CN112910006A

CN112910006A - Universal electromagnetic transient modeling method for direct-drive wind turbine generator

Info

Publication number: CN112910006A
Application number: CN202110297032.2A
Authority: CN
Inventors: 李卫星; 齐金玲; 刘新元; 晁璞璞; 徐式蕴; 郑惠萍; 雷达; 张一帆; 薄利明
Original assignee: Harbin Institute of Technology; Electric Power Research Institute of State Grid Shanxi Electric Power Co Ltd; China Electric Power Research Institute Co Ltd CEPRI
Current assignee: Harbin Institute of Technology; Electric Power Research Institute of State Grid Shanxi Electric Power Co Ltd; China Electric Power Research Institute Co Ltd CEPRI
Priority date: 2021-03-19
Filing date: 2021-03-19
Publication date: 2021-06-04
Anticipated expiration: 2041-03-19
Also published as: CN112910006B

Abstract

A general electromagnetic transient modeling method for a direct-drive wind turbine generator relates to the technical field of power system simulation modeling. According to the method, the voltage, the current, the active power and the reactive power response of the actual direct-drive wind turbine generator are obtained by testing the low-voltage ride through capability of the direct-drive wind turbine generators, a general electromagnetic transient response curve of the whole fault ride through process of the direct-drive wind turbine generators is obtained according to the response, the dynamic behaviors of the active power and the reactive power are analyzed according to the curve, and the behaviors are described; analyzing a reference value of the active component and a reference value of the reactive component of the current, and inputting the obtained reference values into a current controller of a grid-side converter of a universal electromagnetic transient simulation model of the direct-drive wind turbine generator; and identifying fault ride-through control parameters and grid-side converter parameters of the direct-drive wind turbine generator system by adopting step-by-step identification. The method is mainly used for general electromagnetic transient modeling of the direct-drive wind turbine generator.

Description

Universal electromagnetic transient modeling method for direct-drive wind turbine generator

Technical Field

The invention relates to a general electromagnetic transient modeling method for a direct-drive wind turbine generator, and belongs to the technical field of power system simulation modeling.

Background

The growing energy demand and the ever-increasing environmental concerns have greatly facilitated the development of wind power generation. The direct-drive wind turbine generator set has the advantages of high energy density, simple control method and the like, and is more and more commonly applied to onshore and offshore wind power plants. However, as the permeability of the wind turbine generator is continuously improved, the wind power integration brings serious challenges to the safe operation of a power system, and an electromagnetic transient model capable of accurately reflecting the fault ride-through characteristic of the actual direct-drive wind turbine generator under the condition of voltage drop is established, so that the method has important significance for correctly evaluating the influence of the large-scale wind power integration on the power grid.

However, because confidential information is involved, the electromagnetic transient model established by the fan manufacturer is generally in a 'black box' form, and the internal control strategy and control parameters cannot be obtained, which seriously hinders the development of related researches. Therefore, it is highly desirable to build a generic electromagnetic transient model. The general electromagnetic transient model of the direct-drive wind turbine generator set established in the existing research mostly focuses on modeling the fault duration, but fails to completely and specifically model the recovery process after fault clearing and the switching transient state between different fault stages (including the steady-state stage before fault occurrence, the fault duration stage, the recovery stage after fault clearing to the steady-state value of active power and reactive power and the steady-state stage after the recovery stage). Meanwhile, control parameters (including fault ride-through control parameters and converter control parameters) of the direct-drive wind turbine generator set electromagnetic transient model in the whole fault ride-through process are not accurately identified, so that obvious deviation exists between model output and measured data, and engineering use has great limitation.

Disclosure of Invention

The method aims to solve the problem that the conventional method is lack of a universal electromagnetic transient modeling method capable of carrying out the whole fault ride-through process of the direct-drive wind turbine generator system. A general electromagnetic transient modeling method for a direct-drive wind turbine generator is provided.

A general electromagnetic transient modeling method for a direct-drive wind turbine generator comprises the following steps:

step 1: carrying out low voltage ride through test on the plurality of direct-drive wind turbine generators to obtain voltage, current, active power and reactive power responses of the plurality of direct-drive wind turbine generators under different voltage drop conditions, and obtaining a universal electromagnetic transient response curve of the whole fault ride through process of the direct-drive wind turbine generators according to the responses of the voltage, the current, the active power and the reactive power;

step 2: analyzing the dynamic behaviors of the active power and the reactive power in the whole fault ride-through process according to the universal electromagnetic transient response curve of the whole fault ride-through process of the direct-drive wind turbine generator system obtained in the step 1, and describing the dynamic behaviors of the active power and the reactive power in the whole fault ride-through process;

and step 3: analyzing a reference value of a current active component and a reference value of a current reactive component according to the dynamic behavior formulas of the active power and the reactive power in the whole fault ride-through process obtained in the step 2, inputting the obtained reference values into a current controller of a grid-side converter of the universal electromagnetic transient simulation model of the direct-drive wind turbine generator, and automatically adjusting the dynamic behavior of the universal electromagnetic transient simulation model of the direct-drive wind turbine generator by utilizing the tracking action of the current controller of the grid-side converter;

and 4, step 4: and identifying fault ride-through control parameters and grid-side converter parameters of the direct-drive wind turbine generator system by adopting step-by-step identification.

Further, the fault ride-through overall process in the step 1 includes a steady-state stage before the fault occurs, a fault continuation stage, a recovery stage from the fault clearing to the state where both the active power and the reactive power are recovered to the steady-state values, and a steady-state stage after the recovery stage is completed; and obtaining a general electromagnetic transient response curve of the direct-drive wind turbine generator in the whole fault ride-through process, wherein the general electromagnetic transient response curve comprises a response curve of voltage, instantaneous active power and instantaneous reactive power.

Further, in step 2, the dynamic behavior of the active power in the fault ride-through overall process is described as follows:

in the formula, P_normalThe active power representing the normal working state, and the corresponding time range is [ -, t [ ]₁]And [ t₇,～]，P_faultRepresenting the active power during the fault duration, corresponding to a time range t₁,t₃]，P_reThe active power representing the fault recovery process corresponds to the time ranges of t₃,t₇]T represents the current simulation run time; u. of_gRepresenting the port voltage i of the direct-drive wind turbine_{P_normal}Representing the active component of the current in the normal operating state, i_{P_fault}Representing the current active component during the fault duration, I_maxRepresents the maximum current, i_{Q_fault}Representing the reactive component of the current during the fault duration; p (t)₃) Represents t₃Active power at time P (t)₄) Represents t₄Active power at a moment r_PRepresenting the rate of restoration of active power after fault clearance, P₀Representing steady state active power before the fault;

the dynamic behavior of reactive power throughout the fault ride-through is described as follows:

in the formula, Q_normalRepresenting the reactive power in normal working state, and the corresponding time range is [ -, t [ ]₁]And [ t₆,～]，Q_faultRepresenting reactive power during the fault duration, corresponding to a time range t₁,t₃]，Q_reThe reactive power representing the fault recovery process corresponds to time ranges of t₃,t₆]；i_{Q_normal}Is a reactive component of current under normal working condition, i_{Q_fault}For the reactive component of the current during the duration of the fault, i_{lim_Q}Representing the limit value of reactive component of current in fault period, k is reactive power support coefficient, and k is more than or equal to 1.5 according to grid-connected standard, u_setRepresenting a set voltage threshold, constant, according to a grid-connection standard u_setIs 0.9p.u., I_nRepresenting rated current, i_Q0Representing the steady state current reactive component before the fault; q (t)₃) Represents t₃Reactive power at time, Q (t)₅) Represents t₅Reactive power at time, r_QRepresenting the rate of recovery of reactive power after fault clearance, Q₀Representing steady state reactive power before the fault.

Further, the specific process of analyzing the reference value of the current active component and the reference value of the current reactive component according to the dynamic behavior formula of the active power and the reactive power obtained in the step 2 in the whole fault ride-through process, inputting the obtained reference values into a current controller of a grid-side converter of the universal electromagnetic transient simulation model of the direct-drive wind turbine generator, and automatically adjusting the dynamic behavior of the universal electromagnetic transient simulation model of the direct-drive wind turbine generator by utilizing the tracking function of the current controller of the grid-side converter comprises the following steps:

when the direct-drive wind turbine generator system adopts the vector control of grid voltage orientation and the grid voltage is oriented to the d axis of the dq synchronous rotation reference coordinate system, the reference value of the current active component corresponds to the reference value i of the d axis component of the current controller_drefReference value of reactive component of current corresponds to parameter of q-axis component of current controllerExamination value i_qref(ii) a Reference value i of current active component_drefExpressed as:

in the formula i_{dref_normal}Reference value, i, representing the active component of the current in normal operation_{dref_fault}Reference value, i, representing the current active component during the fault duration_{dref_re}A reference value representing the active component of the current during the fault recovery process; k is a radical of_{P_udc}And k_{I_udc}Respectively representing the proportional and integral coefficients, u, of the external loop PI controller for DC voltage_dcrefReference value, u, representing a DC voltage_dcRepresents a direct voltage i_{qref_fault}Reference value, r, representing the reactive component of the current during the duration of the fault_idRepresenting the recovery rate of the active component of the current after the fault is cleared;

reference value i of the reactive component of the current_qrefExpressed as:

in the formula i_{qref_normal}Reference value, i, representing the reactive component of the current in normal operation_{qref_re}A reference value representing a reactive component of current during fault recovery; k is a radical of_{P_Q}And k_{I_Q}Respectively representing the proportional and integral coefficients, Q, of the reactive power outer loop PI controller_refRepresenting a reference value of reactive power, Q representing reactive power, r_iqRepresenting the recovery rate of the reactive component of the current after the fault is cleared;

and (3) assigning values to d-axis and q-axis current reference values of a current controller in a grid-side converter of the direct-drive wind turbine generator set general electromagnetic transient simulation model according to a formula (3) and a formula (4), and automatically adjusting the dynamic behavior of the direct-drive wind turbine generator set general electromagnetic transient simulation model by using the current controller.

Further, the specific process of identifying the fault ride-through control parameter and the grid-side converter parameter of the direct-drive wind turbine generator system by adopting the step-by-step identification in the step 4 comprises the following steps:

step 4.1: analyzing and calculating fault ride-through control parameters of the direct-drive wind turbine generator according to voltage, current, active power and reactive power data of a low-voltage ride-through test of the direct-drive wind turbine generator;

step 4.2: and identifying and obtaining the parameters of the grid-side converter by adopting an optimization algorithm according to the voltage, current, active power and reactive power data of the low voltage ride through test of the direct-drive wind turbine generator.

Further, the direct-drive wind turbine generator fault ride-through control parameters in the step 4.1 include a reactive power support coefficient k and a recovery rate r of an active component of current after fault clearing_idRate of recovery r of reactive component of current after fault clearance_iqActive power recovery delay t after fault clearance_{dealy_P}And reactive power support delay t after fault clearing_{dealy_Q}。

Further, the specific process of calculating the fault ride-through control parameter of the direct-drive wind turbine generator according to the voltage, current, active power and reactive power data analysis of the low voltage ride-through test of the direct-drive wind turbine generator, which is described in the step 4.1, includes the following steps:

decomposing three-phase instantaneous voltage and three-phase instantaneous current of low voltage ride through test of an actual direct-drive wind turbine generator into a dq synchronous rotation reference coordinate system, wherein d-axis components and q-axis components of the three-phase instantaneous voltage are respectively u_dMAnd u_qMThe d-axis component and the q-axis component of the three-phase instantaneous current are i respectively_dMAnd i_qM；

And calculating a reactive power support coefficient k according to the test data of the light voltage drop:

k＝(i_qM0-i_qM)/[I_n(u_set-u_g)] (5)

in the formula i_qM0Test value, i, representing reactive component of current in normal operating condition_qMA test value representing the reactive component of the current during the fault duration; u. of_gMA measurement value representing a voltage during a fault duration;

recovery rate r of active component of current after fault clearance_idAnd the active power recovery delay t after the fault is cleared_{dealy_P}And calculating according to the test data of the direct-drive wind turbine generator running at high wind speed under the condition of deep voltage drop:

in the formula i_dM(t₇) Represents t₇Test value of the active component of the current at a time i_dM(t₄) Represents t₄Testing the active component of the current at the moment;

recovery rate r of reactive component of current after fault clearance_iqAnd reactive power recovery delay t after fault clearance_{dealy_Q}Calculating according to the test data after the direct-drive wind turbine generator fault is cleared; when the direct-drive wind turbine generator set continues to provide reactive support after the fault is cleared, t_{dealy_Q}The calculation is as follows:

t_{delay_Q}＝t₅-t₃ (7)

when the fault is cleared, the reactive power of the direct-drive wind turbine generator has the slope recovery characteristic, and t is the same₅When the reactive power at the moment is not recovered to the steady-state reactive power before the fault, r_iqThe calculation is as follows:

r_iq＝[i_qM(t₆)-i_qM(t₅)]/(t₆-t₅) (8)

in the formula i_qM(t₆) Represents t₆Test value of the reactive component of the current at the moment i_qM(t₅) Represents t₅Testing the reactive component of the current at the moment;

further, the parameters of the grid-side converter of the direct-drive wind turbine generator set in the step 4.2 include a current inner loop PI controller parameter k_{P_c}And k_{I_c}Outer loop PI controller parameter k of DC voltage_{P_udc}And k_{I_udc}And a reactive power outer loop PI controller parameter k_{P_Q}And k_{I_Q}。

Further, in step 4.2, the specific process of identifying and obtaining the grid-side converter parameters by using an optimization algorithm according to the voltage, current, active power and reactive power data of the low voltage ride through test of the direct-drive wind turbine generator set comprises the following steps:

step 4.2.1: carrying out deep voltage drop test on a direct-drive wind turbine generator set running at high wind speed to obtain active power test data P_MAnd reactive power test data Q_MSetting the input wind speed, the voltage drop depth and the voltage drop time which are the same as those of a low voltage ride through test in a universal electromagnetic transient simulation model of the direct-drive wind turbine generator; identification of bandwidth f of current inner loop PI controller by optimization algorithm_c；

Step 4.2.1 the bandwidth f of the current inner loop PI controller is identified by adopting an optimization algorithm_cIn the process of (3), identifying the objective function as:

in the formula, P_SAnd Q_SRespectively representing the active power and the reactive power output by the general electromagnetic transient simulation model, N_sAnd N_eThe numbers of the first simulation data and the last simulation data and the test data of the parameter identification are respectively represented, and i represents the numbers of the simulation data and the test data.

Identifying the bandwidth f of the obtained current inner loop PI controller_cSubstituting formula (10) to calculate current inner loop PI controller parameter k_{P_c}And k_{I_c}：

In the formula, L_fAnd R_fRespectively representing the inductance and resistance of the net side filter, and can be obtained from a fan manufacturer.

Step 4.2.2: carrying out mild voltage drop test on a direct-drive wind turbine generator set running at low wind speed to obtain active power test data P_MSetting the same input wind speed, voltage drop depth and voltage drop as the low voltage ride through test in a universal electromagnetic transient simulation model of the direct-drive wind turbine generatorThe time of fall; method for identifying bandwidth f of direct-current voltage outer-loop PI controller by adopting optimization algorithm_udc；

Step 4.2.2 the bandwidth f of the direct-current voltage outer loop PI controller is identified by adopting an optimization algorithm_udcIn the process of (3), the identified objective function is:

identifying the obtained bandwidth f of the DC voltage outer loop PI controller_udcSubstituting formula (12) to calculate the parameter k of the external loop PI controller of the DC voltage_{P_udc}And k_{I_udc}；

In the formula, C represents a direct current capacitor of the direct-drive wind turbine generator and can be obtained from a fan manufacturer.

Step 4.2.3: according to the low voltage ride through test of the direct-drive wind turbine generator in the steps 4.2.1 and 4.2.2, reactive power test data Q are obtained_MSetting the input wind speed, the voltage drop depth and the voltage drop time which are the same as those of a low voltage ride through test in a general electromagnetic transient simulation model; identification of reactive power outer loop parameter k by optimization algorithm_{P_Q}And k_{I_Q}；

Step 4.2.3 identifying the outer loop parameter k of the reactive power by adopting an optimization algorithm_{P_Q}And k_{I_Q}In the process of (3), the identified objective function is:

the invention has the beneficial effects that:

the method is used for testing the low voltage ride through capability of a plurality of actual direct-driven wind turbines, and a general electromagnetic transient response curve of the whole fault ride through process of the direct-driven wind turbines is provided according to a test result; then, analyzing the dynamic behaviors of the active power and the reactive power in the whole fault ride-through process, performing formulaic description on the dynamic behaviors of the active power and the reactive power in the whole fault ride-through process, then, providing a current reference value calculation method of the whole fault ride-through process of the direct-drive wind turbine generator, inputting the current reference value into a current controller of a grid-side converter, automatically updating the reference value of the current controller of the grid-side converter according to the working state of the direct-drive wind turbine generator, and realizing the simulation of the whole fault ride-through process of the actual direct-drive wind turbine generator. In order to improve the accuracy of the model, a step-by-step identification method is designed to identify the fault ride-through control parameters and the grid-side converter parameters. According to the method, a certain actual direct-drive wind turbine generator is selected, response characteristics of voltage, current, active power and reactive power of the universal electromagnetic transient simulation model of the direct-drive wind turbine generator and the actual direct-drive wind turbine generator are compared under the conditions of the same parameters and the same voltage drop, and the result shows that the universal electromagnetic transient simulation model of the direct-drive wind turbine generator has high precision and can simulate transient response of the whole fault ride-through process of the actual direct-drive wind turbine generator.

Drawings

FIG. 1 is a schematic diagram of the wiring principle of an actual test system;

FIG. 2 is a transient response characteristic curve diagram of 5 groups of actual direct-drive wind turbine generators under the condition of voltage drop;

FIG. 3 is a general electromagnetic transient response curve diagram of the whole fault ride-through process of the direct-drive wind turbine generator;

FIG. 4 is a control schematic diagram of a grid-side converter of the direct-drive wind turbine generator designed by the invention;

FIG. 5 is a general electromagnetic transient simulation model of a direct-drive wind turbine generator set, which is established by the invention;

FIG. 6 is a graph comparing simulation results and measured data for set 1 test data;

FIG. 7 is a graph comparing simulation results and measured data for set 2 test data;

FIG. 8 is a schematic time phase diagram defined in the "wind turbine generator electrical simulation model modeling guide rule" of the Chinese standard.

Detailed Description

The first embodiment is as follows:

the general electromagnetic transient modeling method for the direct-drive wind turbine generator set comprises the following steps:

step 1: according to the Chinese grid-connected standard technical provisions of accessing wind power plants to a power system, a plurality of direct-driven wind power generation sets are subjected to low voltage ride through capability test, the schematic structure diagram of the test system is shown in figure 1, and the transient response curves of voltage, current, active power and reactive power of a plurality of groups of actual direct-driven wind power generation sets are obtained. In order to show the fault ride-through response characteristic of the actual direct-drive wind turbine generator, 5 groups of test results are provided in this embodiment, as shown in fig. 2, where fig. 2(a), fig. 2(b), fig. 2(c), and fig. 2(d) correspond to voltage, current, active power, and reactive power, respectively.

According to the instantaneous active power and the instantaneous reactive power response of the direct-drive wind turbine generator shown in fig. 2, it can be seen that the active power of the direct-drive wind turbine generator is reduced and the reactive power is increased after the voltage drops. After the fault is cleared, the voltage begins to rise, the active power is increased, and the reactive power is reduced. When the voltage is recovered to a normal range (namely the voltage is greater than a threshold value of low voltage ride through and is 0.9p.u. in the Chinese grid-connected standard), the active power of the direct-drive wind turbine generator operated at the low wind speed is rapidly recovered to a steady-state value P before the fault₀No recovery procedure is required (as in tests 2 and 3 in fig. 2); the active power of the direct-drive wind turbine generator operated at high wind speed is subjected to short time delay t_{dealy_P}Then, with a slope r_pIs restored to the steady state value P before the fault₀. Wherein, t_{dealy_P}And r_pAre parameters that can be dynamically adjusted. For example when t_{dealy_P}Active power with slope r ═ 0_pReturn to the pre-failure steady state value without delay (test 5 in fig. 2); when r is_pWhen set to a large value, the active power is quickly restored to P₀(test 5 in figure 2). Thus, by adjusting t_{dealy_P}And r_pThe established model can simulate the active power recovery characteristics of direct-drive wind turbine generators designed by different manufacturers.

After the fault is cleared, the direct-drive wind turbine generator continues to provide reactive power Q for the power grid_suppAt a short delay t_{dealy_Q}Then, the reactive power is in slope r_QRestore to the steady state value Q before failure₀. Wherein, t_{dealy_Q}、Q_suppAnd r_QAre parameters that can be dynamically adjusted. For example when t_{dealy_Q}When equal to 0, the reactive power is given by the slope r_QThe steady state value before the fault is recovered without time delay; when Q is_suppWhen the fault is cleared, t of the direct-drive wind turbine generator is equal to 0_{dealy_Q}No reactive power is provided for the power grid within the time; when r is_QWhen set to a large value, the reactive power is quickly restored to Q₀. Thus, by adjusting t_{dealy_Q}，Q_suppAnd r_QThe established model can simulate the reactive power recovery characteristics of direct-drive wind turbine generators designed by different manufacturers.

Based on the analysis, the invention provides a general electromagnetic transient response curve of the whole fault ride-through process of the direct-drive wind turbine generator to represent possible fault behaviors of the direct-drive wind turbine generators of different manufacturers, as shown in fig. 3. In FIG. 3, [ -, t [ - ]₁]And [ t₇,～]The period represents a steady state stage before the direct-drive wind turbine generator fault occurs and a steady state stage after the recovery stage is completed, and is called stage 1 in the invention; [ t ] of₁，t₃]The period represents the fault duration period from the fault occurrence to the fault clearing period, referred to as period 2 in the present invention; [ t ] of₃，t₇]The period represents the fault clearing to a recovery phase where both active and reactive power are restored to steady state values, referred to herein as phase 3. In order to represent the recovery characteristics of direct-drive wind turbine generators of different manufacturers, 2 sub-stages are respectively adopted in the recovery stage to describe the recovery behaviors of active power and reactive power. The control principle and the main parameters of the direct-drive wind turbine generator in the whole fault ride-through process are shown in the table 1.

TABLE 1 control principle and main parameters of direct-drive wind turbine generator in the whole fault ride-through process

It is to be noted that the stages in table 1 are not necessarily all included in the general electromagnetic transient simulation model of the direct-drive wind turbine, and when the fault behaviors of the direct-drive wind turbines designed by different manufacturers are simulated, only the main parameters of each stage need to be adjusted, so that the general electromagnetic transient response curve of the overall fault ride-through process of the direct-drive wind turbine shown in fig. 3 can flexibly represent the fault behaviors of different direct-drive wind turbines.

Step 2: analyzing the dynamic behaviors of active power and reactive power in the whole fault ride-through process according to a general electromagnetic transient response curve of the whole fault ride-through process of the direct-drive wind turbine generator as shown in FIG. 3;

1) stage 1: steady state phase before fault occurrence and after recovery phase completion

According to the control principles of table 1, the dynamic behavior of active power and reactive power of phase 1 can be represented by equation (1):

in the formula, P_normalThe active power representing the normal working state, and the corresponding time range is [ -, t [ ]₁]And [ t₇,～]，Q_normalRepresenting the reactive power in normal working state, and the corresponding time range is [ -, t [ ]₁]And [ t₆,～]T represents the current simulation run time; u. of_gRepresenting the port voltage of the direct-drive wind turbine generator; i.e. i_{P_normal}Representing the active component of the current in the normal operating state, i_{Q_normal}Is the reactive component of the current under the normal working state.

2) And (2) stage: failure continuation process

According to the control principle of the table 1, the direct-drive wind turbine generator set adjusts the output power according to the grid-connected standard requirement during the fault duration. In order to support the grid voltage, direct-drive wind turbines usually preferentially provide reactive power. Thus, the dynamic behavior of active and reactive power of phase 2 can be represented by equation (2):

in the formula, P_faultRepresenting the active power during the fault duration, corresponding to a time range t₁,t₃]，Q_faultRepresenting reactive power during the fault duration, corresponding to a time range t₁,t₃]；i_{P_fault}Representing the current active component during the fault duration i_{Q_fault}Is the reactive component of the current during the fault duration; i is_maxRepresents the maximum current, i_{lim_Q}Representing the limit value of reactive component of current in fault period, k is reactive power support coefficient, and k is more than or equal to 1.5 according to grid-connected standard, u_setRepresenting a set voltage threshold, constant, according to a grid-connection standard u_setIs 0.9p.u., I_nRepresenting rated current, i_Q0Representing the steady state reactive component of current before the fault.

3) And (3) stage: recovery procedure

The active power recovery process comprises the following steps: according to the control principle of Table 1, at stage 3-1 the direct drive wind turbine is at t_{dealy_P}The active power at the end of phase 2 is maintained for the time. Then, in the stage 3-2, the active power of the direct-drive wind turbine generator is driven by the slope r_PIs restored to the steady state value P before the fault₀. Thus, the dynamic behavior of active power of phase 3 can be represented by equation (3):

in the formula, P_reThe active power representing the fault recovery process corresponds to the time ranges of t₃,t₇]；P(t₃) Represents t₃Active power at time P (t)₄) Represents t₄Active power at a moment r_PRepresenting the rate of restoration of active power after fault clearance, P₀Representing steady state active power before the fault.

And (3) a reactive power recovery process: according to the control principle in the table 1, the direct-drive wind turbine generator continues to provide the power for a period of time t at the stage 3-1_{dealy_Q}Is idleAnd (4) power. Different manufacturers may adopt different control strategies to meet the requirement, and in order to ensure the universality, the invention provides two reactive power support strategies:

strategy 1: the direct-drive wind turbine generator set continuously operates in a reactive support mode, and dynamic reactive support is provided according to the voltage condition of a power grid;

strategy 2: the reactive power output by the direct-drive wind turbine generator is kept at the reactive power at the end moment of the stage 2, and fixed reactive support is provided;

in stage 3-2, the reactive power control of the direct-drive wind turbine generator is switched back to the normal operation mode. If the reactive power Q (t) is present at this time₅) Restore to the steady state value Q before failure₀If so, ending the recovery process; otherwise, in order to avoid the impact of the reactive power switching control strategy on the voltage, the reactive power of some types of direct-drive wind turbine generators has a slope recovery characteristic. Thus, the dynamic behavior of the reactive power of phase 3 can be represented by equation (4):

in the formula, Q_reThe reactive power representing the fault recovery process corresponds to time ranges of t₃,t₆]；Q(t₃) Represents t₃Reactive power at time, Q (t)₅) Represents t₅Reactive power at time, r_QRepresenting the rate of recovery of reactive power after fault clearance, Q₀Representing steady state reactive power before the fault.

And step 3: analyzing a reference value of a current active component and a reference value of a current reactive component according to the dynamic behavior formulas of the active power and the reactive power in the whole fault ride-through process obtained in the step 2, inputting the obtained reference values into a current controller of a grid-side converter of the universal electromagnetic transient simulation model of the direct-drive wind turbine generator, and automatically adjusting the dynamic behavior of the universal electromagnetic transient simulation model of the direct-drive wind turbine generator by utilizing the tracking function of the current controller of the grid-side converter, wherein the specific details are as follows:

according to the direct-drive wind motorAccording to the operation principle of the group, the adjustment of the response characteristics of the active power and the reactive power is realized by adjusting the reference value of the current active component and the reference value of the current reactive component of the current controller of the grid-side converter respectively. Therefore, the key point of modeling the whole fault ride-through process of the direct-drive wind turbine generator system is that the reference value of the current active component and the reference value of the current reactive component in the current controller of the grid-side converter of the direct-drive wind turbine generator system are analyzed according to the dynamic behavior formulas of the active power and the reactive power in the whole fault ride-through process. When the direct-drive wind turbine generator system adopts the vector control of grid voltage orientation and the grid voltage is oriented to the d axis of the dq synchronous rotation reference coordinate system, the reference value of the current active component corresponds to the reference value i of the d axis component of the current controller_drefReference value of reactive component of current corresponds to reference value i of q-axis component of current controller_qref。

Therefore, the invention provides a reference value i of the active component of the current in the whole process of fault ride-through of the direct-drive wind turbine generator in the step_drefAnd a reference value i of the reactive component of the current_drefThe method of (3). Reference value i of current active component_drefExpressed as:

in the formula i_{dref_normal}Reference value, i, representing the active component of the current in normal operation_{dref_fault}Reference value, i, representing the current active component during the fault duration_{dref_re}A reference value representing the active component of the current during the fault recovery process; k is a radical of_{P_udc}And k_{I_udc}Respectively representing the proportional and integral coefficients, u, of the external loop PI controller for DC voltage_dcrefReference value, u, representing a DC voltage_dcRepresents a direct voltage i_{qref_fault}Reference value, r, representing the reactive component of the current during the duration of the fault_idRepresenting the rate of recovery of the real component of the current after the fault has cleared.

Reference value i of the reactive component of the current_qrefExpressed as:

in the formula i_{qref_normal}Reference value, i, representing the reactive component of the current in normal operation_{qref_re}Reference value, i, representing the reactive component of the current during fault recovery_qref0Representing steady state reactive current components prior to a fault; k is a radical of_{P_Q}And k_{I_Q}Respectively representing the proportional and integral coefficients, Q, of a reactive power PI controller_refRepresenting a reference value of reactive power, Q representing reactive power, r_iqRepresenting the recovery rate of the reactive component of the current after the fault has cleared.

Assigning the d-axis current reference value and the q-axis current reference value of a current controller of a grid-side converter of a direct-drive wind turbine generator set general electromagnetic transient simulation model according to formulas (5) and (6), and simultaneously assigning a grid-side current active component i of the direct-drive wind turbine generator set general electromagnetic transient simulation model_dAnd a current reactive component i_qD-axis and q-axis current actual values input to the current controller generate a voltage reference value e of the grid-side converter through the current PI controller_drefAnd e_qref：

Where ω is the angular frequency of the mains voltage, R_fAnd L_fRespectively the resistance and inductance of the network side filter, k_{P_c}And k_{I_c}Respectively representing the proportional and integral coefficients of the current inner loop PI controller.

E is to be_drefAnd e_qrefTransforming from dq synchronous rotation reference coordinate system to abc three-phase stationary coordinate system_abcrefAnd generating a trigger signal of a direct-drive wind turbine generator switch device IGBT by using a pulse width modulation technology. A control block diagram of the grid converter of the direct-drive wind turbine generator in the whole fault ride-through process is shown in fig. 4, the grid-side converter automatically updates the reference value of the current controller of the grid-side converter according to the current working state of the direct-drive wind turbine generator, and therefore the universal electromagnetism of the direct-drive wind turbine generator is adjustedAnd the dynamic behavior of the transient simulation model realizes the simulation of the transient response of the actual fault crossing whole process of the direct-drive wind turbine generator.

And 4, step 4: in order to ensure the accuracy of the established universal electromagnetic transient model of the direct-drive wind turbine generator, the step of identifying the fault ride-through control parameters and the grid-side converter parameters of the direct-drive wind turbine generator specifically comprises the following steps:

fault ride-through control parameters: reactive power support coefficient k, and recovery rate r of current active component_idRate of recovery r of reactive component of current_iqActive power recovery delay t after fault clearance_{dealy_P}And the reactive power support delay t after fault clearing_{dealy_Q}；

Grid-side converter parameters: current inner loop PI controller parameter k_{P_c}And k_{I_c}Outer loop PI controller parameter k of DC voltage_{P_udc}And k_{I_udc}And a reactive outer loop PI controller parameter k_{P_Q}And k_{I_Q}。

During the fault duration, the active power and the reactive power injected into the power grid by the direct-drive wind turbine generator mainly depend on fault ride-through control parameters, and the transient tracking performance of the controller is mainly influenced by the parameters of the grid-side converter. Thus, the present invention employs a two-step identification to determine these parameters.

In step 4.1, analyzing and calculating the fault ride-through control parameters of the direct-drive wind turbine generator according to the voltage, current, active power and reactive power data of the low voltage ride-through test of the direct-drive wind turbine generator, and the specific process is as follows:

decomposing three-phase instantaneous voltage and three-phase instantaneous current of low voltage ride through test of an actual direct-drive wind turbine generator into a dq synchronous rotation reference coordinate system, wherein d-axis components and q-axis components of the three-phase instantaneous voltage are respectively u_dMAnd u_qMThe d-axis component and the q-axis component of the three-phase instantaneous current are i respectively_dMAnd i_qM。

1) Coefficient of reactive power support k

The reactive component of the current injected into the power grid by the direct-drive wind turbine generator is in direct proportion to the voltage deviation during the voltage drop period, and is limited to the maximum reactive component of the current. When slight voltage sag, the current reactive component is less than the maximum current reactive component, so k can be calculated according to the test data of slight voltage sag:

k＝(i_qM0-i_qM)/[I_n(u_set-u_g)] (8)

in the formula i_qM0Test values, u, representing reactive components of current in normal operating conditions_gMRepresenting a measure of the voltage during the fault.

2) Recovery rate r of active component of current after fault clearance_idAnd the active power recovery delay t after the fault is cleared_{dealy_P}

Under the condition of deep voltage drop, when the voltage is recovered to the normal operation range, the current active component of the direct-drive wind turbine generator operated at high wind speed is delayed by t_{dealy_P}Then with a slope r_idAnd (6) recovering. Therefore, r can be calculated according to the test data of the direct-drive wind turbine generator operated at high wind speed under the condition of deep voltage drop_idAnd t_{dealy_P}：

In the formula i_dM(t₇) Represents t₇Test value of the active component of the current at a time i_dM(t₄) Represents t₄And (4) testing the active component of the current at the moment.

3) Recovery rate r of reactive component of current after fault clearance_iqAnd reactive power recovery delay t after fault clearance_{dealy_Q}

r_iqAnd t_{dealy_Q}The method can be used for calculating according to the test data after the fault is cleared, and when the direct-drive wind turbine generator continues to provide reactive power after the fault is cleared, t_{dealy_Q}The calculation is as follows:

t_{delay_Q}＝t₅-t₃ (10)

when the fault is cleared, the reactive power of the direct-drive wind turbine generator has the slope recovery characteristic, and t is the same₅When the reactive power at the moment is not recovered to the steady-state reactive power before the fault, r_iqComputingComprises the following steps:

r_iq＝[i_qM(t₆)-i_qM(t₅)]/(t₆-t₅) (11)

in step 4.2, according to the voltage, current, active power and reactive power data of the low voltage ride through test of the direct-drive wind turbine generator, the specific process of identifying and obtaining the parameters of the PI controller of the grid-side converter by adopting an optimization algorithm is as follows:

firstly, determining parameters to be identified, wherein the parameters of the PI controllers of the grid-side converter comprise three groups:

current inner loop PI controller parameters: k is a radical of_{P_c}And k_{I_c}；

Parameters of a direct-current voltage outer ring PI controller: k is a radical of_{P_udc}And k_{I_udc}；

Parameters of a reactive power outer loop PI controller: k is a radical of_{P_Q}And k_{I_Q}；

Wherein, the current inner loop PI controller parameter k_{P_c}And k_{I_c}Can be expressed as:

in the formula (f)_cIs the bandwidth of the current inner loop, R_fAnd L_fThe circuit parameters can be obtained from a fan manufacturer. Thus, it is possible to identify f_cTo determine k_{P_c}And k_{I_c}。

Parameter k of direct-current voltage outer loop PI controller_{P_udc}And k_{I_udc}Can be expressed as:

in the formula (f)_udcIs the bandwidth of the outer loop of the DC voltage, u_nIs an electric networkThe rated voltage of (C) is a known quantity, C is a circuit parameter, and can be obtained from a fan manufacturer. Thus, it is possible to identify f_udcTo determine k_{P_udc}And k_{I_udc}。

In summary, the grid-side converter PI controller has 4 to-be-identified parameters: bandwidth f of current inner loop PI controller_cBandwidth f of outer loop PI controller for DC voltage_udcOuter loop PI controller parameter k of reactive power_{P_Q}And k_{I_Q}。

Because the inner ring PI controller and the outer ring PI controller are in a cascade relation, the PI controllers cannot be identified at the same time under the same disturbance. Thus, the present invention utilizes different perturbations to identify these parameters. For a direct-drive wind turbine generator set running at a high wind speed, when a deep voltage dip occurs, a reference value of a current active component and a reference value of a current reactive component can be expressed as follows:

at this time, the d-axis and q-axis voltage reference values of the grid-side converter can be expressed as:

according to the formula (15), the d-axis and q-axis voltage reference values of the grid-side converter only depend on the bandwidth f of the current inner loop PI controller_cAnd with the outer loop parameter (f)_udc，k_{P_Q}And k_{I_Q}) Is irrelevant. Therefore, to identify f more efficiently_cAnd test data of the direct-drive wind turbine generator set running at high wind speed under deep voltage drop can be utilized.

For a direct-drive wind turbine generator set running at a low wind speed, when a light voltage drop occurs, a reference value of a current active component and a reference value of a current reactive component can be expressed as follows:

at this time, the d-axis and q-axis voltage reference values of the grid-side converter are as follows:

wherein the content of the first and second substances,

according to the formulas (17) and (18), the d-axis and q-axis voltage reference values of the grid-side converter depend on the bandwidth f of the current inner loop PI controller_cAnd bandwidth f of direct-current voltage outer-loop PI controller_udcAnd with the parameter k of the reactive power outer loop PI controller_{P_Q}And k_{I_Q}Is irrelevant. At the determination of f_cAfter, only f_udcIdentification is required. Therefore, to identify f more efficiently_udcAnd test data of the direct-drive wind turbine generator set running at low wind speed under slight voltage drop can be utilized.

At the determination of f_cAnd f_udcThereafter, the above-mentioned test data pair k may be utilized_{P_Q}And k_{I_Q}And (5) performing identification.

To sum up, first, identify the bandwidth f of the current inner loop PI controller_cAnd secondly the bandwidth f of the DC voltage outer loop PI controller_udcFinally, identifying the parameter k of the reactive power outer loop PI controller_{P_Q}And k_{I_Q}By adopting the sequence, the decoupling identification of the inner ring cascade controller and the outer ring cascade controller can be realized. In this embodiment, taking a 1.5MW direct-drive wind turbine as an example, identifying parameters of a PI controller of a grid-side converter of the direct-drive wind turbine, the specific process is as follows:

step 4.2.1: firstly, a general electromagnetic transient simulation model of the 1.5MW direct-drive wind turbine is established, and as shown in fig. 5, the parameters of the simulation model which are the same as those of the actual 1.5MW direct-drive wind turbine in table 2 are set. Carrying out deep voltage drop test on a direct-drive wind turbine generator set running at high wind speed to obtain active power test data P_MAnd reactive power test data Q_M. Universal electromagnetic transient state for direct-drive wind turbine generatorAnd the simulation model is provided with the same input wind speed, voltage drop depth and voltage drop time as those of the actual direct-drive wind turbine generator low-voltage ride through test. In the embodiment, the bandwidth f of the current inner loop PI controller is identified by taking a genetic algorithm as an example_cThe population number of the genetic algorithm is 100, the cross probability is 0.8, and the mutation probability is 0.05. The identified objective function is:

in the formula, P_SAnd Q_SRespectively representing active and reactive power output by the simulation model, N_sAnd N_eThe numbers of the first simulation data and the last simulation data and the test data of the parameter identification are respectively represented, and i represents the numbers of the simulation data and the test data.

Making the target function L in the identification process₁Minimum, obtaining the bandwidth f of the current inner loop PI controller_cAnd will identify the obtained f_cSubstituting formula (12) to calculate current inner loop PI controller parameter k_{P_c}And k_{I_c}。

TABLE 21.5 MW Main parameters of direct-drive wind turbine

Step 4.2.2: carrying out mild voltage drop test on a direct-drive wind turbine generator set running at low wind speed to obtain active power test data P_M. The input wind speed, the voltage drop depth and the voltage drop time which are the same as those of the actual direct-drive wind turbine generator low-voltage ride through test are set in the universal electromagnetic transient simulation model of the direct-drive wind turbine generator. Method for identifying bandwidth f of direct-current voltage outer-loop PI controller by adopting genetic algorithm_udcThe identified objective function is:

making the target function L in the identification process₂Minimum, obtaining the bandwidth f of the external ring PI controller of the direct current voltage_udcAnd will identify the obtained f_udcSubstituting formula (13) to calculate parameter k of external loop PI controller for DC voltage_{P_udc}And k_{I_udc}。

Step 4.2.3: according to the low voltage ride through test of the direct-drive wind turbine generator in the steps 4.2.1 and 4.2.2, reactive power test data Q are obtained_M. The input wind speed, the voltage drop depth and the voltage drop time which are the same as those of the actual direct-drive wind turbine generator low-voltage ride through test are set in the universal electromagnetic transient simulation model of the direct-drive wind turbine generator. Identification of reactive power outer loop PI controller parameter k by genetic algorithm_{P_Q}And k_{I_Q}The identified objective function is:

making the target function L in the identification process₃Obtaining the parameter k of the outer loop PI controller of the reactive power at minimum_{P_Q}And k_{I_Q}。

After the steps 4.2.1, 4.2.2 and 4.2.3, the identification result of the parameter of the PI controller of the direct-drive wind turbine grid-side converter is obtained, as shown in table 3.

Identification value of PI controller parameter of grid-side converter of direct-drive wind turbine generator set of 31.5 MW

Finally, verifying the accuracy of the universal electromagnetic transient simulation model of the direct-drive wind turbine generator:

taking test data of two groups of actual direct-drive wind turbine generators as an example, the established universal electromagnetic transient simulation model of the direct-drive wind turbine generators and the parameter identification result are verified, and the process is as follows: firstly, setting input wind speed, voltage drop depth and voltage drop time which are the same as those of an actual direct-drive wind turbine generator low-voltage ride-through test to obtain a voltage, current, active power and reactive power response curve of a general electromagnetic transient simulation model of the direct-drive wind turbine generator, and comparing an actual test result with a voltage, current, active power instantaneous value and reactive power instantaneous value of the general electromagnetic transient simulation model of the direct-drive wind turbine generator, wherein the actual test result and the voltage, current, active power and reactive power instantaneous value are respectively shown in fig. 6 (example 1) and fig. 7 (example 2), wherein fig. 6(a), fig. 6(b), fig. 6(c) and fig. 6(d) respectively correspond to voltage, current, active power and reactive power, and fig. 7(a), fig. 7(b), fig. 7(c) and fig. 7(d) respectively correspond to voltage, current, active power. As can be seen from fig. 6 and 7, the established general electromagnetic transient simulation model of the direct-drive wind turbine generator is consistent with the transient response of the actual direct-drive wind turbine generator.

Further, the error between the output of the simulation model and the test data under the voltage drop is calculated according to the Chinese standard 'wind turbine generator electrical simulation model modeling guide rule'. The calculated electrical quantities include active power, reactive power and reactive component of current. The time range of the error calculation includes 5 intervals: a, B₁，B₂，C₁And C₂. Taking active power as an example, the division of 5 intervals is shown in fig. 8, wherein the division point t of the intervals B and C_B1And t_C1The last 20ms when the fluctuation in power or current comes within ± 10% of the mean value of the period is taken.

The error calculation formula is:

in the formula, X represents active power P, reactive power Q and current reactive component i_q，N_StartAnd N_EndThe numbers of the first simulation data and the last simulation data and the test data of the calculation interval are respectively represented, and i represents the numbers of the simulation data and the test data.

According to the Chinese standard 'guide rule for modeling electrical simulation model of wind turbine generator', if each parameter (P, Q and i)_q) At a corresponding stageThe errors are all below the maximum allowable error shown in table 4, and the model is valid.

TABLE 4 maximum allowable error value (%)

Parameter(s)	F_1max	F_2max	F_3max	F_4max	F_5max	F_Gmax
							P	7	20	10	25	15	15
Q	5	20	7	25	10	15
							i_q	7	20	10	30	15	15

P, Q and i of the example 1 corresponding to FIG. 6 and the example 2 corresponding to FIG. 7 were calculated based on the formula (21)_qThe results are shown in Table 5, with errors at the corresponding stages. As can be seen from Table 5, P, Q and i_qThe error at each stage is less than the maximum allowable error shown in table 4. Therefore, the universal electromagnetic transient simulation model of the direct-drive wind turbine generator set obtained by the method can accurately represent the dynamic behaviors of different actual direct-drive wind turbine generator set fault ride-through overall processes.

TABLE 5 error calculation results (%)

The present invention is capable of other embodiments and its several details are capable of modifications in various obvious respects, all without departing from the spirit and scope of the present invention.

Claims

1. A general electromagnetic transient modeling method for a direct-drive wind turbine generator is characterized by comprising the following steps:

2. The general electromagnetic transient modeling method for the direct-drive wind turbine generator set according to claim 1, characterized in that the fault ride-through overall process in the step 1 comprises a steady-state stage before a fault occurs, a fault continuation stage, a recovery stage after the fault is cleared until both active power and reactive power are recovered to a steady-state value, and a steady-state stage after the recovery stage is completed; and obtaining a general electromagnetic transient response curve of the direct-drive wind turbine generator in the whole fault ride-through process, wherein the general electromagnetic transient response curve comprises a response curve of voltage, instantaneous active power and instantaneous reactive power.

3. The method for modeling the universal electromagnetic transient state of the direct-drive wind turbine generator set according to claim 2, wherein in the step 2, the description of the dynamic behavior of the active power in the whole fault ride-through process is as follows:

in the formula, Q_normalRepresenting the reactive power in normal working state, and the corresponding time range is [ -, t [ ]₁]And [ t₆,～]，Q_faultRepresenting reactive power during the fault duration, corresponding to a time range t₁,t₃]，Q_reThe reactive power representing the fault recovery process corresponds to time ranges of t₃,t₆]；i_{Q_normal}Is a reactive component of current under normal working condition, i_{Q_fault}For the reactive component of the current during the duration of the fault, i_{lim_Q}Representing the limit value of reactive component of current in fault period, k is reactive power support coefficient, and k is more than or equal to 1.5 according to grid-connected standard, u_setRepresenting a set voltage threshold, constant, according to a grid-connection standard u_setIs 0.9p.u., I_nRepresenting rated current, i_Q0Representative of a faultA previous steady state current reactive component; q (t)₃) Represents t₃Reactive power at time, Q (t)₅) Represents t₅Reactive power at time, r_QRepresenting the rate of recovery of reactive power after fault clearance, Q₀Representing steady state reactive power before the fault.

4. The direct-drive wind turbine generator universal electromagnetic transient modeling method according to claim 3, characterized in that the step 3 is to analyze a reference value of a current active component and a reference value of a current reactive component according to the active power and reactive power obtained in the step 2 in a dynamic behavior formula of the fault ride-through overall process, input the obtained reference values into a current controller of a grid-side converter of the direct-drive wind turbine generator universal electromagnetic transient simulation model, and automatically adjust a specific process of the dynamic behavior of the direct-drive wind turbine generator universal electromagnetic transient simulation model by using a tracking function of the current controller of the grid-side converter, and the specific process comprises the following steps:

when the direct-drive wind turbine generator system adopts the vector control of grid voltage orientation and the grid voltage is oriented to the d axis of the dq synchronous rotation reference coordinate system, the reference value of the current active component corresponds to the reference value i of the d axis component of the current controller_drefReference value of reactive component of current corresponds to reference value i of q-axis component of current controller_qref(ii) a Reference value i of current active component_drefExpressed as:

in the formula i_{dref_normal}Reference value, i, representing the active component of the current in normal operation_{dref_fault}Reference value, i, representing the current active component during the fault duration_{dref_re}A reference value representing the active component of the current during the fault recovery process; k is a radical of_{P_udc}And k_{I_udc}Respectively representing the proportional and integral coefficients, u, of the external loop PI controller for DC voltage_dcrefReference value, u, representing a DC voltage_dcRepresents a direct voltage i_{qref_fault}Representative of a faultReference value of the reactive component of the current during the duration, r_idRepresenting the recovery rate of the active component of the current after the fault is cleared;

reference value i of the reactive component of the current_qrefExpressed as:

5. The general electromagnetic transient modeling method for the direct-drive wind turbine generator set according to claim 4, wherein the specific process of identifying the fault ride-through control parameters and the grid-side converter parameters of the direct-drive wind turbine generator set by adopting step-by-step identification in the step 4 comprises the following steps:

6. General electricity for direct-drive wind turbine generator set according to claim 5The magnetic transient modeling method is characterized in that the fault ride-through control parameters of the direct-drive wind turbine generator set in the step 4.1 comprise a reactive power support coefficient k and a recovery rate r of an active component of current after fault clearing_idRate of recovery r of reactive component of current after fault clearance_iqActive power recovery delay t after fault clearance_{dealy_P}And reactive power support delay t after fault clearing_{dealy_Q}。

7. The general electromagnetic transient modeling method for the direct-drive wind turbine generator set according to claim 6, wherein the specific process of calculating the fault ride-through control parameters of the direct-drive wind turbine generator set according to the voltage, current, active power and reactive power data analysis of the low voltage ride-through test of the direct-drive wind turbine generator set in the step 4.1 comprises the following steps:

k＝(i_qM0-i_qM)/[I_n(u_set-u_g)] (5)

t_{delay_Q}＝t₅-t₃ (7)

r_iq＝[i_qM(t₆)-i_qM(t₅)]/(t₆-t₅) (8)

in the formula i_qM(t₆) Represents t₆Test value of the reactive component of the current at the moment i_qM(t₅) Represents t₅And (4) testing the reactive component of the current at the moment.

8. The direct-drive wind turbine generator universal electromagnetic transient modeling method according to claim 5, 6 or 7, characterized in that the direct-drive wind turbine generator grid-side converter parameter of step 4.2 comprises a current inner loop PI controller parameter k_{P_c}And k_{I_c}Outer loop PI controller parameter k of DC voltage_{P_udc}And k_{I_udc}And a reactive power outer loop PI controller parameter k_{P_Q}And k_{I_Q}。

9. The general electromagnetic transient modeling method for the direct-drive wind turbine generator set according to claim 8, wherein in step 4.2, the specific process of identifying and obtaining the grid-side converter parameters by adopting an optimization algorithm according to the voltage, current, active power and reactive power data of the low voltage ride through test of the direct-drive wind turbine generator set comprises the following steps:

Step 4.2.2: carrying out mild voltage drop test on a direct-drive wind turbine generator set running at low wind speed to obtain active power test data P_MSetting the input wind speed, the voltage drop depth and the voltage drop time which are the same as those of a low voltage ride through test in a universal electromagnetic transient simulation model of the direct-drive wind turbine generator; method for identifying bandwidth f of direct-current voltage outer-loop PI controller by adopting optimization algorithm_udc；

In the formula, C represents a direct current capacitor of a direct-drive wind turbine generator and can be obtained from a fan manufacturer;

step 4.2.3: direct drive wind turbine generator according to steps 4.2.1 and 4.2.2Voltage ride through test to obtain reactive power test data Q_MSetting the input wind speed, the voltage drop depth and the voltage drop time which are the same as those of a low voltage ride through test in a general electromagnetic transient simulation model; identification of reactive power outer loop parameter k by optimization algorithm_{P_Q}And k_{I_Q}。

10. The general electromagnetic transient modeling method for the direct-drive wind turbine generator set according to claim 9, characterized in that in step 4.2.1, the bandwidth f of the current inner loop PI controller is identified by adopting an optimization algorithm_cIn the process of (3), identifying the objective function as:

in the formula, P_SAnd Q_SRespectively representing the active power and the reactive power output by the general electromagnetic transient simulation model, N_sAnd N_eRespectively representing the serial numbers of the first simulation data and the last simulation data and the test data of the parameter identification, wherein i represents the serial numbers of the simulation data and the test data;