A grid-connected VSC system amplitude limiting stability judgment method, device, medium and equipment

Abstract

The application discloses a grid-connected VSC system amplitude limiting stability judgment method and device, medium and equipment, through the grid-connected VSC switching system model, the common Lyapunov function of the system is determined, the analytical stability domain of the system is calculated, the relationship between the system stability boundary and the system parameters is obtained, according to the boundary of the analytical stability domain, the critical energy function of the system is calculated, so that the grid-connected VSC large disturbance stability under the amplitude limiting constraint can be judged by comparing the size of the critical energy function and the energy function of the disturbed system, time-consuming numerical simulation is avoided, and the large disturbance stability criterion is provided for the grid-connected VSC system with amplitude limiting.

Description

Technical Field

[0001] This invention belongs to the field of new energy grid connection technology, specifically relating to a method, device, medium and equipment for judging the amplitude limiting stability of a grid-connected VSC system. Background Technology

[0002] Voltage source converters (VSCs) are widely used due to their fast and flexible control. New energy power generation, such as photovoltaic and wind power, is connected to power systems via VSCs. Currently, new energy power generation connected via VSCs typically relies on phase-locked loops (PLLs) to track the grid phase and achieve synchronization with the grid. However, when the system is disturbed, this PLL-based synchronization mechanism may cause a continuous increase in the voltage phase at the grid connection point, leading to converter lockout and seriously threatening the safe operation of new power systems. Typically, the output of the PLL's proportional-integral (PI) controller is limited within a certain range to suppress frequency fluctuations in the VSC grid connection point voltage. Therefore, when the system is disturbed, the presence of various limiting components causes the system to become a switching device composed of a series of sub-devices and switching signals.

[0003] Currently, stability assessment methods considering converter phase-locked loop (PLL) limiting are problematic because controller limiting significantly alters the device's dynamic behavior. Under different limiting settings, in scenarios where the PLL output reaches its limit after a large disturbance, the device's stability can be fundamentally altered. Since the switching mechanism of the switching unit is closely related to the limiting settings, different limiting settings can lead to changes in the device's stability boundary in certain situations, rendering stability criteria that do not consider limiting ineffective. Therefore, a method that considers the impact of PLL limiting on the stability of VSC grid-connected devices is urgently needed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method, device, medium and equipment for judging the amplitude limiting stability of a grid-connected VSC system, which addresses the shortcomings of the prior art and solves the technical problem that the original stability criterion of the VSC grid-connected device fails when the output of the VSC phase-locked loop controller reaches the amplitude limit.

[0005] The present invention adopts the following technical solution:

[0006] A method for determining the amplitude limiting stability of a grid-connected VSC system includes the following steps:

[0007] Based on the response characteristics of the grid-connected VSC system after disturbance, the dynamic response of the current loop is simplified, and the limiting constraint of the phase-locked loop controller is considered to generate a switching system model of the grid-connected VSC.

[0008] Determine the common Lyapunov function of the switching system based on the switching system model;

[0009] The analytical stability region of the grid-connected VSC system is calculated based on the common Lyapunov function, and the relationship between the stability boundary and system parameters is derived.

[0010] Based on the boundary of the analytical stability region, the critical energy function of the grid-connected VSC system is calculated. The magnitude of the critical energy function and the energy function of the grid-connected VSC system after being disturbed are used to determine whether the grid-connected VSC can remain stable under amplitude limiting constraints after a large disturbance.

[0011] Specifically, the switching system model for grid-connected VSCs is as follows:

[0012]

[0013] Where x1 and x2 are two state variables of the PLL, x 2min and x 2max Let x1(x1,x2), h2(x1,x2), and h3(x1,x2) represent the lower and upper limits of x2, respectively, and dt represents the derivative.

[0014] Specifically, the common Lyapunov function for switching systems is as follows:

[0015]

[0016] Here, x1 and x2 are two state variables of the PLL.

[0017] Specifically, the relationship between the stability boundary and system parameters is as follows:

[0018]

[0019] Where, θ I Let θ be the left stable boundary of the system. II For the right stability boundary of the system, L l The equivalent inductance of the line, The reference value set for the d-axis current of the current loop. These are the integral parameters of the phase-locked loop. U is the proportional parameter of the phase-locked loop. sL The voltage amplitude of VSC connected to the infinite power bus.

[0020] Specifically, the analytical stability region D of the system is:

[0021] D={(x1,x2)|θ I <x1<θ II}

[0022] Where x1 and x2 are two state variables of the PLL, θ I Let θ be the left stable boundary of the system. II This represents the right stability boundary of the system.

[0023] Specifically, when the system is disturbed, the energy function V(x) 1tc ,x 2tc The critical energy function V of the system crit The system was determined to remain stable.

[0024] Furthermore, the critical energy function V of the system crit for:

[0025]

[0026] Where, θ II Let M be the right stability boundary of the system, and U be the equivalent inertia of the system. sL R is the voltage amplitude of VSC connected to the infinite power bus. l and L l These are the equivalent resistance and equivalent inductance of the line, respectively. and These are the reference values ​​set for the dq-axis current of the current loop, θ. s This is the PLL phase angle equilibrium point.

[0027] Secondly, embodiments of the present invention provide a device for determining the amplitude limiting stability of a grid-connected VSC system, comprising:

[0028] The generation module is used to simplify the dynamic response of the current loop based on the response characteristics of the grid-connected VSC system after disturbance, and to generate a switching system model of the grid-connected VSC considering the limiting constraints of the phase-locked loop controller.

[0029] The determination module is used to determine the common Lyapunov functions of the switching system based on the switching system model;

[0030] The calculation module is used to calculate the analytical stability region of the grid-connected VSC system based on the common Lyapunov function and derive the relationship between the stability boundary and system parameters.

[0031] The judgment module is used to calculate the critical energy function of the grid-connected VSC system based on the boundary of the analytical stability region. Based on the critical energy function and the magnitude of the energy function of the grid-connected VSC system after being disturbed, it determines whether the grid-connected VSC can remain stable under the amplitude limiting constraint after a large disturbance.

[0032] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described grid-connected VSC system amplitude limiting stability judgment method.

[0033] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described method for determining the amplitude limiting stability of a grid-connected VSC system.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] A method for determining the amplitude-limited stability of a grid-connected VSC system is proposed. By considering the amplitude-limiting constraint of the phase-locked loop controller, the dynamic equations of the switching system of the grid-connected VSC are generated, and the common Lyapunov function of the switching system is determined, thereby obtaining the analytical stability region of the grid-connected VSC. This allows for a clear analysis of the relationship between the stability boundary of the VSC system and the system parameters after a large disturbance, providing a basis for setting the parameters of the grid-connected VSC system. Finally, based on the boundary of the stability region, the critical energy function of the system is calculated. By comparing the magnitude of the critical energy function and the energy function after the system is disturbed, the large disturbance stability of the grid-connected VSC under amplitude-limiting constraints can be determined, avoiding time-consuming numerical simulations and providing a large disturbance stability criterion for grid-connected VSC systems with amplitude limits.

[0036] Furthermore, a switching system model is established for the grid-connected VSC system considering the limiting effect, and the limiting value of the state variable is taken as the switching signal, making it possible to realize the synchronization stability analysis of the grid-connected VSC system under the condition of limiting of the phase-locked loop PI controller.

[0037] Furthermore, a common Lyapunov function is established for the switching system model, and the conservative analytical stability boundary of the system can be obtained based on the condition that the common Lyapunov function is positive definite and its time derivative is negative definite.

[0038] Furthermore, the relationship between the system's stability boundary and system parameters was obtained, and the key factors affecting the size of the system's stability boundary were clarified. This can provide a basis for setting the parameters of the VSC grid-connected system, enabling the VSC grid-connected system to have a larger stability boundary, thereby improving the stability of the VSC grid-connected system.

[0039] Furthermore, based on the analytical stability region D of the system, it can be determined that the system state variables can remain stable within the analytical stability region D, which is the critical energy function V of the system. crit This provides a basis for the setting.

[0040] Furthermore, according to the system's critical energy function V crit When the system is disturbed, the energy function V(x)1tc ,x 2tc The critical energy function V of the system crit This allows us to determine that the system remains stable, thus avoiding time-consuming numerical simulations.

[0041] Furthermore, the critical energy function V of the system is set. crit The energy function value at the intersection of the right boundary of the conservative analytical stability domain D of the VSC grid-connected system and the x1 axis of the phase plane of the switching system is determined to ensure that the energy function V(x) remains stable after the system is disturbed. 1tc ,x 2tc The critical energy function V of the system crit Under these conditions, the energy of the VSC grid-connected system decreases over time.

[0042] It is understood that the beneficial effects of the second to fourth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0043] In summary, this invention can provide a basis for setting parameters of grid-connected VSC systems with amplitude limiting constraints, thereby improving system stability. By comparing the critical energy function and the energy function after the system is disturbed, the large disturbance stability of grid-connected VSCs under amplitude limiting constraints can be determined, avoiding time-consuming numerical simulations. This invention can provide a large disturbance stability criterion for grid-connected VSC systems with amplitude limiting constraints.

[0044] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0045] Figure 1 This is a flowchart illustrating the amplitude limiting stability judgment method for a grid-connected VSC system according to an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of a simulation device for a grid-connected VSC using PLL synchronization, as shown in an embodiment of the present invention.

[0047] Figure 3 This is a schematic diagram of the dynamic response of a VSC grid-connected device with PLL synchronization under different fault durations, as shown in an embodiment of the present invention. (a) is the phase trajectory of the system, and (b) is the dynamic process of the energy of the system trajectory changing with time.

[0048] Figure 4 This is a schematic diagram of the structure of the amplitude limiting stability judgment device for a grid-connected VSC system according to an embodiment of the present invention;

[0049] Figure 5 This is a schematic diagram of the structure of a computer device according to an embodiment of the present invention. Detailed Implementation

[0050] 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.

[0051] In the description of this invention, it should be understood that 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.

[0052] 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.

[0053] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" relationship.

[0054] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0055] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0056] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0057] This invention provides a method for determining the amplitude-limited stability of a grid-connected VSC system. By using a grid-connected VSC switching device model, the common Lyapunov function of the device is determined, the analytical stability region of the device is calculated, and the relationship between the device's stability boundary and device parameters is obtained. Based on the boundary of the analytical stability region, the critical energy function of the device is calculated. By comparing the magnitude of the critical energy function and the energy function of the device after disturbance, the large-disturbance stability of the grid-connected VSC under amplitude-limited constraints can be determined, avoiding time-consuming numerical simulations and providing a large-disturbance stability criterion for grid-connected VSC devices with amplitude limits.

[0058] Please see Figure 1 The present invention provides a method for determining the amplitude limiting stability of a grid-connected VSC system, comprising the following steps:

[0059] S101. Based on the response characteristics of VSC after system disturbance, simplify the dynamic response of current loop, consider the limiting constraint of phase-locked loop controller, and generate a switching system model of grid-connected VSC.

[0060] In this step, the dynamic response of the current loop is simplified based on the difference between the current loop and the PLL response time, assuming the dq-axis current is always maintained at the reference value. The PLL controller output limit is set to obtain the preset switching system model for VSC grid connection. The switching system model is used to describe the dynamic response of the VSC grid-connected system under PLL controller limiting constraints after a disturbance.

[0061] For example, when only considering the dynamic response of the PLL connected to the grid via VSC, based on the synchronization strategy of the PLL locking the q-axis voltage at the grid connection point, the dynamic process of the PLL phase angle θ under the limiting condition is expressed as follows:

[0062]

[0063] In formula (1), ω is the angular frequency of the PLL when the amplitude is infinite. s The angular frequency of the power grid. The upper limit set for the PI controller output of the PLL. The lower limit set for the PI controller output of the PLL.

[0064] When the PLL has not reached its limit, the dynamic process of its angular frequency ω is expressed as follows:

[0065]

[0066] In formula (2), These are the proportional parameters of the phase-locked loop. For phase-locked loop integral parameters, This represents the q-axis component of the VSC grid connection point voltage.

[0067] Under the simplified dynamic response of the current loop, assuming the dq-axis current remains at the reference value, the q-axis component of the VSC grid-connected voltage... It can be represented as:

[0068]

[0069] In formula (3), U sL R is the voltage amplitude of VSC connected to the infinite power bus. l and L l These are the equivalent resistance and equivalent inductance of the line, respectively. and These are the reference values ​​set for the dq-axis current of the current loop, respectively.

[0070] Differentiate formula (3) with respect to time and substitute it into formula (2) to eliminate the algebraic variables. The dynamic process of the PLL angular frequency when the amplitude limit is not reached can be further represented as follows:

[0071]

[0072] The equilibrium point (θ) of the PLL when the limit is not reached is calculated according to formulas (1) and (4). s ,ω s Without loss of generality, a coordinate transformation is performed on the PLL state variables to move the equilibrium point of the PLL state equation to the origin, resulting in the new grid-connected VSC state variables (x1, x2) as follows:

[0073] x1=θ-θ s x2=ω-ω s (5)

[0074] Combining formulas (1), (4), and (5), the switching system model for grid-connected VSC is generated as follows:

[0075]

[0076] In formula (6), x 2max The upper limit of x2, x 2min It is the lower bound of x2.

[0077] The specific expressions for g(x1) and f(x1) in the subsystem h1(x1,x2) are as follows:

[0078]

[0079] S102. Determine the common Lyapunov function of the switching system based on the switching system model with PLL controller limiting;

[0080] In this step, optionally, a generalized energy function of subsystem h1(x1,x2) is defined as a pre-selected function for the common Lyapunov function of the switching system. The generalized energy function is then differentiated with respect to time along the vector field directions of subsystems h2(x1,x2) and h3(x1,x2), respectively. The derivative is negative definite and can be used as the common Lyapunov function of the PLL switching system.

[0081] For example, the generalized energy function expression for the subsystem h1(x1,x2) is defined as V(x1,x2):

[0082]

[0083] The generalized energy function in formula (8) is differentiated with respect to time along the vector field direction of the subsystem h2(x1,x2). The derivative is negative and definite. Specifically:

[0084]

[0085] The generalized energy function in formula (9) is differentiated with respect to time along the vector field direction of the subsystem h3(x1,x2). The derivative is negative and definite. Specifically:

[0086]

[0087] Based on formulas (9) and (10), V(x1,x2) in formula (8) is determined to be the common Lyapunov function of the PLL switching system.

[0088] S103. Based on the common Lyapunov function of the switching system, calculate the analytical stability region of the system and derive the relationship between the stability boundary and the system parameters.

[0089] In this step, domain 1 is obtained from the positive definite condition of the Lyapunov function, and domain 2 is obtained from the negative definite condition of the derivative of the Lyapunov function with respect to time. The intersection of domain 1 and domain 2 is taken to obtain the analytical stability domain of the system. Based on the analytical expression of the stability domain, the relationship between the stability boundary and the system parameters is obtained.

[0090] For example, based on the Lyapunov function expression in formula (8) in step S102, the domain S1 under the positive definite condition of the Lyapunov function is obtained, specifically:

[0091]

[0092] Based on the Lyapunov function expression in formula (8) in step S102, the domain S2 under the condition of negative definite derivative of the Lyapunov function with respect to time can be obtained, specifically:

[0093]

[0094] According to formulas (10) and (11), the intersection of domain S1 and domain S2 is taken to calculate the analytic stability region D of the system, which is expressed as:

[0095] D={(x1,x2)||θ I <x1<θ II} (12)

[0096] In formula (12), θ I Let θ be the left stable boundary of the system. II This represents the right stability boundary of the system.

[0097] The relationship between the stability boundary and system parameters is derived from formula (12), specifically as follows:

[0098]

[0099] S104. Based on the boundary of the analytical stability region, calculate the critical energy function of the system, compare the magnitude of the critical energy function with the energy function of the system after disturbance, and determine whether the grid-connected VSC can remain stable under amplitude limiting constraints after a large disturbance.

[0100] Optionally, the right boundary of the system's conservative stability region is taken, and the critical energy function of the system is calculated according to the common Lyapunov function expression. If the system energy function is less than the critical energy function after the system is disturbed, the system is determined to remain stable.

[0101] For example, based on the definition of the generalized energy function of the system in formula (8) in step S102 and the expression of the right boundary of the conservative stability domain of the system in formula (13) in step 3, the critical energy function V of the system is calculated. crit Specifically:

[0102]

[0103] Comparing the critical energy function in formula (14) with the energy function after the system is disturbed, if the energy function after the system is disturbed is less than the critical energy function, then the system can be determined to remain stable. Specifically:

[0104] V(x 1tc ,x 2tc ) <V crit (15)

[0105] In formula (15), x 1tc and x 2tc This refers to the values ​​of the system state variables of the grid-connected VSC system at the end of the last major disturbance.

[0106] Please see Figure 4 In another embodiment of the present invention, a grid-connected VSC system limiting stability judgment device is provided. This device can be used to implement the above-mentioned grid-connected VSC system limiting stability judgment method. Specifically, the grid-connected VSC system limiting stability judgment device includes a generation module 401, a determination module 402, a calculation module 403, and a judgment module 404.

[0107] Among them, the generation module 401: Based on the response characteristics of the grid-connected VSC system after disturbance, the dynamic response of the current loop is simplified, and the limiting constraint of the phase-locked loop controller is considered to generate the switching system model of the grid-connected VSC.

[0108] Determine module 402: Determine the common Lyapunov function of the switching system based on the switching system model;

[0109] Calculation module 403: Calculates the analytical stability region of the grid-connected VSC system based on the common Lyapunov function, and derives the relationship between the stability boundary and system parameters;

[0110] Judgment Module 404: Based on the boundary of the analytical stability region, calculate the critical energy function of the grid-connected VSC system, and determine whether the grid-connected VSC can remain stable under amplitude limiting constraints after a large disturbance based on the magnitude of the critical energy function and the energy function of the grid-connected VSC system after being disturbed.

[0111] In one embodiment, the generation module 401 is specifically used for:

[0112] Obtain the switching system model of the grid-connected VSC. The switching system model of the grid-connected VSC is used to describe the dynamic response of the system under the limiting constraint scenario of the PLL controller after the grid-connected VSC is disturbed.

[0113] The switching system model for grid-connected VSCs is as follows:

[0114]

[0115] Here, x1 and x2 are two state variables of the PLL: x1 = θ - θ s x2=ω-ω s θ is the PLL phase angle, θ s Here is the PLL phase angle equilibrium point, and ω is the PLL angular frequency. s For power grid frequency, x 2min and x 2maxLet be the lower and upper bounds of x2, respectively. dt represents the derivative. h1(x1,x2), h2(x1,x2), and h3(x1,x2) represent the subsystems that the system switches to when x2 does not reach its limit, when x2 reaches its lower bound, and when x2 reaches its upper bound, respectively.

[0116] The expressions for g(x1) and f(x1) in the subsystem h1(x1,x2) are as follows:

[0117]

[0118]

[0119]

[0120] Among them, U sL The voltage amplitude of VSC connected to the infinite power bus. These are the proportional parameters of the phase-locked loop. R is the integral parameter of the phase-locked loop. l and L l These are the equivalent resistance and equivalent inductance of the line, respectively. and These are the reference values ​​set for the dq-axis currents of the current loop, and M is the equivalent inertia of the system.

[0121] In one embodiment, the determining module 402 is specifically used for:

[0122] Define a generalized energy function for subsystem h1(x1,x2) as a pre-selected function for the common Lyapunov function of the switching system. Differentiate this generalized energy function with respect to time along the vector field directions of subsystems h2(x1,x2) and h3(x1,x2), respectively. The derivative is negative and definite, and can be used as the common Lyapunov function of the PLL switching system.

[0123] The determined common Lyapunov function is:

[0124]

[0125] In one embodiment, the computing module 403 is specifically used for:

[0126] Domain 1 is obtained from the positive definite condition of the Lyapunov function, and domain 2 is obtained from the negative definite condition of the derivative of the Lyapunov function with respect to time. The intersection of domain 1 and domain 2 is used to obtain the analytical stability domain of the system. Based on the analytical expression of the stability domain, the relationship between the stability boundary and the system parameters is obtained.

[0127] The analytical stability region expression of the system is as follows:

[0128] D={(x1,x2)|θ I <x1<θII}

[0129]

[0130] Where D is the analytical stability region of the system, and x1 and x2 are two state variables of the PLL: x1 = θ - θ s x2=ω-ω s θ is the PLL phase angle, θ s Here is the PLL phase angle equilibrium point, and ω is the PLL angular frequency. s U is the angular frequency of the power grid. sL The voltage amplitude of VSC connected to the infinite power bus. These are the proportional parameters of the phase-locked loop. L is the integral parameter of the phase-locked loop. l The equivalent inductance of the line, θ is the reference value for the d-axis current of the current loop. I Let θ be the left stable boundary of the system. II This represents the right stability boundary of the system.

[0131] In one embodiment, the determination module 404 includes:

[0132] The computational unit is used to calculate the critical energy function of the system based on the boundary of the analytic stability region, and to calculate the energy function of the system after disturbance. The expression for the critical energy function of the system is:

[0133]

[0134] V crit Let θ be the critical energy function of the system. II Let M be the right stability boundary of the system, and U be the equivalent inertia of the system. sL R is the voltage amplitude of VSC connected to the infinite power bus. l and L l These are the equivalent resistance and equivalent inductance of the line, respectively. and These are the reference values ​​set for the dq-axis current of the current loop, θ. s This is the PLL phase angle equilibrium point.

[0135] The judgment unit is used to compare the magnitude of the critical energy function and the energy function after the system is disturbed, and to determine whether the grid-connected VSC can remain stable under the amplitude limiting constraint after a large disturbance.

[0136] In another embodiment of the present invention, a terminal device is provided, comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, 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, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or corresponding function. The processor described in this embodiment of the present invention can be used in the operation of a grid-connected VSC system amplitude limiting stability judgment method, including:

[0137] Based on the response characteristics of the grid-connected VSC system after disturbance, the dynamic response of the current loop is simplified. Considering the limiting constraint of the phase-locked loop controller, a switching system model of the grid-connected VSC is generated. Based on the switching system model, the common Lyapunov function of the switching system is determined. Based on the common Lyapunov function, the analytical stability region of the grid-connected VSC system is calculated, and the relationship between the stability boundary and the system parameters is derived. Based on the boundary of the analytical stability region, the critical energy function of the grid-connected VSC system is calculated. Based on the magnitude of the critical energy function and the energy function of the grid-connected VSC system after disturbance, it is determined whether the grid-connected VSC can remain stable under the limiting constraint after a large disturbance.

[0138] In another embodiment of the present invention, a storage medium is provided, specifically a computer-readable storage medium (Memory), which is a memory device in a terminal device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and extended storage media supported by the terminal device. The computer-readable storage medium provides storage space that stores the operating devices of the terminal. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device.

[0139] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the method for determining the amplitude limiting stability of the grid-connected VSC system in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor in the following steps:

[0140] Based on the response characteristics of the grid-connected VSC system after disturbance, the dynamic response of the current loop is simplified. Considering the limiting constraint of the phase-locked loop controller, a switching system model of the grid-connected VSC is generated. Based on the switching system model, the common Lyapunov function of the switching system is determined. Based on the common Lyapunov function, the analytical stability region of the grid-connected VSC system is calculated, and the relationship between the stability boundary and the system parameters is derived. Based on the boundary of the analytical stability region, the critical energy function of the grid-connected VSC system is calculated. Based on the magnitude of the critical energy function and the energy function of the grid-connected VSC system after disturbance, it is determined whether the grid-connected VSC can remain stable under the limiting constraint after a large disturbance.

[0141] Please see Figure 5 The computer device 5 in this embodiment includes: at least one processor 50 ( Figure 5 (Only one is shown) a processor, a memory 51, and a computer program 52 stored in the memory 51 and executable on the at least one processor 70, wherein the processor 50 executes the computer program 52 to implement the steps in any of the above method embodiments.

[0142] The computer device 5 may be a smartphone, tablet, desktop computer, or cloud server, among other computing devices. This computer device may include, but is not limited to, a processor 50 and a memory 51. Those skilled in the art will understand that... Figure 5 The computer device 5 is merely an example and does not constitute a limitation on the computer device 5. It may include more or fewer components than shown in the figure, or combine certain components, or different components, such as input / output devices, network access devices, etc.

[0143] The processor 50 may be a Central Processing Unit (CPU), or it may be other general-purpose processors, 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, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0144] In some embodiments, the memory 51 may be an internal storage unit of the computer device 5, such as a hard disk or memory of the computer device 5. In other embodiments, the memory 51 may be an external storage device of the computer device 5, such as a plug-in hard disk, smart media card (SMC), secure digital card (SD), flash card, etc., equipped on the computer device 5. Furthermore, the memory 51 may include both internal and external storage units of the computer device 5. The memory 51 is used to store the operating system, applications, bootloader, data, and other programs, such as the program code of the computer program. The memory 51 can also be used to temporarily store data that has been output or will be output.

[0145] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0146] As an example, and not a limitation, MATLAB is used to demonstrate, for example, by... Figure 2 The simulation system shown is used to verify the amplitude limiting stability judgment method of the grid-connected VSC system proposed in this invention. Figure 2 The simulation uses a system with a VSC connected to an infinite power bus via PLL synchronization as an example. The large disturbance experienced by the system is set as follows: at t = 10 ms, the voltage amplitude of the infinite power bus suddenly drops from 1.0 pu to 0.3 pu and then experiences a period of t... d The system recovered to 1.0 pu after the fault lasted for a period of time.

[0147] The system parameters are designed as shown in the table below:

[0148]

[0149]

[0150] In this embodiment, the dynamic response of the VSC grid-connected system using PLL synchronization under different fault durations is as follows: Figure 3 As shown.

[0151] Figure 3 Comparing the PLL settings with x 2max =12.57 rad / s upper limit and x 2min = -15.70 rad / s lower limit and fault duration t d The values ​​are 36ms, 70ms, and t when the PLL is not set to limit and the fault duration is t. d The dynamic response of the grid-connected VSC to a large disturbance at a time of 70ms.

[0152] Figure 3 (a) The phase trajectory of the system is shown, and comparative analysis is performed. Figure 3 (a) It can be seen that under the condition of PLL setting the amplitude limit, t d At 36ms and 70ms respectively, the grid-connected VSC system behaves as a switching system. The system trajectory reaches the upper limit set by the PLL controller during the fault period, enters subsystem h3, switches back to subsystem h1 after the fault is cleared, and then switches back to subsystem h2 when it reaches the lower limit set by the PLL controller. At t d At 36 ms, the system trajectory remains within the right stability boundary derived from the common Lyapunov function defined in this invention, and the trajectory eventually converges to the origin, indicating that the system can maintain stability. At t d At 70ms, the system trajectory crossed the stability boundary derived from the common Lyapunov function, but the trajectory eventually converged back to the origin, and the system remained stable. However, under the condition that the PLL does not have a limit, at t... d At 70ms, the system has already crossed the true stability boundary after the fault is cleared, and the system becomes unstable. Therefore, the common Lyapunov function defined in this invention can conservatively derive the system's stability boundary, ensuring the effectiveness of the stability criterion.

[0153] Figure 3 (b) illustrates the dynamic process of the system trajectory's energy changing over time. Based on the critical energy criterion proposed by this invention, the critical energy magnitude of this embodiment can be calculated to be 233.94. It can be seen that under the condition of PLL setting a limit, t d When the time is 30ms, the system is at point A during fault clearing, with an energy of 182.12, which is less than the critical energy proposed in this invention; t d When the time is 70ms, the system is at point C during fault clearing, with an energy of 562.89, which is greater than the critical energy proposed in this invention. However, under the condition that the PLL does not have a set limiting, t dAt 70ms, the system energy is already far greater than the critical energy when the fault is cleared, leading to system instability. This demonstrates that after a large disturbance, under PLL limiting conditions, if the system energy is less than the critical energy proposed in this invention, the system can remain stable. Furthermore, the stability criterion proposed in this invention is sufficiently conservative, avoiding system instability caused by criterion failure. This fully verifies the effectiveness of the stability criterion proposed in this invention under PLL limiting conditions, and compared to traditional stability assessment methods, this invention has significant advantages.

[0154] In summary, the present invention provides a method, apparatus, medium, and equipment for determining the amplitude-limited stability of a grid-connected VSC system. This provides a basis for setting parameters of grid-connected VSC systems with amplitude-limited constraints, thereby improving system stability. By comparing the critical energy function and the energy function after the system is disturbed, the large-disturbance stability of the grid-connected VSC under amplitude-limited constraints can be determined, avoiding time-consuming numerical simulations. This invention can provide a large-disturbance stability criterion for grid-connected VSC systems with amplitude-limited constraints.

[0155] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments 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. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above device can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0156] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0157] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. 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 this invention.

[0158] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another device, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0159] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0160] 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.

[0161] If the integrated module / 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, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0162] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (devices), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0163] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0164] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0165] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for judging the amplitude limiting stability of a grid-connected VSC system, characterized in that, Includes the following steps: Based on the simplified dynamic response of the current loop after a disturbance in the grid-connected VSC system, and considering the limiting constraints of the phase-locked loop controller, a switching system model for the grid-connected VSC is generated. The specific switching system model for the grid-connected VSC is as follows: in, and These are two state variables of the PLL. and They are respectively The lower and upper limits, To represent the differential, , and They represent Within the upper and lower limits, Reaching the lower limit and When the limit is reached, the system switches to a subsystem. and The specific expression is: ； Based on the switching system model, the common Lyapunov function of the switching system is determined. The specific common Lyapunov function of the switching system is as follows: in, and These are two state variables of the PLL; The analytical stability region of the grid-connected VSC system is calculated based on the common Lyapunov function, and the relationship between the stability boundary and the system parameters is derived as follows: in, This is the left stability boundary of the system. This is the right stability boundary of the system. The equivalent inductance of the line, For current loop Reference value for shaft current setting. These are the integral parameters of the phase-locked loop. These are the proportional parameters of the phase-locked loop. The voltage amplitude of VSC connected to the infinite power bus; Analytical stability region of the system for: in, and These are two state variables of the PLL. This is the left stability boundary of the system. This represents the right stability boundary of the system. Based on the boundary of the analytical stability region, the critical energy function of the grid-connected VSC system is calculated. The stability of the grid-connected VSC system under amplitude limiting constraints is determined by the magnitude of the critical energy function and the energy function after disturbance. Critical energy function of the system , and To determine the stability of a grid-connected VSC system, we need to find the values ​​of its state variables at the end of the last major disturbance, and define the system's critical energy function. for: in, This is the right stability boundary of the system. The equivalent inertia of the system, The voltage amplitude of VSC connected to the infinite power bus. and These are the equivalent resistance and equivalent inductance of the line, respectively. and Current loops Reference value for shaft current setting. This is the PLL phase angle equilibrium point. This is the angular frequency of the power grid.

2. A device for judging the amplitude limiting stability of a grid-connected VSC system, characterized in that, include: The generation module is used to simplify the dynamic response of the current loop based on the response characteristics of the grid-connected VSC system after disturbance, and to generate a switching system model of the grid-connected VSC considering the limiting constraints of the phase-locked loop controller. The specific switching system model of the grid-connected VSC is as follows: in, and These are two state variables of the PLL. and They are respectively The lower and upper limits, To represent the differential, , and They represent Within the upper and lower limits, Reaching the lower limit and When the limit is reached, the system switches to a subsystem. and The specific expression is: ； The determination module is used to determine the common Lyapunov function of the switching system based on the switching system model. The specific common Lyapunov function of the switching system is as follows: in, and These are two state variables of the PLL; The calculation module is used to calculate the analytical stability region of the grid-connected VSC system based on the common Lyapunov function, and derive the relationship between the stability boundary and the system parameters. The relationship between the stability boundary and the system parameters is as follows: in, This is the left stability boundary of the system. This is the right stability boundary of the system. The equivalent inductance of the line, For current loop Reference value for shaft current setting. These are the integral parameters of the phase-locked loop. These are the proportional parameters of the phase-locked loop. The voltage amplitude of VSC connected to the infinite power bus; Analytical stability region of the system for: in, and These are two state variables of the PLL. This is the left stability boundary of the system. This represents the right stability boundary of the system. The judgment module is used to calculate the critical energy function of the grid-connected VSC system based on the boundary of the analytical stability region. Based on the magnitude of the critical energy function and the energy function of the grid-connected VSC system after a disturbance, it determines whether the grid-connected VSC can remain stable under amplitude limiting constraints after a large disturbance. The module also considers the energy function after the system is disturbed. Critical energy function of the system , and To determine the stability of a grid-connected VSC system, we need to find the values ​​of its state variables at the end of the last major disturbance, and define the system's critical energy function. for: in, This is the right stability boundary of the system. The equivalent inertia of the system, The voltage amplitude of VSC connected to the infinite power bus. and These are the equivalent resistance and equivalent inductance of the line, respectively. and Current loops Reference value for shaft current setting. This is the PLL phase angle equilibrium point. This is the angular frequency of the power grid.

3. A computer-readable storage medium for storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform the method of claim 1.

4. A computing device, characterized in that, include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including steps for performing the method of claim 1.

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