Time sequence fault current-limiting control method and system compatible with grid-connected guide rule for network construction type doubly-fed wind turbine generator

Abstract

The invention discloses a time sequence fault current-limiting control method and system compatible with a grid-connected guide rule for a network construction type doubly-fed wind turbine generator, and the method comprises the following steps: freezing external power control when a low-voltage ride-through event of a power grid is detected at the initial stage of a fault, and suppressing transient overcurrent through dynamically adjusting the resistance component of virtual impedance; in the fault stable stage, an electromotive force compensation increment is calculated on the basis of grid-connected guide rule requirements at the moment 4 tau after the fault occurs; in the fault clearing stage, after it is detected that the fault is cleared, electromotive force compensation is stopped; gradually recovering the virtual impedance to a rated value through the dynamic coefficient A; in the fault recovery stage, active control and reactive control are recovered in sequence, power output is recovered to the level before the fault within one second, and meanwhile the virtual impedance amplitude is gradually recovered to the rated value along with the voltage phase difference; the voltage phase jump amplitude and the voltage drop amplitude determined by the method have high robustness.

Description

Technical Field

[0001] This invention relates to the field of power grid technology, and specifically to a method and system for controlling sequential fault current limiting in grid-connected doubly fed wind turbine generators that is compatible with grid connection guidelines. Background Technology

[0002] In modern power systems with high wind power penetration, doubly-fed induction generators (DFIGs) based on grid forming (GFM) have shown promising application prospects to adapt to the shift from grid-following power sources to grid-connected power sources. They are gradually moving from demonstration projects to large-scale grid connection. Currently, the current-limiting control strategy of GFM-DFIGs during low-voltage transition (LVRT) involves a trade-off between fast current response and voltage support, and still has significant shortcomings in handling transient overcurrents and response delays during fault transitions. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a method and system for time-sequence fault current limiting control of grid-connected doubly fed wind turbine generators that is compatible with grid-connected guidelines, thereby solving the significant shortcomings in handling instantaneous overcurrent and response delay during fault transition.

[0004] Technical solution: The present invention provides a time-fault current limiting control method for grid-connected doubly-fed induction generators compatible with grid connection guidelines, comprising the following steps:

[0005] (1) In the initial stage of the fault, when a low voltage ride-through event is detected, the external power control is frozen, and the resistance component of the virtual impedance is dynamically adjusted. Suppress transient overcurrent;

[0006] (2) During the fault stabilization phase, at 4τ after the fault occurs, the electromotive force compensation increment ΔE is calculated based on the grid connection guidelines. dq ;

[0007] (3) During the fault clearing phase, after the fault is detected to be cleared, electromotive force compensation is stopped; the virtual impedance is gradually restored to the rated value through the dynamic coefficient A.

[0008] (4) During the fault recovery phase, active power control and reactive power control are restored sequentially, and the power output is restored to the level before the fault within 1 second. At the same time, the virtual impedance amplitude is gradually restored to the rated value along with the voltage phase difference.

[0009] Furthermore, in step (1), the resistance and inductance components are:

[0010]

[0011] Among them, tf The parameter m represents the initial value of A, indicating the time of failure; where m > 1; the exponential time constant τ controls the rate at which A decays to 1 over time; E 0dq U represents the virtual electromotive force before the fault along the dq axis. sfdq The stator terminal fault voltage under the dq axis; L vn With R vn These represent the rated virtual inductance and resistance under normal operating conditions; σ is the user-defined virtual impedance ratio; I m This is the maximum operating current of the doubly fed wind turbine.

[0012] Furthermore, in step (2), the electromotive force compensation increment ΔE dq The formula is as follows:

[0013]

[0014] Where K1 is the reactive current proportionality coefficient specified by GC; U sf The stator voltage amplitude during a doubly-fed induction generator (DFIG) fault; ω s For grid frequency; I N The rated current of the doubly-fed wind turbine; during the freeze active power control period, at δ f Calculated by the following formula

[0015] δ f =Arg(U sfd +jU sfq )

[0016] Furthermore, in step (3), the virtual impedance adjustment formula is as follows:

[0017]

[0018] Among them, t c It is the fault clearing moment, σ n =ω s L vn / R vn X corresponds to VI during normal operation v / R v Ratio; U scdq This is the stator terminal voltage under the dq axis during the fault recovery phase; parameters τ and m are the same as those in the first phase.

[0019] The present invention discloses a timing fault current limiting control system for grid-connected doubly-fed wind turbine generators compatible with grid-connection guidelines, comprising:

[0020] Fault initiation module: Used to freeze external power control when a low-voltage ride-through event is detected on the power grid, by dynamically adjusting the resistive component of the virtual impedance. Suppress transient overcurrent;

[0021] Fault stabilization module: Used to calculate the electromotive force compensation increment ΔE at 4τ after a fault occurs, based on grid connection guidelines. dq ;

[0022] Fault clearing module: Used to stop electromotive force compensation after detecting that the fault has been cleared; and to gradually restore the virtual impedance to the rated value through the dynamic coefficient A;

[0023] Fault recovery phase module: used to sequentially restore active and reactive power control, restore power output to the pre-fault level within 1 second, and at the same time, the virtual impedance amplitude gradually recovers to the rated value with the voltage phase difference.

[0024] Furthermore, in the fault initialization module, the resistance and inductance components are:

[0025]

[0026] Among them, t f The parameter m represents the initial value of A, indicating the time of failure; where m > 1; the exponential time constant τ controls the rate at which A decays to 1 over time; E 0dq U represents the virtual electromotive force before the fault along the dq axis. sfdq The stator terminal fault voltage under the dq axis; L vn With R vn These represent the rated virtual inductance and resistance under normal operating conditions; σ is the user-defined virtual impedance ratio; I m This is the maximum operating current of the doubly fed wind turbine.

[0027] Furthermore, in the fault stabilization module, the electromotive force compensation increment ΔE dq The formula is as follows:

[0028]

[0029] Where K1 is the reactive current proportionality coefficient specified by GC; U sf The stator voltage amplitude during a doubly-fed induction generator (DFIG) fault; ω s For grid frequency; I N The rated current of the doubly-fed wind turbine; during the freeze active power control period, at δ f Calculated by the following formula

[0030] δ f =Arg(U sfd +jU sfq )

[0031] Furthermore, in the fault clearing module, the virtual impedance adjustment formula is as follows:

[0032]

[0033] Among them, t c It is the fault clearing moment, σ n =ω s L vn / R vn X corresponds to VI during normal operation v / R v Ratio; U scdq This is the stator terminal voltage under the dq axis during the fault recovery phase; parameters τ and m are the same as those in the first phase.

[0034] An electronic device according to the present invention includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the program to implement the steps of any of the methods described herein.

[0035] The present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of any of the methods described herein.

[0036] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: It not only mitigates transient impacts during fault occurrence and clearing, but also ensures that active and reactive current outputs meet GC standards during fault periods. Furthermore, it can stably restore the internal voltage source (IVS) of the GFM-DFIG to pre-fault levels during the fault recovery phase, avoiding prolonged oscillations. In addition to better aligning with GC requirements throughout the fault period, the proposed FCL strategy also exhibits strong robustness against uncertain voltage phase jumps and voltage dips. Attached Figure Description

[0037] Figure 1 This is a flowchart of the present invention;

[0038] Figure 2 This is an overall control block diagram of the present invention;

[0039] Figure 3 This describes the vector relationship between the internal voltage source of the GFM-DFIG and the grid connection point voltage of the present invention. Detailed Implementation

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0041] like Figure 1-2 As shown, this embodiment of the invention provides a timing fault current limiting control method for grid-connected doubly-fed induction generator (DFIG) wind turbines that is compatible with grid connection guidelines, comprising the following steps:

[0042] (1) In the initial stage of the fault, when a low voltage ride-through event is detected, the external power control is frozen, and the resistance component of the virtual impedance is dynamically adjusted. Suppress transient overcurrents; specifically as follows:

[0043] First, external power control is frozen, causing the internal voltage source (IVS) characteristics of the GFM-DFIG to exhibit completely "static" behavior during low voltage ride-through (LVRT). Figure 2 ΔP in sf and ΔQ sf Directly set to zero, i.e., S1 = S2 = 0. This static behavior ensures the expected active voltage support capability of the GFM-DFIG. During this stage, the GFM-DFIG should effectively suppress temporary overcurrents under sudden symmetrical voltage dips. The amplitude I of the steady-state stator current... sf =||I sfdq ||and Closely related. Larger ||Z v ||This can reduce the risk of temporary overcurrent, but may lead to I sf This reduces the capacity utilization of GFM-DFIG. Furthermore, the shorter time constant T... v =L v / R v This can shorten the duration of overcurrent. To find a balance between these factors, a dynamic resistance that decays over time can be introduced. The resistance increases by ||Z in a short period of time. v ||and reduce T v Based on these considerations, a dynamic coefficient A is proposed to adjust the resistance. The VI setting principles have been updated as shown in equation (1).

[0044]

[0045] Among them, t f The parameter m represents the initial value of A, indicating the time of failure; where m > 1; the exponential time constant τ controls the rate at which A decays to 1 over time; E 0dq U represents the virtual electromotive force before the fault along the dq axis. sfdq The stator terminal fault voltage under the dq axis; L vn With R vn These represent the rated virtual inductance and resistance under normal operating conditions; σ is the user-defined virtual impedance ratio; I m This is the maximum operating current of the doubly fed wind turbine.

[0046] (2) During the fault stabilization phase, at 4τ after the fault occurs, the electromotive force compensation increment ΔE is calculated based on the grid connection guidelines. dq The details are as follows:

[0047] At time 4τ after the fault occurs, the fault phase transitions to fault steady state. During this phase, in addition to meeting the current limiting preconditions, the FCL strategy must also ensure that the GFM-DFIG outputs reactive and active currents according to GC requirements. By analyzing the relationship between the IVS and the external power grid, the steady-state stator output current characteristics of the GFM-DFIG need to be studied, specifically as follows: Figure 2 As shown,

[0048] Figure 3 This is a vector diagram showing the relationship between voltage and current in a GFM-DFIG circuit. (a) shows the equivalent circuit; (b) shows the vector diagram, where U... s0 E0 and E0 represent the stator voltage vector and electromotive force (EMF) vector before the fault, respectively, with a phase difference of δ0 between them. After the fault occurs, the phase difference changes from δ0 to δ... f .angle and φ f These correspond to the VI angle and power factor angle on the stator side, respectively. According to the grid GC requirements, the EMF compensation increment ΔE dq It can be given by the following formula:

[0049]

[0050] Where K1 is the reactive current proportionality coefficient specified by GC; U sf The stator voltage amplitude during a doubly-fed induction generator (DFIG) fault; ω s For grid frequency; I N The rated current of the doubly-fed wind turbine; during the freeze active power control period, at δ f Calculated by the following formula

[0051] δ f =Arg(U sfd +jU sfq (3)

[0052] (3) During the fault clearing phase, after the fault is detected to be cleared, electromotive force compensation is stopped; the virtual impedance is gradually restored to the rated value through the dynamic coefficient A; the details are as follows:

[0053] Once the symmetrical fault is cleared, the need for rapidly supplying reactive current to the grid no longer exists. Therefore, the supply of reactive current to E must be stopped immediately. 0dq The compensation, i.e., ΔE in equation (2) d and ΔE q Set it directly to zero. At this stage, the stator voltage can be assumed to recover to U. scdq And there is ||U scdq ||=||U s0dq ||=1p.u. However, U scdq phase relative to Us0dq Changes will occur. Even if power control and VI are immediately switched back to normal operating mode, the GFM-DFIG may still experience temporary overcurrents and power oscillations. Therefore, the two main objectives at this stage are to suppress potential secondary overcurrents and restore VI to its pre-fault value.

[0054] Based on these objectives, the third stage reintroduces the VI adjustment coefficient A. Unlike the initial fault stage, in the third stage, the amplitude and phase angle of the VI must be gradually restored to their rated values, while voltage phase jumps are eliminated through adaptive phase control (active power control). Taking these factors into account, the user-defined VI ratio σ = X v / R v It was directly restored to its rated value. Furthermore, The amplitude is adjusted by the dynamic coefficient A to prevent overcurrent. Equation (4) outlines the specific VI setting principles for the third stage.

[0055]

[0056] Among them, t c It is the fault clearing moment, σ n =ω s L vn / R vn X corresponds to VI during normal operation v / R v Ratio; U scdq This is the stator terminal voltage under the dq axis during the fault recovery phase; parameters τ and m are the same as those in the first phase.

[0057] (4) During the fault recovery phase, active and reactive power control are restored sequentially, restoring power output to pre-fault levels within 1 second. Simultaneously, the virtual impedance amplitude gradually recovers to its rated value along with the voltage phase difference. Specifically: The sequential recovery mechanism of reactive power control followed by active power control allows the outer power loop to gradually regain regulation of the GFM-DFIG. Active power control is rapidly restored (ΔP). sc =P s0 * -P s ( ), to quickly restore the active power to the pre-fault level P s0 The setting principle for VI at this stage is also given by equation (4). Meanwhile, ||Z v The value of || gradually recovers to ||Z vn ||, with the electromotive force E 0dq With stator voltage U scdq Voltage difference δ between c It gradually recovers to the value δ0 before the fault.

[0058] Because reactive power control remains frozen, the magnitude of the electromotive force remains unchanged (the same as ||E0||). As phase angle δ and VI fully recover to their values ​​under normal operating conditions, the stator steady-state output current I... scdq like Figure 3 As shown in the relationship, the system can be fully restored to its pre-fault state. Once active and reactive power recover to pre-fault levels, reactive power control can be immediately restored (ΔQ). sc =Q s0 * -Q s Furthermore, no further adjustment of reactive power is required. Considering that the active power recovery time span is several seconds, it is recommended to restore reactive power control 1 second after active power control is restored.

Claims

1. A time-fault current-limiting control method for grid-connected doubly-fed induction generator (DFIG) compatible with grid-connection guidelines, characterized in that, Includes the following steps: (1) In the initial stage of the fault, when a low voltage ride-through event is detected, the external power control is frozen, and the resistance component of the virtual impedance is dynamically adjusted. Suppress transient overcurrent; (2) During the fault stabilization phase, at 4τ after the fault occurs, the electromotive force compensation increment ΔE is calculated based on the grid connection guidelines. dq ; (3) During the fault clearing phase, after the fault is detected to be cleared, electromotive force compensation is stopped; the virtual impedance is gradually restored to the rated value through the dynamic coefficient A. (4) During the fault recovery phase, active power control and reactive power control are restored sequentially, and the power output is restored to the level before the fault within 1 second. At the same time, the virtual impedance amplitude is gradually restored to the rated value along with the voltage phase difference.

2. The method for time-sequence fault current limiting control of a grid-connected doubly-fed wind turbine generator compatible with grid-connection guidelines as described in claim 1, characterized in that, In step (1), the resistance and inductance components are: Among them, t f The parameter m represents the initial value of A, indicating the time of failure; where m > 1; the exponential time constant τ controls the rate at which A decays to 1 over time; E 0dq U represents the virtual electromotive force before the fault along the dq axis. sfdq The stator terminal fault voltage under the dq axis; L vn With R vn These represent the rated virtual inductance and resistance under normal operating conditions; σ is the user-defined virtual impedance ratio; I m This is the maximum operating current of the doubly fed wind turbine.

3. The method for time-sequence fault current limiting control of a grid-connected doubly-fed wind turbine generator compatible with grid-connection guidelines as described in claim 1, characterized in that, In step (2), the electromotive force compensation increment ΔE dq The formula is as follows: Where K1 is the reactive current proportionality coefficient specified by GC; U sf The stator voltage amplitude during a doubly-fed induction generator (DFIG) fault; ω s For grid frequency; I N The rated current of the doubly-fed wind turbine; during the freeze active power control period, at δ f Calculated by the following formula δ f =Arg(U sfd +jU sfq )。 4. The method for time-sequence fault current limiting control of a grid-connected doubly-fed wind turbine generator compatible with grid-connection guidelines as described in claim 1, characterized in that, In step (3), the virtual impedance adjustment formula is as follows: Among them, t c It is the fault clearing moment, σ n =ω s L vn / R vn X corresponds to VI during normal operation v / R v Ratio; U scdq This represents the stator terminal voltage under the dq axis during the fault recovery phase; parameters τ and m are the same as those set during the initial fault phase.

5. A timing fault current limiting control system for grid-connected doubly-fed wind turbine generators compatible with grid connection guidelines, characterized in that, include: Fault initiation module: Used to freeze external power control when a low-voltage ride-through event is detected on the power grid, by dynamically adjusting the resistive component of the virtual impedance. Suppress transient overcurrent; Fault stabilization module: Used to calculate the electromotive force compensation increment ΔE at 4τ after a fault occurs, based on grid connection guidelines. dq ; Fault clearing module: Used to stop electromotive force compensation after detecting that the fault has been cleared; and to gradually restore the virtual impedance to the rated value through the dynamic coefficient A; Fault recovery phase module: used to sequentially restore active and reactive power control, restore power output to the pre-fault level within 1 second, and at the same time, the virtual impedance amplitude gradually recovers to the rated value with the voltage phase difference.

6. The timing fault current limiting control system for a grid-connected doubly-fed wind turbine generator compatible with grid-connection guidelines as described in claim 5, characterized in that, In the initial fault module, the resistance and inductance components are: Among them, t f The parameter m represents the initial value of A, indicating the time of failure; where m > 1; the exponential time constant τ controls the rate at which A decays to 1 over time; E 0dq U represents the virtual electromotive force before the fault along the dq axis. sfdq The stator terminal fault voltage under the dq axis; L vn With R vn These represent the rated virtual inductance and resistance under normal operating conditions; σ is the user-defined virtual impedance ratio; I m This is the maximum operating current of the doubly fed wind turbine.

7. The timing fault current limiting control system for a grid-connected doubly-fed wind turbine generator compatible with grid-connection guidelines as described in claim 5, characterized in that, In the fault stabilization module, the electromotive force compensation increment ΔE dq The formula is as follows: Where K1 is the reactive current proportionality coefficient specified by GC; U sf The stator voltage amplitude during a doubly-fed induction generator (DFIG) fault; ω s For grid frequency; I N The rated current of the doubly-fed wind turbine; during the freeze active power control period, at δ f Calculated by the following formula δ f =Arg(U sfd +jU sfq )。 8. The timing fault current limiting control system for a grid-connected doubly-fed wind turbine generator compatible with grid-connection guidelines as described in claim 5, characterized in that, In the fault clearing module, the virtual impedance adjustment formula is as follows: Among them, t c It is the fault clearing moment, σ n =ω s L vn / R vn X corresponds to VI during normal operation v / R v Ratio; U scdq This is the stator terminal voltage under the dq axis during the fault recovery phase; parameters τ and m are the same as those in the first phase.

9. An electronic device, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor executing the program to implement the steps of the method according to any one of claims 1-4.

10. A computer-readable storage medium, characterized in that, The device contains a computer program that, when executed by a processor, implements the steps of the method according to any one of claims 1-4.

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