunction with the capacity circle, upper and lower limits for active power are given, and the active power reference is limited, specifically including: When the angle deviation Δ δ or frequency difference Δ ω When the power increases, the active power is reduced. P m The method to increase the transient stability of the system is as follows: The specific active power reduction value is: In the formula k δ For power angle feedback gain, k ω For frequency difference feedback gain; At this point, a closed-loop system is obtained: The closed-loop characteristic equation is: Introducing frequency difference feedback gain k ω Equivalent to controlling transient damping D q Introducing power angle feedback gain k δ Equivalent to control synchronous torque coefficient K s; By comparing the closed-loop characteristic equation with the standard form of a second-order linear system, we obtain: Specify the desired target natural frequency of the second-order linear system ω n Damping ratio with target ζ Calculate the corresponding k δ , k ω By reconfiguring the characteristic equation through an additional power angle state feedback channel, the VSG can maintain the desired dynamic characteristics of a second-order system under a wide range of operating conditions, including during fault periods. Introducing a capacity circle constraint, let the maximum allowable line current of the device in the VSG be... I max = k I I N ,in I N Rated current, k I If is a coefficient, then the voltage at the grid connection point is U PCC At that time, the upper limit of three-phase capacity is: Given a reactive power instruction Q cmd The maximum allowed active power is as follows: Set active power lower limit P min = γ P N This allows setting upper and lower limits for the active power commands output by the status feedback to meet current limiting and active power support requirements.

4. The method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization according to claim 3, characterized in that: In step S2, the target damping ratio, the target natural frequency setting power angle feedback gain, and the frequency difference feedback gain are used, where the target damping ratio... ζ The value range is 0.6 to 0.9, the target's natural frequency. ω n The value range is 20 to 40 rad / s, to balance the power angle response speed and overshoot.

5. The method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization according to claim 1, characterized in that: In step S3, an adaptive reactive power coefficient is constructed using voltage deviation as input. It maintains the original droop characteristics when there is slight voltage disturbance and automatically amplifies reactive power support when there is a deep voltage drop. Combining capacity circle constraints, the allowable range of reactive power coefficient is calculated from the upper limit of current and the minimum active power output, and reactive power command is limited, specifically including: First, define the normalized voltage deviation. s To characterize the significance of voltage dips, s The expression is: when hour, s ≈ 0, when U 0- U n Approaching or exceeding the threshold Δ U th hour, s →1; The adaptive reactive power coefficient driven by the reconfigured voltage deviation is: For a given U PCC and the lower limit of merit P min From the capacity circle: The upper limit of reactive power amplitude is obtained: To ensure that reactive power commands do not exceed this limit at any time, the following must be satisfied: Therefore, the upper bound of the adaptive reactive power coefficient is: Ultimately, the reactive power coefficient is limited to: 。 6. The method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization according to claim 5, characterized in that: In the adaptive reactive power coefficient described in step S3, α The value range is 1 to 5, and the index is... p The value range is 2 to 4, so as to quickly enhance reactive power support when the voltage drops sharply and maintain the original reactive power droop characteristics when there is slight disturbance.

7. The method for improving the transient stability of a virtual synchronous generator through power outer loop collaborative optimization according to claim 1, characterized in that: Step S4, the current-driven virtual impedance fault current surge suppression, includes real-time monitoring of the current amplitude, increasing the equivalent line reactance to suppress the short-circuit surge current in the early stage of the fault, and gradually reducing the virtual inductance in the later stage of the fault, thereby achieving transient current suppression and power angle stabilization control in coordination with active and reactive power channels; specifically including: remember I rms Set two thresholds for the three-phase current RMS. I th1 < I th2 ,definition: in L 1 represents the virtual inductance during normal operation. L 2 represents the large virtual inductance during fault suppression current surges.

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