Direct-driven fan model construction method oriented to wind field multi-working-condition simulation

Abstract

The invention discloses a direct-driven fan model construction method oriented to multi-working-condition simulation of a wind field. The method comprises the following steps: S1, analyzing the importance degree of influence of each control link in a direct-driven wind turbine generator on grid-connected power output under different working conditions; s2, layered discretization processing is carried out on the continuous full-order electromechanical electromagnetic coupling direct-driven wind turbine generator model, and an explicit discretization model is established; s3, performing approximate processing on nonlinear coupling terms in the explicit discretization model to obtain a detailed model; s4, performing algebraic simplification processing on non-critical control links in the detailed model under different working conditions to obtain a simplified model; s5, constructing a switching module and a resetting module; and S6, packaging the detailed model, the simplified model, the switching module and the resetting module in a unified discrete state space structure to obtain the direct-driven fan model for wind field multi-working-condition simulation. According to the method, collaborative balance of key dynamic high fidelity and calculation reduction in multi-working-condition simulation of the wind field can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wind farm simulation technology, and particularly refers to a direct-drive wind turbine model construction method for wind farm multi-working condition simulation. BACKGROUND

[0002] As a key dynamic unit of wind farm simulation and power system transient analysis, the model accuracy of a wind turbine directly affects the reliability of wind farm simulation. In a complex wind farm environment with a high proportion of wind power connected to the grid, a permanent magnet direct-drive wind turbine needs to cover multiple operating conditions such as normal grid connection, fault ride-through, wind speed sudden change, AGC automatic power generation control, and primary frequency response. There is significant nonlinear strong coupling and multi-time scale dynamic interaction between the machine-side converter, the DC bus, and the grid-side converter.

[0003] Currently, the commonly used wind turbine simulation model in the industry is mostly based on the traditional electromechanical transient general model system. In order to balance generality and solving speed, such models are usually modeled in a single time scale or the variable flow control part is greatly reduced, which weakens or breaks the cross-scale coupling between different control loops, and the key coupling terms are directly simplified or ignored, resulting in 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 restore the dynamic interaction of wind turbine electromagnetic details and control logic more completely, it mainly uses a unified dimension and equation structure, with high model state dimension and dense nonlinear coupling terms, and the calculation overhead grows rapidly with the combination of working conditions, which is particularly evident when the wind farm modeling scale expands, easily causing simulation time extension, "dimension disaster", and resource bottlenecks, and cannot meet the strict requirements of model lightweight and fast convergence in large-scale wind farm efficient multi-working condition batch simulation or long-term-transient integrated simulation scenarios.

[0005] Therefore, the existing wind turbine modeling system still faces systematic technical contradictions and engineering constraints in terms of multi-working condition distinguishable unified representation, multi-scale interaction faithful solving, nonlinear strong coupling stable processing, model reduction and calculation coordination, and precision-efficiency balance mechanism establishment. A direct-drive wind turbine general modeling framework with multi-working condition adaptability, mode switching dynamic fidelity, key coupling interaction reservation, and high-efficiency calculation scalable solving capability is needed to support the application requirements of unified model architecture reuse, fast update solving, and cross-platform adaptation in future large-scale wind farm multi-working condition simulation. SUMMARY

[0006] In order to realize the coordinated balance of key dynamic high fidelity and calculation reduction in wind farm multi-working condition simulation, the present application provides a direct-drive wind turbine model construction method for wind farm multi-working condition simulation.

[0007] In order to solve the above technical problems, the present application adopts the following technical method: a direct-drive wind turbine model construction method for wind farm multi-working condition simulation, comprising: Step S1, setting multiple simulation scenes on a simulation platform, and analyzing the importance of each control link in the direct-drive wind turbine under different working conditions to grid-connected power output; Step S2, using trapezoidal method and forward Euler method to perform layered discretization processing on the direct-drive wind turbine model with continuous full-order electromechanical electromagnetic coupling, and according to the cascade order of the direct-drive wind turbine simulation solution, sequentially combining each part according to time sequence to establish a unified explicit discretization model; Step S3, performing approximation processing on the nonlinear coupling terms in the explicit discretization model to obtain a detailed model; Step S4, according to the importance analysis result obtained in step S1, performing algebraization or quasi-static approximation simplification processing on the non-key control links in the detailed model under different working conditions to obtain a simplified model; Step S5, constructing a switching module and a reset module; The switching module switches the model for the machine side and the grid side control according to the system running working condition: when the system enters a steady state working condition, the switching module switches the machine side and the grid side control to the simplified model; when the system runs in a voltage drop working condition, the switching module switches the grid side control back to the detailed model; when the system runs in a wind speed mutation, primary frequency modulation or AGC automatic generation control working condition, the switching module switches the machine side control back to the detailed model; When the machine side or the grid side control is switched 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 the grid side control is switched from the simplified model back to the detailed model, the reset module performs integrator reset on the machine side or the grid side current inner loop; Step S6, packaging the detailed model, the simplified model, the switching module and the reset module in a unified discrete state space structure to obtain a direct-drive wind turbine model for wind farm multi-working condition simulation.

[0008] Further, in step S1, multiple simulation scenes under four working conditions of voltage drop, wind speed mutation, primary frequency modulation and AGC automatic generation control are set on the simulation platform, the trajectory sensitivity of PI control parameters of each control link in the direct-drive wind turbine to grid-connected power under different working conditions is calculated by using median method, and the control link includes the machine side power outer loop, the machine side current inner loop, the grid side DC voltage outer loop, the grid side current inner loop and the phase-locked loop; (1) (2) (3) (4) wherein, denotes the original value of the PI control parameter; denotes the disturbance value of ; and are the corresponding active power when the PI control parameter is and respectively; is the corresponding output active power when the PI control parameter is ; and are the corresponding reactive power when the PI control parameter is and respectively; is the corresponding output reactive power when the PI control parameter is ; and are the average values of the trajectory sensitivity of the PI control parameter to active power and reactive power respectively during the change of the working condition; denotes the total trajectory sensitivity observation duration; and denote the initial time and the current time of the change of the working condition respectively; According to the calculated average values of the trajectory sensitivity of the PI control parameter of each control link corresponding to each working condition, the importance of each control link to the grid-connected power output under each working condition is sorted, and it is obtained that: under the voltage drop working condition, the average value of the trajectory sensitivity of the PI control parameter of the machine-side current inner loop is relatively minimum, indicating that the machine-side current inner loop has the minimum influence on the grid-connected power output, and the machine-side current inner loop is a non-critical control link under this working condition; under the wind speed mutation, primary frequency modulation or AGC automatic generation control working condition, the average values of the trajectory sensitivity of the PI control parameters of the grid-side current inner loop are all relatively minimum, indicating that the grid-side current inner loop has the minimum influence on the grid-connected power output, and the grid-side current inner loop is a non-critical control link under the three types of working conditions.

[0009] Further, in the step S2, the forward Euler method is used to discretize the machine-side power outer loop, the machine-side current inner loop, the grid-side DC voltage outer loop, the grid-side current inner loop, the phase-locked loop, the time delay link and the variable pitch control link in the continuous full-order electromechanical electromagnetic coupled direct-driven wind turbine model, the trapezoidal method is used to discretize the motor equation and the DC side energy balance equation in the continuous full-order electromechanical electromagnetic coupled direct-driven wind turbine model, after the foregoing hierarchical discretization, according to the cascade order of the direct-driven wind turbine simulation solution, each part is sequentially combined according to the time sequence, and a unified explicit discretization model is established.

[0010] Further, the step S3, for the nonlinear product coupling term of the motor output current and the generator electric angular velocity at unknown time in the explicit discretization model, an explicit decoupling processing is carried out by using a prediction value based substitution method, the generator electric angular velocity prediction value derived by using the state quantity at the last time is used to replace the unknown generator electric angular velocity, and the calculation formula of the generator electric angular velocity prediction value is as follows: ; (5) In the formula, and respectively represent the current time and the previous time of simulation; and are the generator electric angular velocity prediction value and the generator mechanical angular velocity prediction value respectively; is the number of generator pole pairs; is the generator mechanical angular velocity; is the simulation step; is the generator inertia coefficient; is the generator electromagnetic torque; is the generator mechanical torque.

[0011] Further, the step S4, according to the importance degree analysis result obtained in the step S1, the non-key control link under different working conditions in the detailed model is simplified; In the voltage drop working condition, the machine side current inner loop control which is the non-key control link at this time is simplified, and the current reference value output by the machine side control link is directly assigned to the actual value for algebraic processing, as follows: (6) (7) In the formula, and respectively represent the motor d-axis and q-axis output current; is the motor q-axis output current reference value; and respectively represent the motor d-axis and q-axis output voltage; is the generator inductance; is the generator stator resistance; is the generator permanent magnet flux linkage; In the wind speed mutation, primary frequency modulation or AGC automatic power generation control working condition, the network side current inner loop control which is the non-key control link at this time is simplified, and the current reference value output by the network side control link is directly assigned to the actual value for algebraic processing, as follows: (8) (9) wherein, and idqgrid represent grid-side converter d-axis and q-axis output currents; idqgrid represent grid-side converter d-axis and q-axis output currents; and idqgrid represent grid-side converter d-axis and q-axis output currents; and idqgrid represent grid-side converter d-axis and q-axis output currents; and Zf represents filter impedance; ω represents grid frequency; The current inner loop control of the machine side and the grid side is simplified at the same time in the steady state.

[0012] Further, the process of the machine side control is as follows: Step S1, the switching module determines the machine side simplified signal according to the real-time operation condition of the system, when the system operates in the wind speed mutation, primary frequency modulation or AGC automatic generation control condition, the machine side simplified signal is 0, the switching module switches the machine side control to the detailed model, and enters step S2, when the system operates in the steady state, voltage drop condition, the machine side simplified signal is 1, the switching module switches the machine side control to the simplified model, and enters step S3; Step S2, the machine side calls the detailed model to execute the following steps: 1) judge whether it is just switched back from the simplified model, if yes, reset the machine side current inner loop integrator by the reset module, if not, directly enter the next step; 2) machine side power outer loop: calculate the motor output current reference value; 3) machine side current inner loop: calculate the motor output voltage reference value, motor output voltage in turn; 4) permanent magnet synchronous generator model: first predict the generator mechanical angular velocity, then calculate the motor output current, then calculate the updated electromagnetic torque and electromagnetic power of the generator in turn, and send the electromagnetic power to the machine side power outer loop, and then calculate the updated mechanical angular velocity of the generator, and turn to step S1; Step S3, the machine side calls the simplified model to execute the following steps: 1) machine side power outer loop: calculate the motor output current reference value; 2) permanent magnet synchronous generator model: calculate the motor output current, and predict the generator mechanical angular velocity; 3) machine side current inner loop: calculate the motor output voltage, and the motor output voltage is taken as the motor output voltage reference value by the reset module; 4) permanent magnet synchronous generator model: first calculate the updated electromagnetic torque and electromagnetic power of the generator in turn, and send the electromagnetic power to the machine side power outer loop, and then calculate the updated mechanical angular velocity of the generator, and turn to step S1.

[0013] Further, the process of the grid side control is as follows: Step S1, the switching module determines the grid side simplified signal according to the real-time running condition of the system, when the system runs in voltage drop condition, the grid side simplified signal is 0, the switching module switches the grid side control to the detailed model, and enters step S2, when the system runs in steady state, wind speed mutation, primary frequency modulation or AGC automatic power generation control condition, the grid side simplified signal is 1, the switching module switches the grid side control to the simplified model, and enters step S3; Step S2, the grid side calls the detailed model to execute the following steps: 1) grid side DC voltage outer ring: calculate the grid side converter output current reference value; 2) judge whether it is just switched back from the simplified model, if yes, reset the grid side current inner loop integrator by the reset module, if not, directly enter the next step; 3) grid side current inner loop: first calculate the grid side converter output voltage reference value, grid side converter output voltage in turn; then calculate the grid side converter output current; finally calculate the updated grid-connected active power and reactive power, and go to step S1; Step S3, the grid side calls the simplified model to execute the following steps: 1) grid side DC voltage outer ring: calculate the grid side converter output current reference value; 2) grid side current inner loop: first calculate the updated grid side converter output current; then calculate the grid side converter output voltage, and reset the grid side converter output voltage as the grid side converter output voltage reference value by the reset module; finally calculate the updated grid-connected active power and reactive power, and go to step S1.

[0014] Preferably, in step S5, the reset module updates the motor output voltage reference value and the grid side converter output voltage reference value by the following formula (10), and the reset module performs integrator reset on the machine side and grid side current inner loop by the following formula (11) and formula (12); (10) (11) (12) In the formula, and are the motor d-axis and q-axis output voltage reference values respectively; and are the grid side converter d-axis and q-axis output voltage reference values respectively; and represent the integrator values of the machine side current inner loop d-axis and q-axis respectively; and respectively represent the integrator values of the d-axis and q-axis of the grid-side current inner loop; and respectively represent the integral coefficients of the PI regulation of the machine-side and grid-side current inner loop.

[0015] The direct-drive wind turbine model construction method for wind farm multi-working condition simulation provided by the application quantitatively evaluates the influence degree of each control link on the key grid-connected power output under different working conditions through trajectory sensitivity calculation, and accurately identifies the dominant dynamic of the unit operation behavior. Based on this, algebraization and quasi-static approximation processing are implemented on the low-sensitivity and fast-stable control link in the unified discretization architecture, which significantly reduces the number of integral state quantities and the complexity of iterative solution. While ensuring the complete expression of the key dynamic link and important control interaction, the full model solving dimension and nonlinear iteration scale are effectively reduced, thereby realizing the collaborative balance of high-fidelity dynamic characteristics and calculation efficiency under multi-working condition simulation. In addition, the continuous full-order electromechanical-electromagnetic coupling model is uniformly converted into an explicit solvable discrete state space structure, and the local model of different complexity levels is switched by working condition. On this basis, through the integrator reset and state consistency maintenance strategy, the non-impact switching between the detailed model and the simplified model is realized, and the numerical stability in the model switching process is ensured. Since all the multi-working condition models are packaged based on the unified discrete framework and share consistent solving process and interface structure, the application effectively improves the reusability and expandability of the model in the multi-machine parallel simulation of the wind farm, enables the wind farm-level simulation to realize large-scale acceleration under the premise of maintaining consistent accuracy, and provides an efficient, unified and expandable modeling basis for multi-working condition wind farm-grid collaborative simulation. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a flowchart of the direct-drive wind turbine model construction method for wind farm multi-working condition simulation provided by the application; Figure 2 is a working principle block diagram of the direct-drive wind turbine provided in the application; Figure 3 is an architecture diagram of the direct-drive wind turbine model for wind farm multi-working condition simulation provided by the application. DETAILED DESCRIPTION

[0017] In order to facilitate the understanding of those skilled in the art, the application will be further described below in conjunction with the embodiments and the drawings. The content mentioned in the embodiments is not a limitation of the application.

[0018] As shown in Figure 1 , a direct-drive wind turbine model construction method for wind farm multi-working condition simulation, specifically comprising the following steps.

[0019] Step S1, set multiple simulation scenarios on MATLAB or PSCAD simulation platform, analyze the importance of each control link in direct-drive wind turbine under different operating conditions to grid-connected power output.

[0020] Set multiple simulation scenarios of different depths under four operating conditions of voltage drop, wind speed mutation, primary frequency modulation, AGC (Automatic Generation Control) automatic generation control, as follows: (a) Voltage drop: grid voltage drops to 30%, 50%, 80% of the rated voltage, each drop lasts for 0.05s; (b) Wind speed mutation: wind speed increases by 1m / s and decreases by 1m / s within 3 to 8 seconds from the rated wind speed; (c) Primary frequency modulation: grid point frequency drops by 0.05Hz, -0.05Hz, 0.15Hz, -0.15Hz, each drop lasts for 15s; (d) AGC automatic generation control: given active power instruction increases by 4%, -4%, -8% from the rated power.

[0021] Calculate the trajectory sensitivity of PI control parameters of each control link in direct-drive wind turbine to grid-connected power under different operating conditions by median method, as follows (1)-(4), control links include machine-side power outer loop, machine-side current inner loop, grid-side DC voltage outer loop, grid-side current inner loop, and phase-locked loop, machine-side power outer loop PI control parameters include proportional coefficient and integral coefficient in machine-side power outer loop PI regulation; grid-side DC voltage outer loop PI control parameters include proportional coefficient and integral coefficient in grid-side DC voltage outer loop PI regulation; phase-locked loop PI control parameters include proportional coefficient and integral coefficient in phase-locked loop PI regulation; machine-side current inner loop PI control parameters include proportional coefficient and integral coefficient in machine-side current inner loop d-axis PI regulation and proportional coefficient and integral coefficient in machine-side current inner loop q-axis PI regulation; grid-side current inner loop PI control parameters include proportional coefficient and integral coefficient in grid-side current inner loop d-axis PI regulation and proportional coefficient and integral coefficient .

[0022] Under original PI control parameters The disturbance value is set to 1% on the basis of and The influence of the PI control parameters on the power output is calculated according to formula (1) and formula (2) respectively, the active power and reactive power trajectory curves of the direct-drive wind turbine output are recorded, then the average values of the trajectory sensitivity of the PI control parameters to the active power and the reactive power during the working condition change are calculated according to formula (3) and formula (4) , .

[0023] (1) (2) (3) (4) In the formula, represents the original value of the PI control parameter; represents the disturbance value of ; and are the corresponding active powers when the PI control parameters are and , respectively; is the corresponding output active power when the PI control parameter is ; and are the corresponding reactive powers when the PI control parameters are and , respectively; is the corresponding output reactive power when the PI control parameter is ; and are the average values of the trajectory sensitivity of the PI control parameters to the active power and the reactive power during the working condition change, respectively; represents the total trajectory sensitivity observation duration; and represent the initial time and the current time of the working condition change, respectively.

[0024] According to the average values of the trajectory sensitivity of the PI control parameters corresponding to each control link under each working condition, the importance of each control link to the grid-connected power output under each working condition is sorted, in the embodiment, the trajectory sensitivity analysis is performed on a 2MW wind turbine, the simulation parameters are as shown in Table 1, and the importance sorting results are as shown in Tables 2-5, it is worth noting that each value in Tables 2-5 actually represents the (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.

[0025] Table 1 Simulation Parameters ; Table 2. Ranking of Importance under Voltage Dips ; Table 3. Ranking of Importance under Sudden Wind Speed ​​Changes ; Table 4. Ranking of Importance under Primary Frequency Modulation ; Table 5. Ranking of Importance under AGC ; 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.

[0026] Step S2: Establish an explicit discretization model of the direct-drive wind turbine covering various operating conditions.

[0027] The model of a direct-drive wind turbine with continuous full-order electromechanical-electromagnetic coupling is as follows: (1) Wind turbine: Wind turbine wind energy capture power for: (13) 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.

[0028] (14) The mechanical torque generated by the wind turbine generator for: (15) In the formula, This is the reference power output of the wind turbine.

[0029] In maximum power point tracking mode, the wind turbine generates a reference value for the motor speed. Pick: (16) (2) Permanent Magnet Synchronous Generator (PMSG): The voltage equation of the generator in the dq synchronous reference frame is given by equation (17): (17) 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.

[0030] magnetic flux linkage under the dq coordinate axis and Equation is: (18) Electromagnetic torque of generator Equation is: (19) Electromagnetic power of generator Equation is: (20) Equation of motion of generator is: (21) (22) (23) Wherein, is the number of motor pole pairs, is the inertia coefficient, is the motor speed.

[0031] (3) Machine side control: Adopt zero d-axis vector control, double closed loop control of power outer ring and current inner ring.

[0032] (24) (25) In the formula, , The proportional coefficient and integral coefficient of machine side power outer ring PI regulation are respectively; , The proportional coefficient and integral coefficient of machine side current inner ring PI regulation are respectively, and The motor d-axis and q-axis output current reference value are respectively, and The motor d-axis and q-axis output voltage reference value are respectively, is the Laplace operator.

[0033] Considering that the machine side converter exists control delay is The calculation formula of motor output voltage is as follows: (26) In the formula, and The motor d-axis and q-axis output voltage are respectively.

[0034] (4) DC voltage side: The DC side energy balance equation is: (27) In the formula, C is a capacitor connected in parallel on the DC side, V is a DC voltage, , , respectively, the electromagnetic power on the machine side, the grid-side grid-connected power, and the unloading power in the fault ride-through mode, the unloading power is 0 in the normal working condition.

[0035] (5) Grid-side control: The grid voltage is oriented, and the double closed-loop control of the DC voltage outer ring and the current inner ring is adopted.

[0036] (28) (29) In the formula, , respectively, the proportional coefficient and the integral coefficient of the grid-side DC voltage outer ring PI regulation; , respectively, the proportional coefficient and the integral coefficient of the grid-side current inner ring PI regulation, and are the d-axis and q-axis output current references of the grid-side converter, and are the d-axis and q-axis output voltage references of the grid-side converter, V is the DC voltage reference, , respectively, the d-axis and q-axis grid-connected point voltages, and are the filter impedances, is the grid frequency.

[0037] Considering the control delay of the grid-side converter as , the calculation formula of the grid-side converter output voltage is as follows: (30) In the formula, and are the d-axis and q-axis output voltages of the grid-side converter.

[0038] The expressions of the grid-side active power and the reactive power are as follows: (31) (6) Phase-locked loop: The q-axis component of the filtered grid-connected point voltage is input to the PI controller, so as to realize the phase-locked loop of the grid voltage, as follows: (32) In the formula, and are the proportional and integral coefficients of the phase-locked loop PI regulator, respectively, is the delay.

[0039] (7) Fault ride-through module: During the fault, the wind turbine switches to a working mode prioritizing the provision of reactive power support, while using the DC chopper to absorb the surplus energy on the DC side and regulate the DC voltage.

[0040] (33) (34) where, is the maximum current allowed by the inverter to output, and are the rated voltage and rated current, respectively, is the grid point voltage reference, and are the proportional and integral coefficients of the discharge energy PI controller, respectively.

[0041] (7) Variable pitch angle control: When the wind speed exceeds the rated wind speed, the regulation mode based on speed feedback is enabled, and the current speed of the generator is compared with the given reference speed to obtain the pitch angle signal through the PI controller.

[0042] (35) where, and are the proportional and integral coefficients of the variable pitch angle control, respectively, is the variable pitch control delay.

[0043] (8) Primary frequency regulation and AGC automatic generation control: The primary frequency regulation instruction is generated according to the grid frequency obtained by the phase-locked loop, and the AGC automatic generation control instruction is added, superimposed on the wind energy capture power of the wind turbine, as the reference power of the actual output of the wind turbine, to generate mechanical torque, input to the motor.

[0044] (36) (37) where, is the primary frequency regulation coefficient.

[0045] Based on the above continuous full-order electromechanical-magnetic coupling direct-drive wind turbine model, a unified explicit discretization model structure is constructed. The various parts of the direct-drive wind turbine are discretized hierarchically, so that the model is directly adapted to the simulation platform in mathematical structure, avoiding repeated automatic discretization conversion of each sub-module by the simulation software in the running stage, thereby significantly reducing the solving overhead. Among them, for the machine-side power outer loop, machine-side current inner loop, grid-side DC voltage outer loop, grid-side current inner loop, phase-locked loop, delay, variable pitch and other control links, the forward Euler method is used for unified discretization. For the differential equations with high rigidity and sensitive to precision such as motor equation and DC side energy balance equation, trapezoidal method is used for discretization. After the above hierarchical discretization is completed, according to the series order of direct-drive wind turbine simulation solving, each part is sequentially combined in time sequence to establish a unified explicit discretization model.

[0046] For ordinary differential equations of general form, the expressions of trapezoidal method and forward Euler method for discretization are formula (39) and (40) respectively.

[0047] (38) (39) (40) wherein, and represent the current time and the previous time of the simulation respectively; , are the outputs of the last time and the current time respectively, is the simulation step size.

[0048] Use formula (14) and (15) to discretize the integral part in the continuous full-order electromechanical-magnetic coupling direct-drive wind turbine model, wherein the wind turbine model does not contain differential and integral links, and does not need to be discretized. The explicit update formula of each key dynamic quantity at the current time is as follows: At the machine side, take , and the overall solution formula is formula (41)-(48). Among them, , are input from the wind turbine to the machine side.

[0049] (41) (42) (43) (44) (45) (46) (47) (48) In the formula, and respectively represent the motor d-axis and q-axis output currents; , , are respectively the machine-side power outer loop integrator value, the machine-side current inner loop d-axis integrator value, and the machine-side current inner loop q-axis integrator value at the previous time.

[0050] In combination with the fault ride-through module, the DC side solving formula is formula (49)-(51). Wherein, is a fault signal, when , the fault module is started.

[0051] (49) (50) (51) On the grid side, the overall solving formula is formula (52)-(58).

[0052] (52) (53) (54) (55) (56) (57) (58) In the formula, is the grid-side DC voltage outer loop integrator value at the previous time; is the grid-side converter rated output current; and are respectively the grid-side current inner loop d-axis and q-axis integrator values at the previous time.

[0053] In addition, the variable pitch angle control and phase-locked loop solving formula are respectively formula (59), (60).

[0054] (59) (60) In the formula, is the pitch angle of the pitch angle PI control output; 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 represents the value of the phase-locked loop integrator at the previous moment.

[0055] Step S3: Approximate the nonlinear coupling terms in the explicit discretization model to obtain the detailed model.

[0056] 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).

[0057] ; (5) (61) (62) In the formula, and These are the predicted values ​​of the generator's electrical angular velocity and the generator's mechanical angular velocity, respectively.

[0058] 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: 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: (6) (7) 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: (8) (9) The above simplified process is applied to the current inner loop control of both the machine side and the grid side under steady state.

[0059] Step S5: Build the switching module and the reset module.

[0060] 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.

[0061] 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.

[0062] (10) (11) (12) The switching module constructed in the application determines the simplified signals of the machine side and the grid side according to the system operating conditions, and switches the control models of the machine side and the grid side. When the system enters a steady state condition, the switching module determines that the simplified signals of the machine side and the grid side are both 1, and switches the control of the machine side and the grid side to the simplified model to reduce the calculation complexity; when the system operates in a voltage drop condition, the switching module determines that the simplified signal of the machine side is still 1, while the simplified signal of the grid side is 0, the switching module switches the control of the grid side back to the detailed model, and the reset module performs integrator reset on the current inner loop of the grid side, and after the voltage recovers and the system reenters the steady state, the switching module switches the control of the grid side to the simplified model again; when the system operates in a wind speed mutation, primary frequency modulation or AGC automatic generation control condition, the switching module determines that the simplified signal of the grid side is still 1, while the simplified signal of the machine side is 0, the switching module switches the control of the machine side back to the detailed model, and the reset module performs integrator reset on the current inner loop of the machine side, and after the voltage recovers and the system reenters the steady state, the switching module switches the control of the machine side to the simplified model again; at any simulation time, the wind turbine model is preferentially updated, the mechanical torque and power reference are calculated according to the current wind speed and speed, and are used as the input of the subsequent machine side control and state update, and the generated speed state is further used for the calculation of the wind turbine model at the next moment, so that an explicit sequential update and state transmission simulation solution process is formed under the unified discrete time step.

[0063] Step S6, a direct-driven wind turbine model oriented to multi-condition simulation of a wind farm is constructed.

[0064] On the basis of the above-mentioned discretization processing, approximate decoupling of nonlinear coupling terms and sub-condition model simplification, the obtained detailed model, simplified model, switching module and reset module are packaged in a unified discrete state space structure to construct a direct-driven wind turbine model with a condition-adaptive mechanism of automatically selecting a detailed model or a simplified model according to an operating state. The model is kept smooth and continuous in switching between different conditions without numerical shock by introducing the state consistency maintenance and integrator reset strategy in the unified solution framework, and finally the unified model architecture has the characteristics of consistent structure, unified interface and strong scalability, can be directly reused in multi-machine parallel simulation of a wind farm, and realizes efficient solution and universal modeling oriented to multi-condition scenarios.

[0065] In summary, the importance of each control link under multiple conditions is analyzed and evaluated, and algebraization or quasi-static approximation is implemented for low importance links in a unified discretization modeling framework, so as to construct a reduced calculation direct-driven wind turbine model with a condition-adaptive mechanism. The method can significantly reduce the calculation complexity while keeping the key dynamic high fidelity according to the response characteristics of the wind turbine in different operating conditions, so that the single machine model realizes the modeling ability of unified structure, efficient calculation and strong reusability in the multi-condition simulation scenario.

[0066] AsFigure 2 As shown, the direct-drive wind turbine is operating, the pitch control module generates the pitch angle command according to the wind turbine operating state as the input of the wind turbine model. The wind turbine model receives the pitch angle command and wind speed information, calculates the wind turbine reference power corresponding to the current operating state. The reference power is superimposed with the primary frequency modulation command and the AGC automatic generation control command in the simulation process to form the final active power reference, and generates the mechanical torque input permanent magnet synchronous generator model. In the process of machine side control, the cascade control structure of power outer loop and current inner loop is used to complete the machine side control. The active power interaction of machine side and grid side acts on the DC voltage side model, which is used to represent the energy balance state of the DC bus. In the process of grid side control, different control modes are adopted according to different operating conditions: in the non-fault operating condition, the grid side control takes the DC voltage as the control target, and generates the grid side current reference through the DC voltage loop; in the fault operating condition such as voltage drop, the grid side current reference is generated by the fault ride-through control module. The grid side also contains the current inner loop control link, and the grid point is connected to the power grid through the grid impedance.

[0067] After the direct-drive wind turbine model for wind farm multi-condition simulation is constructed, the simulation process of the model is specifically described.

[0068] Referring to Figure 3 , the process of machine side control is as follows: Step S1, the switching module determines the machine side simplified signal according to the real-time operating condition of the system. When the system operates in the wind speed mutation, primary frequency modulation or AGC automatic generation control condition, the machine side simplified signal is 0, the switching module switches the machine side control to the detailed model, and enters step S2. When the system operates in the steady state, voltage drop condition, the machine side simplified signal is 1, the switching module switches the machine side control to the simplified model, and enters step S3; Step S2, the machine side calls the detailed model to execute the following steps: 1) judge whether it is just switched back from the simplified model, if yes, reset the machine side current inner loop integrator by the reset module, see formula (11), if not, directly enter the next step; 2) machine side power outer loop: calculate the motor output current reference value, see formula (41); 3) machine side current inner loop: calculate the motor output voltage reference value, see formula (42)-(43); then calculate the motor output voltage, see formula (44); 4) permanent magnet synchronous generator model: first predict the generator mechanical angular velocity, see formula (5), then calculate the motor output current, see formula (45)-(47), then calculate the updated electromagnetic torque and electromagnetic power of the generator in turn, see formula (19)-(20), and send the electromagnetic power to the machine side power outer loop, and then calculate the updated generator mechanical angular velocity, see formula (48), go to step S1; Step S3, the machine side calls the simplified model to execute the following steps: 1) Machine side power outer loop: calculate the motor output current reference value, see equation (41); 2) Permanent magnet synchronous generator model: calculate the motor output current, see equation (6), and predict the generator mechanical angular velocity, see equation (5); 3) Machine side current inner loop: calculate the motor output voltage, see equation (7), and take the motor output voltage as the motor output voltage reference value by the reset module; see equation (10); 4) Permanent magnet synchronous generator model: first, calculate the updated generator electromagnetic torque and electromagnetic power in sequence, see equations (19)-(20), and send the electromagnetic power to the machine side power outer loop, and then calculate the updated generator mechanical angular velocity, see equation (48), and go to step S1.

[0069] Referring to Figure 3 , the process of the grid side control is as follows: Step S1, the switching module determines the grid side simplified signal according to the real-time running condition of the system. When the system runs in the voltage drop condition, the grid side simplified signal is 0, the switching module switches the grid side control to the detailed model, and enters step S2. When the system runs in the steady state, wind speed mutation, primary frequency modulation or AGC automatic power generation control condition, the grid side simplified signal is 1, the switching module switches the grid side control to the simplified model, and enters step S3; Step S2, the grid side calls the detailed model to execute the following steps: 1) Grid side DC voltage outer loop: calculate the grid side converter output current reference value, see equations (52)-(53); 2) Determine whether it is just switched back from the simplified model. If yes, reset the grid side current inner loop integrator by the reset module, see equation (12). If no, directly enter the next step; 3) Grid side current inner loop: first, calculate the grid side converter output voltage reference value and the grid side converter output voltage in sequence, see equations (54) and (55); then calculate the grid side converter output current, see equations (56)-(58); and finally, calculate the updated grid-connected active power and reactive power, see equation (31), and go to step S1; Step S3, the grid side calls the simplified model to execute the following steps: 1) Grid side DC voltage outer loop: calculate the grid side converter output current reference value, see equations (52)-(53); 2) Grid side current inner loop: first, calculate the updated grid side converter output current, see equation (8); then calculate the grid side converter output voltage, see equation (9), and take the grid side converter output voltage as the grid side converter output voltage reference value by the reset module, see equation (10); and finally, calculate the updated grid-connected active power and reactive power, see equation (31), and go to step S1.

[0070] The above embodiments are the preferred implementation of the present application, in addition to which, the present application can also be implemented in other manners, and any obvious replacements without departing from the technical scheme concept of the present application are within the protection scope of the present application.

[0071] In order to make the person skilled in the art more convenient to understand the improvement of the present application relative to the prior art, some drawings and descriptions of the present application have been simplified, and some other elements have also been omitted in the present application file for the sake of clarity, and the person skilled in the art should realize that these omitted elements can also constitute the content of the present application.

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 to 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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