A method and system for coordinated adjustment of virtual impedance and power reference of a grid-forming converter

Abstract

The application discloses a network-constructing converter virtual impedance and power reference cooperative adjustment method and system, relates to the technical field of power control, and introduces a virtual impedance into a virtual synchronous generator system to increase equivalent output impedance of an inverter; internal voltage reference generated by a virtual synchronous generator algorithm of the inverter is monitored in real time; local voltage measured at a point of common coupling is monitored in real time; based on a vector difference of the internal voltage reference and the local voltage, and in combination with maximum current limit values of power electronic devices, accurate amplitude of the virtual impedance is solved in real time; based on the accurate amplitude of the virtual impedance, a function relationship between an active power reference value and reactive power is determined, reactive power measured at the point of common coupling is monitored in real time, and the active power reference value is adjusted according to the function relationship to retain a stable equilibrium point. The virtual impedance is dynamically calculated to accurately limit current, and the active power reference is adaptively adjusted according to real-time reactive response, so that maximum grid support and safe and stable operation of the converter are realized.

Description

Technical Field

[0001] This invention relates to the field of power control technology, and in particular to a method and system for coordinated adjustment of virtual impedance and power reference of grid converter. Background Technology

[0002] The statements in this section are merely background information relating to this disclosure and do not necessarily constitute prior art.

[0003] Grid-connected converters, by simulating the rotor motion characteristics of synchronous generators, can actively provide inertia support for the system, maintaining high stability even under weak grid conditions. This is a key technology for supporting a high proportion of renewable energy grid integration and enhancing grid resilience. However, due to the low overcurrent capability of power electronic devices, grid-connected converters must be equipped with current limiting strategies to prevent overload and thermal damage. In existing solutions, while direct current limiting can quickly suppress fault currents, it causes the converter to switch from voltage source mode to current source mode, leading to reduced stability margins or even runaway. Traditional virtual impedance current limiting suppresses current by increasing the equivalent output impedance while maintaining the voltage source characteristics of the equipment. However, this method suffers from low bandwidth and poor accuracy, or relies on difficult-to-obtain and unreliable grid-side information. Furthermore, the application of virtual impedance limits the converter's maximum power transmission capacity, potentially causing the stable equilibrium point to disappear, leading to transient instability in the inverter and threatening the stability of the grid-connected system. Therefore, it is necessary to comprehensively consider the impact of virtual impedance and dynamically adjust the active power reference value to avoid power imbalance.

[0004] In summary, existing virtual impedance methods have shortcomings. Traditional current limiting methods have poor accuracy, leading to underutilization of converter capacity. Existing improved methods rely on remote grid information that is difficult to obtain in real time, affecting system reliability and response speed. Furthermore, most existing power regulation strategies fail to comprehensively consider the limitations of virtual impedance on maximum power transmission capacity, thus introducing the risk of transient instability. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention provides a method and system for coordinated adjustment of virtual impedance and power reference of grid-connected converters. During grid faults, this method dynamically adjusts the virtual impedance based on the difference between the output reference voltage of the virtual synchronous generator (VSG) and the voltage of the point of common coupling (PCC) to precisely limit the output current to the maximum allowable value during faults. At the same time, based on the current limiting state, the active power reference value is adaptively adjusted to ensure the stable operation of the system, thereby maximizing the grid support capability of the inverter.

[0006] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0007] In a first aspect, the present invention provides a method for coordinated adjustment of virtual impedance and power reference in a grid-connected converter. The virtual synchronous generator system introduces virtual impedance to increase the equivalent output impedance of the inverter, including:

[0008] Real-time monitoring of the inverter's internal voltage reference generated by the virtual synchronous generator algorithm;

[0009] Real-time monitoring of the local voltage measured at the common coupling point;

[0010] Based on the vector difference between the internal voltage reference and the local voltage, and combined with the maximum current limit of the power electronic device, the accurate amplitude of the virtual impedance is solved in real time.

[0011] The functional relationship between active power reference value and reactive power is determined based on the precise amplitude of virtual impedance. The reactive power measured at the common coupling point is monitored in real time, and the active power reference value is adjusted according to the functional relationship to maintain a stable equilibrium point.

[0012] A further technical solution is that the virtual synchronous generator system predicts the output local voltage at the next moment based on the local voltage at the current moment, expressed as:

[0013]

[0014] in, , They are respectively The dq-axis components of the voltage at point PCC at time t. , They represent The dq-axis components of the voltage at the point of common coupling at any given time. Indicates the system control cycle. This represents the capacitance of the LC filter. , They represent The dq-axis components of the current at the point of common coupling at any given time. This indicates the rated angular frequency of the converter.

[0015] In a further technical solution, the virtual impedance amplitude is expressed as:

[0016]

[0017]

[0018] in, Represents virtual impedance. The resistivity-inductance ratio represents the virtual impedance. Indicates voltage amplitude reference. express Local voltage at any given time , These represent virtual reactance and virtual resistance, respectively. This indicates the maximum current limit.

[0019] A further technical solution also adaptively adjusts the impedance angle of the virtual impedance.

[0020] In a further technical solution, the impedance angle is expressed as:

[0021]

[0022] in, The function representing the change of the resistance-to-inductance ratio over time. Indicates the duration of the fault. This indicates the duration of the inrush current suppression phase. Represents the time constant. and These represent the minimum and maximum values ​​of the impedance angle of the virtual impedance, respectively.

[0023] A further technical solution proposes a collaborative active power regulation strategy, which uses the locally measured reactive power output as a real-time indicator of the severity of the fault. When the reactive power increases, the system adaptively lowers the active power reference value according to a preset functional relationship.

[0024] A further technical solution is that the active power reference value is expressed as follows:

[0025]

[0026] in, This represents the reference value for active power. Indicates the power adjustment coefficient. This represents the reactive power measured and calculated at the point of common coupling. Indicates the output voltage amplitude of the converter. Represents virtual reactance. This represents virtual reactance.

[0027] Secondly, this invention provides a grid-connected converter virtual impedance and power reference coordinated adjustment system. The virtual synchronous generator system introduces virtual impedance to increase the equivalent output impedance of the inverter, including:

[0028] The voltage reference acquisition module is configured to monitor the internal voltage reference of the inverter generated by the virtual synchronous generator algorithm in real time.

[0029] A local voltage acquisition module is configured to monitor the local voltage measured at the common coupling point in real time.

[0030] The dynamic virtual impedance solving module is configured to: solve for the precise amplitude of the virtual impedance in real time based on the vector difference between the internal voltage reference and the local voltage, combined with the maximum current limit of the power electronic device;

[0031] The collaborative active power regulation module is configured to: determine the functional relationship between the active power reference value and the reactive power based on the precise amplitude of the virtual impedance; monitor the reactive power measured at the common coupling point in real time; and adjust the active power reference value according to the functional relationship to maintain a stable equilibrium point.

[0032] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in a method for coordinated adjustment of virtual impedance and power reference of a grid converter as described in the first aspect.

[0033] Fourthly, the present invention provides a computer device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps in the method for coordinated adjustment of virtual impedance and power reference of a grid converter as described in the first aspect.

[0034] The above one or more technical solutions have the following beneficial effects:

[0035] This invention addresses advanced power conversion equipment in renewable energy grid-connected, microgrid, and energy storage systems. It proposes a method for coordinated adjustment of virtual impedance and power reference in grid-connected converters based on local information. This coordinated control strategy relies solely on local measurements to achieve accurate, stable, and robust fault ride-through for grid-connected converters. The method calculates the virtual impedance in real-time based on the difference between the VSG output reference voltage and the PCC voltage, ensuring that the output current is precisely limited to the maximum current-carrying capacity of the power electronic devices during faults, thereby maximizing the grid support potential of the inverter. Simultaneously, to ensure stable system operation under fault conditions, this invention proposes an adaptive active power reference adjustment method that considers the influence of virtual impedance and coordinates with the real-time response of reactive power. By constructing a functional relationship between active power reference and reactive power, the active power reference value is dynamically corrected, enabling the system to maintain a stable equilibrium point under different operating conditions and preventing loss of synchronization. The proposed method does not rely on remote grid information, avoiding the risks associated with communication delays and measurement uncertainties.

[0036] This invention eliminates the need to measure grid impedance and fault depth. Based on local data and preset parameters, it ensures that the grid-connected current does not exceed limits, guaranteeing the safe operation of the converter equipment. This method adaptively adjusts the virtual impedance amplitude and impedance ratio of the VSG according to the degree of grid fault, maximizing the reactive power support capability of the VSG, improving the power angle and voltage stability of the VSG, and enhancing energy absorption capacity.

[0037] This invention ensures that the virtual synchronous generator (VSG) can continue to operate in parallel with the grid under continuous severe grid faults, providing critical voltage and frequency support to the grid, thereby effectively preventing the unplanned islanding of distributed power sources. Attached Figure Description

[0038] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0039] Figure 1 This is a flowchart of a method for coordinated adjustment of virtual impedance and power reference in a grid converter according to an embodiment of the present invention;

[0040] Figure 2 This is an equivalent circuit diagram of the virtual synchronous generator grid-connected system according to an embodiment of the present invention;

[0041] Figure 3 These are power angle curves for different degrees of power grid faults according to embodiments of the present invention;

[0042] Figure 4 This is a control block diagram of an embodiment of the present invention;

[0043] Figure 5 This is the active power given adjustment diagram of the embodiment of the present invention. Detailed Implementation

[0044] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0045] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0046] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0047] Example 1

[0048] like Figure 1 As shown, this embodiment discloses a method for coordinated adjustment of virtual impedance and power reference in a grid-connected converter. A virtual synchronous generator system introduces virtual impedance to increase the equivalent output impedance of the inverter. The method includes:

[0049] The following will take a two-level converter as an example.

[0050] I. VSG System Control Architecture

[0051] In this embodiment, the control architecture of the Virtual Synchronous Generators (VSG) system is based on a typical three-phase grid-connected inverter system, such as... Figure 4 As shown, the grid converter is connected to the power grid via an LC filter and line impedance. Figure 4 middle This indicates the DC-side port voltage of the converter. and These represent the inductance and capacitance of an LC filter, respectively. and These represent the equivalent resistance and inductance of power transmission and distribution lines, respectively. , and These represent the converter port output current, the current flowing through the virtual impedance, and the filtered grid-connected current, respectively. and These represent the grid connection point voltage and the grid voltage, respectively. and These represent the active power and reactive power output of the VSG, respectively. , , , These represent the VSG output power angle reference, internal voltage amplitude reference, output voltage amplitude reference, and output current amplitude reference, respectively.

[0052] The VSG control strategy provides damping support to the power grid by simulating the inertia, damping, and voltage regulation characteristics of synchronous generators. The VSG algorithm module is further divided into active power control (APC) and reactive power control (RPC).

[0053] The active power controller expression is as follows:

[0054]

[0055] in, and These represent the actual output angular frequency and the rated angular frequency of the converter, respectively. This represents the active-frequency droop coefficient of the VSG. This represents the VSG virtual moment of inertia. and These represent the system's mechanical power and the VSG's output active power, respectively. This indicates the frequency deviation. This indicates the phase of the output voltage of the grid converter.

[0056] Simultaneously, the reactive power controller generates a voltage amplitude reference based on the difference between the reference value and the measured value of reactive power, using VQ droop. The expression is as follows:

[0057]

[0058] in, This represents the voltage droop factor. This indicates the rated output voltage of the converter. and These represent the reactive power reference and the reactive power output of the VSG, respectively, under normal operating conditions. .

[0059] Building upon this, VSG systems typically incorporate a virtual impedance module to limit output current and protect hardware from thermal damage during disturbances such as grid faults by increasing the inverter's equivalent output impedance. This module dynamically calculates the virtual voltage drop based on the real-time output current and subtracts it from the aforementioned internal voltage reference, thereby generating an adjusted final voltage reference command, expressed as follows:

[0060]

[0061] in, This indicates the output voltage of the grid converter. This indicates that the current is measured at the PCC point. This is a virtual impedance.

[0062] like Figure 2 The diagram illustrates the equivalent model of the grid converter when VSG control is used. The left side of the diagram shows the equivalent model of VSG: An internal voltage reference generated for the VSG algorithm. Connect a virtual impedance The current flowing through the virtual impedance is This section simulates the electrical characteristics of a synchronous generator. Point of Common Coupling (PCC): The node where the converter connects to the grid; the voltage at this point is... The current is The transmitted active and reactive power are also measured and calculated here. Power grid (right side): Point PCC passes through the equivalent line impedance. Connect to an ideal grid voltage source .

[0063] This invention combines Figure 2 The equivalent circuit of the VSG grid-connected system, taking into account the effect of virtual impedance and the principle of line power transmission, yields the following expression for the output power of the VSG converter:

[0064]

[0065]

[0066] in, This indicates the output voltage amplitude of the converter. , These are virtual reactance and virtual resistance, respectively.

[0067] II. Transient Instability Mechanism of VSG under Different Levels of Power Grid Faults

[0068] In this embodiment, Figure 3 The power angle characteristic curves (P-delta curves) under different degrees of grid faults are shown to illustrate the impact of grid voltage drop depth on VSG transient stability.

[0069] (1) During normal operation: corresponding to the red curve, the system operates stably at operating point a, and the maximum power of the red curve is .

[0070] (2) During a moderate fault: corresponding to the dark blue curve, the grid voltage drops to 0.5 pu, and the upper power limit decreases to But still higher Therefore, after the system falls from point a to point b, due to... The output power at point b is greater than the actual output power at point b, causing the power angle to increase, eventually stabilizing at point c. The phase of the grid-connected converter output voltage at points a and b is... The phase of the output voltage of the grid converter at point c is .

[0071] (3) During a severe fault: the grid voltage drops to 0.2 pu, and the power curve amplitude is significantly compressed to (Light blue curve) At this point, the maximum transmission power is lower than the reference power. After the system operating point drops from point a to point d, due to... The output power at point d is greater than the actual output power at point d, causing the power angle to continuously increase, eventually leading to system loss of synchronism and transient instability. The phase of the grid-connected converter output voltage at point d is... .

[0072] Depend on Figure 3 It can be seen that the voltage drop depth of the power grid directly affects the amplitude of the power angle characteristic curve and the maximum transmittable power. The transient stability of VSG decreases as the voltage decreases. Based on whether there is an equilibrium point after a fault, the transient stability problem of VSG can be divided into two categories.

[0073] Type 1 (Equilibrium Point Exists After Disturbance): When a moderate fault occurs in the power grid, such as a voltage drop to 0.5 pu, although the maximum transmittable power of the system decreases, it still remains close to the active power reference value. There is an intersection point. At the moment of failure, the system operating point will shift from the stable point before the failure. The sudden change to the new work angle curve At this point, because the reference power is greater than the actual output power, the resulting power difference drives the VSG's power angle to increase until the system finds a new stable equilibrium point on the new power angle curve. This restores synchronous and stable operation.

[0074] Type 2 (no equilibrium point after disturbance): When a severe fault occurs in the power grid, such as a voltage drop to 0.2 pu, the power angle curve is significantly compressed, resulting in a decrease in the system's maximum transmittable power. Below the set active power reference value At this point, the system does not have a stable equilibrium point where the input and output power are equal. The reference power is always greater than the maximum power that the system can generate, and the power difference will remain positive, causing the power angle of the VSG to continue to increase, eventually leading to loss of synchronism and transient instability. Therefore, it is necessary to adjust the active power. The active power adjustment method proposed in this invention is used to reduce the active power reference.

[0075] The dynamic virtual impedance and precise current limiting based on local information proposed in this invention are applicable to both the first and second types of transient stability problems, while the active power adjustment method is designed to solve the second type of problem.

[0076] III. A Coordinated Adjustment Method for Virtual Impedance and Power Reference of Grid-Based Converters Based on Local Measurements

[0077] (1) Dynamic virtual impedance and precise current limiting based on local information

[0078] In this embodiment, the present invention proposes a dynamic virtual impedance calculation method to monitor in real time the internal voltage reference generated by the virtual synchronous generator (VSG) algorithm of the inverter. The voltage measured locally at the point of common coupling (after the converter filter capacitor and the point where the line impedance is connected, PCC) The vector difference between them. Based on this voltage difference and the maximum current limit that power electronic devices can withstand. The system calculates the precise amplitude of the required virtual impedance in real time. This impedance generates a precise dynamic voltage drop, which can accurately limit the output current to the maximum allowable value under various fault severity levels, thereby maximizing the use of the inverter's capacity to provide grid voltage support while ensuring safety.

[0079] Locally measured data (local information) refers to values ​​that the converter can directly measure through sensors. This differs from grid-side information, which is spatially distant from the converter and therefore subject to measurement and information transmission errors.

[0080] To further improve the system's response speed and accuracy, the system employs one-step prediction to predict the output voltage at the next moment. The expression is:

[0081]

[0082] in, , They are respectively The dq-axis components of the voltage at point PCC at time t. , They are respectively The dq-axis components of the voltage at point PCC at time t. For the system control cycle, , They are respectively The dq-axis component of the current at point PCC at time t. Locally measured voltage. The voltage at the current moment, i.e. To improve system response speed, the voltage value at time 1 is predicted, i.e., the voltage value at time 2 is predicted. The voltage value at a given moment. By predicting the voltage in one step, the converter can respond an instant earlier, suppressing fault current more quickly.

[0083] The expression for the dynamic virtual impedance magnitude is as follows:

[0084]

[0085]

[0086] in, Represents virtual impedance. The resistivity-inductance ratio represents the virtual impedance. Indicates voltage amplitude reference. express Local voltage at any given time , These represent virtual reactance and virtual resistance, respectively. This indicates the maximum current limit.

[0087] Meanwhile, to suppress transient current surges during grid faults, this invention adaptively adjusts the X / R ratio (i.e., impedance angle) of the virtual impedance. In the initial stage of fault detection, the virtual impedance is set to a low X / R ratio characteristic, primarily resistive. The higher virtual resistance effectively provides damping, rapidly attenuating the transient current component and preventing initial current overshoot. As the system gradually transitions to the steady-state fault stage, the virtual impedance characteristic smoothly transitions to a high X / R ratio characteristic, primarily inductive. This not only facilitates decoupling control of active and reactive power but also better supports reactive power, aiding in grid voltage recovery. The X / R ratio of the virtual impedance, i.e., The expression is:

[0088]

[0089] in, Indicates the duration of the fault. The duration of the inrush current suppression phase, time constant. This determines the rate at which the virtual impedance smoothly transitions from purely resistive to inductive. and These represent the minimum and maximum values ​​of the virtual impedance X / R ratio, respectively. It represents the function of the resistance-inductance ratio as a function of time.

[0090] Based on the system characteristics, this invention sets a fixed time. , Previously considered to be the initial stage, The system was then considered to have entered a steady-state fault phase. Set to 1-3 power frequency cycles, i.e. 20-60ms. The first and second peaks of the fault current are usually the largest. As long as the impact of the first few cycles is suppressed, the subsequent risks will be greatly reduced.

[0091] (2) Coordinated active power regulation and transient stability assurance

[0092] In this embodiment, to address the transient instability problem caused by virtual impedance current limiting, this invention proposes a collaborative active power regulation strategy. This strategy uses the reactive power output of the locally measured VSG as a real-time indicator of fault severity. When the fault deepens (i.e., reactive power increases), the system adaptively lowers the active power reference value according to a preset functional relationship. This ensures that the active power command is always lower than the maximum transmittable power of the system after the fault, thereby maintaining a stable equilibrium point, effectively preventing loss of synchronization, and ensuring transient stability.

[0093] The active power reference value expression (preset functional relationship) is as follows:

[0094]

[0095] in, This represents the reference value of the active power output by the VSG. This is the power adjustment coefficient. This refers to the reactive power measured and calculated at the PCC point. For example... Figure 5 As shown, by dynamically adjusting the active power, a stable equilibrium point can be maintained under different grid voltage drops, reducing the risk of transient instability caused by power imbalance in the system.

[0096] like Figure 5 As shown, the green curve is the power angle curve before the fault, and the purple curve is the power angle curve after the fault. The dashed line is the active power adjustment curve of the method proposed in this invention, and the intersection of the dashed and solid lines is the stable point. point, point, The point is three different under the value The dynamic process is as follows:

[0097] Fault occurs (from point a to point b): A power grid fault causes a voltage drop, and the system operating point instantly shifts to point b.

[0098] Coordinated adjustment (point b to) point / point / Point): According to the strategy proposed by this invention, the system, based on the fault depth (reactive power) and a preset functional relationship, utilizes adjustment coefficients. Dynamically lower the active power reference value.

[0099] Establishing a new equilibrium: As the active power reference value decreases, the system can find a stable equilibrium point on the new power curve (e.g., point / point / This avoids system instability due to lack of an equilibrium point (i.e., the second type of transient instability) and ensures transient stability during the fault period.

[0100] The purpose of active power adjustment is to reduce the active power reference. ,because It is a relatively small value, therefore the new Although and The function is proportional, but the final result is less than the original. Of. Combination Figure 5 As you can see in the picture point, point, Point All smaller than the original .

[0101] In summary, the core of this invention is to propose an adaptive virtual impedance and power setpoint adjustment coordinated control strategy based on local measurements for grid-connected inverters, which ensures that grid-connected inverters can operate safely and stably during grid faults and provide grid support to the maximum extent.

[0102] This invention proposes a coordinated control strategy for virtual impedance and active power reference in grid-connected converters, relying solely on local measurements. This strategy aims to address two core issues during grid faults: precise overcurrent protection and transient stability. By dynamically calculating the virtual impedance through real-time monitoring of the difference between the VSG output reference voltage and the point of common coupling voltage, the strategy precisely limits current. This impedance is resistive in the initial stage of a fault to suppress inrush current, and subsequently becomes inductive to optimize reactive power support. To prevent instability caused by current limiting, the strategy further adaptively adjusts the active power reference based on the real-time reactive power response, ensuring the existence of a stable equilibrium point to prevent loss of synchronization, ultimately achieving maximum grid support and safe, stable operation of the converter.

[0103] Example 2

[0104] This embodiment discloses a grid-connected converter virtual impedance and power reference coordinated adjustment system based on local information. The virtual synchronous generator system introduces virtual impedance to increase the equivalent output impedance of the inverter, including:

[0105] The voltage reference acquisition module is configured to: monitor in real time the internal voltage reference of the inverter generated by the virtual synchronous generator algorithm;

[0106] A local voltage acquisition module is configured to monitor the local voltage measured at the common coupling point in real time.

[0107] The dynamic virtual impedance solving module is configured to: solve for the precise amplitude of the virtual impedance in real time based on the vector difference between the internal voltage reference and the local voltage, combined with the maximum current limit of the power electronic device;

[0108] The collaborative active power regulation module is configured to: determine the functional relationship between the active power reference value and the reactive power based on the precise amplitude of the virtual impedance; monitor the reactive power measured at the common coupling point in real time; and adjust the active power reference value according to the functional relationship to maintain a stable equilibrium point.

[0109] Example 3

[0110] The purpose of this embodiment is to provide a computing device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method of Embodiment 1.

[0111] Example 4

[0112] The purpose of this embodiment is to provide a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, performs the steps of the method of Embodiment 1.

[0113] The steps and methods involved in the apparatuses of Embodiments 3 and 4 above correspond to those in Embodiment 1. For specific implementation details, please refer to the relevant description section of Embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood as including any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and enabling the processor to perform any of the methods in this invention.

[0114] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computer devices. Optionally, they can be implemented using computer-executable program code, thereby allowing them to be stored in a storage device for execution by a computer device, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. The present invention is not limited to any particular combination of hardware and software.

[0115] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0116] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for coordinated adjustment of virtual impedance and power reference in a grid-connected converter, characterized in that, Virtual synchronous generator systems introduce virtual impedance to increase the equivalent output impedance of the inverter, including: Real-time monitoring of the inverter's internal voltage reference generated by the virtual synchronous generator algorithm; Real-time monitoring of the local voltage measured at the common coupling point; Based on the vector difference between the internal voltage reference and the local voltage, and combined with the maximum current limit of the power electronic device, the accurate amplitude of the virtual impedance is solved in real time. The virtual synchronous generator system predicts the output local voltage at the next moment based on the local voltage at the current moment, expressed as: in, , They are respectively The dq-axis components of the voltage at point PCC at time t. , They represent The dq-axis components of the voltage at the point of common coupling at any given time. Indicates the system control cycle. This represents the capacitance of the LC filter. , They represent The dq-axis components of the current at the point of common coupling at any given time. Indicates the rated angular frequency of the converter; The functional relationship between active power reference value and reactive power is determined based on the precise amplitude of virtual impedance. The reactive power measured at the common coupling point is monitored in real time, and the active power reference value is adjusted according to the functional relationship to maintain a stable equilibrium point.

2. The method for coordinated adjustment of virtual impedance and power reference in a grid-connected converter as described in claim 1, characterized in that, The virtual impedance magnitude is expressed as: in, Represents virtual impedance. The resistivity-inductance ratio represents the virtual impedance. Indicates voltage amplitude reference. express Local voltage at any given time , These represent virtual reactance and virtual resistance, respectively. This indicates the maximum current limit.

3. The method for coordinated adjustment of virtual impedance and power reference in a grid-connected converter as described in claim 1, characterized in that, It also adaptively adjusts the impedance angle of the virtual impedance.

4. The method for coordinated adjustment of virtual impedance and power reference in a grid converter as described in claim 3, characterized in that, The impedance angle is expressed as: in, The function representing the change of the resistance-to-inductance ratio over time. Indicates the duration of the fault. This indicates the duration of the inrush current suppression phase. Represents the time constant. and These represent the minimum and maximum values ​​of the impedance angle of the virtual impedance, respectively.

5. The method for coordinated adjustment of virtual impedance and power reference in a grid-connected converter as described in claim 1, characterized in that, A collaborative active power regulation strategy is also proposed, which uses the locally measured reactive power output as a real-time indicator of the severity of the fault. When the reactive power increases, the system adaptively lowers the active power reference value according to a preset functional relationship.

6. The method for coordinated adjustment of virtual impedance and power reference in a grid converter as described in claim 5, characterized in that, The active power reference value is expressed as: in, This represents the reference value for active power. Indicates the power adjustment coefficient. This represents the reactive power measured and calculated at the point of common coupling. Indicates the output voltage amplitude of the converter. Represents virtual reactance. This represents virtual reactance.

7. A system for coordinated adjustment of virtual impedance and power reference in a grid-connected converter, characterized in that, Virtual synchronous generator systems introduce virtual impedance to increase the equivalent output impedance of the inverter, including: The voltage reference acquisition module is configured to monitor the internal voltage reference of the inverter generated by the virtual synchronous generator algorithm in real time. A local voltage acquisition module is configured to monitor the local voltage measured at the common coupling point in real time. The dynamic virtual impedance solving module is configured to: solve for the precise amplitude of the virtual impedance in real time based on the vector difference between the internal voltage reference and the local voltage, combined with the maximum current limit of the power electronic device; The virtual synchronous generator system predicts the output local voltage at the next moment based on the local voltage at the current moment, expressed as: in, , They are respectively The dq-axis components of the voltage at point PCC at time t. , They represent The dq-axis components of the voltage at the point of common coupling at any given time. Indicates the system control cycle. This represents the capacitance of the LC filter. , They represent The dq-axis components of the current at the point of common coupling at any given time. Indicates the rated angular frequency of the converter; The collaborative active power regulation module is configured to: determine the functional relationship between the active power reference value and the reactive power based on the precise amplitude of the virtual impedance; monitor the reactive power measured at the common coupling point in real time; and adjust the active power reference value according to the functional relationship to maintain a stable equilibrium point.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the method for coordinated adjustment of virtual impedance and power reference of a grid converter as described in any one of claims 1-6.

9. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the method for coordinated adjustment of virtual impedance and power reference of a grid converter as described in any one of claims 1-6.

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