Multi-modal analysis method and system for synchronous stability of converter, medium and equipment

Abstract

The invention discloses a multi-modal analysis method, system, medium and equipment for the synchronization stability of a converter, and belongs to the technical field of stability analysis of an electric power system.The method comprises the steps that a second-order motion equation is built based on converter-power grid coupling parameters; according to comparison of power grid impedance and a critical value, a d-axis current state during a fault and an equivalent power angle relation before and after the fault, the transient mode is divided into three types: the first type is that the impedance is smaller than the critical value and the power angle after the fault is larger than the power angle before the fault, the second type is that the impedance is smaller than the critical value and the power angle after the fault is smaller than the power angle before the fault, and the third type is that the impedance is larger than or equal to the critical value; and if not, calculating the acceleration area, the deceleration area and the equivalent damping power integral value of the first period after the fault, and outputting a stability result in combination with the area comparison condition of the mode type and the positive and negative integral values. By implementing the method, the problem of inaccurate judgment of the instability boundary condition due to the fact that the fault mode is not distinguished in the synchronous stability analysis of the converter in the prior art can be solved.

Description

Technical Field

[0001] This invention belongs to the field of power system stability analysis technology, and relates to a multi-modal analysis method, system, medium and equipment for converter synchronization stability. Background Technology

[0002] With the increasing penetration rate of new energy sources, a large number of power electronic devices, such as photovoltaic inverters and wind power converters, are being connected to the power grid, and the power system is gradually developing towards power electronics. These converters achieve synchronous operation with the power grid through control strategies such as phase-locked loops. Under large disturbances such as grid faults, the synchronous stability of the converters is crucial to the safe and stable operation of the entire power system. It is necessary to accurately analyze and evaluate their transient behavior to ensure the reliable operation of the power grid.

[0003] Existing technologies primarily employ the traditional equal-area rule to analyze converter synchronous stability. This method judges system stability by simply comparing the relationship between the acceleration and deceleration areas during the first swing cycle. However, this method directly ignores the impact of the damping term on transient stability and fails to consider the different fault modes the converter may enter under different grid connection conditions and fault scenarios. Because it does not classify modes based on the characteristics of the equivalent power angle change after a fault, such as the differences between acceleration and deceleration phases, the calculation error of the stability boundary is large, easily leading to misjudgments of stability results. Furthermore, it fails to reveal the critical conditions for the switching of the equivalent damping torque between positive and negative intervals, resulting in overly optimistic stability assessments. Moreover, it requires full-time-domain simulation, which is computationally inefficient and fails to meet the needs of rapid and accurate stability assessment in practical engineering applications. Summary of the Invention

[0004] This application provides a multimodal analysis method, system, medium, and device for converter synchronization stability, which can solve the problem of inaccurate determination of instability boundary conditions in the prior art due to the failure to distinguish fault modes in converter synchronization stability analysis.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a multimodal analysis method for the synchronization stability of a converter, comprising:

[0006] Based on the parameters of the converter-grid coupling system, a second-order equation of motion for the coupling between the phase-locked loop and the grid is constructed;

[0007] When a converter fails, mode identification is performed on the transient process of the converter based on the magnitude of the grid impedance, the converter's d-axis current output state during the fault, and the relative relationship between the equivalent power angle at the equilibrium point before and after the fault. Specifically: when the grid impedance is less than the critical impedance value that causes the converter's d-axis current to drop to zero during the fault, and the equivalent power angle at the equilibrium point of the converter after the fault is greater than the equivalent power angle at the equilibrium point before the fault, it is determined to be the first type of mode; when the grid impedance is less than the critical impedance value, and the equivalent power angle at the equilibrium point after the fault is less than the equivalent power angle at the equilibrium point before the fault, it is determined to be the second type of mode; when the grid impedance is greater than or equal to the critical impedance value, it is determined to be the third type of mode.

[0008] When the modal identification result is the second type of mode, the system is directly determined to be synchronously stable; otherwise: based on the second-order equation of motion, calculate the acceleration area corresponding to the acceleration process of the equivalent power angle, the deceleration area corresponding to the deceleration process of the equivalent power angle, and the integral value of the equivalent damping power with respect to the equivalent power angle during the first swing cycle after the fault occurs; determine the stability comparison conditions of the corresponding acceleration area and deceleration area according to the identified modal type, and output the stability judgment result based on the stability comparison conditions and the sign of the integral value.

[0009] Compared to existing technologies, the embodiments of this application have the following advantages: By constructing a second-order equation of motion for the phase-locked loop coupled with the grid based on the parameters of the converter-grid coupling system, a precise mathematical description of the dynamic characteristics of the converter-grid system is achieved, providing a theoretical basis for subsequent multi-mode analysis; furthermore, mode identification is performed based on the magnitude of the grid impedance, the converter d-axis current output state during the fault, and the relative relationship between the equivalent power angle at the equilibrium point before and after the fault. This identification mechanism is based on the physical nature of the converter under different fault conditions—when the grid impedance is less than the critical impedance value and the equivalent power angle after the fault is greater than the fault value. Previously, the system was in the first type of mode. In this mode, after a fault, the equivalent mechanical power is greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate. After crossing the stable equilibrium point, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate, potentially leading to instability. When the grid impedance is less than the critical impedance value and the equivalent power angle after the fault is less than before the fault, the system is in the second type of mode. In this mode, after a fault, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate initially. After crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate. Furthermore, since the maximum acceleration area is always greater than the deceleration area, the system will inevitably... The system is in a stable state when the grid impedance is greater than or equal to the critical damping value. In this state, the converter's d-axis current may drop to zero. After a fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate initially. After crossing the stable equilibrium point, the equivalent mechanical power becomes greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate, potentially leading to instability. When the mode identification result is in the second type of mode, the system is directly determined to be synchronously stable, avoiding redundant calculations for known stable conditions and improving analysis efficiency. Furthermore, by calculating the acceleration area, deceleration area, and equivalent damping power during the first swing cycle, the equivalent power angle is determined to be stable. The design, based on the physical principle that the sum of the acceleration and deceleration areas generated by the equivalent damping power during the change of the equivalent power angle within the same swing cycle (i.e., the integral value), determines the trend of the equivalent power angle change in subsequent swing cycles. If the sum of the acceleration and deceleration areas is less than zero in the first swing cycle, the system kinetic energy decreases and will gradually recover to the equilibrium point in subsequent cycles. If the sum of the areas is greater than zero, the system kinetic energy increases, and it will gradually move away from the equilibrium point and eventually become unstable. Finally, by setting differentiated stability comparison conditions according to different modes and combining the positive and negative output results of the integral value, a precise assessment of the synchronous stability of the converter is achieved. These technical features work together to fundamentally solve the problem of inaccurate determination of instability boundary conditions caused by the traditional equal area method due to its failure to distinguish fault modes by dividing the fault scenario into three different modes and applying stability judgment rules accordingly, while considering the influence of equivalent damping power on stability. This achieves precision, efficiency, and clarity of the physical mechanism in the synchronous stability analysis of the converter.

[0010] In some embodiments of the first aspect of this application, determining the stability comparison conditions for the corresponding acceleration area and deceleration area based on the identified modal type includes:

[0011] If the modal identification result is the first type of mode, then the stability comparison condition is determined to be that the maximum deceleration area during the first swing cycle is greater than the acceleration area; wherein, the maximum deceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the stable equilibrium point;

[0012] If the modal identification result is the third type of mode, then the stability comparison condition is determined to be that the maximum acceleration area during the first swing cycle is greater than the deceleration area; wherein, the maximum acceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the unstable equilibrium point.

[0013] Compared to existing technologies, the above embodiments have the following beneficial effects: By setting the maximum deceleration area greater than the acceleration area within the first swing cycle as a stability comparison condition for the first type of mode, this design is based on the principle of energy conservation—in the first type of mode, after a fault occurs, the equivalent mechanical power is greater than the equivalent electromagnetic power, the equivalent power angle accelerates from the stable equilibrium point, and after crossing the stable equilibrium point, the equivalent mechanical power is less than the equivalent electromagnetic power, and the equivalent power angle decelerates; if the maximum deceleration area is greater than the acceleration area, the system can consume the excess energy gained during acceleration during deceleration, allowing the equivalent power angle to return to the stable equilibrium point region; simultaneously, for the third... The modal design sets the maximum acceleration area greater than the deceleration area within the first swing cycle as a stability comparison condition. This design is also based on the principle of energy conservation—in the third type of mode, after a fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, and the equivalent power angle decelerates first. After crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, and the equivalent power angle accelerates. If the maximum acceleration area is greater than the deceleration area, the energy gained by the system during acceleration is insufficient for the equivalent power angle to cross the unstable equilibrium point, thus ensuring that the system can remain within the stable region. The differentiated processing mechanism for the two modes ultimately realizes a differentiated stability judgment standard for different fault modes.

[0014] In some embodiments of the first aspect of this application, the step of outputting a stability judgment result based on the stability comparison condition and the sign of the integral value includes:

[0015] If the stability comparison condition is met, the stability judgment result is output according to the sign of the integral value of the equivalent damping power with respect to the equivalent power angle: if the integral value is positive, the system is determined to be synchronously stable; if the integral value is zero, the system is determined to be in a critically stable state; if the integral value is negative, the system is determined to be unstable.

[0016] Compared with existing technologies, the above embodiments have the following beneficial effects: By further judging the output stability based on the positive and negative output stability results of the sum of areas generated by the equivalent damping power during the change of the equivalent power angle, under the premise that the stability comparison conditions are met, this design is based on the key influence mechanism of damping on system energy conversion—when the sum of areas is positive, it indicates that the equivalent damping has a positive damping effect, the system kinetic energy decreases, and the equivalent power angle will gradually oscillate and approach the post-fault equilibrium point in subsequent swing cycles; when the sum of areas is zero, it indicates that under the ideal undamped state, the equivalent power angle will oscillate around the post-fault equilibrium point with equal amplitude; when the sum of areas is negative, it indicates that the equivalent damping has a negative damping effect, the system kinetic energy increases, and the equivalent power angle will gradually oscillate and diverge or diverge directly in subsequent swing cycles, thus realizing a precise quantitative assessment of the influence of damping characteristics on system stability.

[0017] In some embodiments of the first aspect of this application, the step of outputting a stability judgment result based on the stability comparison condition and the sign of the integral value further includes:

[0018] If the stability comparison condition is not met, the system is directly determined to be unstable.

[0019] Compared to existing technologies, the above embodiments have the following beneficial effects: The rule for directly determining system instability when the stability comparison condition is not met is based on the fundamental physical principle of energy balance. In the first type of mode, if the maximum deceleration area is not greater than the acceleration area, it indicates that the system cannot consume the excess energy gained during acceleration during deceleration, and the equivalent work angle will continue to increase beyond the stable equilibrium point, leading to system instability. In the third type of mode, if the maximum acceleration area is not greater than the deceleration area, it indicates that the energy gained by the system during acceleration is insufficient to make the equivalent work angle exceed the unstable equilibrium point. However, in reality, since the system can no longer meet the basic energy balance condition, the equivalent work angle will not return to the stable region, leading to system instability. This concise and clear judgment rule avoids redundant calculations for obvious instability situations, simplifies the judgment process, and improves the efficiency of stability analysis. Simultaneously, by ensuring that the system can promptly and accurately identify the instability state when it does not meet the basic stability condition, it provides timely decision-making basis for system protection and control, achieving optimization of the stability judgment process and efficient utilization of computational resources.

[0020] In some embodiments of the first aspect of this application, before performing modal identification on the transient process of the converter, the method further includes:

[0021] In the event of a fault, the equivalent moment of inertia of the system is calculated based on the second-order equation of motion. If the result is less than zero, the system is directly judged to be unstable.

[0022] Compared to existing technologies, the above embodiments have the following beneficial effects: Before modal identification, the equivalent moment of inertia in the second-order equation of motion is checked to see if it is less than zero. If it is less than zero, the system is directly judged to be unstable. This design is based on the fundamental physical principle of system stability—the equivalent moment of inertia is a key parameter describing the inertial characteristics of a system. When the equivalent moment of inertia is less than zero, it indicates that the system has lost its basic inertial characteristics and cannot maintain normal dynamic behavior. Furthermore, this pre-judgment condition avoids unnecessary complex modal identification and stability analysis calculations, improving analysis efficiency. Simultaneously, the simple check of the key parameter, the equivalent moment of inertia, ensures rapid identification of obvious instability situations, providing an efficient preliminary screening mechanism for system stability assessment. Moreover, by performing this check immediately after the system parameters are determined, early judgment of the system's stability state is achieved, optimizing the analysis process and realizing reasonable optimization of the stability analysis process and efficient allocation of computational resources.

[0023] Secondly, the present invention also provides a multi-modal analysis system for converter synchronization stability, comprising: an equation construction module, a mode identification module, and a judgment output module;

[0024] The equation construction module is used to construct the second-order motion equations of the phase-locked loop coupled with the power grid based on the parameters of the converter-grid coupling system.

[0025] The mode identification module is used to identify the transient process of the converter when a converter fails, based on the magnitude of the grid impedance, the converter's d-axis current output state during the fault, and the relative relationship between the equivalent power angle at the equilibrium point before and after the fault. Specifically: when the grid impedance is less than the critical impedance value that causes the converter's d-axis current to drop to zero during the fault, and the equivalent power angle at the equilibrium point of the converter after the fault is greater than the equivalent power angle at the equilibrium point before the fault, it is determined to be a first-type mode; when the grid impedance is less than the critical impedance value, and the equivalent power angle at the equilibrium point after the fault is less than the equivalent power angle at the equilibrium point before the fault, it is determined to be a second-type mode; when the grid impedance is greater than or equal to the critical impedance value, it is determined to be a third-type mode.

[0026] The judgment output module is used to directly determine that the system is synchronously stable when the modal identification result is the second type of mode; otherwise, based on the second-order equation of motion, it calculates the acceleration area corresponding to the acceleration process of the equivalent power angle, the deceleration area corresponding to the deceleration process of the equivalent power angle, and the integral value of the equivalent damping power with respect to the equivalent power angle during the first swing cycle after the fault occurs; according to the identified modal type, it determines the corresponding stability comparison conditions for the acceleration area and deceleration area, and outputs the stability judgment result based on the stability comparison conditions and the sign of the integral value.

[0027] Compared with the prior art, the above embodiments of this application have the following beneficial effects: By constructing the second-order motion equation of the phase-locked loop coupled with the grid based on the parameters of the converter-grid coupling system, a precise mathematical description of the dynamic characteristics of the converter-grid system is achieved, providing a theoretical basis for subsequent multi-mode analysis; furthermore, by performing mode identification based on the magnitude of the grid impedance, the converter d-axis current output state during the fault, and the relative relationship between the equivalent power angle at the equilibrium point before and after the fault, this identification mechanism is based on the physical nature of the converter under different fault conditions—when the grid impedance is less than the critical impedance value and the equivalent power angle after the fault is greater than the critical impedance value. Before the fault, the system is in the first mode. In this mode, after the fault occurs, the equivalent mechanical power is greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate. After crossing the stable equilibrium point, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate, potentially leading to instability. When the grid impedance is less than the critical impedance value and the equivalent power angle after the fault is less than before the fault, the system is in the second mode. In this mode, after the fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate initially. After crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate. Furthermore, since the maximum acceleration area is always greater than the deceleration area, the system will inevitably... Synchronous stability is achieved when the grid impedance is greater than or equal to the critical damping value, indicating that the system is in the third mode. In this mode, the converter's d-axis current may drop to zero. After a fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate initially. After crossing the stable equilibrium point, the equivalent mechanical power exceeds the equivalent electromagnetic power, causing the equivalent power angle to accelerate, potentially leading to instability. By directly determining the system as synchronously stable when the mode identification result is the second mode, redundant calculations for known stable conditions are avoided, improving analysis efficiency. Furthermore, by calculating the acceleration area, deceleration area, and equivalent damping power during the first swing cycle, the equivalent power angle is determined to be stable. The design, based on the physical principle that the sum of the acceleration and deceleration areas generated by the equivalent damping power during the change of the equivalent power angle within the same swing cycle (i.e., the integral value), determines the trend of the equivalent power angle change in subsequent swing cycles. If the sum of the acceleration and deceleration areas is less than zero in the first swing cycle, the system kinetic energy decreases and will gradually recover to the equilibrium point in subsequent cycles. If the sum of the areas is greater than zero, the system kinetic energy increases, and it will gradually move away from the equilibrium point and eventually become unstable. Finally, by setting differentiated stability comparison conditions according to different modes and combining the positive and negative output results of the integral value, a precise assessment of the synchronous stability of the converter is achieved. These technical features work together to fundamentally solve the problem of inaccurate determination of instability boundary conditions caused by the traditional equal area method due to its failure to distinguish fault modes by dividing the fault scenario into three different modes and applying stability judgment rules accordingly, while considering the influence of equivalent damping power on stability. This achieves precision, efficiency, and clarity of the physical mechanism in the synchronous stability analysis of the converter.

[0028] In some embodiments of the second aspect of this application, the determination output module includes: a first condition determination unit and a second condition determination unit;

[0029] The first condition determination unit is used to determine the stability comparison condition as follows if the modal identification result is the first type of mode: the maximum deceleration area within the first swing cycle is greater than the acceleration area; wherein the maximum deceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the stable equilibrium point.

[0030] The second condition determination unit is used to determine the stability comparison condition as follows if the modal identification result is a third type of mode: the maximum acceleration area within the first swing cycle is greater than the deceleration area; wherein the maximum acceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the unstable equilibrium point.

[0031] Compared to existing technologies, the above embodiments have the following beneficial effects: By setting the maximum deceleration area greater than the acceleration area within the first swing cycle as a stability comparison condition for the first type of mode, this design is based on the principle of energy conservation—in the first type of mode, after a fault occurs, the equivalent mechanical power is greater than the equivalent electromagnetic power, the equivalent power angle accelerates from the stable equilibrium point, and after crossing the stable equilibrium point, the equivalent mechanical power is less than the equivalent electromagnetic power, and the equivalent power angle decelerates; if the maximum deceleration area is greater than the acceleration area, the system can consume the excess energy gained during acceleration during deceleration, allowing the equivalent power angle to return to the stable equilibrium point region; simultaneously, for the third... The modal design sets the maximum acceleration area greater than the deceleration area within the first swing cycle as a stability comparison condition. This design is also based on the principle of energy conservation—in the third type of mode, after a fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, and the equivalent power angle decelerates first. After crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, and the equivalent power angle accelerates. If the maximum acceleration area is greater than the deceleration area, the energy gained by the system during acceleration is insufficient for the equivalent power angle to cross the unstable equilibrium point, thus ensuring that the system can remain within the stable region. The differentiated processing mechanism for the two modes ultimately realizes a differentiated stability judgment standard for different fault modes.

[0032] In some embodiments of the second aspect of this application, the determination output module further includes: a result output unit;

[0033] The result output unit is used to output a stability judgment result based on the sign of the integral value of the equivalent damping power with respect to the equivalent power angle if the stability comparison condition is met: if the integral value is positive, the system is determined to be synchronously stable; if the integral value is zero, the system is determined to be in a critically stable state; if the integral value is negative, the system is determined to be unstable.

[0034] Compared with existing technologies, the above embodiments have the following beneficial effects: By further judging the output stability based on the positive and negative output stability results of the sum of areas generated by the equivalent damping power during the change of the equivalent power angle, under the premise that the stability comparison conditions are met, this design is based on the key influence mechanism of damping on system energy conversion—when the sum of areas is positive, it indicates that the equivalent damping has a positive damping effect, the system kinetic energy decreases, and the equivalent power angle will gradually oscillate and approach the post-fault equilibrium point in subsequent swing cycles; when the sum of areas is zero, it indicates that under the ideal undamped state, the equivalent power angle will oscillate around the post-fault equilibrium point with equal amplitude; when the sum of areas is negative, it indicates that the equivalent damping has a negative damping effect, the system kinetic energy increases, and the equivalent power angle will gradually oscillate and diverge or diverge directly in subsequent swing cycles, thus realizing a precise quantitative assessment of the influence of damping characteristics on system stability.

[0035] Thirdly, the present invention also provides a multimodal analysis device for converter synchronization stability, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded onto the processor, it implements the steps of any of the multimodal analysis methods for converter synchronization stability of the present invention.

[0036] Fourthly, embodiments of this application also provide a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of any of the multimodal analysis methods for converter synchronization stability of the present invention. Attached Figure Description

[0037] Figure 1 This is a flowchart illustrating a multimodal analysis method for converter synchronization stability provided in some embodiments of the present invention.

[0038] Figure 2 This is a schematic diagram of the structure of a multimodal analysis system for converter synchronization stability provided in some embodiments of the present invention.

[0039] Figure 3 : This is a structural diagram of a multimodal analysis device for converter synchronization stability provided in some embodiments of the present invention.

[0040] Figure 4 : This is a phase-locked loop structure diagram provided in some embodiments of the present invention. Detailed Implementation

[0041] 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 embodiments of the present invention, and not all embodiments. 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.

[0042] Example 1:

[0043] Please refer to Figure 1 To address the problem of inaccurate determination of instability boundary conditions in existing converter synchronization stability analysis due to the failure to distinguish fault modes, an embodiment of the present invention provides a multi-mode analysis method for converter synchronization stability, comprising steps S1 to S3:

[0044] Step S1: Based on the parameters of the converter-grid coupling system, construct the second-order motion equations of the phase-locked loop coupled with the grid.

[0045] In specific implementation, such as Figure 4 The diagram shows a phase-locked loop (PLL) structure. Based on the PLL's structure and parameters, the PLL equation is constructed as follows:

[0046] θ pll =∫(ω p +ω g )dt;ω p =k ppll U tq +k ipll ∫U tq dt;

[0047] Where, θ pll For the phase angle output of the phase-locked loop, k ppll and k ipll These are the proportional and integral coefficients of the phase-locked loop PI control element, U tq Let ω be the q-axis component of the grid connection point voltage, t be the time variable, and ω be the q-axis component. g Let ω be the angular velocity of the grid voltage. p This is the output value of the phase-locked loop PI control circuit.

[0048] In addition, ω pl The phase-locked loop outputs angular velocity and ω plI =ω p +ω g ω g Since it has a named value, therefore ω p This corresponds to a named value, namely the per-unit value u of the phase-locked loop input. d and u q After PI control, a named value ω is generated. p and ω gCombining the above two equations, we get:

[0049] θ pll =∫(k ppll U tq +k ipll ∫U tq dt+ω g )dt;

[0050] Differentiating the phase-locked loop equations to eliminate integral operations is done as follows:

[0051] Due to the instantaneous grid voltage U during the fault g d-axis current I of the converter d and q-axis current I q Mutation, U tq Mutation, affected by proportional control, ω p The abrupt change means that the combined phase-locked loop equations obtained above are not differentiable at the moment of the fault, while the derivatives before and after the fault are as follows:

[0052] Since the integral sign still exists, further differentiation yields the second-order derivative equation of the phase-locked loop, with the domain still being before and after the fault, as shown below:

[0053]

[0054] Next, based on the power grid structure and corresponding parameters, the power grid voltage equation is constructed as follows:

[0055]

[0056] Among them, U g For grid voltage, δ p ω is the equivalent power angle of the converter from the perspective of the phase-locked loop. pll The phase-locked loop outputs angular velocity, ω0 is the reference value of angular velocity, and I d and I q These are the d-axis current and q-axis current of the converter, respectively. g and R g These are the mains inductance and resistance, respectively, θ g This represents the phase angle of the grid voltage.

[0057] Since the control system actually uses per-unit values ​​for calculations, all variables here are per-unit values. It must be emphasized that... ω pll and ω p For a named value, ω pll_pu and ω p_pu It corresponds to its per-unit value.

[0058] Differentiating the above power grid voltage equation, the domain is also before and after the fault:

[0059]

[0060] Further analysis revealed:

[0061] To facilitate the subsequent derivation, we can further differentiate to obtain:

[0062]

[0063] Finally, by combining the phase-locked loop equations with the grid voltage equations, we obtain:

[0064]

[0065] Furthermore, based on the analytical conventions of the second-order rotor motion equations of a synchronous machine, a second-order motion equation based on a phase-locked loop is organized and constructed; wherein, the domain of the second-order motion equations is the steady-state process before the fault and the transient process after the fault, and the second-order motion equations are expressed as follows:

[0066]

[0067] Where M is the equivalent moment of inertia; P m P is the equivalent mechanical power; e P is the equivalent maximum electromagnetic power; d1 For linear equivalent damping power, P d2 For nonlinear equivalent damping power, T d1 For linear equivalent damping torque, T d2 It is the nonlinear equivalent damping torque.

[0068] After constructing the second-order equations of motion, the analysis begins:

[0069] The dynamics of the converter differ under different fault modes, and there are three synchronous modes in the transient phase of the converter:

[0070] (1) When the impedance is relatively small, I continues to be output during the fault period. d The first type of mode may occur: after the fault occurs, the equivalent mechanical power is greater than the equivalent electromagnetic power, the equivalent power angle accelerates, and after crossing the stable equilibrium point, the equivalent mechanical power is less than the equivalent electromagnetic power, the equivalent power angle decelerates, and the converter may become unstable.

[0071] (2) When the impedance is relatively small, I continues to output during the fault period. d The second type of mode may occur: after the fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, the equivalent power angle decelerates first, and after crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, and the equivalent power angle accelerates. Since the maximum acceleration area is always greater than the deceleration area, the converter will definitely be synchronously stable under this fault mode.

[0072] (3) When the impedance is relatively large, during the fault period I d When the value is 0 or very small, a third mode may occur: after the fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, the equivalent power angle decelerates first, and after crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, the equivalent power angle accelerates, and the converter may become unstable. After entering the stable equilibrium point, the converter changes from generating reactive power to absorbing reactive power faults.

[0073] When the impedance is relatively small, it continues to output I during the fault period. d Under certain conditions, whether the converter fault mode is Type I or Type II depends on the relationship between the magnitudes of the stable equilibrium point before and after the fault. This is related to the fault depth, grid conditions, converter ride-through strategy, and phase-locked loop control parameters. If the equivalent power angle at the equilibrium point after the fault is greater than that before the fault, the converter fault mode is Type I; if the equivalent power angle at the equilibrium point after the fault is less than that before the fault, the converter fault mode is Type II. This can be summarized as follows:

[0074] Step S2: When the converter fails, the transient process of the converter is characterized by mode identification based on the magnitude of the grid impedance, the d-axis current output state of the converter during the fault, and the relative relationship between the equivalent power angle of the balance point before and after the fault. Specifically: when the grid impedance is less than the critical impedance value that causes the d-axis current of the converter to drop to zero during the fault, and the equivalent power angle of the balance point of the converter after the fault is greater than the equivalent power angle of the balance point before the fault, it is determined to be the first type of mode; when the grid impedance is less than the critical impedance value, and the equivalent power angle of the balance point after the fault is less than the equivalent power angle of the balance point before the fault, it is determined to be the second type of mode; when the grid impedance is greater than or equal to the critical impedance value, it is determined to be the third type of mode.

[0075] In practical implementation, for the second type of mode, since the deceleration area is always smaller than the maximum acceleration area, the system satisfies the synchronization stability condition, and therefore the conclusion that the system is synchronously stable can be directly drawn. For the first and third types, the system stability still needs further evaluation.

[0076] First, the traditional equal-area rule analysis method is simplified based on damping characteristics, specifically:

[0077] To determine whether the equivalent moment of inertia meets the stability requirements, since all values ​​in the power grid equations are per-unit values, and all values ​​in the phase-locked loop except for the power angle and its first and second derivatives are per-unit values, the calculation of per-unit values ​​is chaotic. Based on the formula derived above, it is found that... In the formula, ω0 is the base value, and the rest are per-unit values. Since ω0 exists in the denominator and its value is relatively large, M is extremely difficult to be less than 0. Generally speaking, M is usually greater than 0.9. Therefore, when the equivalent moment of inertia M of the system is less than zero, regardless of the equivalent electromagnetic power, equivalent mechanical power, and equivalent damping of the system, the system will quickly become unstable, as follows:

[0078] Furthermore, when the converter fails, before performing mode identification in step S2, step S20 is also included, as follows:

[0079] S20: In case of a fault, calculate the equivalent moment of inertia of the system based on the second-order equation of motion. If the result is less than zero, the system is directly judged to be unstable.

[0080] In this preferred embodiment, before modal identification, the equivalent moment of inertia in the second-order equation of motion is checked to see if it is less than zero. If it is less than zero, the system is directly judged to be unstable. This design is based on the basic physical principle of system stability—the equivalent moment of inertia is a key parameter describing the inertial characteristics of a system. When the equivalent moment of inertia is less than zero, it indicates that the system has lost its basic inertial characteristics and cannot maintain normal dynamic behavior. Furthermore, by using this pre-judgment condition, unnecessary complex modal identification and stability analysis calculations are avoided, thus improving analysis efficiency. At the same time, by simply checking the key parameter of equivalent moment of inertia, the rapid identification of obvious instability situations is ensured, providing an efficient preliminary screening mechanism for system stability assessment. By performing this check immediately after the system parameters are determined, an early judgment of the system's stability state is achieved, optimizing the analysis process and realizing reasonable optimization of the stability analysis process and efficient allocation of computational resources.

[0081] Next, the effective damping mechanism under different fault modes is analyzed:

[0082] In the second-order equations of motion, the equivalent damping term is given by P. d1 and P d2 Composition, P d2 The magnitude is independent of the work angle and is always negative, reflecting constant negative damping; P d1 The size is related to the work angle, when P d1 When it is a positive value, P d1 It is a negative value. In typical phase-locked loop parameter settings, k... ppll <k ipll During grid faults, reduce active power output and improve converter stability, i.e., |I d |<1, such that |P d1_max |>|P d2 |, that is, there exists a damping zero point δ a Make 0 < δ < δ a P d1+P d2 >0, damping exhibits positive damping, the actual acceleration area decreases, and the deceleration area increases; δ a When δ < π, P d1 +P d2 <0 damping manifests as negative damping, resulting in an increase in the actual acceleration area and a decrease in the deceleration area.

[0083] The following section will investigate the effect of damping on the acceleration and deceleration area. The critical work angle δ for switching between positive and negative damping states will be discussed. a P can be obtained by solving the following equation: d1 +P d2 =0 means:

[0084] When |δ a When the fault is large and shallow, the damping is positive; when the fault is deep, the damping is positive and negative. The negative damping is mainly manifested in the deceleration range of the first type of mode and the acceleration range of the third type of mode in the first swing cycle. The existence of negative damping makes the results of traditional analysis methods too optimistic.

[0085] Furthermore, determine the magnitude of the acceleration / deceleration area caused by the equivalent damping term within one swing cycle:

[0086] Within the same swing cycle, the sum of the areas of the equivalent damping power terms determines the change in the equivalent power angle in subsequent swing cycles. Taking the first type of mode as an example, neglecting the effect of equivalent damping, when the maximum deceleration area is greater than the deceleration area, the system will repeatedly move between the two operating points, unable to reach equilibrium, and will be in a critical state. In the first swing cycle, if the sum of the equivalent damping acceleration and deceleration areas S... d A value less than 0 will decrease the system's kinetic energy; in the next cycle, due to the decrease in kinetic energy, the maximum value of the power angle δ will be less than that of the previous cycle, and the minimum value will be greater than that of the previous cycle. The negative damping interval will decrease or even disappear, thus ensuring the condition "S" is met. d If S is less than 0, the system will gradually return to equilibrium under damping in subsequent cycles. Conversely, if S is less than 0 in the first swing cycle, the system will gradually return to equilibrium under damping. d If the value is greater than 0, the system's kinetic energy increases, the maximum value of δ increases, and this will bring a larger S in the next cycle. d The system gradually approaches equilibrium and eventually becomes unstable. Therefore, in determining the synchronous stability of a converter, it is crucial to focus on the S phase during the first oscillation cycle. d The size of the value has a profound impact on the subsequent dynamic characteristics of the system.

[0087] Therefore, in determining the synchronous stability of the first and third modes, it is first necessary to examine whether the acceleration and deceleration areas in the first swing cycle meet the stability requirements, i.e., the maximum deceleration area is greater than the acceleration area in the first mode, and the maximum acceleration area is greater than the deceleration area in the third mode. Simultaneously, the maximum and minimum equivalent power angle values ​​are calculated. Further, based on the maximum and minimum equivalent power angle values ​​in the first swing cycle, the sum of the equivalent damping areas provided by the converter's equivalent damping power during the swing (i.e., the integral of the equivalent damping power with respect to the equivalent power angle) is determined. If the sum of the equivalent damping areas is greater than zero, the equivalent power angle will gradually oscillate towards the post-fault equilibrium point in subsequent swing cycles. If the sum of the equivalent areas is equal to zero, the system is in a critically stable state. Under ideal conditions with no other control intervention and no disturbances, the system's equivalent power angle will oscillate around the post-fault equilibrium point with equal amplitude. If the sum of the equivalent damping areas is less than zero, the equivalent power angle will gradually oscillate and diverge or diverge directly in subsequent swing cycles, as detailed below:

[0088] Step S3: When the modal identification result is the second type of mode, directly determine that the system is synchronously stable; otherwise: based on the second-order equation of motion, calculate the acceleration area corresponding to the acceleration process of the equivalent power angle, the deceleration area corresponding to the deceleration process of the equivalent power angle, and the integral value of the equivalent damping power with respect to the equivalent power angle during the first swing cycle after the fault occurs; determine the stability comparison conditions of the corresponding acceleration area and deceleration area according to the identified modal type, and output the stability judgment result based on the stability comparison conditions and the sign of the integral value.

[0089] Furthermore, in step S3, determining the stability comparison conditions can be implemented through the following preferred embodiments, including steps S31-S32, as follows:

[0090] S31: If the modal identification result is the first type of mode, then the stability comparison condition is determined to be that the maximum deceleration area in the first swing cycle is greater than the acceleration area; wherein, the maximum deceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the stable equilibrium point;

[0091] S32: If the modal identification result is the third type of mode, then the stability comparison condition is determined to be that the maximum acceleration area in the first swing cycle is greater than the deceleration area; wherein, the maximum acceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the unstable equilibrium point.

[0092] In this preferred embodiment, by setting the maximum deceleration area greater than the acceleration area within the first swing cycle as a stability comparison condition for the first type of mode, this design is based on the principle of energy conservation—in the first type of mode, after a fault occurs, the equivalent mechanical power is greater than the equivalent electromagnetic power, and the equivalent power angle accelerates from the stable equilibrium point. After crossing the stable equilibrium point, the equivalent mechanical power is less than the equivalent electromagnetic power, and the equivalent power angle decelerates. If the maximum deceleration area is greater than the acceleration area, the system can consume the excess energy gained during acceleration during deceleration, allowing the equivalent power angle to return to the stable equilibrium point region. Simultaneously, a first... Using the maximum acceleration area being greater than the deceleration area within a single swing cycle as a stability comparison condition, this design is also based on the principle of energy conservation—in the third mode, after a fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, the equivalent power angle decelerates first, and after crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, and the equivalent power angle accelerates; if the maximum acceleration area is greater than the deceleration area, the energy gained by the system during acceleration is insufficient for the equivalent power angle to cross the unstable equilibrium point, thus ensuring that the system can remain within the stable region; the differentiated processing mechanism for the two modes ultimately realizes differentiated stability judgment criteria for different fault modes.

[0093] Furthermore, in step S3, outputting the stability judgment result can be implemented through the following preferred embodiment, including step S33, as follows:

[0094] S33: If the stability comparison condition is met, the stability judgment result is output according to the sign of the integral value of the equivalent damping power with respect to the equivalent power angle: if the integral value is positive, the system is determined to be synchronously stable; if the integral value is zero, the system is determined to be in a critically stable state; if the integral value is negative, the system is determined to be unstable.

[0095] In this preferred embodiment, under the premise that the stability comparison condition is met, the stability judgment is further based on the positive or negative output stability result of the sum of areas generated by the equivalent damping power during the change of the equivalent power angle. This design is based on the key influence mechanism of damping on the energy conversion of the system—when the sum of areas is positive, it indicates that the equivalent damping has a positive damping effect, the system kinetic energy decreases, and the equivalent power angle will gradually oscillate and approach the post-fault equilibrium point in the subsequent swing cycle; when the sum of areas is zero, it indicates that in the ideal undamped state, the equivalent power angle will oscillate around the post-fault equilibrium point with equal amplitude; when the sum of areas is negative, it indicates that the equivalent damping has a negative damping effect, the system kinetic energy increases, and the equivalent power angle will gradually oscillate and diverge or diverge directly in the subsequent swing cycle, thus realizing a precise quantitative assessment of the influence of damping characteristics on system stability.

[0096] Furthermore, in step S3, outputting the stability judgment result also includes step S34, as follows:

[0097] S34: If the stability comparison condition is not met, the system is directly determined to be unstable.

[0098] In this preferred embodiment, the rule for directly determining system instability when the stability comparison condition is not met is based on the fundamental physical principle of energy balance. In the first type of mode, if the maximum deceleration area is not greater than the acceleration area, it indicates that the system cannot dissipate the excess energy gained during acceleration during deceleration, and the equivalent work angle will continue to increase beyond the stable equilibrium point, leading to system instability. In the third type of mode, if the maximum acceleration area is not greater than the deceleration area, it indicates that the energy gained by the system during acceleration is insufficient to make the equivalent work angle exceed the unstable equilibrium point. However, in reality, since the system can no longer meet the basic energy balance condition, the equivalent work angle will not return to the stable region, leading to system instability. This concise and clear determination rule avoids redundant calculations for obvious instability situations, simplifies the judgment process, and improves the efficiency of stability analysis. Simultaneously, by ensuring that the system can promptly and accurately identify the instability state when it does not meet the basic stability condition, it provides timely decision-making basis for system protection and control, achieving optimization of the stability judgment process and efficient utilization of computational resources.

[0099] In summary, compared with the prior art, the above embodiments of this application have the following beneficial effects: By constructing the second-order motion equations of the phase-locked loop and grid coupling based on the parameters of the converter-grid coupling system, a precise mathematical description of the dynamic characteristics of the converter-grid system is achieved, providing a theoretical basis for subsequent multimodal analysis; furthermore, by performing mode identification based on the magnitude of the grid impedance, the converter d-axis current output state during the fault, and the relative relationship between the equivalent power angle at the equilibrium point before and after the fault, this identification mechanism is based on the physical nature of the converter under different fault conditions—when the grid impedance is less than the critical impedance value and the equivalent power angle after the fault is... When the equivalent mechanical power is greater than the pre-fault value, the system is in the first mode. In this mode, after the fault, the equivalent mechanical power is greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate. After crossing the stable equilibrium point, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate, potentially leading to instability. When the grid impedance is less than the critical impedance value and the post-fault equivalent power angle is less than the pre-fault value, the system is in the second mode. In this mode, after the fault, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate initially. After crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate. Furthermore, since the maximum acceleration area is always greater than the deceleration area, the system will inevitably... However, the system is synchronously stable. When the grid impedance is greater than or equal to the critical damping value, the system is in the third mode. At this time, the converter d-axis current may drop to zero. After the fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate first. After crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate, which may lead to instability. When the mode identification result is the second mode, the system is directly determined to be synchronously stable, avoiding redundant calculations for known stable conditions and improving analysis efficiency. In addition, by calculating the acceleration area, deceleration area and equivalent damping power in the first swing cycle, the equivalent... The integral value of the power angle is based on the physical principle that within the same swing cycle, the sum of the acceleration and deceleration areas generated by the equivalent damping power during the change of the equivalent power angle (i.e., the integral value) determines the trend of the equivalent power angle change in subsequent swing cycles. If the sum of the acceleration and deceleration areas is less than zero in the first swing cycle, the system kinetic energy decreases and will gradually recover to the equilibrium point in subsequent cycles. If the sum of the areas is greater than zero, the system kinetic energy increases and will gradually move away from the equilibrium point and eventually become unstable. Finally, by setting differentiated stability comparison conditions according to different modes and combining the positive and negative output results of the integral value, a precise assessment of the synchronous stability of the converter is achieved. These technical features work together to fundamentally solve the problem of inaccurate determination of instability boundary conditions caused by the traditional equal area method due to its failure to distinguish fault modes by dividing the fault scenario into three different modes and applying stability judgment rules accordingly, while considering the influence of equivalent damping power on stability. This achieves precision, efficiency, and clarity of the physical mechanism in the synchronous stability analysis of the converter.

[0100] Example 2:

[0101] Please refer to Figure 2 Based on the same inventive concept, the present invention discloses a multimodal analysis system for the synchronous stability of a converter, comprising: an equation construction module M1, a mode identification module M2, and a judgment output module M3;

[0102] The equation construction module M1 is used to construct the second-order motion equations of the phase-locked loop coupled with the power grid based on the parameters of the converter-grid coupling system.

[0103] The mode identification module M2 is used to identify the transient process of the converter when the converter fails, based on the magnitude of the grid impedance, the d-axis current output state of the converter during the fault, and the relative relationship between the equivalent power angle of the balance point before and after the fault. Specifically, when the grid impedance is less than the critical impedance value that causes the d-axis current of the converter to drop to zero during the fault, and the equivalent power angle of the balance point of the converter after the fault is greater than the equivalent power angle of the balance point before the fault, it is determined to be the first type of mode; when the grid impedance is less than the critical impedance value, and the equivalent power angle of the balance point after the fault is less than the equivalent power angle of the balance point before the fault, it is determined to be the second type of mode; when the grid impedance is greater than or equal to the critical impedance value, it is determined to be the third type of mode.

[0104] Furthermore, the modal recognition module M2 includes: an inertia determination unit;

[0105] Before performing modal identification on the transient process of the converter, the inertia judgment unit is used to calculate the equivalent rotational inertia of the system based on the second-order equation of motion during a fault. If the result is less than zero, the system is directly judged to be unstable.

[0106] In this preferred embodiment, before modal identification, the equivalent moment of inertia in the second-order equation of motion is checked to see if it is less than zero. If it is less than zero, the system is directly judged to be unstable. This design is based on the basic physical principle of system stability—the equivalent moment of inertia is a key parameter describing the inertial characteristics of a system. When the equivalent moment of inertia is less than zero, it indicates that the system has lost its basic inertial characteristics and cannot maintain normal dynamic behavior. Furthermore, by using this pre-judgment condition, unnecessary complex modal identification and stability analysis calculations are avoided, thus improving analysis efficiency. At the same time, by simply checking the key parameter of equivalent moment of inertia, the rapid identification of obvious instability situations is ensured, providing an efficient preliminary screening mechanism for system stability assessment. By performing this check immediately after the system parameters are determined, an early judgment of the system's stability state is achieved, optimizing the analysis process and realizing reasonable optimization of the stability analysis process and efficient allocation of computational resources.

[0107] The judgment output module M3 is used to directly determine that the system is synchronously stable when the modal identification result is the second type of mode; otherwise, based on the second-order equation of motion, it calculates the acceleration area corresponding to the acceleration process of the equivalent power angle, the deceleration area corresponding to the deceleration process of the equivalent power angle, and the integral value of the equivalent damping power with respect to the equivalent power angle during the first swing cycle after the fault occurs; according to the identified modal type, it determines the corresponding stability comparison conditions for the acceleration area and deceleration area, and outputs the stability judgment result based on the stability comparison conditions and the sign of the integral value.

[0108] Furthermore, the judgment output module M3 includes: a first condition determination unit and a second condition determination unit;

[0109] The first condition determination unit is used to determine the stability comparison condition as follows if the modal identification result is the first type of mode: the maximum deceleration area within the first swing cycle is greater than the acceleration area; wherein the maximum deceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the stable equilibrium point.

[0110] The second condition determination unit is used to determine the stability comparison condition as follows if the modal identification result is a third type of mode: the maximum acceleration area within the first swing cycle is greater than the deceleration area; wherein the maximum acceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the unstable equilibrium point.

[0111] In this preferred embodiment, by setting the maximum deceleration area greater than the acceleration area within the first swing cycle as a stability comparison condition for the first type of mode, this design is based on the principle of energy conservation—in the first type of mode, after a fault occurs, the equivalent mechanical power is greater than the equivalent electromagnetic power, and the equivalent power angle accelerates from the stable equilibrium point. After crossing the stable equilibrium point, the equivalent mechanical power is less than the equivalent electromagnetic power, and the equivalent power angle decelerates. If the maximum deceleration area is greater than the acceleration area, the system can consume the excess energy gained during acceleration during deceleration, allowing the equivalent power angle to return to the stable equilibrium point region. Simultaneously, a first... Using the maximum acceleration area being greater than the deceleration area within a single swing cycle as a stability comparison condition, this design is also based on the principle of energy conservation—in the third mode, after a fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, the equivalent power angle decelerates first, and after crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, and the equivalent power angle accelerates; if the maximum acceleration area is greater than the deceleration area, the energy gained by the system during acceleration is insufficient for the equivalent power angle to cross the unstable equilibrium point, thus ensuring that the system can remain within the stable region; the differentiated processing mechanism for the two modes ultimately realizes differentiated stability judgment criteria for different fault modes.

[0112] Furthermore, the judgment output module M3 also includes: a result output unit;

[0113] The result output unit is used to output a stability judgment result based on the sign of the integral value of the equivalent damping power with respect to the equivalent power angle if the stability comparison condition is met: if the integral value is positive, the system is determined to be synchronously stable; if the integral value is zero, the system is determined to be in a critically stable state; if the integral value is negative, the system is determined to be unstable.

[0114] In this preferred embodiment, under the premise that the stability comparison condition is met, the stability judgment is further based on the positive or negative output stability result of the sum of areas generated by the equivalent damping power during the change of the equivalent power angle. This design is based on the key influence mechanism of damping on the energy conversion of the system—when the sum of areas is positive, it indicates that the equivalent damping has a positive damping effect, the system kinetic energy decreases, and the equivalent power angle will gradually oscillate and approach the post-fault equilibrium point in the subsequent swing cycle; when the sum of areas is zero, it indicates that in the ideal undamped state, the equivalent power angle will oscillate around the post-fault equilibrium point with equal amplitude; when the sum of areas is negative, it indicates that the equivalent damping has a negative damping effect, the system kinetic energy increases, and the equivalent power angle will gradually oscillate and diverge or diverge directly in the subsequent swing cycle, thus realizing a precise quantitative assessment of the influence of damping characteristics on system stability.

[0115] Furthermore, the judgment output module M3 also includes: a stability judgment unit;

[0116] The stability judgment unit is used to directly determine that the system is unstable if the stability comparison condition is not met.

[0117] In this preferred embodiment, the rule for directly determining system instability when the stability comparison condition is not met is based on the fundamental physical principle of energy balance. In the first type of mode, if the maximum deceleration area is not greater than the acceleration area, it indicates that the system cannot dissipate the excess energy gained during acceleration during deceleration, and the equivalent work angle will continue to increase beyond the stable equilibrium point, leading to system instability. In the third type of mode, if the maximum acceleration area is not greater than the deceleration area, it indicates that the energy gained by the system during acceleration is insufficient to make the equivalent work angle exceed the unstable equilibrium point. However, in reality, since the system can no longer meet the basic energy balance condition, the equivalent work angle will not return to the stable region, leading to system instability. This concise and clear determination rule avoids redundant calculations for obvious instability situations, simplifies the judgment process, and improves the efficiency of stability analysis. Simultaneously, by ensuring that the system can promptly and accurately identify the instability state when it does not meet the basic stability condition, it provides timely decision-making basis for system protection and control, achieving optimization of the stability judgment process and efficient utilization of computational resources.

[0118] In summary, compared with the prior art, the embodiments of this application have the following beneficial effects: By constructing the second-order motion equations of the phase-locked loop and grid coupling based on the parameters of the converter-grid coupling system, a precise mathematical description of the dynamic characteristics of the converter-grid system is achieved, providing a theoretical basis for subsequent multimodal analysis; furthermore, by performing mode identification based on the magnitude of the grid impedance, the converter d-axis current output state during the fault, and the relative relationship between the equivalent power angle at the equilibrium point before and after the fault, this identification mechanism is based on the physical nature of the converter under different fault conditions—when the grid impedance is less than the critical impedance value and the equivalent power angle after the fault is greater than... Before the fault, the system is in the first mode. In this mode, after the fault occurs, the equivalent mechanical power is greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate. After crossing the stable equilibrium point, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate, potentially leading to instability. When the grid impedance is less than the critical impedance value and the equivalent power angle after the fault is less than before the fault, the system is in the second mode. In this mode, after the fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate initially. After crossing the stable equilibrium point, the equivalent mechanical power is greater than the equivalent electromagnetic power, causing the equivalent power angle to accelerate. Furthermore, since the maximum acceleration area is always greater than the deceleration area, the system will inevitably... Synchronous stability is achieved when the grid impedance is greater than or equal to the critical damping value, indicating that the system is in the third mode. In this mode, the converter's d-axis current may drop to zero. After a fault occurs, the equivalent mechanical power is less than the equivalent electromagnetic power, causing the equivalent power angle to decelerate initially. After crossing the stable equilibrium point, the equivalent mechanical power exceeds the equivalent electromagnetic power, causing the equivalent power angle to accelerate, potentially leading to instability. By directly determining the system as synchronously stable when the mode identification result is the second mode, redundant calculations for known stable conditions are avoided, improving analysis efficiency. Furthermore, by calculating the acceleration area, deceleration area, and equivalent damping power during the first swing cycle, the equivalent power angle is determined to be stable. The design, based on the physical principle that the sum of the acceleration and deceleration areas generated by the equivalent damping power during the change of the equivalent power angle within the same swing cycle (i.e., the integral value), determines the trend of the equivalent power angle change in subsequent swing cycles. If the sum of the acceleration and deceleration areas is less than zero in the first swing cycle, the system kinetic energy decreases and will gradually recover to the equilibrium point in subsequent cycles. If the sum of the areas is greater than zero, the system kinetic energy increases, and it will gradually move away from the equilibrium point and eventually become unstable. Finally, by setting differentiated stability comparison conditions according to different modes and combining the positive and negative output results of the integral value, a precise assessment of the synchronous stability of the converter is achieved. These technical features work together to fundamentally solve the problem of inaccurate determination of instability boundary conditions caused by the traditional equal area method due to its failure to distinguish fault modes by dividing the fault scenario into three different modes and applying stability judgment rules accordingly, while considering the influence of equivalent damping power on stability. This achieves precision, efficiency, and clarity of the physical mechanism in the synchronous stability analysis of the converter.

[0119] Example 3:

[0120] Figure 3 A structural diagram of a multi-mode analysis device for converter synchronization stability according to this application is presented. (See diagram below.) Figure 3 As shown, the multimodal analysis device for the synchronous stability of the converter may include: a processor N1, a memory N2, a data interface N3, and a communication bus N4.

[0121] Wherein: processor N1, memory N2, and data interface N3 communicate with each other through communication bus N4; data interface N3 is used for data communication with other devices such as input devices or output devices; processor N1 is used to execute program N5, which can specifically execute the relevant steps in any of the above embodiments of the multimodal analysis method for converter synchronization stability.

[0122] Specifically, program N5 may include program code, which includes computer-executable instructions.

[0123] The processor N1 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of this application. The multimodal analysis device for converter synchronization stability includes one or more processors, which may be processors of the same type, such as one or more CPUs, or processors of different types, such as one or more CPUs and one or more ASICs.

[0124] Memory N2 is used to store program N5. Memory N2 may include high-speed RAM memory, and may also include non-volatile memory, such as at least one disk storage.

[0125] The algorithms or displays provided herein are not inherently related to any particular computer, virtual system, or other device. Furthermore, the embodiments in this application are not directed to any particular programming language.

[0126] Example 4:

[0127] This invention also provides a computer-readable storage medium storing at least one executable instruction. When the executable instruction is executed on a multimodal analysis device / system for converter synchronization stability, the device / system performs a multimodal analysis method for converter synchronization stability according to any of the above method embodiments.

[0128] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of this application may be practiced without these specific details. Similarly, for the purpose of simplification and aiding understanding of one or more aspects of the invention, in the above description of exemplary embodiments of this application, various features of the embodiments are sometimes grouped together in a single embodiment, figure, or description thereof. The claims, which follow the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of this application.

[0129] Those skilled in the art will understand that the modules in the device of the embodiment can be adaptively changed and placed in one or more devices different from that embodiment. Modules, units, or components in the embodiment can be combined into a single module, unit, or component, and further, they can be divided into multiple sub-modules, sub-units, or sub-components, except that at least some of such features and / or processes or units are mutually exclusive.

Claims

1. A multi-mode analysis method for the synchronization stability of a converter, characterized in that, include: Based on the parameters of the converter-grid coupling system, a second-order equation of motion for the coupling between the phase-locked loop and the grid is constructed; When a converter fails, mode identification is performed on the transient process of the converter based on the magnitude of the grid impedance, the converter's d-axis current output state during the fault, and the relative relationship between the equivalent power angle at the equilibrium point before and after the fault. Specifically: when the grid impedance is less than the critical impedance value that causes the converter's d-axis current to drop to zero during the fault, and the equivalent power angle at the equilibrium point of the converter after the fault is greater than the equivalent power angle at the equilibrium point before the fault, it is determined to be the first type of mode; when the grid impedance is less than the critical impedance value, and the equivalent power angle at the equilibrium point after the fault is less than the equivalent power angle at the equilibrium point before the fault, it is determined to be the second type of mode; when the grid impedance is greater than or equal to the critical impedance value, it is determined to be the third type of mode. When the modal identification result is the second type of mode, the system is directly determined to be synchronously stable; otherwise: based on the second-order equation of motion, calculate the acceleration area corresponding to the acceleration process of the equivalent power angle, the deceleration area corresponding to the deceleration process of the equivalent power angle, and the integral value of the equivalent damping power with respect to the equivalent power angle during the first swing cycle after the fault occurs; determine the stability comparison conditions of the corresponding acceleration area and deceleration area according to the identified modal type, and output the stability judgment result based on the stability comparison conditions and the sign of the integral value.

2. The multi-mode analysis method for converter synchronization stability as described in claim 1, characterized in that, The step of determining the stability comparison conditions for the acceleration and deceleration areas based on the identified modal types includes: If the modal identification result is the first type of mode, then the stability comparison condition is determined to be that the maximum deceleration area during the first swing cycle is greater than the acceleration area; wherein, the maximum deceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the stable equilibrium point; If the modal identification result is the third type of mode, then the stability comparison condition is determined to be that the maximum acceleration area during the first swing cycle is greater than the deceleration area; wherein, the maximum acceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the unstable equilibrium point.

3. The multimodal analysis method for converter synchronization stability as described in claim 2, characterized in that, The stability judgment result is output based on the stability comparison condition and the sign of the integral value, including: If the stability comparison condition is met, the stability judgment result is output according to the sign of the integral value of the equivalent damping power with respect to the equivalent power angle: if the integral value is positive, the system is determined to be synchronously stable; if the integral value is zero, the system is determined to be in a critically stable state; if the integral value is negative, the system is determined to be unstable.

4. The multimodal analysis method for converter synchronization stability as described in claim 3, characterized in that, The process of outputting a stability judgment result based on the stability comparison condition and the sign of the integral value also includes: If the stability comparison condition is not met, the system is directly determined to be unstable.

5. A multi-mode analysis method for converter synchronization stability as described in any one of claims 1-4, characterized in that, Before performing modal identification on the transient process of the converter, the following steps are also included: In the event of a fault, the equivalent moment of inertia of the system is calculated based on the second-order equation of motion. If the result is less than zero, the system is directly judged to be unstable.

6. A multi-modal analysis system for converter synchronization stability, characterized in that, include: The module consists of an equation construction module, a modality recognition module, and a judgment and output module. The equation construction module is used to construct the second-order motion equations of the phase-locked loop coupled with the power grid based on the parameters of the converter-grid coupling system. The mode identification module is used to identify the transient process of the converter when a converter fails, based on the magnitude of the grid impedance, the converter's d-axis current output state during the fault, and the relative relationship between the equivalent power angle at the equilibrium point before and after the fault. Specifically: when the grid impedance is less than the critical impedance value that causes the converter's d-axis current to drop to zero during the fault, and the equivalent power angle at the equilibrium point of the converter after the fault is greater than the equivalent power angle at the equilibrium point before the fault, it is determined to be a first-type mode; when the grid impedance is less than the critical impedance value, and the equivalent power angle at the equilibrium point after the fault is less than the equivalent power angle at the equilibrium point before the fault, it is determined to be a second-type mode; when the grid impedance is greater than or equal to the critical impedance value, it is determined to be a third-type mode. The judgment output module is used to directly determine that the system is synchronously stable when the modal identification result is the second type of mode; otherwise, based on the second-order equation of motion, it calculates the acceleration area corresponding to the acceleration process of the equivalent power angle, the deceleration area corresponding to the deceleration process of the equivalent power angle, and the integral value of the equivalent damping power with respect to the equivalent power angle during the first swing cycle after the fault occurs; according to the identified modal type, it determines the corresponding stability comparison conditions for the acceleration area and deceleration area, and outputs the stability judgment result based on the stability comparison conditions and the sign of the integral value.

7. The multi-mode analysis system for converter synchronization stability as described in claim 6, characterized in that, The judgment output module includes: a first condition determination unit and a second condition determination unit; The first condition determination unit is used to determine the stability comparison condition as follows if the modal identification result is the first type of mode: the maximum deceleration area within the first swing cycle is greater than the acceleration area; wherein the maximum deceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the stable equilibrium point. The second condition determination unit is used to determine the stability comparison condition as follows if the modal identification result is a third type of mode: the maximum acceleration area within the first swing cycle is greater than the deceleration area; wherein the maximum acceleration area represents the integral value of the equivalent damping power with respect to the equivalent power angle during the process from the fault clearing point to the unstable equilibrium point.

8. The multi-mode analysis system for converter synchronization stability as described in claim 7, characterized in that, The judgment output module further includes: a result output unit; The result output unit is used to output a stability judgment result based on the sign of the integral value of the equivalent damping power with respect to the equivalent power angle if the stability comparison condition is met: if the integral value is positive, the system is determined to be synchronously stable; if the integral value is zero, the system is determined to be in a critically stable state; if the integral value is negative, the system is determined to be unstable.

9. A multi-modal analysis device for converter synchronization stability, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the computer program is loaded into the processor, it implements the steps of a multimodal analysis method for converter synchronization stability according to any one of claims 1-5.

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 steps of the multimodal analysis method for converter synchronization stability according to any one of claims 1-5.

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