A fault ride-through control method and system for doubly fed wind turbine units

Abstract

This disclosure provides a fault ride-through control method and system for doubly-fed induction generator (DFIG) wind turbines. By introducing a refined interval segmentation mechanism based on voltage amplitude, the reactive power coefficient is dynamically adjusted under different drop or rise depths. Combined with the reactive power capacity limits of the rotor-side converter and the grid-side converter, optimal reactive power allocation with rotor-side priority and grid-side auxiliary coordination is achieved. Furthermore, by introducing active power feedforward compensation on the grid side to quickly suppress DC bus voltage fluctuations, and adopting a dynamic limiting strategy based on the current circle on the rotor side, the system effectively suppresses rotor overcurrent and DC overvoltage risks while fully supporting grid voltage recovery. This significantly improves the ride-through capability and operational safety of DFIG wind turbines during grid faults, providing reliable technical support to avoid large-scale grid disconnection of the units.

Description

Technical Field

[0001] This invention relates to the field of new energy grid connection control strategy technology, and in particular to a fault ride-through control method and system for doubly fed wind turbine generators. Background Technology

[0002] As wind power installed capacity continues to rise, the instability of wind power has had a significant impact on the power grid. When a grid fault causes a major blackout, it is often accompanied by widespread disconnection of wind turbines from the grid due to voltage drops or rises. Therefore, the grid connection standards for wind turbines are becoming increasingly stringent, requiring not only that wind turbines have frequency and voltage regulation capabilities like traditional turbines, but also that they have a certain degree of fault ride-through capability.

[0003] Doubly fed induction generator (DFIG) wind turbines have been widely adopted due to their advantages such as wide turbine speed range, low converter capacity requirements, and low cost, gradually becoming the mainstream model in the wind power market. To prevent DFIG wind turbines from disconnecting from the grid due to voltage drops or rises during grid faults, it is necessary to ensure that DFIG wind turbines have low voltage ride-through (LVRT) and high voltage ride-through (HVRT) capabilities, and that they can provide sufficient reactive power to the grid to help it recover during fault ride-through.

[0004] Existing research on fault ride-through control strategies for doubly-fed induction generator (DFIG) wind turbines mainly focuses on improving the reactive power support capability of DFIGs, suppressing rotor overcurrent, and suppressing DC bus overvoltage. However, these studies only address control strategy improvements for a single fault ride-through scenario, and their focus is limited to a single control objective. Therefore, further improvements to the fault ride-through control strategy for DFIG wind turbines are needed to ensure their safe and stable operation during grid faults. Summary of the Invention

[0005] The first aspect of this disclosure provides a method for classifying the operating conditions of a gas turbine unit based on information criteria and segmentation networks, comprising the following steps:

[0006] S1: Calculate the reactive power capacity limits of the rotor-side converter and the grid-side converter;

[0007] S2: Monitor the grid voltage. When the grid voltage deviation exceeds the set threshold, determine the voltage range based on the current grid voltage value, and calculate the total reactive power reference value required by the system based on the reactive power coefficient corresponding to the voltage range.

[0008] S3: Based on the total reactive power reference value and the reactive power capacity limit of the rotor-side converter, allocate the reactive power reference values ​​of the rotor-side converter and the grid-side converter according to the preset priority rule, wherein the priority rule is to give priority to using the rotor-side converter to provide reactive power support.

[0009] S4: Based on the allocated reactive power reference value of the grid-side converter, control the reactive power output of the grid-side converter, and introduce a feedforward compensation term in the active power control loop of the grid-side converter to suppress DC bus voltage fluctuations caused by sudden changes in active power at the moment of fault.

[0010] S5: Based on the allocated reactive power reference value of the rotor-side converter, control the reactive power output of the rotor-side converter, and introduce a dynamic limiting circuit based on the maximum allowable rotor current in the rotor-side converter control. By adjusting the allocation of the active current reference value and the reactive current reference value, ensure that the rotor current does not exceed the safety limit.

[0011] In conjunction with the first aspect, the calculation of the total reactive power reference value required by the system based on the reactive power coefficient corresponding to the voltage range, as described in step S2, is specifically achieved in the following way:

[0012] Different reactive power coefficients are set for different voltage ranges. The greater the depth of voltage drop or rise, the larger the reactive power coefficient value is set.

[0013] The total reactive power reference value is calculated based on the current grid voltage and the corresponding reactive power coefficient.

[0014] In conjunction with the first aspect, the total reactive power reference value mentioned in step S2 is calculated using the following formula:

[0015] ,

[0016] in, This is the reference value for total reactive power. The reactive power coefficients for different voltage ranges are: For the pre-set low voltage ride-through recovery threshold and For the pre-set high voltage ride-through recovery threshold, This is a real-time measurement of the grid voltage. This is the per-unit value of the grid voltage.

[0017] In conjunction with the first aspect, the allocation of reactive power reference values ​​according to preset priority rules in step S3 specifically includes:

[0018] In the event of a grid voltage dip fault:

[0019] If the absolute value of the total reactive power reference value is not greater than the absolute value of the maximum reactive power that the rotor-side converter can deliver, then the entire total reactive power reference value is allocated to the rotor-side converter, and the reactive power reference value of the grid-side converter is zero.

[0020] If the absolute value of the total reactive power reference value is greater than the absolute value of the maximum reactive power that the rotor-side converter can generate, then the maximum reactive power value that the rotor-side converter can generate is allocated to the rotor-side converter, and the difference between the total reactive power reference value and the maximum reactive power value that the rotor-side converter can generate is allocated to the grid-side converter.

[0021] In the event of a grid voltage rise fault:

[0022] If the absolute value of the total reactive power reference value is not greater than the absolute value of the maximum reactive power that the rotor-side converter can absorb, then the entire total reactive power reference value is allocated to the rotor-side converter, and the reactive power reference value of the grid-side converter is zero.

[0023] If the absolute value of the total reactive power reference value is greater than the absolute value of the maximum reactive power that the rotor-side converter can absorb, then the maximum reactive power value that the rotor-side converter can absorb is allocated to the rotor-side converter, and the difference between the total reactive power reference value and the maximum reactive power value that the rotor-side converter can absorb is allocated to the grid-side converter.

[0024] In conjunction with the first aspect, the introduction of a feedforward compensation term into the active power control loop of the grid-side converter, as described in step S4, specifically includes:

[0025] The active current feedforward compensation amount for compensating for power imbalance at the moment of fault is calculated by using the mathematical model of the grid-side converter and the power balance relationship.

[0026] The active current feedforward compensation is added to the active current reference value of the grid-side converter to improve the control response speed of the DC bus voltage.

[0027] In conjunction with the first aspect, the introduction of a dynamic limiting element in the rotor-side converter control described in step S5 specifically includes:

[0028] Set the maximum allowable value for rotor current;

[0029] Through formula The active current reference values ​​and reactive current reference values ​​of the dynamically constrained rotor-side converter are specified. This is the active current reference value. This is the reference value for reactive current. This is the maximum allowable value for rotor current;

[0030] When it is necessary to increase the reactive current reference value, the active current reference value should be decreased accordingly to ensure that the total rotor current does not exceed the maximum allowable value.

[0031] A second aspect of this disclosure provides a fault ride-through control system for a doubly-fed wind turbine, the system comprising:

[0032] The reactive power calculation module is used to calculate the reactive power capacity limit of the rotor-side converter and the grid-side converter under the current operating conditions.

[0033] The monitoring module is used to monitor the grid voltage amplitude in real time and detect whether the grid voltage amplitude deviation exceeds the set threshold.

[0034] The determination module is used to determine the voltage range to which the voltage belongs based on the current grid voltage amplitude;

[0035] The reactive power reference value calculation module is used to calculate the total reactive power reference value required by the system based on the reactive power coefficient corresponding to the voltage range.

[0036] The power allocation module is used to allocate the reactive power reference values ​​of the rotor side and the grid side according to the principle of rotor side priority, based on the total reactive power reference value and the reactive power capacity limit of the rotor-side converter.

[0037] The feedforward compensation module is used to introduce a feedforward compensation term into the active power control loop of the grid-side converter and calculate the active current feedforward compensation amount to suppress DC bus voltage fluctuations.

[0038] The dynamic limiting module is used to introduce a dynamic limiting circuit based on the maximum allowable rotor current in the rotor-side converter control to constrain the reference values ​​of active and reactive currents.

[0039] The control execution module is used to control the reactive power output of the rotor-side converter and the grid-side converter respectively according to the allocated reactive power reference value.

[0040] In conjunction with the second aspect, the voltage range defined in the determination module is specifically as follows:

[0041] First voltage range: ;

[0042] Second voltage range: ;

[0043] Third voltage range: ;

[0044] Fourth voltage range: ;

[0045] in, For the pre-set low voltage ride-through recovery threshold and For the pre-set high voltage ride-through recovery threshold, This is a real-time measurement of the grid voltage. This is the per-unit value of the grid voltage.

[0046] A third aspect of this disclosure provides an electronic device, characterized in that it comprises:

[0047] One or more processors;

[0048] A storage unit is used to store one or more programs, which, when executed by one or more processors, enable the one or more processors to implement the doubly-fed wind turbine fault ride-through control method.

[0049] A fourth aspect of this disclosure provides a computer-readable storage medium having a computer program stored thereon, characterized in that the computer program, when executed by a processor, can implement the fault ride-through control method for the doubly-fed wind turbine.

[0050] Beneficial Effects: The fault ride-through control method and system for doubly-fed induction generator (DFIG) wind turbines disclosed herein introduces a refined interval segmentation mechanism based on voltage amplitude to dynamically adjust the reactive power coefficient under different drop or rise depths. Combined with the reactive power capacity limits of the rotor-side converter and the grid-side converter, it achieves optimal reactive power allocation with priority given to the rotor side and coordination from the grid side. Furthermore, by introducing active power feedforward compensation on the grid side to quickly suppress DC bus voltage fluctuations and adopting a dynamic limiting strategy based on the current circle on the rotor side, it effectively suppresses rotor overcurrent and DC overvoltage risks while fully supporting grid voltage recovery. This significantly improves the ride-through capability and operational safety of DFIG wind turbines during grid faults, providing reliable technical support to avoid large-scale grid disconnection of the units. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of a typical doubly-fed wind turbine generator according to an embodiment of the present disclosure;

[0052] Figure 2 This is a flowchart illustrating a fault ride-through control method for a doubly fed wind turbine according to an embodiment of this disclosure.

[0053] Figure 3a The simulation results are for the grid connection point voltage ride-through. Figure 3b The simulation results are for the reactive power ride-through on the stator side. Figure 3c The results are the grid-side reactive power ride-through simulation results. Figure 3d The system's reactive power ride-through simulation results are as follows. Figure 3e The simulation results are for rotor current ride-through. Figure 3f The simulation results are for DC bus voltage ride-through.

[0054] Figure 4a The simulation results are for the grid connection point voltage ride-through. Figure 4b The simulation results are for the reactive power ride-through on the stator side. Figure 4c The results are the grid-side reactive power ride-through simulation results. Figure 4d The system's reactive power ride-through simulation results are as follows. Figure 4e The simulation results are for rotor current ride-through. Figure 4f The simulation results are for DC bus voltage ride-through.

[0055] Figure 5 This is a schematic diagram of the structure of a fault ride-through control system for a doubly fed wind turbine according to an embodiment of this disclosure;

[0056] Figure 6 An electronic device according to an embodiment of this disclosure. Detailed Implementation

[0057] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those disclosed herein.

[0058] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0059] like Figure 1 The diagram shows a typical grid-connected model structure for a doubly-fed induction generator (DFIG) wind turbine, including:

[0060] Wind turbine 1 captures wind energy and converts it into mechanical energy.

[0061] Transmission system 2: includes a gearbox, used to convert the low speed and high torque on the wind turbine side into the high speed and low torque required on the generator side.

[0062] Induction motor 3: includes a stator side 31 and a rotor side 32, wherein,

[0063] The stator side 31 has its windings directly connected to the power grid, so its output active and reactive power are directly injected into the power grid.

[0064] The rotor side 32 has its windings connected to the back-to-back converter 4 via slip rings, forming a controllable, bidirectional power channel. The rotor side can input or output active and reactive power.

[0065] The back-to-back converter 4, consisting of two converters connected via a DC bus, is crucial for achieving unit controllability. It includes a generator-side converter 41 and a grid-side converter 42.

[0066] The generator-side converter 41 controls the current in the rotor circuit, thereby indirectly controlling the reactive power output on the stator side and adjusting the rotor speed to achieve maximum wind energy tracking.

[0067] The grid-side converter 42 controls the stability of the DC bus voltage by adjusting the active power absorbed from or supplied to the grid. Simultaneously, it can also directly control the reactive power exchanged with the grid.

[0068] Combination Figure 2 The diagram shown is a flowchart illustrating a fault ride-through control method for a doubly-fed induction generator (DFIG) wind turbine according to an embodiment of this disclosure, including:

[0069] S1: Calculate the reactive power capacity limits of the rotor-side converter and the grid-side converter;

[0070] Specifically, under idealized assumptions, the reactive current limit of the grid-side converter and the current limit of the grid-side converter have the following relationship:

[0071] (1)

[0072] in, This represents the total effective value of the output current of the grid-side converter. For the output current of the grid-side converter Axis component (amplitude), For the output current of the grid-side converter Axial component (amplitude). This is the maximum permissible effective current value that the grid-side converter can operate safely for a long period of time.

[0073] Voltage-oriented vector control is used for grid-side converter control, and the active and reactive power outputs from the grid side are related to those from the grid side. The shaft currents have the following relationship:

[0074] (2)

[0075] in, For the active power exchanged between the grid-side converter and the grid, The reactive power exchanged between the grid-side converter and the grid. and For the grid-side converter port voltage vector shaft and Axis component (instantaneous value). and For the output current of the grid-side converter shaft and Axis component (instantaneous value). and For the grid-side converter port voltage vector shaft and Axial component (amplitude).

[0076] By combining equations (1) and (2), the reactive power generation and absorption limits of the grid-side converter can be obtained.

[0077] The rotor-side reactive current limit and rotor-side converter current limit are similar to those on the grid side.

[0078] Ultimately, the limit of total reactive power absorbed and generated by the doubly fed wind turbine can be obtained.

[0079] S2: Monitor the grid voltage. When the grid voltage deviation exceeds the set threshold, determine the voltage range based on the current grid voltage value, and calculate the total reactive power reference value required by the system based on the reactive power coefficient corresponding to the voltage range.

[0080] The calculation of the total reactive power reference value required by the system based on the reactive power coefficient corresponding to this voltage range is specifically achieved in the following way:

[0081] Different reactive power coefficients are set for different voltage ranges. The greater the depth of voltage drop or rise, the larger the reactive power coefficient value is set.

[0082] The total reactive power reference value is calculated based on the current grid voltage and the corresponding reactive power coefficient.

[0083] Specifically, after a fault is detected, the control system maps the currently measured grid voltage value to a predefined voltage range. These ranges are finely divided based on the severity of the fault and the varying demands for reactive power support. Taking low-voltage ride-through as an example, the first voltage range is defined as follows: ;

[0084] Second voltage range: ;

[0085] Third voltage range: ;

[0086] Fourth voltage range: ;

[0087] in, For the pre-set low voltage ride-through recovery threshold and For the pre-set high voltage ride-through recovery threshold, This is a real-time measurement of the grid voltage. This is the per-unit value of the grid voltage.

[0088] Each voltage range has a pre-defined reactive power coefficient (K). The principle behind assigning this coefficient directly reflects the intelligence of the control strategy. In the deep voltage dip range, the system assigns a larger K value, aiming to command the wind turbines to generate reactive power as much as possible, using strong reactive power injection to quickly support the grid voltage and prevent system collapse. In the shallow voltage dip range, a smaller K value is assigned, with the aim of providing moderate and appropriate reactive power support, avoiding excessive reactive power injection that could cause the voltage to jump too high after the fault is cleared (overvoltage), thereby maintaining the stability of the system during the recovery process.

[0089] Finally, the system uses the currently monitored grid voltage value and the reactive power coefficient corresponding to its interval to calculate the following formula:

[0090] ,

[0091] in, This is the reference value for total reactive power. This represents the reactive power coefficient corresponding to different voltage ranges.

[0092] Calculate the reference value of the total reactive power that needs to be supplied to the power grid.

[0093] S3: Based on the total reactive power reference value and the reactive power capacity limit of the rotor-side converter, allocate the reactive power reference values ​​of the rotor-side converter and the grid-side converter according to the preset priority rule, wherein the priority rule is to give priority to using the rotor-side converter to provide reactive power support.

[0094] The allocation of reactive power reference values ​​according to preset priority rules includes:

[0095] In the event of a grid voltage dip fault:

[0096] If the absolute value of the total reactive power reference value is not greater than the absolute value of the maximum reactive power that the rotor-side converter can deliver, then the entire total reactive power reference value is allocated to the rotor-side converter, and the reactive power reference value of the grid-side converter is zero.

[0097] If the absolute value of the total reactive power reference value is greater than the absolute value of the maximum reactive power that the rotor-side converter can generate, then the maximum reactive power value that the rotor-side converter can generate is allocated to the rotor-side converter, and the difference between the total reactive power reference value and the maximum reactive power value that the rotor-side converter can generate is allocated to the grid-side converter.

[0098] In the event of a grid voltage rise fault:

[0099] If the absolute value of the total reactive power reference value is not greater than the absolute value of the maximum reactive power that the rotor-side converter can absorb, then the entire total reactive power reference value is allocated to the rotor-side converter, and the reactive power reference value of the grid-side converter is zero.

[0100] If the absolute value of the total reactive power reference value is greater than the absolute value of the maximum reactive power that the rotor-side converter can absorb, then the maximum reactive power value that the rotor-side converter can absorb is allocated to the rotor-side converter, and the difference between the total reactive power reference value and the maximum reactive power value that the rotor-side converter can absorb is allocated to the grid-side converter.

[0101] Specifically, in a grid voltage drop fault scenario, the system requires wind turbines to generate a large amount of inductive reactive power to help raise the voltage. At this point, the control system performs a crucial comparison: it compares the absolute value of the calculated total reactive power demand command with the absolute value of the maximum reactive power capacity that the RSC can currently generate. If the total demand is within the RSC's capacity, the control system will allocate all reactive power output tasks solely to the RSC. In this case, the GSC will withdraw from reactive power regulation, and its task may revert to stabilizing the DC bus voltage, thus achieving optimal resource allocation.

[0102] If the grid voltage drops significantly, causing the total reactive power demand to exceed the independent capacity of the Reactive Power Controller (RSC), the allocation strategy will immediately switch to a coordinated mode. The RSC will be instructed to output reactive power at its maximum capacity to provide full support. The "gap" or "difference" between the total demand and the RSC's capacity will be allocated to the Regional Reactive Power Controller (GSC) to make up the difference. This forms a coordinated operational mode where the RSC takes the lead and the GSC provides assistance, prioritizing the advantages of the RSC while mobilizing all available resources to meet the grid's urgent needs in extreme circumstances.

[0103] In fault scenarios involving grid voltage rise, the system's required operation shifts from "generating reactive power" to "absorbing reactive power." The allocation logic is similar to that in the voltage dip scenario but in the opposite direction. The control system determines whether the total reactive power to be absorbed is within the maximum absorption capacity of the RSC (Reactive Power Controller). If so, the RSC independently completes the absorption task, and the GSC (Ground Controller System) does not participate. If the absorption demand exceeds the RSC's capacity, the RSC operates at its maximum absorption limit, while the remaining additional absorption demand is handled by the GSC. This ensures that, even under overvoltage conditions, the generating units can effectively and progressively help stabilize the grid voltage.

[0104] S4: Based on the allocated reactive power reference value of the grid-side converter, control the reactive power output of the grid-side converter, and introduce a feedforward compensation term in the active power control loop of the grid-side converter to suppress DC bus voltage fluctuations caused by sudden changes in active power at the moment of fault.

[0105] The introduction of a feedforward compensation term into the active power control loop of the grid-side converter specifically includes:

[0106] The active current feedforward compensation amount for compensating for power imbalance at the moment of fault is calculated by using the mathematical model of the grid-side converter and the power balance relationship.

[0107] The active current feedforward compensation is added to the active current reference value of the grid-side converter to improve the control response speed of the DC bus voltage.

[0108] Specifically, firstly, the control system sends the reactive power reference value (Qgsc_ref) allocated in step S3 to the internal control loop of the grid-side converter (GSC). The GSC will then use its own current control strategy to track this command by adjusting its output reactive current, thereby providing reactive power support to the grid.

[0109] However, the sudden drop or rise in voltage during a grid fault can trigger a serious internal problem: a drastic change in active power and the resulting violent fluctuations in the DC bus voltage. The stator side, directly connected to the grid, experiences a momentary decrease in its output active power due to the voltage drop. However, due to inertia and other factors, the rotor side's input active power cannot change instantaneously, leading to a severe imbalance in the power flow transmitted through the converter. For the GSC (Gas Grid Controller), its task is to maintain the stability of the DC bus voltage.

[0110] GSC control can be divided into DC bus voltage outer loop, power outer loop, and current inner loop control. When a fault occurs, the voltage changes abruptly at the moment of the fault, and the active power also changes abruptly, causing the active power on the rotor side and the grid side to become unbalanced, resulting in large fluctuations in the DC bus voltage.

[0111] When grid-side voltage-oriented vector control is used, and assuming the DC bus voltage change rate is zero, we can obtain:

[0112] By adding a feedforward compensation component to the output of the outer loop of the grid-side converter voltage to change the reference value of the active current, the regulation speed of the DC bus voltage is improved, thereby maintaining the stability of the bus voltage.

[0113] However, traditional feedback control based on PI regulators only starts to operate after detecting that the DC voltage has deviated, which has an inherent lag and makes it difficult to suppress such sudden and severe shocks.

[0114] To address this dynamic issue, a feedforward compensation mechanism is introduced. The core idea of ​​feedforward compensation is "proactive action, rather than passive response." It uses the mathematical model of the grid-side converter and real-time power measurements to calculate in real time the amount of active current compensation needed to offset this power imbalance. This calculation is based on the power balance relationship, directly estimating the change in active current required to maintain power balance.

[0115] Ultimately, this calculated feedforward compensation is directly added to the reference value of the active current of the grid-side converter. Before the DC bus voltage has a chance to fluctuate significantly, the control command has already been issued. Based on this new command containing the compensation, the GSC will immediately adjust the active power it absorbs from the DC bus or delivers to the grid, thereby proactively and almost synchronously offsetting the power imbalance caused by the fault.

[0116] S5: Based on the allocated reactive power reference value of the rotor-side converter, control the reactive power output of the rotor-side converter, and introduce a dynamic limiting circuit based on the maximum allowable rotor current in the rotor-side converter control. By adjusting the allocation of the active current reference value and the reactive current reference value, ensure that the rotor current does not exceed the safety limit.

[0117] The introduction of a dynamic limiting element in the rotor-side converter control described in step S5 specifically includes:

[0118] Set the maximum allowable value for rotor current;

[0119] Through formula The active current reference values ​​and reactive current reference values ​​of the dynamically constrained rotor-side converter are specified. This is the active current reference value. This is the reference value for reactive current. This is the maximum allowable value for rotor current;

[0120] When it is necessary to increase the reactive current reference value, the active current reference value should be decreased accordingly to ensure that the total rotor current does not exceed the maximum allowable value.

[0121] Specifically, the control system first sends the rotor-side reactive power reference value allocated in step S3 to the control loop of the RSC. The RSC will switch to the "reactive power priority" control mode, and its internal controller will try to adjust the reactive power component of the rotor current to track this command, thereby injecting or absorbing the required reactive power into the grid through the motor stator.

[0122] However, during faults, especially deep voltage dips, the reactive power required for support can be very large. If the RSC blindly and unilaterally increases the reactive current output, the vector sum of its total current (including active and reactive components) is likely to exceed the maximum permissible current that the rotor-side converter power devices can withstand. Once overcurrent occurs, it will cause the converter to burn out in a very short time, resulting in huge economic losses.

[0123] To resolve this contradiction, this solution introduces a dynamic limiting mechanism. The theoretical basis for this mechanism is the formula... .

[0124] in This is the active current reference value. This is the reference value for reactive current. This is the maximum allowable value for rotor current;

[0125] When it is necessary to increase the reactive current reference value, the active current reference value should be decreased accordingly to ensure that the total rotor current does not exceed the maximum allowable value.

[0126] This formula mathematically defines a circle centered at the origin and with... The radius is a circle. Its physical meaning is that the endpoints of the rotor current vector (determined by the d-axis component of the active current and the q-axis component of the reactive current) must always fall inside this circle to ensure equipment safety.

[0127] The control strategy sets clear priorities: during fault ride-through, outputting reactive current to support the grid takes precedence over generating active power. When the control system calculates that the total current is about to exceed the safety circle in order to track a given reactive power command, it will not limit the reactive current, but will actively and dynamically reduce the active current reference value.

[0128] By reducing the output of active current, sufficient capacity is freed up for reactive current, thus maximizing the satisfaction of the grid's reactive power demand without exceeding the total current limit. This allows the RSC to always operate within the boundary of its maximum safety capacity, fulfilling both the obligations required by grid connection regulations and absolutely ensuring the safety of its own equipment.

[0129] To illustrate the effectiveness of the segmented voltage control strategy of this invention, based on, for example... Figure 1 The typical doubly fed wind turbine generator shown is connected to the grid and simulated electromagnetic transient model. The dynamic response results under this control strategy are tested.

[0130] In this example, the doubly-fed induction generator (DFIG) is a typical 2.5MW unit with a converter capacity of 2MW. Symmetrical voltage low-value and high-value disturbance simulations were triggered at the grid connection point to test the dynamic performance of the control strategy of this invention.

[0131] in Figure 3a The simulation results are for the grid connection point voltage ride-through. Figure 3b The simulation results are for the reactive power ride-through on the stator side. Figure 3c The results are the grid-side reactive power ride-through simulation results. Figure 3d The system's reactive power ride-through simulation results are as follows. Figure 3e The simulation results are for rotor current ride-through. Figure 3f The results are from the DC bus voltage ride-through simulation.

[0132] At 8 seconds, the control voltage at the wind turbine grid connection point was dropped to 0.5 pu, and after 0.6 seconds, it was restored to the pre-disturbance setting. It can be observed that the low voltage ride-through transient process under this control strategy is more rapid, the system reactive power response is faster, the DC bus voltage recovery is faster, and the active power damping effect is also improved compared to the strategy without segmented optimization.

[0133] in Figure 4a The simulation results are for the grid connection point voltage ride-through. Figure 4b The simulation results are for the reactive power ride-through on the stator side. Figure 4c The results are the grid-side reactive power ride-through simulation results. Figure 4d The system's reactive power ride-through simulation results are as follows. Figure 4e The simulation results are for rotor current ride-through. Figure 4f The results are from the DC bus voltage ride-through simulation.

[0134] At 8 seconds, the control voltage at the grid connection point of the wind turbine was switched to 1.3 pu, and after 0.5 seconds, it was restored to the setting value before the disturbance. It can be found that the high voltage ride-through transient process under this control strategy is still faster, the system reactive power response is faster, the DC bus voltage recovery is faster, and the damping effect of active power is also improved compared with the strategy without segmented optimization.

[0135] like Figure 5 The diagram shown is a structural schematic of a fault ride-through control system for a doubly-fed wind turbine according to an embodiment of this disclosure, comprising:

[0136] The reactive power calculation module 510 is used to calculate the reactive power capacity limit of the rotor-side converter and the grid-side converter under the current operating conditions.

[0137] Monitoring module 520 is used to monitor the grid voltage amplitude in real time and detect whether the grid voltage amplitude deviation exceeds the set threshold.

[0138] The determination module 530 is used to determine the voltage range to which the current power grid voltage amplitude belongs.

[0139] The reactive power reference value calculation module 540 is used to calculate the total reactive power reference value required by the system based on the reactive power coefficient corresponding to the voltage range.

[0140] The power distribution module 550 is used to allocate the reactive power reference values ​​of the rotor side and the grid side according to the principle of rotor side priority, based on the total reactive power reference value and the reactive power capacity limit of the rotor-side converter.

[0141] The feedforward compensation module 560 is used to introduce a feedforward compensation term into the active power control loop of the grid-side converter and calculate the active current feedforward compensation amount to suppress DC bus voltage fluctuations.

[0142] The dynamic limiting module 570 is used to introduce a dynamic limiting circuit based on the maximum allowable rotor current in the rotor-side converter control to constrain the reference values ​​of active and reactive currents.

[0143] The control execution module 580 is used to control the reactive power output of the rotor-side converter and the grid-side converter respectively according to the allocated reactive power reference value.

[0144] Electronic device 600 can be a desktop computer, laptop, handheld computer, cloud server, or other electronic device. Electronic device 600 may include, but is not limited to, a processor 601 and a memory 602. Those skilled in the art will understand that... Figure 6 This is merely an example of electronic device 600 and does not constitute a limitation on electronic device 600. It may include more or fewer components than shown, or combine certain components, or different components. For example, electronic device may also include input / output devices, network access devices, buses, etc.

[0145] The processor 601 can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0146] The memory 602 can be an internal storage unit of the electronic device 600, such as a hard disk or RAM of the electronic device 600. The memory 602 can also be an external storage device of the electronic device 600, such as a plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the electronic device 600. Furthermore, the memory 602 can include both internal and external storage units of the electronic device 600. The memory 602 is used to store the computer program 603 and other programs and data required by the electronic device. The memory 602 can also be used to temporarily store data that has been output or will be output.

[0147] The above embodiments are only used to illustrate the technical solutions of this disclosure, and are not intended to limit it. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this disclosure, and should all be included within the protection scope of this disclosure.

Claims

1. A method of fault ride-through control for a doubly-fed wind turbine generator, characterized by, The method comprises the following steps: S1: calculating the reactive power capability limit of the rotor-side converter and the grid-side converter; S2: monitoring the grid voltage, when the grid voltage deviation exceeds a set threshold, determining the voltage interval to which the current grid voltage value belongs, and calculating the total reactive power reference value required by the system based on the reactive power coefficient corresponding to the voltage interval; S3: based on the total reactive power reference value and the reactive power capability limit of the rotor-side converter, the reactive power reference values of the rotor-side converter and the grid-side converter are allocated according to a preset priority rule, wherein the priority rule is to preferentially use the rotor-side converter to provide reactive power support; S4: according to the allocated reactive power reference value of the grid-side converter, the reactive power output of the grid-side converter is controlled, and a feedforward compensation term is introduced in the active control link of the grid-side converter to suppress the DC bus voltage fluctuation caused by the active power mutation at the fault moment; S5: according to the allocated reactive power reference value of the rotor-side converter, the reactive power output of the rotor-side converter is controlled, and a dynamic limiting link based on the maximum allowable rotor current is introduced in the rotor-side converter control, so as to ensure that the rotor current does not exceed the safety limit by adjusting the allocation of the active current reference value and the reactive current reference value.

2. The method of claim 1, wherein, In step S2, the total reactive power reference value is calculated based on the corresponding reactive power coefficient, and the total reactive power reference value is calculated by the following method: Different reactive power coefficients are set for different voltage intervals, and the greater the depth of voltage drop or rise, the greater the set reactive power coefficient value; According to the current grid voltage value and the corresponding reactive power coefficient, the total reactive power reference value is calculated.

3. The method of claim 2, wherein, In step S2, the total reactive power reference value is calculated by the following formula: ， wherein, is the total reactive power reference value, is the reactive power coefficient corresponding to different voltage intervals, is the pre-set low voltage ride through recovery threshold and is the pre-set high voltage ride through recovery threshold, is the real-time measurement value of the grid voltage, is the grid voltage unit.

4. The method of claim 1, wherein, In step S3, the reactive power reference value is allocated according to the preset priority rule, which specifically includes: In the case of grid voltage drop fault: If the absolute value of the total reactive power reference value is not greater than the absolute value of the maximum output reactive power of the rotor-side converter, the total reactive power reference value is allocated to the rotor-side converter, and the reactive power reference value of the grid-side converter is zero, If the absolute value of the total reactive power reference value is greater than the absolute value of the maximum output reactive power of the rotor-side converter, the maximum output reactive power of the rotor-side converter is allocated to the rotor-side converter, and the difference between the total reactive power reference value and the maximum output reactive power of the rotor-side converter is allocated to the grid-side converter; In the case of grid voltage rise fault: If the absolute value of the total reactive power reference value is not greater than the absolute value of the maximum absorbable reactive power of the rotor-side converter, the total reactive power reference value is allocated to the rotor-side converter, and the reactive power reference value of the grid-side converter is zero, If the absolute value of the total reactive power reference value is greater than the absolute value of the maximum absorbable reactive power of the rotor-side converter, the maximum absorbable reactive power of the rotor-side converter is allocated to the rotor-side converter, and the difference between the total reactive power reference value and the maximum absorbable reactive power of the rotor-side converter is allocated to the grid-side converter.

5. The method of claim 1, wherein, In step S4, the feedforward compensation term is introduced in the active control link of the grid-side converter, which specifically includes: The active current feedforward compensation quantity for compensating power imbalance at the fault moment is calculated through a mathematical model of the grid-side converter and a power balance relationship; The active current feedforward compensation quantity is added to the active current reference value of the grid-side converter to improve the control response speed of the DC bus voltage.

6. The method of claim 1, wherein, The dynamic limiting link is introduced in the rotor-side converter control in step S5, and specifically includes: A maximum allowable value of the rotor current is set; by the formula dynamically constraining the active current reference value and the reactive current reference value of the rotor-side converter, wherein is the active current reference value, is the reactive current reference value, is the maximum permissible rotor current value; When it is necessary to increase the reactive current reference value, the active current reference value is correspondingly reduced to ensure that the total rotor current does not exceed the maximum allowable value.

7. A doubly-fed wind turbine generator fault ride-through control system, characterized by, The system includes: A reactive power calculation module for calculating the reactive power capability limit of the rotor-side converter and the grid-side converter under the current operating state; A monitoring module for monitoring the grid voltage amplitude in real time and detecting whether the grid voltage amplitude deviation exceeds a set threshold; A determination module for determining the voltage interval according to the current grid voltage amplitude; A reactive reference value calculation module for calculating the total reactive power reference value required by the system according to the reactive power coefficient corresponding to the voltage interval; A power distribution module for distributing the reactive power reference values of the rotor-side and the grid-side according to the principle of rotor-side priority based on the total reactive power reference value and the reactive power capability limit of the rotor-side converter; A feedforward compensation module for introducing a feedforward compensation term in the active control link of the grid-side converter to calculate the active current feedforward compensation quantity to suppress DC bus voltage fluctuations; A dynamic limiting module for introducing a dynamic limiting link based on the maximum allowable rotor current in the rotor-side converter control to constrain the active and reactive current reference values; A control execution module for controlling the reactive power output of the rotor-side converter and the grid-side converter according to the distributed reactive power reference values.

8. The system of claim 7, wherein, The voltage intervals defined in the determination module are specifically: first voltage interval: ; Second voltage interval: ; Third voltage interval: ; Fourth voltage interval: ; wherein is a pre-set low voltage ride through recovery threshold and is a pre-set high voltage ride through recovery threshold, is a real-time measurement of the grid voltage, is a grid voltage nominal value.

9. An electronic device, comprising: including: One or more processors; A storage unit for storing one or more programs that, when executed by the one or more processors, enable the one or more processors to implement the fault ride-through control method for a doubly-fed wind power generator set according to claim 1.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program, when executed by a processor, can implement the fault ride-through control method for a doubly-fed wind power generator set according to claim 1.

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