A direct-drive wind turbine model construction method for wind farm multi-working condition simulation

Abstract

A method for constructing a direct-drive wind turbine model for multi-condition wind farm simulation includes the following steps: Step S1, analyzing the importance of each control component in the direct-drive wind turbine affecting grid-connected power output under different operating conditions; Step S2, performing hierarchical discretization on the continuous full-order electromechanical-electromagnetic coupling direct-drive wind turbine model to establish an explicit discretization model; Step S3, approximating the nonlinear coupling terms in the explicit discretization model to obtain a detailed model; Step S4, performing algebraic simplification on the non-critical control components under different operating conditions in the detailed model to obtain a simplified model; Step S5, constructing a switching module and a reset module; and Step S6, encapsulating the detailed model, simplified model, switching module, and reset module in a unified discrete state space structure to obtain a direct-drive wind turbine model for multi-condition wind farm simulation. This invention achieves a synergistic balance between high-fidelity key dynamics and computational reduction in multi-condition wind farm simulation.

Description

Technical Field

[0001] This invention relates to the field of wind farm simulation technology, and in particular to a method for constructing a direct-drive wind turbine model for multi-condition simulation of wind farms. Background Technology

[0002] As a key dynamic unit in wind farm simulation and power system transient analysis, the accuracy of wind turbine models directly affects the reliability of wind farm-level simulations. In complex wind farm environments with a high proportion of wind power connected to the grid, permanent magnet direct-drive wind turbines need to cover multiple operating conditions, including normal grid connection, fault ride-through, sudden wind speed changes, AGC automatic generation control, and primary frequency regulation response. Furthermore, there are significant nonlinear strong couplings and multi-timescale dynamic interactions between the turbine-side converter, DC bus, and grid-side converter.

[0003] Currently, most commonly used wind turbine simulation models in the industry are based on traditional electromechanical transient general model systems. In order to balance versatility and solution speed, these models are usually modeled on a single time scale or the converter control part is significantly reduced in order. This results in the weakening or separation of cross-scale coupling effects between different control loops, and key coupling terms are directly simplified or ignored, leading to problems such as transient response distortion, poor numerical convergence, and insufficient simulation stability.

[0004] On the other hand, although the full-order electromagnetic transient model can relatively completely restore the electromagnetic details of the wind turbine and the dynamic interaction of the control logic, it mainly adopts a unified dimension and equation structure. The model has a high state dimension and dense nonlinear coupling terms. The computational cost increases rapidly with the combination of operating conditions, which is particularly obvious when the scale of wind farm modeling is expanded. This can easily lead to extended simulation time, "curse of dimensionality" and resource bottlenecks. It cannot meet the stringent requirements for lightweight and fast convergence of the model in the scenarios of high efficiency, batch simulation of multiple operating conditions or medium- and long-term-transient hybrid integrated simulation of large wind farms.

[0005] It is evident that the existing wind turbine modeling system still faces systemic technical contradictions and engineering constraints in terms of recognizable unified representation of multiple operating conditions, multi-scale interactive fidelity solution, nonlinear strong coupling stability processing, model computation reduction collaboration and the establishment of a precision-efficiency balance mechanism. There is an urgent need for a generalized modeling framework for direct-drive wind turbines that has the ability to adapt to multiple operating conditions, dynamic fidelity during mode switching, retention of key coupling interactions, and efficient and scalable solution capabilities, in order to support the application requirements of future large-scale wind farm-level multi-operating condition simulation for the reuse of a unified model architecture, rapid solution updates, and cross-platform adaptation. Summary of the Invention

[0006] To achieve a synergistic balance between high fidelity in key dynamics and computational efficiency in multi-condition wind farm simulation, this invention provides a method for constructing direct-drive wind turbine models for multi-condition wind farm simulation.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical method: a method for constructing a direct-drive wind turbine model for multi-condition simulation of wind farms, comprising:

[0008] Step S1: Set up multiple simulation scenarios on the simulation platform to analyze the importance of each control link in the direct-drive wind turbine affecting the grid-connected power output under different operating conditions;

[0009] Step S2: The trapezoidal method and forward Euler method are used to perform hierarchical discretization of the direct-drive wind turbine model with continuous full-order electromechanical-electromagnetic coupling. According to the cascade order of the simulation solution of the direct-drive wind turbine, the parts are combined in an orderly manner according to the time series to establish a unified explicit discretization model.

[0010] Step S3: Approximate the nonlinear coupling terms in the explicit discretization model to obtain the detailed model;

[0011] Step S4: Based on the importance analysis results obtained in step S1, the non-critical control links under different working conditions in the detailed model are simplified by algebraization or quasi-static approximation to obtain a simplified model.

[0012] Step S5: Build the switching module and the reset module;

[0013] The switching module switches between generator-side and grid-side control models according to the system's operating conditions: when the system enters a steady-state condition, the switching module switches the generator-side and grid-side control to a simplified model; when the system operates under voltage dip conditions, the switching module switches the grid-side control back to a detailed model; when the system operates under conditions of sudden wind speed changes, primary frequency regulation, or AGC automatic generation control, the switching module switches the generator-side control back to a detailed model.

[0014] When the machine-side or grid-side control switches to the simplified model, the reset module updates the motor output voltage reference value or the grid-side converter output voltage reference value with the motor output voltage or the grid-side converter output voltage; when the machine-side or grid-side control switches back from the simplified model to the detailed model, the reset module performs an integrator reset on the machine-side or grid-side current inner loop.

[0015] Step S6: The detailed model, simplified model, switching module and reset module are encapsulated in a unified discrete state space structure to obtain a direct-drive wind turbine model for multi-condition simulation of wind farms.

[0016] Furthermore, in step S1, multiple simulation scenarios are set on the simulation platform under four operating conditions: voltage drop, sudden wind speed change, primary frequency regulation, and AGC automatic power generation control. The median method is used to calculate the trajectory sensitivity of the PI control parameters of each control link in the direct-drive wind turbine to the grid-connected power under different operating conditions. The control link includes the outer loop of the turbine power, the inner loop of the turbine current, the outer loop of the grid DC voltage, the inner loop of the grid current, and the phase-locked loop.

[0017] (1)

[0018] (2)

[0019] (3)

[0020] (4)

[0021] In the formula, This represents the original value of the PI control parameter; express The disturbance value; and The PI control parameters are respectively and The corresponding active power at that time; The PI control parameters are The corresponding active power output at that time; and The PI control parameters are respectively and The corresponding reactive power; The PI control parameters are The corresponding reactive power output at that time; and These represent the average trajectory sensitivity of the PI control parameters to active and reactive power during the period of operating condition changes. This indicates the total observation time for trajectory sensitivity; and These represent the initial and current moments of the change in operating conditions, respectively.

[0022] Based on the average trajectory sensitivity of the PI control parameters of each control loop under each operating condition, the importance of each control loop in affecting grid-connected power output under each operating condition is ranked. The results are as follows: Under voltage dip conditions, the average trajectory sensitivity of the PI control parameters of the generator-side current inner loop is relatively the smallest, indicating that the generator-side current inner loop has the least impact on grid-connected power output. Therefore, the generator-side current inner loop is a non-critical control loop under this condition. Under wind speed change, primary frequency regulation, or AGC automatic generation control conditions, the average trajectory sensitivity of the PI control parameters of the grid-side current inner loop is relatively the smallest, indicating that the grid-side current inner loop has the least impact on grid-connected power output. Therefore, the grid-side current inner loop is a non-critical control loop under these three operating conditions.

[0023] Furthermore, in step S2, the forward Euler method is used to discretize the outer loop of the turbine power, the inner loop of the turbine current, the outer loop of the grid DC voltage, the inner loop of the grid current, the phase-locked loop, the delay element, and the pitch control element in the continuous full-order electromechanical electromagnetic coupling direct-drive wind turbine model. The trapezoidal method is used to discretize the motor equations and the DC-side energy balance equations in the continuous full-order electromechanical electromagnetic coupling direct-drive wind turbine model. After completing the aforementioned layered discretization, according to the cascade order of the simulation solution of the direct-drive wind turbine, the parts are combined in an orderly manner according to the time series to establish a unified explicit discretization model.

[0024] Furthermore, in step S3, for the nonlinear product coupling terms of the motor output current and generator electric angular velocity at unknown times in the explicit discretization model, an explicit decoupling process is performed using a substitution method based on predicted values. The predicted value of the generator electric angular velocity derived from the state variables at the previous time step is used to replace the unknown generator electric angular velocity. The calculation formula for the predicted value of the generator electric angular velocity is as follows:

[0025] ; (5)

[0026] In the formula, and These represent the current and previous moments in the simulation, respectively. and These are the predicted values ​​of the generator's electrical angular velocity and the generator's mechanical angular velocity, respectively. This represents the number of pole pairs of the generator; The mechanical angular velocity of the generator; This is for simulating step size; The generator's inertia coefficient; This refers to the electromagnetic torque of the generator. This represents the mechanical torque of the generator.

[0027] Furthermore, in step S4, based on the importance analysis results obtained in step S1, the non-critical control links under different working conditions in the detailed model are simplified.

[0028] Under voltage dip conditions, the machine-side current inner loop control, which is a non-critical control element at this time, is simplified by directly assigning the current reference value output by the machine-side control element to the actual value and performing algebraic processing, as shown in the following formula:

[0029] (6)

[0030] (7)

[0031] In the formula, and These represent the output currents of the motor's d-axis and q-axis, respectively. This is the reference value for the q-axis output current of the motor; and These represent the output voltages of the motor's d-axis and q-axis, respectively. For generator inductance; For generator stator resistance; For the permanent magnet flux linkage of the generator;

[0032] Under conditions of sudden wind speed changes, primary frequency regulation, or AGC automatic generation control, the grid-side current inner loop control, which is a non-critical control link at this time, is simplified by directly assigning the current reference value output by the grid-side control link to the actual value and performing algebraic processing, as shown in the following formula:

[0033] (8)

[0034] (9)

[0035] In the formula, and These represent the d-axis and q-axis output currents of the grid-side converter, respectively. This is the reference value for the d-axis output current of the grid-side converter; and These represent the d-axis and q-axis output voltages of the grid-side converter, respectively. and These represent the grid connection point voltages on the d-axis and q-axis, respectively. and For filtering impedance; The power grid frequency;

[0036] The current inner loop control on both the machine side and the grid side is simplified under steady-state conditions.

[0037] Furthermore, the machine-side control process is as follows:

[0038] Step S1: The switching module determines the simplified signal on the generator side based on the real-time operating conditions of the system. When the system is operating under conditions of sudden wind speed change, primary frequency regulation, or AGC automatic power generation control, the simplified signal on the generator side is 0, and the switching module switches the generator side control to the detailed model. Then proceed to step S2. When the system is operating under conditions of steady state or voltage drop, the simplified signal on the generator side is 1, and the switching module switches the generator side control to the simplified model. Then proceed to step S3.

[0039] Step S2, the machine side calls the detailed model and executes the following steps:

[0040] 1) Determine if the model has just switched back from the simplified model. If yes, the reset module will reset the machine-side current inner loop integrator. If no, proceed directly to the next step.

[0041] 2) Machine-side power outer loop: Calculate the reference value of motor output current;

[0042] 3) Machine-side current inner loop: Calculate the reference value of motor output voltage and motor output voltage in sequence;

[0043] 4) Permanent magnet synchronous generator model: First, predict the mechanical angular velocity of the generator, then calculate the motor output current, then calculate and update the electromagnetic torque and electromagnetic power of the generator in sequence, and send the electromagnetic power to the generator-side power outer loop. Then calculate and update the mechanical angular velocity of the generator, and go to step S1.

[0044] Step S3: The simplified model is invoked on the machine side to perform the following steps:

[0045] 1) Machine-side power outer loop: Calculate the reference value of motor output current;

[0046] 2) Permanent magnet synchronous generator model: Calculate the generator output current and predict the generator mechanical angular velocity;

[0047] 3) Machine-side current inner loop: Calculate the motor output voltage, and use the reset module to set the motor output voltage as the reference value for the motor output voltage;

[0048] 4) Permanent magnet synchronous generator model: First, calculate and update the electromagnetic torque and electromagnetic power of the generator in sequence, and send the electromagnetic power to the generator-side power outer loop. Then, calculate and update the mechanical angular velocity of the generator and proceed to step S1.

[0049] Furthermore, the network-side control process is as follows:

[0050] Step S1: The switching module determines the grid-side simplified signal based on the real-time operating conditions of the system. When the system is operating under voltage drop conditions, the grid-side simplified signal is 0, and the switching module switches the grid-side control to the detailed model. Then proceed to step S2. When the system is operating under steady-state, sudden wind speed change, primary frequency regulation, or AGC automatic generation control conditions, the grid-side simplified signal is 1, and the switching module switches the grid-side control to the simplified model. Then proceed to step S3.

[0051] Step S2, the network side calls the detailed model to perform the following steps:

[0052] 1) Outer loop of grid-side DC voltage: Calculate the reference value of the output current of the grid-side converter;

[0053] 2) Determine if the model has just switched back from the simplified model. If yes, the grid-side current inner loop integrator will be reset by the reset module. If no, proceed directly to the next step.

[0054] 3) Inner loop of grid-side current: First, calculate the reference value of grid-side converter output voltage and grid-side converter output voltage in sequence; then calculate the grid-side converter output current; finally, calculate and update the grid-connected active power and reactive power, and go to step S1;

[0055] Step S3: The network side calls the simplified model to perform the following steps:

[0056] 1) Outer loop of grid-side DC voltage: Calculate the reference value of the output current of the grid-side converter;

[0057] 2) Inner loop of grid-side current: First, calculate and update the output current of the grid-side converter; then calculate the output voltage of the grid-side converter, and use the grid-side converter output voltage as the reference value of the grid-side converter output voltage by the reset module; then calculate and update the grid-connected active power and reactive power, and proceed to step S1.

[0058] Preferably, in step S5, the reset module updates the motor output voltage reference value and the grid-side converter output voltage reference value using the following formula (10), and the reset module performs integrator reset on the machine-side and grid-side current inner loops using the following formulas (11) and (12);

[0059] (10)

[0060] (11)

[0061] (12)

[0062] In the formula, and These are the reference values ​​for the motor's d-axis and q-axis output voltages, respectively. and These are the reference values ​​for the d-axis and q-axis output voltages of the grid-side converter, respectively. and These represent the integrator values ​​for the d-axis and q-axis of the inner loop of the machine-side current, respectively. and These represent the integrator values ​​for the d-axis and q-axis of the inner loop of the grid-side current, respectively. and These represent the integral coefficients of the PI regulation within the inner loop of the current on the machine side and the grid side, respectively.

[0063] This invention provides a method for constructing direct-drive wind turbine models for multi-condition simulation of wind farms. It quantitatively assesses the impact of each control element on key grid-connected power output under different operating conditions by calculating trajectory sensitivity, accurately identifying the dominant dynamics of unit operation. Based on this, algebraicization and quasi-static approximation are applied to low-sensitivity, fast-stabilizing control elements within a unified discretization architecture, significantly reducing the number of integral state variables and lowering the complexity of iterative solutions. While ensuring the complete representation of key dynamic links and important control interactions, it effectively reduces the dimensionality of the full model solution and the scale of nonlinear iterations, thus achieving a synergistic balance between high-fidelity dynamic characteristics and reduced computational efficiency under multi-condition simulation. Furthermore, this invention uniformly transforms the continuous full-order electromechanical-electromagnetic coupling model into an explicitly solvable discrete state-space structure, and switches between local models of different complexity levels driven by operating conditions. On this basis, through integrator reset and state consistency maintenance strategies, it achieves shock-free switching between detailed and simplified models, ensuring numerical stability during model switching. Since all the working condition models are encapsulated based on a unified discrete framework and share a consistent solution process and interface structure, this invention effectively improves the reusability and scalability of the model in multi-machine parallel simulation of wind farms, enabling wind farm-level simulation to achieve large-scale acceleration while maintaining accuracy consistency, and providing an efficient, unified and scalable modeling foundation for multi-working condition wind farm-grid collaborative simulation. Attached Figure Description

[0064] Figure 1 This is a flowchart of the direct-drive wind turbine model construction method for multi-condition simulation of wind farms provided by the present invention;

[0065] Figure 2 This is a block diagram illustrating the working principle of the direct-drive wind turbine generator in this invention;

[0066] Figure 3 This is an architecture diagram of the direct-drive wind turbine model for multi-condition simulation of wind farms provided by the present invention. Detailed Implementation

[0067] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0068] like Figure 1As shown, a method for constructing a direct-drive wind turbine model for multi-condition simulation of wind farms includes the following steps.

[0069] Step S1: Set up various simulation scenarios on the MATLAB or PSCAD simulation platform to analyze the importance of each control link in the direct-drive wind turbine to the grid-connected power output under different operating conditions.

[0070] The simulation scenarios, with varying levels of depth, are set up under four operating conditions: voltage drop, sudden wind speed change, primary frequency regulation, and AGC (Automatic Generation Control). These are as follows:

[0071] (a) Voltage dip: The grid voltage dips to 30%, 50% and 80% of the rated voltage, with each dip lasting 0.05s;

[0072] (b) Sudden wind speed change: The wind speed increases by 1 m / s and decreases by 1 m / s from the rated wind speed within 3 to 8 seconds;

[0073] (c) Primary frequency regulation: The frequency at the grid connection point drops by 0.05Hz, -0.05Hz, 0.15Hz, and -0.15Hz, with each drop lasting for 15 seconds;

[0074] (d) Automatic Generation Control (AGC): The given active power command is to increase by 4%, -4%, or -8% from the rated power.

[0075] The median method is used to calculate the trajectory sensitivity of the PI control parameters of each control loop in the direct-drive wind turbine to the grid-connected power under different operating conditions, as shown in equations (1)-(4). The control loop includes the outer loop of the turbine power, the inner loop of the turbine current, the outer loop of the grid DC voltage, the inner loop of the grid current, and the phase-locked loop. The PI control parameters of the outer loop of the turbine power include the proportional coefficient representing the PI adjustment of the outer loop of the turbine power. Integral coefficient The outer loop PI control parameters for the grid-side DC voltage include the proportional coefficient representing the PI regulation in the outer loop of the grid-side DC voltage. Integral system The phase-locked loop (PLL) PI control parameters include the proportional coefficient representing the PI adjustment in the PLL. Integral coefficient The parameters for the machine-side current inner loop PI control include the proportional coefficient representing the d-axis PI adjustment in the machine-side current inner loop. Integral coefficient And the proportional coefficient in the q-axis PI adjustment of the machine-side current inner loop. Integral coefficient The inner loop PI control parameters for the grid-side current include the proportional coefficient representing the d-axis PI adjustment in the inner loop of the grid-side current. Integral coefficient And the proportional coefficient in the q-axis PI regulation of the inner loop of the grid-side current. Integral coefficient .

[0076] In the original PI control parameters Based on this, set up disturbances and The disturbance value is taken as 1%. The influence of the PI control parameter on the power output is calculated according to Equations (1) and (2). The active power and reactive power trajectory curves of the direct-drive wind turbine are recorded. Then, the average trajectory sensitivity of the PI control parameter to active and reactive power during the operating condition change period is calculated according to Equations (3) and (4). , .

[0077] (1)

[0078] (2)

[0079] (3)

[0080] (4)

[0081] In the formula, This represents the original value of the PI control parameter; express The disturbance value; and The PI control parameters are respectively and The corresponding active power at that time; The PI control parameters are The corresponding active power output at that time; and The PI control parameters are respectively and The corresponding reactive power; The PI control parameters are The corresponding reactive power output at that time; and These represent the average trajectory sensitivity of the PI control parameters to active and reactive power during the period of operating condition changes. This indicates the total observation time for trajectory sensitivity; and These represent the initial and current moments of the change in operating conditions, respectively.

[0082] Based on the average trajectory sensitivity of each control link under each operating condition, the importance of each control link affecting grid-connected power output under each operating condition is ranked. In this embodiment, trajectory sensitivity analysis was performed on a 2MW wind turbine. The simulation parameters are shown in Table 1, and the ranking results of importance are shown in Tables 2-5. It is worth noting that the values ​​in Tables 2-5 actually represent all depths under the current operating condition. (or When ranking the importance of each control element based on the mean of the proportional coefficient or integral coefficient of each control element, the larger mean of the proportional coefficient or integral coefficient of each control element is selected as the representative for comparison between the control elements.

[0083] Table 1 Simulation Parameters

[0084] ;

[0085] Table 2. Ranking of Importance under Voltage Dips

[0086] ;

[0087] Table 3. Ranking of Importance under Sudden Wind Speed ​​Changes

[0088] ;

[0089] Table 4. Ranking of Importance under Primary Frequency Modulation

[0090] ;

[0091] Table 5. Ranking of Importance under AGC

[0092] ;

[0093] As shown in Table 2, for voltage dip conditions, for active power, the d-axis PI control parameters of the inner loop of the generator-side current are... The mean is the lowest, while the q-axis PI control parameters of the inner loop of the machine-side current and the PI control parameters of the outer loop (dominant control element) of the machine-side power are... The mean values ​​show a significant difference of 3 to 4 orders of magnitude. For reactive power, the d-axis PI control parameters and q-axis PI control parameters of the machine-side current inner loop... The average values ​​are all at the bottom, which is consistent with the outer loop PI control parameters of the machine-side power. The mean values ​​showed a significant difference of 4 to 7 orders of magnitude, thus simplifying the generator-side current control under this condition. Based on trajectory sensitivity analysis of three operating conditions—primary frequency regulation, sudden wind speed changes, and AGC—the grid-side current inner-loop PI control parameters affect the active / reactive power... / Mean and outer loop PI control parameters of machine-side power under various operating conditions / The mean values ​​show a significant difference of 5 to 9 orders of magnitude, placing them among the less influential variables. Therefore, when performing dynamic full-process simulation modeling for this operating condition, the detailed dynamics of the grid-side current control can be ignored and simplified.

[0094] Step S2: Establish an explicit discretization model of the direct-drive wind turbine covering various operating conditions.

[0095] The model of a direct-drive wind turbine with continuous full-order electromechanical-electromagnetic coupling is as follows:

[0096] (1) Wind turbine:

[0097] Wind turbine wind energy capture power for:

[0098] (13)

[0099] In the formula, Wind speed, in m / s; Air density, unit: kg / m³ 3 ; The radius of the wind turbine is in meters (m). The wind energy utilization coefficient is determined by the pitch angle. Speed ​​ratio of leaf tip We obtain the formula, =0.5176, =116, =0.4, =5, =21, =0.0068, This represents the mechanical angular velocity of the generator.

[0100] (14)

[0101] The mechanical torque generated by the wind turbine generator for:

[0102] (15)

[0103] In the formula, This is the reference power output of the wind turbine.

[0104] In maximum power point tracking mode, the wind turbine generates a reference value for the motor speed. Pick:

[0105] (16)

[0106] (2) Permanent Magnet Synchronous Generator (PMSG):

[0107] The voltage equation of the generator in the dq synchronous reference frame is given by equation (17):

[0108] (17)

[0109] In the formula, and These are the motor output voltage and output current, respectively. , They are respectively Components along the d and q axes; , They are respectively Components along the d and q axes For stator resistance, The electric angular velocity of the generator. and These are the d-axis and q-axis inductances of the generator, respectively. For the permanent magnet flux linkage of the generator.

[0110] magnetic flux linkage under the dq coordinate axis and The equation is:

[0111] (18)

[0112] Electromagnetic torque of generator The equation is:

[0113] (19)

[0114] Electromagnetic power of generator The equation is:

[0115] (20)

[0116] The equation of motion for the generator is:

[0117] (twenty one)

[0118] (twenty two)

[0119] (twenty three)

[0120] in, This represents the number of pole pairs of the motor. The inertia coefficient, This represents the motor speed.

[0121] (3) Machine-side control:

[0122] It employs zero-d-axis vector control and dual closed-loop control consisting of an outer power loop and an inner current loop.

[0123] (twenty four)

[0124] (25)

[0125] In the formula, , These are the proportional coefficient and integral coefficient of the outer loop PI regulation of the machine-side power, respectively; , These are the proportional and integral coefficients of the PI regulation in the inner loop of the machine-side current, respectively. and These are reference values ​​for the motor's d-axis and q-axis output current. and These are the reference values ​​for the motor's d-axis and q-axis output voltages, respectively. For the Laplace operator.

[0126] Considering the control delay of the machine-side converter Motor output voltage The calculation formula is as follows:

[0127] (26)

[0128] In the formula, and These are the output voltages for the motor's d-axis and q-axis, respectively.

[0129] (4) DC voltage side:

[0130] The DC-side energy balance equation is:

[0131] (27)

[0132] In the formula, A capacitor connected in parallel on the DC side. DC voltage , , These are the electromagnetic power on the machine side, the grid-connected power on the grid side, and the unloading power under fault ride-through mode, respectively. The unloading power is 0 under normal operating conditions.

[0133] (5) Grid-side control:

[0134] It adopts grid voltage-oriented control and dual closed-loop control with DC voltage outer loop and current inner loop.

[0135] (28)

[0136] (29)

[0137] In the formula, , These are the proportional coefficient and integral coefficient of the outer loop PI regulation of the grid-side DC voltage, respectively. , These are the proportional and integral coefficients of the PI regulation in the inner loop of the grid-side current, respectively. and These are the reference values ​​for the d-axis and q-axis output currents of the grid-side converter. and These are the reference values ​​for the d-axis and q-axis output voltages of the grid-side converter. This is the DC voltage reference value. , These represent the grid connection point voltages on the d-axis and q-axis, respectively. and For filter impedance, This refers to the power grid frequency.

[0138] Considering the control delay of the grid-side converter is Grid-side converter output voltage The calculation formula is as follows:

[0139] (30)

[0140] In the formula, and These are the d-axis and q-axis output voltages of the grid-side converter, respectively.

[0141] Grid-connected active power and reactive power The expression is:

[0142] (31)

[0143] (6) Phase-locked loop:

[0144] The q-axis component of the filtered grid connection point voltage is input into the PI controller to achieve phase-locked loop (PLL) with the grid voltage, as shown in the following equation:

[0145] (32)

[0146] In the formula, and These are the proportional and integral coefficients of the phase-locked loop PI control. For delay.

[0147] (7) Fault Traversal Module:

[0148] During a fault, the wind turbine switches to a mode that prioritizes providing reactive power support, while using a DC chopper to absorb surplus energy on the DC side and regulate the DC voltage.

[0149] (33)

[0150] (34)

[0151] In the formula, It is the maximum current that the inverter is allowed to output. and These are the rated voltage and rated current, respectively. It is the per-unit value of the grid connection point voltage. and These are the proportional and integral coefficients of the PI controller for releasing energy.

[0152] (7) Pitch angle control:

[0153] When the wind speed exceeds the rated wind speed, the speed feedback-based regulation mode is activated, and the current generator speed and the given reference speed are compared through the PI controller to obtain the pitch angle signal.

[0154] (35)

[0155] In the formula, and These are the proportional and integral coefficients for pitch angle control. It is the pitch control delay.

[0156] (8) Primary frequency regulation and AGC automatic generation control:

[0157] A primary frequency regulation command is generated based on the grid connection frequency obtained from the phase-locked loop, and combined with the AGC automatic generation control command. The combined power is added to the wind turbine's wind energy capture power and used as a reference power for the actual output of the wind turbine, generating mechanical torque which is then input into the motor.

[0158] (36)

[0159] (37)

[0160] In the formula, This is the primary frequency modulation coefficient.

[0161] Based on the above continuous full-order electromechanical-electromagnetic coupled direct-drive wind turbine model, a unified explicit discretization model structure is constructed. Each part of the direct-drive wind turbine is discretized hierarchically, allowing the model to directly adapt to the simulation platform mathematically. This avoids repeated automatic discretization conversions of sub-modules during simulation software operation, significantly reducing solution overhead. Specifically, the forward Euler method is used for unified discretization of control loops such as the turbine-side power outer loop, turbine-side current inner loop, grid-side DC voltage outer loop, grid-side current inner loop, phase-locked loop, time delay, and pitch control. For differential equations with high rigidity and precision sensitivity, such as the motor equations and DC-side energy balance equations, the trapezoidal rule is used for discretization. After completing the hierarchical discretization, the parts are sequentially combined according to the time series, based on the cascade order of the direct-drive wind turbine simulation solution, to establish a unified explicit discretization model.

[0162] For ordinary differential equations of general form, the discretization expressions using the trapezoidal method and the forward Euler method are respectively (39) and (40).

[0163] (38)

[0164] (39)

[0165] (40)

[0166] in, and These represent the current and previous moments in the simulation, respectively. , These are the outputs of the previous time step and the current time step, respectively. This is the simulated step size.

[0167] Equations (14) and (15) are used to discretize the integral components in the continuous full-order electromechanical-electromagnetic coupled direct-drive wind turbine model. The wind turbine model does not contain differential or integral components and therefore does not require discretization. The resulting key dynamic quantities are as follows: The explicit update formula is shown below:

[0168] On the machine side, take The overall solution is given by equations (41)-(48). Wherein, , The wind turbine inputs the signal to the turbine side.

[0169] (41)

[0170] (42)

[0171] (43)

[0172] (44)

[0173] (45)

[0174] (46)

[0175] (47)

[0176] (48)

[0177] In the formula, and These represent the output currents of the motor's d-axis and q-axis, respectively. , , These represent the values ​​of the outer loop integrator of the machine-side power, the d-axis integrator of the inner loop of the machine-side current, and the q-axis integrator of the inner loop of the machine-side current, respectively, at the previous time step.

[0178] Combining the fault ride-through module, the DC side solution is given by equations (49)-(51). Wherein, This is a fault signal, when When this happens, the fault module is activated.

[0179] (49)

[0180] (50)

[0181] (51)

[0182] On the network side, the overall solution is given by equations (52)-(58).

[0183] (52)

[0184] (53)

[0185] (54)

[0186] (55)

[0187] (56)

[0188] (57)

[0189] (58)

[0190] In the formula, The value of the outer loop integrator of the grid-side DC voltage at the previous moment; This refers to the rated output current of the grid-side converter. and These are the d-axis and q-axis integrator values ​​of the inner loop current on the grid side at the previous time step.

[0191] In addition, the pitch angle control and phase-locked loop solutions are equations (59) and (60), respectively.

[0192] (59)

[0193] (60)

[0194] In the formula, The pitch angle is the output of the variable pitch angle PI control. The value of the pitch angle control integrator at the previous moment; The frequency of the output controlled by the phase-locked loop PI control; This is the value of the phase-locked loop integrator at the previous moment.

[0195] Step S3: Approximate the nonlinear coupling terms in the explicit discretization model to obtain the detailed model.

[0196] Solving on the machine side At that time, there is an unknown. Nonlinear product coupling term of motor output current and generator electric angular velocity at time t. , An explicit decoupling process is adopted using a substitution method based on predicted values, utilizing the predicted generator electric angular velocity obtained from the state variables of the previous time step. Replace the unknown generator electric angular velocity Therefore, to solve The coefficient matrices (46) and (47) are updated to equations (61) and (62), and the speed calculation is still obtained by the trapezoidal method according to equation (48).

[0197] ; (5)

[0198] (61)

[0199] (62)

[0200] In the formula, and These are the predicted values ​​of the generator's electrical angular velocity and the generator's mechanical angular velocity, respectively.

[0201] Step S4: Based on the importance analysis results obtained in Step S1, the non-critical control links under different operating conditions in the detailed model are simplified. Specifically:

[0202] Under voltage dip conditions, the machine-side current inner loop control, which is a non-critical control element at this time, is simplified. This invention determines that the current control loop can quickly reach stability and the current can quickly track the reference value. Therefore, the current reference value output by the machine-side control loop is directly assigned to the actual value and algebraically processed, as shown in the following formula:

[0203] (6)

[0204] (7)

[0205] Under conditions of sudden wind speed changes, primary frequency regulation, or AGC automatic generation control, the grid-side current inner loop control, which is a non-critical control link at this time, is simplified. The grid-side simplification principle is the same. This invention determines that the current control link can quickly achieve the control target and the current can quickly track the reference value. Therefore, the current reference value output by the grid-side control link is directly assigned to the actual value and algebraically processed, as shown in the following formula:

[0206] (8)

[0207] (9)

[0208] The above simplified process is applied to the current inner loop control of both the machine side and the grid side under steady state.

[0209] Step S5: Build the switching module and the reset module.

[0210] During the operation of a direct-drive wind turbine, the grid connection point voltage, frequency, wind speed, and AGC active power commands are monitored to determine the system operating condition. To achieve "the grid side calls the detailed model and the turbine side calls the simplified model under voltage drop conditions; the grid side calls the simplified model and the turbine side calls the detailed model under wind speed change, primary frequency regulation, and AGC automatic power generation control conditions; and the turbine and grid sides call the simplified model simultaneously under steady state conditions," this invention constructs a switching module to automatically complete the calling of detailed or simplified models on the turbine and grid sides.

[0211] Considering that direct-drive wind turbines can seamlessly switch from a simplified model back to a detailed model during operation, this invention requires resetting the integrator of the PI regulation of the inner current loop on the turbine side or grid side during switching. Furthermore, when the simplified model is invoked on the turbine side or grid side, the current generated by the inner current loop... , Synchronize separately , The update is performed as shown in equation (10). The expressions for the integrators on the machine side and the network side are shown in equations (11) and (12), respectively. Thus, the present invention constructs a reset module.

[0212] (10)

[0213] (11)

[0214] (12)

[0215] The switching module constructed in this invention determines simplified signals on the generator side and grid side based on the system operating conditions, forming a switching model for generator-side and grid-side control. When the system enters steady-state operation, the switching module determines that both the simplified signals on the generator side and grid side are 1, switching the generator-side and grid-side control to the simplified model to reduce computational complexity. When the system operates under voltage dip conditions, the switching module determines that the generator-side simplified signal remains 1, while the grid-side simplified signal is 0. The switching module switches the grid-side control back to the detailed model, and the reset module performs an integrator reset on the grid-side current inner loop. After the voltage recovers and the system re-enters steady state, the switching module switches the grid-side control back to the simplified model. When the system operates under conditions of sudden wind speed changes, primary frequency regulation, or AGC automatic generation control, the switching module determines the grid-side simplified signal... The value remains 1, while the simplified signal on the turbine side is 0. The switching module switches the turbine-side control back to the detailed model, and the reset module performs an integrator reset on the turbine-side current inner loop. After the voltage recovers and the system re-enters steady state, the switching module switches the turbine-side control back to the simplified model. At any simulation moment, the wind turbine model prioritizes data updates, calculates mechanical torque and power references based on the current wind speed and rotational speed, and uses these as inputs for subsequent turbine-side control and state updates. The generated rotational speed state is further used for the calculation of the wind turbine model at the next moment, thus forming a clear simulation solution process of sequential updates and state transfer under a unified discrete time step.

[0216] Step S6: Construct a direct-drive wind turbine model for multi-condition simulation of wind farms.

[0217] Based on the aforementioned discretization processing, approximate decoupling of nonlinear coupling terms, and simplification of the multi-condition model, the obtained detailed model, simplified model, switching module, and reset module are encapsulated within a unified discrete state space structure. This constructs a direct-drive wind turbine model with an adaptive mechanism that automatically selects between the detailed and simplified models based on the operating state. This invention introduces state consistency maintenance and integrator reset strategies within a unified solution framework, ensuring smooth and continuous switching between different operating conditions without numerical shocks. The resulting unified model architecture features structural consistency, unified interfaces, and strong scalability, allowing direct reuse in multi-machine parallel simulations of wind farms, achieving efficient solution and generalized modeling for multiple operating conditions.

[0218] In summary, this invention analyzes and evaluates the importance of each control component under various operating conditions. Within a unified discretization modeling framework, it implements algebraic or quasi-static approximations for low-importance components, thereby constructing a computationally efficient direct-drive wind turbine model with an adaptive operating condition mechanism. This method can significantly reduce computational complexity while maintaining high fidelity in key dynamics, based on the wind turbine's response characteristics under different operating conditions. This provides a foundation for a single-machine model to achieve structural uniformity, computational efficiency, and strong reusability in multi-condition simulation scenarios.

[0219] like Figure 2 As shown, when a direct-drive wind turbine is operating, the pitch control module generates a pitch angle command based on the turbine's operating status, which serves as input to the turbine model. The turbine model receives the pitch angle command and wind speed information, and calculates the turbine reference power corresponding to the current operating status. This reference power is superimposed on the primary frequency regulation command and the AGC automatic generation control command during the simulation to form the final active power reference, and generates a permanent magnet synchronous generator model with mechanical torque input. In the turbine-side control process, turbine-side control is completed through a cascaded control structure of the power outer loop and the current inner loop. The active power of the turbine side and the grid side interact and act on the DC voltage side model to characterize the energy balance state of the DC bus. In the grid-side control process, different control methods are adopted according to different operating conditions: under non-fault conditions, grid-side control uses DC voltage as the control target and generates a grid-side current reference through the DC voltage loop; under fault conditions such as voltage dips, the grid-side current reference is generated by the fault ride-through control module. The grid side also includes a current inner loop control link, and the grid connection point is connected to the grid through the grid impedance.

[0220] After constructing the direct-drive wind turbine model for multi-condition simulation of wind farms, the simulation process of the model will be described in detail below.

[0221] Reference Figure 3 The specific process of machine-side control is as follows:

[0222] Step S1: The switching module determines the simplified signal on the generator side based on the real-time operating conditions of the system. When the system is operating under conditions of sudden wind speed change, primary frequency regulation, or AGC automatic power generation control, the simplified signal on the generator side is 0, and the switching module switches the generator side control to the detailed model. Then proceed to step S2. When the system is operating under conditions of steady state or voltage drop, the simplified signal on the generator side is 1, and the switching module switches the generator side control to the simplified model. Then proceed to step S3.

[0223] Step S2, the machine side calls the detailed model and executes the following steps:

[0224] 1) Determine whether the model has just switched back from the simplified model. If yes, the reset module resets the machine-side current inner loop integrator, see equation (11). If no, proceed directly to the next step.

[0225] 2) Machine-side power outer loop: Calculate the reference value of the motor output current, see equation (41);

[0226] 3) Machine-side current inner loop: Calculate the reference value of the motor output voltage, see equation (42)-(43); then calculate the motor output voltage, see equation (44);

[0227] 4) Permanent magnet synchronous generator model: First, predict the mechanical angular velocity of the generator, see equation (5), then calculate the motor output current, see equations (45)-(47), then calculate and update the electromagnetic torque and electromagnetic power of the generator in sequence, see equations (19)-(20), and send the electromagnetic power to the generator side power outer loop, then calculate and update the mechanical angular velocity of the generator, see equation (48), and go to step S1;

[0228] Step S3: The simplified model is invoked on the machine side to perform the following steps:

[0229] 1) Machine-side power outer loop: Calculate the reference value of the motor output current, see formula (41);

[0230] 2) Permanent magnet synchronous generator model: Calculate the generator output current, see equation (6), predict the generator mechanical angular velocity, see equation (5);

[0231] 3) Machine-side current inner loop: Calculate the motor output voltage, see equation (7), and use the motor output voltage as the reference value of the motor output voltage by the reset module; see equation (10);

[0232] 4) Permanent magnet synchronous generator model: First, calculate and update the electromagnetic torque and electromagnetic power of the generator in sequence, see equations (19)-(20), and send the electromagnetic power to the generator side power outer loop. Then calculate and update the mechanical angular velocity of the generator, see equation (48), and go to step S1.

[0233] Reference Figure 3 The network-side control process is as follows:

[0234] Step S1: The switching module determines the grid-side simplified signal based on the real-time operating conditions of the system. When the system is operating under voltage drop conditions, the grid-side simplified signal is 0, and the switching module switches the grid-side control to the detailed model. Then proceed to step S2. When the system is operating under steady-state, sudden wind speed change, primary frequency regulation, or AGC automatic generation control conditions, the grid-side simplified signal is 1, and the switching module switches the grid-side control to the simplified model. Then proceed to step S3.

[0235] Step S2, the network side calls the detailed model to perform the following steps:

[0236] 1) Outer loop of grid-side DC voltage: Calculate the reference value of the output current of the grid-side converter, see equations (52)-(53);

[0237] 2) Determine whether the model has just switched back from the simplified model. If yes, the grid-side current inner loop integrator will be reset by the reset module, see equation (12). If no, proceed directly to the next step.

[0238] 3) Inner loop of grid-side current: First, calculate the reference value of grid-side converter output voltage and grid-side converter output voltage in sequence, see equation (54) and equation (55); then calculate the grid-side converter output current, see equation (56)-(58); then calculate the updated grid-connected active power and reactive power, see equation (31), and go to step S1;

[0239] Step S3: The network side calls the simplified model to perform the following steps:

[0240] 1) Outer loop of grid-side DC voltage: Calculate the reference value of the output current of the grid-side converter, see equations (52)-(53);

[0241] 2) Inner loop of grid-side current: First, calculate and update the output current of the grid-side converter, see Equation (8); then calculate the output voltage of the grid-side converter, see Equation (9), and the reset module uses the output voltage of the grid-side converter as the reference value of the output voltage of the grid-side converter, see Equation (10); then calculate and update the grid-connected active power and reactive power, see Equation (31), and go to step S1.

[0242] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0243] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this invention.

Claims

1. A method for constructing a direct-drive wind turbine model for multi-condition simulation of wind farms, characterized in that, include: Step S1: Set up multiple simulation scenarios on the simulation platform to analyze the importance of each control link in the direct-drive wind turbine affecting the grid-connected power output under different operating conditions; Step S2: Perform hierarchical discretization on the direct-drive wind turbine model with continuous full-order electromechanical-electromagnetic coupling to establish an explicit discretization model. Step S3: Approximate the nonlinear coupling terms in the explicit discretization model to obtain the detailed model; Step S4: Based on the importance analysis results of Step S1, the non-critical control links under different working conditions in the detailed model are simplified to obtain a simplified model. Step S5: Construct a switching module and a reset module. The switching module switches between a simplified model and a detailed model for the control on both the machine side and the grid side according to the system operating conditions. When the machine side or the grid side calls the simplified model, the reset module updates the voltage reference value on the machine side or the grid side with the actual value. When the machine side or the grid side calls back to the detailed model from the simplified model, the reset module resets the integrator of the current inner loop on the machine side or the grid side. Step S6: Encapsulate the detailed model, simplified model, switching module, and reset module under a unified discrete state space structure to obtain the direct-drive wind turbine model.

2. The method for constructing a direct-drive wind turbine model for multi-condition simulation of wind farms according to claim 1, characterized in that: In step S1, multiple simulation scenarios are set on the simulation platform under four operating conditions: voltage drop, sudden wind speed change, primary frequency regulation, and AGC automatic power generation control. The median method is used to calculate the trajectory sensitivity of the PI control parameters of each control link in the direct-drive wind turbine to the grid-connected power under different operating conditions. The control link includes the outer loop of the turbine power, the inner loop of the turbine current, the outer loop of the grid DC voltage, the inner loop of the grid current, and the phase-locked loop. （1） （2） （3） （4） In the formula, This represents the original value of the PI control parameter; express The disturbance value; and The PI control parameters are respectively and The corresponding active power at that time; The PI control parameters are The corresponding active power output at that time; and The PI control parameters are respectively and The corresponding reactive power; The PI control parameters are The corresponding reactive power output at that time; and These represent the average trajectory sensitivity of the PI control parameters to active and reactive power during the period of operating condition changes. This indicates the total observation time for trajectory sensitivity; and These represent the initial and current moments of the change in operating conditions, respectively. Based on the average trajectory sensitivity of the PI control parameters of each control loop under each operating condition, the importance of each control loop in affecting grid-connected power output under each operating condition is ranked. The results are as follows: Under voltage dip conditions, the average trajectory sensitivity of the PI control parameters of the generator-side current inner loop is relatively the smallest, indicating that the generator-side current inner loop has the least impact on grid-connected power output. Therefore, the generator-side current inner loop is a non-critical control loop under this condition. Under wind speed change, primary frequency regulation, or AGC automatic generation control conditions, the average trajectory sensitivity of the PI control parameters of the grid-side current inner loop is relatively the smallest, indicating that the grid-side current inner loop has the least impact on grid-connected power output. Therefore, the grid-side current inner loop is a non-critical control loop under these three operating conditions.

3. The method for constructing a direct-drive wind turbine model for multi-condition simulation of wind farms according to claim 2, characterized in that: In step S2, the forward Euler method is used to discretize the outer loop of the turbine power, the inner loop of the turbine current, the outer loop of the grid DC voltage, the inner loop of the grid current, the phase-locked loop, the delay element, and the pitch control element in the continuous full-order electromechanical electromagnetic coupling direct-drive wind turbine model. The trapezoidal method is used to discretize the motor equations and the DC-side energy balance equations in the continuous full-order electromechanical electromagnetic coupling direct-drive wind turbine model. After completing the aforementioned hierarchical discretization, according to the cascade order of the simulation solution of the direct-drive wind turbine, the parts are combined in an orderly manner according to the time series to establish a unified explicit discretization model.

4. The method for constructing a direct-drive wind turbine model for multi-condition simulation of wind farms according to claim 3, characterized in that: In step S3, for the nonlinear product coupling terms of the motor output current and generator electric angular velocity at unknown times in the explicit discretized model, an explicit decoupling process is performed using a substitution method based on predicted values. The predicted generator electric angular velocity obtained from the state variables at the previous time step is used to replace the unknown generator electric angular velocity. The calculation formula for the predicted generator electric angular velocity is as follows: ； （5） In the formula, and These represent the current and previous moments in the simulation, respectively. and These are the predicted values ​​of the generator's electrical angular velocity and the generator's mechanical angular velocity, respectively. This represents the number of pole pairs of the generator; The mechanical angular velocity of the generator; This is for simulating step size; The generator's inertia coefficient; This refers to the electromagnetic torque of the generator. This represents the mechanical torque of the generator.

5. The method for constructing a direct-drive wind turbine model for multi-condition simulation of wind farms according to claim 4, characterized in that: In step S4, based on the importance analysis results obtained in step S1, the non-critical control links under different working conditions in the detailed model are simplified. Under voltage drop conditions, the machine-side current inner loop control, which is a non-critical control link at this time, is simplified as follows: Equation (6) - Equation (7); （6） （7） In the formula, and These represent the output currents of the motor's d-axis and q-axis, respectively. This is the reference value for the q-axis output current of the motor; and These represent the output voltages of the motor's d-axis and q-axis, respectively. For generator inductance; For generator stator resistance; For the permanent magnet flux linkage of the generator; Under the conditions of sudden wind speed change, primary frequency regulation or AGC automatic generation control, the grid-side current inner loop control, which is a non-critical control link at this time, is simplified as follows: Equation (8)-Equation (9); （8） （9） In the formula, and These represent the d-axis and q-axis output currents of the grid-side converter, respectively. This is the reference value for the d-axis output current of the grid-side converter; and These represent the d-axis and q-axis output voltages of the grid-side converter, respectively. and These represent the grid connection point voltages on the d-axis and q-axis, respectively. and For filtering impedance; The power grid frequency; The current inner loop control on both the machine side and the grid side is simplified under steady-state conditions.

6. The method for constructing a direct-drive wind turbine model for multi-condition simulation of wind farms according to claim 5, characterized in that: In step S5, the reset module uses the following formula (10) to update the reference value of the motor output voltage and the reference value of the grid-side converter output voltage. The reset module uses the following formulas (11) and (12) to perform integrator reset on the machine-side and grid-side current inner loop. （10） （11） （12） In the formula, and These are the reference values ​​for the motor's d-axis and q-axis output voltages, respectively. and These are the reference values ​​for the d-axis and q-axis output voltages of the grid-side converter, respectively. and These represent the integrator values ​​for the d-axis and q-axis of the inner loop of the machine-side current, respectively. and These represent the integrator values ​​for the d-axis and q-axis of the inner loop of the grid-side current, respectively. and These represent the integral coefficients of the PI regulation within the inner loop of the current on the machine side and the grid side, respectively.

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