A network-connection-mixed system cycle power elimination method and system

Abstract

A method and system for eliminating cyclic power in a grid-connected hybrid system are disclosed. The method includes: establishing a small-signal model of the grid-connected hybrid system; substituting the active and reactive power deviation transmission equations of both systems into the load power balance equation to obtain the active power decomposition formula; determining the initial parameters of the system based on the set impedance and damping matching rules and dynamic characteristic synchronization rules; real-time acquisition of the system's output active power and load active power to determine the corresponding small-signal deviation, and substituting it into the active power decomposition formula to obtain the cyclic power component; calculating correction coefficients based on the corresponding cyclic power component to correct the parameters of the grid-connected virtual synchronous generator and the grid-connected converter, and verifying the corrected parameters through constraint conditions. This invention effectively suppresses cyclic power and improves system stability and operating efficiency by constructing a small-signal model of the grid-connected hybrid system and realizing cyclic power decomposition and adaptive parameter adjustment.

Description

Technical Field

[0001] This invention belongs to the field of power electronic conversion and microgrid control technology, specifically relating to a method and system for eliminating cyclic power in a grid-connected hybrid system. Background Technology

[0002] With the rapid development of distributed generation technology, microgrids often adopt a parallel operation mode of grid-connected converters (such as virtual synchronous generators, VSGs) and grid-connected converters (GFLs): grid-connected VSGs provide autonomous frequency and voltage support by simulating the rotor motion characteristics of synchronous generators, ensuring the power supply reliability of the microgrid; grid-connected GFLs rely on phase-locked loops (PLLs) to track the voltage phase of the point of common coupling (PCC), achieving rapid power tracking and grid connection, and are suitable for the access of intermittent power sources such as photovoltaics and wind power.

[0003] However, there are significant differences in the dynamic characteristics between grid-type VSG and grid-type GFL: grid-type VSG has virtual inertia and droop damping, resulting in a smooth dynamic response and large inertia; grid-type GFL is dominated by PLL and current loop in dynamics, with fast response speed and almost no inertia. This heterogeneous characteristic makes it very easy to generate transient cyclic power when the two types of converters are connected in parallel.

[0004] Currently, existing methods for suppressing circulating current between converters include: Patent application CN120016577A provides a method for suppressing circulating current in a hybrid parallel system of a grid-connected energy storage converter and a grid-connected photovoltaic inverter. This method uses the state-space averaging method to model the impedance of the two types of converters, derives the power circulating current expression of the hybrid parallel system, and divides it into differential voltage circulating current and differential impedance circulating current. While keeping the control of the grid-connected photovoltaic inverter unchanged, a differential notch filter current inner loop controller is designed for the grid-connected energy storage converter to suppress the differential impedance circulating current. This significantly reduces the internal power circulating current of the hybrid parallel system, improves equipment efficiency, and extends the lifespan of the power switches. The patent application with publication number CN121689194A provides a method for suppressing circulating current between grid-connected energy storage units based on repetitive control. It utilizes a three-loop control architecture of power, voltage, and current, introduces a repetitive controller in the inner current loop to suppress periodic harmonic circulating currents, combines LC filter state feedback and pole configuration to eliminate resonance peaks, and specifically suppresses integer multiple harmonic circulating currents through parallel narrowband resonant circuits. It can achieve efficient suppression of circulating currents between units and uniform power distribution without complex distributed communication, thereby improving the power sharing capability, grid-connected adaptability, and operational reliability of grid-connected energy storage systems and improving the output power quality.

[0005] In existing technologies, methods for suppressing cyclic power in grid-connected hybrid systems mainly focus on single methods such as virtual impedance adjustment, PLL parameter optimization, or additional damping injection. These are ex-post suppression strategies and have the following shortcomings: First, a complete mechanistic model has not been established, making it impossible to accurately trace the root cause of cyclic power generation, resulting in a lack of theoretical support for control strategies and reliance on experience for parameter tuning. Second, a systematic set of parameter design rules has not been formed, making it impossible to avoid the generation of cyclic power from the source, thus limiting the suppression effect. Third, most methods alter the original control nature of the converter (such as changing the grid-connected characteristics of the GFL) or rely on complex communication coordination, making engineering implementation difficult and easily introducing new oscillation risks. Summary of the Invention

[0006] To address the technical problems in existing grid-connected hybrid systems, such as unclear cyclic power generation mechanisms, difficulty in eliminating cyclic power at its source, limited effectiveness of traditional post-event suppression methods, easy alteration of converter's original control characteristics, and reliance on complex communication or additional hardware leading to significant engineering implementation difficulties, this invention provides a method and system for eliminating cyclic power in grid-connected hybrid systems. The method includes: establishing a small-signal model of the grid-connected hybrid system; simultaneously establishing the active and reactive power deviation transmission equations of both systems and substituting them into the load power balance equation to obtain the active power decomposition formula; determining the initial parameters of the system based on the set impedance and damping matching rules and dynamic characteristic synchronization rules; real-time acquisition of the system's output active power and load active power to determine the corresponding small-signal deviation, and substituting it into the active power decomposition formula to obtain the cyclic power component; calculating correction coefficients based on the corresponding cyclic power component to correct the parameters of the grid-connected virtual synchronous generator and the grid-connected converter, and verifying the corrected parameters through constraint conditions. This invention constructs a small-signal model of a grid-connected hybrid system and realizes cyclic power decomposition and adaptive parameter adjustment, effectively suppressing cyclic power and improving system stability and operating efficiency.

[0007] The present invention adopts the following technical solution: A first aspect of the present invention provides a method for eliminating cyclic power in a grid-connected hybrid system, comprising: S1. Establish small-signal models for the grid-type virtual synchronous generator and the grid-type converter respectively; based on the small-signal models, solve the active and reactive power deviation transmission equations of the two, substitute them into the load power balance equation to obtain the active power decomposition formula, and decompose the output active power into load distribution component and circulating power component. S2. Based on the set impedance and damping matching rules, and combined with the predefined initial droop damping of the virtual synchronous generator, determine the initial equivalent damping of the grid converter; based on the set dynamic characteristic synchronization rules, and combined with the predefined initial virtual inertia of the virtual synchronous generator, determine the initial equivalent virtual inertia of the grid converter. S3. Real-time acquisition of the output active power and load active power of the grid-type virtual synchronous generator and the grid-connected converter, determination of the corresponding small-signal deviation, and substitution into the active power decomposition formula to obtain the cyclic power component; in any detection period, based on the corresponding cyclic power component and combined with the output active power, calculate the corresponding correction coefficient; based on the correction coefficient, combined with the dynamic characteristic synchronization rule and impedance and damping matching rule, correct the virtual inertia and droop damping of the grid-type virtual synchronous generator and the equivalent virtual inertia and equivalent damping of the grid-connected converter; verify the corrected parameters through predefined constraints.

[0008] Preferably, in S1, the rotor motion equation of the virtual synchronous generator under predefined disturbance and the proportional equation of voltage amplitude deviation and reactive power deviation are established to determine the small-signal model of the grid-type virtual synchronous generator. Establish phase-locked loop, current loop and voltage loop models of the grid-connected converter under predefined disturbances, and determine the small-signal model of the grid-connected converter. The active and reactive power deviation transmission equations are established for the grid-type virtual synchronous generator and the grid-type converter, respectively. The active power deviation transmission equations are substituted into the load power balance equations to decompose the load distribution component and the circulating power component.

[0009] Preferably, the process of establishing the active and reactive power deviation transmission equations is as follows: Near the steady-state operating point, a first-order Taylor expansion is performed on the grid-connected power equation. When only the influence of power angle fluctuations on active power and voltage amplitude fluctuations on reactive power are considered, the first-order Taylor expansion is approximated as the small-signal deviations of active and reactive power. The output voltage amplitude of the grid-connected virtual synchronous generator is multiplied by the voltage amplitude at the point of common coupling and the cosine of the steady-state power angle as the numerator, and the total equivalent inductive impedance on the grid-connected virtual synchronous generator side is used as the denominator to obtain the corresponding active power coefficient. The output voltage amplitude of the grid-connected virtual synchronous generator is multiplied by the voltage amplitude at the point of common coupling and the sine of the steady-state power angle as the numerator, and the total equivalent inductive impedance is used as the denominator to obtain the corresponding reactive power coefficient. The small-signal deviation of active power is converted into the product of the active power coefficient and the small-signal deviation of the power angle of the grid-connected virtual synchronous generator, and the small-signal deviation of reactive power is converted into the product of the reactive power coefficient and the small-signal deviation of the output voltage amplitude of the grid-connected virtual synchronous generator, thus obtaining the active and reactive power deviation transmission equations of the grid-connected virtual synchronous generator. Using the same method, the power deviation transmission equation of the grid converter is determined.

[0010] Preferably, the process of determining the load distribution component and the cyclic power component is as follows: For grid-connected virtual synchronous generators and grid-connected converters, the corresponding active power coefficient is used as the numerator, the active power coefficients of the grid-connected virtual synchronous generator and the grid-connected converter are added together as the denominator, and the ratio of the numerator to the denominator is multiplied by the small-signal deviation of the load active power to obtain the corresponding load distribution component. The numerator is the product of the active power coefficients of the grid-type virtual synchronous generator and the grid-type converter. The denominator is the sum of the active power coefficients of the two generators. The ratio of the numerator to the denominator is multiplied by the difference in the small-signal deviation of the power angle between the grid-type virtual synchronous generator and the grid-type converter. This value is the cyclic power component of the grid-type virtual synchronous generator. The negative of the cyclic power component of the grid-type virtual synchronous generator is the cyclic power component of the grid-type converter.

[0011] Preferably, the process of determining the initial equivalent virtual inertia of the grid converter in S2 is as follows: Based on the impedance and damping matching rule, the ratio of the total equivalent inductive impedance of the virtual synchronous generator to the total equivalent inductive impedance of the grid converter is multiplied by the predefined initial droop damping of the virtual synchronous generator, and used as the initial equivalent damping of the grid converter. Based on the dynamic characteristic synchronization rule, the ratio of the initial equivalent damping of the grid converter to the droop damping of the virtual synchronous generator is multiplied by the predefined initial virtual inertia of the virtual synchronous generator, and this ratio is used as the initial equivalent virtual inertia of the grid converter.

[0012] Preferably, the process of calculating the correction coefficient in S3 is as follows: The active power output of the grid-type virtual synchronous generator and the grid-type converter, and the active power of the load are collected. The corresponding steady-state operating point power is then subtracted to obtain the corresponding small signal deviation. This deviation is then substituted into the active power decomposition formula in S1 to obtain the cyclic power components of the grid-type virtual synchronous generator and the grid-type converter. In any detection period, the absolute value of the cyclic power component is used as the numerator, and the active power outputs of the collected grid-type virtual synchronous generator and grid-type converter are added together as the denominator to obtain the correction coefficient.

[0013] Preferably, the process of correcting the virtual inertia of the grid-type virtual synchronous generator and the equivalent virtual inertia of the grid-type converter in S3 is as follows: Based on the dynamic characteristic synchronization rule and the influence of cyclic power on VSG inertia, a correction formula is derived. The ratio of the total equivalent inductive impedance of the virtual synchronous generator to the sum of the total equivalent inductive impedance of the virtual synchronous generator and the grid-connected converter is calculated and multiplied by the small-signal deviation of the load active power to obtain the small-signal deviation of the rated output active power of the virtual synchronous generator. In any detection period, the ratio of the cyclic power component of the corresponding grid-connected virtual synchronous generator to the small-signal deviation of the rated output active power is multiplied by the correction coefficient of the corresponding detection period to obtain the corresponding correction term. After subtracting the correction term from 1, the result is multiplied by the corresponding initial virtual inertia to obtain the corrected virtual inertia of the virtual synchronous generator for the corresponding detection period. Multiply the ratio of the corrected equivalent damping to the droop damping by the corrected virtual inertia of the virtual synchronous generator to obtain the equivalent virtual inertia of the grid-type converter after the corresponding detection period correction.

[0014] Preferably, the process of correcting the droop damping of the grid-type virtual synchronous generator and the equivalent damping of the grid-type converter in S3 is as follows: Based on impedance and damping matching rules, and combined with the inherent relationship between cyclic power and damping coefficient, a correction formula is derived. In any detection period, the ratio of the total equivalent inductive impedance on the virtual synchronous generator side to the total equivalent inductive impedance on the grid converter side is multiplied by the correction coefficient of the corresponding detection period, which is used as the correction term for droop damping. After adding the correction term for droop damping to 1, multiplying it by the initial droop damping of the virtual synchronous generator, the droop damping after correction for the corresponding detection period is obtained. Multiply the ratio of the total equivalent inductive impedance on the virtual synchronous generator side to the total equivalent inductive impedance on the grid converter side by the droop damping corrected for the corresponding detection period to obtain the equivalent damping of the grid converter after the corresponding detection period correction.

[0015] Preferably, the process of verifying the corrected parameters in S3 is as follows: For any parameter among the virtual inertia, droop damping of the virtual synchronous generator and the equivalent virtual inertia and equivalent damping of the grid converter, if the parameter after correction in the current detection cycle is not less than the parameter after correction in the previous detection cycle, take the minimum value among the difference between the parameter after correction in the current detection cycle and the parameter after correction in the previous detection cycle, the upper limit of the correction rate, the upper limit of the corresponding parameter, and the difference between the parameter after correction in the current detection cycle, and add the parameter after correction in the previous detection cycle to obtain the corrected parameter after verification. If the corrected parameter for the current detection cycle is less than the corrected parameter for the previous detection cycle, take the maximum value among the difference between the corrected parameter for the current detection cycle and the corrected parameter for the previous detection cycle, the lower limit of the correction rate, the lower limit of the corresponding parameter, and the difference between the corrected parameter for the current detection cycle, and add the corrected parameter for the previous detection cycle to obtain the corrected parameter after verification.

[0016] A second aspect of the present invention provides a cyclic power cancellation system for a grid-connected hybrid system, and a method for cyclic power cancellation in a grid-connected hybrid system, comprising: The grid-connected hybrid system construction module establishes small-signal models for the grid-connected virtual synchronous generator and the grid-connected converter respectively. Based on the small-signal models, the active and reactive power deviation transmission equations of the two are combined and substituted into the load power balance equation for solution to obtain the active power decomposition formula. The output active power is decomposed into load distribution component and circulating power component. The initial control parameter determination module determines the initial equivalent damping of the grid converter based on the set impedance and damping matching rules and the predefined initial droop damping of the virtual synchronous generator; and determines the initial equivalent virtual inertia of the grid converter based on the set dynamic characteristic synchronization rules and the predefined initial virtual inertia of the virtual synchronous generator. The cyclic power elimination module collects the output active power and load active power of the grid-type virtual synchronous generator and the grid-connected converter in real time, determines the corresponding small signal deviation, and substitutes it into the active power decomposition formula to obtain the cyclic power component. In any detection period, based on the corresponding cyclic power component and combined with the output active power, the corresponding correction coefficient is calculated. Based on the correction coefficient, combined with the dynamic characteristic synchronization rule and impedance and damping matching rule, the virtual inertia and droop damping of the grid-type virtual synchronous generator, as well as the equivalent virtual inertia and equivalent damping of the grid-connected converter, are corrected. The corrected parameters are verified through predefined constraints.

[0017] Compared with the prior art, the beneficial effects of the present invention include at least the following: 1. This invention establishes small-signal models for both the grid-connected virtual synchronous generator and the grid-connected converter, and simultaneously establishes active and reactive power deviation transmission equations. Combining this with the load power balance relationship, the system output active power is decomposed into load-distribution components and cyclic power components. Compared to existing technologies that only analyze from a macroscopic power perspective and struggle to accurately identify the source of cyclic power, this invention can precisely characterize the formation mechanism of each power component at the small-signal modeling level, achieving quantitative expression and independent extraction of cyclic power. This improves the accuracy of system analysis and significantly enhances the analyzability and controllability of the grid-connected hybrid system.

[0018] 2. Based on impedance and damping matching rules and dynamic characteristic synchronization rules, this invention constructs a parameter coordination configuration method between a grid-connected virtual synchronous generator and a grid-connected converter. Through the coupled design of virtual inertia and damping parameters, consistency in the dynamic response characteristics of the two types of equipment is achieved. Compared with the problem of independent parameter design in the prior art, which easily leads to dynamic inconsistency or even oscillation, this invention can complete reasonable parameter matching during the system initialization stage, effectively suppressing low-frequency oscillations and power fluctuations caused by impedance mismatch or inertia differences, thereby significantly improving the small disturbance stability and dynamic response performance of the system.

[0019] 3. This invention collects system operating data in real time, calculates the cyclic power component, and constructs correction coefficients based on the cyclic power. It then dynamically corrects the virtual inertia and droop damping of the virtual synchronous generator, as well as the equivalent parameters of the grid-connected converter, online. Simultaneously, a parameter constraint mechanism is used to verify the correction results. Compared to traditional control methods that use fixed control parameters and are difficult to adapt to changes in operating conditions, this invention can adaptively adjust key control parameters according to the system's operating state, achieving continuous suppression and dynamic optimization control of cyclic power. This not only effectively reduces the flow of ineffective power within the system, decreasing energy loss and equipment stress, but also improves the overall operating efficiency and long-term stability of the system. Attached Figure Description

[0020] Figure 1 A flowchart of a method for eliminating cyclic power in a grid-connected hybrid system provided by the present invention; Figure 2 This is a network control block diagram provided in an embodiment of the present invention; Figure 3 This is a network control block diagram provided in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0022] Example 1 Embodiment 1 of the present invention provides a method for eliminating cyclic power in a grid-connected hybrid system, see reference. Figure 1 This includes the following steps: S1. Establish small-signal models for the grid-type virtual synchronous generator and the grid-type converter respectively. Based on the small-signal models, solve the active and reactive power deviation transmission equations of the two, substitute them into the load power balance equation, and obtain the active power decomposition formula. Then decompose the output active power into load distribution component and circulating power component.

[0023] S1.1 Establish the rotor motion equation of the virtual synchronous generator under predefined disturbances and the proportional equation of voltage amplitude deviation and reactive power deviation, and determine the small-signal model of the grid-type virtual synchronous generator (VSG). See Figure 2 In the small-signal model of a grid-type VSG, the active power control loop simulates the rotor motion equation of a synchronous generator, and the reactive power control loop adopts droop control. The model is defined as follows: ; in, The active power reference small-signal deviation of VSG; For the small signal deviation of the electromagnetic power of the VSG; For the virtual inertia of VSG; The active-frequency droop factor of VSG; For the small signal deviation of the VSG's angular frequency; This is the rated angular frequency; For the Laplace operator; This refers to the small signal deviation of the VSG output voltage amplitude; The reactive power-voltage droop factor of VSG; The small signal deviation of the reactive power output of VSG.

[0024] S1.2 Establish the phase-locked loop model, current loop model and voltage loop model of the grid converter under predefined disturbances, and determine the small-signal model of the grid converter GFL; See Figure 3 In the small-signal model of the grid-type GFL, the phase-locked loop (PLL) small-signal model adopts a typical second-order PLL. In the small-signal models of the current loop and voltage loop, the current loop is approximated as a first-order inertial element, and the model is defined as follows: ; in, This refers to the small phase signal deviation tracked by the GFL, i.e., the small phase signal deviation output by the GFL phase-locked loop PLL. For small-signal disturbances in PCC voltage; , The proportional and integral gains of the PLL determine its bandwidth and dynamic response speed. This represents the bandwidth of the current loop. The current command small signal deviation is generated by the power loop; This represents the small-signal deviation of the GFL current reference value; This refers to the small signal deviation of the GFL output voltage amplitude; Small signal deviation of the GFL reactive power reference value; , These are the proportional gain and integral gain of the voltage loop, respectively. This refers to the small signal deviation of the reactive power output of the GFL.

[0025] S1.3 Establish the active and reactive power deviation transmission equations for the grid-type virtual synchronous generator and the grid-type converter respectively; substitute the active power deviation transmission equation into the load power balance equation to decompose the load distribution component and the circulating power component.

[0026] Assuming the line is inductive, active and reactive power decoupling is achieved under small-signal conditions. Ignoring line resistance, the VSG's output power fully follows the grid-connected power equation of the virtual synchronous generator. Near the steady-state operating point, a first-order Taylor expansion of the grid-connected power equation is performed. When only considering the effects of power angle fluctuations on active power and voltage amplitude fluctuations on reactive power, the first-order Taylor expansion is approximated as the small-signal deviation of active and reactive power. The output voltage amplitude of the grid-connected virtual synchronous generator is multiplied sequentially by the cosine of the point of common coupling voltage amplitude and the steady-state power angle as the numerator. The total equivalent inductive impedance on the grid-connected virtual synchronous generator side is then calculated. Using the denominator, the corresponding active power coefficient is obtained; multiplying the output voltage amplitude of the grid-type virtual synchronous generator by the sine of the point of common coupling voltage amplitude and the steady-state power angle in sequence, and using the total equivalent inductive impedance as the denominator, the corresponding reactive power coefficient is obtained; converting the small-signal deviation of active power into the product of the active power coefficient and the small-signal deviation of the power angle of the grid-type virtual synchronous generator, and converting the small-signal deviation of reactive power into the product of the reactive power coefficient and the small-signal deviation of the output voltage amplitude of the grid-type virtual synchronous generator, the transmission equations for active power and reactive power deviation of the grid-type VSG are obtained; specifically expressed as: ; in, The total equivalent inductive impedance on the VSG side. The output impedance of the VSG is... The line impedance between VSG and PCC. The virtual impedance of the VSG; This refers to the output voltage amplitude of the VSG. The voltage amplitude at the point of common coupling (PCC); This is the steady-state power angle; , These are the active and reactive power coefficients, respectively. This refers to the small-signal deviation of the VSG power angle; This refers to the small signal deviation of the VSG output voltage amplitude; If the power deviation transmission equation for a grid-connected GFL adopts the same form as the power deviation transmission equation for a VSG, then the active and reactive power deviation transmission equations for a grid-connected GFL are: ; in, The total equivalent inductive impedance on the GFL side is... For GFL output impedance, The line impedance between GFL and PCC, The virtual impedance of GFL; This refers to the output voltage amplitude of the GFL. , These are the active and reactive power coefficients of the GFL, respectively. Small signal deviation of GFL output active power; Substituting the active power deviation transmission equations of the grid-connected virtual synchronous generator and the grid-connected converter into the load power balance equation; where the load power balance equation is: the sum of the small-signal deviation of the active power output of the grid-connected virtual synchronous generator and the small-signal deviation of the active power output of the grid-connected converter is always equal to the small-signal deviation of the load active power; specifically expressed as: ; In the formula, This represents the small signal deviation of the load's active power; Small signal deviation in the output active power of the network-type VSG; To minimize the small signal deviation in the active power output of the grid-type GFL; The active power decomposition formula is obtained by solving the equations simultaneously. The output active power of the grid-type virtual synchronous generator and the grid-type converter are decomposed into the corresponding load distribution component and the circulating power component, respectively, and the expressions of the load distribution component and the circulating power component are generated. For grid-connected virtual synchronous generators and grid-connected converters, the corresponding active power coefficient is used as the numerator, the active power coefficients of the grid-connected virtual synchronous generator and the grid-connected converter are added together as the denominator, and the ratio of the numerator to the denominator is multiplied by the small-signal deviation of the load active power to obtain the corresponding load distribution component. The numerator is the product of the active power coefficients of the grid-type virtual synchronous generator and the grid-type converter; the denominator is the sum of their active power coefficients; the ratio of the numerator to the denominator is multiplied by the difference in small-signal deviation of the power angle between the grid-type virtual synchronous generator and the grid-type converter to obtain the cyclic power component of the grid-type virtual synchronous generator; the negative of the cyclic power component of the grid-type virtual synchronous generator is taken as the cyclic power component of the grid-type converter; specifically expressed as: ; In the formula, For the small-signal deviation of the load active power; first term The load distribution component, determined by the equivalent impedance, characterizes the initial power distribution ratio between the two converters during a sudden load change; the second term... The cyclic power component is determined by the phase difference. drive, This is caused by the mismatch between the inertia-damping dynamics of the VSG and the PLL-current loop dynamics of the GFL.

[0027] In this embodiment, power decomposition clearly shows that the root cause of the cyclic power generation is the imbalance in initial power distribution caused by equivalent impedance mismatch and the phase difference caused by dynamic characteristic mismatch. Both of these factors jointly drive the reciprocating power flow between the two types of converters.

[0028] S2. Based on the set impedance and damping matching rules, and combined with the predefined initial droop damping of the virtual synchronous generator, determine the initial equivalent damping of the grid converter; based on the set dynamic characteristic synchronization rules, and combined with the predefined initial virtual inertia of the virtual synchronous generator, determine the initial equivalent virtual inertia of the grid converter.

[0029] Based on the S1 mechanism analysis, it is clear that the active power of the hybrid system consists of two parts: a load distribution component and a circulating power component. The load distribution component is determined by the equivalent power coefficients of the VSG and GFL, directly corresponding to the initial power distribution ratio during load abrupt changes. The circulating power component is driven by the phase difference between the two and is the core product of the mismatch in control characteristics of heterogeneous systems. Based on this, and considering the dynamic response characteristics of the hybrid system, a dual-parameter design rule of initial power distribution matching and dynamic characteristic matching is proposed. Initial power distribution matching ensures precise load allocation according to system requirements, eliminating circulating current inducements caused by distribution imbalance. Dynamic characteristic matching eliminates the phase difference between the VSG and GFL at the source, completely cutting off the driving conditions for circulating power, ultimately eliminating the source of circulating power in the hybrid system and ensuring the stable and efficient operation of the heterogeneous parallel system.

[0030] To ensure strict matching between the initial power distribution and the converter capacity during load surges, an impedance and damping matching rule is proposed: the ratio of the droop damping of the virtual synchronous generator to the equivalent damping of the grid-connected converter is equal to the ratio of the total equivalent inductive impedance of the grid-connected converter to the total equivalent inductive impedance of the virtual synchronous generator; specifically expressed as: ; in, To obtain the equivalent damping from the dynamic equivalent of the PLL and current loop in the grid-type GFL, the equivalent damping term is extracted by simplifying the small-signal model of the GFL. For the droop damping of VSG, , These are the total equivalent inductive impedances of GFL and VSG, respectively; This rule ensures that the initial power allocation ratio at the moment of load change is consistent with the capacity ratio of VSG and GFL, thus avoiding cyclic power caused by allocation imbalance from the source.

[0031] Based on impedance and damping matching rules, the ratio of the total equivalent inductive impedance of the virtual synchronous generator to the total equivalent inductive impedance of the grid converter is multiplied by the predefined initial droop damping of the virtual synchronous generator, and used as the initial equivalent damping of the grid converter; specifically expressed as: ; In the formula, This is the initial equivalent damping of the grid converter; The initial droop damping for the grid-type virtual synchronous generator; To eliminate the dynamic characteristic mismatch between VSG and GFL and prevent frequency difference from being converted into phase difference, a dynamic characteristic synchronization rule is proposed, namely, the ratio of the virtual inertia of the virtual synchronous generator to the droop damping is equal to the ratio of the equivalent virtual inertia to the equivalent damping of the grid-type converter; specifically expressed as: ; in, To obtain the equivalent virtual inertia of the network-type GFL from the dynamic equivalence of PLL bandwidth and current loop, the equivalent inertia term is extracted by performing second-order equivalence on the small-signal model of the PLL and current loop of the GFL. This is the virtual inertia of VSG.

[0032] This rule synchronizes the dynamic response characteristics of the GFL with those of the VSG, eliminating the dynamic drive chain of frequency difference, phase difference, and cyclic power, and further suppressing the generation of cyclic power.

[0033] Based on the dynamic characteristic synchronization rule, the ratio of the initial equivalent damping of the grid-connected converter to the droop damping of the virtual synchronous generator is multiplied by the predefined initial virtual inertia of the virtual synchronous generator, and this is taken as the initial equivalent virtual inertia of the grid-connected converter; specifically expressed as: .

[0034] In the formula, This is the initial equivalent virtual inertia of the grid converter; The initial virtual inertia of the grid-type virtual synchronous generator.

[0035] S3. Real-time acquisition of the output active power and load active power of the grid-type virtual synchronous generator and the grid-connected converter, determination of the corresponding small-signal deviation, and substitution into the active power decomposition formula to obtain the cyclic power component; in any detection period, based on the corresponding cyclic power component and combined with the output active power, calculate the corresponding correction coefficient; based on the correction coefficient, combined with the dynamic characteristic synchronization rule and impedance and damping matching rule, correct the virtual inertia and droop damping of the grid-type virtual synchronous generator and the equivalent virtual inertia and equivalent damping of the grid-connected converter; verify the corrected parameters through predefined constraints.

[0036] By real-time monitoring of cyclic power and combining it with the real-time operating status of the system, the virtual inertia and droop damping of the VSG, as well as the equivalent damping and equivalent virtual inertia of the GFL, are dynamically adjusted to achieve stable suppression of cyclic power under all operating conditions. The corrected logic closed-loop dynamic adaptive correction forms a complete closed loop of real-time monitoring, formula correction, parameter updating, and feedback verification. After each monitoring cycle, real-time operating parameters of the system are collected, and the cyclic power and correction coefficients are calculated. Based on the correction formula, the corrected virtual inertia, droop damping of the VSG, and equivalent damping and equivalent virtual inertia of the GFL are calculated synchronously. The corrected parameters are checked to ensure they meet the constraints. If they do, the system control parameters are updated; otherwise, the closest value within the constraint range is used for updating. The process is repeated in the next monitoring cycle to achieve dynamic suppression of cyclic power under all operating conditions, ensuring that the system always maintains a stable operating state.

[0037] S3.1. Real-time acquisition of the output active power and load active power of the grid-connected virtual synchronous generator (VSG) and grid-connected converter (GFL), and subtraction of the corresponding steady-state operating point power to obtain the corresponding small-signal deviation; substituting the small-signal deviations of the output active power and load active power of the grid-connected virtual synchronous generator and grid-connected converter into the active power decomposition formula in S1, to obtain the cyclic power components of the grid-connected virtual synchronous generator and grid-connected converter; specifically expressed as: ; ; In the formula, The cyclic power component of the grid-type virtual synchronous generator; For the cyclic power components of the grid converter; S3.2 In any detection cycle, the absolute value of the cyclic power component is used as the numerator, and the active power outputs of the collected grid-type virtual synchronous generator and the grid-type converter are added together as the denominator to obtain the correction coefficient. Based on the correction coefficient, combined with the impedance and damping matching rules and dynamic characteristic synchronization rules of S2, the virtual inertia and droop damping of the virtual synchronous generator and the equivalent virtual inertia and equivalent damping of the grid-type converter are corrected in each detection cycle.

[0038] The specific formula for the correction factor is as follows: ; in, This is a correction factor; , The active power outputs of the network-type virtual synchronous generator and the grid-type converter are collected, respectively.

[0039] S3.2.1. Based on the dynamic characteristic synchronization rule and the influence of cyclic power on VSG inertia, the correction formula is derived; the ratio of the total equivalent inductive impedance of the virtual synchronous generator to the sum of the total equivalent inductive impedance of the virtual synchronous generator and the grid-connected converter is calculated, and multiplied by the small-signal deviation of the load active power as the small-signal deviation of the rated output active power of the virtual synchronous generator; in any detection period, the ratio of the cyclic power component of the corresponding grid-connected virtual synchronous generator to the small-signal deviation of the rated output active power is multiplied by the correction coefficient of the corresponding detection period as the corresponding correction term; 1 is subtracted from the correction term and multiplied by the corresponding initial virtual inertia to obtain the corrected virtual inertia of the virtual synchronous generator for the corresponding detection period; the specific formula is: ; in, The virtual inertia after VSG correction for the (k+1)th detection cycle; The initial virtual inertia of VSG for S2; The small signal deviation of the rated output active power of VSG after S2 tuning; , It is calculated in real time during each detection cycle; When the cycle power A positive value indicates that the VSG is supplying circulating power to the GFL, suggesting that the VSG's inertia is relatively too large and its dynamic response is too slow. Adjusting the product of the power ratio (i.e., the correction term) reduces Accelerate VSG dynamic response; when A negative value indicates that the GFL is supplying circulating power to the VSG, suggesting that the VSG's inertia is relatively too small, and increasing it will help. This enhances the stability of VSG frequency support and ensures that it always maintains synchronous matching with the equivalent inertia of GFL.

[0040] S3.2.2. Based on impedance and damping matching rules, and combined with the inherent relationship between cyclic power and damping coefficient, the correction formula is derived. In any detection period, the ratio of the total equivalent inductive impedance on the virtual synchronous generator side to the total equivalent inductive impedance on the grid converter side is multiplied by the correction coefficient for the corresponding detection period, serving as the correction term for droop damping. Adding the correction term to 1 and multiplying it by the initial droop damping of the virtual synchronous generator yields the corrected droop damping for the corresponding detection period. Specifically, it is expressed as follows: ; in, The VSG droop damping is corrected for the (k+1)th detection cycle; The initial droop damping of the VSG for S2; , These are the total equivalent inductive impedances on the VSG and GFL sides, respectively, which are inherent parameters of the system and are monitored and updated in real time. This is calculated for real-time detection. The greater the cycle power, the better. The larger the value, the greater the damping matching deviation, which is determined by the impedance ratio. The coordinated adjustment and synchronous correction This ensures that the impedance-damping matching rule is always met, accelerates the decay rate of the cyclic power, and maintains the frequency droop characteristics of the VSG unchanged.

[0041] S3.2.3. Based on impedance and damping matching rules, and combined with the feedback correlation between GFL equivalent damping and circulating power, the correction formula is derived synchronously from the VSG-corrected droop damping. In any detection period, the ratio of the total equivalent inductive impedance on the virtual synchronous generator side to the total equivalent inductive impedance on the grid converter side is multiplied by the corrected droop damping for the corresponding detection period to obtain the corrected equivalent damping of the grid converter for the corresponding detection period; specifically expressed as: ; in, The equivalent damping after GFL correction for the (k+1)th detection cycle; This refers to the VSG droop damping after the same period correction; , These are inherent system parameters, and are monitored and updated in real time. Synchronous correction with VSG droop damping strictly maintains the impedance-damping matching rule of S2, ensuring that the load distribution ratio always matches the converter capacity, and suppressing the cyclic power fluctuation caused by damping mismatch from the source.

[0042] S3.2.4. Based on the dynamic characteristic synchronization rule and combined with the feedback correlation between the equivalent virtual inertia of the GFL and the cyclic power, the correction formula is derived from the virtual inertia corrected by VSG. In any detection period, the ratio of the corresponding corrected equivalent damping to the droop damping is multiplied by the virtual inertia of the corrected virtual synchronous generator, which is taken as the equivalent virtual inertia of the grid-connected converter after correction in the corresponding detection period; specifically expressed as: ; in, The equivalent virtual inertia after GFL correction for the (k+1)th detection cycle; , , These are the VSG virtual inertia, VSG droop damping, and GFL equivalent damping, respectively, after the same period correction. Synchronous correction with VSG virtual inertia strictly maintains the dynamic characteristic synchronization rule of S2, eliminates the dynamic response difference between VSG and GFL, cuts off the generation path of phase difference, and realizes real-time suppression of cyclic power.

[0043] S3.3 To avoid system oscillation caused by sudden parameter changes during the correction process, parameter correction constraints are set as follows: The virtual inertia constraint of the virtual synchronous generator is: In this embodiment, the lower limit of the virtual inertia of the virtual synchronous generator is... The upper limit of virtual inertia of a virtual synchronous generator ; The equivalent virtual inertia constraint of the mesh converter is: In this embodiment, the lower limit of the equivalent virtual inertia of the mesh converter is used. The upper limit of the equivalent virtual inertia of the mesh converter ; The droop damping constraint of the virtual synchronous generator is: In this embodiment, the lower limit of the droop damping of the virtual synchronous generator is... Upper limit of droop damping of virtual synchronous generator ; The equivalent damping constraint of the grid converter is: In this embodiment, the equivalent damping lower limit of the grid converter is... The upper limit of the equivalent damping of the grid converter ; The correction rate constraint is: the parameter change in adjacent detection cycles ≤ 5% of the initial parameter. Taking the virtual inertia of a virtual synchronous generator as an example, the correction rate constraint for the virtual inertia of the virtual synchronous generator is expressed as follows: The same applies to the other parameters, ensuring a smooth and dynamic transition of the system.

[0044] For any parameter among the virtual inertia, droop damping of the virtual synchronous generator and the equivalent virtual inertia and equivalent damping of the grid converter, if the parameter after correction in the current detection cycle is not less than the parameter after correction in the previous detection cycle, take the minimum value among the difference between the parameter after correction in the current detection cycle and the parameter after correction in the previous detection cycle, the upper limit of the correction rate, the upper limit of the corresponding parameter, and the difference between the parameter after correction in the current detection cycle, and add the parameter after correction in the previous detection cycle to obtain the corrected parameter after verification. If the corrected parameter of the current detection cycle is less than the corrected parameter of the previous detection cycle, take the maximum value among the difference between the corrected parameter of the current detection cycle and the previous detection cycle, the lower limit of the correction rate, the lower limit of the corresponding parameter, and the difference between the corrected parameter of the current detection cycle, and add the corrected parameter of the previous detection cycle to obtain the corrected parameter after verification. Taking the virtual inertia of a virtual synchronous generator as an example, the verified virtual inertia is expressed as follows: ; In the formula, The virtual inertia difference between adjacent detection cycles; This is the corrected virtual inertia of the virtual synchronous generator after verification in the (k+1)th detection cycle.

[0045] Example 2 Embodiment 2 of the present invention applies a method for eliminating cyclic power in a grid-connected heterogeneous system to a grid-connected heterogeneous system; wherein, the grid-connected hybrid system includes one grid-connected VSG and one grid-connected GFL, connected in parallel to the point of common coupling (PCC), jointly supplying power to a resistive-inductive load, the system rated voltage is 380V, the rated frequency is 50Hz, the VSG capacity is 100kW, the GFL capacity is 50kW, and the line impedance is... , VSG output impedance GFL output impedance The specific steps and procedures include: S1. Establish small-signal models for the grid-type virtual synchronous generator and the grid-type converter respectively. Based on the small-signal models, solve the active and reactive power deviation transmission equations of the two, substitute them into the load power balance equation, and obtain the active power decomposition formula. Then decompose the output active power into load distribution component and circulating power component.

[0046] S1.1: Establish the rotor motion equations of the virtual synchronous generator under predefined disturbances and the proportional equations of voltage amplitude deviation and reactive power deviation, and determine the small-signal model of the grid-type virtual synchronous generator (VSG): Setting the virtual inertia of VSG droop damping Virtual impedance Then the total equivalent impedance on the VSG side ; Rotor motion equations: , transform into .

[0047] S1.2 Establish the phase-locked loop model, current loop model, and voltage loop model of the grid-connected converter under predefined disturbances, and determine the small-signal model of the grid-connected converter GFL: Setting PLL proportional gain Integral gain Current loop bandwidth Virtual impedance Then the total equivalent impedance on the GFL side ; PLL small-signal transfer function: ; Current loop transfer function: .

[0048] S1.3 Establish the active and reactive power deviation transmission equations for the grid-type virtual synchronous generator and the grid-type converter respectively; substitute the active power deviation transmission equations into the load power balance equations to decompose the load distribution component and the circulating power component. Given the output voltage amplitudes and steady-state power angles of the VSG and GFL, the active power deviation transmission equation for the VSG is as follows: ; GFL active power deviation transmission equation: ; Will Substituting into the power decomposition equation, we get: ; The calculated load distribution ratio is as follows: , The capacity ratio of VSG and GFL is mismatched, and the dynamic inertia of VSG differs greatly from that of GFL PLL, resulting in significant circulating power.

[0049] S2. Based on the set impedance and damping matching rules, and combined with the predefined initial droop damping of the virtual synchronous generator, determine the initial equivalent damping of the grid converter; based on the set dynamic characteristic synchronization rules, and combined with the predefined initial virtual inertia of the virtual synchronous generator, determine the initial equivalent virtual inertia of the grid converter.

[0050] Impedance and damping matching rules: According to Substitute , , Calculations yielded ; Dynamic characteristic synchronization rules: based on Substitute , , Calculations yielded .

[0051] S3. Real-time acquisition of the output active power and load active power of the grid-type virtual synchronous generator and the grid-connected converter, determination of the corresponding small-signal deviation, and substitution into the active power decomposition formula to obtain the cyclic power component; in any detection period, based on the corresponding cyclic power component and combined with the output active power, calculate the corresponding correction coefficient; based on the correction coefficient, combined with the dynamic characteristic synchronization rule and impedance and damping matching rule, correct the virtual inertia and droop damping of the grid-type virtual synchronous generator and the equivalent virtual inertia and equivalent damping of the grid-connected converter; verify the corrected parameters through predefined constraints.

[0052] Real-time cyclic power detection: The detection cycle is set to 0.02s. Real-time acquisition of the output active power of the grid-connected virtual synchronous generator (VSG) and the grid-connected converter (GFL), as well as the load active power, is used to determine... , , ,calculate The correction factor is ; Initial correction parameters: , , , ; , ; Assuming that within a certain detection period, real-time detection results are obtained... , , ,calculate ; ; Dynamic correction calculation: (satisfy (constraints and correction rate constraints). (satisfy (constraints and correction rate constraints). (satisfy (constraints and correction rate constraints). (satisfy (constraints and correction rate constraints). After the parameters are updated, the next detection cycle will detect... , The circulating power is significantly reduced, achieving dynamic suppression; if a sudden load change occurs, the correction system can respond quickly and maintain the circulating power within a very small range by adjusting parameters to ensure stable system operation.

[0053] Example 3 Embodiment 2 of the present invention provides a cyclic power cancellation system for a grid-connected hybrid system, which implements the cyclic power cancellation method for a grid-connected hybrid system of Embodiment 1, including: The grid-connected hybrid system construction module establishes small-signal models for the grid-connected virtual synchronous generator and the grid-connected converter respectively. Based on the small-signal models, the active and reactive power deviation transmission equations of the two are combined and substituted into the load power balance equation for solution to obtain the active power decomposition formula. The output active power is decomposed into load distribution component and circulating power component. The initial control parameter determination module determines the initial equivalent damping of the grid converter based on the set impedance and damping matching rules and the predefined initial droop damping of the virtual synchronous generator; and determines the initial equivalent virtual inertia of the grid converter based on the set dynamic characteristic synchronization rules and the predefined initial virtual inertia of the virtual synchronous generator. The cyclic power elimination module collects the output active power and load active power of the grid-type virtual synchronous generator and the grid-connected converter in real time, determines the corresponding small signal deviation, and substitutes it into the active power decomposition formula to obtain the cyclic power component. In any detection period, based on the corresponding cyclic power component and combined with the output active power, the corresponding correction coefficient is calculated. Based on the correction coefficient, combined with the dynamic characteristic synchronization rule and impedance and damping matching rule, the virtual inertia and droop damping of the grid-type virtual synchronous generator, as well as the equivalent virtual inertia and equivalent damping of the grid-connected converter, are corrected. The corrected parameters are verified through predefined constraints.

[0054] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0055] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0056] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0057] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0058] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for eliminating cyclic power in a grid-connected hybrid system, characterized in that, include: S1. Establish small-signal models for the grid-type virtual synchronous generator and the grid-connected converter, respectively; Based on the small-signal model, the active and reactive power deviation transmission equations of the two are combined and substituted into the load power balance equation for solution to obtain the active power decomposition formula. The output active power is then decomposed into load distribution component and circulating power component. S2. Based on the set impedance and damping matching rules, and combined with the predefined initial droop damping of the virtual synchronous generator, determine the initial equivalent damping of the grid converter; based on the set dynamic characteristic synchronization rules, and combined with the predefined initial virtual inertia of the virtual synchronous generator, determine the initial equivalent virtual inertia of the grid converter. S3. Real-time acquisition of the output active power and load active power of the grid-type virtual synchronous generator and the grid-connected converter, determination of the corresponding small-signal deviation, and substitution into the active power decomposition formula to obtain the cyclic power component; in any detection period, based on the corresponding cyclic power component and combined with the output active power, calculate the corresponding correction coefficient; based on the correction coefficient, combined with the dynamic characteristic synchronization rule and impedance and damping matching rule, correct the virtual inertia and droop damping of the grid-type virtual synchronous generator and the equivalent virtual inertia and equivalent damping of the grid-connected converter; verify the corrected parameters through predefined constraints.

2. The method for eliminating cyclic power in a grid-connected hybrid system according to claim 1, characterized in that: In S1, the rotor motion equation of the virtual synchronous generator under predefined disturbances and the proportional equation of voltage amplitude deviation and reactive power deviation are established to determine the small-signal model of the grid-type virtual synchronous generator. Establish phase-locked loop, current loop and voltage loop models of the grid-connected converter under predefined disturbances, and determine the small-signal model of the grid-connected converter. The active and reactive power deviation transmission equations are established for the grid-type virtual synchronous generator and the grid-type converter, respectively. The active power deviation transmission equations are substituted into the load power balance equations to decompose the load distribution component and the circulating power component.

3. The method for eliminating cyclic power in a grid-connected hybrid system according to claim 2, characterized in that: The process of establishing the active and reactive power deviation transmission equations is as follows: Near the steady-state operating point, a first-order Taylor expansion is performed on the grid-connected power equation. When only the influence of power angle fluctuations on active power and voltage amplitude fluctuations on reactive power are considered, the first-order Taylor expansion is approximated as the small-signal deviations of active and reactive power. The output voltage amplitude of the grid-connected virtual synchronous generator is multiplied by the voltage amplitude at the point of common coupling and the cosine of the steady-state power angle as the numerator, and the total equivalent inductive impedance on the grid-connected virtual synchronous generator side is used as the denominator to obtain the corresponding active power coefficient. The output voltage amplitude of the grid-connected virtual synchronous generator is multiplied by the voltage amplitude at the point of common coupling and the sine of the steady-state power angle as the numerator, and the total equivalent inductive impedance is used as the denominator to obtain the corresponding reactive power coefficient. The small-signal deviation of active power is converted into the product of the active power coefficient and the small-signal deviation of the power angle of the grid-connected virtual synchronous generator, and the small-signal deviation of reactive power is converted into the product of the reactive power coefficient and the small-signal deviation of the output voltage amplitude of the grid-connected virtual synchronous generator, thus obtaining the active and reactive power deviation transmission equations of the grid-connected virtual synchronous generator. Using the same method, the power deviation transmission equation of the grid converter is determined.

4. The method for eliminating cyclic power in a grid-connected hybrid system according to claim 3, characterized in that: The process of determining the load distribution component and the cyclic power component is as follows: For grid-connected virtual synchronous generators and grid-connected converters, the corresponding active power coefficient is used as the numerator, the active power coefficients of the grid-connected virtual synchronous generator and the grid-connected converter are added together as the denominator, and the ratio of the numerator to the denominator is multiplied by the small-signal deviation of the load active power to obtain the corresponding load distribution component. The numerator is the product of the active power coefficients of the grid-type virtual synchronous generator and the grid-type converter. The denominator is the sum of the active power coefficients of the two generators. The ratio of the numerator to the denominator is multiplied by the difference in the small-signal deviation of the power angle between the grid-type virtual synchronous generator and the grid-type converter. This value is the cyclic power component of the grid-type virtual synchronous generator. The negative of the cyclic power component of the grid-type virtual synchronous generator is the cyclic power component of the grid-type converter.

5. The method for eliminating cyclic power in a grid-connected hybrid system according to claim 1, characterized in that: The process of determining the initial equivalent virtual inertia of the grid converter in S2 is as follows: Based on the impedance and damping matching rule, the ratio of the total equivalent inductive impedance of the virtual synchronous generator to the total equivalent inductive impedance of the grid converter is multiplied by the predefined initial droop damping of the virtual synchronous generator, and used as the initial equivalent damping of the grid converter. Based on the dynamic characteristic synchronization rule, the ratio of the initial equivalent damping of the grid converter to the droop damping of the virtual synchronous generator is multiplied by the predefined initial virtual inertia of the virtual synchronous generator, and this ratio is used as the initial equivalent virtual inertia of the grid converter.

6. The method for eliminating cyclic power in a grid-connected hybrid system according to claim 1, characterized in that: The process of calculating the correction factor in S3 is as follows: The active power output of the grid-type virtual synchronous generator and the grid-type converter, and the active power of the load are collected. The corresponding steady-state operating point power is then subtracted to obtain the corresponding small signal deviation. This deviation is then substituted into the active power decomposition formula in S1 to obtain the cyclic power components of the grid-type virtual synchronous generator and the grid-type converter. In any detection period, the absolute value of the cyclic power component is used as the numerator, and the active power outputs of the collected grid-type virtual synchronous generator and grid-type converter are added together as the denominator to obtain the correction coefficient.

7. The method for eliminating cyclic power in a grid-connected hybrid system according to claim 1, characterized in that: The process of correcting the virtual inertia of the grid-type virtual synchronous generator and the equivalent virtual inertia of the grid-type converter in S3 is as follows: Based on the dynamic characteristic synchronization rule and the influence of cyclic power on VSG inertia, a correction formula is derived. The ratio of the total equivalent inductive impedance of the virtual synchronous generator to the sum of the total equivalent inductive impedance of the virtual synchronous generator and the grid-connected converter is calculated and multiplied by the small-signal deviation of the load active power to obtain the small-signal deviation of the rated output active power of the virtual synchronous generator. In any detection period, the ratio of the cyclic power component of the corresponding grid-connected virtual synchronous generator to the small-signal deviation of the rated output active power is multiplied by the correction coefficient of the corresponding detection period to obtain the corresponding correction term. After subtracting the correction term from 1, the result is multiplied by the corresponding initial virtual inertia to obtain the corrected virtual inertia of the virtual synchronous generator for the corresponding detection period. Multiply the ratio of the corrected equivalent damping to the droop damping by the corrected virtual inertia of the virtual synchronous generator to obtain the equivalent virtual inertia of the grid-type converter after the corresponding detection period correction.

8. The method for eliminating cyclic power in a grid-connected hybrid system according to claim 1, characterized in that: The process of correcting the droop damping of the grid-type virtual synchronous generator and the equivalent damping of the grid-type converter in S3 is as follows: Based on the impedance and damping matching rules, and combined with the inherent relationship between cyclic power and damping coefficient, the correction formula is derived. In any detection period, the ratio of the total equivalent inductive impedance on the virtual synchronous generator side to the total equivalent inductive impedance on the grid converter side is multiplied by the correction coefficient of the corresponding detection period, which is used as the correction term for droop damping. Add the droop damping correction term to 1 and multiply it by the initial droop damping of the virtual synchronous generator to obtain the droop damping after the corresponding detection period correction. Multiply the ratio of the total equivalent inductive impedance on the virtual synchronous generator side to the total equivalent inductive impedance on the grid converter side by the droop damping corrected for the corresponding detection period to obtain the equivalent damping of the grid converter after the corresponding detection period correction.

9. The method for eliminating cyclic power in a grid-connected hybrid system according to claim 1, characterized in that: The process of verifying the corrected parameters in S3 is as follows: For any parameter among the virtual inertia, droop damping of the virtual synchronous generator and the equivalent virtual inertia and equivalent damping of the grid converter, if the parameter after correction in the current detection cycle is not less than the parameter after correction in the previous detection cycle, take the minimum value among the difference between the parameter after correction in the current detection cycle and the parameter after correction in the previous detection cycle, the upper limit of the correction rate, the upper limit of the corresponding parameter, and the difference between the parameter after correction in the current detection cycle, and add the parameter after correction in the previous detection cycle to obtain the corrected parameter after verification. If the corrected parameter for the current detection cycle is less than the corrected parameter for the previous detection cycle, take the maximum value among the difference between the corrected parameter for the current detection cycle and the corrected parameter for the previous detection cycle, the lower limit of the correction rate, the lower limit of the corresponding parameter, and the difference between the corrected parameter for the current detection cycle, and add the corrected parameter for the previous detection cycle to obtain the corrected parameter after verification.

10. A network-in-network hybrid system cyclic power cancellation system using the method of any one of claims 1-9. include: The module for constructing a grid-connected hybrid system establishes small-signal models for both the grid-connected virtual synchronous generator and the grid-connected converter. Based on the small-signal model, the active and reactive power deviation transmission equations of the two are combined and substituted into the load power balance equation for solution to obtain the active power decomposition formula. The output active power is then decomposed into load distribution component and circulating power component. The initial control parameter determination module determines the initial equivalent damping of the grid converter based on the set impedance and damping matching rules and the predefined initial droop damping of the virtual synchronous generator; and determines the initial equivalent virtual inertia of the grid converter based on the set dynamic characteristic synchronization rules and the predefined initial virtual inertia of the virtual synchronous generator. The cyclic power elimination module collects the output active power and load active power of the grid-type virtual synchronous generator and the grid-connected converter in real time, determines the corresponding small signal deviation, and substitutes it into the active power decomposition formula to obtain the cyclic power component. In any detection period, based on the corresponding cyclic power component and combined with the output active power, the corresponding correction coefficient is calculated. Based on the correction coefficient, combined with the dynamic characteristic synchronization rule and impedance and damping matching rule, the virtual inertia and droop damping of the grid-type virtual synchronous generator, as well as the equivalent virtual inertia and equivalent damping of the grid-connected converter, are corrected. The corrected parameters are verified through predefined constraints.

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