Direct-drive wind turbine high and low voltage continuous ride-through control system and method

Abstract

This invention relates to the field of wind power grid connection control technology, specifically to a high and low voltage continuous ride-through control system and method for direct-drive wind turbines. The system includes a command generation unit, a fault simulation unit, an electrical quantity acquisition unit, a wind turbine protection execution unit, and a continuous ride-through coordination unit. The command generation unit generates the circuit breaker action sequence. The fault simulation unit simulates various voltage faults through a combination of opening and closing circuit breakers. The electrical quantity acquisition unit captures parameter characteristics and marks faults using multi-rate sampling. The wind turbine protection execution unit reduces active power and enhances reactive power absorption for voltage rises, and increases reactive current for voltage dips. In the event of a two-phase fault, it generates a reverse reactive current to offset the negative sequence component. The continuous ride-through coordination unit switches fault identifiers and resets strategies during voltage alternation. After normal operation is restored, it outputs a ride-through signal and an authentication report. This addresses the problems of insufficient adaptability to alternating faults and indiscriminate handling of phase faults in traditional control systems, improving the grid connection stability of wind turbines and ensuring the safe grid connection of wind power.

Description

Technical Field

[0001] This invention relates to the field of wind power grid connection control technology, and more specifically, to a high and low voltage continuous ride-through control system and method for direct-drive wind turbines. Background Technology

[0002] Grid connection control for wind power generation is an important technology. In wind power generation systems, grid voltage often rises or falls suddenly due to faults. Direct-drive wind turbines must have the ability to overcome these voltage anomalies to maintain grid connection stability and avoid large-scale grid disconnection accidents. This technology is of great significance for ensuring grid security after large-scale wind power integration and improving the utilization efficiency of renewable energy. Traditional ride-through control methods for single voltage faults are no longer able to cope with the voltage fluctuation scenarios that may occur in the grid.

[0003] However, traditional direct-drive wind turbine voltage ride-through technology suffers from core problems such as insufficient adaptability to continuous faults and conflicting control strategies. Existing solutions can only handle single-type voltage rise or fall faults, without considering the alternation of the two. When the grid experiences a voltage rise followed by a rapid fall, the wind turbine's original power reduction and reactive power absorption strategies cannot switch in time, resulting in insufficient reactive power regulation and overcurrent in the equipment. At the same time, the same control logic is used for two-phase and three-phase faults, without differentiated regulation for the negative sequence voltage component, which exacerbates voltage waveform distortion and leads to malfunction of the wind turbine protection system, triggering grid disconnection. These problems combined cause a sharp drop in the stability of the wind turbine under complex voltage faults, affecting not only the continuity of wind power output but also potentially triggering cascading grid faults. This makes it difficult to meet the stringent requirements of high-proportion renewable energy grids for wind turbine ride-through capabilities. To solve this problem, we provide a direct-drive wind turbine high and low voltage continuous ride-through control system and method. Summary of the Invention

[0004] The purpose of this invention is to provide a high and low voltage continuous ride-through control system and method for direct-drive wind turbines to solve the problems mentioned in the background art.

[0005] 1. Because traditional systems cannot cope with alternating voltage rises and falls, and the control strategy switching is not timely, resulting in equipment overcurrent, this case study uses a continuous cross-coordination unit to monitor voltage alternation and reset the control strategy, which can ensure the stability of the wind turbine under complex faults.

[0006] 2. Since traditional systems use the same control logic for two-phase and three-phase faults, the lack of differentiated adjustment of the negative sequence component exacerbates waveform distortion. Therefore, in this case, the negative sequence component is calculated by the wind turbine protection execution unit and a reverse reactive current is generated, which can reduce voltage distortion and prevent the protection system from malfunctioning.

[0007] To achieve the above objectives, a high and low voltage continuous ride-through control system for direct-drive wind turbines is provided, including:

[0008] The instruction generation unit is used to generate circuit breaker operation timing instructions based on the target fault type.

[0009] The fault simulation unit, connected to the instruction generation unit, actively generates any one of the following voltage fault conditions on the high-voltage side of the direct-drive wind turbine transformer by executing circuit breaker opening or closing operations:

[0010] No-load voltage rise fault, two-phase voltage rise fault, or three-phase voltage rise fault when the voltage rises to the preset rise ratio of the rated voltage.

[0011] No-load voltage drop fault, two-phase voltage drop fault, or three-phase voltage drop fault, where the voltage drops to the preset voltage drop ratio or zero of the rated voltage.

[0012] The electrical quantity acquisition unit is connected to the fault simulation unit and acquires the line voltage, positive sequence voltage, active power, reactive power and reactive current parameters of the high voltage side of the transformer in real time.

[0013] The wind turbine protection execution unit is connected to the electrical quantity acquisition unit and dynamically executes the wind turbine control strategy based on the acquired electrical quantity parameters.

[0014] When a voltage rise fault is detected, the active power output of the wind turbine is reduced and the reactive power absorption is increased.

[0015] When a voltage drop fault is detected, the reactive current output of the wind turbine is increased and the active power ramp-up rate is limited.

[0016] The continuous traversal coordination unit connects to the wind turbine protection execution unit during the duration of a single fault:

[0017] If alternating voltage rises and falls are detected, the voltage fault type identifier is switched and the control strategy of the wind turbine protection execution unit is reset.

[0018] When the electrical parameters return to the rated range, the control strategy restriction is lifted and a successful crossover signal is output.

[0019] The second objective of this invention is to provide a method for implementing a high and low voltage continuous ride-through control system for a direct-drive wind turbine, comprising the following steps:

[0020] S1. The instruction generation unit generates circuit breaker operation timing instructions according to the target fault type. The fault simulation unit actively generates voltage fault conditions with preset rise ratio or drop ratio on the high voltage side of the transformer substation through combination of opening and closing operations. Among them, no-load rise only operates the collector line circuit breaker, two-phase faults perform differentiated impedance control, three-phase faults are synchronously connected to the current limiting reactor, and all circuit breakers are sequentially operated according to adjustable time intervals.

[0021] S2. The electrical quantity acquisition unit uses a multi-rate sampling mechanism to capture the high-frequency distortion characteristics of line voltage and the trend of power parameter changes in real time. When the positive sequence voltage continuously exceeds the threshold, the fault type is marked, and a protection reference benchmark is generated based on the sliding average value of the parameters before the fault.

[0022] S3, when the wind turbine protection execution unit responds to the voltage rise, it reduces the active power output in stages and enhances the reactive power absorption intensity in steps. When the voltage drops, it increases the reactive current output and limits the active power climb rate. Under two-phase faults, it generates reverse reactive current to offset the negative sequence component and dynamically limits the active power upper limit. When high and low voltages alternate, it switches the fault flag and resets the control strategy by continuously passing through the coordination unit, retaining reactive power reserve or resetting the power reduction start point.

[0023] S4. When the electrical parameters return to the rated range, the continuous crossing coordination unit releases the control restrictions and outputs a crossing success signal, and simultaneously generates an authentication report containing the fault type, line voltage waveform, and power curve.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The continuous cross-coordination unit monitors the alternating changes of voltage rise and fall in real time. Once the alternation is identified, the fault type identifier is immediately switched and the control strategy is reset according to the switching direction. When switching from rise to fall, some reactive power absorption capacity is reserved as a backup. When switching from fall to rise, the current active power is used as a new starting point to perform power reduction control. This avoids the insufficient reactive power regulation capacity caused by the switching lag of traditional strategies, effectively prevents equipment overcurrent, and ensures the stable operation of the wind turbine under complex voltage fluctuations.

[0026] 2. For two-phase faults, the wind turbine protection execution unit calculates the negative sequence voltage component in real time, generates a reactive current in the opposite phase to offset the negative sequence effect, and dynamically adjusts the upper limit of active power output according to the severity of the negative sequence component, thus solving the voltage waveform distortion problem caused by traditional unified control logic. For three-phase faults, it achieves proportional voltage suppression by synchronously connecting a current-limiting reactor, reducing the maloperation of the protection system caused by waveform distortion and reducing the risk of grid disconnection.

[0027] 3. The fault simulation unit and the electrical quantity acquisition unit work together to enhance efficiency. The fault simulation unit executes the opening and closing operations according to the preset circuit breaker combination logic sequence, accurately simulating the transient process of various voltage faults. The electrical quantity acquisition unit adopts a multi-rate sampling mechanism, which captures voltage waveform distortion at high frequency, tracks power change trends at medium frequency, and generates a protection benchmark based on the sliding average value before the fault, providing accurate data support for the control strategy, improving the accuracy and reliability of ride-through control, ensuring the continuity of wind power output, and adapting to the stringent requirements of a high proportion of new energy power grids. Attached Figure Description

[0028] Figure 1This is an overall block diagram of the present invention;

[0029] Figure 2 This is the overall flowchart of the present invention.

[0030] The meanings of the labels in the diagram are as follows:

[0031] 1. Command generation unit; 2. Fault simulation unit; 3. Electrical quantity acquisition unit; 4. Fan protection execution unit; 5. Continuous crossing coordination unit. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention provides a high and low voltage continuous ride-through control system for direct-drive wind turbines. Please refer to [link / reference]. Figure 1 As shown, it includes:

[0034] Instruction generation unit 1 is used to generate circuit breaker operation timing instructions according to the target fault type;

[0035] Fault simulation unit 2, connected to command generation unit 1, actively generates any one of the following voltage fault conditions on the high-voltage side of the direct-drive wind turbine transformer by executing circuit breaker opening or closing operations:

[0036] No-load voltage rise fault, two-phase voltage rise fault, or three-phase voltage rise fault when the voltage rises to the preset rise ratio of the rated voltage.

[0037] No-load voltage drop fault, two-phase voltage drop fault, or three-phase voltage drop fault, where the voltage drops to the preset voltage drop ratio or zero of the rated voltage.

[0038] To accurately simulate different types of voltage faults, the fault simulation unit 2, when performing opening and closing operations, matches the preset circuit breaker combination logic according to the fault type, and generates fault conditions that closely resemble the actual power grid through differentiated operations. The specific implementation method is as follows:

[0039] For the no-load voltage rise fault, i.e., the abnormal voltage increase when the wind turbine is not under load, only the collector line connection circuit breaker is operated to reduce power interference. The voltage needs to be raised to a preset percentage of the rated voltage, ensuring no active power fluctuations interfere during the fault. The circuit breaker connecting the collector line to the wind turbine is disconnected, placing the wind turbine in a no-load state to prevent the wind turbine output power from affecting voltage detection. The voltage is gradually raised by adjusting the voltage regulator on the grid side, while keeping the high and low voltage circuit breakers on the transformer substation closed to ensure the voltage rise only affects the high-voltage side. Once the voltage stabilizes at the preset rise percentage, this state is maintained until the fault simulation ends. In the no-load state, only the opening and closing of the collector line circuit breaker is used to isolate the wind turbine power output from the voltage, ensuring the simulated voltage rise fault is effectively controlled. The fault is clean and repeatable. For two-phase rise faults, i.e., voltage rise in any two phases of a three-phase circuit, differential impedance control is used to raise the voltage of designated phases, raising the voltage of phases A and B to 110% of the rated voltage, while phase C maintains the rated voltage. Simulating a grid asymmetry fault, the corresponding circuit breakers of phases A and B are disconnected, and a current-limiting resistor with a preset resistance value is connected in their circuit (e.g., 5 ohms for phase A and 5 ohms for phase B). The circuit breaker of phase C remains closed with no impedance connection. When the circuit breakers of phases A and B are reclosed, the voltage of these two phases is raised due to voltage division using the connected impedance, while phase C maintains the rated voltage due to the lack of impedance connection. The line voltage is monitored in real time, and the voltage of phases A and B is stabilized at the preset rise ratio by adjusting the impedance value. The logic of differential impedance control is as follows:

[0040] By individually connecting the faulty phase to an impedance, an asymmetrical voltage distribution is artificially created, accurately simulating common two-phase voltage anomalies in the power grid. This provides a typical scenario for verifying subsequent wind turbine protection strategies. For three-phase drop faults, where the three-phase voltages simultaneously drop to a preset proportion of the rated voltage, current-limiting reactors are synchronously connected to achieve proportional voltage suppression. Furthermore, all circuit breaker actions are sequentially executed at adjustable time intervals to simulate power grid transients, causing the voltages of phases A, B, and C to simultaneously drop to 20% of the rated voltage, simulating a severe symmetrical fault in the power grid. Current-limiting reactors of the same specification are connected in series in the three-phase lines on the high-voltage side of the transformer substation. For example, each phase is connected to 10 millihenries. Command generation unit 1 sends synchronous opening and closing signals to control the three-phase circuit breakers to simultaneously open and then close, ensuring that the reactors are synchronously connected to the three-phase circuit. Utilizing the inductive reactance characteristics of the reactors, the three-phase voltages decrease simultaneously due to the inductive reactance voltage drop, maintaining the symmetry of the three-phase voltages and ensuring consistent drop proportions. The logic for synchronous connection is:

[0041] Three-phase faults require maintaining voltage symmetry. This is achieved through reactors with identical parameters and synchronous operation, ensuring proportional voltage drops across all three phases. This avoids introducing additional negative sequence components due to asynchronous operation, which could affect the accuracy of fault simulation. Circuit breaker operations for all types of faults are executed sequentially at adjustable time intervals to simulate transient power grid processes. An operation timing table is set as follows:

[0042] In a three-phase drop fault scenario, the process is as follows: "Disconnect the three-phase circuit breaker (50 ms) → Connect the reactor (50 ms) → Close the three-phase circuit breaker (50 ms)," with a total time of 150 ms. This closely reflects the rapid changes in actual power grid faults. A verification step is set between each operation step. After the circuit breaker is disconnected, the circuit current is checked to ensure that the operation is in place before proceeding to the next step, thus avoiding distortion of the fault simulation caused by misoperation. For example, when simulating a continuous fault of "first two-phase rise, then three-phase drop," the two-phase rise sequence is executed first (total time 200 ms), and the three-phase drop sequence is automatically started after a 100 ms interval. By controlling the time interval, the dynamic evolution process of the power grid fault is restored. Fault simulation unit 2 can accurately generate various voltage fault conditions, ensuring the diversity of fault types and restoring the transient characteristics of the power grid through serialized operations. This provides a realistic and reliable fault environment for electrical quantity acquisition and verification of wind turbine protection strategies.

[0043] Electrical quantity acquisition unit 3 is connected to fault simulation unit 2 to collect line voltage, positive sequence voltage, active power, reactive power and reactive current parameters on the high voltage side of the transformer in real time.

[0044] To accurately capture the dynamic characteristics of electrical parameters on the high-voltage side of the direct-drive wind turbine transformer, electrical quantity acquisition unit 3 adopts a multi-rate sampling mechanism, combined with a fault marking system and benchmark generation logic, to provide reliable data support for wind turbine protection strategies. The specific implementation method is as follows:

[0045] Based on the varying characteristics of different electrical parameters, differentiated sampling rates are employed to ensure that key features are not missed. Voltage signals are sampled at high frequency to capture waveform distortion. For line voltage, positive sequence voltage, and other voltage signals, high-frequency sampling is used, sampling 10 times per millisecond to focus on capturing voltage waveform distortion features, such as spikes during voltage surges, dips during voltage drops, and asymmetrical waveforms during two-phase faults. For example, when a two-phase rise fault occurs, high-frequency sampling can clearly record the instantaneous jump details of the fault phase voltage, while the minute fluctuations of the normal phase voltage can also be accurately captured, providing raw data for subsequent negative sequence component calculations. Power parameters are sampled at medium frequency to track trend changes. For power parameters such as active power, reactive power, and reactive current, medium-frequency sampling is used, sampling 100 times per second to track their changing trends, such as the gradual decrease of active power and the stepwise increase of reactive current during voltage rises. For example, during voltage dips, medium-frequency sampling can record the continuous change curve of reactive current slowly rising from the rated value to the safety limit, reflecting its adjustment trend without high-frequency sampling, avoiding data redundancy. The logic of multi-rate sampling is:

[0046] Voltage waveform distortion is often instantaneous (milliseconds), requiring high-frequency capture to preserve details. Power parameter changes, on the other hand, are relatively gradual (seconds), and intermediate-frequency sampling can reflect the trend. Combining both ensures data integrity while reducing data processing pressure. A fault marking system is established to monitor the positive-sequence voltage status in real time and trigger corresponding fault flags. When the positive-sequence voltage exceeds a high-voltage threshold or falls below a low-voltage threshold within a preset time range, a corresponding fault flag is triggered. Preset high-voltage thresholds (e.g., 110% of rated voltage) and low-voltage thresholds (e.g., 90% of rated voltage) are used, along with a duration condition: the positive-sequence voltage exceeding the high-voltage threshold for 20 milliseconds or falling below the low-voltage threshold for 20 milliseconds to avoid false markings caused by instantaneous interference. When the positive-sequence voltage exceeds the high-voltage threshold and meets the duration condition, it is marked as a "voltage rise fault," and further combined with line voltage data to distinguish whether it is a two-phase rise or a voltage rise. If only the voltages of phases A and B exceed the threshold, it is marked as "two-phase rise". When the positive sequence voltage is lower than the low voltage threshold and meets the duration condition, it is marked as "voltage drop fault". Similarly, it distinguishes between two-phase drop and three-phase drop. For example, if the positive sequence voltage is at 115% of the rated voltage (ultra-high voltage threshold) for 30 milliseconds and the line voltage shows that all three phases exceed the threshold, the system marks it as "three-phase rise fault". This provides clear fault type information for the wind turbine protection execution unit 4 and generates a protection strategy reference benchmark based on the sliding average value of parameters before the fault occurs. This ensures the rationality of strategy adjustment. The sliding window duration before the fault is set. The window contains all sampled data 1 second before the fault occurs, i.e., the historical values ​​of voltage and power. The average value of the parameters in the sliding window, i.e., the active power and reactive current during normal operation, is calculated as the "baseline state" before the fault occurs. For example, the sliding average of active power within one second before the fault is 800 kW. This value serves as the reference starting point for power reduction during voltage rise. The power is reduced in stages starting from 800 kW, and the reference benchmark is updated in real time as the window scrolls, ensuring that it always reflects the stable operating state before the fault. For example, if the wind turbine is in a power fluctuation phase before the fault, the sliding average will be dynamically adjusted to avoid reference distortion caused by using a single fixed value. The electrical quantity acquisition unit 3 not only accurately captures the details of voltage distortion and power change trends through multi-rate sampling, but also clarifies the fault type through the fault marking system. Furthermore, it provides an adjustment starting point for the protection strategy based on the sliding average, making the control of the subsequent wind turbine protection execution unit 4 more in line with the actual operating state, thus improving the accuracy and reliability of high and low voltage ride-through control.

[0047] The fan protection execution unit 4 is connected to the electrical quantity acquisition unit 3, and dynamically executes the fan control strategy based on the acquired electrical quantity parameters.

[0048] When a voltage rise fault is detected, the active power output of the wind turbine is reduced and the reactive power absorption is increased.

[0049] When a voltage drop fault is detected, the reactive current output of the wind turbine is increased and the active power ramp-up rate is limited.

[0050] To ensure stable operation of the wind turbine during voltage anomalies, the wind turbine protection actuator 4 employs differentiated dynamic adjustment strategies for voltage rise and fall faults. High and low voltage ride-through is achieved through phased, stepped power control. The specific implementation method is as follows:

[0051] When the wind turbine protection actuator 4 responds to a voltage rise fault, it reduces active power and enhances reactive power absorption according to preset stages, as follows:

[0052] The system reduces the active power output of the wind turbine in stages and enhances the reactive power absorption intensity in steps. When responding to voltage drop faults, it increases the reactive current output to a safe limit and limits the active power ramp-up rate. The power change rate of each stage is set to a configurable gradient value. The system is divided into three stages according to the voltage rise: 10%-20% is stage 1, 20%-30% is stage 2, and above 30% is stage 3. Each stage corresponds to a configurable power change rate gradient. For example, stage 1 reduces rated active power by 10% per minute, stage 2 by 20% per minute, and stage 3 by 30% per minute. The reactive power absorption intensity is set in a step gradient simultaneously. Stage 1 absorbs 20% of rated reactive power, stage 2 absorbs 40%, and stage 3 absorbs 60%, and the maximum absorption intensity does not exceed the rated reactive power capacity of the wind turbine.

[0053] Phase 1: When a voltage rise of 15% is detected (Phase 1 range), the active power is reduced at a rate of 10% per minute, i.e., from the rated 1000 kW to 900 kW, while absorbing 20% ​​of the rated reactive power to prevent the voltage from rising further.

[0054] Phase 2: If the voltage continues to rise to 25% (Phase 2 range), the active power reduction rate is accelerated to 20% per minute, from 900 kW to 720 kW, and the reactive power absorption is enhanced to 40%, thereby suppressing the voltage rise by increasing reactive power consumption;

[0055] Phase 3: If the voltage exceeds 30%, the active power will be reduced to a safe value (300 kW) at a rate of 30% per minute, while reactive power absorption will be increased to 60%. This will stabilize the grid voltage to the maximum extent possible. The greater the voltage rise, the more significant the impact on the grid. By gradually increasing the adjustment intensity, secondary disturbances caused by power surges can be avoided, and voltage anomalies can be specifically suppressed. When a "voltage drop fault" is detected, i.e., the positive sequence voltage is lower than 90% of the rated value, a strategy that primarily increases reactive current while limiting active power rise will be implemented.

[0056] The voltage drop is divided into stages based on its depth: 10%-30% is Stage A, 30%-50% is Stage B, and above 50% is Stage C. Each stage corresponds to a reactive current output gradient: Stage A outputs 30% of the rated current, Stage B outputs 60%, and Stage C outputs 90%, all within the rated current safety limit. For example, if the voltage drops by 20% (Stage A), the reactive current is immediately increased from the rated 200 amps to 30% (60 amps); if it drops to 40% (Stage B), it is increased to 60% (120 amps). Reactive power is injected to support the grid voltage recovery. The maximum active power ramp-up rate is set, not exceeding 10% of the rated value per minute, to avoid increasing the grid load due to a rapid increase in active power during voltage drops. For example, during voltage recovery, when the active power recovers from 300 kW, it increases by a maximum of 100 kW per minute (10% of the rated value) to ensure that no additional active power is generated before the voltage stabilizes. When new power fluctuations occur and voltage drops occur, reactive current is used to support the voltage first, while the active power ramp-up rate is limited to prevent the grid from bearing additional load in a vulnerable state and to ensure the smoothness of voltage recovery. The power change rate gradient value of each stage can be flexibly configured according to the wind turbine model and grid requirements. For large-capacity wind turbines (such as 5 MW and above), the gradient value can be set small (such as 5% per minute in stage 1) to avoid excessive adjustment range affecting grid stability. For wind turbines connected to weak grids, the gradient value can be set large (such as 15% per minute in stage 1) to speed up the response and suppress the spread of voltage anomalies. For example, if a 2 MW wind turbine is connected to a strong grid, the active power reduction gradient in stage 1 of voltage rise is set to 8% per minute, while when connected to a weak grid, the gradient in the same stage is set to 12% per minute to ensure that the adjustment strategy matches the actual operating environment. While ensuring the safety of the wind turbine itself, it effectively supports grid stability and achieves continuous high and low voltage ride-through.

[0057] When dealing with two-phase rise faults or two-phase drop faults, the wind turbine protection execution unit 4 calculates the negative sequence voltage component in real time and generates a reverse phase reactive current accordingly. At the same time, it dynamically adjusts the upper limit of active power output based on the severity of the negative sequence voltage component.

[0058] To address the voltage waveform distortion caused by the negative sequence voltage component in two-phase faults, the wind turbine protection actuator 4, for two-phase rise or fall faults, achieves precise suppression by real-time calculation of the negative sequence component, generation of reverse reactive current, and dynamic adjustment of the active power upper limit. The specific implementation method is as follows:

[0059] When the electrical quantity acquisition unit 3 marks "two-phase rise fault" (e.g., voltage rise in phases A and B, phase C is normal) or "two-phase drop fault" (e.g., voltage drop in phases A and B, phase C is normal), the fan protection execution unit 4 immediately starts the calculation of the negative sequence voltage component:

[0060] Real-time line voltage values ​​of phases A, B, and C on the high-voltage side of the transformer substation are obtained through high-frequency sampling (e.g., phase A 1100V, phase B 1100V, phase C 1000V, rated voltage 1000V). Based on the asymmetric characteristics of the three-phase voltage, the negative-sequence voltage component is extracted using the symmetrical component method, a method to decompose asymmetric three-phase quantities into symmetrical components. The magnitude of the negative-sequence component reflects the degree of asymmetry in the three-phase voltage; the larger the component, the more severe the disturbance to the power grid caused by a two-phase fault. The calculated negative-sequence voltage component is 100V, indicating a high degree of asymmetry. The core characteristic of a two-phase fault is three-phase voltage asymmetry, and the negative-sequence component is a key indicator for quantifying this asymmetry. Its value directly determines the strength of subsequent suppression strategies. The negative-sequence voltage component generates a reverse-phase reactive current to counteract its influence. The phase of the reverse-phase reactive current is opposite to that of the negative-sequence voltage component; that is, the negative-sequence voltage component has a phase of 60 degrees, while the current has a phase of 240 degrees. The amplitude is proportional to the magnitude of the negative-sequence voltage component. For example, a negative-sequence component of 100 volts corresponds to a reverse reactive current of 200 amperes, and a component of 50 volts corresponds to 100 amperes. This ensures that the current accurately neutralizes the interference of the negative-sequence component. Through the converter of the wind turbine, a device used for power conversion, the generated reverse-phase reactive current is injected into the power grid, preferentially from the faulty phases, namely phases A and B. The symmetry changes of the three-phase voltage are monitored in real time. After injection, the voltage of phases A and B gradually decreases to 1050 volts, while phase C remains at 10 volts. At 00 volts, the degree of three-phase asymmetry is reduced. For example, in a two-phase rise fault, the negative sequence voltage component is 80 volts. A reactive current with opposite phase and amplitude of 160 amperes is injected into phases A and B, canceling the negative sequence component to below 30 volts. The voltage waveform distortion is significantly improved. At the same time, the upper limit of active power output is adjusted in stages according to the severity of the negative sequence voltage component to avoid active power fluctuations exacerbating voltage asymmetry. The threshold range of negative sequence component is preset: 0-50 volts is mild, 50-100 volts is moderate, and above 100 volts is severe. Corresponding to different active power upper limit adjustment ratios, the upper limit is 90% of the rated value for mild, 70% for moderate, and 50% for severe. If the negative sequence component is 60 volts, which is moderate, the upper limit of active power output will be adjusted from the rated value. The active power delivered by the wind turbine to the grid is limited from 1000 kW to 700 kW. If the negative sequence component drops to 40 volts (mild), the upper limit is raised to 900 kW. This reduces power generation loss while ensuring grid stability. The more severe the negative sequence component, the weaker the grid's ability to withstand active power fluctuations. Lowering the active power limit can reduce additional impacts on the grid. Combined with the injection of reverse reactive current, a coordinated control of "suppressing negative sequence + stabilizing active power" is formed. The wind turbine protection execution unit 4, targeting the asymmetrical characteristics of two-phase faults, directly cancels negative sequence interference through reverse reactive current and avoids secondary fluctuations by dynamically adjusting the active power limit. This effectively improves voltage waveform distortion, reduces the risk of malfunction of the wind turbine protection system, and ensures grid connection stability under two-phase faults.

[0061] The reactive power absorption intensity of the wind turbine protection actuator 4 increases with the rise of the positive sequence voltage, and the reactive current output intensity increases with the drop depth of the positive sequence voltage. The maximum regulation intensity does not exceed the safety limits of the wind turbine's rated reactive capacity and rated current.

[0062] To ensure that the reactive power regulation of the wind turbine effectively stabilizes the power grid while remaining within its safe operating range during voltage rise or fall, the following implementation method is used: dynamically matching the positive sequence voltage change amplitude with the reactive power regulation intensity and strictly limiting the upper limit of regulation.

[0063] When a positive sequence voltage rise is detected, the reactive power absorption intensity is increased in stages according to the magnitude of the rise, as follows:

[0064] The positive sequence voltage rise is divided into multiple intervals: 10%-20% of the rated voltage (Interval 1), 20%-30% (Interval 2), and above 30% (Interval 3). Each interval corresponds to a preset reactive power absorption ratio: Interval 1 absorbs 20% of the rated reactive power capacity, Interval 2 absorbs 40%, and Interval 3 absorbs 60%. The electrical quantity acquisition unit 3 continuously monitors the positive sequence voltage value. When the rise increases from 15% (Interval 1) to 25% (Interval 2), the fan protection execution unit 4 automatically increases the reactive power absorption intensity from 20% to 40%. That is, when the rated reactive power capacity is 1000 kV, the absorption is adjusted from 200 kV to 400 kV. Before adjustment, it is verified whether the current reactive power absorption intensity exceeds the rated reactive power capacity of the wind turbine, i.e., the maximum should not exceed 1000 kvar. If the increase is too large and the calculated absorption intensity exceeds the limit, the rated capacity will be automatically used as the upper limit. For example, if the theoretical absorption of interval 3 is 600 kvar, and it does not exceed the limit, it will be executed. If the calculated value reaches 1200 kvar due to special circumstances, it will be absorbed as 1000 kvar. The greater the voltage increase, the more excess reactive power in the grid, and it is necessary to balance the grid by increasing the absorption intensity, but it must be limited by the reactive power capacity of the wind turbine itself to avoid equipment overload. When a positive sequence voltage drop is detected, the reactive current output intensity is increased in stages according to the depth of the drop, as follows:

[0065] The positive sequence voltage sag depth is divided into multiple intervals: 10%-30% of the rated voltage is interval A, 30%-50% is interval B, and above 50% is interval C. Each interval corresponds to a preset reactive current output ratio: interval A outputs 30% of the rated current, interval B outputs 60%, and interval C outputs 90%. When the voltage sag deepens from 20% (interval A) to 40% (interval B), the actuator will reduce the reactive current output from 30% of the rated current, i.e., when the rated current is 500 amperes. The output is initially 150 amps, then increased to 60% (300 amps). Reactive power injection supports voltage recovery. Before each adjustment, the current output current is checked to ensure it does not exceed the wind turbine's rated current, i.e., the maximum should not exceed 500 amps. If the voltage drop is too deep, causing the calculated output strength to exceed the limit, the rated current will be used as the upper limit. That is, the theoretical output for interval C should be 450 amps. If it does not exceed the limit, it will be executed. If the calculated value reaches 550 amps, then 500 amps will be output. The greater the voltage drop, the more urgent the grid's demand for reactive power, requiring an increase in output strength. The system replenishes reactive power, but must keep it within the rated current range to prevent damage to components such as converters due to overcurrent. To ensure the safety and continuity of the adjustment process, the actuator has a built-in real-time monitoring and feedback mechanism. It continuously compares the current reactive power absorption / output value with the rated capacity / current. When it reaches 90%, it issues an early warning to remind users to be cautious in subsequent adjustments. If a sudden voltage change causes the adjustment intensity to approach the limit instantaneously, a buffer mechanism is automatically triggered, gradually increasing the value to the limit within 0.5 seconds instead of an instantaneous jump, thus avoiding current or power surges. For example, if a sudden rise in positive sequence voltage causes the calculated reactive power absorption intensity to reach 95% of the rated capacity, the actuator will first absorb at 90%, gradually increasing to 95% within 1 second, while monitoring the equipment temperature and current waveform. After confirming that there are no abnormalities, it will maintain a stable output. Through such dynamic adjustment and limit control, the wind turbine protection actuator 4 can accurately match the reactive power adjustment intensity according to the degree of voltage abnormality, and prevent equipment damage through safety limit constraints. This ensures the stability of the power grid while achieving the safe operation of the wind turbine itself.

[0066] If alternating voltage rises and falls are detected, switch the voltage fault type identifier and reset the control strategy of the fan protection execution unit 4.

[0067] When the electrical parameters return to the rated range, the control strategy restriction is lifted and a successful crossover signal is output.

[0068] When the continuous crossing coordination unit 5 detects alternating voltage rises and falls, it immediately switches the voltage fault type identifier and resets the control strategy of the wind turbine protection execution unit 4. When the voltage rises and falls, it retains a portion of the reactive power absorption capacity for backup. When the voltage falls and rises, it executes power reduction control with the current active power value as the new starting point.

[0069] To address the complex fault scenarios involving alternating voltage rises and falls, the continuous pass-through coordination unit 5 ensures that the control logic of the wind turbine protection execution unit 4 quickly adapts to changes in fault type through real-time monitoring and strategy reset. The specific implementation method is as follows:

[0070] The continuous traversal coordination unit 5 continuously receives positive sequence voltage data transmitted by the electrical quantity acquisition unit 3. When it detects that the voltage state changes from rising to falling or from falling to rising, it immediately performs the following operations:

[0071] The conditions for state switching are set. When the positive sequence voltage drops from above the high voltage threshold (110% of the rated voltage) to below the low voltage threshold (90% of the rated voltage), and this change is completed within 50 milliseconds, it is determined as "voltage rise to voltage drop". When the positive sequence voltage rises from below the low voltage threshold to above the high voltage threshold, and this change is completed within 50 milliseconds, it is determined as "voltage drop to voltage rise". Once the state switch is determined, the fan protection actuator 4 immediately switches from "voltage rise fault" to "voltage drop fault" and synchronizes the new identifier as the basis for adjusting its control strategy. For example, if the positive sequence voltage drops from 115% (rise state) of the rated voltage (fall state) to 85% (fall state) within 30 milliseconds, the coordination unit determines it as "voltage rise to voltage drop", updates the fault identifier to "voltage drop fault", and notifies the actuator to switch to the drop response strategy. When the fault type changes from voltage rise to voltage drop, the continuous crossing coordination unit 5 guides the wind turbine protection execution unit 4 to reset the strategy according to the following logic: when switching from the rise state to the drop state, the reactive power absorption function is not immediately and completely shut down. Instead, 30%-50% of the current reactive power absorption intensity is retained, that is, the original absorption is 400 kVAR, and 150 kVAR is retained as a backup regulation capacity to cope with the possible rise again. While retaining the backup capacity, the core control logic of voltage drop is executed first to quickly increase the reactive current output, that is, the reactive current is output according to the gradient value corresponding to the drop depth, and the active power climb rate is limited. Voltage changes are monitored in real time. If the drop state continues to be stable, that is, maintained for more than 100 milliseconds, the retained reactive power absorption backup capacity is gradually reduced, such as 10% every 20 milliseconds, until it is completely shut down to ensure full support for voltage recovery.If a voltage spike occurs again in the short term, immediately activate the backup capacity to enhance the absorption strength. For example, when transitioning from a spike to a drop, maintain a reactive power absorption reserve of 200 kvar and simultaneously output 300 amps of reactive current to support the voltage. After 100 milliseconds, when the voltage stabilizes, gradually reduce the backup absorption capacity to 0, focusing on drop response. When the fault type changes from voltage drop to spike, continuously guide the execution unit through coordination unit 5 to reset the strategy according to the following logic: set the active power output value at the moment of switching, such as the current active power of 600 kW, as the new starting point for power reduction, and no longer trace back to the baseline value before the fault to avoid grid fluctuations caused by rapid power recovery. Starting from the current active power value, reduce the power in stages according to the gradient value corresponding to the voltage spike magnitude. For example, if a 20% spike corresponds to a 20% reduction per minute, then starting from 600 kW, the power will be reduced in stages. The power output is reduced to 480 kW and 384 kW per minute. Simultaneously, the reactive power absorption intensity is increased in a stepped gradient corresponding to the increase in power output. A 20% increase corresponds to the absorption of 40% of the rated reactive power, ensuring coordinated suppression of voltage rise with the power reduction operation. For example, when transitioning from a drop to a rise, if the current active power is 500 kW and the increase is 25%, then starting from 500 kW, the output is reduced to 400 kW and 320 kW at a rate of 20% per minute. Simultaneously, reactive power absorption is gradually increased from 0 to 40% of the rated capacity. This continuous operation through coordination unit 5 solves the problem of lag in strategy switching in traditional control: when transitioning from a rise to a drop, reserve capacity is maintained to cope with repeated fluctuations; when transitioning from a drop to a rise, the current active power is used as the starting point to avoid power surges. This ensures that the wind turbine maintains stable regulation capability under alternating faults, guaranteeing grid connection safety.

[0072] To ensure that the direct-drive wind turbine can stably recover to normal operation after a voltage anomaly, the continuous crossing coordination unit 5 strictly determines the conditions for successful crossing through multi-dimensional parameter monitoring. The specific implementation method is as follows:

[0073] The positive sequence voltage remains stable within the rated range, and the active power fluctuation rate and reactive power deviation rate meet the preset tolerance thresholds. The positive sequence voltage data transmitted by the electrical quantity acquisition unit 3 is continuously received by the coordination unit 5 in real time. The primary judgment condition is that the positive sequence voltage must remain stable within the rated range, such as 90%-110% of the rated voltage. The upper and lower limits of the rated range of the positive sequence voltage are set, that is, when the rated voltage is 1000 volts, the lower limit is 900 volts and the upper limit is 1100 volts. When the positive sequence voltage is detected to rise back into this range, the timing starts. The positive sequence voltage is required to run stably within the rated range for a preset time, such as 2 seconds, during which there should be no fluctuations exceeding the range, that is, the voltage is always between 950-1050 volts within 2 seconds. If the voltage exceeds the range again midway, the timing is restarted to ensure the stability of voltage recovery rather than instantaneous fluctuations. Positive sequence voltage is a core indicator reflecting the overall state of the power grid, and its continuous stability is the basis for wind turbines to resume normal operation. This avoids misjudging a successful cross-through due to a brief period of voltage compliance. On the basis of voltage stability, the fluctuation of active power is monitored to ensure that its fluctuation rate is within the preset tolerance threshold. The active power fluctuation rate is the ratio of the maximum change in active power per unit time, such as 1 second, to the current average active power. For example, if the active power increases from 800 kW to 820 kW in 1 second, and the average value is 810 kW, the fluctuation rate is 20 / 810. The preset tolerance threshold is determined when the calculated active power fluctuation rate is below the threshold for 3 consecutive unit time periods, i.e., 3 seconds. For example, if the threshold is 5%, and the fluctuation rates are 3%, 4%, and 2% respectively within 3 consecutive seconds, then the condition is met. Excessive active power fluctuations will cause secondary impacts on the power grid. It is necessary to ensure that the active power remains stable during the recovery phase to avoid the voltage from becoming unstable again due to power fluctuations just as it stabilizes. At the same time, the deviation of reactive power should be monitored to ensure that its deviation rate from the rated reactive power is within the preset range. The reactive power deviation rate is the ratio of the difference between the current reactive power and the rated reactive power to the rated reactive power. For example, if the rated reactive power is 500 kVAR and the current reactive power is 520 kVAR, the deviation rate is 20 / 500. The preset tolerance threshold is 10%. When the reactive power deviation rate is lower than this threshold for 3 consecutive units of time, such as 3 seconds, the reactive power deviation is judged to meet the standard.For example, if the threshold is 10% and the deviation rates for three consecutive seconds are 6%, 8%, and 5%, then the conditions are met. When all three conditions—positive sequence voltage stability, active power fluctuation rate compliance, and reactive power deviation rate compliance—are simultaneously met, the continuous crossing coordination unit 5 immediately outputs a crossing success signal. This signal contains key information such as fault type, voltage recovery time, and power stabilization duration, and is simultaneously sent to the wind turbine control system and the power grid dispatch center, indicating that the wind turbine has met the conditions for normal grid connection. At the same time, the control strategy restrictions on the wind turbine protection execution unit 4 are lifted, the active power ramp-up rate is no longer restricted, and reactive power regulation is restored. The normal mode of the circuit allows the wind turbine to gradually return to normal operation. For example, after a wind turbine experiences a voltage drop fault, if the positive sequence voltage remains stable at 950-1050 volts for 2 seconds, the active power fluctuation rate is below 5% for 3 consecutive seconds, and the reactive power deviation rate is below 10% for 3 consecutive seconds, the coordination unit determines that the crossing is successful, outputs a signal, and removes the control restrictions. Through such multi-condition verification, the continuous crossing coordination unit 5 ensures the recovery quality of the wind turbine after crossing the voltage abnormality. This avoids grid instability caused by premature judgment and prevents excessive delay from affecting the wind turbine's power generation efficiency, providing a reliable guarantee for the safe connection of wind power to the grid.

[0074] When a successful crossing signal is generated, a certification report is simultaneously output, including the fault type, the line voltage waveform recorded by the electrical quantity acquisition unit 3, the active power curve, and the reactive current curve.

[0075] In this invention, the instruction generation unit 1 generates the circuit breaker action sequence, the fault simulation unit 2 simulates various voltage faults through opening and closing combinations, the electrical quantity acquisition unit 3 captures parameter features and marks faults by sampling at multiple rates, the wind turbine protection execution unit 4 reduces active power and enhances reactive power absorption for voltage rise, increases reactive current for voltage drop, generates reverse reactive current to cancel negative sequence components during two-phase faults, and the continuous crossing coordination unit 5 switches fault labels and resets strategies during voltage alternation. After normal operation is restored, it outputs a crossing signal and authentication report. This solves the problems of insufficient adaptability to alternating faults and indiscriminate handling of phase faults in traditional control, improves the grid connection stability of wind turbines, and ensures the safe grid connection of wind power.

[0076] The second objective of this invention is to provide a method for implementing a high-low voltage continuous ride-through control system for a direct-drive wind turbine, comprising the following steps:

[0077] S1. The instruction generation unit 1 generates circuit breaker operation timing instructions according to the target fault type. The fault simulation unit 2 actively generates voltage fault conditions with preset rise ratio or drop ratio on the high voltage side of the transformer through the combination of opening and closing operations. Among them, no-load rise only operates the collector line circuit breaker, two-phase faults perform differentiated impedance control, three-phase faults are synchronously connected to the current limiting reactor, and all circuit breakers are sequentially operated according to adjustable time intervals.

[0078] S2 and the electrical quantity acquisition unit 3 use a multi-rate sampling mechanism to capture the high-frequency distortion characteristics of line voltage and the trend of power parameter changes in real time. When the positive sequence voltage continuously exceeds the threshold, the fault type is marked, and a protection reference benchmark is generated based on the sliding average value of parameters before the fault.

[0079] S3, when the wind turbine protection execution unit 4 responds to the voltage rise, it reduces the active power output in stages and enhances the reactive power absorption intensity in steps. When the voltage drops, it increases the reactive current output and limits the active power climb rate. Under two-phase faults, it generates reverse reactive current to offset the negative sequence component and dynamically limits the active power upper limit. When high and low voltages alternate, it switches the fault flag and resets the control strategy through the continuous crossing coordination unit 5, retaining reactive power reserve or resetting the power reduction start point.

[0080] S4. When the electrical parameters return to the rated range, the continuous crossing coordination unit 5 releases the control restrictions and outputs a crossing success signal, and simultaneously generates an authentication report containing the fault type, line voltage waveform and power curve.

[0081] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A direct drive wind turbine high-low voltage continuous ride through control system, characterized in that, The application relates to a wind turbine protection system, comprising: an instruction generating unit (1) for generating a circuit breaker action timing instruction according to a target fault type; a fault simulation unit (2) connected with the instruction generating unit (1) and capable of generating any one of the following voltage fault conditions on a high-voltage side of a box transformer by performing a circuit breaker opening or closing operation: a no-load lifting fault of voltage lifting to a preset lifting ratio of a rated voltage, a two-phase lifting fault or a three-phase lifting fault; a no-load dropping fault of voltage dropping to a preset dropping ratio of the rated voltage or zero, a two-phase dropping fault or a three-phase dropping fault; an electrical quantity collecting unit (3) connected with the fault simulation unit (2) and capable of collecting line voltage, positive sequence voltage, active power, reactive power and reactive current parameters of the high-voltage side of the box transformer in real time; a wind turbine protection executing unit (4) connected with the electrical quantity collecting unit (3) and capable of dynamically executing a wind turbine control strategy according to the collected electrical quantity parameters: when detecting the voltage lifting fault, reducing the wind turbine active power output and increasing the reactive power absorption; when detecting the voltage dropping fault, increasing the wind turbine reactive current output and limiting the active power climbing rate; a continuous crossing coordination unit (5) connected with the wind turbine protection executing unit (4) and capable of switching a voltage fault type identifier and resetting the control strategy of the wind turbine protection executing unit (4) if monitoring that the voltage lifting and dropping occur alternately during a single fault duration; when the electrical quantity parameters recover to a rated range, releasing the control strategy limitation and outputting a crossing success signal. When performing the opening or closing operation, preset circuit breaker combination logic is matched according to different fault types:

2. The direct drive wind turbine high-low voltage ride through control system of claim 1, wherein, wherein for the no-load lifting fault, only the collector line connected circuit breaker is operated to reduce power interference, for the two-phase lifting fault, differential impedance control is performed to make the specified phase voltage lifting, for the three-phase dropping fault, a current limiting reactor is synchronously connected to realize equal proportion voltage suppression, and all the circuit breaker actions are sequentially performed according to an adjustable time interval to simulate a power grid transient process. The electrical quantity collecting unit (3) adopts a multi-rate sampling mechanism to capture the dynamic characteristics of electrical parameters:

3. The direct drive wind turbine high-low voltage ride through control system of claim 1, wherein, voltage signals are sampled at a high frequency to capture waveform distortion, power parameters are sampled at a medium frequency to track trend changes, a fault marking system is established, corresponding fault identification is triggered when the positive sequence voltage exceeds a high voltage threshold or is lower than a low voltage threshold within a preset time range, and a protection strategy reference benchmark is generated based on the sliding average value of the parameters before the fault occurs. The wind turbine protection executing unit (4) reduces the wind turbine active power output in stages and enhances the reactive power absorption strength in steps in response to the voltage lifting fault, and increases the reactive current output to a safety limit value and limits the active power climbing rate in response to the voltage dropping fault, wherein the power change rate of each stage is set as a configurable gradient value.

4. The direct drive wind turbine high-low voltage ride through control system of claim 1, wherein, When processing the two-phase lifting fault or the two-phase dropping fault, the wind turbine protection executing unit (4) calculates a negative sequence voltage component in real time and generates a reverse phase reactive current according to the negative sequence voltage component, and dynamically adjusts an upper limit value of the active power output according to the severity of the negative sequence voltage component.

5. The direct drive wind turbine high-low voltage ride through control system of claim 4, wherein, ​ 6. The direct drive wind turbine high-low voltage ride through control system of claim 1, wherein, The continuous crossing coordination unit (5) switches the voltage fault type identification and resets the control strategy of the fan protection execution unit (4) immediately when it monitors that voltage rise and drop occur alternately, wherein part of reactive power absorption capacity is reserved as standby when the rise turns to drop, and the current active power value is taken as the new starting point to execute the power reduction control when the drop turns to rise.

7. The direct drive wind turbine high-low voltage ride through control system of claim 3, wherein, The reactive power absorption strength of the fan protection execution unit (4) is enhanced with the increase of the positive sequence voltage rise amplitude, and the reactive current output strength is improved with the increase of the positive sequence voltage drop depth, and the maximum adjustment strength does not exceed the safety limit of the rated reactive capacity and the rated current of the fan.

8. The direct drive wind turbine high-low voltage ride through control system of claim 1, wherein, The conditions for the continuous crossing coordination unit (5) to output the crossing success signal are: The positive sequence voltage is continuously stable in the rated range, and the active power fluctuation rate and the reactive power deviation rate meet the preset tolerance threshold.

9. The direct drive wind turbine high-low voltage ride through control system of claim 1, wherein, The authentication report containing the fault type, the line voltage waveform, the active power curve and the reactive current curve recorded by the electrical quantity acquisition unit (3) is output synchronously when the crossing success signal is generated.

10. A method for implementing a direct-drive wind turbine high-low voltage ride-through control system comprising the direct-drive wind turbine high-low voltage ride-through control system of any one of claims 1-9, characterized by: The method comprises the following steps: S1, the instruction generation unit (1) generates a circuit breaker action time sequence instruction according to a target fault type, and the fault simulation unit (2) generates a voltage fault working condition with a preset rise ratio or drop ratio on the high-voltage side of the box transformer by a combination of opening and closing operations, wherein the no-load rise only operates the collector line circuit breaker, the two-phase fault executes differential impedance control, the three-phase fault synchronously accesses a current limiting reactor, and all circuit breakers are sequentially operated according to an adjustable time interval; S2, the electrical quantity acquisition unit (3) captures the line voltage high-frequency distortion characteristics and the power parameter change trend in real time by a multi-rate sampling mechanism, marks the fault type when the positive sequence voltage continuously exceeds the threshold value, and generates a protection reference benchmark based on the sliding average value of the parameters before the fault; S3, the fan protection execution unit (4) reduces the active output and enhances the reactive absorption strength in stages in response to the voltage rise, increases the reactive current output and limits the active climbing rate in response to the voltage drop, generates a reverse reactive current to offset the negative sequence component and dynamically limits the active upper limit under two-phase fault, switches the fault identification and resets the control strategy through the continuous crossing coordination unit (5) when the high and low voltages are alternated, and reserves the reactive standby or resets the power reduction starting point; S4, when the electrical quantity parameters recover to the rated range, the continuous crossing coordination unit (5) removes the control limitation and outputs the crossing success signal, and synchronously generates an authentication report containing the fault type, the line voltage waveform and the power curve.

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