CN103034761A - Electromechanical transient simulation method for doubly-fed variable speed constant frequency wind generation set system - Google Patents

Abstract

An electromechanical transient simulation method for a doubly-fed variable-speed constant-frequency wind turbine system, relating to a wind power generation system, in particular to a method for modeling and analyzing a doubly-fed wind turbine system using a computer program, comprising the following steps: establishing a wind power model for simulation The wind power absorbed by the wind turbine; establish the shafting model of the fan; establish the pitch control system model; establish the electrical simulation model of the double-fed asynchronous induction motor; establish the controller model of the inverter on the grid side and the inverter on the rotor side; use the wind turbine simulation model, Establish a double-fed fan single-unit infinite system model; set the simulation operating conditions and fault states of the wind turbine system, and perform electromechanical transient simulation and fault simulation. Transient and electromechanical transient simulation can investigate the dynamic characteristics of wind turbines under various faults and working conditions, making it possible to simulate wind turbines in large-scale power grids.

Description

Electromechanical transient simulation method for doubly-fed variable-speed constant-frequency wind turbine system

technical field

The invention relates to a wind power generation system, in particular to a method for modeling and analyzing a doubly-fed wind power generating set system by using a computer program.

Background technique

Since the 1980s, the application of wind power generation has attracted more and more attention from all over the world. With the rapid development of science and technology, especially the application of aerodynamics, cutting-edge aerospace technology and high-power power electronics technology to the development and development of new wind turbines, wind power has made great progress in the past two decades. Today's wind power generation is gradually moving toward scale and industrialization, and the proportion of wind power generation in the power grid is increasing, becoming the most mature and realistic clean energy power generation method besides hydropower generation. Vigorously developing wind power generation is of great significance to environmental protection, energy conservation and ecological balance.

However, wind power generation is a special kind of electricity, which has many characteristics different from conventional energy generation. The grid-connected operation of wind power plants will have negative impacts on the safety and stability of the power grid, power quality and many other aspects. With the increase in the scale of wind farms Increasingly, the influence of wind power characteristics on the power grid is becoming more and more significant, and it has become a serious obstacle restricting the scale and capacity of wind farms. What kind of impact large-scale wind power integration will have on the power grid has become an urgent problem to be solved.

Chinese utility model patent "Double-fed wind turbine simulation device" (utility model patent number: ZL201220127917.4 authorized announcement number: CN202548295U) discloses a double-fed wind turbine simulation device, including: double-fed induction generator, wind turbine Prime mover, monitoring and protection equipment and rotor side converter equipment. The prime mover of the wind turbine is connected to the double-fed induction generator, and the prime mover of the wind turbine drives the rotor of the double-fed induction generator to rotate under the wind force. The monitoring protection equipment is connected to the doubly-fed induction generator, and measures the output voltage and current of the doubly-fed induction generator. The rotor-side converter equipment is connected to the double-fed induction generator, and the rotor-side converter equipment controls the voltage amplitude and phase of the double-fed induction generator, and performs active power decoupling control and reactive power decoupling control. The simulation device of the double-fed wind turbine of the utility model can accurately reflect the physical characteristics of the wind turbine and the working condition of the double-fed induction generator, and can meet the complete test requirements of the wind power grid-connected specification for the grid-connected wind turbine.

Chinese invention patent application "a simulation modeling method for double-fed wind turbine equivalent simulation" (patent application number: 201210008656.9 publication number: CN102592026A) discloses a simulation modeling method for double-fed wind turbine equivalent simulation, the double-fed The inverter part of the wind turbine is simulated by controlled source, and the modeling method includes the following steps: (1) Establishing a circuit model of a double-fed wind turbine; (2) Establishing an equivalent model of a double-fed wind turbine; (3) Establishing a double-fed wind turbine and (4) Build a multi-fan test system; wherein, in step 2: the equivalent model of the double-fed fan is established based on the characteristics of the AC-side controlled voltage source and the DC-side controlled current source of the double-fed fan inverter . The simulation modeling method for the equivalent simulation of double-fed wind turbines provided by the invention can accurately simulate the transient characteristics of double-fed wind turbines, and can take into account the different characteristics and mutual influence between multiple wind turbines; it does not need to take into account the full-control type The high-frequency on-off of the device greatly improves the simulation efficiency; the more the number of simulated fans is, the more significant the efficiency improvement is; while maintaining the accuracy, a larger simulation step size can be used to greatly improve the simulation efficiency.

The wind turbine model used for stability research is still not implemented in domestic power system simulation software. There are built-in wind turbine models in PSS/E and BPA, but they are not suitable for dynamic performance simulation of wind turbines under grid short-circuit faults. . DIgSILENT/PowerFactory is a powerful power system simulation software. Its built-in double-fed asynchronous fan model can more accurately reflect its actual physical characteristics. Transient simulation makes it possible to simulate wind turbines in large-scale power grids. In addition, PSCAD/EMTDC can also establish the electromechanical transient model of the fan, and the modeling accuracy can reach the device level, so it is an ideal tool for investigating the dynamic characteristics of the fan stand-alone system under various working conditions and faults, but it is not suitable for the connection of the fan Simulation after the big net.

Contents of the invention

The purpose of the present invention is to provide a method for simulating the electromechanical transient state of the doubly-fed variable-speed constant-frequency wind turbine system, to establish a detailed model conforming to the physical characteristics of the doubly-fed variable-speed constant-frequency wind turbine system, so as to use the detailed model for electromagnetic transient and electromechanical transient Simulation to investigate the dynamic characteristics of the fan under various faults and working conditions.

The technical solution adopted by the present invention to solve the problems of the technologies described above is:

An electromechanical transient simulation method for a double-fed variable-speed constant-frequency wind turbine system. The wind turbine includes a prime mover model composed of a wind turbine model, a shafting model, and a pitch control system. An induction generator model and a rotor-side frequency conversion A doubly-fed wind turbine model composed of an inverter control and protection system, and a grid-side inverter control system, the electromechanical transient simulation method includes the following steps:

S100) Establishing a wind turbine model, simulating the wind power absorbed by the wind turbine according to the relationship between wind speed, wind energy conversion efficiency, blade tip speed ratio and blade pitch angle;

S200) Using the two-mass shafting structure composed of the generator mass and the wind turbine mass, establishing a fan shafting model, simulating the energy transfer relationship between the wind turbine mechanical torque and the generator electromagnetic torque;

S300) Establish a pitch control system model, use the pitch angle control simulation to optimize the power of the wind turbine, seek the maximum output power of the wind turbine at a given wind speed; simulate the overload of the pitch control system when the wind speed exceeds the rated wind speed Protective function;

S400) Constructing a T-type equivalent circuit of a double-fed asynchronous induction motor according to the equation of the double-fed induction motor and the flux linkage equation, and establishing a DFIG electrical simulation model;

S500) According to the DFIG electrical simulation model, the instantaneous electromagnetic power equation of the stator of the doubly-fed induction generator, the relationship between the rotor current and the stator current, and the rotor voltage equation, establish the grid-side inverter and rotor-side inverter controller models;

S600) Using the wind turbine simulation model established in the above steps, establish a double-fed fan single-unit infinite system model;

S700) Set the initial operating conditions of the wind turbine simulation model, set the simulation step size at the millisecond level, and enter the electromechanical transient simulation running state of the wind turbine system;

S720) Apply negative wind speed step and positive wind speed step signals to the wind turbine model respectively, perform electromechanical transient simulation of wind speed step, and analyze the active output, rotational speed, wind power, wind energy utilization efficiency and pitch of the wind turbine Angle response, the dynamic response characteristics of the established DFIG detailed model in the face of wind speed changes, verify the effectiveness of maximum wind energy tracking;

S740) Apply a reactive power step signal to the double-fed fan single-unit infinite system model, perform electromechanical transient simulation of the reactive step, and analyze changes in the terminal voltage, active output, reactive output, and rotational speed of the wind turbine , the established detailed model of the double-fed wind turbine faces the dynamic response characteristics of the reactive load change of the external power grid, and verifies the dynamic characteristics of the reactive power control link in the vector control of the double-fed wind turbine;

S760) Simulate the three-phase symmetrical fault and asymmetrical fault of the external power grid on the single-machine infinite system model of the double-fed fan, and perform electromechanical transient simulation of the fault state for the double-fed asynchronous fan with and without low voltage ride-through function, and analyze the wind power The machine terminal voltage, active power, reactive power, stator current, and rotor current waveforms of the unit compare the dynamic response of doubly-fed asynchronous fans with and without low-voltage ride-through function under grid faults, and verify the dynamic characteristics of doubly-fed fan fault protection.

A better technical solution of the electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention is characterized in that the DFIG module uses a switchable Crowbar device to realize the low-voltage ride-through function. When an external fault causes the rotor When the side inverter detects the rotor overcurrent, or the inverter DC bus overvoltage, the switch element IGBT in the Crowbar device is turned on, and the Crowbar is put into operation to bypass the rotor overcurrent. At the same time, the trigger signal of the rotor side inverter is blocked. The winding is directly short-circuited through the series resistor Rc.

The beneficial effects of the present invention are:

1. The electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention can establish a detailed model conforming to the physical characteristics of the double-fed variable-speed constant-frequency wind turbine, and use the detailed model to perform electromagnetic transient and electromechanical transient simulations. Investigate the dynamic characteristics of the fan under various faults and working conditions.

2. The electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention can not only simulate the electrical characteristics of the double-fed variable-speed constant-frequency wind turbine, but also simulate the mechanical operating conditions of the wind prime mover, and perform wind power changes on the wind farm. Simulation research on the influence of wind turbines can not only carry out detailed electromechanical transient simulation on double-fed generators, but also conduct electromechanical transient simulations, making it possible to simulate wind turbines in large-scale power grids.

Description of drawings

Fig. 1 is the main flowchart of the electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention;

Fig. 2 is a structural schematic diagram of the double-fed variable-speed constant-frequency wind turbine model;

Fig. 3 is a schematic diagram of a shafting model of two mass blocks of a wind turbine;

Fig. 4 is a block diagram of the transfer function of the wind turbine shafting model;

Fig. 5 is a block diagram of the pitch control system;

Figure 6 is the T-type equivalent circuit of DFIG in the synchronous rotating coordinate system;

Fig. 7 is a model diagram of DFIG flux linkage directional vector control;

Fig. 8 is a model diagram of the control system of the frequency converter on the grid side;

Figure 9 is a model diagram of the control and protection system of the inverter on the rotor side of the doubly-fed machine;

Figure 10 is a model diagram of a doubly-fed asynchronous wind turbine with switchable crowbar;

Fig. 11 is a model diagram of a single wind turbine infinite system model established by using the wind turbine simulation model.

Detailed ways

In order to better understand the above technical solutions of the present invention, a further detailed description will be given below in conjunction with the drawings and embodiments.

Fig. 2 is a structural schematic diagram of a doubly-fed variable-speed constant-frequency wind turbine model. The wind turbine includes a prime mover module 100 composed of a wind turbine model 110, a shafting model 120, and a pitch control system 130, and an induction generator model 210 and rotor-side frequency conversion The doubly-fed wind turbine module composed of the inverter control and protection system 220, and the grid-side inverter control system (not shown in the figure).

The doubly-fed variable-speed constant-frequency wind turbine can realize the following functions through its control system: control the reactive power exchange between the generator and the grid, control the active power generated by the wind turbine to track the optimal operating point of the wind turbine or in the case of high wind speed Lower limit wind turbine output. The above functions are mainly realized through the control of the rotor-side inverter of the variable-speed wind turbine and the control of the pitch angle of the wind turbine.

The rotor-side frequency converter 220 is used to control the voltage amplitude and phase of the rotor side of the double-fed machine, realize the decoupling control of the active power and reactive power of the wind turbine, and complete the maximum power tracking strategy of the wind turbine, including the following modules: Maximum wind energy tracking module 221 , a power measurement module 222 , a voltage and current measurement module 223 , a power controller 224 , a current controller 225 , and a coordinate transformation module 226 . The protection model 227 of the DFIG is also included in the model of the DFIG.

The main flow chart of the electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention is shown in Figure 1, including the following steps:

S100) Establishing a wind turbine model, simulating the wind power absorbed by the wind turbine according to the relationship between wind speed, wind energy conversion efficiency, blade tip speed ratio and blade pitch angle;

S200) Using the two-mass shafting structure composed of the generator mass and the wind turbine mass, establishing a fan shafting model, simulating the energy transfer relationship between the wind turbine mechanical torque and the generator electromagnetic torque;

S300) Establish a pitch control system model, use the pitch angle control simulation to optimize the power of the wind turbine, seek the maximum output power of the wind turbine at a given wind speed; simulate the overload of the pitch control system when the wind speed exceeds the rated wind speed Protective function;

S400) Constructing a T-type equivalent circuit of a doubly-fed asynchronous induction motor (DFIG) according to the equation of the doubly-fed induction motor and the flux linkage equation, and establishing a DFIG electrical simulation model;

S500) According to the DFIG electrical simulation model, the instantaneous electromagnetic power equation of the stator of the doubly-fed induction generator, the relationship between the rotor current and the stator current, and the rotor voltage equation, establish the grid-side inverter and rotor-side inverter controller models;

S600) Using the wind turbine simulation model established in the above steps, establish a double-fed fan single-unit infinite system model;

An example of a doubly-fed fan single-unit infinite system model established using the wind turbine simulation model is shown in Figure 11. The wind turbine is connected to the step-up transformer through the WT low-voltage bus, and after boosting, it is connected to the external power grid through the outlet bus PCC, and the wind turbine is set. And the parameters of the step-up transformer and the external power grid constitute a double-fed fan single-machine infinite system, and the electromagnetic transient simulation, electromechanical transient simulation and fault simulation of the wind turbine system can be performed.

The electromagnetic transient simulation of the detailed model of the wind turbine can accurately reflect the dynamic performance of the wind turbine when the power grid fails. However, if the electromagnetic transient simulation method is used in the large-scale network simulation, the speed is relatively slow. The transient simulation results are compared to verify their correctness.

The electromechanical transient process refers to the change process of the mechanical motion of the motor rotor caused by the change of the electromagnetic torque of the generator and the motor in the power system, and the duration is usually from a few seconds to a dozen seconds. Electromechanical transient process simulation is a comprehensive analysis and research of mechanical transient process and electromagnetic transient process in power system, and the calculation step is usually about 10ms. The simulation of the electromechanical transient process of the power system is mainly used to analyze the stability of the power system, that is, to analyze whether the power system can return to the original operation after a certain period of time after being disturbed in a certain normal operating state. state or transition to a new stable operating state. It mainly includes: the transient stability of the system after a large disturbance and the static stability of the system after a small disturbance.

S700) Set the initial operating conditions of the wind turbine simulation model, set the simulation step size at the millisecond level, and enter the electromechanical transient simulation running state of the wind turbine system;

S720) Apply negative wind speed step and positive wind speed step signals to the wind turbine model respectively, perform electromechanical transient simulation of wind speed step, and analyze the active output, rotational speed, wind power, wind energy utilization efficiency and pitch of the wind turbine Angle response, the dynamic response characteristics of the established DFIG detailed model in the face of wind speed changes, verify the effectiveness of maximum wind energy tracking;

The wind speed negative step simulation working conditions are as follows: the initial active output of the fan is 4.5MW, the reactive output is 0.0Mvar, the slip is +8%, and the wind speed suddenly decreases by 2m/s after 1.0s. The active output, speed and wind energy utilization efficiency of the fan are investigated. Positive step of wind speed Under the same initial working condition, the wind speed changes in a step of +2m/s. According to the analysis of the wind speed jump simulation results, the electromechanical transient simulation results are basically consistent with the electromagnetic transient simulation results.

S740) Apply a reactive power step signal to the double-fed fan single-unit infinite system model, perform electromechanical transient simulation of the reactive step, and analyze changes in the terminal voltage, active output, reactive output, and rotational speed of the wind turbine , the established detailed model of the double-fed wind turbine faces the dynamic response characteristics of the reactive load change of the external power grid, and verifies the dynamic characteristics of the reactive power control link in the vector control of the double-fed wind turbine;

The reactive power step response mainly verifies the dynamic characteristics of the reactive power control link in the vector control of doubly-fed wind turbines. The simulation conditions are as follows: the initial active output of the fan is 4.5MW, the reactive output is 0Mvar, and the slip is +8%. After 1.0s, the reference value of the reactive power is made a step of 0.9MVar, and the terminal voltage, active power, reactive power and speed of the fan are investigated. The change. According to the analysis of reactive jump simulation results, it can be seen that the electromechanical transient simulation results are basically consistent with the electromagnetic transient simulation results. .

S760) Simulate the three-phase symmetrical fault and asymmetrical fault of the external power grid on the single-machine infinite system model of the double-fed fan, and perform electromechanical transient simulation of the fault state for the double-fed asynchronous fan with and without low voltage ride-through function, and analyze the wind power The machine terminal voltage, active power, reactive power, stator current, and rotor current waveforms of the unit compare the dynamic response of doubly-fed asynchronous fans with and without low-voltage ride-through function under grid faults, and verify the dynamic characteristics of doubly-fed fan fault protection.

1) Symmetric fault simulation:

When a three-phase symmetrical fault occurs in the external power grid, due to the sudden drop in the terminal voltage of the fan and the vector control of the inverter on the rotor side, the rotor current will suddenly increase and cause the inverter to over-current. At the same time, after a short-circuit fault, the active power cannot be sent out, and the active current of the inverter on the grid side will not change suddenly, causing the inverter on the grid side to charge the DC capacitor, which may also cause overvoltage of the DC capacitor. In this case, the inverter must be out of operation. At this time, for fans with low voltage ride-through function, only the frequency converter is cut off, and the double-fed generator is still connected to the grid to run, while for fans without low voltage ride-through function, they are directly shut down. Therefore, it is necessary to compare the two in detail under grid failure dynamic response.

With low voltage ride through function:

For the doubly-fed asynchronous fan with low voltage ride-through function, the fault dynamic characteristics under the following working conditions are investigated:

(1) The initial operating point of the fan: active power 4.5MW, reactive power 0Mvar, slip + 8%, the terminal voltage drop is small when a fault occurs, and the Crowbar does not operate;

(2) The initial operating point of the wind turbine: active power 4.5MW, reactive power 0Mvar, slip +8%, terminal voltage drops greatly when a fault occurs, crowbar operates, and crowbar cut-off time is 60ms;

(3) The initial operating point of the wind turbine: active power 2.8MW, reactive power 0Mvar, slip -10%, when the failure occurs, the terminal voltage drops greatly, the crowbar operates, and the crowbar cut-off time is 60ms;

(4) The initial operating point of the fan: active power 4.5MW, reactive power 0Mvar, slip + 8%, terminal voltage drops greatly when a fault occurs, crowbar operates, and crowbar cut-off time is 500ms;

The following are the electromechanical transient simulation results under the above working conditions one by one:

(1) The initial operating point of the fan: active power 4.5MW, reactive power 0Mvar, slip + 8%, the terminal voltage drop is small when the fault occurs, and the Crowbar does not operate; the single-unit infinite system of the fan is shown in Figure 11, and the simulation conditions are as follows: fan The initial active output is 4.5MW, the reactive power is 0Mvar, the initial slip is +8%, and the crowbar cut-off time is 60ms. At 0s, a three-phase short-circuit fault occurs on the outlet bus PCC of the fan step-up transformer, and the grounding impedance is 0.1+j1.0Ω, and the fault clears after 0.15s. Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that there is no high-frequency component greater than 50 Hz in the electromechanical transient simulation results, and its waveform is basically the average curve of the electromagnetic transient simulation results.

(2) The initial operating point of the wind turbine: active power 4.5MW, reactive power 0Mvar, slip +8%, when the failure occurs, the terminal voltage drops greatly, the crowbar operates, and the crowbar cut-off time is 60ms; simulation working conditions: the initial active power output of the wind turbine is 4.5MW, no Power 0Mvar, initial slip +8%, crowbar cut-off time 60ms. At 0s, a three-phase short-circuit fault occurs on the outlet bus PCC of the fan booster transformer, and the grounding impedance is 0.01+j0.1Ω, and the fault clears after 0.15s. Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that the electromechanical transient simulation results are the average curve of the electromagnetic transient simulation results.

(3) The initial operating point of the wind turbine: active power 2.8MW, reactive power 0Mvar, slip -10%, the terminal voltage drop is large when a fault occurs, the crowbar operates, and the crowbar cut-off time is 60ms; simulation working conditions: the initial active power output of the wind turbine is 2.8MW, no Power 0Mvar, initial slip -10%, crowbar cut-off time 60ms. At 0s, a three-phase short-circuit fault occurs on the outlet bus PCC of the fan booster transformer, and the grounding impedance is 0.01+j0.1Ω, and the fault clears after 0.15s. Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that the electromechanical transient simulation results are the average curve of the electromagnetic transient simulation results.

(4) The initial operating point of the wind turbine: active power 4.5MW, reactive power 0Mvar, slip +8%, the terminal voltage drop is large when the fault occurs, the crowbar operates, and the crowbar cut-off time is 500ms; simulation working conditions: the initial active power of the wind turbine is 4.5MW, the reactive power 0Mvar, initial slip +8%, Crowbar cut-off time setting value 500ms. At 0s, a three-phase short-circuit fault occurs at the outlet busbar PCC of the booster transformer of the fan, and the short-circuit impedance is 0.01+j0.1Ω, and the fault is cleared at 0.15s. Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that the electromechanical transient simulation results are the average curve of the electromagnetic transient simulation results.

No low voltage ride through function:

(1) The voltage drop at the machine terminal is relatively large, and the fan is cut off. Simulation working conditions: the initial active power of the fan is 4.5MW, the reactive power is 0Mvar, the initial slip is +8%, the three-phase short-circuit fault grounding impedance is 0.01+j0.1Ω, and the fault is cleared in 0.15s. Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that the electromechanical transient simulation results are completely consistent with the electromagnetic transient simulation results.

(2) The voltage drop at the machine terminal is small, and the fan is not cut off. Simulation working conditions: the initial operating point of the fan is the same as before, the grounding impedance of the three-phase short-circuit fault is 0.1+j1.0Ω, and the fault is cleared in 0.15s. Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that the electromechanical transient simulation results are the average curve of the electromagnetic transient simulation results.

2) Asymmetric fault simulation

When the three-phase asymmetry fault occurs, the wind turbine will also cause overcurrent of the inverter or overvoltage of the DC capacitor due to the sudden drop of the machine terminal voltage. At the same time, the three-phase asymmetry protection action of the inverter may also be triggered due to the serious three-phase imbalance. , therefore, it is necessary to analyze and compare the dynamic response of wind turbines with and without low voltage ride-through under asymmetric grid faults.

With low voltage ride through function

(1) The voltage drop at the terminal of the single-phase fault is small, and the Crowbar does not operate. Simulation working conditions: the initial active power of the fan is 4.5MW, the reactive power is 0Mvar, the initial slip is +8%, the crowbar cut-off time is 60ms, and at 0s, a phase-a ground fault occurs on the PCC of the outlet busbar of the fan booster transformer, and the short-circuit impedance is 0.2+j2.0Ω, 0.15s fault cleared. Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that the electromechanical transient simulation results are the average curve of the electromagnetic transient simulation results.

(2) The voltage drop at the terminal of the phase-to-phase fault is small, and the Crowbar does not operate. Simulation working conditions: The initial operating point of the fan and the Crowbar parameters are the same as before. At 0s, the bc phase-to-phase short-circuit fault occurs on the PCC of the outlet busbar of the fan booster transformer, the short-circuit impedance is 0.35+j3.5Ω, and the fault is cleared after 0.15s. Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that the electromechanical transient simulation results are the average curve of the electromagnetic transient simulation results.

(3) The voltage drop at the terminal of the single-phase fault is relatively large, and the Crowbar operates. Simulation working conditions: the initial operating point of the fan and the Crowbar parameters are the same as before, the single-phase grounding impedance is 0.01+j0.1Ω, and the fault is cleared in 0.15s. The electromechanical transient simulation results of asymmetric faults are slightly different from the electromagnetic transient simulation results, because the three-phase asymmetric protection of the fan is considered here, so the number of Crowbar actions is more than when only the inverter overcurrent protection is considered, 0.18s When the crowbar is completely removed, the fan absorbs more reactive power from the grid during the fault recovery process.

(4) The voltage drop at the terminal of the phase-to-phase fault is relatively large, and the Crowbar operates. Simulation working condition: the initial working condition of the fan and the Crowbar parameters are the same as before, at 0s, the bc-phase short-circuit impedance is 0.01+j0.1Ω, and the fault is cleared in 0.15s. Similar to the single-phase ground fault, the crowbar is switched 3 times during the fault ride-through process, and the fan absorbs a certain amount of reactive power from the grid.

No low voltage ride through function

(1) The voltage drop at the terminal of the single-phase fault is small, and the fan is not cut off. Simulation working conditions: the initial active power of the fan is 4.5MW, the reactive power is 0Mvar, the initial slip is +8%, and at 0s, a single-phase grounding fault occurs on the PCC of the outlet busbar of the fan booster transformer, and the short-circuit impedance is 0.2+j2.0Ω, 0.15s time the fault clears. Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that the electromechanical transient simulation results are basically the average curve of the electromagnetic transient simulation results.

(2) The terminal voltage of the phase-to-phase fault drops greatly, and the fan is cut off. Simulation working conditions: the initial active power of the wind turbine is 4.5MW, the reactive power is 0Mvar, the initial slip is +8%, and at 0s, a bc-phase short-circuit fault occurs on the PCC of the fan booster variable outlet busbar, the short-circuit impedance is 0.01+j0.1Ω, and the fault is cleared in 0.15s . Compared with the electromagnetic transient simulation results under the same working conditions, it can be seen that the electromechanical transient simulation results are completely consistent with the electromagnetic transient simulation results.

According to an embodiment of the electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention, step S100 is based on the formula

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; wind</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&rho;\&pi;</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Establish a wind turbine model to simulate the wind power absorbed by the wind turbine, where P _wind is the wind power, ρ is the air density, R is the radius of the fan impeller, λ=Rω _tur /V _w is the blade tip speed ratio, and β is the pitch angle , ω _tur is the speed of the wind turbine impeller, C _p is the wind energy conversion efficiency of the wind turbine, which is a function of λ and β, and V _w is the wind speed. In this embodiment, the relationship between Cp and λ and β is represented by a two-dimensional table, where β varies from -20 to 300 with an interval of 0.50, and λ varies from 0 to 19.6 with an interval of 0.4, so a 66*49 According to this table, the Cp under any β and λ can be obtained by using the spline fitting method.

According to an embodiment of the electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention, the two-mass shafting model including the generator mass and the wind turbine mass in the double-fed variable-speed constant-frequency wind turbine is shown in Figure 3 As shown in Fig. 3, the mathematical equation of the two-mass shafting model can be obtained

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; tur</span>}}\frac{{\mathrm{<span\; class="notranslate">\; d\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; tur</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; tur</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; tur</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; gene</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; tur</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; tur</span>}}\\ {\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; the\; gene</span>}}\frac{{\mathrm{<span\; class="notranslate">\; d\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; gene</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; tur</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; gene</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; gene</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; gene</span>}}\\ \frac{{\mathrm{<span\; class="notranslate">\; d\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; tur</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; gene</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Step S200 establishes a two-mass shafting model consisting of a generator mass and a wind turbine mass according to formula 2, where H _tur and H _gen are the inertial time constants of the wind turbine and generator respectively; K _{s is} the elasticity of the shaft D _tur and D _gen are the self-damping coefficients of the wind turbine rotor and the generator rotor respectively; D _s is the mutual damping coefficient of the wind turbine mass and the generator mass; θ _s is the relative angular displacement; T _tur and T _E are the mechanical torque of the wind turbine and the electromagnetic torque of the generator, respectively; ω _tur and ω _gen are the rotor speeds of the wind turbine and generator, respectively, and ω ₀ is the synchronous speed. The block diagram of the transfer function of the shafting model of the wind turbine is shown in Figure 4. The mass model of the generator has been included in DFIG, but it is not shown in Figure 4.

According to an embodiment of the electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention, when the double-fed asynchronous fan is lower than the rated wind speed, in order to make the blades absorb as much wind energy as possible, the pitch angle is generally set at 0 degrees, so the pitch control is not enabled when the wind speed is lower than the rated wind speed. When the wind speed is higher than the rated wind speed, since the energy acquisition is limited by the physical properties of the unit, the rotor speed and energy conversion of the wind turbine must be lower than a certain limit value, otherwise the mechanical and fatigue strength of each component will be challenged. Therefore, at high wind speeds, it is necessary to use pitch control to adjust the wind energy utilization efficiency of the wind turbine, so as to limit the mechanical power of the wind turbine to not exceed its rated power, and at the same time limit the speed of the generator within the allowable range. The model of the pitch control system is shown in Figure 5. The pitch control system reads the rotational speed measurement value speed, compares it with the preset maximum rotational speed reference value speed_ref, and obtains an error signal that is sent to the input PI controller; the PI Controller produces pitch angle reference value Beta_ref, compares with actual pitch angle Beta again, draws pitch angle error signal, inputs to pitch angle control system servomechanism; In pitch control system model, described propeller The servo mechanism of the pitch control system is represented by the servo time constant T, the pitch adjustment limit values Vrmax, Vrmin and the pitch change gradient limit values Rate_max, Rate_min.

An embodiment of the electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention is based on the electromagnetic equation of the double-fed induction motor under the synchronous rotating coordinate system

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; d\&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; d\&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; d\&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; d\&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

and the flux equation

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}\\ {\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}\\ {\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}\\ {\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Establish the T-type equivalent circuit of the doubly-fed asynchronous induction motor (DFIG) in the synchronous rotating coordinate system, as shown in Figure 6. Step S400 establishes the DFIG electrical simulation model, wherein, U _sd , U _sq , U _rf , u _rd , U _rq are the d-axis and q-axis components of the stator winding and rotor winding voltages respectively; RS and K are the stator windings and the rotor windings respectively Phase resistance; i _sd , i _sq , i _rd .i _rq , are the d-axis and q-axis components of the stator winding and rotor winding currents respectively, ω ₁ is the synchronous angular velocity, ω _s is the slip angular velocity, Ψ _sd , Ψ _sq , Ψ _rd and Ψ _rq are the flux linkages of the stator and rotor d-axis and q-axis, L _s =L _m +L _σs , L _r =L _m +L _σr , are the stator and rotor inductance, L _σs , L _σr , L _m Leakage inductance and mutual inductance of stator and rotor.

An embodiment of the electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention, step S500 is based on the instantaneous electromagnetic power equation of the double-fed induction generator stator of the DFIG electrical simulation model

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}\\ \mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

The relationship formula between rotor current and stator current

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}\\ {\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

and the rotor voltage equation

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&sigma;\; L</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&sigma;\; L</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sq</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Psi;</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

The controller models of grid-side inverter and rotor-side inverter are established, where P is active power and Q is reactive power. The system adopts a double closed-loop structure, the outer loop is a power control loop, and the inner loop is a current control loop. In the power loop, the active power reference value P _ref is calculated according to the best wind energy tracking curve, and the reactive power reference value Q _ref can be calculated according to the requirements of the grid for reactive power, or from the perspective of generator power consumption. The reference value of P _ref and Q _ref is compared with the feedback value, and the difference value is calculated by the power regulator (PI type), and the reference value of reactive and active components of the rotor current is output I _{rq_ref} and I _{rd_ref} , I _{rq_ref} and I _{rd_ref} and the rotor current The difference after the feedback quantity comparison is sent to the current regulator (PI type), and the adjusted output voltage component plus the voltage compensation item can obtain the rotor voltage command V _{rd_ref} , V _{rq_ref} , and then obtain the generator rotor three Phase voltage control quantities U _{ra_ref} , U _{rb_ref} , U _{rc_ref} , refer to FIG. 7 .

The grid-side inverter adopts the stator voltage-oriented vector control scheme, which is used to control the DC bus voltage of the AC-DC inverter and the reactive power generated by the grid-side inverter. The inverter control system on the grid side also adopts a double closed-loop structure, the outer loop is a DC voltage control loop, and the inner loop is a current control loop, as shown in Figure 8.

The grid-side inverter control system consists of the following parts:

DC voltage measurement module: used to measure the DC voltage value of the DC link of the double-fed machine inverter;

Inverter current measurement module: used to measure the three-phase AC current of the grid-side inverter;

PLL voltage phase-locked loop: measure the phase angle of the grid-side voltage connected to the grid-side inverter, so as to realize the decoupling control of the grid-side inverter by adopting the grid voltage-oriented vector control method;

Coordinate transformation module: Since the grid-side voltage and current are expressed in the fixed reference coordinate system of the grid, and the grid-side inverter adopts the grid voltage-oriented vector control method under the grid voltage reference coordinate, so the grid-side inverter The input and output signals of the controller need coordinate transformation;

Grid-side inverter: the controller outputs pulse width modulation (PWM) commands to the inverter, and the inverter adjusts the duty cycle of the upper and lower bridge arms to achieve the corresponding control effect;

Grid-side inverter controller: composed of cascaded two-stage PI controllers, the slow outer loop is used to control the DC voltage of the DC link and the reactive power generated by the inverter, and the fast inner loop is used to control the current (I _d , I _q ) to the current reference value (I _{d_ref} , I _{q_ref} ) determined by the outer loop control; the output signal of the inverter controller on the grid side defines the amplitude and phase angle of the output voltage on the AC side of the inverter. In the vector control mode, the inverter current is decomposed into two mutually perpendicular current components, where the d-axis current I _d is the active current, the q-axis current I _q is the reactive current, and the d-axis active current is used to control the DC voltage of the DC link , the q-axis reactive current is used to control the reactive power generated by the inverter; the modulation coefficient of the inverter output by the current inner loop controller of the inverter on the grid side is the expression mode under the voltage orientation of the inverter on the grid side, which needs to be transformed by coordinate transformation Converting to the representation mode under the fixed reference coordinate system of the system is the signal that the inverter on the grid side can handle;

The control and protection system of the inverter on the rotor side is shown in Figure 9 and consists of the following parts:

Active and reactive power measurement link: used to measure the active and reactive power generated by the entire doubly-fed induction generator and transmit the signal to the rotor-side inverter controller;

Coordinate transformation module: perform coordinate transformation functions under different reference coordinate systems;

dq→αβ conversion module: used to transform the frequency converter modulation coefficient signal in the stator flux orientation reference coordinate system output by the current controller into a signal in the double-fed motor rotor reference coordinate system and input it into DFIG;

αβ→dq transformation module: used to transform the rotor current of double-fed motor from the expression method in the rotor reference coordinate system to the expression method in the stator flux orientation coordinate system, so as to realize the rotor-side inverter control of the stator flux orientation;

及定、转子磁通实部和虚部Ψ_s_r，Ψ_s_i，Ψ_r_r，Ψ_r_i；DFIG module: It is composed of induction generator and rotor-side inverter model, its model equations and input and output are expressed in the rotor reference coordinate system, and its output signals include rotor current I _ra , I _rβ , rotor position angle

And stator and rotor flux real and imaginary parts Ψ _s _r, Ψ _s _i, Ψ _r _r, Ψ _r _i;

Power control module: According to Formula 5 and Formula 6, the active power can be adjusted by adjusting the q-axis component of the rotor excitation current, and the reactive power can be adjusted by adjusting the d-axis component. The difference between the actual measured P, Q and the reference value of active power and reactive power passes through two PI controllers to obtain the reference values I _{rd_ref} and I _{rq_ref} of the d and q axis components of the rotor excitation current;

Current control module: The rotor excitation current d output by the power outer loop control, the reference value I _{rd_ref} and I _{rq_ref} of the q-axis component are used as the input of the current inner loop control, and the closed loop of the rotor current generates the inverter pulse width modulation for controlling the rotor excitation voltage coefficient; in the PWM inverter, the pulse width modulation coefficients Pmd and Pmq are the control variables of the inverter, if the DC voltage of the inverter is u _dc , then the following formula holds:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; md</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; mq</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Therefore, inputting the inverter pulse width modulation coefficients Pmd and Pmq obtained by the current inner loop control into the double-fed motor can change the amplitude and phase angle of the rotor excitation voltage through the inverter, thereby controlling the rotor current of the generator to indirectly control the power generation The purpose of machine active and reactive power;

Maximum wind energy tracking module: Only by changing the speed of the wind turbine can the wind turbine achieve the best wind energy utilization efficiency at different wind speeds. Since the best wind energy tracking control is only used when the wind speed is lower than the rated wind speed, the pitch control is not used during this period. , the pitch angle is 0 degrees, therefore, there is an optimal tip speed ratio when the wind speed is lower than the rated wind speed, so that the wind energy utilization efficiency is maximized; in formula 1, Cp is constant, and Where k is the speed-up ratio of the gearbox, and R is the radius of the wind rotor. Substitute this formula into formula 1 to get:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&rho;\&pi;</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 5</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; max</span>}}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; op</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; gene</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; K</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; gene</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

Therefore, through the actual measurement of the generator speed, the reference value of the active power in the maximum wind energy tracking module is proportional to the cube of the speed, and the tracking and capture of the maximum wind energy can be realized; The reference value is limited to the maximum output;

According to another embodiment of the electromechanical transient simulation method of the double-fed variable-speed constant-frequency wind turbine system of the present invention, the DFIG module uses the switchable Crowbar device to realize the low voltage ride-through function, and the double-fed wind turbine with the switchable Crowbar device The wind turbine (DFIG) is shown in Fig. 10. When an external fault causes the rotor-side inverter to detect rotor overcurrent, or the inverter DC bus overvoltage, the switching element IGBT in the Crowbar device is turned on, and the Crowbar is put into operation to bypass the rotor overcurrent, and at the same time, the rotor-side inverter triggers signal blocking , the rotor winding of the doubly-fed machine is directly short-circuited through the series resistor Rc.

Low Voltage Ride Through (LVRT, Low Voltage Ride Through) capability means that when the grid fault or disturbance causes the voltage drop at the grid-connected point of the wind power plant, within a certain range of voltage drop, the wind turbine can operate uninterruptedly connected to the grid. The low-voltage ride-through capability of the doubly-fed asynchronous fan is mainly realized through the switchable Crowbar device.

The structure of the doubly-fed variable-speed constant-frequency wind turbine with switchable crowbar device is shown in Figure 10. The crowbar switching process is as follows: When the external fault causes the rotor-side inverter to detect rotor overcurrent, or the inverter DC bus overvoltage, the switching element IGBT in the Crowbar device is turned on, and the Crowbar is put into operation to bypass the rotor overcurrent. The trigger signal of the side inverter is blocked, and the rotor winding of the double-fed machine is directly short-circuited through the resistor. The additional short-circuit resistance of each phase is about 2/3 of the value of the Crowbar series resistance. Motor (depending on the motor speed before the failure).

In the first 10-15ms when the Crowbar is put on, the reactive power generated by the DFIG will have a positive impact, and then the DFIG will start to absorb reactive power, and the amount of active power will depend on the positive and negative values of the slip. Certainly. Due to the small resistance value of the Crowbar in series and the low machine terminal voltage during the short-circuit fault, the flux linkage and current of the stator and rotor of the double-fed machine decay quickly. After the crowbar is turned on for 60-100ms, the rotor current decays to a smaller value, and the DC voltage basically returns to the normal value. When the crowbar is cut off, the trigger signal of the rotor-side inverter recovers, and the DFIG recovers its control capability.

If the external fault is more serious, for example, the fault lasts for a long time or the decay speed of the rotor overcurrent is slow, the crowbar may switch on and off more than once during the fault period. If the crowbar keeps acting repeatedly, the over-speed protection or low-voltage protection may eventually cause shutdown. , therefore, the setting value of Crowbar investment time needs to be carefully selected.

The protection of double-fed machine and frequency converter mainly includes the following types: frequency converter overcurrent protection, frequency converter asymmetry protection, generator end overvoltage and undervoltage protection, generator overspeed and low speed protection, as shown in Figure 9 . In the fan with low voltage ride through function, when the frequency converter is over-current or asymmetrical protection action, the bypass flag position is 1, so the state variables of the PI link of the power controller and current controller are all cleared, the frequency converter trigger signal is blocked, and the Crowbar Put into operation, at this time the doubly-fed machine enters the asynchronous motor running state where the rotor winding is short-circuited. When the fault is eliminated and the Crowbar is out of operation, if the inverter detects no overcurrent or asymmetry, the controller will be put into operation again, the trigger signal of the inverter will be unlocked, and the wind turbine will resume its control capability. In fans without low-voltage ride-through function, when any of the protection actions of inverter over-current, asymmetry, generator over-speed, low-speed, machine-end over-voltage, or under-voltage, the double-fed machine will stop running and cannot be automatically re-started. .

In the protection of doubly-fed asynchronous fan, the over-voltage and low-voltage protection at the machine end, the over-speed and low-speed protection of the generator all adopt the inverse time-limit setting principle. The following focuses on the modeling method and setting principle of the inverter over-current protection and three-phase asymmetry protection.

Inverter overcurrent protection:

It can be known from Figure 9 and Formula 9 that the signal quantity collected in the overcurrent protection of the frequency converter is the rotor current amplitude of the phase with the most serious overcurrent. Therefore, can the rotor current of the DFIG reflect the current actually flowing through the IGBT? Through the electromechanical transient simulation, it can be found that the current flowing through each IGBT group is a unipolar PWM wave, and its envelope is the current corresponding to the phase of the bridge arm where the IGBT is located.

It can be seen that the calculation of the rotor current amplitude of the phase with the most serious overcurrent can properly reflect the overcurrent situation in the IGBT.

When a short-circuit fault occurs, the three-phase current of the rotor of the DFIG may be asymmetrical. The rotor current amplitude calculation module in Figure 9 is used to calculate the rotor current amplitude of the phase with the most serious overcurrent. The calculation formula is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; rot</span>}}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

The overcurrent protection is set according to the following method: assuming that the rotor current under the rated output of the fan is I _rN (the reactive power is considered according to the power factor of 0.95), and the rotor current actually detected and calculated according to formula 10 is I _rot , then if I _rot >1.21I _rN , the protection delay is 10ms, if I _rot >1.32I _rN , the protection operates instantaneously.

Three-phase asymmetry protection:

The three-phase asymmetry protection of the frequency converter is set as follows: the phase difference between any two adjacent phases of the wind turbine terminal is less than 1140 or greater than 1260 (that is, the unbalance of the three-phase voltage is greater than ±5%), and the protection has no delay action. Crowbar is put into operation for fans with low-voltage ride-through capability, and cuts off directly for fans without low-voltage ride-through capability.

When the protection model is implemented, the phases of the three-phase voltages can be obtained by measuring the real and imaginary parts of the three-phase voltage vector at the machine terminal, and then the maximum phase difference between any two-phase voltages can be obtained to judge whether the protection is satisfied. action condition.

Those of ordinary skill in the technical field should recognize that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not used as limitations to the present invention. All changes and modifications will fall within the protection scope of the claims of the present invention.

Claims (2)

1. A doubly-fed variable-speed constant-frequency wind turbine system electromechanical transient simulation method, said wind turbine comprises a prime mover model composed of a wind turbine model, a shafting model and a pitch control system, an induction generator model and a rotor A doubly-fed wind turbine model composed of a side converter control and protection system, and a power grid side converter control system, the electromechanical transient simulation method includes the following steps: S100) Establishing a wind turbine model, simulating the wind power absorbed by the wind turbine according to the relationship between wind speed, wind energy conversion efficiency, blade tip speed ratio and blade pitch angle; S200) Using the two-mass shafting structure composed of the generator mass and the wind turbine mass, establishing a fan shafting model, simulating the energy transfer relationship between the wind turbine mechanical torque and the generator electromagnetic torque; S300) Establish a pitch control system model, use the pitch angle control simulation to optimize the power of the wind turbine, seek the maximum output power of the wind turbine at a given wind speed; simulate the overload of the pitch control system when the wind speed exceeds the rated wind speed Protective function; S400) Constructing a T-type equivalent circuit of a double-fed asynchronous induction motor according to the equation of the double-fed induction motor and the flux linkage equation, and establishing a DFIG electrical simulation model; S500) According to the DFIG electrical simulation model, the instantaneous electromagnetic power equation of the stator of the doubly-fed induction generator, the relationship between the rotor current and the stator current, and the rotor voltage equation, establish the grid-side inverter and rotor-side inverter controller models; S600) Using the wind turbine simulation model established in the above steps, establish a double-fed fan single-unit infinite system model; S700) Set the initial operating conditions of the wind turbine simulation model, set the simulation step size at the millisecond level, and enter the electromechanical transient simulation running state of the wind turbine system; S720) Apply negative wind speed step and positive wind speed step signals to the wind turbine model respectively, perform electromechanical transient simulation of wind speed step, and analyze the active output, rotational speed, wind power, wind energy utilization efficiency and pitch of the wind turbine Angle response, the dynamic response characteristics of the established DFIG detailed model in the face of wind speed changes, verify the effectiveness of maximum wind energy tracking; S740) Apply a reactive power step signal to the double-fed fan single-unit infinite system model, perform electromechanical transient simulation of the reactive step, and analyze changes in the terminal voltage, active output, reactive output, and rotational speed of the wind turbine , the established detailed model of the double-fed wind turbine faces the dynamic response characteristics of the reactive load change of the external power grid, and verifies the dynamic characteristics of the reactive power control link in the vector control of the double-fed wind turbine; S760) Simulate the three-phase symmetrical fault and asymmetrical fault of the external power grid on the single-machine infinite system model of the double-fed fan, and perform electromechanical transient simulation of the fault state for the double-fed asynchronous fan with and without low voltage ride-through function, and analyze the wind power The machine terminal voltage, active power, reactive power, stator current, and rotor current waveforms of the unit compare the dynamic response of doubly-fed asynchronous fans with and without low-voltage ride-through function under grid faults, and verify the dynamic characteristics of doubly-fed fan fault protection. 2. The electromechanical transient simulation method of the doubly-fed variable-speed constant-frequency wind turbine system according to claim 1, characterized in that the DFIG module uses a switchable Crowbar device to realize the low-voltage ride-through function, and when an external fault causes the frequency conversion on the rotor side When the rotor overcurrent is detected by the inverter or the DC bus of the frequency converter is overvoltage, the switching element IGBT in the Crowbar device is turned on, and the Crowbar is put into operation to bypass the rotor overcurrent. Short circuit through series resistor Rc.

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