CN112910006B - A general electromagnetic transient modeling method for direct-drive wind turbines - Google Patents

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 a plurality of direct-drive wind turbine generators, a universal 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 behavior is 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 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. The method is mainly used for general electromagnetic transient modeling of the direct-drive wind turbine generator.

Description

A general electromagnetic transient modeling method for direct drive wind turbines

technical field

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

Background technique

The ever-increasing energy demand and increasingly severe environmental problems have greatly promoted the development of wind power generation. Direct-drive wind turbines have the advantages of high energy density and simple control methods, and are more and more widely used in onshore and offshore wind farms. However, as the penetration rate of wind turbines continues to increase, the integration of wind power into the grid has brought serious challenges to the safe operation of the power system. Establishing an electromagnetic transient model that can accurately reflect the fault ride-through characteristics of actual direct-drive wind turbines under voltage dips , it is of great significance to correctly evaluate the possible impact of large-scale wind power grid integration on the grid.

However, due to the confidential information involved, the electromagnetic transient models established by wind turbine manufacturers are generally in the form of "black boxes", and their internal control strategies and control parameters cannot be known, which seriously hinders the development of related research. Therefore, it is urgent to establish a general electromagnetic transient model. The general electromagnetic transient models of direct-drive wind turbines established in existing studies mostly focus on the modeling of the duration of the fault, but fail to analyze the recovery process after the fault is cleared and between different fault stages (including the steady state before the fault occurs). complete and detailed modeling of the switching transients during the fault-clearing phase to the recovery phase in which both active and reactive powers return to steady-state values, and the steady-state phase after the recovery phase). At the same time, due to the failure to accurately identify the control parameters (including fault ride-through control parameters and converter control parameters) of the direct-drive wind turbine electromagnetic transient model in the whole process of fault ride-through, there is a significant deviation between the model output and the measured data. Use has great limitations.

Contents of the invention

The invention aims to solve the existing problem of lack of general electromagnetic transient modeling for the whole fault ride-through process of the direct drive wind turbine. A general electromagnetic transient modeling method for direct drive wind turbines is provided.

A general electromagnetic transient modeling method for a direct drive wind turbine, comprising the following steps:

Step 1: Conduct low-voltage ride-through tests on multiple direct-drive wind turbines to obtain the voltage, current, active power and reactive power responses of multiple direct-drive wind turbines under different voltage dips. According to the voltage, current, active power and Response of reactive power, get the general electromagnetic transient response curve of the direct drive wind turbine through the whole process of fault;

Step 2: According to the general electromagnetic transient response curve of the direct drive wind turbine in the whole process of fault ride-through obtained in step 1, analyze the dynamic behavior of active power and reactive power in the fault ride-through process, and analyze the active power and reactive power in the fault ride-through process Describe the dynamic behavior through the whole process;

Step 3: According to the dynamic behavior formula of active power and reactive power in the whole process of fault ride-through obtained in step 2, analyze the reference value of the current active component and the reference value of the current reactive component, and input the obtained reference value into the direct drive wind power plant In the current controller of the grid side converter of the general electromagnetic transient simulation model of the unit, the dynamic behavior of the general electromagnetic transient simulation model of the direct drive wind turbine is automatically adjusted by using the tracking function of the current controller of the grid side converter;

Step 4: Use step-by-step identification to identify the fault ride-through control parameters and grid-side converter parameters of the direct-drive wind turbine.

Further, the whole process of fault ride-through described in step 1 includes the steady state stage before the fault occurs, the fault continuation stage, the restoration stage when the fault is cleared until both active power and reactive power return to the steady state value, and the restoration stage after the restoration stage is completed. Steady-state stage: obtain the general electromagnetic transient response curve of the direct-drive wind turbine in the whole process of fault ride-through, including the response curves of voltage, instantaneous active power and instantaneous reactive power.

Further, in 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, P _normal represents the active power in the normal working state, and the corresponding time range is [～,t ₁ ] and [t ₇ ,～], P _fault represents the active power during the fault duration, and the corresponding time range is [ t ₁ ,t ₃ ], P _re represents the active power in the fault recovery process, and the corresponding time ranges are [t ₃ ,t ₇ ], t represents the current simulation running time; u _g represents the port voltage of the direct drive wind turbine, i _{P_normal} represents the current active component in normal working state, i _{P_fault} represents the current active component during the fault duration, I _max represents the maximum current, i _{Q_fault} represents the current reactive component during the fault duration; P(t ₃ ) represents the active power at time t ₃ , P(t ₄ ) represents the active power at time t ₄ , r _P represents the recovery rate of active power after the fault is cleared, and P ₀ represents the steady-state active power before the fault;

The dynamic behavior of reactive power in the whole process of fault ride-through is described as follows:

In the formula, Q _normal represents the reactive power in normal working state, and the corresponding time range is [～,t ₁ ] and [t ₆ ,～], Q _fault represents the reactive power during the fault duration, and the corresponding time range is [t ₁ , t ₃ ], Q _re represents the reactive power in the fault recovery process, and the corresponding time ranges are [t ₃ , t ₆ ]; i _{Q_normal} is the current reactive component in the normal working state, and i _{Q_fault} is The current reactive component during the fault duration, i _{lim_Q} represents the limit value of the current reactive component during the fault period, k is the reactive power support coefficient, according to the grid-connected standard k≥1.5, u _set represents the set voltage threshold, which is a constant, according to The grid-connected standard u _set is 0.9pu, I _n represents the rated current, i _Q0 represents the reactive component of the steady state current before the fault; Q(t ₃ ) represents the reactive power at time t ₃ , and Q(t ₅ ) represents the reactive power at t ₅ The reactive power _at time, _rQ represents the recovery rate of reactive power after the fault is cleared, and Q0 represents the steady-state reactive power before the fault.

Further, the reference value of the current active component and the reference value of the current reactive component are analyzed according to the dynamic behavior formula of active power and reactive power obtained in step 2 in the whole process of fault ride-through in step 3, and the obtained reference value Input to the current controller of the grid-side converter of the general electromagnetic transient simulation model of the direct-drive wind turbine, and use the tracking function of the current controller of the grid-side converter to automatically adjust the general electromagnetic transient simulation model of the direct-drive wind turbine The specific process of dynamic behavior includes the following steps:

When the direct-drive wind turbine adopts grid voltage-oriented vector control and the grid voltage is oriented on the d-axis of the dq synchronous rotating reference frame, the reference value of the active component of the current corresponds to the reference value _idref of the d-axis component of the current controller, and the reactive component of the current The reference value of corresponds to the reference value i _qref of the q-axis component of the current controller; the reference value i _dref of the current active component is expressed as:

In the formula, _{idref_normal} represents the reference value of the current active component in the normal working state, _{idref_fault} represents the reference value of the current active component during the fault duration, and _{idref_re} represents the reference value of the current active component in the fault recovery process; k _{P_udc} and k _{I_udc} are respectively Represents the proportional and integral coefficients of the DC voltage outer loop PI controller, u _dcref represents the reference value of the DC voltage, u _dc represents the DC voltage, i _{qref_fault} represents the reference value of the reactive component of the current during the fault duration, and r _id represents the current after the fault is cleared Recovery rate of active components;

The reference value i _qref of the reactive component of the current is expressed as:

In the formula, i _{qref_normal} represents the reference value of current reactive component in normal working state, i _{qref_re} represents the reference value of current reactive component in the fault recovery process; k _{P_Q} and k _{I_Q} represent the ratio of reactive power outer loop PI controller and integral coefficient, Q _ref represents the reference value of reactive power, Q represents reactive power, r _iq represents the recovery rate of current reactive component after the fault is cleared;

According to the formula (3) and formula (4), the d and q axis current reference values of the current controller in the grid-side converter of the general electromagnetic transient simulation model of the direct-drive wind turbine are assigned, and the direct-drive wind power is automatically adjusted by using the current controller Dynamic Behavior of a Generic Electromagnetic Transient Simulation Model for Units.

Further, the specific process of identifying the fault ride-through control parameters and grid-side converter parameters of the direct-drive wind turbine by step-by-step identification described in step 4 includes the following steps:

Step 4.1: According to the analysis and calculation of the voltage, current, active power and reactive power data of the direct-drive wind turbine low-voltage ride-through test, the fault ride-through control parameters of the direct-drive wind turbine are calculated;

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, an optimization algorithm is used to identify and obtain the parameters of the grid-side converter.

Further, the fault ride-through control parameters of the direct-drive wind turbine described in step 4.1 include the reactive power support coefficient k, the recovery rate r _id of the active component of the current after the fault is cleared, the recovery rate r _iq of the reactive component of the current after the fault is cleared, and the fault Active power recovery delay t _{dealy_P} after fault clearing and reactive power support delay t _{dealy_Q} after fault clearing.

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

Decompose the three-phase instantaneous voltage and three-phase instantaneous current of the low-voltage ride-through test of the actual direct-drive wind turbine into the dq synchronous rotating reference frame. The d and q-axis components of the three-phase instantaneous voltage are u _dM and u _qM respectively, and the three-phase The d and q axis components of the instantaneous current are i _dM and i _qM respectively;

The reactive power support coefficient k is calculated according to the test data of mild voltage drop:

k＝(i _qM0 -i _qM )/[I _n (u _set -u _g )] (5)

In the formula, i _qM0 represents the test value of the reactive component of the current under normal working conditions, i _qM represents the test value of the reactive component of the current during the fault duration; u _gM represents the measured value of the voltage during the fault duration;

The recovery rate r _id of the active component of the current after the fault is cleared and the delay t _{dealy_P} of the active power recovery after the fault is cleared are calculated according to the test data of the direct-drive wind turbine operating at high wind speed under the condition of deep voltage sag:

In the formula, i _dM (t ₇ ) represents the test value of current active component at time t ₇ , and i _dM (t ₄ ) represents the test value of current active component at time t ₄ ;

The recovery rate r _iq of the current reactive component after the fault is cleared and the reactive power recovery delay t _{dealy_Q} after the fault is cleared are calculated according to the test data of the direct drive wind turbine after the fault is cleared; when the fault is cleared, the direct drive wind turbine continues to provide reactive power When supported, t _{dealy_Q} is calculated as:

t _{delay_Q} =t ₅ -t ₃ (7)

When the reactive power of the direct-drive wind turbine has a slope recovery characteristic after the fault is cleared, and the reactive power at time t5 has not recovered to the steady _- state reactive power before the fault, r _iq is calculated as:

r _iq =[i _qM (t ₆ )-i _qM (t ₅ )]/(t ₆ -t ₅ ) (8)

In the formula, i _qM (t ₆ ) represents the test value of current reactive component at time t ₆ , and i _qM (t ₅ ) represents the test value of current reactive component at time t ₅ ;

Further, the grid-side converter parameters of the direct-drive wind turbine in step 4.2 include current inner-loop PI controller parameters k _{P_c} and k _{I_c} , DC voltage outer-loop PI controller parameters k _{P_udc} and k _{I_udc} , and reactive power Outer loop PI controller parameters k _{P_Q} and k _{I_Q} .

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

Step 4.2.1: Conduct deep voltage drop test on direct-drive wind turbines operating at high wind speeds, obtain active power test data P _M and reactive power test data Q _M , and set and Low voltage ride through test with the same input wind speed, voltage drop depth and voltage drop time; use optimization algorithm to identify the bandwidth f _c of the current inner loop PI controller;

In step 4.2.1, in the process of using the optimization algorithm to identify the bandwidth f _c of the current inner loop PI controller, the identification objective function is:

In the formula, P _S and Q _S respectively represent the active power and reactive power output by the general electromagnetic transient simulation model, N _s and Ne represent the numbers of the first and last simulation and test data of parameter identification, and _i represents Number of simulation and test data.

Substituting the bandwidth f _c of the current inner-loop PI controller obtained through identification into formula (10) to calculate the parameters k _{P_c} and k _{I_c} of the current inner-loop PI controller:

In the formula, L _f and R _f represent the inductance and resistance of the grid side filter respectively, which can be obtained from the fan manufacturer.

Step 4.2.2: Conduct a mild voltage drop test on the direct-drive wind turbine operating at low wind speed, obtain the active power test data P _M , and set the same input as the low-voltage ride-through test in the general electromagnetic transient simulation model of the direct-drive wind turbine Wind speed, voltage drop depth and voltage drop time; use optimization algorithm to identify bandwidth f _udc of DC voltage outer loop PI controller;

In step 4.2.2, in the process of using the optimization algorithm to identify the bandwidth f _udc of the DC voltage outer loop PI controller, the objective function for identification is:

Substituting the bandwidth f _udc of the DC voltage outer loop PI controller obtained through identification into formula (12) to calculate the parameters k _{P_udc} and k _{I_udc} of the DC voltage outer loop PI controller;

In the formula, C represents the DC capacitance of the direct drive wind turbine, which can be obtained from the wind turbine manufacturer.

Step 4.2.3: According to the direct-drive wind turbine low-voltage ride-through test in steps 4.2.1 and 4.2.2, obtain the reactive power test data Q _M , and set the same Input wind speed, voltage drop depth and voltage drop time; use optimization algorithm to identify reactive power outer loop parameters k _{P_Q} and k _{I_Q} ;

In the process of identifying reactive power outer loop parameters _{kP_Q} and _{kI_Q} using the optimization algorithm described in step 4.2.3, the objective function of identification is:

The beneficial effects of the present invention are:

The present invention tests the low voltage ride-through ability of multiple actual direct-drive wind turbines, and proposes a general electromagnetic transient response curve for the whole process of fault ride-through of direct-drive wind turbines according to the test results; The dynamic behavior of the whole process of fault ride-through is described, and the dynamic behavior of active power and reactive power in the whole process of fault ride-through is formulated. The current reference value is input to the current controller of the grid-side converter, and the reference value of the current controller of the grid-side converter is automatically updated according to the working status of the direct-drive wind turbine, so as to realize the monitoring of the whole process of fault ride-through of the actual direct-drive wind turbine simulation. 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 grid-side converter parameters. In the present invention, by selecting a certain actual direct-drive wind turbine, under the same parameters and the same voltage drop, the general electromagnetic transient simulation model of the direct-drive wind turbine and the voltage, current, active power and reactive power of the actual direct-drive wind turbine The power response characteristics are compared, and the results show that the general electromagnetic transient simulation model of the direct-drive wind turbine has high accuracy, and can simulate the transient response of the actual direct-drive wind turbine during the fault ride-through process.

Description of drawings

Figure 1 is a schematic diagram of the wiring principle of the actual test system;

Figure 2 is a graph of the transient response characteristics of 5 groups of actual direct-drive wind turbines under the condition of voltage drop;

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

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

Fig. 5 is the general electromagnetic transient simulation model of the direct-drive wind turbine established by the present invention;

Fig. 6 is for the 1st group of test data, the comparative figure of simulation result and measured data;

Fig. 7 is for the 2nd group of test data, the comparative figure of simulation result and measured data;

Figure 8 is a schematic diagram of the time stages defined in the Chinese standard "Guidelines for Modeling Electrical Simulation Models of Wind Turbines".

detailed description

Specific implementation mode one:

A general electromagnetic transient modeling method for a direct drive wind turbine described in this embodiment includes the following steps:

Step 1: According to the Chinese grid-connected standard "Technical Regulations for Connecting Wind Farms to Power Systems", conduct low-voltage ride-through capability tests on multiple direct-drive wind turbines. The principle structure diagram of the test system is shown in Figure 1, and multiple groups of actual direct-drive The transient response curves of voltage, current, active power and reactive power of wind turbines. In order to demonstrate the fault ride-through response characteristics of the actual direct-drive wind turbine, this embodiment gives 5 sets of test results, as shown in Figure 2, where Figure 2(a), Figure 2(b), Figure 2(c), Figure 2 (d) correspond to voltage, current, active power and reactive power respectively.

According to the instantaneous active power and instantaneous reactive power responses of the direct-drive wind turbine shown in Figure 2, it can be seen that the active power of the direct-drive wind turbine decreases and the reactive power increases after the voltage drops. After the fault is cleared, the voltage starts to rise, the active power increases, and the reactive power decreases. When the voltage returns to the normal range (that is, the voltage is greater than the low voltage ride-through threshold, which is 0.9 pu in the Chinese grid-connected standard), the active power of the direct-drive wind turbine operating at low wind speed quickly recovers to the steady-state value P ₀ before the fault, There is no need for a recovery process (tests 2 and 3 in Figure 2); while the active power of the direct-drive wind turbine operating at high wind speeds returns to the steady-state value P before the fault with a slope r _p after a short delay t _{dealy_P 0} . Among them, t _{dealy_P} and r _p are parameters that can be adjusted dynamically. For example, when t _{dealy_P} = 0, the active power recovers to the steady-state value before the fault with the slope r _p without delay (test 5 in Figure 2); when r _p is set to a large value, the active power quickly recovers to P ₀ (test 5 in Figure 2). Therefore, by adjusting t _{dealy_P} and r _p , the established model can simulate the active power recovery characteristics of direct-drive wind turbines designed by different manufacturers.

After the fault is cleared, the direct-drive wind turbine continues to provide reactive power Q _supp to the grid. After a short delay t _{dealy_Q} , the reactive power returns to the steady state value Q ₀ before the fault with a slope r _Q. Among them, t _{dealy_Q} , Q _supp and r _Q are parameters that can be adjusted dynamically. For example, when t _{dealy_Q} = 0, the reactive power _recovers to the steady-state value before the fault with the slope r _Q without delay _; Provide reactive power; when r _Q is set to a large value, the reactive power quickly recovers to Q ₀ . Therefore, by adjusting t _{dealy_Q} , Q _supp and r _Q , the established model can simulate the reactive power recovery characteristics of direct-drive wind turbines designed by different manufacturers.

Based on the above analysis, the present invention proposes a general electromagnetic transient response curve of the direct-drive wind turbine through the whole fault ride-through process to characterize possible fault behaviors of direct-drive wind turbines from different manufacturers, as shown in FIG. 3 . In Fig. 3, the periods [～, t ₁ ] and [t ₇ ,～] represent the steady-state stage before the failure of the direct-drive wind turbine and the steady-state stage after the recovery stage, which is called stage 1 in the present invention; [ _The period t ₁ , t ₃ ] represents the fault continuation stage from the fault occurrence to the fault clearing period, which is called stage 2 in the present invention _; The value recovery stage is called stage 3 in the present invention. In order to characterize the recovery characteristics of direct-drive wind turbines from different manufacturers, two sub-stages are used to describe the recovery behavior of active power and reactive power in the recovery phase. The control principle and main parameters of the direct drive wind turbine in the whole process of fault ride through are shown in Table 1.

Table 1 The control principle and main parameters of the direct drive wind turbine in the whole process of fault ride through

It is worth noting that the stages in Table 1 are not necessarily included in the general electromagnetic transient simulation model of direct-drive wind turbines. When simulating the fault behavior of direct-drive wind turbines designed by different manufacturers, only the main parameters of each stage need to be adjusted. Therefore, the general electromagnetic transient response curve of the direct-drive wind turbine through the whole fault ride-through process shown in Fig. 3 can flexibly characterize the fault behavior of different direct-drive wind turbines.

Step 2: Analyze the dynamic behavior of active power and reactive power in the whole process of fault ride-through according to the general electromagnetic transient response curve of the direct drive wind turbine in the whole process of fault ride-through as shown in Figure 3;

1) Phase 1: The steady state phase before the fault occurs and the steady state phase after the recovery phase is completed

According to the control principle in Table 1, the dynamic behavior of active power and reactive power in stage 1 can be expressed by formula (1):

In the formula, P _normal represents the active power in the normal working state, and the corresponding time range is [～,t ₁ ] and [t ₇ ,～], Q _normal represents the reactive power in the normal working state, and the corresponding time range is [～,t ₁ ] and [t ₆ ,～], t represents the current simulation running time; u _g represents the port voltage of the direct drive wind turbine; i _{P_normal} represents the active component of the current under normal working conditions, and i _{Q_normal} is the current under normal working conditions reactive component.

2) Phase 2: fault continuation process

According to the control principle in Table 1, the output power of the direct-drive wind turbine is adjusted according to the requirements of the grid-connected standard during the fault duration. In order to support the grid voltage, direct-drive wind turbines usually give priority to providing reactive power. Therefore, the dynamic behavior of active power and reactive power in stage 2 can be expressed by Equation (2):

In the formula, P _fault represents the active power during the fault duration, and the corresponding time range is [t ₁ , t ₃ ], Q _fault represents the reactive power during the fault duration, and the corresponding time range is [t ₁ , t ₃ ]; i _{P_fault} represents the current active component during the fault duration, i _{Q_fault} represents the current reactive component during the fault duration; I _max represents the maximum current, i _{lim_Q} represents the limit value of the current reactive component during the fault period, k is the reactive power support coefficient, According to the grid-connected standard k≥1.5, _uset represents the set voltage threshold, which is a constant. According to the grid-connected standard, _uset is 0.9pu, I _n represents the rated current, and i _Q0 represents the reactive component of the steady-state current before the fault.

3) Phase 3: Recovery process

The recovery process of active power: according to the control principle in Table 1, the direct drive wind turbine in stage 3-1 maintains the active power at the end of stage 2 within t _{dealy_P} time. Then, in stage 3-2, the active power of the direct-drive wind turbine returns to the steady-state value P ₀ before the fault with the slope r _P . Therefore, the dynamic behavior of active power in stage 3 can be expressed by Equation (3):

In the formula, P _re represents the active power in the fault recovery process, and the corresponding time ranges are [t ₃ , t ₇ ]; P(t ₃ ) represents the active power at time t ₃ , and P(t _{4 )} represents the , r _P represents the recovery rate of active power after the fault is cleared, and P ₀ represents the steady-state active power before the fault.

The recovery process of reactive power: according to the control principle in Table 1, the direct-drive wind turbine continues to provide reactive power for a period of time t _{dealy_Q} in stage 3-1. Different manufacturers may adopt different control strategies to meet this requirement. In order to ensure versatility, the present invention provides two reactive support strategies:

Strategy 1: Direct drive wind turbines continue to operate in reactive power support mode, and provide dynamic reactive power support according to grid voltage conditions;

Strategy 2: The reactive power output by the direct-drive wind turbine is maintained at the reactive power at the end of stage 2, providing fixed reactive support;

In phase 3-2, the reactive power control of the direct drive wind turbine is switched back to the normal operation mode. If the reactive power Q(t ₅ ) recovers to the steady-state value Q ₀ before the fault at this time, the recovery process ends; otherwise, in order to avoid the voltage impact caused by switching the reactive power control strategy, the reactive power Work power has a slope recovery characteristic. Therefore, the dynamic behavior of reactive power in stage 3 can be expressed by Equation (4):

In the formula, Q _re represents the reactive power in the fault recovery process, and the corresponding time ranges are [t ₃ , t ₆ ]; Q(t ₃ ) represents the reactive power at time t ₃ , and Q(t ₅ ) represents t The reactive power _at time ₅ , _rQ represents the recovery rate of reactive power after the fault is cleared, and Q0 represents the steady-state reactive power before the fault.

Step 3: According to the dynamic behavior formula of active power and reactive power in the whole process of fault ride-through obtained in step 2, analyze the reference value of the current active component and the reference value of the current reactive component, and input the obtained reference value into the direct drive wind power plant In the current controller of the grid-side converter of the general electromagnetic transient simulation model of the unit, the tracking function of the current controller of the grid-side converter is used to automatically adjust the dynamic behavior of the general electromagnetic transient simulation model of the direct drive wind turbine. Details as follow:

According to the operating principle of the direct-drive wind turbine, it is known that the adjustment of the response characteristics of active power and 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. . Therefore, the key to modeling the whole process of fault ride-through of the direct-drive wind turbine is to analyze the current in the current controller of the grid-side converter of the direct-drive wind turbine according to the dynamic behavior formula of active power and reactive power in the whole process of fault ride-through. The reference value of the active component and the reference value of the reactive component of the current. When the direct-drive wind turbine adopts grid voltage-oriented vector control and the grid voltage is oriented on the d-axis of the dq synchronous rotating reference frame, the reference value of the active component of the current corresponds to the reference value _idref of the d-axis component of the current controller, and the reactive component of the current The reference value of corresponds to the reference value i _qref of the q-axis component of the current controller.

Therefore, in this step, the present invention proposes a calculation method for the reference value _idref of the active component of the current and the reference value _idref of the reactive component of the current during the fault ride-through process of the direct drive wind turbine. The reference value _idref of the current active component is expressed as:

In the formula, _{idref_normal} represents the reference value of the current active component in the normal working state, _{idref_fault} represents the reference value of the current active component during the fault duration, and _{idref_re} represents the reference value of the current active component in the fault recovery process; k _{P_udc} and k _{I_udc} are respectively Represents the proportional and integral coefficients of the DC voltage outer loop PI controller, u _dcref represents the reference value of the DC voltage, u _dc represents the DC voltage, i _{qref_fault} represents the reference value of the reactive component of the current during the fault duration, and r _id represents the current after the fault is cleared The recovery rate of the active component.

The reference value i _qref of the reactive component of the current is expressed as:

In the formula, i _{qref_normal} represents the reference value of current reactive component in normal working state, i _{qref_re} represents the reference value of current reactive component in the fault recovery process, i _qref0 represents the steady-state reactive current component before fault; k _{P_Q} and k _{I_Q} represent the proportional and integral coefficients of the reactive power PI controller respectively, Q _ref represents the reference value of reactive power, Q represents the reactive power, _riq represents the recovery rate of the reactive component of the current after the fault is cleared.

According to the formulas (5) and (6), the current controller d and q axis current reference values of the grid side converter of the general electromagnetic transient simulation model of the direct drive wind turbine are assigned, and at the same time the general electromagnetic transient simulation model of the direct drive wind turbine is The grid-side current active component i _d and current reactive component i _q are input to the actual values of d and q-axis currents of the current controller, and the grid-side converter voltage reference values e _dref and e _qref are generated by the current PI controller:

In the formula, ω is the angular frequency of the grid voltage, R _f and L _f are the resistance and inductance of the grid-side filter, respectively, and k _{P_c} and k _{I_c} represent the proportional and integral coefficients of the current inner loop PI controller, respectively.

transform e _dref and e _qref from dq synchronous rotating reference frame to e _abcref in abc three-phase static frame, and use pulse width modulation technique to generate trigger signal of IGBT of direct drive wind turbine switching device. The control block diagram of the grid-side converter of the direct-drive wind turbine in the whole process of fault ride-through is shown in Figure 4. The grid-side converter will automatically update the current controller of the grid-side converter according to the current working status of the direct-drive wind turbine. In order to adjust the dynamic behavior of the general electromagnetic transient simulation model of the direct-drive wind turbine, and realize the simulation of the transient response of the actual direct-drive wind turbine through the fault ride-through process.

Step 4: In order to ensure the accuracy of the established general electromagnetic transient model of the direct-drive wind turbine, this step identifies the fault ride-through control parameters and grid-side converter parameters of the direct-drive wind turbine, including:

Fault ride-through control parameters: reactive power support coefficient k, recovery rate r _id of current active component, recovery rate r _iq of current reactive component, active power recovery delay t _{dealy_P} after fault clearing, and reactive power support after fault clearing Delay t _{dealy_Q} ;

Grid-side converter parameters: current inner loop PI controller parameters k _{P_c} and k _{I_c} , DC voltage outer loop PI controller parameters k _{P_udc} and k _{I_udc} , and reactive power outer loop PI controller parameters k _{P_Q} and k _{I_Q} .

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

In step 4.1, the fault ride-through control parameters of the direct-drive wind turbine are calculated 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. The specific process is as follows:

Decompose the three-phase instantaneous voltage and three-phase instantaneous current of the low-voltage ride-through test of the actual direct-drive wind turbine into the dq synchronous rotating reference frame. The d and q-axis components of the three-phase instantaneous voltage are u _dM and u _qM respectively, and the three-phase The d and q axis components of the instantaneous current are respectively i _dM and i _qM .

1) Reactive power support coefficient k

Since the current reactive component injected into the grid by the direct drive wind turbine during the voltage drop is proportional to the voltage deviation, and is limited to the maximum current reactive component. When the voltage drops slightly, the current reactive component is smaller than the maximum current reactive component, so k can be calculated according to the test data of the slight voltage drop:

k＝(i _qM0 -i _qM )/[I _n (u _set -u _g )] (8)

In the formula, i _qM0 represents the test value of the reactive component of the current under normal working conditions, and u _gM represents the measured value of the voltage during the fault duration.

2) The recovery rate r _id of the current active component after the fault is cleared and the recovery delay of active power after the fault is cleared t _{dealy_P}

In the case of deep voltage sag, when the voltage returns to the normal operating range, the current active component of the direct-drive wind turbine operating at high wind speed recovers with the slope r _id after the time delay t _{dealy_P} . Therefore, r _id and t _{dealy_P} can be calculated according to the test data of the direct-drive wind turbine operating at high wind speed under deep voltage drop:

In the formula, i _dM (t ₇ ) represents the test value of current active component at time t ₇ , and i _dM (t ₄ ) represents the test value of current active component at time t ₄ .

3) The recovery rate r _iq of the current reactive component after the fault is cleared and the reactive power recovery delay t _{dealy_Q} after the fault is cleared

r _iq and t _{dealy_Q} can be calculated according to the test data after the fault is cleared. When the direct drive wind turbine continues to provide reactive power after the fault is cleared, t _{dealy_Q} is calculated as:

t _{delay_Q} =t ₅ -t ₃ (10)

When the reactive power of the direct-drive wind turbine has a slope recovery characteristic after the fault is cleared, and the reactive power at time t5 has not recovered to the steady _- state reactive power before the fault, r _iq is calculated as:

r _iq =[i _qM (t ₆ )-i _qM (t ₅ )]/(t ₆ -t ₅ ) (11)

In the formula, i _qM (t ₆ ) represents the test value of current reactive component at time t ₆ , and i _qM (t ₅ ) represents the test value of current reactive component at time t ₅ ;

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, the specific process of using the optimization algorithm to identify and obtain the PI controller parameters of the grid-side converter is as follows:

Firstly, determine the parameters to be identified. The parameters of the grid-side converter PI controller include three groups:

Current inner loop PI controller parameters: k _{P_c} and k _{I_c} ;

DC voltage outer loop PI controller parameters: k _{P_udc} and k _{I_udc} ;

Reactive power outer loop PI controller parameters: k _{P_Q} and k _{I_Q} ;

Among them, the current inner loop PI controller parameters k _{P_c} and k _{I_c} can be expressed as:

In the formula, f _c is the bandwidth of the current inner loop, and R _f and L _f are circuit parameters, which can be obtained from the fan manufacturer. Therefore, k _{P_c} and k _{I_c} can be determined by identifying f _c .

The parameters k _{P_udc} and k _{I_udc} of the DC voltage outer loop PI controller can be expressed as:

In the formula, f _udc is the bandwidth of the DC voltage outer loop, u _n is the rated voltage of the power grid, which is a known quantity, and C is a circuit parameter, which can be obtained from the fan manufacturer. Therefore, k _{P_udc} and k _{I_udc can be determined by identifying f udc .}

To sum up, the grid-side converter PI controller has four parameters to be identified: the bandwidth f _c of the current inner loop PI controller, the bandwidth f _udc of the DC voltage outer loop PI controller, and the reactive power outer loop PI control Parameters k _{P_Q} and k _{I_Q} .

Due to the cascade relationship between the inner and outer loop PI controllers, they cannot be identified simultaneously under the same disturbance. Therefore, the present invention uses different perturbations to identify these parameters. For direct-drive wind turbines operating at high wind speeds, when a deep voltage drop occurs, the reference value of the current active component and the reference value of the current reactive component can be expressed as:

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

According to the formula (15), it can be seen that the d and q axis voltage reference values of the grid-side converter only depend on the bandwidth f _c of the current inner loop PI controller, and have nothing to do with the outer loop parameters ( _fudc , k _{P_Q} and k _{I_Q} ) . Therefore, in order to identify f _c more effectively, the test data of the direct-drive wind turbine operating at high wind speed under deep voltage drop can be used.

For direct-drive wind turbines operating at low wind speeds, when a slight voltage drop occurs, the reference value of the active component of the current and the reference value of the reactive component of the current can be expressed as:

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

in,

According to formulas (17) and (18), it can be seen that the d and q axis voltage reference values of the grid-side converter depend on the bandwidth f _c of the current inner loop PI controller and the bandwidth f _udc of the DC voltage outer loop PI controller, while It has nothing to do with the reactive power outer loop PI controller parameters k _{P_Q} and k _{I_Q} . After determining f _c , only f _udc needs to be identified. Therefore, in order to identify f _udc more effectively, the test data of direct-drive wind turbines operating at low wind speeds under mild voltage drops can be used.

After determining f _c and f _udc , the above test data can be used to identify k _{P_Q} and k _{I_Q} .

To sum up, first identify the bandwidth f _c of the current inner loop PI controller, secondly identify the bandwidth f _udc of the DC voltage outer loop PI controller, and finally identify the parameters k _{P_Q} and k _{I_Q} of the reactive power outer loop PI controller, using This sequence can realize the decoupling identification of inner and outer loop cascaded controllers. In this embodiment, a 1.5MW direct-drive wind turbine is taken as an example to identify the PI controller parameters of its grid-side converter. The specific process is as follows:

Step 4.2.1: First, establish a general electromagnetic transient simulation model of the 1.5MW direct-drive wind turbine, as shown in Figure 5, and set the same parameters for the simulation model as the actual 1.5MW direct-drive wind turbine in Table 2. The deep voltage drop test is carried out on the direct-drive wind turbine operating at high wind speed, and the active power test data P _M and reactive power test data Q _M are obtained. In the general electromagnetic transient simulation model of the direct drive wind turbine, set the same input wind speed, voltage drop depth and voltage drop time as the actual direct drive wind turbine low voltage ride through test. In this embodiment, the genetic algorithm is used as an example to identify the bandwidth f _c of the PI controller of the current inner loop. The population number of the genetic algorithm is 100, the crossover probability is 0.8, and the mutation probability is 0.05. The identified objective function is:

In the formula, P _S and Q _S represent the active power and reactive power output by the simulation model respectively, N _s and Ne represent the numbers of the first and last simulation and test data of parameter identification respectively, and _i represents the simulation and test data number.

During the identification process, the objective function L ₁ is minimized to obtain the bandwidth fc of the current inner-loop PI controller, and the fc obtained from the identification is substituted into formula (12) to calculate the parameters k _{P_c} and k _{I_c of} the current inner-loop PI controller _.

Table 2 Main parameters of 1.5MW direct drive wind turbine

Step 4.2.2: Perform a mild voltage drop test on the direct-drive wind turbine operating at a low wind speed to obtain active power test data P _M . In the general electromagnetic transient simulation model of the direct drive wind turbine, set the same input wind speed, voltage drop depth and voltage drop time as the actual direct drive wind turbine low voltage ride through test. The genetic algorithm is used to identify the bandwidth f _udc of the DC voltage outer loop PI controller, and the objective function of the identification is:

During the identification process, the objective function L ₂ is minimized to obtain the bandwidth f _udc of the DC voltage outer loop PI controller, and the f _udc obtained from the identification is substituted into formula (13) to calculate the parameters k _{P_udc} and k _{I_udc} of the DC voltage outer loop PI controller .

Step 4.2.3: Obtain the reactive power test data Q _M according to the direct drive wind turbine low voltage ride through test in steps 4.2.1 and 4.2.2. In the general electromagnetic transient simulation model of the direct drive wind turbine, set the same input wind speed, voltage drop depth and voltage drop time as the actual direct drive wind turbine low voltage ride through test. The genetic algorithm is used to identify the reactive power outer loop PI controller parameters k _{P_Q} and k _{I_Q} , and the objective function of the identification is:

In the identification process, the objective function L ₃ is minimized, and the parameters k _{P_Q} and k _{I_Q} of the outer loop PI controller of reactive power are obtained.

After step 4.2.1, step 4.2.2 and step 4.2.3, the identification results of the PI controller parameters of the grid-side converter of the direct drive wind turbine are obtained, as shown in Table 3.

Table 3 Identification values of PI controller parameters for grid-side converter of 1.5MW direct-drive wind turbine

Finally, verify the accuracy of the general electromagnetic transient simulation model for direct-drive wind turbines:

Taking the test data of two sets of actual direct-drive wind turbines as an example to verify the established general electromagnetic transient simulation model and parameter identification results of direct-drive wind turbines, the process is as follows: First, the settings are the same as those for the actual direct-drive wind turbine low-voltage ride-through test According to the input wind speed, voltage drop depth and voltage drop time, the response curves of voltage, current, active power and reactive power of the general electromagnetic transient simulation model of the direct-drive wind turbine are obtained, and the actual test results are compared with the general-purpose direct-drive wind turbine. The voltage, current, instantaneous value of active power and instantaneous value of reactive power of the electromagnetic transient simulation model are shown in Fig. 6 (Calculation Example 1) and Fig. 7 (Calculation Example 2), where Fig. 6(b), Figure 6(c), and Figure 6(d) respectively correspond to voltage, current, active power, and reactive power. Figure 7(a), Figure 7(b), Figure 7(c), and Figure 7( d) Corresponding to voltage, current, active power and reactive power respectively. It can be seen from Figure 6 and Figure 7 that the established general electromagnetic transient simulation model of the direct-drive wind turbine is consistent with the transient response of the actual direct-drive wind turbine.

Further, the error between the output of the simulation model and the test data under voltage drop is calculated according to the Chinese standard "Guidelines for Modeling Electrical Simulation Models of Wind Turbines". The calculated electrical quantities include active power, reactive power, and current reactive components. The time range for error calculation includes 5 intervals: A, B ₁ , B ₂ , C ₁ and C ₂ . Taking active power as an example, the division of the five intervals is shown in Figure 8, where the division points t _B1 and t _C1 of intervals B and C are taken after the fluctuation of power or current enters the range of ±10% of the average value of this period. 20ms.

The error calculation formula is:

In the formula, X represents the active power P, reactive power Q and current reactive component i _q , N _Start and N _End represent the numbers of the first and last simulation and test data in the calculation interval respectively, and i represents the simulation and test data number.

According to the Chinese standard "Guidelines for Modeling Electrical Simulation Models of Wind Turbines", if the error of each parameter (P, Q and _iq ) at the corresponding stage is lower than the maximum allowable error shown in Table 4, then the model is valid.

Table 4 Maximum allowable value of error (%)

parameter 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

According to formula (21), the errors of P, Q and _iq at the corresponding stages of Calculation Example 1 corresponding to Fig. 6 and Calculation Example 2 corresponding to Fig. 7 are calculated, and the results are shown in Table 5. It can be seen from Table 5 that the errors of P, Q and _iq at each stage are smaller than the maximum allowable errors shown in Table 4. Therefore, the general electromagnetic transient simulation model of the direct-drive wind turbine obtained by the method of the present invention can accurately characterize the dynamic behavior of different actual direct-drive wind turbines during the fault ride-through process.

Table 5 Error Calculation Results of Examples 1 and 2 (%)

The present invention can also have other various embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations are all Should belong to the scope of protection of the appended claims of the present invention.

Claims (9)

1. A general electromagnetic transient modeling method for direct drive wind turbines, characterized in that it comprises the following steps: Step 1: Conduct low-voltage ride-through tests on multiple direct-drive wind turbines to obtain the voltage, current, active power and reactive power responses of multiple direct-drive wind turbines under different voltage dips. According to the voltage, current, active power and Response of reactive power, get the general electromagnetic transient response curve of the direct drive wind turbine through the whole process of fault; Step 2: According to the general electromagnetic transient response curve of the direct drive wind turbine in the whole process of fault ride-through obtained in step 1, analyze the dynamic behavior of active power and reactive power in the fault ride-through process, and analyze the active power and reactive power in the fault ride-through process Describe the dynamic behavior through the whole process; The description of the dynamic behavior of the active power in the whole process of fault ride-through is as follows:

In the formula, P _normal represents the active power in the normal working state, and the corresponding time range is [～,t ₁ ] and [t ₇ ,～], P _fault represents the active power during the fault duration, and the corresponding time range is [ t ₁ ,t ₃ ], P _re represents the active power in the fault recovery process, and the corresponding time ranges are [t ₃ ,t ₇ ], t represents the current simulation running time; u _g represents the port voltage of the direct drive wind turbine, i _{P_normal} represents the current active component in normal working state, i _{P_fault} represents the current active component during the fault duration, I _max represents the maximum current, i _{Q_fault} represents the current reactive component during the fault duration; P(t ₃ ) represents the active power at time t ₃ , P(t ₄ ) represents the active power at time t ₄ , r _P represents the recovery rate of active power after the fault is cleared, and P ₀ represents the steady-state active power before the fault; The dynamic behavior of reactive power in the whole process of fault ride-through is described as follows:

In the formula, Q _normal represents the reactive power in normal working state, and the corresponding time range is [～,t ₁ ] and [t ₆ ,～], Q _fault represents the reactive power during the fault duration, and the corresponding time range is [t ₁ , t ₃ ], Q _re represents the reactive power in the fault recovery process, and the corresponding time ranges are [t ₃ , t ₆ ]; i _{Q_normal} is the current reactive component in the normal working state, and i _{Q_fault} is The current reactive component during the fault duration, i _{lim_Q} represents the limit value of the current reactive component during the fault period, k is the reactive power support coefficient, according to the grid-connected standard k≥1.5, u _set represents the set voltage threshold, which is a constant, according to The grid-connected standard u _set is 0.9pu, I _n represents the rated current, i _Q0 represents the reactive component of the steady state current before the fault; Q(t ₃ ) represents the reactive power at time t ₃ , and Q(t ₅ ) represents the reactive power at t ₅ The reactive power _at time, r _Q represents the recovery rate of reactive power after the fault is cleared, and Q0 represents the steady-state reactive power before the fault; Step 3: According to the dynamic behavior formula of active power and reactive power in the whole process of fault ride-through obtained in step 2, analyze the reference value of the current active component and the reference value of the current reactive component, and input the obtained reference value into the direct drive wind power plant In the current controller of the grid side converter of the general electromagnetic transient simulation model of the unit, the dynamic behavior of the general electromagnetic transient simulation model of the direct drive wind turbine is automatically adjusted by using the tracking function of the current controller of the grid side converter; Step 4: Use step-by-step identification to identify the fault ride-through control parameters and grid-side converter parameters of the direct-drive wind turbine. 2. A general electromagnetic transient modeling method for direct-drive wind turbines according to claim 1, wherein the fault ride-through process described in step 1 includes a steady state stage before the fault occurs, a fault continuation stage, The recovery phase from the fault clearing to the recovery of both active power and reactive power to the steady-state value and the steady-state phase after the completion of the recovery phase; obtain the general electromagnetic transient response curve of the direct-drive wind turbine in the whole process of fault ride-through, including voltage, instantaneous active power Response curves for power and instantaneous reactive power. 3. The general electromagnetic transient modeling method of a direct drive wind turbine according to claim 2, characterized in that the dynamics of active power and reactive power obtained according to step 2 in the fault ride-through process described in step 3 The behavioral formula analyzes the reference value of the current active component and the reference value of the current reactive component, and inputs the obtained reference value into the current controller of the grid-side converter of the general electromagnetic transient simulation model of the direct drive wind turbine, and uses the network The specific process of automatically adjusting the dynamic behavior of the general electromagnetic transient simulation model of the direct drive wind turbine through the tracking function of the current controller of the side converter includes the following steps: When the direct-drive wind turbine adopts grid voltage-oriented vector control and the grid voltage is oriented on the d-axis of the dq synchronous rotating reference frame, the reference value of the active component of the current corresponds to the reference value _idref of the d-axis component of the current controller, and the reactive component of the current The reference value of corresponds to the reference value i _qref of the q-axis component of the current controller; the reference value i _dref of the current active component is expressed as:

In the formula, _{idref_normal} represents the reference value of the current active component in the normal working state, _{idref_fault} represents the reference value of the current active component during the fault duration, and _{idref_re} represents the reference value of the current active component in the fault recovery process; k _{P_udc} and k _{I_udc} are respectively Represents the proportional and integral coefficients of the DC voltage outer loop PI controller, u _dcref represents the reference value of the DC voltage, u _dc represents the DC voltage, i _{qref_fault} represents the reference value of the reactive component of the current during the fault duration, and r _id represents the current after the fault is cleared Recovery rate of active components; The reference value i _qref of the reactive component of the current is expressed as:

In the formula, i _{qref_normal} represents the reference value of current reactive component in normal working state, i _{qref_re} represents the reference value of current reactive component in the fault recovery process; k _{P_Q} and k _{I_Q} represent the ratio of reactive power outer loop PI controller and integral coefficient, Q _ref represents the reference value of reactive power, Q represents reactive power, r _iq represents the recovery rate of current reactive component after the fault is cleared; According to the formula (3) and formula (4), the d and q axis current reference values of the current controller in the grid-side converter of the general electromagnetic transient simulation model of the direct-drive wind turbine are assigned, and the direct-drive wind power is automatically adjusted by using the current controller Dynamic Behavior of a Generic Electromagnetic Transient Simulation Model for Units. 4. A general-purpose electromagnetic transient modeling method for direct-drive wind turbines according to claim 3, characterized in that step-by-step identification is used to identify the fault ride-through control parameters and grid-side transformers of direct-drive wind turbines described in step 4. The specific process of identifying flowmeter parameters includes the following steps: Step 4.1: According to the analysis and calculation of the voltage, current, active power and reactive power data of the direct-drive wind turbine low-voltage ride-through test, the fault ride-through control parameters of the direct-drive wind turbine are calculated; 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, an optimization algorithm is used to identify and obtain the parameters of the grid-side converter. 5. A general electromagnetic transient modeling method for direct-drive wind turbines according to claim 4, characterized in that the fault ride-through control parameters of the direct-drive wind turbines described in step 4.1 include reactive power support coefficient k, fault clearing The recovery rate r _id of the active component of the current after the fault is cleared, the recovery rate r _iq of the reactive component of the current after the fault is cleared, the delay time of active power recovery after the fault is cleared t _{dealy_P} and the delay time of reactive power support after the fault is cleared t _{dealy_Q} . 6. A general electromagnetic transient modeling method for direct-drive wind turbines according to claim 5, characterized in that the voltage, current, active power and passive The specific process of calculating the fault ride-through control parameters of the direct drive wind turbine by analyzing power data includes the following steps: Decompose the three-phase instantaneous voltage and three-phase instantaneous current of the low-voltage ride-through test of the actual direct-drive wind turbine into the dq synchronous rotating reference frame. The d and q-axis components of the three-phase instantaneous voltage are u _dM and u _qM respectively, and the three-phase The d and q axis components of the instantaneous current are i _dM and i _qM respectively; The reactive power support coefficient k is calculated according to the test data of mild voltage drop: k＝(i _qM0 -i _qM )/[I _n (u _set -u _g )] (5) In the formula, i _qM0 represents the test value of the reactive component of the current under normal working conditions, i _qM represents the test value of the reactive component of the current during the fault duration; u _gM represents the measured value of the voltage during the fault duration; The recovery rate r _id of the active component of the current after the fault is cleared and the delay t _{dealy_P} of the active power recovery after the fault is cleared are calculated according to the test data of the direct-drive wind turbine operating at high wind speed under the condition of deep voltage sag:

In the formula, i _dM (t ₇ ) represents the test value of current active component at time t ₇ , and i _dM (t ₄ ) represents the test value of current active component at time t ₄ ; The recovery rate r _iq of the current reactive component after the fault is cleared and the reactive power recovery delay t _{dealy_Q} after the fault is cleared are calculated according to the test data of the direct drive wind turbine after the fault is cleared; when the fault is cleared, the direct drive wind turbine continues to provide reactive power When supported, t _{dealy_Q} is calculated as: t _{delay_Q} =t ₅ -t ₃ (7) When the reactive power of the direct-drive wind turbine has a slope recovery characteristic after the fault is cleared, and the reactive power at time t5 has not recovered to the steady _- state reactive power before the fault, r _iq is calculated as: r _iq =[i _qM (t ₆ )-i _qM (t ₅ )]/(t ₆ -t ₅ ) (8) In the formula, i _qM (t ₆ ) represents the test value of current reactive component at time t ₆ , and i _qM (t ₅ ) represents the test value of current reactive component at time t ₅ . 7. A general electromagnetic transient modeling method for direct-drive wind turbines according to claim 4, 5 or 6, characterized in that the grid-side converter parameters corresponding to the direct-drive wind turbines in step 4.2 include the current inner loop PI controller parameters k _{P_c} and k _{I_c} , DC voltage outer loop PI controller parameters k _{P_udc} and k _{I_udc} , and reactive power outer loop PI controller parameters k _{P_Q} and k _{I_Q} . 8. A general electromagnetic transient modeling method for direct-drive wind turbines according to claim 7, characterized in that, according to the voltage, current, active power and reactive power of the low-voltage ride-through test of the direct-drive wind turbines described in step 4.2 Power data, the specific process of using the optimization algorithm to identify and obtain the parameters of the grid-side converter includes the following steps: Step 4.2.1: Conduct deep voltage drop test on direct-drive wind turbines operating at high wind speeds, obtain active power test data P _M and reactive power test data Q _M , and set and Low voltage ride through test with the same input wind speed, voltage drop depth and voltage drop time; use optimization algorithm to identify the bandwidth f _c of the current inner loop PI controller; Substituting the bandwidth f _c of the current inner-loop PI controller obtained through identification into formula (10) to calculate the parameters k _{P_c} and k _{I_c} of the current inner-loop PI controller:

In the formula, L _f and R _f represent the inductance and resistance of the grid-side filter respectively, which are obtained from the fan manufacturer; Step 4.2.2: Conduct a mild voltage drop test on the direct-drive wind turbine operating at low wind speed, obtain the active power test data P _M , and set the same input as the low-voltage ride-through test in the general electromagnetic transient simulation model of the direct-drive wind turbine Wind speed, voltage drop depth and voltage drop time; use optimization algorithm to identify bandwidth f _udc of DC voltage outer loop PI controller; Substituting the bandwidth f _udc of the DC voltage outer loop PI controller obtained through identification into formula (12) to calculate the parameters k _{P_udc} and k _{I_udc} of the DC voltage outer loop PI controller;

In the formula, C represents the DC capacitance of the direct drive wind turbine, which is obtained from the wind turbine manufacturer; u _n is the rated voltage of the power grid; Step 4.2.3: According to the direct-drive wind turbine low-voltage ride-through test in steps 4.2.1 and 4.2.2, obtain the reactive power test data Q _M , and set the same Input wind speed, voltage drop depth and voltage drop time; use optimization algorithm to identify reactive power outer loop parameters k _{P_Q} and k _{I_Q} . 9. The general electromagnetic transient modeling method of a direct drive wind turbine according to claim 8, characterized in that, in step 4.2.1, in the process of using an optimization algorithm to identify the bandwidth _f of the current inner loop PI controller , the identification objective function is:

In the formula, P _S and Q _S respectively represent the active power and reactive power output by the general electromagnetic transient simulation model, N _s and Ne represent the numbers of the first and last simulation and test data for parameter identification, and _i represents Number of simulation and test data; In step 4.2.2, in the process of using the optimization algorithm to identify the bandwidth f _udc of the DC voltage outer loop PI controller, the objective function for identification is:

In the process of identifying reactive power outer loop parameters _{kP_Q} and _{kI_Q} using the optimization algorithm described in step 4.2.3, the objective function of identification is:

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