Modeling method of AHO and GFL inverter grid-connected hybrid system

Abstract

The invention discloses a modeling method for an AHO and GFL inverter grid-connected hybrid system, and the method comprises the steps: constructing a mathematical model of an AHO inverter, and obtaining the nonlinear output characteristics of the AHO inverter; the non-linear output characteristic comprises an output end voltage amplitude and a relation between an output end voltage phase and a power instruction; constructing a mathematical model of a grid-connected hybrid system comprising an AHO inverter, a GFL inverter and a power grid; the GFL inverter detects the voltage phase of a grid-connected point through a phase-locked loop and adjusts the output power through a current loop; and the nonlinear output characteristic of the AHO inverter and the phase-locked loop dynamic characteristic of the GFL inverter are coupled through the grid-connected point voltage to obtain a state-space equation describing the synchronization stability of the grid-connected hybrid system. According to the method, the output characteristics of the AHO inverter, the dynamic characteristics of the phase-locked loop of the GFL inverter and the power transmission relation among the power supplies are combined, a mathematical model for describing the synchronization relation of the AHO and GFL inverter grid-connected hybrid system is established, control parameters are designed, and stable operation of the system is ensured.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and more specifically to a modeling method for a grid-connected hybrid system of AHO and GFL inverters. Background Technology

[0002] Currently, based on the synchronization method, grid-connected inverters can be divided into grid-forming (GFM) and grid-following types. Grid-forming inverters can actively support the system voltage. GFM strategies include droop, virtual synchronous generator (VSG), and virtual oscillator control (VOC). Droop and VSG control simulate the output characteristics of a synchronous generator, while VOC control enables the inverter to simulate the dynamic characteristics of a nonlinear oscillator.

[0003] In comparison, VOC inverters eliminate the need for power calculation stages, exhibit better dynamic response characteristics, and leverage the strong controllability of power electronic devices. Andronov-Hopf VOC inverters, with their low output voltage harmonics, are suitable for three-phase systems and are currently a hot research topic. However, their control circuitry exhibits strong nonlinearity, making analysis more complex.

[0004] GFL inverters are grid-connected inverters that employ a grid-following (GFL) control strategy. They use a phase-locked loop for synchronization and can achieve maximum power point tracking through a current loop, thus appearing as a current source to the outside world.

[0005] Existing synchronous stability analyses of AHO inverters are limited to stand-alone infinite bus systems and islanded hybrid systems. On the one hand, there is a lack of mathematical models describing the coupling relationship between the AHO inverter, GFL inverter, and the grid in grid-connected hybrid systems. On the other hand, the impact of various parameters in grid-connected hybrid systems on synchronous stability is unclear, and unreasonable parameter settings can lead to system oscillations and instability.

[0006] Therefore, establishing a mathematical model for a three-way grid-connected hybrid system and designing control parameters is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of the above problems, this invention is proposed to provide a modeling method for a grid-connected hybrid system of AHO and GFL inverters that overcomes or at least partially solves the above problems. In the grid-connected hybrid system, the VOC inverter, GFL inverter and the power grid are coupled through line impedance and control parameters are designed to ensure the stable operation of the system.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a modeling method for a grid-connected hybrid system of AHO and GFL inverters, comprising: A mathematical model of the AHO inverter is constructed to obtain the nonlinear output characteristics of the AHO inverter; the nonlinear output characteristics include the relationship between the output voltage amplitude and the output voltage phase and the power command. A mathematical model is constructed for a grid-connected hybrid system including the AHO inverter, GFL inverter and the power grid; wherein, the GFL inverter is a grid-connected inverter that detects the voltage phase at the grid connection point through a phase-locked loop and adjusts the output power through a current loop. The nonlinear output characteristics of the AHO inverter and the phase-locked loop dynamic characteristics of the GFL inverter are coupled through the grid connection point voltage to obtain the state-space equation describing the synchronous stability of the grid-connected hybrid system.

[0009] Furthermore, the structure of the AHO inverter includes a DC power supply, a three-phase full-bridge power electronic topology, a filter, and a digital controller; The DC power supply is an energy storage power supply; The three-phase full-bridge power electronic topology converts the energy storage power supply into current based on the pulse commands output by the digital controller. ; The filter uses a filter inductor and a filter capacitor to control the current. Perform filtering.

[0010] Furthermore, the digital controller includes a power command module, a coordinate transformation module, an AHO module, and a PWM generation module; The power command module is used to obtain the active power and reactive power commands of the grid-connected system. The coordinate transformation module is used to convert the active power and reactive power commands into the output current of the AHO module. α , β Command values ​​of axis components , , used to Converted into the output current of the AHO module α , β Axial components i α , i β It is also used to... , and i α , i β Perform interpolation and input the result into the AHO module; The AHO module calculates the virtual capacitor voltage based on the nonlinear differential equation established by the virtual oscillator control strategy, using the input quantity. Virtual inductor current and AHO output voltage α , β Axial components v α , v β ; The PWM generation module will v α , v β As a reference voltage, a corresponding trigger pulse is generated to control the on and off of the switching transistors in the three-phase full-bridge power electronic topology.

[0011] Furthermore, the nonlinear output characteristics of the AHO inverter are expressed by the following formula:

[0012] in, Indicates active power command. Indicates reactive power command. The voltage convergence coefficient is... For voltage scaling parameters, For current scaling parameters, For custom angles related to the output characteristics of AHO inverters, For virtual capacitors, For the rated frequency, This refers to the output voltage amplitude of the inverter. The phase angle of the inverter output voltage. This is the dynamic expression for the output voltage amplitude. V is the dynamic expression for the output voltage phase. N This is the rated voltage.

[0013] Furthermore, the GFL inverter detects the voltage phase at the grid connection point through a phase-locked loop to obtain... :

[0014] in, The voltage phase at the grid connection point, , These are the proportional and integral coefficients of the PI controller. Where is the rated frequency, and s is the Laplace operator. for q-axis component, This is the terminal voltage of the GFL inverter.

[0015] Furthermore, the upper limit of the current command of the GFL inverter. ,for:

[0016] Among them, X AHO X is the linear impedance connecting the AHO inverter to the grid connection point. GFL X is the linear impedance connecting the GFL inverter to the grid connection point. g U is the linear impedance connecting the grid connection point to the power grid. g The voltage at the grid connection point. This represents the phase difference between the AHO inverter terminal voltage and the grid voltage.

[0017] Furthermore, the coupling of the nonlinear output characteristics of the AHO inverter with the phase-locked loop dynamic characteristics of the GFL inverter through the grid connection point voltage specifically includes: The AHO inverter, based on its nonlinear output characteristics, outputs voltage and current, which in turn affect the phase and amplitude of the grid connection point voltage. The phase-locked loop of the GFL inverter detects the changed grid connection point voltage, and the dynamic characteristics of the phase-locked loop start to take effect, causing the phase of the output current to change; the active and reactive power injected into the grid-connected hybrid system changes. Changes in GFL power output alter the power flow and voltage distribution of the grid-connected hybrid system, affecting the electrical conditions of the AHO inverter ports and triggering dynamic adjustments of the AHO inverter based on its nonlinear output characteristics.

[0018] Furthermore, the state-space equations include: The dynamic characteristic equation of the phase-locked loop angular frequency of the GFL inverter:

[0019] AHO inverter output voltage dynamic characteristic equation:

[0020] The output voltage angular frequency equation of the AHO inverter:

[0021] Dynamic characteristic equation of phase difference between AHO inverter and grid voltage:

[0022] Where z is a defined intermediate parameter. This is the d-axis current command. The phase difference between the GFL inverter and the grid voltage. For the terminal voltage angular frequency of the AHO inverter, For the phase-locked loop angular frequency of the GFL inverter, For the terminal voltage of the AHO inverter, , These represent the power angle of the AHO inverter and the phase of the grid voltage, respectively. This refers to the voltage phase of the AHO inverter.

[0023] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a modeling method for a grid-connected hybrid system of AHO and GFL inverters, which has the following beneficial effects: This invention combines the output characteristics of AHO inverters and the phase-locked loop characteristics of GFL inverters to establish a mathematical model of synchronization characteristics that describes the coupling relationship between AHO inverters, GFL inverters, and the power grid in a grid-connected hybrid system. This model fills the gap in existing research on the synchronization stability analysis of grid-connected hybrid systems, providing a new theoretical foundation and analytical tool for in-depth research on the synchronization stability of such systems.

[0024] This invention also provides an in-depth analysis of the influence of various parameters in the mathematical model of synchronization characteristics of grid-connected hybrid systems on phase trajectories. It clearly reveals the mechanism by which various parameters of grid-connected hybrid systems affect synchronization stability, thus providing scientific and effective guidance for parameter design of grid-connected hybrid systems and avoiding system oscillation and instability caused by unreasonable parameter settings. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 This is a flowchart of a modeling method for a grid-connected hybrid system of AHO and GFL inverters provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the AHO inverter provided in an embodiment of the present invention; Figure 3 This is a simplified schematic diagram of the connection structure of the grid-connected hybrid system provided in an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Before introducing the embodiments of the present invention, the following explanation is required: AHO inverter: A grid-connected inverter that adopts the Andronov-Hopf type Virtual Oscillator Control (VOC) strategy.

[0029] GFL inverter: A grid-connected inverter that adopts a grid-following (GFL) control strategy.

[0030] Phase-locked loop (PLL): A component in the GFL control strategy that can measure the voltage phase and amplitude at the grid connection point.

[0031] Grid-connected hybrid system: A system consisting of AHO inverters, GFL inverters and grid-side power supplies.

[0032] This invention discloses a modeling method for a grid-connected hybrid system of AHO and GFL inverters, referring to... Figure 1 As shown, it includes: A mathematical model of the AHO inverter is constructed to obtain its nonlinear output characteristics. The nonlinear output characteristics include the relationship between the output voltage amplitude and the output voltage phase and the power command. A mathematical model is constructed for a grid-connected hybrid system that includes an AHO inverter, a GFL inverter, and the power grid. The GFL inverter is a grid-connected inverter that detects the voltage phase at the grid connection point through a phase-locked loop and adjusts the output power through a current loop. By coupling the nonlinear output characteristics of the AHO inverter with the phase-locked loop dynamic characteristics of the GFL inverter through the grid connection point voltage, a state-space equation describing the synchronous stability of the grid-connected hybrid system is obtained.

[0033] This embodiment is applied to a grid-connected system, where the energy storage system is connected to the grid via an AHO inverter, and the new energy source is connected via a GFL inverter. To achieve stable operation of the system after grid connection, this embodiment first establishes a mathematical model of the AHO inverter; then, combining the line transmission relationship of the grid-connected hybrid system and the phase-locked loop characteristics of the GFL inverter, a mathematical model of the grid-connected hybrid system is established; based on this, the influence of various parameters in the system on synchronization stability is analyzed using the phase plane method, and design references for control parameters and command parameters are provided.

[0034] The specific implementation steps of this embodiment are described in detail below.

[0035] First, establish the mathematical model of the AHO inverter.

[0036] The structure of the AHO inverter in this embodiment is referenced. Figure 2 As shown, powered by a DC power supply It consists of a three-phase full-bridge power electronic topology, filters, and a digital controller; Figure 2 L f and C f These are the filter inductor and filter capacitor, respectively. The output current of the three-phase full-bridge power electronic topology is detected by the digital controller during operation. and combined with power commands and The corresponding trigger pulse is calculated to control the on and off states of the switching transistors in the three-phase full-bridge power electronic topology. In this embodiment, the DC power supply is a grid-connected energy storage power supply, which is converted and outputs current through the three-phase full-bridge power electronic topology. After being filtered by a filter, it is then input to the grid connection point.

[0037] The digital controller in this embodiment includes a power command module, a coordinate transformation module, an AHO module, and a PWM generation module. During operation, the power command module of the digital controller acquires the active and reactive power commands of the grid-connected system. and The coordinate transformation module will and Convert to AHO module output current α , β Command values ​​of axis components , It can be expressed by the formula:

[0038] in, Represents the 2-norm operation. , These represent the voltages of AHO respectively. α , β Which of the axis components is the reference voltage? , These are the current command reference values. α , β Axial components.

[0039] In this embodiment, the coordinate transformation module, based on the abc / αβ coordinate transformation, further obtains the α and β axis components of the AHO inverter output current. iα , i β .

[0040] This embodiment will , and i α , i β The difference is calculated by transforming the coordinate matrix and then comparing it with the current scaling factor. Multiplying them together gives the input values ​​of the AHO module. and It can be expressed by the formula:

[0041] in, It is a constant. .

[0042] Will and Input the AHO module. Based on circuit laws, this embodiment uses the virtual capacitor voltage. and virtual inductor current The dynamic equation is expressed as:

[0043]

[0044]

[0045]

[0046]

[0047] In the formula, and These are virtual inductance and virtual capacitance, respectively. v m It is a nonlinear voltage source. i m It is a nonlinear current source, and ε is the characteristic impedance. For the rated frequency, The rated amplitude of the oscillator. The voltage convergence coefficient is... x For state variables, This represents the 2-norm operation.

[0048] This embodiment defines the α and β axis components of the AHO output voltage. v α and v β , , It can be used as a reference voltage input PWM module to generate trigger pulses and control the on and off of the switching transistors in the three-phase full-bridge power electronic topology.

[0049] v α and v β The dynamic characteristics are expressed by the formula:

[0050] In the formula, For voltage scaling parameters, For current scaling parameters, Custom angles related to the output characteristics of AHO inverters.

[0051] v α and v β The dynamic characteristics are also a form of representation of AHO (Average-Hydraulic Oscillator). Unlike Drop control and VSG control, AHO is a strongly coupled nonlinear differential equation system, making it difficult to directly analyze the relationship between the output voltage amplitude and phase of an AHO inverter and its power. Therefore, polar coordinate transformation is used to define the inverter output voltage amplitude. and voltage phase angle It can be expressed by the formula:

[0052] in, v α and v β These are the output voltages of AHO respectively. α、β Axis components. Differentiating the above equation, the amplitude dynamic characteristics and phase dynamic characteristics of the AHO inverter output voltage in polar coordinates are expressed as:

[0053] in, v α and v β These are the output voltages of AHO respectively. α、β Axial components, This refers to the output voltage amplitude of the inverter. The phase angle of the inverter output voltage. This is the dynamic expression for the output voltage amplitude. V is the dynamic expression for the output voltage phase. N This is the rated voltage.

[0054] when At that time, the AHO inverter exhibits PV, Q-ω characteristics. At this time, the AHO inverter exhibits QV, P-ω characteristics.

[0055] Under the assumption that the line impedance is inductive, choose The correspondence between the theoretical model and the time-domain simulation model is analyzed. Under light load, rated load, and heavy load conditions, the theoretical model can effectively describe the output characteristics of the AHO inverter. Meanwhile, the output characteristics of the AHO inverter approximate a drooping curve.

[0056] Secondly, refer to Figure 3 As shown, a grid-connected hybrid system including AHO inverters, GFL inverters, and the power grid is constructed.

[0057] This embodiment considers the dynamics of the GFL inverter's PLL lock and the output characteristics of the AHO inverter, and studies... Figure 3 Synchronous stability of the grid-connected hybrid system composed of AHO inverters and GFL inverters.

[0058] In a grid-connected hybrid system, GFL inverters and AHO inverters are respectively connected through line impedance. and Connected to the grid connection point PCC, the line impedance between the grid connection point and the infinite power supply of the grid is... . This refers to the DC source voltage of the GFL inverter. The filter inductor is used for this purpose. During operation, the GFL inverter achieves grid synchronization by detecting the voltage phase through a phase-locked loop, and the grid-connected current I is measured. GFL The current feedback is obtained after transformation and compared with the reference current I. ld and I lq A current command is generated during the comparison in the Current Loop; simultaneously, I GFL The voltage phase is locked into the PLL after coordinate transformation. The modulation angle is determined; finally, the current command, combined with the phase-locked angle, generates a drive signal through PWM to achieve grid-connected control, and the d-axis and q-axis current commands are used. and The inverter's output power is adjusted via the Current Loop. The AHO inverter detects the output current and adjusts the output power through the AHO module to achieve grid synchronization.

[0059] definition , They are respectively , The admittance of the corresponding line; , and These represent the currents of the GFL inverter, the AHO inverter, and the grid, respectively. , , These represent the GFL inverter, the GFM inverter, and the grid voltage, respectively. Based on circuit theorems, the voltage equation for the grid-connected hybrid system can be expressed as:

[0060]

[0061] In the formula, Y eq This is the equivalent admittance.

[0062] The voltage phasor representation of the common grid connection point is:

[0063] The terminal voltage of a GFL inverter is expressed as follows:

[0064] The output current of an AHO inverter is expressed as:

[0065] This embodiment will , and Defined respectively , and Phase in the stationary coordinate system. Then the output active power and reactive power of the AHO inverter are expressed as:

[0066]

[0067] During operation, the intermediate parameter z is defined as follows in this embodiment:

[0068] This embodiment considers that the GFL inverter mainly generates active power when connected to the grid, assuming... Then there is Therefore, based on the changes in Park, we obtain... The q-axis component is represented as:

[0069] In the formula, The voltage phase at the grid connection point, This refers to the voltage phase of the AHO inverter. This represents the phase of the grid voltage.

[0070] Furthermore, combining the characteristics of PLL, define , These are the proportional and integral coefficients of the PI controller, respectively. Consider that the PI controller locks the voltage frequency deviation at the converter port, and the phase is calculated by the integral controller.

[0071] Will Represented as:

[0072] The equivalent power angle is defined with reference to the grid-side voltage phase angle:

[0073]

[0074] Equivalent angular frequency:

[0075]

[0076] In the formula, For the angle The rate of change.

[0077] Will Substitution From the expression, and combining it with the formulas for the output active and reactive power of the AHO inverter, we obtain: The dynamic characteristic equation of the phase-locked loop angular frequency of the GFL inverter:

[0078] AHO inverter output voltage dynamic characteristic equation:

[0079] The output voltage angular frequency equation of the AHO inverter:

[0080] Dynamic characteristic equation of phase difference between AHO inverter and grid voltage:

[0081] in, The phase difference between the GFL inverter and the grid voltage. For the terminal voltage angular frequency of the AHO inverter, For the phase-locked loop angular frequency of the GFL inverter, For the terminal voltage of the AHO inverter, , These represent the power angle of the AHO inverter and the phase of the grid voltage, respectively. This refers to the voltage phase of the AHO inverter.

[0082] Finally, this embodiment constructs a test platform for a grid-connected hybrid system consisting of GFL and AHO inverters to perform synchronous stability analysis.

[0083] This embodiment analyzes the phase trajectory of the system under different operating conditions using the phase plane method, revealing the influence of control parameters and system parameters on the system's synchronous stability. First, the impact of the GFL inverter current command on the phase trajectory is analyzed. Under the active power command... =2500, control parameters of AHO inverter =0.2, Under the condition of =80, set The phase trajectories of the GFL inverter side and the AHO inverter side are obtained by setting the current to 30A, 35A and 40A respectively.

[0084] The results showed that, Under a current of 30A, the GFL inverter can stabilize to the equilibrium point. AHO inverters can stabilize to the equilibrium point. The entire grid-connected hybrid system is in a synchronous and stable state. With As the magnitude of the phase increases, both phase trajectories on both sides show an upward trend, causing the system to lose its stable equilibrium point and oscillate. Combined with... As the formula shows, with The increase in the equivalent mechanical power on the GFL inverter side As the current command of the GFL inverter increases, the GFL inverter becomes unstable. Meanwhile, based on the output voltage angular frequency equation of the AHO inverter, it can be seen that an increase in the current command of the GFL inverter will lead to an increase in the equivalent electromagnetic power on the AHO inverter side. The decline eventually leads to system instability.

[0085] exist Under the condition of 35A, analyze the impact of active power command and voltage / current scaling parameters on the phase trajectory of the AHO inverter. =0.2, Under the condition of 80, set three active power commands. =2000, =2500 and =3000, as the active power command decreases, the phase trajectories on both the GFL and AHO inverter sides show a downward trend. Under the test conditions, the mechanical power of the AHO inverter side and electromagnetic power AHO inverters can achieve balance and converge to the equilibrium point. Meanwhile, the GFL inverter is able to converge to the equilibrium point. The system remains synchronized and stable.

[0086] Furthermore, the voltage and current scaling parameters of AHO are analyzed. and The impact on the system's phase trajectory. =2500, Under the condition of 0.2, the phase trajectories on the GFL and AHO inverter sides are obtained. When the value is 70, the system has a stable operating point. and .along with As the values ​​increase to 80 and 90, the phase trajectory shows an upward trend, and the system loses its equilibrium point. =2500, Under the condition of =80, the phase trajectories on the GFL and AHO inverter sides are obtained. When the value is 0.1, the system has a stable operating point. and .along with Increasing the values ​​to 0.2 and 0.3, the phase trajectory shows an upward trend, and the system loses its equilibrium point. Combining this with the dynamic characteristic equation of the phase-locked loop angular frequency of the GFL inverter, it can be seen that... and The reduction of [something] helps to improve the voltage rigidity of the AHO inverter, thereby increasing the equivalent electromagnetic power on the AHO inverter side and thus improving the synchronous stability of the system.

[0087] Based on the above analysis, the synchronization stability of the grid-connected hybrid system depends more on the matching of voltage / current scaling parameters. Excessive scaling gain will amplify the voltage dynamic response and exacerbate the power coupling between the AHO inverter and the GFL side, causing the system to lose its stable equilibrium point. Appropriately reducing this parameter can improve the voltage rigidity of the AHO inverter and enhance its ability to suppress GFL power supply current command disturbances, thereby maintaining stable synchronization.

[0088] Under extreme conditions, considering that AHO has strong voltage stiffness, there exists If the system can stabilize at this time, that is, satisfy the condition... Therefore, in this embodiment, the current command of the GFL inverter has an upper limit. It can be expressed by the formula:

[0089] in, This represents the phase difference between the AHO inverter terminal voltage and the grid voltage.

[0090] This embodiment combines the output characteristics of the AHO inverter, the phase-locked loop characteristics of the GFL inverter, and the system power transmission relationship to establish a mathematical model describing the synchronization characteristics of the grid-connected hybrid system. Using the phase plane method, it analyzes the influence of various parameters on the phase trajectory under different scenarios, guides the parameter design of the grid-connected hybrid system, and ensures the stable operation of the system.

[0091] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0092] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A modeling method of an AHO and GFL inverter grid-connected hybrid system, characterized in that, The application relates to a grid-connected hybrid system and a method for analyzing the stability of the grid-connected hybrid system. The application comprises: a mathematical model of an AHO inverter is constructed, and a nonlinear output characteristic of the AHO inverter is obtained; the nonlinear output characteristic comprises the relationship between the output terminal voltage amplitude and the output terminal voltage phase and the power instruction; a mathematical model of a grid-connected hybrid system comprising the AHO inverter, a GFL inverter and a power grid is constructed; wherein the GFL inverter is a grid-following inverter, the voltage phase of a grid-connected point is detected through a phase-locked loop, and the output power is adjusted through a current loop; 2. The method of claim 1, wherein, the nonlinear output characteristic of the AHO inverter is coupled with the dynamic characteristic of the phase-locked loop of the GFL inverter through the voltage of the grid-connected point, and a state space equation describing the synchronization stability of the grid-connected hybrid system is obtained. The structure of the AHO inverter comprises a direct-current power supply, a three-phase full-bridge power electronic topology structure, a filter and a digital controller. The three-phase full-bridge power electronic topology converts the energy storage power supply into current based on the pulse instructions output by the digital controller ; The filter adopts a filter inductance and a filter capacitance to filter the current for filtering.

3. The method of claim 2, wherein, The direct-current power supply is an energy storage power supply. The digital controller comprises a power instruction module, a coordinate transformation module, an AHO module and a PWM generation module. The coordinate transformation module is configured to convert the active power and reactive power instructions into the AHO module output current α , β , the instruction value of the axis component , , for converting into the AHO module output current α , β , the axis component i α , i β , for converting , and i α , i β , and inputting the difference value into the AHO module; The AHO module calculates input quantity according to nonlinear differential equation established by virtual oscillator control strategy to obtain virtual capacitor voltage , virtual inductor current and AHO output voltage α , β axis component v α , v β ; The PWM generation module will v α , v β As a reference voltage, the corresponding trigger pulse is generated to control the conduction and turn-off of the switch tube in the three-phase full-bridge power electronic topology.

4. The method of claim 1, wherein, The power instruction module is used for acquiring the active power and the reactive power instructions of the grid-connected system. wherein, represents an active power command, represents a reactive power command, is a voltage convergence coefficient, is a voltage scaling parameter, is a current scaling parameter, is a custom angle related to the AHO inverter output characteristic, is a virtual capacitance, is a nominal frequency, is an inverter output voltage magnitude, is an inverter output voltage phase angle, is an output terminal voltage magnitude dynamic expression, is an output terminal voltage phase dynamic expression, V N is a nominal voltage.

5. The method of claim 1, wherein, The GFL inverter detects the voltage phase of the grid-connected point through a phase-locked loop to obtain : wherein, is the voltage phase of the point of common coupling, , are the proportional and integral coefficients of the PI controller, respectively, is the rated frequency, s is the Laplace operator, is the q-axis component of , is the terminal voltage of the GFL inverter.

6. The method of claim 1, wherein, The upper limit of the current command of the GFL inverter To: wherein, X AHO linear impedance connected between the AHO inverter and the point of common coupling, X GFL linear impedance connected between the GFL inverter and the point of common coupling, X g linear impedance connected between the point of common coupling and the power grid, U g voltage at the point of common coupling, phase difference between the voltage at the AHO inverter terminal and the voltage at the power grid.

7. The method of claim 1, wherein, The nonlinear output characteristic of the AHO inverter is expressed by a formula as follows: the coupling of the nonlinear output characteristic of the AHO inverter and the dynamic characteristic of the phase-locked loop of the GFL inverter through the voltage of the grid-connected point specifically comprises: the AHO inverter outputs the voltage and the current according to the nonlinear output characteristic, and influences the phase and the amplitude of the voltage of the grid-connected point; the phase-locked loop of the GFL inverter detects the changed voltage of the grid-connected point, and the dynamic characteristic of the phase-locked loop starts to act, so that the phase of the output current is changed; the active power and the reactive power injected into the grid-connected hybrid system are changed; 8. The method of claim 1 or 7, wherein, the change of the GFL power output changes the power flow and the voltage distribution of the grid-connected hybrid system, influences the electrical conditions of the port of the AHO inverter, and triggers the dynamic adjustment of the AHO inverter based on the nonlinear output characteristic again. The state space equation comprises: a phase-locked loop angular frequency dynamic characteristic equation of the GFL inverter: an output terminal voltage dynamic characteristic equation of the AHO inverter: an output terminal voltage angular frequency equation of the AHO inverter: a dynamic characteristic equation of the phase difference between the AHO inverter and the voltage of the power grid. wherein z is an intermediate parameter defined as is a d-axis current command, is a difference between the GFL inverter and grid voltage phase, is an end voltage angular frequency of the AHO inverter, is a GFL inverter phase-locked loop angular frequency, is an end voltage of the AHO inverter, , are an AHO inverter power angle and grid voltage phase, respectively, is an AHO inverter voltage phase.

Images