A network-configuration type power supply fault current suppression method based on additional virtual impedance and power angle control

Abstract

A network type power supply fault current suppression method based on additional virtual impedance and power angle control, comprising: if it is judged that the network type power supply with virtual synchronous generator (VSG) as the main structure is below the threshold after the fault occurs, the reactive power reference value is calculated and adjusted according to the drop degree to meet the low voltage ride through condition; the difference between the VSG output voltage and the grid voltage and the maximum bearing current of the inverter are used to quantitatively calculate the virtual impedance required for current limiting; the active power reference value is modified by using the reactive loop reference voltage before and after the fault to maintain the VSG power angle stability; the mathematical model of the inverter in the VSG is constructed, the virtual impedance is added to the control loop by using the coordinate transformation and the grid side current transformation, and the output drive signal is controlled by inputting the voltage modulation into the SVPWM, so that the inverter completes the overcurrent limiting. The application solves the problem that the output current of the network type new power system increases too fast to cause system instability when the fault occurs.

Description

Technical Field

[0001] This invention relates to the field of power system stability control, and specifically to a method for suppressing fault current in grid-connected power sources based on additional virtual impedance and power angle control. Background Technology

[0002] With the large-scale grid connection of power generation units such as wind power and photovoltaics, which use power electronic converters as interfaces, significant changes have occurred in the structure and dynamic characteristics of the power system. When faced with large disturbances such as short-circuit faults, problems may arise such as current over-limit, inability to achieve low-voltage ride-through, and generator power angle instability.

[0003] For overcurrent suppression and low-voltage ride-through strategies in grid-type power systems, one approach is to switch the grid-type control mode to a grid-following control mode (Chen Tianyi, Chen Laijun, Zheng Tianwen, et al. Low-voltage ride-through control method for virtual synchronous generators based on smooth mode switching [J]. Power System Technology, 2016). However, this approach cannot fully utilize the active support capability of the grid-type control mode, abandoning the advantages of the grid-type control model, and also faces problems in the fault recovery process. Another approach is to design virtual resistors to suppress overcurrent (Shang Lei, Hu Jiabing, Yuan Xiaoming, et al. Modeling and improved control of virtual synchronous generators under symmetrical grid faults [J]. Proceedings of the CSEE, 2017). At present, most applications of virtual impedance do not provide specific calculations, only qualitatively proposing the concept of virtual impedance. At the same time, when designing virtual impedance, the impact on the stability of the system power angle after its addition is not considered, and the assumption is too idealistic, which to some extent affects the stable operation of the system. Summary of the Invention

[0004] To suppress overcurrent, low-voltage ride-through, and power angle stability after a large disturbance in the power system, this invention proposes a grid-type power source fault current suppression method based on additional virtual impedance and power angle control. By calculating and correcting the power reference value, quantitatively designing the virtual impedance, and adding it to the system, low-voltage ride-through and effective overcurrent suppression can be achieved, significantly improving power system stability. Simultaneously, it can maintain power angle stability while adaptively and quantitatively calculating the virtual impedance for current limiting, thus completing the system's current limiting task and meeting the low-voltage ride-through requirements. This fully leverages the advantages of the grid-type control model and ensures system stability.

[0005] The technical solution adopted in this invention is:

[0006] A method for suppressing fault current in a grid-type power supply based on additional virtual impedance and power angle control includes the following steps:

[0007] Step 1: If the voltage drop falls below the threshold after a grid-type power supply fault with VSG as the main structure, calculate and adjust the reactive power reference value according to the degree of voltage drop. To meet low voltage ride-through requirements;

[0008] Step 2: Quantitatively calculate the virtual impedance Z required for current limiting using the difference between the output voltage of the virtual synchronous generator (VSG) and the grid voltage, as well as the maximum current that the inverter in the VSG can withstand. v ;

[0009] Step 3: Utilize the reference voltage of the reactive power circuit before and after the fault. Modify active power reference value To maintain VSG power angle stability;

[0010] Step 4: Construct a mathematical model of the inverter in the VSG. Use coordinate transformation and grid-side current transformation to add the virtual impedance calculated in Step 2 into the control loop of the mathematical model. Control the inverter to limit overcurrent by outputting the drive signal in the voltage modulation input SVPWM.

[0011] Furthermore, in step one, a reference value of reactive power that satisfies the low-voltage ride-through condition is calculated based on the degree of voltage drop. Specifically:

[0012]

[0013] In the formula: λ represents the voltage drop; U gNd The d-axis component represents the rated voltage of the power grid; I Q U is the reactive current that needs to be satisfied after a voltage drop. gNd By analyzing U gN The Park transformation is obtained by performing the Park transformation. Angle through the grid connection point voltage U g Phase-locked loop (PLL) is performed to obtain the data.

[0014] Furthermore, the reactive current I that needs to be satisfied after the voltage drop... Q The calculation formula is as follows:

[0015]

[0016] In the formula: I N Indicates the rated current of the VSG; U g This represents the per-unit value of the grid connection point voltage.

[0017] Furthermore, step two involves quantitatively calculating the virtual impedance Z required for current limiting. v Specifically, it includes:

[0018]

[0019]

[0020] In the formula: Z d Z q For virtual impedance Z v d-axis and q-axis components; E d E q R represents the d-axis and q-axis components of the VSG output voltage. eq ,X eq These are the equivalent resistance and equivalent reactance of the line before the fault, respectively; U gd U gq The d-axis and q-axis components of the grid voltage after the fault occur; considering both steady-state and transient aspects: for transient stability, the maximum current that the inverter can withstand over a long period of time is taken as... I N K is the rated current of the VSG. s The inverter's long-term current withstand factor is taken as [value]. Similarly, considering steady-state conditions, the maximum peak current that the inverter can withstand is [value]. K t Z is the peak current withstand factor of the inverter; where Z v =R v +jL v , where R v =Z v ×cosθ,L v =Z v ×sinθ, where θ is the line impedance angle before the fault.

[0021] Furthermore, step three utilizes the reference voltage of the reactive power circuit before and after the fault. Modify active power reference value To maintain VSG power angle stability, specifically including: the reference voltage of the reactive power circuit before and after the fault. As shown in equation (5):

[0022]

[0023] In the formula: D q This refers to the reactive power voltage droop factor.

[0024] The active power reference value is modified by equation (6) to maintain a stable power angle.

[0025]

[0026] In the formula: This is the revised active power reference value; P ref This is the original power reference value.

[0027] Furthermore, step four specifically includes:

[0028] The grid-side current is introduced into the control loop using a feedback method. The loop is then transformed to the (α, β) coordinate system. The closed-loop transfer function U of the capacitor voltage is obtained based on the control loop through which the grid-side current passes the feedback point. cv (s):

[0029]

[0030] In the formula: s is a complex frequency domain variable; G v (s) is a voltage controller that tracks the reference voltage; G d (s) is the transfer function of the delay element; L f C f For the filter's capacitor and inductor; K i Z is the active damping coefficient of the VSG side current; v (s) is the virtual impedance, satisfying Z v (s)=R v +G s (s)L v G s (s) is the differentiating element used to realize the virtual inductance;

[0031] After determining that the grid voltage has dropped, the low voltage ride-through control strategy is activated. At the same time, the virtual impedance calculated in step two is added to the control loop for current limiting. The capacitor voltage transfer function U obtained by equation (7) is used. cv (s) Obtain the capacitor voltage U cv The voltage is then transformed into (α, β) coordinates to obtain the components of the capacitor voltage on the α and β axes. These components are then introduced into the voltage inner loop control to modulate the calculated voltage. The calculated voltage value is then introduced into Space Vector Pulse Width Modulation (SVPWM) using a reference voltage controller and damping coefficient to output a drive signal to control the inverter, thereby achieving the effect of suppressing overcurrent.

[0032] The beneficial effects of this invention are as follows:

[0033] (1) This invention considers both the current limiting target and the low voltage ride-through requirement, which helps to ensure that new energy sources do not disconnect from the grid during faults.

[0034] (2) The adaptive virtual impedance quantitative calculation method proposed in this invention only needs to focus on the voltage difference between the two sides, so it has strong adaptability under different fault conditions;

[0035] (3) In this invention, after adding virtual impedance, the impact on system stability is considered. A corrected active power reference value is added to prevent power angle divergence and ensure system stability. Attached Figure Description

[0036] Figure 1 This is the equivalent diagram of VSG operating in parallel with the network;

[0037] Figure 2 It is the equivalent mathematical model of the inverter in VSG;

[0038] Figure 3 This is a system structure diagram of the present invention after adding virtual impedance in an embodiment;

[0039] Figure 4 This is a flowchart illustrating a grid-type power supply fault current suppression method based on additional virtual impedance and power angle control, according to an embodiment of the present invention.

[0040] Figure 5 This is a graph showing the grid voltage and VSG output current when the grid voltage drops to 0.8 pu;

[0041] Figure 6 This is a graph showing the output current and reactive power of the VSG after current limiting measures are implemented when the grid voltage drops to 0.8 pu.

[0042] Figure 7 This is the power angle curve of the system after the grid voltage drops to 0.8 pu and a current limiting strategy is adopted;

[0043] Figure 8 This is a graph showing the grid voltage and VSG output current when the grid voltage drops to 0.6 pu;

[0044] Figure 9 This is a graph showing the output current and reactive power of the VSG after current limiting measures are implemented when the grid voltage drops to 0.6 pu.

[0045] Figure 10 This is the power angle curve of the system after the grid voltage drops to 0.6 pu and a current limiting strategy is adopted;

[0046] Figure 11 This is a graph showing the grid voltage and VSG output current when the grid voltage drops to 0.2 pu.

[0047] Figure 12 This is a graph showing the output current and reactive power of the VSG after current limiting measures are implemented when the grid voltage drops to 0.2 pu.

[0048] Figure 13 This is the power angle curve of the system after the grid voltage drops to 0.2 pu and a current limiting strategy is adopted;

[0049] Figure 14 This is a comparison chart showing the effects of current limiting strategies on different voltage drop levels. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0051] like Figure 4 As shown, this embodiment of the invention provides an overcurrent suppression method for a grid-type new energy system based on virtual impedance quantitative design and power angle control, comprising the following steps:

[0052] Step 1: Determine whether the voltage drops below a threshold (e.g., 0.9 pu) after a grid-connected power source with VSG as its main structure experiences a fault. If the voltage drops, adjust the reactive power reference value Q of the virtual synchronous generator (VSG). ref for Provide reactive power support to the system to meet the low-voltage ride-through requirements of national standards. According to national requirements for low-voltage ride-through of renewable energy power plants, the reactive current I required after a voltage dip must meet certain conditions. Q As shown in equation (1):

[0053]

[0054] In the formula: I N Indicates the rated current of the VSG; U g This represents the per-unit value of the grid connection point voltage.

[0055] The voltage control loop of the VSG includes a reactive power-voltage droop stage, which can spontaneously increase reactive power output after the grid voltage drops. When the VSG is connected to the grid, the reactive power output changes when the grid voltage deviates and drops, which can easily lead to overcurrent risk for the VSG when the grid voltage fluctuates. Therefore, when the VSG is connected to the grid, in order to maintain stable operation, the reactive power output is switched off after the reactive power-voltage droop stage is switched off. Its steady-state reactive power output is the same as the reactive power reference value. The reactive power reference value is changed by equation (2) to provide reactive power support to the system, and the requirement for reactive current output of the VSG during the grid voltage drop is transformed into a requirement for reactive power. The reactive power reference value after VSG correction As shown in equation (2):

[0056]

[0057] In the formula: λ represents the voltage drop; U gNd The d-axis component represents the rated voltage of the power grid.

[0058] By calculating I that satisfies the low voltage ride-through condition Q and U gNd reactive power reference value at time Among them I Q U should be taken as shown in equation (1). gNd For U gN The d-axis component obtained through the Park transform, in the Park transform Angle through the grid connection point voltage U g Phase-locked loop (PLL) is used to ensure that the invention satisfies the low-voltage ride-through condition while performing the current-limiting task.

[0059] Step 2: Calculate the virtual impedance value required for current limiting using the relationship between the VSG, grid voltage, and line impedance during the voltage sag. Let the VSG output voltage be E and the grid voltage be U. g Before the fault, the total impedance between the VSG output voltage and the mains voltage was R. eq +jωL eq The virtual impedance added to achieve overcurrent suppression and low voltage ride-through is Z. v =R v +jωL v .according to Figure 1 The equivalent circuit diagram of the VSG during grid-connected operation shown below can be used for steady-state analysis:

[0060]

[0061] The output current amplitude |I| of the VSG is obtained by solving:

[0062]

[0063] In the formula: t0 is the time when the fault occurs; ΔE is the voltage difference between the VSG and the power grid before the fault occurs; U' g This represents the grid voltage after the fault.

[0064] Since the DC component rapidly decays to zero after a fault, and the fault current reaches its maximum value I when the voltage difference is at its maximum, it can be considered that the fault current reaches its maximum value I. max As shown in equation (5):

[0065]

[0066] As shown in equation (5), fault current can be suppressed by increasing the equivalent resistance and decreasing the voltage difference. Since the attenuation rate of the VSG output voltage E is much lower than that of the grid voltage, it can be approximated as a constant value. Therefore, the current limiting condition can be met by limiting the maximum fault current to below the maximum current that the inverter can withstand. This invention proposes to add the virtual impedance calculation values ​​shown in equations (6) and (7) to the system to achieve the current limiting effect:

[0067]

[0068] In the formula: Z d Z q For virtual impedance Z v d-axis and q-axis components; E d E q R represents the d-axis and q-axis components of the VSG output voltage. eq ,X eq These are the equivalent resistance and equivalent reactance of the line before the fault, respectively; U gd U gq The d-axis and q-axis components of the grid voltage after the fault occur; considering both steady-state and transient aspects, the maximum current that the inverter can withstand over a long period is taken as the steady-state value. K s I is the long-term current withstand factor of the inverter. N The rated current of the VSG output is taken as the maximum peak current that the inverter can withstand in transient mode. K t Z is the peak current withstand factor of the inverter. v =R v +jL v , where R v =Z v ×cosθ,L v =Z v ×sinθ, where θ is the line impedance angle before the fault. To facilitate stable control of the power angle, the impedance angle is assumed to remain unchanged before and after the grid voltage drop.

[0069] Step 3: Adjust the reference voltage value according to the reactive power voltage droop coefficient after the fault to adjust the active power command value and complete the control of power angle stability. By controlling the reactive power circuit to keep the voltage difference between the VSG output voltage and the grid voltage unchanged before and after the fault, the active power reference value is reduced to maintain power angle stability. It can be seen that the reference voltage of the reactive power circuit before and after the fault is as shown in equation (8):

[0070]

[0071] In the formula: D q This is the reactive power voltage droop coefficient.

[0072] As shown in equation (8), keeping the voltage difference constant can keep the output current constant before and after the fault, but this process will cause the output voltage of the VSG to decrease, thereby endangering the transient power angle stability of the VSG. Therefore, the active power reference value is modified by equation (9) to improve its power angle stability.

[0073]

[0074] In the formula: This is the revised active power reference value; P ref This is the original power reference value.

[0075] Step 4: Construct the mathematical model of the inverter in the VSG. Utilize grid-side current transformation to incorporate the calculated virtual impedance into the system's voltage inner-loop control to achieve current limiting. Based on the topology of the inverter's main circuit in the VSG, use Kirchhoff's current-voltage law to obtain the time-domain expression of the inverter in the three-phase stationary coordinate system. Then, perform a Laplace transform to obtain the frequency expression, thus deriving the mathematical model of the inverter. Figure 2 Because the mathematical model is complex to solve, the Clark transformation is used to reduce its order to obtain a mathematical model in a two-phase stationary coordinate system, thus completing the modeling.

[0076] Since the gain of the feedback method is 1, there is no need to verify the previously calculated virtual impedance value. Therefore, the feedback method is used to introduce the grid-side current into the control loop, and the coordinates are transformed to the (α, β) coordinate system. The closed-loop transfer function U of the capacitor voltage is obtained from the control loop through which the grid-side current passes through the feedback point. cv (s):

[0077]

[0078] In the formula: s is a complex frequency domain variable, G v (s) is a voltage controller that tracks the reference voltage, G d (s) is the transfer function of the delay element, L f C f K represents the capacitor and inductor of the filter. i Z is the active damping coefficient of the VSG side current. v (s) is the virtual impedance, satisfying Z v (s)=R v +G s (s)L v G s (s) is the differentiating element used to realize the virtual inductance, which is simulated using a non-ideal generalized integrator.

[0079]

[0080] After determining that the grid voltage has dropped, this invention initiates a low-voltage ride-through control strategy while simultaneously adding a virtual impedance to the control loop for current limiting, through the capacitor voltage transfer function U in equation (10). cv (s) Obtain the capacitor voltage U cvThe voltage is transformed in (α, β) coordinates to obtain its components on the α and β axes. These components are then introduced into the voltage inner loop control to modulate the calculated voltage. Using a reference voltage controller and damping coefficient, the calculated voltage value is fed into the SVPWM output drive signal to control the inverter, thereby suppressing overcurrent. The system structure after adding virtual impedance is as follows: Figure 3 As shown.

[0081] Example: Data synchronization simulation was performed to verify the effectiveness of the strategy and the results were compared with those under different voltage drop conditions. A VSG model was built in MATLAB / Simulink for data synchronization simulation. A photovoltaic power generation model was constructed and connected to an inverter as a grid-connected power source. The system was set to experience a voltage drop at t0 = 1.2s and recover at 1.7s. Experimental parameters are shown in Table 1.

[0082] Table 1

[0083] physical quantity numerical values physical quantity numerical values <![CDATA[Rated amplitude U of grid voltage gn / V]]> 311 DC voltage rating / V 2000 <![CDATA[Inverter long-term current tolerance coefficient K s > 0.1 <![CDATA[Inverter peak current withstand coefficient K t > 0.3 <![CDATA[Rated frequency f n / Hz]]> 50 <![CDATA[Filter capacitor C f / μF]]> 10 <![CDATA[Line inductance L g / mH]]> 1.2 <![CDATA[Reactive power voltage droop coefficient D q > <![CDATA[2.2×10 -4 ]]> <![CDATA[Line resistance R g / Ω]]> 0.05 <![CDATA[Parasitic resistance R of the filtering inductor g / Ω]]> 0.05 <![CDATA[Rated capacity S N / kVA]]> 100 <![CDATA[Filter inductor L f / mH]]> 4

[0084] At time t0, the grid voltage drops, and the VSG output current also changes. Based on the degree of grid voltage drop, the required reactive current is calculated according to equation (1). The calculated reactive current demand is converted into reactive power demand according to the reactive power command value adjustment method proposed in this invention. Simultaneously, according to the virtual impedance calculation method proposed in this invention, the d-axis and q-axis components of the VSG voltage and grid voltage at this time are obtained by performing a Park transformation. The inverter's maximum withstand current value and maximum withstand peak value, along with the required reactive current I at this time, are then used. Q The virtual impedance d and q-axis components Z required to complete the current limiting task at this time are calculated using equation (6). d Z q Thus, the required virtual impedance value Z can be obtained using equation (7). v Then, the calculated capacitor voltage transfer function is added to the control loop of the model to complete the current limiting task.

[0085] Case 1: When the mains voltage drops to 0.8 pu, the mains voltage and VSG output current are as follows: Figure 5 As shown, the peak current reaches 760A, exceeding the rated current. To prevent impact on system stability, a current-limiting strategy is required. Based on the above analysis and calculations, reactive power adjustment is performed during voltage dips, and a virtual impedance is added for overcurrent limiting. The added virtual impedance R... v It is 8.1Ω, L v The reactive power adjustment and current limiting effect is 10.85mH. Figure 6As shown, it can be clearly observed that after implementing current limiting measures, the reactive power increased from zero when the fault occurred, and returned to zero when the fault disappeared. The peak overcurrent was 540A, and the system was within the safe range. Compared with before the current limiting strategy, the peak overcurrent was significantly suppressed. Simultaneously, the system power angle before and after the fault... Figure 7 The data shows fluctuations during the occurrence and disappearance of faults, but the overall process remains stable and does not diverge.

[0086] Case 2: When the mains voltage drops to 0.6 pu, the mains voltage and VSG output current are as follows: Figure 8 As shown, during a VSG fault, the peak output current reaches 800A, exceeding the inverter's maximum withstand value and severely impacting system stability. Based on the above analysis and calculations, reactive power adjustment is performed during voltage dips, and a virtual impedance is added for overcurrent limiting. The added virtual impedance includes R... v It is 9.57Ω, L v The reactive power curve and VSG output current curve after adjustment are as follows: 2.38mH Figure 9 As shown, it can be observed that reactive power increases when a fault occurs to enable the system to meet low-voltage requirements, while in contrast... Figure 8 The magnitude of overcurrent after a VSG fault in the middle. Figure 9 The VSG output current curve in the figure demonstrates the current-limiting effect of the proposed strategy. After the current-limiting strategy is implemented, the peak overcurrent is 400A, which is within the inverter's tolerance range. The system's power angle is as follows: Figure 10 As shown, the system remained relatively stable both before and after a fault occurred and after the fault disappeared.

[0087] Case 3: When the mains voltage drops to 0.2 pu, due to the excessive drop, the VSG output current cannot recover to its pre-fault state after the fault is cleared. (Combined with...) Figure 11 The system exhibits severe current fluctuations. Without the current limiting strategy proposed in this invention, the system becomes unstable, the power angle diverges, and it is difficult to restore stability. However, this strategy can still achieve similar stability to a certain extent under these circumstances. Figure 12 The diagram shows the limitation of overcurrent magnitude and adjustment of reactive power to meet low-voltage requirements. Based on the above analysis and calculations, a virtual impedance R needs to be added at this time. v It is 6.29Ω, L v It is 20.65mH. While completing the current limiting task, such as... Figure 13 As shown, although the power angle did not completely return to the state before the fault after current limiting, it can be seen from the power angle curve that after power angle stabilization control, the power angle curve tends to a new stable value, the current waveform is relatively stable, the power angle does not diverge, and the system remains stable.

[0088] The current limiting effect is measured by the ratio of the difference in overcurrent before and after current limiting to the overcurrent before current limiting. The current limiting effect varies with different voltage drop levels, as shown below. Figure 14 As shown, this scheme effectively limits overcurrent while meeting the requirements of low voltage ride-through. Even with excessive voltage drops, it still effectively limits overcurrent and effectively controls the power angle to prevent divergence, thus improving system stability to a certain extent.

[0089] This invention provides overcurrent suppression, power angle control, and low-voltage ride-through for grid-connected new energy power systems. Utilizing the characteristics of grid-connected power systems, it quantitatively calculates the required virtual impedance value and controls the power angle by calculating a new active power reference value to maintain stability. Overcurrent suppression is achieved by incorporating a digital model of the equipment into the control loop. This invention solves the problem of system instability caused by excessively rapid increases in output current during faults in grid-connected new power systems. It is crucial for the reliable operation of new power systems primarily based on new energy sources and provides valuable reference for researching control strategies for overcurrent faults in new power systems.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for suppressing fault current in a grid-type power supply based on additional virtual impedance and power angle control, characterized in that, Includes the following steps: Step 1: If the voltage drop falls below the threshold after a grid-type power supply fault with VSG as the main structure, calculate and adjust the reactive power reference value according to the degree of voltage drop. To meet low voltage ride-through requirements; Step 2: Quantitatively calculate the virtual impedance required for current limiting using the difference between the output voltage of the virtual synchronous generator (VSG) and the grid voltage, as well as the maximum current that the inverter in the VSG can withstand. ; Step 3: Utilize the reference voltage of the reactive power circuit before and after the fault. Modify active power reference value To maintain VSG power angle stability; Step 4: Construct a mathematical model of the inverter in the VSG. Use coordinate transformation and grid-side current transformation to add the virtual impedance calculated in Step 2 into the control loop of the mathematical model. Control the inverter to limit overcurrent by outputting the drive signal in the voltage modulation input SVPWM.

2. The method for suppressing fault current in a grid-type power supply based on additional virtual impedance and power angle control according to claim 1, characterized in that, In step one, the reactive power reference value that meets the low voltage ride-through condition is calculated based on the degree of voltage drop. Specifically: （2）； In the formula: Indicates the degree of voltage drop; The d-axis component represents the rated value of the grid voltage; This refers to the reactive current that needs to be satisfied after a voltage drop. Through the The Park transformation is obtained by performing the Park transformation. Angle through the voltage at the grid connection point Phase-locked loop (PLL) is performed to obtain the data.

3. The method for suppressing fault current in a grid-type power supply based on additional virtual impedance and power angle control according to claim 1, characterized in that, Reactive current required to be met after voltage drop The calculation formula is as follows: ； In the formula: Indicates the rated current of the VSG; This represents the per-unit value of the grid connection point voltage.

4. The method for suppressing fault current in a grid-type power supply based on additional virtual impedance and power angle control according to claim 1, characterized in that, Step 2: Quantitatively calculate the virtual impedance required for current limiting. Specifically, it includes: ； ； In the formula: , Virtual impedance The d-axis and q-axis components; , These are the d-axis and q-axis components of the VSG output voltage; , These are the equivalent resistance and equivalent reactance of the line before the fault, respectively; , The d-axis and q-axis components of the grid voltage after the fault occur; considering both steady-state and transient aspects: for transient stability, the maximum current that the inverter can withstand over a long period of time is taken as... , This is the rated current of the VSG. The inverter's long-term current withstand factor is taken as [value]. Similarly, considering steady-state conditions, the maximum peak current that the inverter can withstand is [value]. , is the peak current withstand factor of the inverter; where ,in , , This represents the line impedance angle before the fault.

5. The method for suppressing fault current in a grid-type power supply based on additional virtual impedance and power angle control as described in claim 1, characterized in that: Step 3: Utilize the reference voltage of the reactive power circuit before and after the fault. Modify active power reference value To maintain VSG power angle stability, specifically including: the reference voltage of the reactive power circuit before and after the fault. As shown in equation (5): ； In the formula: This refers to the reactive power voltage droop factor. The active power reference value is modified by equation (6) to maintain a stable power angle: ； In the formula: This is the revised active power reference value; This is the original power reference value.

6. The method for suppressing fault current in a grid-type power supply based on additional virtual impedance and power angle control as described in claim 1, characterized in that: Step four specifically includes: The feedback method is used to introduce the grid-side current into the control loop, and its coordinates are transformed to... In the coordinate system, the closed-loop transfer function of the capacitor voltage is obtained from the control loop of the grid-side current passing through the feedback point. : ； In the formula: s is a complex frequency domain variable; A voltage controller for tracking a reference voltage; This is the transfer function for the delay element; For the capacitor and inductor of the filter; The active damping coefficient for the VSG side current; For virtual impedance, satisfying ; This is the differentiating element used to realize the virtual inductance; After determining that the grid voltage has dropped, the low voltage ride-through control strategy is initiated, and the virtual impedance calculated in step two is added to the control loop for current limiting. The capacitor voltage transfer function obtained by equation (7) is used. Obtain the capacitor voltage and conduct it Coordinate transformation yields the capacitor voltage at... The component on the axis is introduced into the voltage inner loop control to modulate the calculated voltage. The calculated voltage value is then introduced into the SVPWM output drive signal to control the inverter using the reference voltage controller and damping coefficient, thereby achieving the effect of suppressing overcurrent.

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