Virtual synchronous generator grid-connected control method and system based on transient energy flow

Abstract

The present invention discloses a virtual synchronous generator grid-connected control method and system based on transient energy flow, which relates to the technical field of power electronic inverter grid-connected control. The key points of the technical solution are: linearizing the inverter VSG control system using a small signal analysis method to construct a VSG small signal model; analyzing the transfer function between the inverter active power and the grid-connected side voltage phase oscillation according to the VSG small signal model, and determining the phase-frequency characteristics of the transfer function; calculating the phase difference between the inverter active power and the grid-connected side voltage phase oscillation according to the phase-frequency characteristics; when the phase difference is not less than a set threshold, correcting the virtual moment of inertia and virtual damping coefficient in the active link control parameters until the phase difference is less than the set threshold. The present invention can analyze the transmission of the system transient energy flow and adjust the VSG control parameters to improve the low-frequency oscillation suppression capability of the inverter grid-connected system.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic inverter grid-connected control, and more specifically, to a virtual synchronous generator grid-connected control method and system based on transient energy flow. Background Art

[0002] With the increasing application of renewable energy and energy storage systems, the installed capacity of distributed power generation has grown rapidly. Power electronic inverters are widely used in distributed power generation. Power electronic inverters with traditional control strategies focus on the control of power generation and power quality, and have the characteristics of fast response speed and low inertia. This makes the stability problem of the system more complicated. Since synchronous generators have the advantage of being naturally friendly to the power grid, some scholars have proposed virtual synchronous generator (VSG) technology based on the operation experience of traditional power systems, which can enable grid-connected inverters to simulate the operation mechanism of synchronous generators. Specifically, by simulating the main body model, active frequency regulation and reactive voltage regulation of synchronous generators, the grid-connected inverter can be comparable to traditional synchronous generators in terms of operation mechanism and external characteristics. Virtual synchronous generator technology enables inverters to simulate the operation mechanism of synchronous generators and is conducive to improving the stability of power systems, so it has broad application prospects. However, while simulating the rotor motion equation, VSG also inherits the characteristic of easy oscillation of the shaft system in synchronous generators. However, if the function of VSG actively participating in system oscillation suppression can be superimposed, oscillation suppression of the distributed power system can be achieved, which is beneficial to the stable operation of the power system.

[0003] At present, some scholars have proposed strategies for power electronic equipment to participate in system oscillation suppression. For example, let the inverter periodically measure the system impedance online, use the gain adaptive adjustment table to determine the controller parameters according to the measurement results to improve the stability of the system, or modify certain parameters of the controller online according to the measured oscillation trajectory. However, in these studies, both the adaptive adjustment table and the strategy of modifying controller parameters are often empirical in nature, and the effectiveness of the control strategy is only verified by simulation, while the analysis of the oscillation suppression mechanism still needs to be deepened. In recent years, methods based on port energy functions have been widely used in the study of transient stability of traditional large power grids. As an oscillation analysis method, the port energy function method can be used to evaluate the damping characteristics of components, locate negatively damped generators, and the location of external periodic disturbances.

[0004] Based on this, it is an urgent problem to study and design a virtual synchronous generator grid-connected control method and system based on transient energy flow that can overcome the above-mentioned defects. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the purpose of the present invention is to provide a virtual synchronous generator grid-connected control method and system based on transient energy flow. According to the conversion and transmission of energy in the transient process of the inverter grid-connected system, additional parameter adjustments are made to suppress the low-frequency oscillations generated in the system to adapt to the operation control of the inverter in an environment with a high proportion of renewable energy grid-connected.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] In a first aspect, a virtual synchronous generator grid-connected control method based on transient energy flow is provided, comprising the following steps:

[0008] The inverter VSG control system is linearized using the small signal analysis method, and the VSG small signal model is constructed;

[0009] The transfer function between the inverter active power and the grid-connected voltage phase oscillation is analyzed based on the VSG small signal model to determine the phase-frequency characteristics of the transfer function.

[0010] The phase difference between the inverter active power and the grid-connected side voltage phase oscillation is calculated based on the phase-frequency characteristics;

[0011] When the phase difference is not less than the set threshold, the virtual moment of inertia and the virtual damping coefficient in the active link control parameters are corrected until the phase difference is less than the set threshold.

[0012] Furthermore, the specific process of the linearization processing of the inverter VSG control system is as follows:

[0013] Calculate the output active power of the inverter;

[0014] Calculate the virtual angular frequency of the inverter and the phase angle of the modulation wave;

[0015] According to the phase relationship between different voltages in the rotating coordinate system, the phase difference power angle between the inverter modulation signal and the bus voltage is determined;

[0016] According to the output active power of the inverter, the virtual angular frequency of the inverter, the phase angle of the modulation wave and the phase difference power angle, linear processing is performed to obtain the VSG small signal model.

[0017] Furthermore, the calculation formula of the phase difference power angle is specifically:

[0018]

[0019] Wherein, δ represents the phase difference angle between the inverter modulation signal and the bus voltage; Indicates the phase of the inverter modulation signal; α indicates the phase of the bus voltage; ω0 indicates the angular frequency reference value; ω gIndicates the per-unit value of the grid angular frequency; V pcc Indicates the bus voltage amplitude; V pcc,d 、V pcc,q are the components of the bus voltage on the dq axis respectively.

[0020] Furthermore, the calculation formula of the VSG small signal model is specifically:

[0021]

[0022] Where, s represents the Laplace operator; Δ represents the change of the corresponding character; ω represents the virtual angular frequency of the inverter; m represents the active droop coefficient; J represents the virtual moment of inertia of the inverter; P represents the output active power of the inverter; K d represents the virtual damping coefficient of the inverter; δ represents the phase difference angle between the inverter modulation signal and the bus voltage; ω g represents the per-unit value of the grid angular frequency; c1 represents the model parameter.

[0023] Furthermore, the calculation formula of the transfer function is specifically:

[0024]

[0025] Wherein, Φ(s) represents the transfer function; α represents the phase of the bus voltage.

[0026] Furthermore, the process of determining the phase-frequency characteristic of the transfer function is specifically as follows:

[0027]

[0028]

[0029] Wherein, j represents the imaginary unit; A represents the real part of the standard complex form; and B represents the imaginary part of the standard complex form.

[0030] Furthermore, the calculation formula of the phase difference between the inverter active power and the grid-connected side voltage phase oscillation is specifically as follows:

[0031]

[0032] Where Δθ represents the phase difference between the inverter active power and the grid-connected voltage phase oscillation.

[0033] Furthermore, the calculation formula of the model parameters is specifically:

[0034] c1=a1[-i d0 R a +u d0 -i q0 L f ]+b1[id0 L f -i q0 R a +u q0 ]

[0035] Where a1 represents the first parameter; b1 represents the second parameter; i d0 ,i q0 ,u d0 ,u q0 are the dq components of the inverter output current and voltage at the machine end in the steady state before the disturbance; R a Indicates the resistance of the filter.

[0036] Furthermore, the calculation formulas of the first parameter and the second parameter are specifically:

[0037]

[0038] Among them, δ0 represents the inverter modulation signal in the steady state before the disturbance With bus voltage V pcc The phase difference between ∠α and V pcc0 is the voltage on the grid side in the steady state before the disturbance; R a , L f Respectively represent the resistance and inductance of the filter; R E , L E They represent the resistance and inductance of the line respectively; ω0 is the angular frequency reference value.

[0039] In a second aspect, a virtual synchronous generator grid-connected control system based on transient energy flow is provided, comprising the following steps:

[0040] A model building module is used to linearize the inverter VSG control system using a small signal analysis method and build a VSG small signal model;

[0041] Function analysis module, used to analyze the transfer function between the inverter active power and the grid-connected side voltage phase oscillation according to the VSG small signal model, and determine the phase-frequency characteristics of the transfer function;

[0042] A phase calculation module, used to calculate the phase difference between the inverter active power and the grid-connected side voltage phase oscillation according to the phase-frequency characteristic;

[0043] The parameter correction module is used to correct the virtual moment of inertia and virtual damping coefficient in the active link control parameters when the phase difference is not less than the set threshold value, until the phase difference is less than the set threshold value.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The virtual synchronous generator grid-connected control method based on transient energy flow proposed in the present invention applies the port energy function to VSG, derives the calculation method of VSG port energy function and analyzes the internal mechanism of VSG suppressing low-frequency oscillation of the power system. It can analyze the transmission situation of the system transient energy flow and adjust the VSG control parameters to improve the low-frequency oscillation suppression capability of the inverter grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0047] Figure 1 is the main circuit topology structure of the inverter controller in the embodiment of the present invention;

[0048] Figure 2 is a control block diagram of an inverter controller in an embodiment of the present invention;

[0049] Figure 3 is a schematic diagram of the phase relationship between voltages on the phase plane in an embodiment of the present invention;

[0050] Figure 4 It is a small signal control block diagram of the active link of VSG control in an embodiment of the present invention;

[0051] Figure 5 is a phase-frequency characteristic curve diagram under initial parameters in an embodiment of the present invention;

[0052] Figure 6 is a phase-frequency characteristic curve diagram under adjusted parameters in an embodiment of the present invention;

[0053] Figure 7 It is a comparison diagram of the low-frequency oscillation suppression effect of the system before and after parameter adjustment in the embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0055] Embodiment 1: Virtual synchronous generator grid-connected control method based on transient energy flow

[0056] Figure 1The inverter grid-connected circuit topology with the additional VSG control strategy proposed in the present invention includes a power circuit part and a controller part. The power circuit part includes a DC side, an inverter, an LC filter, a transmission line and a grid-connected side. The controller part mainly generates and outputs a control signal based on the control strategy calculated by the input of voltage and current measurement, which is used for the drive circuit to control the on and off of the power electronic device.

[0057] like Figure 2 As shown, the present invention proposes a virtual synchronous generator grid-connected control strategy based on transient energy flow, which includes a power terminal voltage calculation module, a reactive link modulation voltage amplitude calculation module, an active link parameter adjustment module based on transient energy flow, and a PWM modulation module.

[0058] Among them, the power terminal voltage calculation module is mainly used to calculate the output active power, reactive power and terminal voltage amplitude of the inverter. First, measure the three-phase voltage of the inverter end LC filter a 、e b 、e c and three-phase current i a 、i b 、i c , the original three-phase voltage and three-phase current are transformed to the dq axis of the synchronous rotating coordinate system through dq decomposition, and the dq axis components of the voltage and current are obtained as u d 、u q and i d 、i q .

[0059] The calculation formula of the output active and reactive power and terminal voltage effective value calculation module is as follows:

[0060]

[0061] Among them, P is the active power output by the inverter, Q is the reactive power output by the inverter, and E t is the voltage amplitude at the inverter terminal.

[0062] The reactive link modulation voltage amplitude calculation module is used to calculate the modulation voltage amplitude Uq, and the calculation formula is:

[0063] U q =∫K e [(E * -E t )-n(QQ * )]dt

[0064] In the formula, E * is the set value of the inverter terminal voltage; Q * is the setting value of the inverter reactive power; K eis the amplification gain; n is the droop coefficient of the reactive voltage link; U q is the q-axis component of the inverter modulation wave signal, and the 0-axis and d-axis components of the modulation wave signal are both 0.

[0065] The parameter adjustment module of the active link based on transient energy flow is used to calculate the virtual angular frequency ω of the inverter and the phase φ of the modulation wave. The calculation formula is as follows:

[0066]

[0067] Where J is the virtual moment of inertia of the inverter; m is the active droop coefficient; P * K is the set value of the inverter output active power; d is the virtual damping coefficient of the inverter; is the inverter modulation wave phase; ω0 is the angular frequency reference value.

[0068] The analysis of transient energy flow is mainly based on the above active link. According to the definition of energy function, the transient energy flow W out of the inverter port is port The calculation formula is as follows:

[0069]

[0070] In the formula, E t,s and θ s is the steady-state value of the voltage amplitude and phase at the inverter output, E t and θ are the current output voltage amplitude and phase value of the inverter, △P and △Q represent the increment of active power and reactive power in the transient process. It should be pointed out that the analysis of transient energy flow in the present invention does not take into account the reactive link of VSG, and the above formula can be simplified as follows:

[0071]

[0072] According to the above formula, it can be deduced that if △ω θ The oscillation change of △P shows a phase opposite law, that is, the phase difference between the two is 180°, which can ensure that W port is negative, indicating that the transient energy flow of the inverter is from the grid side to the inverter port, that is, the inverter absorbs energy. From the energy point of view, this will be beneficial to the stability of the system and can have a positive effect on VSG to suppress low-frequency oscillation of the power system. θ The phase difference between the two is 90°, so if △ω θ If the phase difference between △P and the terminal voltage is 180°, the phase difference between △P and the terminal voltage phase change △θ must be 90°.

[0073] Therefore, the steps of the VSG active link parameter adjustment strategy based on transient energy flow are as follows:

[0074] Firstly, the inverter VSG control system is linearized by small signal analysis method to build the VSG small signal model. In the process of construction, the VSG reactive link is not taken into account, so the change of inverter output voltage and the voltage change on the grid side are ignored.

[0075] according to Figure 1 The topology of the grid-connected inverter is obtained, and the steady-state model of the LC filter and the system impedance is:

[0076]

[0077] In the formula, u dq =[u d u q ] is the inverter output voltage E t The dq axis component of i dq =[i d i q ] is the dq axis component of the inverter output current i; U dq =[U d U q ] is the dq axis component of the inverter modulation signal U, where the dq reference coordinate axis is the inverter modulation wave angular frequency ω and phase For reference; R a , L f , C f are the resistance, inductance and capacitance of the filter; the line impedance is determined by the resistance R E and inductor L E Composition; V pccdq is the voltage dq-axis component connected to the grid end, and ω0 is the virtual angular frequency reference value.

[0078] Figure 3 The phase relationship between different voltages in the rotating coordinate system is given.

[0079] Define the inverter modulation signal U∠φ and bus voltage V pcc The phase difference between ∠α and the power angle δ is:

[0080]

[0081] In the formula, ω g is the per unit value of the grid angular frequency.

[0082] Eliminate e according to the steady-state model dq Get dq Substitute the expression into the phase difference power angle calculation formula and ignore the changes in the inverter output voltage and bus voltage. Then linearize it and get:

[0083]

[0084] In the formula, the expressions of parameters a1 and b1 are:

[0085]

[0086] Where δ0 is the inverter modulation signal in the steady state before the disturbance The phase difference between the bus voltage Vpcc∠α and the power angle.

[0087] Calculate the output active power, the virtual angular frequency ω of the inverter and the phase of the modulation wave The calculation and phase difference power angle calculation are linearized to obtain the VSG small signal model:

[0088]

[0089] Where s is the Laplace operator; the expression of parameter c1 is:

[0090] c1=a1[-i d0 R a +u d0 -i q0 L f ]+b1[i d0 L f -i q0 R a +u q0 ].

[0091] The small signal block diagram of the VSG control active link is as follows: Figure 4 shown.

[0092] Then, the transfer function between active power and terminal voltage phase oscillation is derived through the small signal model. Since the grid-connected voltage phase is basically the same as the inverter terminal voltage phase change, the transfer function between the inverter active power and the grid-connected voltage phase oscillation can be derived here, as shown below:

[0093]

[0094] Let s = jω, and analyze the phase-frequency characteristics of the above transfer function, we get:

[0095]

[0096] Among them, parameters A and B are as follows:

[0097]

[0098] According to the phase-frequency characteristics, the phase difference △θ between the inverter active power and the grid-connected voltage phase oscillation can be expressed as:

[0099]

[0100] Definition error △θ e is the difference between △θ and 90°. In the low-frequency oscillation frequency range, i.e. 0.1 to 2.5 Hz, take a frequency value every 0.2 Hz. Find the △θ corresponding to these 13 frequency values. e And sum it up, denoted as θ S This strategy requires θ S Set the threshold to θ c In this embodiment, θ c =360°, so θ needs to be satisfied S <360°. Therefore, the virtual moment of inertia J and virtual damping coefficient K in the active link control parameters are selected. d As the adjustment object, a set of initial parameters J0 and K are set d0 According to the above process, the phase difference θ between the inverter active power and the grid-connected voltage phase oscillation is calculated. S If the threshold condition is not met, then J0 and K d0 Make some corrections to △J and △K d , repeat the above steps after correction until a set of S The optimal parameters of the threshold conditions are used as the final VSG active link control parameters.

[0101] The PWM modulation module is used to obtain the modulation voltage signal u after the calculation results of the reactive link modulation voltage amplitude and the active link phase calculation results are dq inversely transformed. a 、u b 、u c , and then generate a PWM control signal according to the PWM algorithm to drive the three-phase inverter bridge to achieve the inverter function.

[0102] As an example, the following provides specific parameters of an inverter controller that participates in the suppression of low-frequency oscillations in a power system. The rated voltage of the three-phase inverter is 380V, the rated frequency is 50Hz, and the rated power is 50kW. Correspondingly, the rated voltage U dc =600V. The power electronic device of the three-phase full-bridge inverter circuit is IGBT (Insulated Gate Bipolar Transistor), model is Infineon F150R12RT4. The PWM carrier frequency is 10kHz. The inductance L of the LC filter is 2.8mH and the capacitance is 40μF.

[0103] The parameters in the inverter controller are set to E*=1.05 and P*=4.431, both of which are per unit values. n =314.15927rad / s, the control parameters of the virtual synchronous generator active link are selected as m=0.01. The initial virtual moment of inertia J0=20, the initial virtual damping coefficient K d0 =9.5, the calculated phase-frequency characteristic curve is as follows Figure 5 After the active link parameter adjustment module is adjusted and optimized, the final virtual moment of inertia J = 0.05, the virtual damping coefficient K d =1, the calculated phase-frequency characteristic curve is as follows Figure 6 Observation Figure 6 The corresponding θ under this set of control parameters can be calculated S =354.3°, fully satisfying θ S <360° threshold condition.

[0104] The simulation experiment tests the suppression effect of the system low-frequency oscillation before and after parameter adjustment. The results are as follows: Figure 7 It can be seen that under the VSG control parameters adjusted based on the transient energy flow, the inverter grid-connected system achieves a better low-frequency oscillation suppression effect.

[0105] Embodiment 2: A virtual synchronous generator grid-connected control system based on transient energy flow comprises the following steps: a model building module, a function analysis module, a phase calculation module and a parameter correction module.

[0106] Among them, the model construction module is used to linearize the inverter VSG control system using the small signal analysis method to construct a VSG small signal model; the function analysis module is used to analyze the transfer function between the inverter active power and the grid-connected voltage phase oscillation according to the VSG small signal model, and determine the phase-frequency characteristics of the transfer function; the phase calculation module is used to calculate the phase difference between the inverter active power and the grid-connected voltage phase oscillation according to the phase-frequency characteristics; the parameter correction module is used to correct the virtual moment of inertia and virtual damping coefficient in the active link control parameters when the phase difference is not less than the set threshold until the phase difference is less than the set threshold.

[0107] Working principle: The virtual synchronous generator grid-connected control method based on transient energy flow proposed in the present invention applies the port energy function to VSG, derives the calculation method of VSG port energy function and analyzes the internal mechanism of VSG suppressing low-frequency oscillation of power system. It can analyze the transmission situation of transient energy flow in the system and adjust VSG control parameters to improve the low-frequency oscillation suppression capability of the inverter grid-connected system.

[0108] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0109] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0110] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0111] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0112] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A virtual synchronous generator grid-connected control method based on transient energy flow, characterized in that: The following steps are involved: The inverter VSG control system is linearized using the small signal analysis method, and the VSG small signal model is constructed; The transfer function between the inverter active power and the grid-connected voltage phase oscillation is analyzed based on the VSG small signal model to determine the phase-frequency characteristics of the transfer function. The phase difference between the inverter active power and the grid-connected side voltage phase oscillation is calculated based on the phase-frequency characteristics; When the phase difference is not less than the set threshold, the virtual moment of inertia and virtual damping coefficient in the active link control parameters are corrected until the phase difference is less than the set threshold; The calculation formula of the VSG small signal model is specifically: Where, s represents the Laplace operator; Δ represents the change of the corresponding character; ω represents the virtual angular frequency of the inverter; m represents the active droop coefficient; J represents the virtual moment of inertia of the inverter; P represents the output active power of the inverter; K d represents the virtual damping coefficient of the inverter; δ represents the phase difference angle between the inverter modulation signal and the bus voltage; ω g represents the per-unit value of the grid angular frequency; c1 represents the model parameter; The calculation formula of the transfer function is specifically: Wherein, Φ(s) represents the transfer function; α represents the phase of the bus voltage; and ω0 represents the angular frequency reference value.

2. The method for controlling a virtual synchronous generator connected to the grid based on transient energy flow according to claim 1 is characterized in that: The specific process of linearization of the inverter VSG control system is as follows: Calculate the output active power of the inverter; Calculate the virtual angular frequency of the inverter and the phase angle of the modulation wave; According to the phase relationship between different voltages in the rotating coordinate system, the phase difference power angle between the inverter modulation signal and the bus voltage is determined; According to the output active power of the inverter, the virtual angular frequency of the inverter, the phase angle of the modulation wave and the phase difference power angle, linear processing is performed to obtain the VSG small signal model.

3. The method for controlling the virtual synchronous generator grid connection based on transient energy flow according to claim 2 is characterized in that: The calculation formula of the phase difference power angle is specifically: Wherein, δ represents the phase difference angle between the inverter modulation signal and the bus voltage; Indicates the phase of the inverter modulation signal; α indicates the phase of the bus voltage; ω g Indicates the per-unit value of the grid angular frequency; V pcc Indicates the bus voltage amplitude; V pcc,d 、V pcc,q are the components of the bus voltage on the dq axis respectively.

4. The method for controlling a virtual synchronous generator connected to the grid based on transient energy flow according to claim 1 is characterized in that: The process of determining the phase-frequency characteristic of the transfer function is specifically as follows: Wherein, j represents the imaginary unit; A represents the real part of the standard complex form; and B represents the imaginary part of the standard complex form.

5. The method for controlling the virtual synchronous generator grid connection based on transient energy flow according to claim 4 is characterized in that: The calculation formula of the phase difference between the inverter active power and the grid-connected side voltage phase oscillation is specifically: Where △θ represents the phase difference between the inverter active power and the grid-connected voltage phase oscillation.

6. The method for controlling the virtual synchronous generator grid connection based on transient energy flow according to claim 1 is characterized in that: The calculation formula of the model parameters is specifically: c1=a1[-i d0 R a +u d0 -i q0 L f ]+b1[i d0 L f -i q0 R a +u q0 ] Where a1 represents the first parameter; b1 represents the second parameter; i d0 ,i q0 ,u d0 ,u q0 are the dq components of the inverter output current and voltage at the machine end in the steady state before the disturbance; R a Indicates the resistance of the filter.

7. The method for controlling the virtual synchronous generator grid connection based on transient energy flow according to claim 6 is characterized in that: The calculation formulas of the first parameter and the second parameter are specifically: Among them, δ0 represents the inverter modulation signal in the steady state before the disturbance With bus voltage V pcc The phase difference between ∠α and V pcc0 is the voltage on the grid side in the steady state before the disturbance; R a , L f Respectively represent the resistance and inductance of the filter; R E , L E They represent the resistance and inductance of the line respectively.

8. A virtual synchronous generator grid-connected control system based on transient energy flow, characterized in that: The system is used to implement the virtual synchronous generator grid-connected control method based on transient energy flow as described in any one of claims 1 to 7, comprising the following steps: A model building module is used to linearize the inverter VSG control system using a small signal analysis method and build a VSG small signal model; Function analysis module, used to analyze the transfer function between the inverter active power and the grid-connected side voltage phase oscillation according to the VSG small signal model, and determine the phase-frequency characteristics of the transfer function; A phase calculation module, used to calculate the phase difference between the inverter active power and the grid-connected side voltage phase oscillation according to the phase-frequency characteristic; The parameter correction module is used to correct the virtual moment of inertia and virtual damping coefficient in the active link control parameters when the phase difference is not less than the set threshold value, until the phase difference is less than the set threshold value.

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