Current acquisition method at fault recovery moment of wind turbine generator and related equipment

Abstract

The embodiment of the invention discloses a current acquisition method at a fault recovery moment of a wind turbine generator and related equipment, and the method comprises the steps: carrying out the partitioning of a fault current in a fault recovery interval, and obtaining a fault current partitioning result; substituting the control parameters and the operation parameters into different fault current partition results to obtain active current and reactive current of each fault current partition result; and during low-voltage fault ride-through, active current and reactive current are accessed to a full-power fan fault transfer function, and current analytic expressions of fault recovery moments corresponding to different fault current partition results are obtained. According to the method, the control strategy of the active and reactive current during low voltage ride through is analyzed, and the current analysis formula of the fault recovery moment corresponding to each fault current partition is obtained by combining different fault current partitions, so that the accuracy and the applicability of the obtained current are improved.

Description

[Technical field]

[0001] The present invention relates to the field of electric power technology, and in particular to a current acquisition method and related equipment at the time of wind turbine generator set fault recovery. [Background technology]

[0002] Studying the fault current characteristics of new energy units during the entire fault-crossing process can provide an important basis for the analysis, control and protection of large-scale access systems for new energy. The transient current components of traditional synchronous generators and asynchronous motors are affected by the characteristics of the motors themselves, and the fault current components are mainly power frequency components and DC quantities. Most new energy units are converter-controlled equipment, and the transient fault current is affected by the grid-connected controller, but the transient fault current is affected by the fault recovery interval. The existing current analysis method does not analyze the true relationship between the control parameters and the fault current analysis formula between different fault recovery intervals for full-power wind turbines, which affects the accuracy and applicability of the final current obtained. [Summary of the invention]

[0003] In view of this, the present invention provides a current acquisition method and related equipment at the time of wind turbine generator set fault recovery.

[0004] The specific technical scheme of the first embodiment of the present invention is: a method for obtaining current at the time of fault recovery of a wind turbine generator set, the method comprising: obtaining control parameters and operating parameters of the wind turbine generator set; partitioning the fault current in the fault recovery interval according to the fault control switching logic to obtain a fault current partitioning result; the fault current partitioning result includes a fault recovery sub-transient interval, a fault recovery transient interval and a fault constant slope recovery interval; substituting the control parameters and operating parameters into different fault current partitioning results to obtain the active current and reactive current of each fault current partitioning result; when a low voltage fault passes through, connecting the active current and the reactive current to the full-power wind turbine fault transfer function to obtain the current analytical expression at the fault recovery time corresponding to different fault current partitioning results; wherein, the current analytical expression at the fault recovery time corresponding to different fault current partitioning results includes a sub-transient interval current analytical expression, a transient interval current analytical expression and a constant slope recovery interval current analytical expression at the current recovery time.

[0005] Preferably, the full-power fan fault transfer function is obtained using the following formula:

[0006]

[0007] Among them, i gd (s) is the d-axis grid current in the frequency domain, i gdref (s) is the d-axis grid current reference value in the frequency domain, k p is the current inner loop proportional coefficient, k iis the current inner loop integral coefficient, L f is the grid-side filter inductor, R f is the grid-side filter resistor, and s is the Laplace operator in the frequency domain.

[0008] Preferably, the sub-transient interval current analytical formula is obtained using the following formula:

[0009] i gd_C1 =i gd_C1_2 (t,T1)+i gd_C1_2 (t,T2)

[0010] Among them, i gd_C1 is the d-axis current in the sub-transient interval, i gd_C1_2 (t,T1) is the voltage filter inertia current, i gd_C1_2 (t,T2) is the PWM delayed inertia current;

[0011] in,

[0012]

[0013] Among them, e gd (t 3- ) is the d-axis voltage of the power grid before time t3, e gd (t 3+ ) is the d-axis voltage of the power grid after time t3, k p is the current inner loop proportional coefficient, R f is the grid-side filter resistance, k i is the current inner loop integral coefficient, L f is the grid-side filter inductor, T is the voltage filter inertia and PWM delay inertia time constant, b1, b2, b3 are analytical coefficients, t is the actual time, and t3 is the fault removal moment.

[0014] Preferably, the transient interval current analytical formula is obtained using the following formula:

[0015]

[0016] Among them, i gd_C2 (t) is the d-axis current in the transient interval, i gd (t4) is the grid d-axis current before time t4, and t4 is the time when the control logic switches after the fault is cleared;

[0017] in,

[0018] Among them, i max is the maximum current of the fan, i gqref is the reference value of the q-axis grid current, i d_limit is the d-axis grid current limit, kp is the current inner loop proportional coefficient, R f is the grid-side filter resistance, k i is the current inner loop integral coefficient, L f It is the grid-side filter inductor.

[0019] Preferably, the constant slope recovery interval current analytical formula is obtained using the following formula:

[0020] i gd_C3 (t) = i gd (t5)+k rate (t-t5)t5<t<t6

[0021] Among them, i gd_C3 (t) is the d-axis current in the fixed slope recovery interval, i gd (t5) is the d-axis current of the power grid before time t5, k rate (t-t5) is the recovery slope, t5 is the switching moment of the fault ride-through control logic, and t6 is the switching-out moment of the fault ride-through control logic.

[0022] Preferably, the method further includes: after the low voltage fault is recovered, determining the fault control logic switching time according to the fundamental positive sequence voltage of the grid connection point and the low voltage ride-through exit threshold; the fault control logic switching time is the time of exiting the low voltage ride-through control.

[0023] Preferably, the fault control logic switching time is obtained using the following formula:

[0024]

[0025] Among them, t4 is the fault control logic switching time, t3 is the low voltage fault recovery time, U out is the fundamental positive sequence voltage at the grid connection point of the low voltage ride-through exit threshold, U fault is the fundamental positive sequence voltage at the grid connection point.

[0026] The specific technical solution of the second embodiment of the present invention is: a current acquisition system at the time of fault recovery of a wind turbine generator set, the system comprising: a parameter acquisition module, a fault partitioning module, a first analysis module and a second analysis module; the parameter acquisition module is used to acquire control parameters and operating parameters of the wind turbine generator set;

[0027] The fault partitioning module is used to partition the fault current in the fault recovery interval according to the fault control switching logic to obtain the fault current partitioning result; the fault current partitioning result includes the fault recovery sub-transient interval, the fault recovery transient interval and the fault constant slope recovery interval; the first analytical module is used to substitute the control parameters and the operating parameters into different fault current partitioning results to obtain the active current and reactive current of each fault current partitioning result; the second analytical module is used to connect the active current and the reactive current to the full-power wind turbine fault transfer function when a low voltage fault passes through, to obtain the current analytical expression at the fault recovery moment corresponding to different fault current partitioning results; wherein, the current analytical expression at the fault recovery moment corresponding to different fault current partitioning results includes the sub-transient interval current analytical expression, the transient interval current analytical expression and the constant slope recovery interval current analytical expression at the current recovery moment.

[0028] The specific technical solution of the third embodiment of the present invention is: a current acquisition system device at the moment of wind turbine fault recovery, including a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method described in any one of the first embodiments of the present application.

[0029] The specific technical solution of the fourth embodiment of the present invention is: a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to perform the steps of the method described in any one of the first embodiments of the present application.

[0030] The present invention partitions the fault current in the fault recovery interval to obtain the fault current partitioning result; substitutes the control parameters and the operating parameters into different fault current partitioning results to obtain the active current and reactive current of each fault current partitioning result; when the low voltage fault is crossed, the active current and the reactive current are connected to the full power wind turbine fault transfer function to obtain the current analytical formula at the fault recovery time corresponding to the different fault current partitioning results. The present invention analyzes the control strategy of active and reactive currents during low voltage crossing, and combines different fault current partitions to obtain the current analytical formula at the fault recovery time corresponding to each fault current partition, thereby improving the accuracy and applicability of the obtained current.

Brief Description of the Drawings

[0031] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 A flow chart of the steps of a method for obtaining current when a wind turbine generator set recovers from a fault;

[0033] Figure 2 This is the control block diagram of the internal and external loops of the grid-side converter;

[0034] Figure 3 It is the current response curve of the whole process of low voltage fault ride-through;

[0035] Figure 4 It is low-power reactive power control logic;

[0036] Figure 5 It is the low wear active power control logic;

[0037] Figure 6 It is the ideal transmission control block diagram of the d-axis current inner loop command value and the d-axis current;

[0038] Figure 7 This is the current inner loop control block diagram;

[0039] Figure 8 This is the control block diagram of the PWM delay link;

[0040] Fig. 9 It is a structural schematic diagram of the current acquisition system at the moment of wind turbine fault recovery;

[0041] Among them, 201 is a parameter acquisition module; 202 is a fault partitioning module; 203 is a first analysis module; 204 is a second analysis module. [Specific implementation method]

[0042] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0043] The terms "first", "second", etc. in the specification, claims and drawings of this application are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or modules is not limited to the listed steps or modules, but optionally includes steps or modules that are not listed, or optionally includes other steps or modules that are inherent to these processes, methods, products or devices.

[0044] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0045] See also Figure 1 , is a flow chart of the steps of a method for obtaining current at the time of wind turbine fault recovery in the first embodiment of the present application, thereby improving the accuracy and applicability of the obtained current, the method comprising:

[0046] Step 101, obtaining control parameters and operating parameters of a wind turbine generator set;

[0047] Step 102: partition the fault current in the fault recovery interval according to the fault control switching logic to obtain a fault current partition result; the fault current partition result includes a fault recovery sub-transient interval, a fault recovery transient interval and a fault constant slope recovery interval;

[0048] Step 103: Substitute the control parameters and operating parameters into different fault current partition results to obtain the active current igdref and reactive current igqref of each fault current partition result;

[0049] Step 104, when a low voltage fault occurs, the active current and the reactive current are connected to the full-power wind turbine fault transfer function to obtain the current analytical expression at the fault recovery time corresponding to different fault current partitioning results; wherein, the current analytical expression at the fault recovery time corresponding to different fault current partitioning results includes the sub-transient interval current analytical expression, the transient interval current analytical expression and the constant slope recovery interval current analytical expression at the current recovery time.

[0050] Specifically, the full-power wind turbine injects wind power into the grid through a back-to-back converter, and the grid-side converter controller determines the grid-connected characteristics of the unit. The corresponding steady-state controller model is constructed, and the fault ride-through controller model is constructed. After the fault ride-through controller model is constructed, the current is analyzed based on the full-power wind turbine fault transfer function and the fault current analytical formula at the full-power wind turbine fault recovery time, including:

[0051] S1. Obtain the control parameters and operating parameters of the full-power wind turbine, including the active power command value P ref , Rated voltage U on low voltage side of transformer N , below the exit threshold U out , current inner loop proportional coefficient k p , current inner loop integral coefficient k i, DC bus voltage command value U dcref , DC bus capacitance C, DC side input power P m , voltage filter time constant T1, PWM delay time constant T2, grid-side filter inductor L f , grid-side filter resistor R f , reactive current command value before fault i gqref_t0 , total current limit of the converter i max , active delay coefficient k delay , Active delay setting current i delay_set , Slope recovery slope coefficient k rate .

[0052] S2, Fault current partition:

[0053] The fault current in the fault recovery interval is partitioned according to the fault control switching logic. The fault current is divided into a fault recovery sub-transient interval, a fault recovery transient interval and a fault constant slope recovery interval.

[0054] S3, substituting various parameters determined in step S1 into the fault current analytical formula for fault current partitioning in S2;

[0055] When a low voltage fault occurs, the parameters obtained in step S1 are brought into the fault ride-through controller model to obtain i gdref and i gqref , change i gdref and i gqref They are respectively connected to the full-power wind turbine fault transfer function to obtain the analytical formula of the full-power wind turbine fault current corresponding to the low voltage fault.

[0056] The method in this embodiment partitions the fault current in the fault recovery interval to obtain the fault current partition result; substitutes the control parameters and operating parameters into different fault current partition results to obtain the active current and reactive current of each fault current partition result; when the low voltage fault is crossed, the active current and the reactive current are connected to the full power wind turbine fault transfer function to obtain the current analytical formula at the fault recovery moment corresponding to the different fault current partition results. The present invention analyzes the control strategy of active and reactive currents during low voltage crossing, and combines different fault current partitions to obtain the current analytical formula at the fault recovery moment corresponding to each fault current partition, thereby improving the accuracy and applicability of the obtained current.

[0057] In a specific embodiment, the full-power wind turbine fault transfer function is obtained using the following formula:

[0058]

[0059] Among them, i gd(s) is the d-axis grid current in the frequency domain, i gdref (s) is the d-axis grid current reference value in the frequency domain, k p is the current inner loop proportional coefficient, k i is the current inner loop integral coefficient, L f is the grid-side filter inductor, R f is the grid-side filter resistor, and s is the Laplace operator in the frequency domain.

[0060] In a specific embodiment, the sub-transient interval current analytical formula is obtained using the following formula:

[0061] i gd_C1 =i gd_C1_2 (t,T1)+i gd_C1_2 (t,T2)

[0062] Among them, i gd_C1 is the d-axis current in the sub-transient interval, i gd_C1_2 (t,T1) is the voltage filter inertia current, i gd_C1_2 (t,T2) is the PWM delayed inertia current;

[0063] in,

[0064]

[0065] Among them, e gd (t 3- ) is the d-axis voltage of the power grid before time t3, e gd (t 3+ ) is the d-axis voltage of the power grid after time t3, k p is the current inner loop proportional coefficient, R f is the grid-side filter resistance, k i is the current inner loop integral coefficient, L f is the grid-side filter inductor, T is the voltage filter inertia and PWM delay inertia time constant, b1, b2, b3 are analytical coefficients, t is the actual time, and t3 is the fault removal moment.

[0066] In a specific embodiment, the transient interval current analytical expression is obtained using the following formula:

[0067]

[0068] Among them, i gd_C2 (t) is the d-axis current in the transient interval, i gd (t4) is the grid d-axis current before time t4, and t4 is the time when the control logic switches after the fault is cleared;

[0069] in,

[0070] Among them, i max is the maximum current of the fan, i gqref is the reference value of the q-axis grid current, i d_limit is the d-axis grid current limit, k p is the current inner loop proportional coefficient, R f is the grid-side filter resistance, k i is the current inner loop integral coefficient, L f It is the grid-side filter inductor.

[0071] The fault current in the transient interval of the q-axis current is as follows:

[0072]

[0073] Among them, Δi q =-K q ×(U in -U t )×I N , where igq_ C2 (t) is the q-axis current in the transient interval, igq(t4) is the q-axis current of the power grid before time t4, K q is the reactive support coefficient, U in is the reactive low breakdown voltage, U t is the actual voltage, I N is the current rating.

[0074] In a specific embodiment, the constant slope recovery interval current analytical formula is obtained using the following formula:

[0075] i gd_C3 (t) = i gd (t5)+k rate (t-t5)t5<t<t6

[0076] Among them, i gd_C3 (t) is the d-axis current in the fixed slope recovery interval, i gd (t5) is the d-axis current of the power grid before time t5, k rate (t-t5) is the recovery slope, t5 is the switching moment of the fault ride-through control logic, and t6 is the switching-out moment of the fault ride-through control logic.

[0077] In a specific embodiment, the steady-state controller model includes: the inner and outer loop controllers of the grid-side controller adopt grid voltage-oriented vector control, the d-axis maintains the stability of the DC voltage to achieve power balance on both sides of the converter, and the q-axis controls the reactive power exchange between the unit and the grid;

[0078] Among them, the frequency domain model of the converter output voltage in the steady-state controller model is:

[0079]

[0080] Among them, u gdref is the converter d-axis voltage reference value, u gqref is the converter q-axis voltage reference value, R f is the filter resistance, i gd is the d-axis grid current, ω g is the synchronous speed of the power grid, L f is the filter inductance, i gq is the q-axis grid current, e gd is the d-axis grid voltage, u' gd 、u' gq are the output results of the d-axis and q-axis currents through the PI link, and their expressions are:

[0081]

[0082] In a specific embodiment, the method further includes: after the low voltage fault is restored, the fault control logic switching time is determined according to the fundamental positive sequence voltage at the grid connection point and the low voltage ride through exit threshold; the fault control logic switching time is the time to exit the low voltage ride through control. Specifically, for a full-power wind turbine, it is determined whether to exit the low voltage ride through control by judging whether the fundamental positive sequence voltage at the grid connection point is higher than the low voltage ride through exit threshold. After the fault is restored, the fundamental positive sequence voltage detection value will reach the low voltage ride through exit threshold after a period of time.

[0083] In a specific embodiment, the fault control logic switching time is obtained by using the following formula:

[0084]

[0085] Among them, t4 is the fault control logic switching time, t3 is the low voltage fault recovery time, U out is the fundamental positive sequence voltage at the grid connection point of the low voltage ride-through exit threshold, U fault is the fundamental positive sequence voltage at the grid connection point.

[0086] In a specific embodiment, in the case of a low voltage fault, the corresponding reactive current i gqref Use the following formula to obtain:

[0087] i gqref =min{i gq0 +K q ×(U in -U t )×I N ,i q_limit}

[0088] Among them, i gq0 is the steady-state value of the q-axis current before the fault; iq_limit is the maximum limit value of the q-axis current, K q is the reactive current support factor; U t is the positive sequence voltage at the grid connection point; U in is the low penetration voltage threshold; I N is the rated current of the wind turbine.

[0089] The active current i corresponding to the entire fault process in the case of low voltage fault gdref Use the following formula to obtain:

[0090]

[0091] Among them, i max is the maximum current of the fan, i gqref is the q-axis current reference value, k delay is the fault delay coefficient, i gd_fault is the d-axis current during the fault period, i delay_set is the delay current, k rate is the fault recovery slope, Δt is the fault recovery time, i gd_delay is the d-axis fault delay current.

[0092] In a specific embodiment, the DC bus voltage outer loop is locked at the time of fault recovery, and the d-axis current calculation form in the fault sub-transient interval is as follows:

[0093] Affected by the voltage filtering link and the PWM delay link, the transfer functions of the voltage filtering link and the PWM delay link are as follows:

[0094]

[0095] Among them, i gd (s,T) is the transfer function of the voltage filter link and the PWM delay link, e gd (t 3- ) is the d-axis voltage of the power grid before time t3, e gd (t 3+ ) is the d-axis voltage of the power grid after time t3, T is the time constant of voltage filter inertia and PWM delay inertia, s is the Laplace operator in the frequency domain, L f is the grid-side filter inductance, k p is the current inner loop proportional coefficient, R f is the grid-side filter resistance, k i is the current inner loop integral coefficient.

[0096] When the fault control logic module detects that the fundamental positive sequence voltage of the grid connection point is higher than the set low-breakthrough exit threshold, the fault control logic module is switched out, and the frequency domain mathematical model of the d-axis current response is as follows:

[0097]

[0098] After a period of time, the fault control logic switches to constant slope recovery control at time t5.

[0099] The q-axis current only needs to calculate the current in the transient interval, and its response frequency domain mathematical model is as follows:

[0100]

[0101] Specifically, an embodiment of the fault current analysis method of a full-power wind turbine generator set is as follows:

[0102] 1. Mathematical model of electrical part

[0103] Permanent magnet synchronous motors have the advantages of small size, light weight, high efficiency, no rotor heating problems, no need for additional excitation, and simple control. In recent years, the rapid development of control theory and power electronics technology has provided a broader application basis for the refined control of synchronous motors. Therefore, permanent magnet synchronous motors have received widespread attention at home and abroad.

[0104] In the synchronous rotating d / q coordinate system, the generator outputs instantaneous active power P s and reactive power Q s It can be calculated that:

[0105]

[0106] In the formula, u sd 、u sq is the d-axis and q-axis voltage on the machine side; i sd 、i sq is the d and q axis current on the machine side.

[0107] The mathematical model between the grid-side converter output voltage and the grid voltage can be expressed as:

[0108]

[0109] In the formula, u gd 、u gq 、e gd 、e gq are the d-axis and q-axis voltages of the grid-side converter and the d-axis and q-axis voltages of the grid-side, respectively; i gd 、i gq is the d and q axis current; L f , R f Is the main circuit inductance and resistance; ω g The main circuit is the loop between the grid-side outlet of the fan and the low-voltage side of the transformer, which is mainly a filter circuit.

[0110] 2. Mathematical model of steady-state controller on the grid side

[0111] The grid-side converter generally adopts grid voltage oriented vector control. The d-axis outer loop adopts the DC bus voltage outer loop to maintain the balance between the machine-side input active power and the grid-side output active power. The q-axis adopts a reactive current control strategy. Under normal conditions, the reference value of the q-axis current is 0. When the grid-connected point voltage resumes fluctuation, the fault control logic will change the q-axis current reference value to inject reactive power into the grid. The converter voltage command value is as shown in formula (3):

[0112]

[0113] In the formula, u' gd 、u' gq are the output results of the d-axis and q-axis currents through the PI link, and their expressions are:

[0114]

[0115] Where: k p , k i are the proportional coefficient and integral coefficient of the inner current loop.

[0116] The important role of the controller is to control the machine-side converter and the grid-side converter. The controller of the grid-side converter is divided into a steady-state controller and a fault ride-through controller. The steady-state controller model is as follows: Figure 2 As shown, the d-axis current control loop uses a DC bus voltage outer loop to balance the machine-side input power and the grid-side output power, and the q-axis current control loop directly gives a command value to control the reactive power output by the grid-side converter.

[0117] 3. Mathematical model of fault ride-through controller on the grid side

[0118] When a voltage fault occurs in the power grid, wind turbines need to generate or absorb a certain amount of reactive power according to the severity of the voltage drop or rise and limit the output of active power when necessary.

[0119] The low voltage fault ride-through response curves of active power and reactive power of wind turbines are as follows: Figure 3 shown.

[0120] A. When the grid recovers from the low voltage fault at time t2, the wind turbine detects that the system voltage has recovered to above the threshold and switches to the low voltage ride-through control logic. When the fault control logic is triggered, the command value of the q-axis current during the whole fault process is shown in formula (5):

[0121] i gqref =min{i gq0 +K q ×(U in -U t )×I N ,i q_limit} (5)

[0122] In the formula, i gq0 is the steady-state value of the q-axis current before the fault; i q_limit is the maximum limit value of q-axis current; K q is the reactive current support factor; U t is the positive sequence voltage at the grid connection point; U in is the low penetration voltage threshold; I N is the rated current of the wind turbine.

[0123] To ensure that wind turbines can effectively generate reactive power to support grid voltage during faults, mainstream units mostly use reactive power priority control, that is, the active current is limited by the output of the reactive current.

[0124] i gqref In the fault recovery interval, it is directly given by the fault control module:

[0125]

[0126] Among them, the fault period corresponds to the fault recovery sub-transient interval, the delayed recovery period corresponds to the fault recovery transient interval, and the slope recovery interval corresponds to the fault fixed slope recovery interval. Based on the above discussion, the low-through fault control logic can be obtained as follows: Figure 4 and Figure 5 .

[0127] 4. Full power fan fault current analysis

[0128] S1, the sub-transient interval of the fault current at the time of fault recovery is calculated. After the fault is restored, the fundamental positive sequence voltage detection value will reach the low-breakout exit threshold after a period of time. In this interval, the fault control logic module has not been switched, and the reference value of the d-axis current is given by the maximum current control. The reference value of the d-axis current i gdref_C1 The steady-state value before fault recovery is shown in formula (7):

[0129]

[0130] d-axis current inner loop command value i gdref and d-axis current i gd The ideal transfer control block diagram is simplified as follows Figure 6 As shown, gdref with i gd The transfer function expression between is shown in formula (8):

[0131]

[0132] The preliminary analysis of the fault current is based on the assumption that the control system is completely decoupled from the main circuit. However, in order to improve the performance of the converter, the controller often extracts the fundamental frequency of the grid side through the power filter for more in-depth control. This process can be equivalently simulated by a first-order inertia link with a large time constant. The effect of the power filter on the fundamental frequency corresponds to the slower decay component. In addition, the delay caused by the switching frequency and sampling frequency of the converter itself can also be equivalent to a first-order inertia link with a small time constant, corresponding to the faster decay component.

[0133] Before the fault is restored, the fundamental voltage and current on the grid side remain stable. At this time, the influence of the first-order inertia link can be ignored, and it is considered that the control system and the main circuit are completely decoupled. After the fault is restored, the existence of the filter inductor in the main circuit prevents the current from changing immediately, so the influence of current decoupling can be ignored. However, the instantaneous drop in the grid voltage shows that the influence of the first-order inertia link on voltage decoupling should not be ignored. Therefore, the decoupling between the control loop and the main circuit is no longer complete during the fault, which affects the calculation of the short-circuit current. This influence on voltage decoupling can be seen through Figure 7 and Figure 8 The control block diagram is shown.

[0134] observe Figure 7 and Figure 8 From the difference between the two, it can be found that the structures of the two transfer function control block diagrams are the same, except that the time constants of the inertia links in the two transfer functions are different. Therefore, the frequency domain mathematical models of the step response during fault recovery are the same except for the time constants of the inertia links. Formula (16) is the frequency domain mathematical model of the step response during fault recovery. When T is T1, it is the frequency domain mathematical model of the voltage filter inertia decoupling link. When T is T2, it is the frequency domain mathematical model of the PWM delay inertia decoupling link.

[0135]

[0136] By performing a reverse transformation on equation (9), its time domain expression is shown in equation (10):

[0137]

[0138] Where:

[0139]

[0140] The analytical solution of the fault current in the sub-transient interval at the time of fault recovery is shown in formula (12):

[0141] i gd_C1 =i gd_C1_2 (t,T1)+i gd_C1_2 (t,T2) (12)

[0142] S2, the transient interval of the fault current fault recovery time is calculated. When the fault control logic module detects that the fundamental positive sequence voltage of the grid connection point is higher than the set low-breakout exit threshold, the fault control logic module switches. At this time, the d-axis current reference value is shown in formula (13):

[0143]

[0144] Substituting equation (13) into equation (8) can obtain the fault current component of the d-axis current in the transient interval at the time of fault recovery, as shown in equation (14):

[0145]

[0146] Where:

[0147]

[0148] At this time, the q-axis current reference value is shown in formula (16):

[0149]

[0150] The frequency domain mathematical model of the output response of the q-axis current at the time of fault switching is the same as that of the d-axis. Substituting equation (16) into the frequency domain mathematical model, the fault current component of the q-axis current in the transient interval at the time of fault recovery can be obtained, as shown in equation (17):

[0151]

[0152] In the formula, Δi q =K q ×(U in -U t )×I N .

[0153] S3. The fixed slope recovery interval at the fault current fault recovery time is calculated, and the fault control logic module switches from active delay recovery control to fixed slope recovery control. The corresponding time domain analytical formula of fixed slope recovery control is:

[0154] i gd_C3 (t) = i gd (t5)+k rate (t-t5)t5<t<t6 (18)

[0155] In the specific embodiments, see Fig. 9, is a structural schematic diagram of a current acquisition system at the moment of fault recovery of a wind turbine in the second embodiment of the present application, the system comprising: a parameter acquisition module 201, a fault partitioning module 202, a first analysis module 203 and a second analysis module 204; the parameter acquisition module 201 is used to obtain control parameters and operating parameters of the wind turbine; the fault partitioning module 202 is used to partition the fault current in the fault recovery interval according to the fault control switching logic to obtain a fault current partitioning result; the fault current partitioning result includes a fault recovery sub-transient interval, a fault recovery transient interval and a fault fixed slope recovery interval; the first analysis module 203 and the ... Module 203 is used to substitute the control parameters and operating parameters into different fault current partitioning results to obtain the active current and reactive current of each fault current partitioning result; the second analytical module 204 is used to connect the active current and the reactive current to the full-power wind turbine fault transfer function when a low voltage fault is crossed, to obtain the current analytical expression at the fault recovery moment corresponding to different fault current partitioning results; wherein, the current analytical expression at the fault recovery moment corresponding to different fault current partitioning results includes the sub-transient interval current analytical expression, the transient interval current analytical expression and the constant slope recovery interval current analytical expression at the current recovery moment.

[0156] In a specific embodiment, the third embodiment of the present application provides a current acquisition system device at the moment of fault recovery of a wind turbine generator set, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method as described in any one of the first embodiments of the present application.

[0157] In a specific embodiment, the fourth embodiment of the present application provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of the method as described in any one of the first embodiments of the present application.

[0158] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0159] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

[0160] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for obtaining current at the time of wind turbine fault recovery, characterized in that: The method comprises: Obtain control parameters and operating parameters of wind turbines; Partition the fault current in the fault recovery interval according to the fault control switching logic to obtain a fault current partition result; the fault current partition result includes a fault recovery sub-transient interval, a fault recovery transient interval and a fault constant slope recovery interval; Substituting the control parameters and operating parameters into different fault current partition results to obtain active current and reactive current of each fault current partition result; When a low voltage fault occurs, the active current and the reactive current are connected to the full-power wind turbine fault transfer function to obtain the current analytical expression at the fault recovery moment corresponding to different fault current partitioning results; wherein, the current analytical expression at the fault recovery moment corresponding to different fault current partitioning results includes the sub-transient interval current analytical expression, the transient interval current analytical expression and the constant slope recovery interval current analytical expression at the current recovery moment.

2. The method for obtaining current at the time of wind turbine fault recovery according to claim 1, characterized in that: The full-power fan fault transfer function is obtained using the following formula: Among them, i gd (s) is the d-axis grid current in the frequency domain, i gdref (s) is the d-axis grid current reference value in the frequency domain, k p is the current inner loop proportional coefficient, k i is the current inner loop integral coefficient, L f is the grid-side filter inductor, R f is the grid-side filter resistor, and s is the Laplace operator in the frequency domain.

3. The current acquisition method at the time of wind turbine fault recovery according to claim 1, characterized in that: The sub-transient interval current analytical formula is obtained by the following formula: i gd_C1 =i gd_C1_2 (t,T1)+i gd_C1_2 (t,T2) Among them, i gd_C1 is the d-axis current in the sub-transient interval, i gd_C1_2 (t,T1) is the voltage filter inertia current, i gd_C1_2 (t,T2) is the PWM delayed inertia current; in, Among them, e gd (t 3- ) is the d-axis voltage of the power grid before time t3, e gd (t 3+ ) is the d-axis voltage of the power grid after time t3, k p is the current inner loop proportional coefficient, R f is the grid-side filter resistance, k i is the current inner loop integral coefficient, L f is the grid-side filter inductor, T is the voltage filter inertia and PWM delay inertia time constant, b1, b2, b3 are analytical coefficients, t is the actual time, and t3 is the fault removal moment.

4. The method for obtaining current at the time of wind turbine fault recovery according to claim 1, characterized in that: The transient interval current analytical formula is obtained by the following formula: Among them, i gd_C2 (t) is the d-axis current in the transient interval, i gd (t4) is the grid d-axis current before time t4, and t4 is the time when the control logic switches after the fault is cleared; in, Among them, i max is the maximum current of the fan, i gqref is the reference value of the q-axis grid current, i d_limit is the d-axis grid current limit, k p is the current inner loop proportional coefficient, R f is the grid-side filter resistance, k i is the current inner loop integral coefficient, L f It is the grid-side filter inductor.

5. The method for obtaining current at the time of wind turbine fault recovery according to claim 1, characterized in that: The constant slope recovery interval current analytical formula is obtained by the following formula: i gd_C3 (t)=i gd (t5)+k rate (t-t5)t5<t<t6 Among them, i gd_C3 (t) is the d-axis current in the fixed slope recovery interval, i gd (t5) is the d-axis current of the power grid before time t5, k rate (t-t5) is the recovery slope, t5 is the switching moment of the fault ride-through control logic, and t6 is the switching-out moment of the fault ride-through control logic.

6. The current acquisition method at the time of wind turbine fault recovery according to claim 1, characterized in that: The method further comprises: After the low voltage fault is restored, the fault control logic switching time is determined according to the fundamental positive sequence voltage of the grid connection point and the low voltage ride through exit threshold; the fault control logic switching time is the time to exit the low voltage ride through control.

7. The method for obtaining current at the time of wind turbine fault recovery according to claim 6, characterized in that: The fault control logic switching time is obtained using the following formula: Among them, t4 is the fault control logic switching time, t3 is the low voltage fault recovery time, U out is the fundamental positive sequence voltage at the grid connection point of the low voltage ride-through exit threshold, U fault is the fundamental positive sequence voltage at the grid connection point.

8. A current acquisition system for wind turbine fault recovery, characterized in that: The system comprises: a parameter acquisition module, a fault partitioning module, a first analysis module and a second analysis module; The parameter acquisition module is used to acquire the control parameters and operating parameters of the wind turbine generator set; The fault partitioning module is used to partition the fault current in the fault recovery interval according to the fault control switching logic to obtain a fault current partitioning result; the fault current partitioning result includes a fault recovery sub-transient interval, a fault recovery transient interval and a fault constant slope recovery interval; The first analysis module is used to substitute the control parameters and the operating parameters into different fault current partition results to obtain the active current and reactive current of each fault current partition result; The second analytical module is used to connect the active current and the reactive current to the full-power wind turbine fault transfer function when a low voltage fault occurs, so as to obtain the current analytical expression at the fault recovery moment corresponding to different fault current partitioning results; wherein, the current analytical expression at the fault recovery moment corresponding to different fault current partitioning results includes the sub-transient interval current analytical expression, the transient interval current analytical expression and the constant slope recovery interval current analytical expression at the current recovery moment.

9. A current acquisition system device for wind turbine fault recovery, comprising a memory and a processor, characterized in that: The memory stores a computer program, and when the computer program is executed by the processor, the processor is caused to perform the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the processor is caused to perform the steps of the method according to any one of claims 1 to 7.

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