Network construction type converter fault current limiting method considering power angle stability

Abstract

The invention discloses a network construction type converter fault current limiting method considering power angle stability, and belongs to the power electronic technology. According to the method, firstly, an active power adaptive adjustment coefficient is introduced into an active-frequency control loop, the power angle variation of the converter at the moment of a fault is suppressed, and the transient power angle stability of the converter is guaranteed; secondly, an output voltage reference value is adjusted through a reactive power-voltage control loop, the voltage difference between the converter and the power grid is reduced, and the current steady-state component in the fault period is restrained; and finally, a variable virtual reactance is introduced into a voltage outer ring, and a transient current impact component at the fault moment is suppressed. The current limiting method is provided for the grid-forming type converter when the grid-side voltage symmetrically drops, continuous increase of the output current in the converter fault period can be restrained, meanwhile, power angle instability is prevented, and the method has the advantages of being high in response speed, good in current limiting effect and high in power angle stability.

Description

TECHNICAL FIELD

[0001] The application relates to a grid-connected converter fault current limiting method considering power angle stability, and belongs to the technical field of power electronics. BACKGROUND

[0002] With the increasing proportion of renewable energy generation represented by photovoltaic and wind power generation in the power grid, the power electronic characteristics in the power system become more and more obvious. The grid-connected converter controlled by the power electronic device does not have the strong current tolerance capability of the traditional synchronous generator, and a large fault current is generated when the voltage of the power grid drops, which may cause damage to the semiconductor device of the converter if not handled in time. The grid-side voltage drop also reduces the transient power angle stability of the grid-connected converter, and there is a risk of power angle instability. The traditional fault current limiting method often does not consider both aspects at the same time. SUMMARY

[0003] The application provides a grid-connected converter fault current limiting method considering power angle stability, which improves the active-frequency control loop and the reactive-voltage control loop, and introduces a variable virtual reactance to effectively suppress short-circuit overcurrent under different grid-side voltage drop degrees and ensure power angle stability during faults.

[0004] Technical scheme: To achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0005] A grid-connected converter fault current limiting method considering power angle stability comprises the following steps:

[0006] Step 1: introducing an active power self-adaptive adjustment coefficient in the active-frequency control loop to suppress the power angle change of the converter at the fault moment and guarantee the transient power angle stability of the converter;

[0007] Step 2: adjusting the output voltage reference value through the reactive-voltage control loop to reduce the voltage difference between the converter and the power grid and suppress the steady-state current component during the fault;

[0008] Step 3: introducing a variable virtual reactance in the voltage outer loop to suppress the transient current impact component at the fault moment.

[0009] Specifically, in step 1, the active power self-adaptive adjustment coefficient is introduced in the active-frequency control loop to suppress the power angle change of the converter at the fault moment and guarantee the transient power angle stability of the converter, which comprises the following steps:

[0010] S11, based on the rotor motion characteristics of the synchronous generator, an expression of the power angle change Δδ of the converter at the moment of grid-side voltage drop is constructed: Wherein: t is the moment of grid-side voltage drop, ω nP is the active power reference value of the converter before the fault, and P is the active power actual value of the converter after the fault, J and D are the moment of inertia and the damping coefficient respectively; ref P and P e are the active power reference value and the active power actual value of the converter after the fault respectively, J and D are the moment of inertia and the damping coefficient respectively;

[0011] S12, the active power output by the converter before the fault is the power angle and the active power output by the converter after the fault are δ F = δ0+ Δδ and wherein: P e0 and P eF are the active power output by the converter before and after the fault, U0 and U F are the voltage of the converter before and after the fault, δ0 and δ F are the power angle of the converter before and after the fault, U g0 and U gF are the grid-side voltage before and after the fault, X g is the line reactance;

[0012] S12, by adjusting the active power reference value P ref , the power angle change Δδ is minimized, and the active power output by the converter after the fault is designed as an active power self-adaptive adjustment coefficient K F is constructed, and the expression is:

[0013] Specifically, in order to prevent the active power self-adaptive adjustment coefficient K F from causing the active power to be unstable due to frequent switching, the grid-side voltage U g is set to drop to 0.9U g0 , and the trigger signal S = 0, the active power self-adaptive adjustment coefficient K F is effective, the active power reference value P ref = P ref0 × K F ; otherwise, the trigger signal S = 1, the active power self-adaptive adjustment coefficient K F is not effective, the active power reference value P ref = P ref0 , P ref0 is the active power reference value of the converter before the fault.

[0014] Specifically, in step 2, the output voltage reference value is adjusted by the reactive power-voltage control loop to reduce the voltage difference between the converter and the power grid, and to suppress the steady-state component of the current during the fault, including the following steps:

[0015] S21, the steady-state current component of the converter is analyzed to obtain the power angle expression of the converter during normal operation and during the fault: and wherein: U gF = kU g0 , k is a voltage drop coefficient, I0 and I F are the steady-state currents of the converter during normal operation and during a fault, respectively; the change in power angle of the converter Δδ is minimized after adjustment by the active power self-adaptive adjustment coefficient, and the voltage reference value during the fault is constructed as I F may be selected according to the actual requirements of the converter, and may be selected as the steady-state current threshold of the converter during the fault;

[0016] S22, a voltage drop coefficient k is introduced to the output voltage reference value E0 of the converter in the reactive-voltage control loop, and during the fault, the output voltage reference value is adjusted to kE0, so as to quickly match the voltage drop of different degrees on the grid side and accelerate the response speed of the reactive-voltage control loop;

[0017] S23, the droop characteristic of the reactive-voltage control loop will cause a deviation between the output voltage of the converter and the output voltage reference value, which will affect the fault current limiting effect; in order to ensure that the current amplitude does not exceed the safe range, the reactive power reference value Q ref is frozen as the actual value of the reactive power Q e , so that the converter provides reactive power support for the grid while ensuring the accuracy of the fault current limiting.

[0018] Specifically, in order to prevent the active power from being unstable due to frequent switching of the voltage drop coefficient k, the voltage on the grid side U g drops to 0.9U g0 , a trigger signal S = 0 is triggered, the voltage drop coefficient k works, the reactive power reference value Q ref is frozen as the actual value of the reactive power Q e , and the output voltage reference value E0 associated with the rated voltage reference value U n is adjusted to kE0, and the voltage outer loop reference value U ref is linked according to the correction logic of the rated voltage reference value U n ; otherwise, the trigger signal S = 1 is triggered, the voltage drop coefficient k does not work, the reactive power reference value Q ref , the rated voltage reference value U n and the voltage reference value E0 return to the normal operation mode, and the system stability is maintained.

[0019] Specifically, in step 3, a variable virtual reactance is introduced in the voltage outer loop to suppress the transient current impact component at the moment of the fault, including the following steps:

[0020] S31, a variable virtual reactance X vF is introduced to the voltage reference value E0 of the converter, and the dq-axis voltage is designed as wherein: i d and i q are the dq-axis components of the output current, the variable virtual reactance X vF produces the dq-axis voltage components u dv and u qv directly act on the voltage outer loop, which can avoid affecting the normal operation of the converter;

[0021] S32, the variable virtual reactance is designed as wherein: i max is a single-phase transient current shock threshold, X v0 is a rated virtual reactance, i * is a maximum fault phase current of the converter, i * = max(i a , i b , i c ), i a , i b , i c is a three-phase current output by the converter, I0 is a steady-state current of the converter during normal operation; the single-phase transient current shock threshold i max is set to be slightly greater than a steady-state current threshold of the converter during the fault, and when the transient current shock component decays to zero, the variable virtual reactance X vF is not triggered, and X vF only suppresses the transient current shock component during the fault.

[0022] Advantages: the network configuration type converter fault current limiting method considering power angle stability provided by the application has the following advantages compared with the prior art: 1. The application can suppress the fault overcurrent caused by symmetrical voltage drop of the power grid, and can ensure the transient power angle stability during the fault, and prevent the power angle instability risk existing when the voltage drops; 2. The application introduces a voltage drop coefficient in the reactive power-voltage control loop, which can accelerate the response speed of the reactive power-voltage control loop; 3. The application directly acts the voltage of the variable virtual reactance on the voltage-current double closed loop, and the bandwidth is much greater than that of the power loop, so that the network configuration type converter can quickly track the voltage reference value; and when the current amplitude is below the set threshold, the application automatically exits, which does not affect the steady-state operation of the system. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a topological structure diagram for realizing the method of the application;

[0024] Figure 2 is an improved active power-frequency control loop in the application;

[0025] Figure 3 is an improved reactive power-voltage control loop in the application;

[0026] Figure 4 a voltage outer loop for introducing virtual reactance in the present application;

[0027] Figure 5 Fig. 5 shows simulation results of the converter obtained by the method of the present application: Fig. 5(a) is a curve of output current of the converter; Fig. 5(b) is a curve of active power and a curve of reactive power of the converter; and Fig. 5(c) is a curve of power angle of the converter. DETAILED DESCRIPTION

[0028] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0029] As Figure 1 shown in Fig. 1 is a topology of a network-type converter fault current limiting method considering power angle stability, first, an active power self-adaptive adjustment coefficient is introduced in the active-frequency control loop to suppress the power angle variation of the converter at the moment of fault and guarantee the transient power angle stability of the converter; second, the output voltage reference value is adjusted through the reactive-voltage control loop to reduce the voltage difference between the converter and the power grid and suppress the steady-state current component during the fault; and finally, a variable virtual reactance is introduced in the voltage outer loop to suppress the transient current impulse component at the moment of fault.

[0030] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0031] Step 1, improving the active-frequency control loop

[0032] An active power self-adaptive adjustment coefficient is introduced in the active-frequency control loop to suppress the power angle variation of the converter at the moment of fault and guarantee the transient power angle stability of the converter.

[0033] S11, constructing the network-type converter to simulate the prime mover governor control and rotor motion characteristics of the synchronous generator:

[0034]

[0035] wherein ω n and ω are the angular speed reference value and the angular speed actual value, P ref and P e are the active power reference value and the active power actual value, and J and D are the moment of inertia and the damping coefficient respectively.

[0036] The power angle variation of the converter at the moment of grid-side voltage drop is Δδ = ∫ω n dt, and the above formula can be obtained by substitution:

[0037]

[0038] wherein t is the moment of grid-side voltage drop.

[0039] S12, the power angle of the converter after the fault can be expressed as δ F = δ0+ Δδ, the active power output of the converter before and after the fault is P and P respectively. e0 eF U0and U F are the voltages of the converter before and after the fault respectively, δ0and δ F are the power angles of the converter before and after the fault respectively, U g0 and U gF are the voltages of the grid side before and after the fault respectively, and X g is the line reactance.

[0040] S13, by adjusting the active power reference value P ref , the power angle of the converter before and after the fault changes little, i.e. δ F ≈ δ0, Δδ is a minimum value, then sinΔδ≈Δδ, cosΔδ≈1, thus, the active power output of the converter after the fault can be designed as P The expression of the active power self-adaptive adjustment coefficient is further designed as:

[0041]

[0042] Due to the fluctuation of the actual grid voltage, in order to prevent the power instability caused by the frequent switching of the active power self-adaptive adjustment coefficient K F , the grid side voltage U g is set to drop to 0.9U g0 , below which the trigger signal S=0, the active power self-adaptive adjustment coefficient K F is in effect, the active power reference value P ref =P ref0 ×K F ; otherwise, the trigger signal S=1, the active power self-adaptive adjustment coefficient K F is not in effect, the active power reference value P ref =P ref0 , P ref0 is the active power reference value of the converter before the fault.

[0043] The improved active-frequency control loop is shown in Figure 2 , which is used to prevent the power angle instability.

[0044] ① When in normal operation, S=1, U g ≥0.9U g0 : the trigger switch is on, the "normal branch" is connected, P ref =P ref0 , the active-power loop operates according to the droop characteristic of the synchronous machine (simulates the prime mover speed regulation, maintains the frequency stability).​

[0045] ② After the fault is triggered, S = 0, U g <0.9U g0 : First, derive minimize Δδ; then, trigger the switch to turn on the "fault branch", P ref = P ref0 × K F , by actively reducing the active target, avoid the power angle when the fault is large fluctuations due to power imbalance, to ensure transient power angle stability.

[0046] ③ After the fault is recovered, S = 1, U g ≥ 0.9U g0 : Trigger switch back to normal branch, K F exit, P ref = P ref0 , active-frequency ring continues to maintain frequency stability.

[0047] Step 2, improve the reactive-voltage control loop

[0048] Adjust the output voltage reference value through the reactive-voltage control loop to reduce the voltage difference between the converter and the grid, and suppress the steady-state component of the current during the fault.

[0049] S21, analyze the steady-state current component of the converter, and get the converter power angle expression during normal operation and during the fault:

[0050]

[0051] Where: U gF = kU g0 , k is the voltage drop coefficient, I0 and I F are the steady-state currents of the converter during normal operation and during the fault, respectively.

[0052] After adjusting the active power self-adaptive adjustment coefficient K F , the converter power angle changes little before and after the fault, that is, cosδ0≈cosδ F , so the voltage reference value during the fault can be constructed as:

[0053]

[0054] Where: I F can be selected according to the maximum current that the semiconductor device of the converter can withstand, to achieve accurate current limiting. In the experiment, the steady-state current threshold of the converter during the fault is selected.

[0055] S22, voltage drop coefficient k is introduced to voltage reference value E0 of converter of reactive-voltage control loop, so that output voltage of converter can reach voltage reference value faster, and transient impact current component in initial stage of fault is reduced. During fault, voltage reference value is adjusted to kE0, so that voltage reference value E0 can quickly match voltage drop of different degrees of grid side, and response speed of reactive-voltage control loop is accelerated.

[0056] S23, voltage difference between converter and grid during fault makes output reactive power of converter increase, and droop characteristic of reactive-voltage control loop makes deviation between output voltage of converter and voltage reference value, thereby affecting fault current limiting effect; in order to ensure that current amplitude does not exceed safe range, reactive power reference value Q ref is frozen to actual value Q e of reactive power after voltage drop of grid side, so that converter provides reactive support for grid while ensuring accuracy of fault current limiting.

[0057] In order to prevent active power instability caused by frequent switching of voltage drop coefficient k, grid side voltage U g drops to 0.9U g0 , and trigger signal S is 0, voltage drop coefficient k works, and reactive power reference value Q ref is frozen to actual value Q e of reactive power, output voltage reference value E0 associated with rated voltage reference value U n is adjusted to kE0, and voltage outer loop reference value U ref is linked according to correction logic of rated voltage reference value U n ; otherwise, trigger signal S is 1, voltage drop coefficient k does not work, reactive power reference value Q ref , rated voltage reference value U n and voltage reference value E0 return to normal operation mode, and system stability is maintained.

[0058] Improved reactive-voltage control loop is as shown in Figure 3 , and is used for preventing voltage instability.

[0059] ① During normal operation, S is 1, U g ≥0.9U g0 : in reactive loop, Q ref is adjusted according to reactive-voltage droop characteristic (reactive power is increased when grid voltage is low, and reactive power is reduced when grid voltage is high); in voltage loop, E0=U n , and U ref follows E0, so that system voltage stability is maintained.

[0060] ② after fault triggering, S is 0, U g <0.9U g0 : first, freeze switch is connected, Qref = Q e (Forced reactive reference equals the actual value), avoid voltage deviation caused by droop characteristics interference limit current accuracy; then, E0 is adjusted to kE0 (fast matching grid voltage drop, reduce the voltage difference between the converter and the grid), suppress the steady-state component of fault current; finally, according to the correction logic of U n , the modified U ref .

[0061] ③ After the fault is recovered, S = 1, U g ≥ 0.9U g0 : Freeze switch off, Q ref restore droop regulation; E0, U ref return to rated value, continue to maintain voltage stability.

[0062] Step 3, improve the voltage outer loop

[0063] Introduce variable virtual reactance in the voltage outer loop to suppress the transient current impact component at the moment of fault.

[0064] S31, introduce variable virtual reactance X vF Feedforward correction is made to the voltage reference value E0 of the converter, and the dq axis voltage is designed as:

[0065]

[0066] Where: i d and i q are the dq axis components of the output current, and the dq axis voltage components u vF and u dv generated by the variable virtual reactance X qv directly act on the voltage outer loop, as shown in Figure 4 , which can avoid affecting the normal operation of the converter.

[0067] S32, design the variable virtual reactance as:

[0068]

[0069] Where: i max is the single-phase current impact threshold, X v0 is the rated virtual reactance, i * is the maximum fault phase current of the converter, i * = max(i a , i b , i c ), i a , i b , i c is the three-phase current output by the converter; The size of the variable virtual reactance X vF is related to the current difference i* -i max proportional, i * less than i max , the value of variable virtual reactance X vF is 0.

[0070] The single-phase current shock threshold i max is set to be slightly greater than the steady-state current threshold of the converter during the fault, and when the transient current shock component decays to zero, the variable virtual reactance X vF is not triggered, X vF only suppresses the fault current transient shock component.

[0071] The improved voltage outer loop is shown in Figure 4 to prevent device damage.

[0072] ① Normal operation / steady-state fault, i * ≤ i max : X vF = 0, the virtual reactance module does not act, and the voltage outer loop operates according to the conventional logic (receives the corrected E0 as the reference). Figure 3

[0073] ② Transient triggering, i * >i max , fault instant: first, calculate X vF , the more serious the current overrun, the larger the X vF (simulate "dynamic series reactance", quickly limit the current); then, feedforward correct the voltage outer loop, directly superimpose the dq-axis voltage u dv and u qv generated by the virtual reactance on the voltage outer loop reference value, which is equivalent to "instantly increasing the reactance" of the converter output, suppressing the transient current shock component (the response speed is much faster than the power loop, achieving "millisecond-level current limiting").

[0074] ③ After the transient ends, i * ≤ i max , transient component decays: X vF automatically returns to 0, the virtual reactance module exits, and the voltage outer loop restores to the conventional control, without affecting the steady-state operation of the system.

[0075] To verify the superiority of the control method provided in the case, simulation analysis is performed in MATLAB / simulink, and the main simulation parameters are shown in Table 1. The converter operates normally before the fault, the grid-side voltage drops to 0.3pu at t=0.5s, and the grid-side voltage returns to the rated voltage at t=1.5s.

[0076] Table 1: Main simulation parameters

[0077] ​

[0078]

[0079] The simulation results are shown in Figure 5 .

[0080] In the output current curve of Figure 5 (a), in the transient stage (at 0.5 s), the current peak is quickly suppressed by the variable virtual reactance of Figure 4 (millisecond-level response), and i max is not exceeded (slightly greater than 1.2 pu), verifying the effect of “transient shock suppression”. In the steady state stage (0.5-1.5 s), the current is stabilized at about 1.2 pu (close to I F ), which is dominated by the reactive-voltage loop of Figure 3 , and the voltage difference between the converter and the power grid is reduced by modifying E0=kE0, thereby limiting the steady-state current.

[0081] In the active power curve and the reactive power curve of Figure 5 (b), at the time of fault triggering (0.5 s), the active power quickly drops, which is caused by the K F modification of P ref of Figure 2 (active reduction of active target, suppression of power angle deviation); the reactive power quickly rises, because the Q ref of the reactive-voltage loop of Figure 3 is frozen at Q e , and the converter provides reactive power support to the grid (grid voltage drop, converter needs to compensate reactive power). In the fault steady state (0.5-1.5 s), the active power is stabilized at a low value with small fluctuations, indicating that the power angle has not changed significantly (K F successfully suppresses power angle instability); the reactive power is stabilized at a high value, which not only meets the reactive power demand of the grid, but also avoids the interference of droop characteristics with current limiting (ensures that the current is stabilized at I F ) through “freezing Q ref ”. After the fault recovery (1.5 s), the active power returns to the rated value, K F exits, and the active loop resumes frequency regulation; the reactive power falls, the reactive loop is unfrozen, and the droop regulation is restored.

[0082] In the power angle curve of the converter of Figure 5 (c), in the whole fault process (0.5-1.5 s), the power angle changes little (fluctuates smoothly without large jumps or oscillations), and K F effectively suppresses the power angle deviation. After the fault recovery (after 1.5 s), the power angle returns to the rated value, and the system recovers synchronization.

[0083] In summary, the current limiting strategy provided in the case can still guarantee the output current of the converter at the set threshold when the grid voltage drops severely, the power angle is effectively controlled during the fault, and the converter can provide certain reactive power support to the grid during the fault.

[0084] The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the above embodiments do not limit the present application in any form, and any technical solutions obtained by equivalent replacement or equivalent transformation fall within the protection scope of the present application.

Claims

1. A network configuration type converter fault current limiting method considering power angle stability, characterized in that: The method comprises the following steps: Step 1, introducing an active power adaptive adjustment coefficient in the active-frequency control loop to suppress the power angle variation of the converter at the fault moment and guarantee the transient power angle stability of the converter; Step 2, adjusting the output voltage reference value through the reactive-voltage control loop to reduce the voltage difference between the converter and the power grid and suppress the steady-state current component during the fault; Step 3, introducing a variable virtual reactance in the voltage outer loop to suppress the transient current impact component at the fault moment. 2.The networked converter fault current limiting method with consideration of power angle stability according to claim 1, characterized in that: In the step 1, the active power adaptive adjustment coefficient is introduced in the active-frequency control loop to suppress the power angle variation of the converter at the fault moment and guarantee the transient power angle stability of the converter, comprising the following steps: S11, based on the rotor motion characteristics of the synchronous generator, the expression of the power angle variation of the converter Δδ at the moment of grid voltage drop is constructed: Wherein: t is the moment of grid voltage drop, ω n is the angular velocity reference value, P ref and P e are the active power reference value and the actual value of the active power of the converter after the fault, J and D are the moment of inertia and the damping coefficient respectively; S12, the active power outputted by the converter before the fault is the power angle and the active power outputted by the converter after the fault are δ F = δ0+ Δδ and wherein: P e0 and P eF are the active power outputted by the converter before and after the fault respectively, U0 and U F are the voltage of the converter before and after the fault respectively, δ0 and δ F are the power angle of the converter before and after the fault respectively, U g0 and U gF are the voltage of the grid side before and after the fault respectively, X g is the line reactance; S12, adjust the active power reference value P ref , make the converter power angle change amount Δδ minimum, and design the active power output by the converter after the fault as , construct the active power self-adaptive adjustment coefficient K F Expression: 3.The networked converter fault current limiting method with consideration of power angle stability according to claim 2, characterized in that: Setting the grid-side voltage U g Fall to 0.9U g0 Below, the trigger signal S = 0, the active power adaptive adjustment coefficient K F Active, the active power reference value P ref = P ref0 × K F ; otherwise, the trigger signal S = 1, the active power adaptive adjustment coefficient K F Not active, the active power reference value P ref = P ref0 , P ref0 is the active power reference value of the converter before the fault.

4. The method of claim 1, wherein the method is a network-forming converter fault current limiting method considering power angle stability. In the step 2, the output voltage reference value of the converter is adjusted through the reactive-voltage control loop to reduce the voltage difference between the converter and the power grid and suppress the steady-state current component during the fault, comprising the following steps: S21, the steady-state current component of the converter is analyzed to obtain the power angle expression of the converter during normal operation and during failure: and Wherein: U gF =kU g0 , k is the voltage drop coefficient, I0 and I F are the steady-state current of the converter during normal operation and during failure respectively; after being adjusted by the active power self-adaptive adjustment coefficient, the power angle change amount Δδ of the converter is minimum, and the voltage reference value during failure is constructed as S22, introducing a voltage drop coefficient k to the output voltage reference value E0 of the converter in the reactive-voltage control loop, and adjusting the output voltage reference value to kE0 during the fault; S23, after the voltage drop of the network side, the reactive power ring is frozen, and the reactive power reference value Q ref The frozen is the actual value of the reactive power Q e .

5. The method of claim 4, wherein the method is a network-forming converter fault current limiting method considering power angle stability. Setting the grid-side voltage U g Dropping to 0.9U g0 When the following, trigger signal S = 0, voltage drop coefficient k works, reactive power reference value Q ref Frozen as the actual value of reactive power Q e , the output voltage reference value E0 associated with the rated voltage reference value U n Adjustment to kE0, voltage outer loop reference value U ref According to the rated voltage reference value U n The modified logic linkage; otherwise, trigger signal S = 1, voltage drop coefficient k does not work, reactive power reference value Q ref , rated voltage reference value U n And the voltage reference value E0 return to normal operation mode, maintain system stability.

6. The method of claim 1, wherein the method is a network-forming converter fault current limiting method considering power angle stability. In the step 3, the variable virtual reactance is introduced in the voltage outer loop to suppress the transient current impact component at the fault moment, comprising the following steps: S31, introducing variable virtual reactance X vF The voltage reference value E0 of the converter is feedforward corrected, and the dq-axis voltage is designed as Wherein: i d And i q The dq-axis components of the output current, the variable virtual reactance X vF The dq-axis voltage components u dv And u qv Directly act on the voltage outer loop; S32, the variable virtual reactance is designed as wherein: i max is a single-phase transient current shock threshold, X v0 is a rated virtual reactance, i * is a maximum fault phase current of the converter, i * = max(i a , i b , i c ), i a , i b , i c is a three-phase current output by the converter, I0is a steady-state current of the converter during normal operation; the single-phase transient current shock threshold i max is set to be greater than a steady-state current threshold of the converter during the fault, and after the transient current shock component is attenuated to zero, the variable virtual reactance X vF is not triggered, and X vF only suppresses the transient current shock component during the fault.

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