Networking type doubly-fed motor low voltage ride through control method, device and system based on flux linkage suppression and storage medium

Abstract

The invention discloses a flux linkage suppression-based low-voltage ride-through control method, device and system for a grid-forming doubly-fed motor, and a storage medium, and belongs to the technical field of power generation, power transformation or power distribution. The method comprises the following steps: firstly, locking a network construction control unit and obtaining an internal potential phase based on a virtual synchronous machine principle when a voltage drop occurs in a power grid; the proportionality coefficient of the excitation flux linkage ring is dynamically adjusted, so that the system damping is maximized, and the attenuation of the transient component of the stator flux linkage is accelerated; on the basis, a rotor current instruction is generated in real time according to voltage and current capacity limitation of a rotor-side converter, and a modulation signal is output to drive the converter in combination with a feed-forward compensation strategy and a resonance controller. According to the method, rotor overcurrent and overvoltage during a fault period can be effectively suppressed without adding any hardware circuit, the attenuation speed of a transient flux linkage is remarkably improved, meanwhile, the reactive power supporting capacity of a unit to a power grid is enhanced, and high-performance low-voltage ride-through of the grid-forming type doubly-fed motor is achieved.

Description

Technical Field

[0001] This invention relates to doubly-fed motor control and new energy grid connection technology, specifically disclosing a low-voltage ride-through control method, device, system, and storage medium for a grid-type doubly-fed induction motor based on flux linkage suppression when the grid voltage drops, belonging to the technical field of power generation, transformation, or distribution. Background Technology

[0002] Doubly fed induction motors have been widely used in many fields due to their wide speed range, excellent grid connection performance, and high cost-effectiveness, mainly in wind power generation, pumped storage systems, and ship shaft-driven power generation systems.

[0003] Taking wind power systems as an example, modern grid connection standards require wind turbines to have low-voltage ride-through capability, meaning they must remain connected to the grid during grid faults and provide reactive power support to the grid within a specified timeframe. Similarly, pumped storage systems must also meet similar low-voltage ride-through requirements.

[0004] Doubly fed induction motors have their stator windings directly connected to the power grid, making them highly sensitive to grid voltage fluctuations. During grid faults, extremely high induced electromotive forces are generated on the rotor side, leading to overvoltage and overcurrent faults. Therefore, doubly fed induction motor systems have inherent drawbacks, including difficulty in suppressing rotor overcurrent and overvoltage during grid voltage dips, slow transient flux decay, and insufficient reactive power support capacity.

[0005] Currently, improved rotor-side converter excitation control strategies to enhance the low-voltage ride-through capability of generator units are attracting widespread attention due to their advantages of requiring no additional hardware and offering flexible control. Several studies have already addressed improving the low-voltage ride-through capability of doubly-fed induction generators (DFIGs) by modifying rotor-side converter excitation control methods: The paper "Control of DFIG Induction Generator under Symmetrical Voltage Drop" controls the rotor current to track the free component of the stator flux linkage to accelerate its decay rate; however, this requires a large rotor current, is overly dependent on converter capacity, and affects system feasibility. The paper "Improved Low-Voltage Ride-Through Control Strategy for DFIG Asynchronous Generators During Grid Faults" introduces virtual impedance into the demagnetization control method, broadening its ride-through operating range; however, it is only applicable to grid-connected systems and requires... Phase-locked loops (PLLs) are susceptible to the impact of PLL accuracy during grid faults, which weakens phase stability and control robustness during grid faults. The paper "Improved Virtual Synchronous Generator Control for Doubly Fed Wind Turbines to Overcome Symmetrical Voltage Faults" proposes a grid-type doubly fed induction motor control strategy with an outer power loop and an inner excitation flux loop. This strategy can accelerate the attenuation of transient components through excitation flux feedback control. However, it introduces additional current-limiting control for current limiting, and the current-limiting control and excitation flux feedback control interfere with each other, weakening the effect of excitation flux feedback control. At the same time, it does not maximize the utilization of the rotor-side converter capacity to accelerate the attenuation of transient components. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the aforementioned background technology by providing a low-voltage ride-through control method, device, system, and storage medium for a grid-type doubly-fed induction motor based on a flux linkage suppression strategy. By improving the low-voltage ride-through control strategy of the rotor-side converter, this invention solves the technical problems of high rotor current demand, reliance on phase-locked loop accuracy, and the weakening of flux linkage suppression effect while limiting rotor current. Through the integrated coordination of flux linkage suppression and current limiting, the invention aims to achieve the safe and stable operation of the grid-type doubly-fed induction motor under fault conditions and to quickly provide reactive power support to the power grid.

[0007] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0008] A low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression.

[0009] When the grid voltage drops, the grid control unit is locked, and the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault occurs is locked. The rotor mechanical angle and slip angle of the doubly fed motor are calculated based on the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault occurs. The rotor current of the doubly fed motor in the synchronous rotating coordinate system of internal potential is obtained based on the slip angle. The stator current and stator voltage of the doubly fed motor in the synchronous rotating coordinate system of internal potential are obtained based on the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault occurs. Under the capacity constraint of the rotor-side converter, the excitation flux linkage proportional coefficient is increased and the excitation flux linkage integral coefficient is set to 0 to obtain the reference value of the rotor current.

[0010] Based on the rotor current, stator current, stator voltage, and stator flux linkage of the doubly-fed motor in the internal potential synchronous rotating coordinate system, the rotor voltage feedforward compensation value is calculated. The error signal of the rotor current of the doubly-fed motor in the internal potential synchronous rotating coordinate system compared with the reference value is subjected to closed-loop regulation and resonant control to obtain the rotor voltage control quantity. Based on the rotor voltage feedforward compensation value and the rotor voltage control quantity, the rotor voltage demand value is calculated. The switching signal of the rotor-side converter is generated based on the rotor voltage demand value.

[0011] As a further optimization of the low-voltage ride-through control method for grid-type doubly-fed induction generators based on flux linkage suppression, the excitation flux linkage proportional coefficient is increased under the constraint of rotor-side converter capacity. Specifically, based on... The excitation flux linkage proportional coefficient is iteratively updated, where... , They are the first sequence The excitation flux linkage proportional coefficient value calculated in the next iteration. To synchronize rotational angular velocity, For stator inductance, For mutual inductance between stator and rotor, For stator resistance, The initial value of the excitation flux proportional coefficient is the sampling period. for , This is the maximum current withstand value of the rotor-side converter. This is the voltage drop depth coefficient. , This represents the amplitude of the stator terminal voltage.

[0012] As a further optimization of the low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression, a reference value for the rotor current is obtained by introducing a transition function. The rotor q-axis current reference value is attenuated at all times to obtain the real-time reference value of the rotor q-axis current; the error of the d-axis excitation flux linkage is adjusted in a closed loop to obtain the reference value of the rotor d-axis current.

[0013] As a further optimization of the low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression, the transition function is: Real-time reference value of rotor q-axis current for , for Reference value of rotor q-axis current at any time The time when the fault occurred Rotor q-axis current reference value , = .

[0014] As a further optimization of the low-voltage ride-through control method for a grid-type doubly-fed induction generator (DFIG) based on flux linkage suppression, the rotor voltage feedforward compensation value is calculated based on the rotor current, stator current, and stator voltage of the DFIG in the synchronous rotating coordinate system of the internal potential. Specifically: ,in, , These are the feedforward compensation values ​​for the rotor's d-axis and q-axis voltages. The slip angular frequency, Leakage inductance coefficient, For rotor inductance, , The rotor d-axis and q-axis currents of the doubly-fed induction generator in a synchronous rotating coordinate system with internal electromotive force. , For the stator d-axis and q-axis magnetic flux linkages, , The stator d-axis and q-axis voltages of the doubly-fed induction generator in a synchronous rotating coordinate system with internal potential are given. , These are the stator d-axis and q-axis currents of a doubly fed motor in a synchronous rotating coordinate system with internal electromotive force.

[0015] As a further optimization of the low-voltage ride-through control method for a grid-type doubly-fed induction generator (DFIG) based on flux linkage suppression, closed-loop regulation and resonant control are performed on the error signal of the rotor current of the DFIG compared to the reference value in the synchronous rotating coordinate system of the internal potential to obtain the rotor voltage control quantity, specifically:

[0016] The error signal between the rotor q-axis current of the doubly fed motor and the real-time reference value of the rotor q-axis current in the synchronous rotating coordinate system of internal potential is adjusted in a closed loop by proportional-integral resonant control to obtain the rotor q-axis voltage control quantity.

[0017] The AC component of the rotor d-axis current of the doubly fed motor in the synchronous rotating coordinate system of internal potential is extracted. The error signal of the AC component of the rotor d-axis current relative to the reference value of the rotor d-axis current is adjusted in a closed loop by proportional-integral resonant control to obtain the control quantity of the AC component of the rotor d-axis voltage. The error signal of the DC component of the rotor d-axis current relative to the reference value 0 is adjusted in a closed loop by proportional-integral control to obtain the control quantity of the DC component of the rotor d-axis voltage.

[0018] As a further optimization of the low-voltage ride-through control method for grid-type doubly-fed induction generators based on flux linkage suppression, the rotor voltage demand value is calculated based on the rotor voltage feedforward compensation value and the rotor voltage control quantity, specifically: ,in, , These are the voltage requirements for the rotor's d-axis and q-axis. This is the AC component control quantity of the rotor d-axis voltage. This is the DC component control quantity of the rotor d-axis voltage. This is the rotor q-axis voltage control quantity.

[0019] A low-voltage ride-through control device for a grid-type doubly-fed induction generator (DFIG) based on flux linkage suppression includes: a rotor current command generation module and a modulation signal generation module based on feedforward compensation strategy and resonant control. The rotor current command generation module is used to, when the grid voltage drops, lock the grid control unit, lock the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault, calculate the rotor mechanical angle and slip angle of the DFIG under the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault, obtain the rotor current of the DFIG in the synchronous rotating coordinate system based on the slip angle, and obtain the internal potential current of the DFIG in the synchronous rotating coordinate system based on the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault. The stator current and stator voltage of the motor are increased by increasing the proportional coefficient of the excitation flux linkage under the constraint of the rotor-side converter capacity, and the integral coefficient of the excitation flux linkage is set to 0 to obtain the reference value of the rotor current. The modulation signal generation module based on the feedforward compensation strategy and resonance control is used to calculate the rotor voltage feedforward compensation value according to the rotor current, stator current, stator voltage and stator flux linkage of the doubly fed motor in the internal potential synchronous rotating coordinate system. The error signal of the rotor current of the doubly fed motor in the internal potential synchronous rotating coordinate system compared with the reference value is subjected to closed-loop regulation and resonance control to obtain the rotor voltage control quantity. The rotor voltage demand value is calculated according to the rotor voltage feedforward compensation value and the rotor voltage control quantity. The switching signal of the rotor-side converter is generated according to the rotor voltage demand value.

[0020] A computer system includes a memory and a processor. The memory stores a computer program that runs on the processor. When the processor runs the computer program, it executes the steps of the above-described low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression.

[0021] A computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the above-described low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression.

[0022] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0023] 1. No additional hardware required, achieving cost and reliability optimization: This invention achieves low voltage ride-through function entirely based on control algorithm, without the need for any additional hardware such as crowbar circuits or energy storage units. This not only reduces system cost but also avoids potential fault points introduced by additional circuits, thus improving overall operational reliability.

[0024] 2. Dynamically adjusting the excitation proportional coefficient significantly improves transient response speed: By iteratively calculating and dynamically adjusting the proportional coefficient of the excitation flux linkage in real time, the system damping is maximized, thereby significantly accelerating the decay of the transient component of the stator flux linkage. While ensuring rapid flux linkage decay, the demand on rotor current is significantly reduced, avoiding excessive dependence on converter capacity and improving system feasibility. Simulation results show that this method can shorten the decay time of transient flux linkage to about 40% under fixed parameter control, effectively suppressing electromagnetic torque fluctuations and DC bus voltage fluctuations caused by flux linkage oscillations.

[0025] 3. Fully utilize converter capacity to achieve safe ride-through and rapid tracking: This method generates the optimal rotor current command in real time based on the voltage and current capacity limits of the rotor-side converter; through a strategy combining feedforward compensation and resonant control, it achieves rapid and accurate tracking of the current command while strictly limiting the rotor current within the safety threshold, thus avoiding converter damage caused by overcurrent.

[0026] 4. Enhance reactive power support during faults and improve grid stability: During voltage dips, through rapid switching of control strategies and rapid decay of flux linkage, the unit can quickly provide effective reactive power support to the grid, such as outputting rated reactive power within 200ms, to help the grid voltage recover and improve the transient stability and fault ride-through success rate of the grid-connected system.

[0027] 5. Applicable to grid-type systems, eliminating dependence on phase-locked loops: This method obtains the internal potential phase based on the principle of virtual synchronous machine, and can maintain a stable synchronous reference coordinate system during grid faults without the need for a phase-locked loop. This not only enhances the phase stability and operational robustness of the system under weak grids and severe faults, but also provides an effective control solution for the promotion and application of grid-type doubly-fed induction generators.

[0028] 6. Achieve coordinated control of flux suppression and current limiting: By combining dynamic excitation regulation with current command generation based on converter capacity, the problem of mutual interference between current limiting control and flux control in traditional methods is fundamentally avoided, and integrated coordinated control of rapid flux decay and equipment safety protection is achieved. Attached Figure Description

[0029] Figure 1 The equivalent circuit diagram of a doubly fed motor in a synchronous rotating coordinate system.

[0030] Figure 2 This is the equivalent circuit diagram of the rotor side of a doubly fed motor.

[0031] Figure 3 This is a block diagram of the network control unit.

[0032] Figure 4 This is a block diagram of the dual closed-loop control for the rotor-side converter.

[0033] Figure 5 This is a control diagram for a grid-type doubly-fed induction generator after a voltage drop in the power grid.

[0034] Figure 6 The figure shows the current simulation results of the dynamic adjustment of the excitation flux proportional coefficient control method when the grid voltage drops by 80%.

[0035] Figure 7 The figure shows the simulation results of reactive power when the grid voltage drops by 80% using the dynamic adjustment of the excitation flux proportional coefficient control method.

[0036] Figure 8 The figure shows a comparison of the stator q-axis flux linkage simulation results under two different excitation flux linkage scaling factors. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0038] Figure 1 The figure shows the equivalent circuit model of a doubly-fed induction generator in a synchronous rotating coordinate system. Starting from the internal electromagnetic relationships of the motor, this figure clearly depicts the voltage equations and flux linkage equations on the stator and rotor sides, as well as their coupling relationship. These are the d-axis and q-axis components of the stator voltage; and These are the d-axis and q-axis components of the stator and rotor currents, respectively. and These are the d-axis and q-axis components of the stator and rotor flux linkages, respectively. , These are the stator and rotor resistances, respectively. , These are the stator and rotor self-inductances, respectively, where, , , , For stator and rotor leakage inductance, For mutual inductance between stator and rotor; It is synchronous rotational angular velocity. It is the slip angular frequency. This equivalent circuit is the theoretical basis for deriving the flux linkage calculation, feedforward compensation, and system dynamic analysis in the control algorithm of this invention, and intuitively reflects the inherent mechanism of influencing the stator flux linkage through rotor current control.

[0039] Depend on Figure 1 The transient differential equation for the stator flux linkage can be obtained as follows:

[0040] (1)

[0041] In equation (1), For the transient component of the stator flux linkage, This represents the transient component of the rotor current.

[0042] Therefore, based on the transient flux suppression control strategy, i.e., controlling the rotor transient current... The transient differential equation of the stator flux linkage at time t is:

[0043] (2)

[0044] Therefore, the characteristic roots of the system at this time can be obtained as follows:

[0045] (3)

[0046] According to the eigenvalues, when When >0, The larger the value, the greater the system damping, and the faster the transient flux decays. This is also the proportional coefficient for dynamically designing the excitation flux. The theoretical basis for accelerating the transient components of the system.

[0047] Figure 2 This is the rotor-side equivalent circuit of a doubly-fed induction generator in a rotating coordinate system based on rotor angular velocity. Its circuit structure includes the stator flux linkage induced electromotive force, the output voltage of the rotor-side converter (RSC), and the series-connected rotor equivalent resistance. Equivalent rotor leakage inductance The circuit contains the rotor current flowing through it; this circuit is used to accurately characterize the electrical interaction characteristics of the rotor side of the doubly-fed induction generator, providing a core electrical modeling foundation for the control algorithm of the rotor-side converter, and can be directly correlated with the stator flux linkage induced electromotive force. Rotor-side converter (RSC) output voltage With rotor current , where superscript This is expressed in the rotor rotating coordinate system. From the rotor-side equivalent circuit, the rotor-side converter voltage drop can be obtained. The minimum requirement is that the following conditions must be met simultaneously:

[0048] Condition 1: Stator flux linkage induced electromotive force Minimum;

[0049] Condition 2: Voltage drop across the rotor's equivalent impedance The amplitude is the largest and the direction is the same as the stator flux induced electromotive force. The directions are opposite.

[0050] For condition 1, where the stator flux linkage induced electromotive force is minimized, since the stator flux linkage induced electromotive force is mainly generated by the transient component of the stator flux linkage, that is:

[0051] (4)

[0052] In equation (4), The stator flux linkage in the rotor rotating coordinate system. This represents the transient component of the stator flux linkage in the rotor rotating coordinate system.

[0053] Therefore, the rotor transient current can be controlled according to the transient flux suppression strategy. Therefore, the maximum capacity can be designed according to the converter capacity. This maximizes the system's damping, resulting in the fastest and smallest transient decay of the stator flux linkage, and consequently, the minimum induced electromotive force of the stator flux linkage.

[0054] For condition 2, since When controlling rotor current At that time, the voltage drop of the rotor equivalent impedance Therefore, the rotor impedance voltage drop at this time The voltage drop of the induced electromotive force is However, the direction is opposite; combined with condition 1, the rotor current is further controlled. , because Since the current is a transient component of the stator flux linkage, the rotor current is entirely transient at this time, and the angular frequency of the transient component is the rotor angular frequency. The slip frequency is much greater than that of the steady-state component. Therefore, the voltage drop across the rotor's equivalent impedance at this time The amplitude is the largest, which helps to offset the stator flux linkage induced electromotive force. Moreover, the voltage drop across the rotor's equivalent impedance at this time... induced electromotive force voltage drop Therefore, the voltage drop across the rotor's equivalent impedance at this time With respect to electromotive force voltage drop The directions are nearly opposite, and the amplitude is at its maximum at this point, thus satisfying condition 2. Furthermore, because the rotor current is at this time... This increases system damping, accelerates transient flux decay, and reduces the amplitude of the stator flux induced electromotive force, thus satisfying condition 1. Therefore, the rotor current is controlled. Both conditions 1 and 2 are satisfied, achieving integrated coordination of flux suppression and current limiting.

[0055] Figure 3 The diagram shows the active and reactive power decoupling control of a virtual synchronous generator. It is divided into an active power control module (red dashed box) and a reactive power control module (blue dashed box), enabling independent regulation of both: the active power control module uses the active power setpoint... For input, and actual active power After making the difference, pass The process converts the power difference into a torque difference, combined with an active damping element. Introduced rated angular frequency Compared with actual angular frequency After correcting the active power deviation, the virtual moment of inertia element is used. Integrating yields the actual angular frequency. Actual angular frequency Through the points process The phase angle of the internal potential vector is obtained. The reactive power control module uses the reactive power setpoint. and actual reactive power As input, through a reactive power damping circuit Introduced rated voltage With actual voltage After correcting the reactive power deviation, through Adjustment of the process, and then compared with the voltage amplitude on the grid side | | Combined with the magnitude of the output internal potential vector | |, The excitation flux is used; the two modules do not interact with each other by signal, realizing complete decoupling of active power-frequency and reactive power-voltage, which can improve the stability of grid frequency and voltage.

[0056] Figure 4 The block diagram for the dual closed-loop control of the rotor-side converter adopts a structure of "excitation flux outer loop + rotor current inner loop": the internal potential vector is used as the reference. With respect to the actual internal potential vector The rotor current is obtained by PI regulation of the deviation. , As the excitation flux reference, the inner loop current deviation is then used as the output signal to drive the RSC via PI regulation. Where: , for Figure 2The amplitude of the internal potential vector output by the reactive power control module of the grid control unit. This refers to the phase angle of the internal potential vector output by the active power control module of the grid control unit. When a voltage drop occurs, the grid control unit is locked out, and the outer loop of the excitation flux is set. , Therefore, according to Figure 4 achievable ,in, Determined based on the output of the network control unit, and at this time... ≈ , , , These are the steady-state and transient components of the excitation flux linkage, respectively. Therefore, at this time... ≈ To satisfy the previous Figure 2 Derived minimum condition for induced electromotive force voltage drop This also increases system damping and accelerates transient flux decay.

[0057] To ensure that the rotor current amplitude remains within the maximum current withstand value of the rotor-side converter, the following constraints must be met:

[0058] (5)

[0059] From this, the proportionality coefficient can be derived. The theoretical range of values ​​is:

[0060] (6)

[0061] In equation (6), The equivalent time constant of the system, , This refers to the stator terminal voltage amplitude. This is the voltage drop depth coefficient. .

[0062] To prevent overcurrent and facilitate digital controller implementation, the above relationship is discretized and linearized to obtain the proportional coefficient iterative update formula for real-time control:

[0063] (7)

[0064] Initial value of excitation flux proportional coefficient Determined by the system security boundary, it is set as follows:

[0065] (8)

[0066] In equations (7) and (8): , They are the first sequence The excitation flux linkage proportional coefficient value calculated in the next iteration. It is synchronous rotational angular velocity. It is the stator resistance. It is mutual inductance between the stator and rotor. It is a stator inductor. It is the sampling period. This is the maximum current withstand value of the rotor-side converter. This represents the stator terminal voltage amplitude after the voltage drop. Using this iterative formula, the proportional gain of the excitation flux linkage can be calculated in real-time and linearly increased in each sampling cycle. This dynamic adjustment mechanism enables the system to dynamically generate continuously increasing demagnetizing current commands based on flux linkage errors. This provides maximum equivalent damping for stator transient flux linkage within the allowable range of converter capacity, directly and significantly accelerating its decay process. Furthermore, this method achieves inherent synergy between dynamic excitation regulation and current command generation based on converter capacity through deep integration. This is reflected in: command generation integration safety constraint: the initial value of the excitation flux linkage proportional coefficient. (0) The maximum withstand current value of the rotor-side converter and the grid voltage drop are jointly determined, ensuring that the current command generation is strictly within the safe capacity boundary from the source; integrated control objectives: the design objective of the excitation flux outer loop is to find the optimal gain to maximize the flux decay rate under the above safe capacity constraints, thereby unifying "rapidly suppressing flux" and "strictly limiting current" into a coordinated optimization problem.

[0067] The low-voltage ride-through control method proposed in this invention employs a control strategy that dynamically adjusts the proportional coefficient of the excitation flux linkage to accelerate transient flux decay, thereby enhancing the unit's low-voltage ride-through capability and reactive power support capability. The method is as follows: Figure 5 As shown, the specific steps include:

[0068] 1. When a voltage dip in the mains power grid is detected, immediately perform the following operations: lock the grid control unit, and... , ;

[0069] 2. Recall pre-stored motor parameters, including stator resistance. mutual inductance between stator and rotor Stator inductor Rotor inductance and the number of motor pole pairs ;

[0070] 3. Real-time acquisition of stator three-phase voltage via current transformers and voltage transformers. Stator three-phase current and rotor three-phase current ;

[0071] 4. Maintain the internal potential vector calculated by the network control unit based on the virtual synchronous machine principle at the last moment before the fault occurs. phase angle Unchanged, that is, let freeze;

[0072] 5. Obtain the rotor mechanical angle of the doubly-fed motor using an encoder. ;

[0073] 6. Based on the phase angle of the internal potential vector obtained in step 4. and the rotor mechanical angle obtained in step 5 Through formula The slip angle can be calculated, and the slip angular frequency can be obtained by differentiation. ;

[0074] 7. Based on the slip angle obtained in step 6 The rotor three-phase current obtained in step 3 above A coordinate transformation abc / dq is performed to obtain the rotor d-axis current of the doubly-fed motor in the synchronous rotating coordinate system of internal potential. Rotor q-axis current ;

[0075] 8. Based on the internal potential vector obtained in step 4 phase angle The stator three-phase current obtained in step 3 above and stator three-phase voltage A coordinate transformation of abc / dq is performed to obtain the stator d-axis current of the doubly-fed motor in the synchronous rotating coordinate system of internal potential. Stator q-axis current Stator d-axis voltage and stator q-axis voltage ;

[0076] 9. According to the formula The d-axis excitation flux linkage values ​​were calculated respectively. q-axis excitation flux linkage ,in, , , ;

[0077] 10. Calculate the proportional coefficient of the excitation flux linkage in real time according to the iterative formula (7). Simultaneously, a PI controller with given excitation flux linkage The value is 0; to ensure the rotor q-axis current loop tracks the reference value, a transition function is introduced. right The rotor q-axis current reference value is constantly decayed to obtain the real-time rotor q-axis current reference value. , ,in, , The moment the fault occurs is the moment the grid voltage drops. = The reference value for the rotor d-axis current is still given by the error of the excitation flux linkage via a PI controller. In order to make the rotor d-axis current loop track the reference value, the AC component of the rotor d-axis current is extracted by the state observer SOGI. Then the DC component of the rotor d-axis current is Then, the AC components of the rotor d-axis current are controlled separately. and DC component .

[0078] 11. Based on the stator and rotor currents obtained in steps 7 and 8 respectively, then use the formula... and The stator d-axis flux linkage was calculated separately. and stator q-axis flux linkage Simultaneously, based on the stator and rotor inductances obtained from step 2, the formula is used... Obtain the leakage inductance coefficient Finally, based on the slip frequency obtained in step 6... The stator d-axis flux linkage obtained in step 11 Stator q-axis flux linkage Leakage inductance coefficient To calculate the feedforward compensation values ​​of the rotor d-axis and q-axis voltages. , The calculation formula is as follows: ;

[0079] 12. Based on the rotor d-axis current obtained in step 7 Rotor q-axis current and the rotor d-axis current command obtained in step 10 Rotor q-axis command To obtain the AC component error signal of the rotor d-axis current Error signal of DC component of rotor d-axis current and rotor q-axis current error signal ,in, , as well as ;

[0080] 13. The rotor q-axis current error signal is controlled by a proportional-integral-resonant (PIR) controller. Closed-loop processing is performed to obtain the rotor q-axis voltage control quantity. Additionally, the error of the AC component of the rotor d-axis current is obtained through PIR. The AC component control quantity of the rotor d-axis voltage is obtained by performing closed-loop processing. The error of the DC component of the rotor d-axis current is obtained through the PI converter. The DC component control quantity of the rotor d-axis voltage is obtained by performing closed-loop processing. ;

[0081] 14. Based on the rotor voltage feedforward compensation value obtained in step 11 , And the AC component control quantity and DC component control quantity of the rotor d-axis voltage obtained in step 13. , To calculate the voltage requirements of the rotor's d-axis and q-axis. , The calculation formula is as follows: ;

[0082] 15. The required voltage values ​​for the rotor d-axis and q-axis obtained in step 14. , Space vector pulse width modulation is required to obtain the switching signals for the rotor-side converter switching transistors. , , .

[0083] This invention uses a 0.1MW doubly-fed induction generator under typical parameters as an example for simulation research. The simulation conditions are: 1. Before the fault occurs, the motor is operating in supersynchronous condition with slip rate... for 2. At t=1s, a power grid fault occurs. Key parameters: rated voltage 690V, stator resistance... Mutual induction The maximum current of the rotor-side converter is set at twice the rated value.

[0084] according to Figure 6 The simulation results are as follows: the peak rotor current is effectively limited to the set maximum current withstand value, which is twice the rated value, thus protecting the safety of the converter.

[0085] according to Figure 7 The simulation results are as follows: After the fault, the stator side can output the rated reactive power within about 200ms, providing rapid reactive power support to the power grid.

[0086] according to Figure 8 The simulation results are as follows: The blue curve represents the dynamic adjustment method used in this study. The stator transient flux decays almost completely within 40ms; the red curve represents the traditional method using a fixed... At that time, the decay time is approximately 100ms. The method of this invention dynamically increases... By maximizing the system's equivalent damping, the decay rate of the transient flux linkage was increased by approximately 60%. This not only verified the correctness of the theoretical analysis but also directly brought about subsequent positive effects: the rotor overvoltage stress induced by the transient flux linkage was significantly reduced.

[0087] Simulation results fully demonstrate that the dynamic control method based on flux linkage suppression proposed in this invention performs excellently in terms of rotor overcurrent suppression, transient process acceleration, reactive power support strength, and overall system stability. This method achieves a balance of safety, speed, and support during low-voltage ride-through of a grid-type doubly-fed induction generator without any hardware modifications, fully meeting the intended objectives of the invention.

[0088] The above specific implementation methods and embodiments are specific support for the inventive concept proposed in this invention, which is to achieve the integrated coordination of flux suppression and current limiting to realize the safe and stable operation of grid-type doubly fed motors under fault conditions and to quickly provide reactive power support to the power grid. They should not be used to limit the scope of protection of this invention. Any equivalent changes or modifications made on the basis of the technical solution of this invention in accordance with the technical ideas proposed in this invention shall still fall within the scope of protection of this invention.

Claims

1. A low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression, characterized in that, When the grid voltage drops, the grid control unit is locked, and the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault occurs is locked. The rotor mechanical angle and slip angle of the doubly fed motor are calculated under the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault occurs. The rotor current of the doubly fed motor in the internal potential synchronous rotating coordinate system is obtained according to the slip angle. The stator current and stator voltage of the doubly fed motor in the internal potential synchronous rotating coordinate system are obtained according to the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault occurs. Under the capacity constraint of the rotor-side converter, the excitation flux linkage proportional coefficient is increased and the excitation flux linkage integral coefficient is set to 0 to obtain the reference value of the rotor current. Based on the rotor current, stator current, stator voltage, and stator flux linkage of the doubly-fed motor in the synchronous rotating coordinate system of internal potential, the rotor voltage feedforward compensation value is calculated. The error signal of the rotor current of the doubly-fed motor in the synchronous rotating coordinate system of internal potential compared with the reference value is subjected to closed-loop regulation and resonant control to obtain the rotor voltage control quantity. Based on the rotor voltage feedforward compensation value and the rotor voltage control quantity, the rotor voltage demand value is calculated. The switching signal of the rotor-side converter is generated based on the rotor voltage demand value.

2. The low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression according to claim 1, characterized in that, The method of increasing the excitation flux ratio under the capacity constraint of the rotor-side converter is specifically as follows: based on The excitation flux linkage proportional coefficient is iteratively updated, where... , They are the first sequence The excitation flux linkage proportional coefficient value calculated in the next iteration. To synchronize rotational angular velocity, For stator inductance, For mutual inductance between stator and rotor, For stator resistance, The initial value of the excitation flux proportional coefficient is the sampling period. for , This is the maximum current withstand value of the rotor-side converter. This is the voltage drop depth coefficient. , This represents the amplitude of the stator terminal voltage.

3. The low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression according to claim 2, characterized in that, The specific method for obtaining the reference value of the rotor current is as follows: A transition function is introduced to... The rotor q-axis current reference value is attenuated at all times to obtain the real-time reference value of the rotor q-axis current; the error of the d-axis excitation flux linkage is adjusted in a closed loop to obtain the reference value of the rotor d-axis current.

4. The low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression according to claim 3, characterized in that, The transition function is: Real-time reference value of rotor q-axis current for , for Reference value of rotor q-axis current at any time The time when the fault occurred Rotor q-axis current reference value , = .

5. The low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression according to claim 4, characterized in that, The calculation of the rotor voltage feedforward compensation value based on the rotor current, stator current, and stator voltage of the doubly-fed motor in the synchronous rotating coordinate system of internal potential is specifically as follows: ,in, , These are the feedforward compensation values ​​for the rotor's d-axis and q-axis voltages. The slip angular frequency, Leakage inductance coefficient, For rotor inductance, , The rotor d-axis and q-axis currents of the doubly-fed induction generator in a synchronous rotating coordinate system with internal electromotive force. , For the stator d-axis and q-axis magnetic flux linkages, , The stator d-axis and q-axis voltages of the doubly-fed induction generator in a synchronous rotating coordinate system with internal potential are given. , These are the stator d-axis and q-axis currents of a doubly fed motor in a synchronous rotating coordinate system with internal electromotive force.

6. The low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression according to claim 5, characterized in that, The error signal between the rotor current of the doubly fed motor in the internal potential synchronous rotating coordinate system and the reference value is adjusted in a closed loop and controlled resonantly to obtain the rotor voltage control quantity, specifically: The error signal between the rotor q-axis current of the doubly fed motor and the real-time reference value of the rotor q-axis current in the synchronous rotating coordinate system of internal potential is adjusted in a closed loop by proportional-integral resonant control to obtain the rotor q-axis voltage control quantity. The AC component of the rotor d-axis current of the doubly fed motor in the synchronous rotating coordinate system of internal potential is extracted. The error signal of the AC component of the rotor d-axis current relative to the reference value of the rotor d-axis current is adjusted in a closed loop by proportional-integral resonant control to obtain the control quantity of the AC component of the rotor d-axis voltage. The error signal of the DC component of the rotor d-axis current relative to the reference value 0 is adjusted in a closed loop by proportional-integral control to obtain the control quantity of the DC component of the rotor d-axis voltage.

7. The low-voltage ride-through control method for a grid-type doubly-fed induction generator based on flux linkage suppression according to claim 6, characterized in that, Based on the rotor voltage feedforward compensation value and the rotor voltage control quantity, the rotor voltage demand value is calculated as follows: ,in, , These are the voltage requirements for the rotor's d-axis and q-axis. This is the AC component control quantity of the rotor d-axis voltage. This is the DC component control quantity of the rotor d-axis voltage. This is the rotor q-axis voltage control quantity.

8. A low-voltage ride-through control device for a grid-type doubly-fed induction generator based on flux linkage suppression, characterized in that, include: The rotor current command generation module is used to lock the grid control unit when the grid voltage drops, lock the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault occurs, calculate the rotor mechanical angle and slip angle of the doubly fed motor under the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault occurs, obtain the rotor current of the doubly fed motor in the internal potential synchronous rotating coordinate system according to the slip angle, obtain the stator current and stator voltage of the doubly fed motor in the internal potential synchronous rotating coordinate system according to the phase angle of the internal potential vector obtained by the grid control unit at the last moment before the fault occurs, increase the excitation flux proportional coefficient under the capacity constraint of the rotor-side converter, and set the excitation flux integral coefficient to 0 to obtain the reference value of the rotor current. and, The modulation signal generation module based on feedforward compensation strategy and resonant control is used to calculate the rotor voltage feedforward compensation value based on the rotor current, stator current, stator voltage and stator flux linkage of the doubly fed motor in the internal potential synchronous rotating coordinate system, perform closed-loop regulation and resonant control on the error signal of the rotor current of the doubly fed motor in the internal potential synchronous rotating coordinate system compared with the reference value, obtain the rotor voltage control quantity, calculate the rotor voltage demand value based on the rotor voltage feedforward compensation value and the rotor voltage control quantity, and generate the switching signal of the rotor-side converter based on the rotor voltage demand value.

9. A computer system comprising a memory and a processor, wherein the memory stores a computer program that runs on the processor, characterized in that, When the processor runs a computer program, it executes the steps of the low-voltage ride-through control method for a grid-type doubly-fed motor based on flux linkage suppression as described in claim 1.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the low-voltage ride-through control method for a grid-type doubly-fed motor based on flux linkage suppression as described in claim 1.

Images