Wind turbine equivalent modeling methods, devices, media, and equipment considering low voltage ride-through strategies

Abstract

The present invention discloses a wind turbine equivalent modeling method, device, medium, and equipment that considers a low voltage ride-through strategy. The method is applied to a doubly-fed wind turbine wind farm station with a load unloading protection circuit and a crowbar protection circuit. Under the condition of a power grid failure, the operating status of the wind turbine is indirectly judged by obtaining the terminal voltage of the doubly-fed wind turbine, and the wind farm station is grouped and equivalently modeled based on this. This method can accurately simulate the low voltage ride-through process after a wind farm failure while only modeling the main characteristic cluster, which is a significant improvement compared to traditional equivalent models. In addition, this method only needs to obtain the current terminal voltage of the doubly-fed wind turbine and compare it with various voltage thresholds. There is no need to obtain parameters such as the DC side voltage of the converter and the rotor current of the doubly-fed wind turbine, effectively reducing the complexity of data monitoring.

Description

Technical Field

[0001] The present invention relates to the field of power grid technology, and in particular to a wind turbine equivalent modeling method, device, medium and equipment considering a low voltage ride-through strategy. Background Art

[0002] Large wind farms typically consist of dozens or even hundreds of turbines. Building a detailed wind farm model results in a high-order model and computational inefficiency. Simply grouping turbines as one and performing equivalent aggregation results in an inaccurate representation of the wind farm's operating status. Therefore, appropriately constructing equivalent models for wind farms that incorporate low-voltage ride-through strategies is a current research hotspot.

[0003] When implementing a low voltage ride-through (LVRT) strategy, a doubly-fed wind turbine needs to determine whether to enter the LVRT control strategy based on the terminal voltage, whether to activate the crowbar circuit based on the rotor current, and whether to activate the chopper circuit based on the DC voltage of the wind turbine converter. Due to the varying distribution of wind turbines within a wind farm, the operating states of each wind turbine vary. In the event of a grid fault, the operating state of each wind turbine will also vary. Traditional modeling methods require not only monitoring the terminal voltage of the DFIG wind turbine but also the rotor current, DC voltage of the wind turbine converter, and other signals. This significantly increases the complexity of data monitoring and wind turbine classification. Summary of the Invention

[0004] Based on this, it is necessary to provide wind turbine equivalent modeling methods, devices, media and equipment that consider low voltage ride-through strategies to solve the problem that existing models cannot balance computational efficiency and model accuracy and have certain complexity in data monitoring.

[0005] A wind turbine equivalent modeling method considering a low voltage ride-through strategy is applied to any doubly-fed wind turbine with a load shedding protection circuit and a crowbar protection circuit. The method comprises:

[0006] When a power grid fault occurs, the current terminal voltage of the target doubly fed wind turbine is obtained;

[0007] If the terminal voltage is greater than a preset first voltage threshold, it is determined that the target doubly fed wind turbine has not entered a low-breakthrough state, and the target doubly fed wind turbine is classified into a first type of turbine group;

[0008] If the terminal voltage is less than or equal to the first voltage threshold and greater than a preset second voltage threshold, it is determined that the target doubly fed wind turbine enters a low-breakthrough state, and the target doubly fed wind turbine is classified into the second type of turbine group;

[0009] If the terminal voltage is less than or equal to the second voltage threshold and greater than a preset third voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit for protection, and the target doubly fed wind turbine is classified into the third type of turbine group;

[0010] If the terminal voltage is less than or equal to the third voltage threshold and greater than a preset fourth voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit and the crowbar protection circuit for protection, and the target doubly fed wind turbine is classified into the fourth type of turbine group;

[0011] If the terminal voltage is less than or equal to the fourth voltage threshold, it is determined that the target doubly fed wind turbine is disconnected from the power grid, and the target doubly fed wind turbine is classified into the fifth type of turbine group;

[0012] In one embodiment, the method further comprises:

[0013] Constructing a first relationship between the rotor current and the terminal voltage drop ratio during low voltage ride-through;

[0014] Obtaining a rotor current threshold; wherein the rotor current threshold is a predetermined rotor current when the crowbar protection circuit is put into protection;

[0015] According to the first relationship, the machine terminal voltage drop ratio when the rotor current reaches the rotor current threshold is used as the first target ratio, and the voltage when the steady-state machine terminal voltage drops below the first target ratio is used as the third voltage threshold.

[0016] In one embodiment, the first relationship between the rotor current and the terminal voltage drop ratio during the low voltage ride-through period includes:

[0017] The rotor voltage expression is constructed based on the equivalent circuit diagram of the doubly fed wind turbine;

[0018] The flux linkage part in the rotor voltage expression is quadratically defined as the induced electromotive force to obtain the rotor induced electromotive force expression, the stator flux linkage expression is set based on the flux linkage conservation theorem, and the stator flux linkage expression is substituted into the induced electromotive force expression to obtain the associated expression of the induced electromotive force;

[0019] Constructing a reference voltage in space vector form to obtain a reference voltage expression;

[0020] Constructing a differential equation for the rotor current based on the rotor voltage expression, the correlation expression, and the reference voltage expression;

[0021] The differential equation is solved to obtain the first relationship.

[0022] In one embodiment, the first relational expression is expressed as:

[0023]

[0024] In the above formula, s represents the slip rate of the generator; k s Indicates the coupling coefficient between the stator and rotor circuits; u s0 Represents the steady-state terminal voltage; T sn It represents the decay time constant of the induced electromotive force after a fault occurs; L' r Indicates the value of the rotor circuit inductance referred to the stator side; K d represents the voltage drop ratio at the machine end; e represents the induced electromotive force; α1 and α2 represent the two solutions of the differential equation; i r0 Indicates the initial value of the rotor current; i r,ref Represents the reference current; ω r represents the rotor angular velocity; R r Indicates the resistance of the rotor circuit; k i k represents the proportional coefficient of the rotor current inner loop PI controller; p It represents the time constant of the rotor current inner loop PI controller.

[0025] In one embodiment, the method further comprises:

[0026] Based on the expression between the rotor current and the rotor voltage and the first relationship, a second relationship between the rotor voltage and the proportion of the terminal voltage drop during the low voltage ride-through period is constructed;

[0027] Under the premise that the rotor voltage is less than the DC bus voltage in real time, the rotor voltage threshold is determined according to the acquired DC bus voltage threshold; wherein the DC bus voltage threshold is the predetermined DC bus voltage when the unloading protection circuit is put into protection;

[0028] According to the second relationship, the terminal voltage drop ratio when the rotor voltage reaches the rotor voltage threshold is used as the second target ratio, and the voltage when the steady-state terminal voltage drops by the second target ratio is used as the second voltage threshold.

[0029] In one embodiment, the second relational expression is expressed as:

[0030]

[0031] A wind turbine equivalent modeling device considering a low voltage ride-through strategy is applied to a doubly-fed wind turbine with a load shedding protection circuit and a crowbar protection circuit. The wind turbine equivalent modeling device considering a low voltage ride-through strategy includes:

[0032] The terminal voltage acquisition module is used to obtain the current terminal voltage of the target doubly fed wind turbine when a power grid fault occurs;

[0033] The equivalent modeling module is used to determine that the target doubly fed wind turbine has not entered the low-through state if the terminal voltage is greater than a preset first voltage threshold, and the target doubly fed wind turbine is classified into the first type of group; if the terminal voltage is less than or equal to the first voltage threshold and greater than a preset second voltage threshold, the target doubly fed wind turbine is determined to have entered the low-through state, and the target doubly fed wind turbine is classified into the second type of group; if the terminal voltage is less than or equal to the second voltage threshold and greater than a preset third voltage threshold, the target doubly fed wind turbine is determined to have been put into the unloading protection circuit for protection, and the target doubly fed wind turbine is classified into the third type cluster; if the terminal voltage is less than or equal to the third voltage threshold and greater than a preset fourth voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit and the crowbar protection circuit for protection, and the target doubly fed wind turbine is classified into the fourth type of cluster; if the terminal voltage is less than or equal to the fourth voltage threshold, it is determined that the target doubly fed wind turbine is disconnected from the power grid, and the target doubly fed wind turbine is classified into the fifth type of cluster; equivalent modeling is performed on the first type of cluster, the second type of cluster, the third type of cluster and the fourth type of cluster respectively to simulate the dynamic response process after the wind farm fails.

[0034] A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the processor executes the steps of the above-mentioned wind turbine equivalent modeling method considering the low voltage ride-through strategy.

[0035] A wind turbine equivalent modeling device considering a low voltage ride-through strategy includes a memory and a processor, wherein the memory stores a computer program. When the computer program is executed by the processor, the processor executes the steps of the above-mentioned wind turbine equivalent modeling method considering a low voltage ride-through strategy.

[0036] The present invention provides a wind turbine equivalent modeling method, device, medium, and equipment that considers a low voltage ride-through strategy. The method is applied to wind farms equipped with unloading protection circuits and crowbar protection circuits. In the event of a power grid failure, the wind turbine's operating status is indirectly determined by obtaining the terminal voltage of the doubly fed wind turbine, and the wind farm is then grouped and equivalently modeled. This allows accurate simulation of the low voltage ride-through process after a wind farm failure while only modeling the main characteristic clusters, significantly improving upon traditional equivalent models. Furthermore, the method only requires obtaining the current terminal voltage of the doubly fed wind turbine and comparing it with various voltage thresholds, eliminating the need to obtain parameters such as the converter DC side voltage and the doubly fed wind turbine rotor current, effectively reducing the complexity of data monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0038] in:

[0039] Figure 1 A schematic diagram of a wind farm station including multiple doubly fed wind turbines;

[0040] Figure 2 Schematic diagram of a doubly-fed wind turbine with both a load shedding protection circuit and a crowbar protection circuit;

[0041] Figure 3 A schematic flow chart of a wind turbine equivalent modeling method considering a low voltage ride-through strategy in one embodiment;

[0042] Figure 4 is the equivalent circuit diagram of the doubly fed wind turbine;

[0043] Figure 5 This is a comparison chart of the active power output of the model over time when the bus voltage at the PCC drops to 0.65pu;

[0044] Figure 6 This is a comparison chart of the reactive power output of the model over time when the bus voltage at the PCC drops to 0.65pu;

[0045] Figure 7 This is a comparison chart of the active power output of the model over time when the bus voltage at the PCC drops to 0.82pu;

[0046] Figure 8 This is a comparison chart of the reactive power output of the model over time when the bus voltage at the PCC drops to 0.82pu;

[0047] Figure 9 This is a schematic diagram of the structure of the wind turbine equivalent modeling device considering the low voltage ride-through strategy;

[0048] Figure 10 Block diagram of the device for modeling wind turbine equivalents considering low voltage ride-through strategies. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0050] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0051] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0052] A wind farm is a facility or location that uses renewable wind energy to generate electricity and transmits it to the grid. Figure 1 The figure shows a wind farm containing multiple doubly-fed wind turbines. This wind farm can be simulated using a simulation platform such as PSCAD. Each doubly-fed wind turbine has a terminal voltage of 690V. After passing through a terminal transformer (690V / 35kV), the voltage is transmitted via a cable to the busbar's point of common connection (PCC). The voltage is then fed into the grid via a main transformer (35kV / 220kV). During this period, if a fault occurs at the busbar PCC, the terminal voltage of the corresponding doubly-fed wind turbines may experience varying degrees of voltage drop due to the different geographic locations and operating states of the wind turbines. This may result in different states exhibited by the doubly-fed wind turbines within the farm after a PCC fault occurs.

[0053] Large-scale wind farms are usually composed of dozens or even hundreds of wind turbines. If a detailed wind farm model is constructed, the overall model order will be very high and the calculation will be very inefficient. Simply grouping the wind turbines into one and performing equal aggregation will result in an inaccurate reflection of the operating status of the wind farm.

[0054] Moreover, when traditional wind farms implement low voltage ride-through strategies, they need to first identify the type of each wind turbine system and then decide whether to monitor the rotor current or DC bus voltage for that wind turbine. This significantly increases the complexity of data monitoring.

[0055] In view of the above problems, the present invention simulates and constructs Figure 2 The doubly-fed wind turbine shown here is equipped with both a load unloading protection circuit and a crowbar protection circuit, and a wind turbine equivalent modeling method considering the low voltage ride-through strategy is proposed accordingly.

[0056] like Figure 3 As shown, Figure 3 This is a flow chart of a wind turbine equivalent modeling method considering a low voltage ride-through strategy in one embodiment. The steps provided by the wind turbine equivalent modeling method considering a low voltage ride-through strategy in this embodiment include:

[0057] S301, when a power grid fault occurs, obtaining the current terminal voltage of the target doubly-fed wind turbine.

[0058] The fault can be a short circuit or ground fault at the PCC, which can cause a voltage drop across the entire or local grid, thereby affecting the generator-end voltage. The target DFIG is any one of the multiple DFIGs, meaning that the same operation is performed on all simulated DFIGs.

[0059] S302: If the terminal voltage is greater than a preset first voltage threshold, it is determined that the target doubly fed wind turbine has not entered a low-breakthrough state, and the target doubly fed wind turbine is classified into a first type of turbine group.

[0060] Optionally, the first voltage threshold is set to 0.9u s0 , where u s0 The steady-state terminal voltage indicates the output voltage of the generator under normal operating conditions. s0 , it is determined that the target doubly fed wind turbine has not entered the low penetration state, and the target doubly fed wind turbine is classified into the first category of turbines.

[0061] S303: If the terminal voltage is less than or equal to the first voltage threshold and greater than a preset second voltage threshold, it is determined that the target doubly fed wind turbine enters a low-breakthrough state, and the target doubly fed wind turbine is classified into the second type of turbine group.

[0062] Optionally, the second voltage threshold is set to 0.835*u s0 Therefore, when 0.835*u is satisfied s0 <Terminal voltage≤0.9u s0 When the target doubly fed wind turbine enters the low penetration state, the target doubly fed wind turbine is classified into the second type of turbine group.

[0063] S304: If the terminal voltage is less than or equal to the second voltage threshold and greater than a preset third voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit for protection, and the target doubly fed wind turbine is classified into the third type of turbine group.

[0064] Optionally, the third voltage threshold is set to 0.611*u s0 Therefore, when 0.611*u is satisfied s0 <Terminal voltage≤0.835*u s0 When the load shedding protection circuit is activated, the target doubly fed wind turbine is classified into the third category of turbines.

[0065] S305: If the terminal voltage is less than or equal to the third voltage threshold and greater than the preset fourth voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit and the crowbar protection circuit for protection, and the target doubly fed wind turbine is classified into the fourth type of turbine group.

[0066] Optionally, the fourth voltage threshold is set to 0.2u s0 Therefore, when 0.2u s0 <Terminal voltage≤0.611*u s0 When , it is determined that the target doubly fed wind turbine is put into the unloading protection circuit and the crowbar protection circuit for protection, and the target doubly fed wind turbine is classified into the fourth category of turbines.

[0067] S306: If the terminal voltage is less than or equal to the fourth voltage threshold, it is determined that the target doubly-fed wind turbine is disconnected from the power grid, and the target doubly-fed wind turbine is classified into the fifth type of turbine group.

[0068] Therefore, when the terminal voltage is less than 0.2u s0 When the target doubly fed wind turbine is disconnected from the grid, the target doubly fed wind turbine is classified into the fifth type of turbine group.

[0069] S307 , performing equivalent modeling on the first type of turbine group, the second type of turbine group, the third type of turbine group, and the fourth type of turbine group, respectively, to simulate a dynamic response process after a wind farm station failure.

[0070] Among them, since the fifth type of cluster has been disconnected from the power grid and will not affect the low voltage ride-through process after the fault, only the first type of cluster, the second type of cluster, the third type of cluster and the fourth type of cluster are equivalently modeled.

[0071] In this step, a simplified mathematical model is created for each turbine type. This model represents the collective behavioral characteristics of all turbines in that type of turbine. Equivalent models do not model each turbine in detail. Instead, they use certain mathematical and physical simplifications to condense the overall characteristics of a particular type of turbine into a simplified model. Through equivalent modeling, the performance of different types of wind turbines under these fault conditions can be simulated and analyzed, thereby understanding the dynamic response of the entire wind farm under low voltage conditions.

[0072] The above-mentioned wind turbine equivalent modeling method, which considers low-voltage ride-through strategies, is applied to wind farms equipped with unloading protection circuits and crowbar protection circuits. In the event of a grid fault, the terminal voltage of the doubly-fed wind turbine is used to indirectly determine the operating status of the wind turbine. This is then used to group and perform equivalent modeling of the wind farm. This method accurately simulates the low-voltage ride-through process after a wind farm fault while modeling only the primary characteristic clusters, significantly improving upon traditional equivalent models. Furthermore, this method only requires obtaining the current terminal voltage of the doubly-fed wind turbine and comparing it with various voltage thresholds, eliminating the need to obtain parameters such as the converter DC-side voltage and the doubly-fed wind turbine rotor current, effectively reducing the complexity of data monitoring.

[0073] Furthermore, how to determine the second voltage threshold and the third voltage threshold is further explained below.

[0074] In a specific embodiment, the process of determining the third voltage threshold includes:

[0075] A1. Construct a first relationship between the rotor current and the terminal voltage drop ratio during low voltage ride-through.

[0076] The voltage drop ratio is used to represent the ratio of the voltage drop to the steady-state terminal voltage. By constructing and applying the first relationship, the impact of the rotor current on the terminal voltage drop during low voltage ride-through can be accurately predicted. The first relationship can be simply expressed as:

[0077] i r =f(K d ,t)

[0078] Among them, i r Indicates the rotor current; K d It indicates the voltage drop ratio at the machine end, and t indicates the time.

[0079] A2. Obtain the rotor current threshold.

[0080] The rotor current threshold is the predetermined rotor current at which the crowbar protection circuit is activated. That is, when the rotor current in the system reaches the set threshold, the crowbar protection circuit will be activated to protect the system. The rotor current threshold is obtained in advance through experiments and is represented by i r，max .

[0081] A3. According to the first relationship, the terminal voltage drop ratio when the rotor current reaches the rotor current threshold is used as the first target ratio, and the voltage when the steady-state terminal voltage drops below the first target ratio is used as the third voltage threshold.

[0082] will i r，max Substituting the formula in step A1 and calculating the third voltage threshold, we have:

[0083]

[0084]

[0085] In the above formula, represents the first target ratio; Indicates the moment corresponding to the rotor current threshold; U2 indicates the third voltage threshold.

[0086] It is understood that once the third voltage threshold is calculated and set through the above-described specific embodiment, the system no longer needs to acquire and monitor the rotor current in real time during the subsequent low voltage ride-through process. The system only needs to monitor the generator terminal voltage and compare it with the third voltage threshold. This greatly simplifies the complexity and implementation of the protection system.

[0087] Optionally, step A1 specifically includes the following steps:

[0088] A11. Construct the rotor voltage expression based on the equivalent circuit diagram of the doubly fed wind turbine.

[0089] like Figure 4 As shown, Figure 4 This is the equivalent circuit diagram of a doubly fed wind turbine. When executing S302-S303, the unprotected circuit is activated; when executing S304, Rchopper is activated; and when executing S305, Rcrowbar is activated. The constructed rotor voltage expression is expressed as:

[0090]

[0091] In the above formula, L′ r Indicates the value of the rotor circuit inductance referred to the stator side; i r represents the rotor current; ω r represents the rotor angular velocity; R r Indicates the resistance of the rotor circuit; k srepresents the coupling coefficient between the stator and rotor circuits; ψ s Represents the stator flux.

[0092] A12. Define the flux linkage part in the rotor voltage expression as the induced electromotive force twice to obtain the rotor induced electromotive force expression. Set the stator flux linkage expression based on the flux conservation theorem. Substitute the stator flux linkage expression into the induced electromotive force expression to obtain the associated expression of the induced electromotive force.

[0093] Among them, the expression of the induced electromotive force of the rotor is expressed as:

[0094]

[0095] The stator winding impedance can generally be ignored. Based on the flux conservation theorem, the stator flux expression is set as:

[0096]

[0097] In the above formula, ω s represents the stator angular velocity; T s Indicates the stator circuit decay time constant.

[0098] Substituting the stator flux expression into the induced electromotive force expression, we get the associated expression of the induced electromotive force, which is expressed as:

[0099]

[0100] Where, e1 = sk s (1-K d )u s0 , e2=(s-1)k s K d u s0 , s represents the slip rate of the generator, T sn It represents the decay time constant of the rotor induced electromotive force e after a short circuit fault occurs.

[0101] A13. Construct a reference voltage in space vector form to obtain the reference voltage expression.

[0102] The reference voltage expression is expressed as:

[0103] u r,ref =R r i r,ref +jω r L r i r,ref +jω r L m i s,estim +k p (i r,ref -i r)+k i ∫(i r,ref -i r )dt

[0104] In the above formula, i s,estim Represents the estimated value of the stator current in the dq coordinate system; i r,ref represents the rotor current reference value in the dq coordinate system; k i k represents the proportional coefficient of the rotor current inner loop PI controller; p It represents the time constant of the rotor current inner loop PI controller.

[0105] A14. Construct the differential equation of the rotor current based on the rotor voltage expression, the associated expression and the reference voltage expression.

[0106] The rotor voltage expression, the correlation expression and the reference voltage expression are combined to derive the second-order differential equation of the rotor current, which is expressed as:

[0107]

[0108] In the above formula, T s is the stator circuit decay time constant.

[0109] A15. Solve the differential equation to obtain the first relationship.

[0110] The equation for the rotor current is a second-order non-homogeneous linear ordinary differential equation. Solving it yields the following expression for the rotor current:

[0111]

[0112] Where, are the two solutions of the nonhomogeneous ordinary differential characteristic equation of the rotor current.

[0113] The initial value of the rotor current satisfies the following relationship:

[0114]

[0115] The rotor current can be expressed as the first relation, which is expressed as:

[0116]

[0117] In the above formula, s represents the slip rate of the generator; k s Indicates the coupling coefficient between the stator and rotor circuits; u s0 Represents the steady-state terminal voltage; T sn It represents the decay time constant of the induced electromotive force after a fault occurs; L' r Indicates the value of the rotor circuit inductance referred to the stator side; Kd represents the voltage drop ratio at the machine end; e represents the induced electromotive force; α1 and α2 represent the two solutions of the differential equation; i r0 Indicates the initial value of the rotor current; i r,ref Represents the reference current; ω r represents the rotor angular velocity; R r Indicates the resistance of the rotor circuit; k i k represents the proportional coefficient of the rotor current inner loop PI controller; p It represents the time constant of the rotor current inner loop PI controller.

[0118] It can be seen that the rotor current during the low voltage ride-through period is a time function of the proportion of the terminal voltage drop, that is:

[0119] i r =f(e2,t)=f(K d ,t).

[0120] In a specific embodiment, the process of determining the second voltage threshold includes:

[0121] B1. Based on the expression between the rotor current and the rotor voltage and the first relationship, a second relationship between the rotor voltage and the terminal voltage drop ratio during the low voltage ride-through period is constructed.

[0122] The second relationship can be simply expressed as:

[0123] u r =f(K d ,t)

[0124] Optionally, if the formula in step A15 is converted in combination with the expression between the rotor current and the rotor voltage, the second relationship is expressed as:

[0125]

[0126] It can also be seen that the rotor voltage during the low voltage ride-through period is a time function of the proportion of the terminal voltage drop, that is:

[0127] u r =f(e2,t)=f(K d ,t).

[0128] B2. Under the premise that the rotor voltage is less than the DC bus voltage in real time, the rotor voltage threshold is determined according to the acquired DC bus voltage threshold.

[0129] The DC bus voltage threshold is the predetermined DC bus voltage at which the unloading protection circuit is activated. That is, when the DC bus voltage drops to or below this value, the unloading protection circuit will be activated. The DC bus voltage threshold is obtained in advance through experiments and is expressed as U dc，th .

[0130] The process is expressed as:

[0131]

[0132] In the above formula, u rmax Indicates the rotor voltage threshold.

[0133] B3. According to the second relationship, the terminal voltage drop ratio when the rotor voltage reaches the rotor voltage threshold is used as the second target ratio, and the voltage when the steady-state terminal voltage drops by the second target ratio is used as the second voltage threshold.

[0134] will u rmax Substituting the simplified formula in step B1 and calculating the second voltage threshold, we have:

[0135]

[0136]

[0137] In the above formula, represents the second target ratio; Indicates the moment corresponding to the rotor voltage threshold; U1 represents the second voltage threshold.

[0138] It is understood that once the second voltage threshold is calculated and set through the above-described specific embodiment, the system no longer needs to obtain and monitor the DC bus voltage in real time during the subsequent low voltage ride-through process. The system only needs to monitor the generator-side voltage and compare it with the second voltage threshold. This greatly simplifies the complexity and implementation of the protection system.

[0139] To verify the accuracy of the model of the present invention, we set a fault at each busbar PCC in the PSCAD simulation platform and set the first voltage threshold to 0.9u s0 , set the second voltage threshold to 0.835*u s0 , set the third voltage threshold to 0.611*u s0 , set the fourth voltage threshold to 0.2u s0 Then, the method of the present invention is used to group and model the wind farms, and compared with the detailed model and the rough model, the following can be obtained: Figure 5-Figure 8 Schematic diagram of .

[0140] Among them, when a three-phase short circuit fault occurs in the system at 1.5s, the bus voltage at the PCC drops to 0.65pu. When the fault is cleared at 2s, the comparison of the active power output of the model over time is shown in the figure below. Figure 5 shown.

[0141] When a three-phase short circuit fault occurs in the system at 1.5s, the bus voltage at the PCC drops to 0.65pu. When the fault is cleared at 2s, the reactive power output of the model is compared with time. Figure 6 shown.

[0142] When a three-phase short circuit fault occurs in the system at 1.5s, the bus voltage at the PCC drops to 0.82pu. When the fault is cleared at 2s, the active power output of the model is compared with time as shown in the figure below. Figure 7 shown.

[0143] When a three-phase short circuit fault occurs in the system at 1.5s, the bus voltage at the PCC drops to 0.82pu. When the fault is cleared at 2s, the reactive power output of the model is compared with time. Figure 8 shown.

[0144] from Figures 5 to 8 It can be seen that compared with the coarse model, the power curve corresponding to the model of the present invention is closer to the power curve of the detailed model, which means that the present invention can accurately simulate the fault ride-through process of the doubly fed wind turbine and can better characterize the output characteristics of the wind farm, which is a significant improvement compared with the traditional equivalent model.

[0145] In one embodiment, Figure 9 As shown in FIG, a wind turbine equivalent modeling device considering the low voltage ride-through strategy is proposed, which includes:

[0146] The terminal voltage acquisition module 901 is used to obtain the current terminal voltage of the target doubly fed wind turbine when a power grid fault occurs;

[0147] The equivalent modeling module 902 is used to determine that the target doubly fed wind turbine has not entered the low-through state if the terminal voltage is greater than a preset first voltage threshold, and the target doubly fed wind turbine is classified into the first type of wind turbine group; if the terminal voltage is less than or equal to the first voltage threshold and greater than a preset second voltage threshold, the target doubly fed wind turbine is determined to have entered the low-through state and the target doubly fed wind turbine is classified into the second type of wind turbine group; if the terminal voltage is less than or equal to the second voltage threshold and greater than a preset third voltage threshold, the target doubly fed wind turbine is determined to have entered the unloading protection circuit for protection, and the target doubly fed wind turbine is classified into the second type of wind turbine group. The target doubly fed wind turbine is classified into the third category of clusters; if the terminal voltage is less than or equal to the third voltage threshold and greater than the preset fourth voltage threshold, the target doubly fed wind turbine is determined to be put into the unloading protection circuit and the crowbar protection circuit for protection, and the target doubly fed wind turbine is classified into the fourth category of clusters; if the terminal voltage is less than or equal to the fourth voltage threshold, the target doubly fed wind turbine is determined to be disconnected from the grid, and the target doubly fed wind turbine is classified into the fifth category of clusters; equivalent modeling is performed on the first category of clusters, the second category of clusters, the third category of clusters and the fourth category of clusters respectively to simulate the dynamic response process after the wind farm fails.

[0148] Figure 10 FIG. 1 shows an internal structure diagram of a wind turbine equivalent modeling device considering a low voltage ride-through strategy in one embodiment. Figure 10 As shown, the wind turbine equivalent modeling device considering the low voltage ride-through strategy includes a processor, a memory and a network interface connected via a system bus. Among them, the memory includes a non-volatile storage medium and an internal memory. The non-volatile storage medium of the wind turbine equivalent modeling device considering the low voltage ride-through strategy stores an operating system and may also store a computer program. When the computer program is executed by the processor, the processor can implement the wind turbine equivalent modeling method considering the low voltage ride-through strategy. The internal memory may also store a computer program. When the computer program is executed by the processor, the processor can execute the wind turbine equivalent modeling method considering the low voltage ride-through strategy. Those skilled in the art can understand that, Figure 10 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the wind turbine equivalent modeling device considering the low voltage ride-through strategy to which the solution of the present application is applied. The specific wind turbine equivalent modeling device considering the low voltage ride-through strategy may include more or fewer components than shown in the figure, or combine certain components, or have a different component arrangement.

[0149] A computer-readable storage medium stores a computer program, which implements the following steps when executed by a processor: when a power grid fault occurs, obtain the current terminal voltage of a target doubly fed wind turbine; if the terminal voltage is greater than a preset first voltage threshold, determine that the target doubly fed wind turbine has not entered a low-through state, and classify the target doubly fed wind turbine into a first type of turbine group; if the terminal voltage is less than or equal to the first voltage threshold and greater than a preset second voltage threshold, determine that the target doubly fed wind turbine has entered a low-through state, and classify the target doubly fed wind turbine into a second type of turbine group; if the terminal voltage is less than or equal to the second voltage threshold and greater than a preset third voltage threshold , then the target doubly fed wind turbine is determined to be put into the unloading protection circuit for protection, and the target doubly fed wind turbine is classified into the third category of clusters; if the terminal voltage is less than or equal to the third voltage threshold and greater than the preset fourth voltage threshold, then the target doubly fed wind turbine is determined to be put into the unloading protection circuit and the crowbar protection circuit for protection, and the target doubly fed wind turbine is classified into the fourth category of clusters; if the terminal voltage is less than or equal to the fourth voltage threshold, then the target doubly fed wind turbine is determined to be disconnected from the grid, and the target doubly fed wind turbine is classified into the fifth category of clusters; equivalent modeling is performed on the first category of clusters, the second category of clusters, the third category of clusters and the fourth category of clusters respectively to simulate the dynamic response process after the wind farm station fails.

[0150] A wind turbine equivalent modeling device considering a low voltage ride-through strategy includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the following steps are implemented: when a power grid fault occurs, the current terminal voltage of the target doubly fed wind turbine is obtained; if the terminal voltage is greater than a preset first voltage threshold, it is determined that the target doubly fed wind turbine has not entered a low voltage ride-through state, and the target doubly fed wind turbine is classified into a first type of group; if the terminal voltage is less than or equal to the first voltage threshold and greater than a preset second voltage threshold, it is determined that the target doubly fed wind turbine has entered a low voltage ride-through state, and the target doubly fed wind turbine is classified into a second type of group; if the terminal voltage is less than or equal to the second voltage threshold , and is greater than the preset third voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit for protection, and the target doubly fed wind turbine is classified into the third category of clusters; if the terminal voltage is less than or equal to the third voltage threshold and greater than the preset fourth voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit and the crowbar protection circuit for protection, and the target doubly fed wind turbine is classified into the fourth category of clusters; if the terminal voltage is less than or equal to the fourth voltage threshold, it is determined that the target doubly fed wind turbine is disconnected from the grid, and the target doubly fed wind turbine is classified into the fifth category of clusters; equivalent modeling is performed on the first category of clusters, the second category of clusters, the third category of clusters and the fourth category of clusters respectively to simulate the dynamic response process after the wind farm station fails.

[0151] It should be noted that the above-mentioned wind turbine equivalent modeling method, device, equipment and computer-readable storage medium considering the low voltage ride-through strategy belong to a general inventive concept, and the contents of the embodiments of the wind turbine equivalent modeling method, device, equipment and computer-readable storage medium considering the low voltage ride-through strategy can be applied to each other.

[0152] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program, which can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0153] The technical features of the above embodiments can 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.

[0154] The above embodiments merely illustrate several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A wind turbine equivalent modeling method considering low voltage ride-through strategy, characterized in that: The method is applied to a simulated wind farm station, the wind farm station including a plurality of doubly-fed wind turbines, each doubly-fed wind turbine having a corresponding unloading protection circuit and a crowbar protection circuit, and includes: When a power grid fault occurs, obtaining the current terminal voltage of a target doubly-fed wind turbine; wherein the target doubly-fed wind turbine is any one of the multiple doubly-fed wind turbines; If the terminal voltage is greater than a preset first voltage threshold, it is determined that the target doubly fed wind turbine has not entered a low-breakthrough state, and the target doubly fed wind turbine is classified into a first type of turbine group; If the terminal voltage is less than or equal to the first voltage threshold and greater than a preset second voltage threshold, it is determined that the target doubly fed wind turbine enters a low-breakthrough state, and the target doubly fed wind turbine is classified into the second type of turbine group; If the terminal voltage is less than or equal to the second voltage threshold and greater than a preset third voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit for protection, and the target doubly fed wind turbine is classified into the third type of turbine group; If the terminal voltage is less than or equal to the third voltage threshold and greater than a preset fourth voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit and the crowbar protection circuit for protection, and the target doubly fed wind turbine is classified into the fourth type of turbine group; If the terminal voltage is less than or equal to the fourth voltage threshold, it is determined that the target doubly-fed wind turbine is disconnected from the power grid, and the target doubly-fed wind turbine is classified into the fifth type of turbine group; Equivalent modeling is performed on the first type of machine group, the second type of machine group, the third type of machine group, and the fourth type of machine group, respectively, to simulate a dynamic response process after a wind farm station fails.

2. The method according to claim 1, characterized in that The method further comprises: Constructing a first relationship between the rotor current and the terminal voltage drop ratio during low voltage ride-through; Obtaining a rotor current threshold; wherein the rotor current threshold is a predetermined rotor current when the crowbar protection circuit is put into protection; According to the first relationship, the machine terminal voltage drop ratio when the rotor current reaches the rotor current threshold is used as the first target ratio, and the voltage when the steady-state machine terminal voltage drops below the first target ratio is used as the third voltage threshold.

3. The method according to claim 2, characterized in that The first relationship between the rotor current and the terminal voltage drop ratio during the low voltage ride-through period includes: The rotor voltage expression is constructed based on the equivalent circuit diagram of the doubly fed wind turbine; The flux linkage part in the rotor voltage expression is quadratically defined as the induced electromotive force to obtain the rotor induced electromotive force expression, the stator flux linkage expression is set based on the flux linkage conservation theorem, and the stator flux linkage expression is substituted into the induced electromotive force expression to obtain the associated expression of the induced electromotive force; Constructing a reference voltage in space vector form to obtain a reference voltage expression; Constructing a differential equation for the rotor current based on the rotor voltage expression, the correlation expression, and the reference voltage expression; The differential equation is solved to obtain the first relationship.

4. The method according to claim 3, characterized in that The first relational expression is expressed as: In the above formula, Indicates the slip rate of the generator; represents the coupling coefficient between the stator and rotor circuits; Indicates the steady-state terminal voltage; Indicates the decay time constant of the induced electromotive force after a fault occurs; Indicates the value of the rotor circuit inductance referred to the stator side; Indicates the voltage drop ratio at the machine end; represents the induced electromotive force; 、 Represent two solutions to a differential equation; Indicates the initial value of the rotor current; Indicates the reference current; represents the rotor angular velocity; Indicates the resistance of the rotor circuit; Represents the proportional coefficient of the rotor current inner loop PI controller; Represents the time constant of the rotor current inner loop PI controller; represents the rotor current; t represents the time.

5. The method according to claim 4, characterized in that The method further comprises: Based on the expression between the rotor current and the rotor voltage and the first relationship, a second relationship between the rotor voltage and the proportion of the terminal voltage drop during the low voltage ride-through period is constructed; Under the premise that the rotor voltage is less than the DC bus voltage in real time, the rotor voltage threshold is determined according to the acquired DC bus voltage threshold; wherein the DC bus voltage threshold is the predetermined DC bus voltage when the unloading protection circuit is put into protection; According to the second relationship, the terminal voltage drop ratio when the rotor voltage reaches the rotor voltage threshold is used as the second target ratio, and the voltage when the steady-state terminal voltage drops by the second target ratio is used as the second voltage threshold.

6. The method according to claim 5, characterized in that The second relational expression is expressed as: in, is the rotor voltage.

7. A wind turbine equivalent modeling device considering low voltage ride-through strategy, characterized in that: Applied to a doubly-fed wind turbine with a load shedding protection circuit and a crowbar protection circuit, the wind turbine equivalent modeling device considering the low voltage ride-through strategy includes: The terminal voltage acquisition module is used to obtain the current terminal voltage of the target doubly fed wind turbine when a power grid fault occurs; The equivalent modeling module is used to determine that the target doubly fed wind turbine has not entered the low-through state if the terminal voltage is greater than a preset first voltage threshold, and the target doubly fed wind turbine is classified into the first type of group; if the terminal voltage is less than or equal to the first voltage threshold and greater than a preset second voltage threshold, the target doubly fed wind turbine is determined to have entered the low-through state, and the target doubly fed wind turbine is classified into the second type of group; if the terminal voltage is less than or equal to the second voltage threshold and greater than a preset third voltage threshold, the target doubly fed wind turbine is determined to have been put into the unloading protection circuit for protection, and the target doubly fed wind turbine is classified into the third type cluster; if the terminal voltage is less than or equal to the third voltage threshold and greater than a preset fourth voltage threshold, it is determined that the target doubly fed wind turbine is put into the unloading protection circuit and the crowbar protection circuit for protection, and the target doubly fed wind turbine is classified into the fourth type of cluster; if the terminal voltage is less than or equal to the fourth voltage threshold, it is determined that the target doubly fed wind turbine is disconnected from the power grid, and the target doubly fed wind turbine is classified into the fifth type of cluster; equivalent modeling is performed on the first type of cluster, the second type of cluster, the third type of cluster and the fourth type of cluster respectively to simulate the dynamic response process after the wind farm fails.

8. A computer-readable storage medium, characterized in that A computer program is stored, and 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 6.

9. A wind turbine equivalent modeling device considering low voltage ride-through strategy, characterized in that: The method comprises 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 according to any one of claims 1 to 6.

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