New energy converter transient angle of attack voltage instability observation method based on energy function and bifurcation theory

Abstract

The application discloses a new energy converter transient power angle voltage instability observation method based on an energy function and a bifurcation theory, and the system stable equilibrium point and the system unstable equilibrium point are divided by obtaining the system operation state change before and after the new energy converter fault through transient time domain simulation simulation of the parallel connection of a synchronous machine and a VSG, at the fault clearing moment of the transient time domain simulation simulation, the system energy value of the system stable equilibrium point and the system critical energy value of the system unstable equilibrium point are calculated through the system energy function, the system energy value and the system critical energy value are compared, the system transient power angle instability is determined based on the comparison result, the system transient power angle instability determination result is obtained, the system singular point is determined under the system power angle stable state based on the system transient power angle instability determination result, the system operation trajectory is obtained to perform system singular point coincidence judgment, and the transient voltage instability is determined based on the coincidence state. The method has the effect of simultaneously detecting the stability of the system transient power angle and voltage.

Description

Technical Field

[0001] This invention relates to the technical field of transient stability detection of converters in new energy grid-connected systems, and in particular to a method for observing transient power angle voltage instability of new energy converters based on energy function and bifurcation theory. Background Technology

[0002] Currently, with the continuous development of new energy power systems, wind power, photovoltaics, and other new energy sources are being connected to the power system in large quantities, and the single power source structure is becoming more diversified, bringing new challenges to the stable operation of the power system. Direct-drive wind turbines and photovoltaic power generation typically use power electronic converters as the interface for grid connection. Virtual synchronous generator (VSG) control, as a new type of control method for power electronic converters, is widely used because it simulates the inertia and damping characteristics of synchronous generators to provide voltage and frequency support to the grid. Unlike traditional synchronous generators, VSGs have fast response speeds and flexible dynamic characteristics, which can be approximated as power algebra constraints in electromechanical transient processes, transforming the system model from ordinary differential equations to differential algebraic equations. However, this can easily lead to profound changes in the transient stability mechanism of the system, especially the increasingly prominent coupling problem between transient power angle and voltage stability. As new power systems shift from being dominated by synchronous generators to having synchronous generators and power electronic equipment coexisting, the interaction between equipment is significantly enhanced, resulting in tight coupling between voltage dynamics and power angle dynamics across multiple time scales, further increasing the complexity of transient stability problems. Traditional detection methods based on the slow dynamics of synchronous machines are no longer suitable for the current development needs of power systems.

[0003] To address the aforementioned challenges, existing research has analyzed transient power angle instability, voltage instability, and the coupling relationship between the two. In power angle instability detection, current methods mainly include time-domain simulation, energy function methods, and artificial intelligence methods. Time-domain simulation methods are computationally intensive and lack quantitative and unified stability criteria. Artificial intelligence methods utilize trained evaluator models to assess the transient stability of the system online, but this method is highly dependent on data and requires model restructuring when the system structure changes. Energy function methods have a clear theoretical basis, quantitatively estimating system stability by calculating the system's stability domain. Regarding voltage stability critical point calculation, existing methods include constructing voltage stability indices using Thevenin equivalents, but this method struggles to consider system constraints. Another approach is to calculate the bifurcation point discrimination conditions based on a complete system model, thereby accurately estimating the voltage stability critical point. However, the stability phenomena of renewable energy grid-connected systems are not independent; different types of stability are interconnected and coupled. Therefore, a detection method that can simultaneously consider both transient power angle and voltage stability in renewable energy grid-connected systems is needed. Summary of the Invention

[0004] To address the problem that existing technologies for renewable energy grid-connected systems do not fully consider the coupling relationship between transient power angle and voltage stability, making it difficult to simultaneously address both transient power angle and voltage stability, this application provides a method for observing transient power angle and voltage instability in renewable energy converters based on energy functions and bifurcation theory. This method, based on a parallel system of a virtual synchronous machine and a synchronous generator, calculates the system's attraction domain using the energy function method and compares the simulated phase plane trajectory with the attraction domain to determine transient power angle stability. For cases where transient voltage instability occurs while the power angle remains stable, the critical point of transient voltage instability is calculated based on the differential-algebraic equations of the grid-connected system. Voltage stability is then determined using singular bifurcation theory. By combining two instability detection methods, the stability of both the transient power angle and voltage of the system can be detected simultaneously.

[0005] Firstly, the above-mentioned inventive objective of this application is achieved through the following technical solution: A method for observing transient power angle and voltage instability in renewable energy converters based on energy function and bifurcation theory is proposed. This method uses a synchronous machine and a VSG in parallel to jointly detect the coupled transient power angle and voltage instability in the renewable energy converter. The method includes: Under transient time-domain simulation of synchronous machine and VSG in parallel, the changes in system operating state before and after the failure of new energy converter are obtained, and the system stable equilibrium point and system unstable equilibrium point are divided based on the changes in system operating state. At the fault clearing time in the transient time-domain simulation, the system energy value of the system stable equilibrium point and the system critical energy value of the system unstable equilibrium point are calculated using the system energy function. By comparing the system energy value with the system critical energy value, and based on the comparison result, the system transient power angle instability is determined, and the system transient power angle instability determination result is obtained; Based on the system transient power angle instability determination result, the system singularity is determined in the system power angle stable state and the system running trajectory is obtained to determine the system singularity coincidence. Based on the coincidence state, transient voltage instability is determined.

[0006] In a preferred embodiment, this application can be further configured as follows: under transient time-domain simulation of the synchronous machine and VSG in parallel, the changes in the system operating state before and after the failure of the renewable energy converter are obtained, and the system stable equilibrium point and the system unstable equilibrium point are divided based on the changes in the system operating state, specifically including: Under transient time-domain simulation, the initial state of the system before the fault of the new energy converter and the fault state of the system after the fault are obtained and the states are compared to obtain the changes in the system operating state before and after the fault. System equilibrium points where the change in operating state exceeds a preset threshold are marked as unstable equilibrium points, while system equilibrium points where the change in operating state does not exceed the preset threshold are marked as stable equilibrium points.

[0007] In a preferred embodiment, this application can be further configured such that: at the fault clearing time in the transient time-domain simulation, calculating the system energy value at the stable equilibrium point and the system critical energy value at the unstable equilibrium point of the system through the system energy function specifically includes: Obtain the stable equilibrium point angle of the system, and calculate the system energy value at the time of fault clearance using the system energy function. The expression for calculating the system energy value is as follows: (1) in, This represents the system energy value at the moment the fault was cleared. This represents the equivalent inertial constant of the two-machine system. This represents the actual angular velocity at the stable equilibrium point. Represents equivalent mechanical power. , These represent the actual and maximum values ​​of the equivalent electromagnetic power, respectively. This indicates the relative rotor phase angle between the synchronous machine and the VSG. , These represent the phase angles of the synchronous machine rotor and the simulated VSG rotor, respectively. Indicates the angle of the stable equilibrium point. As an intermediate variable; Obtain the angle of the unstable equilibrium point of the system, and calculate the critical energy value of the system at the moment of fault clearance using the system energy function to determine the critical instability state of the system.

[0008] In a preferred embodiment, this application can be further configured as follows: comparing the system energy value and the system critical energy value, and performing a system transient power angle instability determination based on the comparison result to obtain a system transient power angle instability determination result, specifically including: Based on the comparison between the system energy value and the system critical energy value, it is determined whether an energy exceedance occurred at the fault clearing moment; If so, the system is determined to be transiently unstable in terms of power angle; otherwise, the system is determined to be stable in terms of power angle, thus obtaining the result of the determination of transient power angle instability.

[0009] In a preferred embodiment, this application can be further configured such that: the determination of whether an energy boundary violation occurs at the fault clearing moment based on the comparison result between the system energy value and the system critical energy value specifically includes: Energy boundary determination is based on the energy boundary condition, which is that the system energy value is greater than the system critical energy value.

[0010] In a preferred embodiment, this application can be further configured as follows: based on the system transient power angle instability determination result, determining system singularities and obtaining the system operating trajectory in a stable system power angle state to determine system singularity coincidence, and determining transient voltage instability based on the coincidence state, specifically including: Under the stable state of the system's power angle, determine whether the system's equilibrium point meets the criteria for a singular point. If it does, mark it as a singular point of the system. The system's operating trajectory is obtained, and it is determined whether the system's operating trajectory coincides with the system's singularity. If they coincide, it is determined that a transient voltage instability has occurred; if they do not coincide, it is determined that the system's transient voltage is stable.

[0011] In a preferred embodiment, this application can be further configured as follows: When the system is in a stable power angle state, determining whether the system equilibrium point meets the singularity criteria, and if so, marking it as a system singularity, specifically includes: The singularity determination criteria are as follows: (2) in, It represents the partial derivative of an algebraic equation with respect to the algebraic variable.

[0012] Secondly, the above-mentioned inventive objective of this application is achieved through the following technical solutions: A transient power angle voltage instability monitoring system for a new energy converter based on energy function and bifurcation theory, the system comprising: The equilibrium point division module is used to obtain the changes in the system operating state before and after the failure of the new energy converter under transient time-domain simulation of the synchronous machine and VSG in parallel, and to divide the system stable equilibrium point and the system unstable equilibrium point based on the changes in the system operating state. The energy value calculation module is used to calculate the system energy value at the stable equilibrium point of the system and the system critical energy value at the unstable equilibrium point of the system through the system energy function at the fault clearing time of the transient time domain simulation. The transient power angle instability determination module is used to compare the system energy value with the system critical energy value, and to determine the system transient power angle instability based on the comparison result, thereby obtaining the system transient power angle instability determination result. The transient voltage instability determination module is used to determine system singularities and obtain the system running trajectory under the stable system power angle state based on the transient power angle instability determination result of the system, and to determine the coincidence of system singularities based on the coincidence state.

[0013] Thirdly, the above-mentioned objectives of this application are achieved through the following technical solutions: A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the aforementioned method for observing transient power angle voltage instability of a new energy converter based on energy function and bifurcation theory.

[0014] Fourthly, the above-mentioned objectives of this application are achieved through the following technical solutions: A computer-readable storage medium storing a computer program that, when executed by a processor, implements the aforementioned method for observing transient power angle voltage instability in a new energy converter based on energy functions and bifurcation theory.

[0015] In summary, this application includes at least one of the following beneficial technical effects: 1. This application addresses the coupled scenario of transient power angle instability and voltage instability. By combining the detection methods of both instability forms, under the transient time-domain simulation of a synchronous machine and a VSG in parallel, the system unstable equilibrium point is divided based on the changes in the system's operating state. The transient power angle instability judgment condition is constructed by calculating the actual energy value and the critical energy value of the system through the system energy function. The transient power angle instability is quantitatively judged. In the transient fair cross-stable state, the transient voltage instability judgment is made by judging whether the system's operating trajectory coincides with the singular point. Thus, the two coupled instability forms are taken into account, and the transient instability type is accurately detected and classified. 2. This application is based on a parallel system of virtual synchronous machine and synchronous generator. It calculates the attraction domain of the system using the energy function method and compares its phase plane simulation trajectory with the attraction domain to determine the transient power angle stability. For the case of transient voltage instability but stable power angle, it calculates the critical point of transient voltage instability based on the differential algebraic equation of the grid-connected system and judges the system voltage stability from the perspective of singular bifurcation theory. 3. This application sets singularity criteria based on the det function. Based on the relationship between the differential algebraic equation and the singularity of the function in the dynamic process of the new energy power generation output characteristics during the transient process, the application sets the condition of no solution of the differential algebraic equation as the singularity criteria, and quantifies the criteria for determining transient voltage instability in the new energy grid-connected system. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0017] Figure 1 This is a flowchart illustrating the implementation of the transient power angle voltage instability observation method for the new energy converter in this embodiment.

[0018] Figure 2 This is a schematic diagram of the parallel connection between the synchronizer and the VSG in this embodiment.

[0019] Figure 3 This is a control block diagram of the VSG in this embodiment.

[0020] Figure 4 This is an overall data flow diagram of the transient power angle voltage instability observation method for new energy converters in this embodiment.

[0021] Figure 5 This is a simulation diagram of the system's attraction domain and phase plane when the VSG reference power is 30kW in this embodiment.

[0022] Figure 6 This is a schematic diagram of the simulation results of VSG voltage and power angle when the VSG reference power is 30kW in this embodiment.

[0023] Figure 7 This is a simulation diagram of the system's attraction domain and phase plane when the VSG reference power is 40kW in this embodiment.

[0024] Figure 8 This is a schematic diagram of the simulation results of VSG voltage and power angle when the VSG reference power is 40kW in this embodiment.

[0025] Figure 9 This is a simulation diagram of the system's attraction domain and phase plane when the VSG reference power is 20kW in this embodiment.

[0026] Figure 10 The determinant value det(A) of the state matrix of the reduced-order differential equation in this embodiment is... g ).

[0027] Figure 11 This is a schematic diagram of the simulation results of VSG voltage and power angle when the VSG reference power is 20kW in this embodiment.

[0028] Figure 12 This is a block diagram of the transient power angle voltage instability observation system for the new energy converter in this embodiment.

[0029] Figure 13 This is a schematic diagram of the internal structure of a computer device used to implement a method for observing transient power angle voltage instability in renewable energy converters. Detailed Implementation

[0030] 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.

[0031] It should be understood that, when used in this specification, 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.

[0032] 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, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” are intended to include the plural forms.

[0033] It should also be further understood that the term "and / or" as used in this specification refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0034] In one embodiment, such as Figure 1 As shown, this application discloses a method for observing transient power angle and voltage instability in renewable energy converters based on energy function and bifurcation theory. It uses a parallel connection of a synchronous machine and a VSG (virtual synchronous generator) to jointly detect the coupled transient power angle and voltage instability in renewable energy converters. A schematic diagram of the parallel connection structure of the synchronous machine and VSG in this embodiment is shown below. Figure 2 As shown in the diagram, the synchronous machine and VSG are connected in parallel to a common bus via a line, and then connected to the power grid via the bus. P w This represents the actual active power output by the VSG. E SG , δ SG These represent the voltage amplitude and phase angle of the synchronous machine, respectively. U S The mains voltage is used. The control block diagram of the VSG is as follows: Figure 3 As shown, V dc This is the DC side voltage value; v abc , i abc These are the sampled VSG output voltage and current, respectively; D p The damping coefficient is... M2 represents the rotational inertia of the VSG. The active power control loop simulates the frequency droop characteristics and rotor motion equations of the synchronous generator, while the reactive power control loop simulates the voltage droop characteristics of the synchronous generator. The specific steps include: S1: Under transient time-domain simulation of synchronous machine and VSG in parallel, obtain the changes in system operating state before and after the failure of new energy converter, and divide the system stable equilibrium point and the system unstable equilibrium point based on the changes in system operating state.

[0035] Specifically, step S1 includes: S11: Under transient time-domain simulation, obtain the initial state of the system before the fault of the new energy converter and the fault state of the system after the fault, and compare the states to obtain the changes in the system operating state before and after the fault.

[0036] Specifically, in the transient time-domain simulation of VSG, the initial state of the system before the fault of the renewable energy converter and the fault state of the system after the fault simulation are obtained, and the changes in the system operating state before and after the fault are obtained by comparing the states.

[0037] S12: Mark the system equilibrium point where the change in operating state exceeds the preset change threshold as the system unstable equilibrium point, and mark the system equilibrium point where the change in operating state does not exceed the preset change threshold as the system stable equilibrium point.

[0038] Specifically, a threshold for changes in operating status is set. System equilibrium points where the actual changes in operating status exceed the preset threshold are marked as unstable equilibrium points, while system equilibrium points where the changes do not exceed the preset threshold are marked as stable equilibrium points.

[0039] S2: At the fault clearing moment in the transient time-domain simulation, the system energy value at the stable equilibrium point and the system critical energy value at the unstable equilibrium point are calculated using the system energy function.

[0040] Specifically, step S2 includes: S21: Obtain the stable equilibrium point angle of the system, and calculate the system energy value at the time of fault clearance using the system energy function. The system energy value calculation expression is as follows: (1) in, This represents the system energy value at the moment the fault was cleared. This represents the equivalent inertial constant of the two-machine system. This represents the actual angular velocity at the stable equilibrium point. Represents equivalent mechanical power. , These represent the actual and maximum values ​​of the equivalent electromagnetic power, respectively. This indicates the relative rotor phase angle between the synchronous machine and the VSG. , These represent the phase angles of the synchronous machine rotor and the simulated VSG rotor, respectively. Indicates the angle of the stable equilibrium point. It is an intermediate variable.

[0041] The derivation process of the system energy function in this embodiment specifically includes: Obtain the rotor motion equation of the synchronous machine: (3) In the formula, and These represent the inertia constant and damping coefficient of the synchronous machine, respectively. and These are the electromagnetic and mechanical power of the synchronous machine, respectively. and These are the reference value and the actual angular velocity of the synchronous machine, respectively. This indicates the phase angle of the synchronous machine rotor.

[0042] Constructing an equivalent mathematical model of the VSG (Virtual Synchronous Machine) based on the rotor motion equations of the synchronous machine: (4) in, The voltage phase angle of the virtual synchronous machine. For VSG angular velocity, and These are the electromagnetic and reference power of the VSG, respectively. and These represent the inertia constant and damping coefficient of the synchronizing machine, respectively. Let the relative rotor phase angle of the two machines be used as an example. Combining this with the equivalent mathematical model, the equivalent swing equations for the two machines are obtained as follows: (5) in, , , , , The specific calculation formula is as follows: (6) (7) (8) (9) (10) in, This represents the cross-differentiation of the node admittance matrices between the VSG and the synchronous machine. Indicates the phase angle of the mutual derivatives. This indicates the magnitude of the internal potential of the VSG.

[0043] The system energy function is derived by using the first integration method and combining it with the two-stage equivalent swing equation.

[0044] S22: Obtain the angle of the unstable equilibrium point of the system, and calculate the critical energy value of the system at the moment of fault clearance using the system energy function.

[0045] Specifically, the angle of the unstable equilibrium point of the system is obtained, and it is substituted into the angle of the stable equilibrium point in formula (1) to calculate the critical energy value of the unstable equilibrium point of the system, thereby quantifying the critical instability state of the system.

[0046] S3: Compare the system energy value with the system critical energy value, and make a transient power angle instability determination based on the comparison result to obtain the transient power angle instability determination result.

[0047] Specifically, step S3 includes: S31: Based on the comparison between the system energy value and the system critical energy value, determine whether an energy exceedance has occurred at the fault clearing time.

[0048] Specifically, the system energy value at the time of fault clearing is compared with the system critical energy value. Whether an energy out-of-bounds event has occurred is determined based on whether the comparison result meets the energy out-of-bounds condition. In this embodiment, the energy out-of-bounds condition is that the system energy value is greater than the system critical energy value. Specifically, if the system energy value is greater than the system critical energy value, it is determined that an energy out-of-bounds event has occurred at the time of fault clearing. If the system energy value is not greater than the system critical energy value, it is determined that no energy out-of-bounds event has occurred at the time of fault clearing.

[0049] S32: If so, the system is determined to be transiently unstable at the power angle; otherwise, the system is determined to be stable at the power angle, and the result of the transient power angle instability determination is obtained.

[0050] Specifically, if an energy overflow occurs, the system is determined to be in transient power angle instability; otherwise, if no energy overflow occurs, the system is determined to be in stable power angle, and the next step of the voltage instability detection procedure is initiated to obtain the system transient power angle instability determination result.

[0051] S4: Based on the system transient power angle instability judgment result, determine the system singularity under the system power angle stable state and obtain the system running trajectory to judge the system singularity coincidence, and judge the transient voltage instability based on the coincidence state.

[0052] Specifically, step S4 includes: S41: Under the stable state of the system's power angle, determine whether the system's equilibrium point meets the criteria for a singular point. If it does, mark it as a singular point of the system.

[0053] Specifically, under the stable state of the system's power angle, the system determines whether the equilibrium point is a singular point based on the singular point determination criteria. If the criteria are met, the point is marked as a singular point of the system.

[0054] The singularity determination criteria in this embodiment are as follows: (2) in, It represents the partial derivative of an algebraic equation with respect to the algebraic variable.

[0055] The derivation process of the singularity determination criteria in this embodiment specifically includes: When new energy power generation equipment is connected to the distribution network through a power electronic interface, due to its multi-timescale characteristics, the output characteristics of new energy power generation during the transient process can be expressed by differential algebraic equations as follows: (11) In the formula, x These are the state variables of dynamic components in the system, such as the power angle and speed of a generator, and the slip of a motor; y These are the algebraic variables of the system, such as the magnitude and phase angle of the node voltages; f ( x,y () represents the dynamic characteristic relationship between synchronous generators, loads, and power electronic converters; g ( x,y ) is the algebraic equation of the system. Assume that at the equilibrium point ( x 0, y 0) at det( g y Since 0 ≠ 0, according to the implicit function theorem, 0 = g ( x 0 ,y 0) can be represented as y 0=φ( x 0), the differential algebraic equation can be reduced to a differential equation as shown in equation (13), and its state matrix is ​​equation (14), as follows: (12) (13) In the formula, Let be the partial derivative of the algebraic equation with respect to the state variables.

[0056] Formulas (13)-(14) show that the stability of the system's differential algebraic equation and its reduced-order differential equation is consistent with the stability under small perturbations, but when ( x 0, y 0) at det( g yWhen )=0, according to the relationship between the solution of the equation and the singularity of the function, equation (12) becomes unsolvable near this point, the differential algebraic equation loses its definition, and this point is called a singular point. When the new energy grid-connected system encounters a singular point, transient voltage instability will occur.

[0057] S42: Obtain the system running trajectory and determine whether the system running trajectory coincides with the system singularity. If they coincide, it is determined that transient voltage instability has occurred. If they do not coincide, it is determined that the system transient voltage is stable.

[0058] Specifically, based on simulation platforms such as PSCAD and Matlab programming results, the system running trajectory, i.e. the simulation results, is obtained. It is then determined whether the system running trajectory coincides with the coordinates of the system singular point. If so, it is determined that a transient power grid instability has occurred; if not, it is determined that the system transient voltage is stable.

[0059] The overall data flow diagram of the transient power angle voltage instability observation method for the new energy converter in this embodiment is as follows: Figure 4 As shown.

[0060] In one embodiment, to verify the effectiveness of the proposed transient power angle voltage instability detection method for new energy grid-connected converters, the feasibility of the method will be verified through PSCAD simulation and Matlab programming. Figure 1 The circuit topology was constructed, in which the synchronous generator used the built-in synchronous generator module of PSCAD. The grid was set to experience a voltage drop fault at 5 seconds. During the fault, the effective value of the grid line voltage dropped from 380V to 130V, and the fault was cleared at 6 seconds.

[0061] The circuit and control parameter table of the novel power distribution system in this embodiment is shown in Table 1. The simulation parameters are set according to Table 1, as shown in Table 1 below: Table 1 When the VSG reference power is 30kW, the simulation of the system's attractive region and phase plane characterized by the above energy function is as follows: Figure 5 As shown, after the fault, the system asymptotically stabilizes and returns to a stable operating state, at which point the system is transiently stable. The simulation results for the VSG voltage and power angle are as follows: Figure 6 As shown, by Figure 6 It can be seen that after the fault was cleared, the output phase voltage amplitude of the VSG oscillated between 320V and 395V, but the oscillation amplitude gradually decreased and finally stabilized at 367V. At the same time, after the fault was cleared, the power angle of the VSG stabilized at 15°, and neither the power angle nor the voltage became unstable.

[0062] When the VSG reference power is 40kW, the simulation of the system's attraction domain and phase plane is as follows: Figure 7As shown, before the fault, the system reached a stable point. After the fault, the system trajectory crossed the boundary of the attraction domain. The simulation results of the VSG voltage and power angle at this point are as follows: Figure 8 As shown in the figure, after the fault is cleared, the VSG power angle continues to increase and quickly exceeds 180°. The VSG power angle loses synchronization, and the system first experiences transient power angle instability, which leads to periodic voltage fluctuations and voltage instability.

[0063] When the VSG reference power is 20kW, the simulation of the system's attraction domain and phase plane is as follows: Figure 9 As shown, before the fault, the system reached a stable point. After the fault, the system trajectory did not cross the attraction region, but it did not converge to a stable operating point. At this point, it is necessary to determine whether the system trajectory has encountered a singularity. The determinant value of the reduced-order differential equation state matrix, det(A... g )like Figure 10 As shown, after the fault occurs, det(A) g The voltage rapidly drops to zero, indicating that the system trajectory has encountered a singularity and transient voltage instability has occurred. The simulation results for the VSG voltage and power angle at this point are as follows: Figure 11 As shown in the figure, after the fault was cleared, the VSG power angle stabilized and no transient power angle instability occurred. However, the VSG phase voltage amplitude oscillated between 300V and 390V, and the voltage became unstable.

[0064] Through the above simulation verification, the transient power angle and voltage instability observation method of new energy converter based on energy function and bifurcation theory in this embodiment can comprehensively judge the transient power angle and voltage instability of new energy grid-connected system, accurately detect and classify its transient instability type, and verify the feasibility of the method through simulation.

[0065] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0066] In one embodiment, a transient power angle voltage instability observation system for renewable energy converters based on energy functions and bifurcation theory is provided. This system corresponds one-to-one with the transient power angle voltage instability observation method for renewable energy converters based on energy functions and bifurcation theory described in the above embodiments. Figure 12 As shown, this transient power angle voltage instability observation system for new energy converters based on energy function and bifurcation theory includes an equilibrium point partitioning module, an energy value calculation module, a transient power angle instability determination module, and a transient voltage instability determination module. Detailed descriptions of each functional module are as follows: The equilibrium point division module is used to obtain the changes in the system operating state before and after the failure of the renewable energy converter under transient time-domain simulation of synchronous machine and VSG in parallel, and to divide the system into stable equilibrium points and unstable equilibrium points based on the changes in the system operating state.

[0067] The energy value calculation module is used to calculate the system energy value at the stable equilibrium point and the system critical energy value at the unstable equilibrium point of the system through the system energy function at the fault clearing moment in transient time-domain simulation.

[0068] The transient power angle instability determination module is used to compare the system energy value with the system critical energy value, and to determine the system transient power angle instability based on the comparison result, thereby obtaining the system transient power angle instability determination result.

[0069] The transient voltage instability determination module is used to determine system singularities and obtain the system running trajectory under the stable state of system power angle based on the transient power angle instability determination results, and to determine the overlap of system singularities based on the overlap state.

[0070] Specific limitations regarding the transient power angle voltage instability observation system for renewable energy converters based on energy functions and bifurcation theory can be found in the limitations of the transient power angle voltage instability observation method for renewable energy converters based on energy functions and bifurcation theory mentioned above, and will not be repeated here. Each module in the aforementioned transient power angle voltage instability observation system for renewable energy converters based on energy functions and bifurcation theory can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in hardware or independent of the processor in a computer device, or stored in software in the memory of a computer device, so that the processor can call and execute the corresponding operations of each module.

[0071] In one embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as follows: Figure 13 As shown, the computer device includes a processor, memory, network interface, and database connected via a system bus. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and database. The internal memory provides the environment for the operation of the operating system and computer programs in the non-volatile storage media. The database stores data related to the detection of transient power angle instability and voltage instability in renewable energy converters. The network interface communicates with external terminals via a network connection. When the computer program is executed by the processor, it implements a method for observing transient power angle and voltage instability in renewable energy converters based on energy functions and bifurcation theory.

[0072] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements a method for observing transient power angle voltage instability of a new energy converter based on energy function and bifurcation theory.

[0073] Those skilled in the art will recognize that the units of the various examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application of the technical solution and the constraints involved. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the invention.

[0074] In the embodiments provided by the present invention, it should be understood that the division of units is only a logical functional division. In actual implementation, there may be other division methods, such as multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored.

[0075] 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.

[0076] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for observing transient power angle voltage instability in a new energy converter based on energy function and bifurcation theory, characterized in that, The method describes a joint detection of transient power angle instability and voltage instability coupled in a new energy converter by connecting a synchronous machine and a VSG in parallel. The method includes: Under transient time-domain simulation of synchronous machine and VSG in parallel, the changes in system operating state before and after the failure of new energy converter are obtained, and the system stable equilibrium point and system unstable equilibrium point are divided based on the changes in system operating state. At the fault clearing time in the transient time-domain simulation, the system energy value of the system stable equilibrium point and the system critical energy value of the system unstable equilibrium point are calculated using the system energy function. By comparing the system energy value with the system critical energy value, and based on the comparison result, the system transient power angle instability is determined, and the system transient power angle instability determination result is obtained; Based on the system transient power angle instability determination result, the system singularity is determined in the system power angle stable state and the system running trajectory is obtained to determine the system singularity coincidence. Based on the coincidence state, transient voltage instability is determined.

2. The method for observing transient power angle voltage instability of a new energy converter based on energy function and bifurcation theory according to claim 1, characterized in that, The transient time-domain simulation under the parallel connection of the synchronous machine and VSG obtains the changes in the system operating state before and after the failure of the renewable energy converter. Based on the changes in the system operating state, the system stable equilibrium point and the system unstable equilibrium point are divided, specifically including: Under transient time-domain simulation, the initial state of the system before the fault of the new energy converter and the fault state of the system after the fault are obtained and the states are compared to obtain the changes in the system operating state before and after the fault. System equilibrium points where the change in operating state exceeds a preset threshold are marked as unstable equilibrium points, while system equilibrium points where the change in operating state does not exceed the preset threshold are marked as stable equilibrium points.

3. The method for observing transient power angle voltage instability of a new energy converter based on energy function and bifurcation theory according to claim 1, characterized in that, The calculation of the system energy value at the stable equilibrium point and the system critical energy value at the unstable equilibrium point using the system energy function at the fault clearing time in the transient time-domain simulation specifically includes: Obtain the stable equilibrium point angle of the system, and calculate the system energy value at the time of fault clearance using the system energy function. The expression for calculating the system energy value is as follows: （1） in, This represents the system energy value at the moment the fault was cleared. This represents the equivalent inertial constant of the two-machine system. This represents the actual angular velocity at the stable equilibrium point. Represents equivalent mechanical power. , These represent the actual and maximum values ​​of the equivalent electromagnetic power, respectively. This indicates the relative rotor phase angle between the synchronous machine and the VSG. , These represent the phase angles of the synchronous machine rotor and the simulated VSG rotor, respectively. Indicates the angle of the stable equilibrium point. As an intermediate variable; Obtain the angle of the unstable equilibrium point of the system, and calculate the critical energy value of the system at the moment of fault clearance using the system energy function to determine the critical instability state of the system.

4. The method for observing transient power angle voltage instability of a new energy converter based on energy function and bifurcation theory according to claim 1, characterized in that, The comparison of the system energy value and the system critical energy value, and the determination of system transient power angle instability based on the comparison result, yields the system transient power angle instability determination result, specifically including: Based on the comparison between the system energy value and the system critical energy value, it is determined whether an energy exceedance occurred at the fault clearing moment; If so, the system is determined to be transiently unstable in terms of power angle; otherwise, the system is determined to be stable in terms of power angle, thus obtaining the result of the determination of transient power angle instability.

5. The method for observing transient power angle voltage instability of a new energy converter based on energy function and bifurcation theory according to claim 4, characterized in that, The determination of whether an energy exceedance occurred at the fault clearing moment, based on the comparison result between the system energy value and the system critical energy value, specifically includes: Energy boundary determination is based on the energy boundary condition, which is that the system energy value is greater than the system critical energy value.

6. The method for observing transient power angle voltage instability of a new energy converter based on energy function and bifurcation theory according to claim 1, characterized in that, Based on the system transient power angle instability determination result, the system singularity is determined in the system power angle stable state, and the system running trajectory is obtained to determine the system singularity coincidence. Based on the coincidence state, transient voltage instability is determined, specifically including: Under the stable state of the system's power angle, determine whether the system's equilibrium point meets the criteria for a singular point. If it does, mark it as a singular point of the system. The system's operating trajectory is obtained, and it is determined whether the system's operating trajectory coincides with the system's singularity. If they coincide, it is determined that a transient voltage instability has occurred; if they do not coincide, it is determined that the system's transient voltage is stable.

7. The method for observing transient power angle voltage instability of a new energy converter based on energy function and bifurcation theory according to claim 6, characterized in that, Under the stable state of the system's power angle, it is determined whether the system's equilibrium point meets the singularity criteria. If it does, it is marked as a system singularity. This specifically includes: The singularity determination criteria are as follows: （2） in, It represents the partial derivative of an algebraic equation with respect to the algebraic variable.

8. A transient power angle voltage instability observation system for a new energy converter based on energy function and bifurcation theory, characterized in that, The system includes: The equilibrium point division module is used to obtain the changes in the system operating state before and after the failure of the new energy converter under transient time-domain simulation of the synchronous machine and VSG in parallel, and to divide the system stable equilibrium point and the system unstable equilibrium point based on the changes in the system operating state. The energy value calculation module is used to calculate the system energy value at the stable equilibrium point of the system and the system critical energy value at the unstable equilibrium point of the system through the system energy function at the fault clearing time of the transient time domain simulation. The transient power angle instability determination module is used to compare the system energy value with the system critical energy value, and to determine the system transient power angle instability based on the comparison result, thereby obtaining the system transient power angle instability determination result. The transient voltage instability determination module is used to determine system singularities and obtain the system running trajectory under the stable power angle state based on the transient power angle instability determination result of the system, and to determine the coincidence of system singularities based on the coincidence state.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the transient power angle voltage instability observation method for new energy converters based on energy function and bifurcation theory as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the transient power angle voltage instability observation method for new energy converters based on energy function and bifurcation theory as described in any one of claims 1 to 7.

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