A virtual impedance dynamic term control method of a virtual synchronous generator for inhibiting current transient mutation in case of failure

Abstract

The application discloses a virtual synchronous generator virtual impedance dynamic term control method for inhibiting current transient mutation during a fault, and the method introduces a virtual impedance dynamic term between a power loop and a voltage and current double closed loop of a virtual synchronous generator (VSG), monitors an inverter output current peak value in real time, and adaptively adjusts the virtual impedance according to fault depth; meanwhile, the method applies virtual power compensation and virtual electromotive force compensation to the power loop, and restricts fault current peak value and inhibits power and frequency oscillation. When a fault occurs, the virtual impedance dynamic term is increased to inhibit impact current; after the fault is removed, the dynamic term is reduced, so that the output current is quickly and smoothly restored to a rated value, and secondary impact and power oscillation are avoided. Under the premise of retaining line inductance and guaranteeing power loop decoupling, the method significantly improves inverter fault current limiting capability and low voltage ride through performance, speeds up system recovery speed, reduces fault loss, and is suitable for micro-grid grid-connected stable control containing a distributed power supply.

Description

Technical Field

[0001] This invention belongs to the technical field of virtual synchronous generators, specifically relating to a method for controlling the dynamic term of virtual impedance in a virtual synchronous generator to suppress instantaneous current changes during faults. Background Technology

[0002] In recent years, the global energy structure has been accelerating its transformation towards cleaner and lower-carbon energy, with distributed renewable energy sources, represented by wind and solar power, seeing a continuous increase in their penetration rate in microgrids and distribution networks. Traditional synchronous generators (SGs), with their inherent rotational inertia and damping characteristics, play a core role in grid frequency regulation, voltage support, and fault ride-through, and are a key support for ensuring the safe and stable operation of large power grids.

[0003] However, distributed generation systems generally use power electronic inverters as the grid connection interface. These inverters have fast control response, no mechanical inertia, and weak damping, resulting in microgrids lacking sufficient inertia and voltage support during grid-connected operation. When the grid experiences disturbances such as power surges, load switching, or voltage drops, microgrids are prone to severe frequency fluctuations, voltage instability, and even grid disconnection, seriously restricting the safe and stable operation of high-proportion renewable energy power systems.

[0004] To compensate for the deficiencies in inertia and damping of traditional inverters, Virtual Synchronous Generator (VSG) control technology has been proposed and widely applied. By simulating the rotor motion equations, active-frequency droop characteristics, and reactive-voltage excitation regulation characteristics of a synchronous generator, VSG endows grid-connected inverters with virtual inertia, virtual damping, and active voltage and frequency regulation capabilities, significantly improving the grid-connected stability of microgrids under steady-state and conventional disturbances.

[0005] However, under grid voltage dip fault conditions, the voltage source characteristics of a grid-connected VSG cause its output voltage to be constrained by control inertia, making it unable to instantaneously follow the sudden drop in grid voltage. This results in a large instantaneous voltage difference between the inverter's internal potential and the grid voltage. This voltage difference directly affects the line impedance and filter impedance, causing the inverter's output current to surge rapidly within milliseconds, forming an inrush current far exceeding the rated value. This can easily trigger overcurrent protection, damage power devices, and even cause a cascading grid disconnection accident.

[0006] Meanwhile, after the fault is cleared, due to the inertia and damping characteristics of the VSG, the output current is difficult to recover to the rated value quickly and smoothly. It is often accompanied by secondary current surges, power oscillations and frequency oscillations, which prolong the system recovery time, increase line losses and equipment stress, and significantly reduce the fault ride-through capability and power supply reliability of the microgrid.

[0007] In existing VSG control schemes, virtual impedance technology is used to improve power decoupling and current limiting effects. However, fixed virtual impedance values ​​are generally used, which cannot be adaptively adjusted according to the full cycle of fault occurrence, fault duration, and fault clearance. During a fault, insufficient impedance leads to limited current limiting capability, while after a fault, excessive impedance results in slow recovery and increased losses.

[0008] On the other hand, traditional VSG power loops are designed only for steady-state conditions and do not introduce dynamic compensation mechanisms for voltage dip faults. They cannot effectively suppress power oscillations and phase changes caused by faults, and it is difficult to achieve the three major goals of fault current limiting, oscillation suppression, and fast recovery in a coordinated manner.

[0009] In summary, existing VSG control technologies suffer from significant drawbacks under grid fault scenarios, including large inrush currents, poor current limiting effects, slow recovery speeds, and pronounced power oscillations, failing to meet the requirements of high-reliability microgrids for low-voltage ride-through and stable operation. Therefore, there is an urgent need to propose a control method capable of dynamically adjusting the virtual impedance in real time based on the fault depth, coupled with dynamic power loop compensation, to fundamentally suppress instantaneous changes in fault current and improve the system's fault tolerance and rapid recovery capabilities. Summary of the Invention

[0010] The main objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a virtual synchronous generator virtual impedance dynamic term control method to suppress instantaneous current changes during faults. By dynamically adjusting the virtual impedance and power loop compensation, the smooth suppression and rapid recovery of fault current can be achieved.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] In a first aspect, the present invention provides a method for controlling the dynamic term of virtual impedance of a virtual synchronous generator to suppress instantaneous current changes during a fault, comprising the following steps:

[0013] S1. After the reference voltage is generated by the power loop of the virtual synchronous generator (VSG) and before it is sent to the voltage and current dual closed-loop control, a total virtual impedance consisting of the basic virtual impedance and the virtual impedance dynamic term is introduced to adjust the reference voltage.

[0014] S2. Monitor the peak value of the inverter output current in real time, and adaptively adjust the virtual impedance dynamic term according to the current fault depth to suppress instantaneous current changes during the fault.

[0015] S3. Based on the real-time difference between the inverter output voltage and the grid voltage, apply virtual power compensation and virtual electromotive force compensation to the VSG power loop to constrain the peak fault current and suppress power oscillation.

[0016] S4. After the fault is cleared, gradually reduce the virtual impedance dynamic term to allow the output current to quickly and smoothly recover to the rated value and avoid secondary impact.

[0017] As a preferred technical solution, in step S1, the expression for the total virtual impedance is:

[0018] ;

[0019] ;

[0020] ;

[0021] Among them, Z V For the overall virtual impedance, Z base For the original virtual impedance, Z aqa For dynamic terms; K pz K iz For the proportional and integral parameters of the PI controller; S i To monitor the real-time change signal of the peak output current; I L_peak I represents the peak value of the inverter output current. th It is twice the peak value of the inverter output filter current under normal operating conditions, making the dynamic response smoother.

[0022] As a preferred technical solution, in step S2, the adjustment strategy for the virtual impedance dynamic term is as follows:

[0023] When a fault occurs and the peak current exceeds the threshold, the virtual impedance dynamic term is increased to suppress the inrush current;

[0024] When the fault is cleared and the current falls back to within the threshold, the virtual impedance dynamic term is reduced to accelerate current recovery.

[0025] As a preferred technical solution, the voltage and current dual closed loop adopts a PI controller, and the basic virtual impedance makes the line equivalent impedance inductive, thereby achieving decoupling of the active power loop and the reactive power loop.

[0026] As a preferred technical solution, in step S3, after applying virtual power compensation to the VSG active power loop, the mechanical power satisfies:

[0027] ;

[0028] in, This is the virtual power compensation amount. For reference active power, This is the active power droop coefficient. The angular frequency of the power grid synchronization. Set the operating angular frequency for VSG.

[0029] As a preferred technical solution, the virtual power compensation amount The results are calculated from the α and β axis voltages of the inverter side and the grid side:

[0030] ;

[0031] in, This is the virtual power compensation coefficient. , This is the inverter-side voltage. , This is the grid-side voltage.

[0032] As a preferred technical solution, virtual electromotive force compensation specifically involves:

[0033] ;

[0034] in, For no-load electromotive force, k i Q is the integral coefficient. ref For reference reactive power, Q e k is the instantaneous reactive power output at the inverter terminal. q Here, Un is the reactive power droop factor, Un is the inverter terminal voltage reference value, and U is the inverter terminal voltage. This is the virtual electromotive force.

[0035] As a preferred technical solution, virtual electromotive force Specifically:

[0036] ;

[0037] in, This is the virtual electromotive force compensation coefficient. , After the inverter is filtered output axis, shaft voltage, , After being output to the power grid axis, Shaft voltage.

[0038] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0039] (1) By introducing a virtual impedance dynamic term, the present invention adaptively increases the impedance when the grid voltage drops, effectively suppressing the peak value of the inrush current output of the inverter and protecting the power electronic devices.

[0040] (2) After the fault is cleared, the virtual impedance dynamic term decreases smoothly, avoiding the secondary impact of the current, so that the output current can be quickly restored to the rated value, and reducing the energy loss during the system recovery process.

[0041] (3) The present invention reduces the difference between the VSG output voltage and the grid voltage by compensating for the virtual power and virtual electromotive force of the power loop, effectively suppressing the active and reactive power oscillations during the fault period and improving the low voltage ride-through capability of the system. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 The main circuit topology and control system structure diagram of the virtual synchronous generator provided in the embodiments of the present invention;

[0044] Figure 2 The diagrams show the uncompensated grid-connected output current waveform and the compensated grid-connected output current waveform of this invention.

[0045] Figure 3 The following are waveform diagrams of the uncompensated grid-connected inrush current and the compensated grid-connected current, according to embodiments of the present invention.

[0046] Figure 4 This is a comparison waveform of fault current before and after power loop compensation, provided in an embodiment of the present invention.

[0047] Figure 5 Comparison waveform diagrams of the output current recovery process after fault clearance provided in embodiments of the present invention;

[0048] Figure 6 This is a flowchart of a virtual synchronous generator virtual impedance dynamic term control method for suppressing instantaneous current changes during faults, according to an embodiment of the present invention. Detailed Implementation

[0049] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort are within the scope of protection of the present application.

[0050] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0051] This embodiment provides a virtual impedance dynamic term control method for virtual synchronous generators to suppress instantaneous current surges during faults. This method adjusts the reference voltage generated by the power loop before it participates in the voltage and current dual loops using a virtual impedance dynamic term. The voltage and current dual loops are designed using a traditional PI controller, and the virtual impedance ensures the line impedance is inductive, facilitating power loop decoupling. When a VSG encounters a grid voltage drop, the inrush current arises from the coupling effect between the voltage source characteristics of the grid-connected VSG and the sudden drop in grid voltage. During a sudden grid voltage drop, the internal voltage of the VSG cannot instantaneously follow the grid voltage change due to the inertia of the control loop, resulting in a significant combined voltage difference. This voltage difference directly affects the total impedance of the inverter output side, including the lines and filters. Combined with the inherent characteristics of circuit transient processes, this causes the inverter output current to rise sharply in a short time. Simultaneously, the phase deviation caused by the instantaneous imbalance of the active power angle is superimposed, ultimately forming an inrush current far exceeding the rated value. If effective suppression measures are not taken, this current can easily trigger equipment protection or even damage the inverter.

[0052] Power oscillation analysis reveals that, due to the voltage inertia of the VSG, its output voltage does not align with the grid voltage for a short period. A sudden drop in grid voltage causes the output current to be a superposition of steady-state sinusoidal and transient DC components, resulting in a significantly increased peak value. Small-signal modeling shows that increased voltage drop depth reduces system damping, leading to overshoot and oscillation. Therefore, parameter optimization and compensation control are necessary to suppress power oscillations and ensure low-voltage ride-through capability.

[0053] The method comprises two parts: virtual impedance dynamic term design and power loop virtual compensation term design on the MATLAB simulation platform. The virtual impedance dynamic term design steps on the MATLAB simulation platform include:

[0054] A grid-connected inverter system mainly consists of three parts: a DC voltage source, a three-phase three-level grid-connected inverter, and an AC power grid. The inverter's virtual synchronous generator (VSG) control mimics the external characteristics of a synchronous generator (SG), giving the system virtual inertia and virtual damping, thereby achieving frequency and voltage regulation functions and facilitating grid-connection. Its main circuit topology and control system are as follows: Figure 1As shown in the figure. The meanings of the parameters in the figure are as follows: Udc is the DC side power supply; Cdc1 and Cdc2 are the DC side capacitors; Lf and Cf are the filter inductor and filter capacitor, respectively; Usabc is the three-phase voltage at the grid connection point; Vg is the three-phase voltage on the grid side; ILabc is the three-phase filter output current of the inverter; Iabc is the three-phase output current of the inverter.

[0055] Because the inductive nature of the line impedance facilitates power loop parameter tuning, a virtual impedance can be connected in series before filtering to increase the inverter's inductance. During fault occurrence and clearing, the grid voltage often experiences short-term, drastic fluctuations. Due to limitations in the control system's response speed, these voltage fluctuations can easily trigger large transient inrush currents and aperiodic components in the grid-connected inverter, thus adversely affecting the stability of the grid operation and power quality.

[0056] To improve the reliability of power system operation, dynamic virtual impedance technology demonstrates significant control capabilities under various fault conditions. It adaptively adjusts impedance values ​​based on the severity of the grid fault to respond to real-time operating conditions. During fault clearance, a decrease in the dynamic virtual impedance term helps the system maintain sufficient power output, preventing additional losses and efficiency degradation due to excessive impedance, thereby promoting efficient power transmission and accelerating the system's return to normal operation.

[0057] In the event of a significant voltage drop in the power grid, appropriately increasing the dynamic term of the virtual impedance can effectively suppress overcurrent, mitigate the current surge caused by short-circuit faults, and reduce the risk of equipment tripping or being damaged due to excessive current. By increasing the virtual impedance, the system can limit the current flow path, alleviate the operational stress caused by voltage drops or short-circuit faults, thereby maintaining the overall stability of the power grid and preventing sudden current disturbances from threatening power equipment.

[0058] like Figure 6 As shown in the figure, this embodiment provides a method for controlling the virtual impedance dynamic term of a virtual synchronous generator to suppress instantaneous current changes during faults. The method specifically includes the following steps:

[0059] S1. After the reference voltage is generated by the power loop of the virtual synchronous generator (VSG) and before it is sent to the voltage and current dual closed-loop control, a total virtual impedance consisting of the basic virtual impedance and the virtual impedance dynamic term is introduced to adjust the reference voltage.

[0060] Furthermore, the virtual impedance is composed of the following:

[0061]

[0062]

[0063]

[0064] Z V For the total virtual impedance, Z base For the original virtual impedance, Z aqa For dynamic terms; K pz K iz For the proportional and integral parameters of the PI controller; S i To monitor the real-time change signal of the peak output current; I L_peak I represents the peak value of the inverter output current. th It is twice the peak value of the inverter output filter current under normal operating conditions, resulting in a smoother dynamic response;

[0065] S2. Monitor the peak value of the inverter output current in real time, and adaptively adjust the virtual impedance dynamic term according to the current fault depth to suppress instantaneous current changes during the fault.

[0066] Furthermore, this method constructs a variable virtual impedance between the inverter's virtual internal potential and the output terminal. This not only preserves the original virtual impedance, making the line inductive and preventing the line impedance from affecting the power loop decoupling after fault clearance, but also enables it to dynamically adjust the term and output signal S based on the real-time changes in the monitored output current peak value. i When a fault occurs, i.e., the peak current exceeds the threshold, the dynamic virtual impedance term increases to suppress the inrush current, preventing damage to system equipment and maintaining a small abrupt change during faults. When the fault is cleared, the dynamic virtual impedance term decreases to stabilize the current, allowing the output current to recover to its peak value under normal operating conditions as quickly as possible, reducing line losses. Furthermore, the dynamic virtual impedance can also increase the decay rate of short-circuit current, helping the system recover to a stable operating state more quickly, thereby enhancing the overall robustness and dynamic response capability of the power grid.

[0067] S3. Based on the real-time difference between the inverter output voltage and the grid voltage, apply virtual power compensation and virtual electromotive force compensation to the VSG power loop to constrain the peak fault current and suppress power oscillation.

[0068] Furthermore, the design of the power loop virtual compensation term includes:

[0069] Virtual synchronous generator (VSG) control technology is an advanced grid-connected control strategy developed based on the traditional power electronic converter control architecture by introducing the dynamic behavior mechanism of a synchronous generator. This technology can simulate the active-frequency regulation and reactive-voltage regulation capabilities of a synchronous generator in terms of external characteristics, thereby giving the converter inertia and droop characteristics similar to those of a traditional synchronous generator, enabling it to actively participate in the dynamic support of grid frequency and voltage.

[0070] exist Figure 1In the active droop control loop shown, the VSG achieves closed-loop control of the virtual mechanical torque by integrating the droop control principle of the virtual speed governor with the rotor mechanical motion equations. The droop control formula is as follows:

[0071]

[0072] In the formula, Pref is the reference active power of the inverter, kp is the active power droop coefficient, Pm is the mechanical power of the virtual synchronous generator, w is the mechanical angular frequency of the synchronous generator, and w0 is the grid synchronization angular frequency.

[0073] Two key parameters were introduced into the machine part: virtual inertia. and damping coefficient Among them, virtual inertia The introduction of this damping coefficient gives the VSG mechanical inertia during active power regulation, which can slow down the rate of power change; while the damping coefficient... This is used to suppress dynamic power oscillations during the regulation process and improve the dynamic response stability of the system. The corresponding rotor motion equation is shown below:

[0074]

[0075] In the formula, θ is the phase of the synchronous generator, and Pe is the electromagnetic power of the virtual synchronous generator.

[0076] In addition to simulating the frequency regulation response of a synchronous generator through an active power-frequency control loop, a virtual synchronous generator (VSG) also possesses excitation regulation capabilities, simulating the excitation current control method of a synchronous generator (SG) to achieve dynamic adjustment of the terminal voltage amplitude. Figure 1 In the reactive power droop control - electrical section shown, referring to the modeling approach of the rotor motion equation, a mathematical expression describing the reactive power-voltage regulation relationship can be derived, as shown below.

[0077]

[0078] In the formula, Un is the reference value of the inverter terminal voltage, U is the inverter terminal voltage, and Q is the inverter terminal voltage. ref For reference reactive power, Q e k is the instantaneous reactive power output at the inverter terminal. q k is the reactive power droop factor. i E is the integral coefficient, E is the electromotive force of the virtual synchronous generator, and E0 is the no-load electromotive force.

[0079] The current output from the VSG to the main grid can be fully characterized by a set of expressions, and its instantaneous value follows a sinusoidal variation law, i.e. ,in The magnitude of the output current. This represents the phase angle by which the current lags behind the grid voltage. Current amplitude. VSG output voltage amplitude Grid voltage amplitude The power angle between the two The equivalent reactance X of the connecting line determines the specific calculation relationship as follows: And current phase Then by With power angle The magnitude relationship constraint is expressed as follows: The power delivered by the VSG to the main grid can be expressed as: .

[0080] As described above, when a symmetrical voltage drop occurs in the power grid, the grid voltage drops sharply. However, due to inertia, the VSG output voltage does not align with it, causing a rapid increase in both amplitude and phase difference. This results in a sharp rise in output current accompanied by a sudden phase change, directly triggering severe fluctuations and continuous oscillations in active and reactive power. At this time, the system damping is significantly reduced, and power oscillations are difficult to decay quickly, severely affecting grid stability. Therefore, dynamic compensation of the power loop is necessary to suppress oscillations and ensure stable system operation.

[0081] Therefore, the improved power loop virtual compensation is as follows:

[0082]

[0083] Among them, power loop compensation For virtual power, This represents the virtual electromotive force. Specifically, it is expressed as follows:

[0084]

[0085]

[0086] In the formula, Kpp is the virtual power compensation coefficient, and Kpu is the virtual electromotive force compensation coefficient. , After the inverter is filtered output axis, shaft voltage, , After being output to the power grid axis, Shaft voltage.

[0087] In the virtual compensation loop, dynamic compensation adaptively adjusts the amplitude and phase of the VSG output voltage by tracking the grid voltage dip in real time, directly affecting the amplitude and phase characteristics of the output current. This reduces the difference in voltage between the VSG output voltage and the grid voltage, minimizes phase abrupt changes, suppresses surges in transient current peaks, and smooths power angle changes, preventing drastic current phase jumps. This effectively suppresses power oscillations, enabling stable operation during and after faults, and improving the system's low-voltage ride-through capability.

[0088] S4. After the fault is cleared, gradually reduce the virtual impedance dynamic term to allow the output current to quickly and smoothly recover to the rated value and avoid secondary impact.

[0089] Furthermore, after the fault was cleared, the grid voltage returned to its rated value, and the peak value of the inverter output current gradually dropped back to within the threshold.

[0090] The virtual impedance dynamic term gradually decreases and exits, and the total virtual impedance returns to the basic virtual impedance;

[0091] With the combined effect of compensation control and virtual impedance, the output current quickly and smoothly recovers to the rated value, avoiding secondary current surges and power oscillations, shortening system recovery time, and reducing line losses.

[0092] In specific simulation experiments, the algorithm's performance is verified under a scenario of 30% voltage symmetric fading. Specifically:

[0093] In this scenario, the virtual synchronous generator (VSG) operates in parallel with the main grid under normal conditions. Subsequently, a 30% symmetrical voltage drop occurs at t=2 seconds, lasting until t=2.5 seconds, after which the grid voltage returns to normal operation for 4 seconds. The simulation results are as follows... Figure 2 As shown, where, Figure 2 Part (a) is the output current before compensation. Figure 2 Part (b) is the output current after compensation.

[0094] Depend on Figure 3 As seen in part (a), after the fault occurs at t=2 seconds, the output current experiences a short-term, drastic fluctuation, resulting in an inrush current that differs significantly from the output current under normal operating conditions, thus affecting the quality of the inverter's output current to the grid. Compared to the algorithm that incorporates a virtual impedance dynamic term control, i.e. Figure 3 The output current waveform in part (b) shows that the peak value of the inrush current is significantly suppressed, and the difference between the output current under normal operating conditions is small, which reduces the instantaneous loss of the inverter's working components when a fault occurs.

[0095] Depend on Figure 4As shown in part (a), the fault current before power loop compensation is much greater than the output filter current under normal operating conditions, increasing power loss during the fault period. Furthermore, the frequency oscillation causes the output filter current to reach stable output very slowly. Figure 4 As can be seen from part (b) in the text, after the virtual electromotive force and virtual power are compensated by the power loop, the fault current is less than the threshold current, ensuring that the inverter works at the maximum value that the working devices can withstand. Moreover, after compensation, the frequency oscillation amplitude is smaller, making it easier for the output current to reach stability and reducing the system's operating losses under fault conditions.

[0096] Depend on Figure 5 As can be seen in part (a), after exiting the fault condition, the time required for the inverter output filter current to recover to the peak output current under normal operating conditions is relatively long. Due to the inertial damping effect of the VSG, the frequency recovers to be in phase with the grid very slowly, thus the output current lags behind the output voltage in slowly recovering to the normal peak current. Figure 5 As shown in part (b), under virtual impedance control, the output current recovers to the rated current under normal operating conditions in a shorter time because the phase oscillation amplitude is smaller than before compensation. Furthermore, the virtual impedance dynamic term design allows for a slower exit after fault clearance, thus enabling a more rapid return from the relatively high current peak to the output current peak under normal operating conditions.

[0097] In summary, this embodiment achieves coordinated control through four steps: introducing total virtual impedance, dynamically adjusting the virtual impedance dynamic term, applying power loop and electromotive force compensation, and smoothly exiting current limiting after fault clearance. While preserving line inductance and ensuring stable decoupling of the power loop, it effectively suppresses instantaneous changes and peak values ​​in inverter output current during grid faults, significantly reducing power and frequency oscillations during fault periods. After fault clearance, it can quickly and smoothly return to rated operating conditions, avoiding secondary impacts and additional losses. This comprehensively improves the fault current limiting capability, low-voltage ride-through performance, and system operational stability of the virtual synchronous generator, fully achieving the technical objectives described in this invention.

[0098] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0099] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0100] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for controlling the virtual impedance dynamic term of a virtual synchronous generator to suppress instantaneous current changes during faults, characterized in that, Includes the following steps: S1. After the reference voltage is generated by the power loop of the virtual synchronous generator (VSG) and before it is sent to the voltage and current dual closed-loop control, a total virtual impedance consisting of the basic virtual impedance and the virtual impedance dynamic term is introduced to adjust the reference voltage. S2. Monitor the peak value of the inverter output current in real time, and adaptively adjust the virtual impedance dynamic term according to the current fault depth to suppress instantaneous current changes during the fault. S3. Based on the real-time difference between the inverter output voltage and the grid voltage, apply virtual power compensation and virtual electromotive force compensation to the VSG power loop to constrain the peak fault current and suppress power oscillation. S4. After the fault is cleared, gradually reduce the virtual impedance dynamic term to allow the output current to quickly and smoothly recover to the rated value and avoid secondary impact.

2. The method for controlling the virtual impedance dynamic term of a virtual synchronous generator to suppress instantaneous current changes during faults, as described in claim 1, is characterized in that... In step S1, the expression for the total virtual impedance is: ； ； ； Among them, Z V For the overall virtual impedance, Z base For the original virtual impedance, Z aqa For dynamic terms; K pz K iz For the proportional and integral parameters of the PI controller; S i To monitor the real-time change signal of the peak output current; I L_peak I represents the peak value of the inverter output current. th It is twice the peak value of the inverter output filter current under normal operating conditions, making the dynamic response smoother.

3. The method for controlling the virtual impedance dynamic term of a virtual synchronous generator to suppress instantaneous current changes during faults, as described in claim 2, is characterized in that... In step S2, the adjustment strategy for the virtual impedance dynamic term is as follows: When a fault occurs and the peak current exceeds the threshold, the virtual impedance dynamic term is increased to suppress the inrush current; When the fault is cleared and the current falls back to within the threshold, the virtual impedance dynamic term is reduced to accelerate current recovery.

4. The method for controlling the virtual impedance dynamic term of a virtual synchronous generator to suppress instantaneous current changes during faults, as described in claim 1, is characterized in that... The voltage and current dual closed loop uses a PI controller, and the basic virtual impedance makes the line equivalent impedance inductive, thereby decoupling the active power loop from the reactive power loop.

5. The method for controlling the virtual impedance dynamic term of a virtual synchronous generator to suppress instantaneous current changes during faults, as described in claim 1, is characterized in that... In step S3, after applying virtual power compensation to the VSG active power loop, the mechanical power satisfies: ； in, This is the virtual power compensation amount. For reference active power, This is the active power droop coefficient. The angular frequency of the power grid synchronization. Set the operating angular frequency for VSG.

6. The method for controlling the virtual impedance dynamic term of a virtual synchronous generator to suppress instantaneous current changes during faults, as described in claim 5, is characterized in that... The virtual power compensation amount The results are calculated from the α and β axis voltages of the inverter side and the grid side: ； in, This is the virtual power compensation coefficient. , This is the inverter-side voltage. , This is the grid-side voltage.

7. The method for controlling the virtual impedance dynamic term of a virtual synchronous generator to suppress instantaneous current changes during faults, as described in claim 1, is characterized in that... The virtual electromotive force compensation is specifically as follows: ； in, For no-load electromotive force, k i Q is the integral coefficient. ref For reference reactive power, Q e k is the instantaneous reactive power output at the inverter terminal. q Here, Un is the reactive power droop factor, Un is the inverter terminal voltage reference value, and U is the inverter terminal voltage. This is the virtual electromotive force.

8. The method for controlling the virtual impedance dynamic term of a virtual synchronous generator to suppress instantaneous current changes during faults, as described in claim 7, is characterized in that... Virtual electromotive force Specifically: ； in, This is the virtual electromotive force compensation coefficient. , After the inverter is filtered output axis, shaft voltage, , After being output to the power grid axis, Shaft voltage.

Images