Low voltage ride through control method for wind turbine generator

Abstract

The invention discloses a low-voltage ride-through control method for a wind turbine generator, relates to the technical field of wind power generation, and solves the problem that for a mainstream doubly-fed induction wind turbine generator, huge transient overcurrent can be induced on the rotor side of the mainstream doubly-fed induction wind turbine generator by power grid voltage drop, and the safety of a converter on the rotor side is threatened. According to the technical scheme, a hybrid energy storage system composed of a super capacitor and a storage battery is connected to a direct-current bus of a wind turbine generator converter in parallel, and an intelligent cooperative control mechanism linked with the hybrid energy storage system is designed. The method comprises the steps of generating a total power absorption instruction of the hybrid energy storage system according to a deviation and a change rate of a direct-current bus voltage when detecting that a power grid voltage drops; the method has the advantages that it can be ensured that the grid-side converter continuously provides reactive power support for the power grid during the fault period, the defect that a traditional crowbar circuit absorbs reactive power is fundamentally overcome, meanwhile, rapidness, smoothness and high reliability of the low-voltage ride-through process are achieved, and the grid connection performance of a wind turbine generator is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of wind power generation technology, specifically a low voltage ride-through control method for wind turbine generators. Background Technology

[0002] As wind power accounts for an increasingly larger share of the energy mix, its grid connection stability has become crucial for the safe operation of the power grid. Grid regulations mandate that wind turbines possess low-voltage ride-through capability, meaning that when the grid voltage experiences a short-term drop, the wind turbine must not disconnect from the grid and must provide reactive power to the grid to assist in voltage recovery.

[0003] For mainstream doubly-fed induction generators, grid voltage dips can induce huge transient overcurrents on the rotor side, threatening the safety of the rotor-side converter. Simultaneously, the imbalance between the unit's output power and the grid's absorbed power can cause a sharp increase in the DC bus voltage.

[0004] Existing low voltage ride-through technologies mainly have the following limitations and drawbacks: Crowbar circuit: A resistor is connected in parallel on the rotor side. It is activated during a fault to consume energy and limit rotor current. However, its activation can cause the rotor-side converter to become uncontrollable, leading the unit to absorb reactive power from the grid, which contradicts grid demand and worsens grid voltage recovery. Furthermore, its switching process can cause torque and power surges.

[0005] DC-side load shearing circuit: A braking resistor controlled by a power electronic switch is connected in parallel on the DC bus. When the DC voltage is too high, the switch is turned on, causing the resistor to dissipate excess energy. Although this method can protect the DC side, the energy is wasted as heat and cannot provide reactive power support. Furthermore, the heat dissipation design for large-capacity resistors is complex.

[0006] Single energy storage solution: Some studies have proposed connecting energy storage devices, such as batteries or supercapacitors, to the DC side. However, batteries have low power density and slow response speed, making them difficult to cope with instantaneous high-power surges; while supercapacitors have a fast response, their low energy density makes them unable to support power for extended periods. A single energy storage element cannot simultaneously meet the stringent requirements of power response speed and energy support time in LVRT processes.

[0007] Therefore, there is an urgent need in this field for a new low-voltage ride-through control scheme that can synergistically address instantaneous power surges and continuous energy throughput, and ensure that grid-side converters continuously provide reactive power support. Summary of the Invention

[0008] The purpose of this invention is to provide a low-voltage ride-through control method for wind turbines. This method achieves fast, smooth, and efficient low-voltage ride-through by complementing the advantages and disadvantages of supercapacitors and batteries and through intelligent coordination, and effectively supports grid voltage recovery.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A low-voltage ride-through control method for wind turbine generators specifically includes the following steps: Step 1: Monitor the grid voltage in real time. When the grid voltage drops to the low voltage crossing threshold, start the hybrid energy storage system connected in parallel to the DC bus of the wind turbine converter. The hybrid energy storage system includes at least one power-type energy storage branch and one energy-type energy storage branch. Step 2: Generate the total power command Pess_ref that the hybrid energy storage system needs to absorb based on the deviation value ΔUdc of the DC bus voltage; Step 3: Based on the total power command Pess_ref, and taking into account the real-time status of the power-type energy storage branch and the energy-type energy storage branch, dynamically generate the power command allocated to each energy storage branch through an adaptive power allocation strategy. Step 4: Control each energy storage branch to absorb power according to the power command to stabilize the DC bus voltage. During low voltage ride-through, control the grid-side converter to preferentially inject reactive current into the grid to support grid voltage recovery.

[0010] Preferably, the adaptive power allocation strategy in step S4 employs fuzzy logic control. Its input variables are ΔUdc, dΔUdc / dt, SOC_sc, and SOC_bat, and its output variable is the power allocation coefficient Ksc of the supercapacitor. The design principle of the fuzzy rule is: "High-frequency, high-power fluctuations are handled by the supercapacitor, while low-frequency, continuous energy is handled by the battery, simultaneously considering the protection of both's state of charge." For example, the rule includes: "When ΔUdc is greater than the first voltage threshold (100V) and dΔUdc / dt is greater than the first rate of change threshold (500 V / s), power is preferentially allocated to the supercapacitor with the faster response speed"; "If SOC_sc is high, then Ksc is low (to prevent overcharging)."

[0011] Throughout the low voltage ride-through process, the grid-side converter is controlled to prioritize the output of reactive current. Based on grid dispatch requirements or the local voltage dip depth, it injects reactive current into the grid to actively support grid voltage recovery.

[0012] Preferably, the principles for formulating the fuzzy rule base include: When ΔUdc is greater than the first voltage threshold (100V) and dΔUdc / dt is greater than the first rate of change threshold (500 V / s), power is preferentially allocated to the supercapacitor with fast response speed. When SOC_sc is higher than its set upper limit, Ksc is reduced to limit the charging of the supercapacitor; When SOC_bat is lower than its set lower limit, it decreases by (1-Ksc) to protect the battery from over-discharge.

[0013] Preferably, the adaptive power allocation strategy in step four is as follows: An optimization function was constructed to minimize the operating losses of a hybrid energy storage system. This function comprehensively considers the impact of power allocation strategies for supercapacitors and batteries on the overall system efficiency. During the optimization process, the total power command (Pess_ref) of the hybrid energy storage system, the state of charge (SOC_sc) of the supercapacitor, and the state of charge (SOC_bat) of the battery are used as key constraints to ensure that the system simultaneously meets power requirements and the safe operation requirements of the energy storage devices under optimal operating conditions. By employing advanced real-time optimization algorithms, we can quickly and accurately calculate the optimal power reference values ​​(Psc_ref) for the supercapacitor and Pbat_ref for the battery, thereby achieving efficient and stable operation of the hybrid energy storage system while minimizing system losses and extending equipment lifespan.

[0014] Preferably, under low-voltage ride-through operation conditions, to ensure stable grid operation, the grid-side converter control system will automatically switch to a reactive current priority control strategy. When a voltage dip is detected in the grid, the control system will accurately calculate the reactive current value to be injected into the grid based on the real-time monitored voltage dip depth, according to a preset control algorithm and grid specifications. By rapidly adjusting the phase and amplitude of the converter's output current, dynamic reactive current conforming to standard requirements is injected into the grid, thereby effectively supporting the rapid recovery of grid voltage. This control process achieves coordinated operation of the converter and the grid during grid faults, meeting the ride-through requirements of grid-connected equipment while providing the necessary voltage support capability for the grid.

[0015] Preferably, the startup process and power command generation mechanism of the hybrid energy storage system operate in parallel and in coordination with the dynamic current control strategy of the rotor-side converter and the precise reactive power regulation function of the grid-side converter. These three components work together to construct a complete and efficient low-voltage ride-through coordinated control system. In this system, the hybrid energy storage system is responsible for quickly responding to grid voltage dips, providing necessary power support through timely startup and precise power allocation; the rotor-side converter ensures the stable operation of the generator set through its advanced current control algorithm; and the grid-side converter maintains grid voltage stability through a flexible reactive power control strategy. The coordinated operation of these three key control links enables the entire system to achieve smooth low-voltage ride-through during grid faults, ensuring the safe and stable operation of the power system.

[0016] Preferably, in step three, the PI controller generates the total power command Pess_ref based on ΔUdc, and its calculation formula is: Pess_ref=Kp×ΔUdc+Ki×∫ΔUdcdt, and the output is subjected to amplitude limiting processing.

[0017] Preferably, in step two, when the low voltage ride-through control mode is activated, a control strategy combining current limiting and stator flux feedforward compensation is adopted for the rotor-side converter to actively suppress rotor overcurrent.

[0018] Preferably, the reference value of the reactive current injected by the grid-side converter is dynamically calculated according to the grid voltage drop depth and in accordance with the grid connection regulations.

[0019] Preferably, the startup and power command generation of the hybrid energy storage system, the current control of the rotor-side converter, and the reactive power control of the grid-side converter are executed in parallel by the system main controller, forming a collaborative control system for low voltage ride-through.

[0020] Compared with the prior art, the beneficial effects of the present invention are: This invention innovatively introduces a hybrid energy storage system composed of supercapacitors and batteries. This system actively participates in the stable control of the DC bus voltage, allowing the grid-side converter to operate continuously and stably in a "reactive power priority" mode, completely unaffected by voltage fluctuations. This technical solution fundamentally resolves the inherent contradiction between the "reactive power absorption" function in traditional crowbar circuit designs and the actual "reactive power requirement" of the power grid. Through the rapid response characteristics of the hybrid energy storage system and the coordinated control of the grid-side converter, it achieves active and precise support for the grid voltage. Compared to traditional solutions, this invention not only improves the system's dynamic response speed but also significantly enhances the stability of the grid voltage, providing a more reliable technical solution for renewable energy grid-connected systems.

[0021] This invention creatively introduces a hybrid energy storage system (composed of supercapacitors and batteries) into the low-voltage ride-through (LVRT) field of wind turbines, proposing a novel solution. Specifically, this invention designs an adaptive power allocation mechanism based on multivariate feedback (including voltage deviation, voltage change rate, and the SOC state of the energy storage system). By monitoring grid voltage fluctuations and the energy storage system status in real time, it dynamically adjusts the power output ratio of different energy storage units. This innovative design enables refined and intelligent management of the power surplus generated by wind turbines during LVRT at different time scales (milliseconds, seconds, and minutes) and with different characteristics (instantaneous impact and continuous fluctuation), effectively solving the technical challenge of traditional single energy storage systems struggling to balance rapid response and continuous power supply. Experimental verification shows that this solution significantly improves the LVRT capability of wind turbines, representing a groundbreaking breakthrough in this field and providing a new technical path for stable grid-connected wind power operation.

[0022] Through the synergistic control and optimization of HESS (Hybrid Energy Storage System), the system can efficiently stabilize the DC bus voltage, thereby ensuring that the grid-side converter can reliably and continuously provide reactive power support during grid voltage fluctuations. This innovative solution fundamentally overcomes the inherent contradiction of traditional crowbar protection circuits—that is, the crowbar resistor inevitably absorbs a large amount of reactive power when protecting the unit, while the grid needs reactive power support most during faults. The system creatively combines supercapacitors (with extremely high power density and millisecond-level fast charging and discharging capabilities) and batteries (with significant energy density advantages and continuous and stable power supply characteristics) in a complementary and organic way, achieving perfect coordination of the two energy storage media in terms of time scale and power characteristics through intelligent energy management strategies. This synergistic effect not only achieves a system performance improvement of "1+1>2", but more importantly, it solves the technical problems that cannot be overcome by using supercapacitors alone (limited capacity), batteries alone (slow response), or traditional unloading resistors (high energy consumption and unable to provide reactive power), providing a better fault ride-through solution for new energy power plants.

[0023] The adaptive power allocation mechanism (such as fuzzy logic or optimization algorithm) based on multivariate feedback (voltage deviation, rate of change, SOC) proposed in this invention can perform refined and intelligent management of power surplus with different time scales and characteristics. This strategy not only responds quickly but also effectively protects energy storage components and extends their service life.

[0024] This method ensures the speed, smoothness, and high reliability of the low-voltage ride-through process. It avoids the power and torque surges caused by crowbar switching, improving the mechanical and electrical stability of the unit. Simultaneously, the hybrid energy storage system absorbs energy that would otherwise be wasted, enhancing the overall energy efficiency of the system.

[0025] All hardware components (supercapacitor, battery, DC-DC converter, DSP controller) in this invention are mature commercial products. The software algorithm can be embedded in the existing wind turbine main control program without major modifications to the main structure of the wind turbine. It is easy to implement and promote industrialization, and can be widely used in various wind turbine units such as doubly-fed and permanent magnet direct drive. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] The main contents of this invention include: The low-voltage ride-through control system of this embodiment mainly includes: I. System Hardware Configuration and Initialization The core component of a wind power generation system is a doubly-fed induction generator (DFIG), an asynchronous generator widely used in modern wind power generation. The generator's rotor is flexibly connected to the grid via a sophisticated back-to-back converter system. This back-to-back converter system consists of two key parts: the rotor-side converter (RSC) regulates the rotor current, while the grid-side converter (GSC) controls the power output on the grid side. Energy is buffered between the two via a DC bus capacitor, thus forming a stable DC bus voltage platform.

[0028] The innovative design of this system lies in the Hybrid Energy Storage System (HESS) directly connected in parallel to the DC bus, which is the core hardware device for achieving efficient energy management. The HESS employs a dual-branch architecture, with each branch possessing unique functional characteristics: The first branch is a supercapacitor branch, consisting of high-performance supercapacitor modules and a bidirectional DC-DC converter connected in series. The specially selected supercapacitors possess extremely low internal resistance and an ultra-long cycle life (typically exceeding one million cycles), specifically designed for rapid response to instantaneous, high-frequency power fluctuations in the system, such as sudden rises or falls in grid voltage. The second branch is a battery branch, composed of large-capacity lithium-ion battery modules and a matching bidirectional DC-DC converter. Leveraging its high energy density, the battery primarily handles the system's long-duration, low-frequency energy regulation needs, such as smoothing out wind power fluctuations.

[0029] The system's intelligent control hub comprises an advanced sensing and control system, including a high-precision voltage / current sensor network and a powerful system main controller. The sensor network collects key parameters in real time, such as grid voltage, DC bus voltage, rotor current, and grid-side current. The main controller integrates three main functional modules: a fault detection unit for system safety monitoring, a converter control module for precise power regulation, and a newly added HESS control module specifically responsible for optimizing the operation of the hybrid energy storage system.

[0030] Upon system startup, the main controller executes a comprehensive initialization procedure, presetting and calibrating all operating parameters. During operation, the controller continuously monitors the real-time status of the HESS, focusing on tracking the state of charge (SOC_sc) of the supercapacitor and the state of charge (SOC_bat) of the battery. Through intelligent algorithms, it ensures that both remain within their optimal operating range, thereby guaranteeing stable operation and optimal performance of the system under various operating conditions.

[0031] II. Cooperative Control Process for Low Voltage Ride-Through When a voltage drop occurs in the power grid, the system performs coordinated control according to the following steps: Step S201: Fault Detection and Mode Switching As a crucial protective component of the wind power generation system, the fault detection unit uses a high-precision ADC converter to sample and monitor the grid voltage in real time, and employs advanced software phase-locked loop (PLL) technology to accurately track changes in the phase angle and amplitude of the grid voltage. When the system detects an abnormal drop in the grid voltage amplitude that remains below the preset low-voltage ride-through (LVRT) threshold (typically set at 0.9 times the rated voltage), the intelligent controller can respond rapidly within 5 milliseconds. It sends an emergency switching command to the converter control module via the high-speed communication bus, seamlessly switching the entire wind power generation system from the conventional maximum power point tracking (MPPT) operating mode to the specially designed low-voltage ride-through protection mode, ensuring that the unit can maintain grid-connected operation during grid faults.

[0032] Step S202: Fast response of the converter Upon receiving the mode switching command, the converter control module will simultaneously initiate two parallel control processes: First, for the control of the rotor-side converter (RSC), the system will employ a composite control strategy integrating current limiting and flux tracking. Specifically, the control module will monitor the d-axis and q-axis components of the rotor current in real time and dynamically limit their reference values ​​to ensure that the current value does not exceed the converter's designed safe operating threshold under any operating condition. Simultaneously, the control algorithm will also introduce a feedforward compensation stage specifically for the DC component of the stator flux. This design can actively offset rotor overcurrent caused by sudden drops in grid voltage. Compared to traditional passive crowbar protection schemes, this active compensation mechanism has a faster response speed and better suppression effect.

[0033] Secondly, regarding the control of the grid-side converter (GSC), the system switches its control objective from the conventional DC voltage stabilization mode to a "reactive current priority" mode. Under this special operating condition, the GSC's reactive current reference value Iq_ref is dynamically calculated based on the real-time detected grid voltage drop, strictly adhering to grid connection technical specifications (e.g., when the grid voltage drops to 50% of its rated value, the converter needs to provide 1.0 per-unit reactive current support). Through this adaptive adjustment mechanism, the GSC can inject the maximum possible capacitive reactive current into the grid, effectively supporting the rapid recovery of the grid voltage. It is worth noting that in this operating mode, the control responsibility for maintaining DC bus voltage stability is primarily undertaken by the hybrid energy storage system (HESS). This collaborative control architecture ensures both grid support and the overall safe and stable operation of the system.

[0034] Step S203 (Core): HESS Linkage and Intelligent Power Distribution The HESS control module is activated, and its internal workflow is as follows: The total power command generation module is responsible for calculating the total power demand of the energy storage system in real time based on the system status. The power calculation unit continuously monitors the actual measured value of the DC bus voltage Udc and compares it in real time with the preset reference voltage value Udc_ref (typically 1150V) to obtain the voltage deviation signal ΔUdc. To improve the dynamic response performance of the system and suppress overshoot, this embodiment specifically designs a PI (proportional-integral) regulator with output limiting function to accurately calculate the total power command Pess_ref. The mathematical expression of this regulator is: Pess_ref = Kp ΔUdc+Ki ∫ΔUdcdt, where Kp is the proportional coefficient and Ki is the integral coefficient. When ΔUdc is detected to be positive (i.e., the DC bus voltage is higher than the reference value), Pess_ref outputs a positive power command, indicating that the Hybrid Energy Storage System (HESS) needs to absorb excess power to maintain voltage stability; Adaptive Power Allocation Strategy (Intelligent Control Based on Fuzzy Logic): This strategy is the core control algorithm for achieving efficient and coordinated operation of various components in a hybrid energy storage system. The adaptive power divider (implemented in this scheme using an advanced fuzzy logic controller) automatically starts working based on the system's operating status. This controller achieves optimal power allocation to energy storage components such as batteries and supercapacitors through steps including fuzzifying input variables, establishing an expert knowledge base, designing a fuzzy rule set, performing fuzzy inference, and defuzzifying the output. This intelligent allocation strategy fully considers the dynamic characteristics, state of charge, and power limitations of each energy storage component, ensuring that the system always operates at its optimal efficiency point.

[0035] The domain of the DC voltage change ΔUdc ranges from 0 to 500 volts, and its linguistic variables are divided into four levels: zero (Z) indicates a very small or negligible voltage change, small (S) indicates slight voltage fluctuations, medium (M) indicates a moderate voltage change, and large (B) indicates a significant voltage change. The domain of the DC voltage change rate dΔUdc / dt ranges from -1000 to 1000 volts per second, and this parameter is further subdivided into five linguistic values: negative large (NB) indicates a sharp voltage drop, negative small (NS) indicates a slow voltage drop, zero (Z) indicates a stable voltage, positive small (PS) indicates a slow voltage rise, and positive large (PB) indicates a rapid voltage increase. These linguistic values ​​are primarily used to assess the severity of DC voltage changes. The domain of the supercapacitor's state of charge (SOC_sc) is set between 0.2 and 0.9, and its linguistic variables are low (L) indicating insufficient energy storage, medium (M) indicating moderate energy storage, and high (H) indicating sufficient energy storage. The domain of the battery's state of charge (SOC_bat) ranges from 0.3 to 0.9, and it is also described using three linguistic variables: low (L) indicates insufficient battery power, medium (M) indicates that the battery power is at a medium level, and high (H) indicates that the battery power is sufficient.

[0036] In power distribution control systems, the supercapacitor power distribution coefficient Ksc is a key adjustment parameter, with its value strictly limited to between 0 and 1, i.e., its universe of discourse is [0, 1]. To facilitate fuzzy processing and control decisions, this parameter is divided into four linguistic variable values ​​with clear semantics: zero (Z) indicates no use of supercapacitor power; small (S) indicates a small amount of supercapacitor power is used; medium (M) indicates a moderate level of supercapacitor power use; and large (B) indicates that power is mainly provided by the supercapacitor. This linguistic value division method not only meets practical engineering needs but also effectively supports the implementation of fuzzy control algorithms, ensuring that the power distribution process is both accurate and flexible.

[0037] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

[0038] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A low-voltage ride-through control method for wind turbine generators, characterized in that, Includes the following steps: Step 1: Monitor the grid voltage in real time. When the grid voltage drops to the low voltage crossing threshold, start the hybrid energy storage system connected in parallel to the DC bus of the wind turbine converter. The hybrid energy storage system includes at least one power-type energy storage branch and one energy-type energy storage branch. Step 2: Generate the total power command Pess_ref that the hybrid energy storage system needs to absorb based on the deviation value ΔUdc of the DC bus voltage; Step 3: Based on the total power command Pess_ref, and taking into account the real-time status of the power-type energy storage branch and the energy-type energy storage branch, dynamically generate the power command allocated to each energy storage branch through an adaptive power allocation strategy. Step 4: Control each energy storage branch to absorb power according to the power command to stabilize the DC bus voltage. During low voltage ride-through, control the grid-side converter to preferentially inject reactive current into the grid to support grid voltage recovery.

2. The low-voltage ride-through control method for wind turbine generators according to claim 1, characterized in that, The power-type energy storage branch is a supercapacitor branch, and the energy-type energy storage branch is a battery branch. The supercapacitor branch and the battery branch are respectively connected to the DC bus through a bidirectional DC-DC converter.

3. The low-voltage ride-through control method for wind turbine generators according to claim 2, characterized in that, The total power command Pess_ref is generated based on the deviation value ΔUdc of the DC bus voltage and its rate of change dΔUdc / dt.

4. The low-voltage ride-through control method for wind turbine generators according to claim 3, characterized in that, The PI controller generates the total power command Pess_ref based on ΔUdc and dΔUdc / dt. The calculation formula is: Pess_ref = Kp × ΔUdc + Ki × ∫ΔUdc dt, where Kp is the proportional coefficient and Ki is the integral coefficient. The output is then limited.

5. The low-voltage ride-through control method for wind turbine generators according to claim 4, characterized in that, The adaptive power allocation strategy is a fuzzy logic control strategy. Its input variables include ΔUdc, dΔUdc / dt, the state of charge (SOC_sc) of the power-type energy storage branch and the state of charge (SOC_bat) of the energy-type energy storage branch. The output variable is the power allocation coefficient (Ksc) of the power-type energy storage branch. The power command Psc_ref = Ksc × Pess_ref for the power-type energy storage branch, and the power command Pbat_ref = (1 - Ksc) × Pess_ref for the energy-type energy storage branch.

6. The low-voltage ride-through control method for wind turbine generators according to claim 5, characterized in that, The rules for formulating the fuzzy logic control include: When ΔUdc is greater than the first voltage threshold (100V) and dΔUdc / dt is greater than the first rate of change threshold (500 V / s), power is preferentially allocated to the supercapacitor with fast response speed. When the state of charge (SOC_sc) of the power-type energy storage branch is higher than its set upper limit, Ksc is reduced to limit its charging. When the state of charge (SOC_bat) of the energy storage branch is lower than its set lower limit, it is reduced by (1-Ksc) to protect it from over-discharge.

7. The low-voltage ride-through control method for wind turbine generators according to claim 6, characterized in that, The adaptive power allocation strategy is as follows: construct an optimization function with the goal of minimizing the operating losses of the hybrid energy storage system; use the total power command Pess_ref, the SOC_sc, and the SOC_bat as constraints; and solve for the optimal power allocation command through a real-time optimization algorithm.

8. The low-voltage ride-through control method for wind turbine generators according to claim 7, characterized in that, When the low voltage ride-through control mode is activated, a control strategy combining current limiting and stator flux feedforward compensation is adopted for the rotor-side converter to actively suppress rotor overcurrent.

9. A low-voltage ride-through control method for wind turbine generators according to claim 8, characterized in that, The reference value of reactive current injected by the grid-side converter is dynamically calculated according to the grid voltage drop depth and in accordance with the grid connection regulations.

10. A low-voltage ride-through control method for wind turbine generators according to claim 9, characterized in that, The startup and power command generation of the hybrid energy storage system, the current control of the rotor-side converter, and the reactive power control of the grid-side converter are executed in parallel by the system's main controller, forming a collaborative control system for low-voltage ride-through.