Coordination control method and system for low-voltage and high-voltage cascading fault ride-through of converter

Abstract

The invention provides a coordinated control method and system for low-high voltage cascading failure ride-through of a converter. The method comprises the following steps: acquiring a real-time voltage of a wind turbine generator connected to a power grid and a signal whether to enter a low-high voltage cascading failure ride-through mode or not; determining a positive sequence vector per unit value of the real-time voltage based on the real-time voltage of the power grid; and when the positive sequence vector per unit value of the real-time voltage is greater than a preset positive sequence vector threshold value and the low and high voltage cascading failure ride-through mode signal is a signal entering the acquired low and high voltage cascading failure ride-through mode, controlling a grid-side converter, a direct current unloading Chopper device and a machine-side converter based on a preset control strategy. Coordinated control of low-voltage and high-voltage cascading failure ride-through of the wind turbine generator converter is realized; wherein the preset control strategy comprises a low-voltage and high-voltage interlocking control strategy, a network side Chopper control strategy and a single closed-loop current control strategy. According to the scheme, continuous active output of the converter in the fault ride-through period can be guaranteed, and a power grid operates safely and stably.

Description

Technical Field

[0001] The present application relates to the technical field of fault ride-through, and in particular to a coordinated control method and system for low- and high-voltage cascading fault ride-through of a converter. Background Art

[0002] With the increase of wind power installed capacity, the impact of wind power grid-connected power generation systems on the power grid is increasing. From the perspective of maintaining the stability of the power system, wind turbines are required to remain connected to the grid when the grid voltage fails, and relevant technical standards have been formulated. Doubly-fed wind turbines are the most widely used wind turbines in wind farms, and are also the most sensitive wind turbines to grid failures. According to the standards for wind turbine grid connection, wind turbines must have low voltage ride-through capability and high voltage ride-through capability under grid failures.

[0003] When the low and high voltages of the power grid are chained, the transient process of the system is more unstable and the fault situation is more severe. The traditional high voltage ride-through control strategy may cause the wind turbine to be disconnected from the grid due to faults. The traditional high voltage ride-through control strategy is applicable to power grid faults in which the grid voltage suddenly rises from the rated Pu value to a voltage value between 1.1Pu and 1.3Pu, and the maximum grid voltage mutation is 0.3Pu. However, when the low voltage is chained to the high voltage fault, the grid voltage suddenly rises from 0.2Pu to 0.9Pu to 1.1Pu to 1.3Pu, and the maximum grid voltage mutation is 1.1Pu, and the grid fault situation is more severe. Obviously, the traditional high voltage ride-through control strategy is not applicable to the special situation of chained high voltage faults after low voltage faults in the power grid. If the traditional high voltage ride-through control strategy is still used when the power grid voltage is low voltage chained to high voltage faults, it is easy to cause the double-fed wind turbine to be disconnected from the grid and shut down, and the low and high voltage chained fault ride-through of the power grid cannot be completed. Therefore, it is urgent to propose a low and high voltage chained fault ride-through control scheme that can ensure the safe and stable operation of the power grid. Summary of the invention

[0004] The present application provides a coordinated control method and system for converter low- and high-voltage cascading fault ride-through, so as to at least solve the technical problem that the low- and high-voltage cascading fault ride-through of the power grid cannot be completed.

[0005] A first aspect of the present application provides a coordinated control method for low- and high-voltage cascading fault ride-through of a converter, the method comprising:

[0006] Obtain the real-time voltage of the wind turbine connected to the grid and whether it has entered the low-high voltage cascading fault ride-through mode signal;

[0007] Determining a per-unit value of a positive sequence vector of the real-time voltage based on the real-time voltage of the power grid;

[0008] When the positive sequence vector per unit value of the real-time voltage is greater than the preset positive sequence vector threshold and the low-high voltage interlocking fault ride-through mode signal is collected to enter the low-high voltage interlocking fault ride-through mode signal, the grid-side converter, the DC load unloading Chopper device and the machine-side converter are controlled based on the preset control strategy to achieve coordinated control of the low-high voltage interlocking fault ride-through of the wind turbine converter;

[0009] Among them, the preset control strategies include: low and high voltage interlocking control strategy, grid-side Chopper control strategy, and single closed-loop current control strategy.

[0010] Preferably, the preset positive sequence vector threshold is 1.1 pu.

[0011] Further, the controlling of the grid-side converter, the DC load shedding Chopper device and the machine-side converter based on a preset control strategy includes:

[0012] Controlling the grid-side converter based on the low-high voltage interlocking control strategy;

[0013] Controlling the DC load unloading Chopper device based on the grid-side Chopper control strategy;

[0014] The machine-side converter is controlled based on the single closed-loop current control strategy.

[0015] Furthermore, the controlling the grid-side converter based on the low-high voltage interlocking control strategy includes:

[0016] When the power grid is in a transient process, the pulse of the grid-side converter is blocked for a period of T, and then the DC bus voltage reference value is dynamically adjusted according to the real-time voltage of the power grid;

[0017] When the power grid is in a steady state, the current of the power grid is controlled by using a current controller with reference and error filter decoupling.

[0018] Furthermore, the controlling the grid-side converter based on the low-high voltage interlocking control strategy further includes:

[0019] When the power grid is in a transient state or a steady state, an active current priority control strategy is adopted to control the grid side of the double-fed converter, or a reactive current priority control strategy is adopted to control the grid side of the full-power converter.

[0020] Furthermore, the controlling of the DC load unloading Chopper device based on the grid-side Chopper control strategy includes:

[0021] When the DC bus voltage connected to the grid-side converter is greater than the preset upper threshold of the Chopper device action voltage, the Chopper circuit is controlled to be enabled, and the load shedding enable duty cycle is set to 1;

[0022] When the DC bus voltage connected to the grid-side converter is lower than the preset lower limit threshold of the Chopper device action voltage, the Chopper circuit is controlled to be cut out and the load shedding input duty cycle is set to 0.

[0023] Furthermore, the controlling the doubly-fed converter based on the single closed-loop current control strategy includes:

[0024] The given active current given value is subtracted from the active current of the fed-back rotor current to obtain the active current difference value, and the given reactive current given value is subtracted from the reactive current of the fed-back rotor current to obtain the reactive current difference value;

[0025] The active current difference and the reactive current difference are input into a PI controller to obtain an active voltage value and a reactive voltage value of the rotor, and the machine-side converter is controlled based on the active voltage value and the reactive voltage value.

[0026] Furthermore, the calculation formula of the blocking time is as follows:

[0027]

[0028] Where T is the blocking time, ΔU = Udp HVRT -Udp LVRT , Udp HVRT is the per-unit value of the positive sequence vector when the high voltage of the power grid is stable due to cascading faults, Udp LVRT It is the per-unit value of the positive sequence vector when the low voltage of the power grid is stable due to cascading faults.

[0029] Furthermore, the method further comprises:

[0030] When the detection channel pulse blocking timing time is equal to T, the pulse of the grid-side converter is unlocked, and the DC bus voltage setting value is increased according to the grid voltage value after the voltage surge.

[0031] The second aspect of the present application provides a coordinated control system for low-high voltage cascading fault ride-through of a converter, comprising:

[0032] An acquisition module is used to obtain the real-time voltage of the wind turbine connected to the grid and whether it has entered the low-high voltage cascading fault ride-through mode signal;

[0033] A determination module, configured to determine a per-unit value of a positive sequence vector of the real-time voltage based on the real-time voltage of the power grid;

[0034] A control module, for controlling the grid-side converter, the DC load shedding Chopper device and the machine-side converter based on a preset control strategy to achieve coordinated control of the low-high voltage interlocking fault ride-through of the wind turbine converter when the positive-sequence vector per-unit value of the real-time voltage is greater than a preset positive-sequence vector threshold and a low-high voltage interlocking fault ride-through mode signal is collected to enter a low-high voltage interlocking fault ride-through mode signal;

[0035] Among them, the preset control strategies include: low and high voltage interlocking control strategy, grid-side Chopper control strategy, and single closed-loop current control strategy.

[0036] Furthermore, the preset positive sequence vector threshold is 1.1 pu.

[0037] The technical solution provided by the embodiments of the present application brings at least the following beneficial effects:

[0038] The present application proposes a coordinated control method and system for low-high voltage interlocking fault ride-through of a converter, the method comprising: obtaining the real-time voltage of the wind turbine connected to the power grid and whether to enter the low-high voltage interlocking fault ride-through mode signal; determining the positive sequence vector per unit value of the real-time voltage based on the real-time voltage of the power grid; when the positive sequence vector per unit value of the real-time voltage is greater than the preset positive sequence vector threshold and the low-high voltage interlocking fault ride-through mode signal is to enter the low-high voltage interlocking fault ride-through mode signal, the grid-side converter, the DC unloading Chopper device and the machine-side converter are controlled based on the preset control strategy to achieve coordinated control of the low-high voltage interlocking fault ride-through of the wind turbine converter; wherein the preset control strategy includes: low-high voltage interlocking control strategy, grid-side Chopper control strategy, and single closed-loop current control strategy. The technical solution proposed in the present application effectively improves the reliability of the wind turbine in the doubly-fed wind turbine converter when a low-high voltage interlocking fault occurs in the power grid, and ensures that the converter continues to have active output during the fault ride-through.

[0039] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0041] Figure 1 A flowchart of a coordinated control method for converter low-high voltage cascading fault ride-through provided according to an embodiment of the present application;

[0042] Figure 2A schematic diagram of a current control algorithm based on decoupling of reference and error filter signals according to an embodiment of the present application;

[0043] Figure 3 A schematic diagram of a generator-side single closed-loop current control strategy provided according to an embodiment of the present application;

[0044] Figure 4 A detailed flow chart of a coordinated control method for low- and high-voltage cascading fault ride-through of a converter provided according to an embodiment of the present application;

[0045] Figure 5 A structural diagram of a coordinated control system for converter low- and high-voltage cascading fault ride-through provided according to an embodiment of the present application. DETAILED DESCRIPTION

[0046] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0047] The present application proposes a coordinated control method and system for low-high voltage interlocking fault ride-through of a converter, the method comprising: obtaining the real-time voltage of the wind turbine connected to the power grid and whether it enters the low-high voltage interlocking fault ride-through mode signal; determining the positive sequence vector per unit value of the real-time voltage based on the real-time voltage of the power grid; when the positive sequence vector per unit value of the real-time voltage is greater than the preset positive sequence vector threshold and the low-high voltage interlocking fault ride-through mode signal is the signal of entering the low-high voltage interlocking fault ride-through mode, the grid-side converter, the DC unloading Chopper device and the machine-side converter are controlled based on the preset control strategy to achieve coordinated control of the low-high voltage interlocking fault ride-through of the wind turbine converter; wherein the preset control strategy includes: low-high voltage interlocking control strategy, grid-side Chopper control strategy, and single closed-loop current control strategy. The technical solution proposed in the present application effectively improves the reliability of the wind turbine in the doubly-fed wind turbine converter when a low-high voltage interlocking fault occurs in the power grid, and ensures that the converter continues to output active power during the fault ride-through.

[0048] The following describes a coordinated control method and system for converter low- and high-voltage cascading fault ride-through according to an embodiment of the present application with reference to the accompanying drawings.

[0049] Embodiment 1

[0050] Figure 1 Flow chart of a coordinated control method for converter low-high voltage cascading fault ride-through provided according to one embodiment of the present application, such as Figure 1 As shown, the method includes:

[0051] Step 1: Obtain the real-time voltage of the wind turbine connected to the grid and whether it has entered the low-high voltage cascading fault ride-through mode signal;

[0052] It should be noted that the converter has independent low voltage ride through and high voltage ride through capabilities.

[0053] The converter may be a full-power machine-side converter or a grid-side converter, a doubly-fed machine-side converter or a grid-side converter.

[0054] Step 2: Determine the positive sequence vector per unit value of the real-time voltage based on the real-time voltage of the power grid;

[0055] It should be noted that, based on the real-time voltage of the power grid, the power grid voltage positive sequence vector per unit value Udp is obtained by decoupling the dual synchronous reference coordinate system phase-locked loop.

[0056] Step 3: When the positive sequence vector per unit value of the real-time voltage is greater than a preset positive sequence vector threshold and the low-high voltage interlocking fault ride-through mode signal is a signal for entering the low-high voltage interlocking fault ride-through mode, the grid-side converter, the DC load shedding Chopper device and the machine-side converter are controlled based on a preset control strategy to achieve coordinated control of the low-high voltage interlocking fault ride-through of the wind turbine converter;

[0057] Among them, the preset control strategies include: low and high voltage interlocking control strategy, grid-side Chopper control strategy, and single closed-loop current control strategy.

[0058] It should be noted that the preset positive sequence vector threshold is 1.1pu. If Udp is greater than 1.1pu, it is detected whether LVRT_Tr igF l ag is 1 at the same time. If it is 1, the low-high voltage cascading fault ride-through mode is entered; wherein, LVRT_Tr igFl ag is the low voltage ride-through trigger end flag. When the low voltage ride-through trigger ends, this flag is set to 1 and maintained cleared to 0 for a period of time, which is used for low-high voltage cascading fault judgment.

[0059] After entering the low-high voltage cascading fault ride-through mode, the grid-side converter, DC unloading Chopper device, and machine-side converter are coordinated and controlled to survive the transient process of voltage transition during the low-high voltage cascading fault. At the same time, rotor overcurrent is suppressed to prevent the Crowbar device on the machine side from being put into operation, ensuring continuous active output of the converter during the fault ride-through period.

[0060] In the embodiment of the present disclosure, the controlling of the grid-side converter, the DC load shedding Chopper device and the generator-side converter based on a preset control strategy includes:

[0061] Controlling the grid-side converter based on the low-high voltage interlocking control strategy;

[0062] Controlling the DC load unloading Chopper device based on the grid-side Chopper control strategy;

[0063] The machine-side converter is controlled based on the single closed-loop current control strategy.

[0064] Furthermore, the controlling the grid-side converter based on the low-high voltage interlocking control strategy includes:

[0065] When the power grid is in a transient process, the pulse of the grid-side converter is blocked for a period of T, and then the DC bus voltage reference value is dynamically adjusted according to the real-time voltage of the power grid;

[0066] Among them, the bus voltage adjustment coefficient k (default is 690V), bus voltage adjustment base U b (The default is the rated grid voltage per unit value, such as 1), bus voltage setting value U dc (The default value is the initial value of the bus voltage, such as 1065V), the height of the grid voltage rise is U max .

[0067] Transform the above formula: Reference value of DC bus voltage Perform maximum and minimum value limiting to ensure operation within a safe range.

[0068] When the power grid is in a steady state, the current of the power grid is controlled by using a current controller with reference and error filter decoupling.

[0069] It should be noted that the control of the grid-side converter based on the low-high voltage interlocking control strategy also includes:

[0070] When the power grid is in a transient state or a steady state, an active current priority control strategy is adopted to control the grid side of the double-fed converter, or a reactive current priority control strategy is adopted to control the grid side of the full-power converter.

[0071] Furthermore, the calculation formula of the blocking time is as follows:

[0072]

[0073] Where T is the blocking time, ΔU = Udp HVRT -Udp LVRT , Udp HVRT is the per-unit value of the positive sequence vector when the high voltage of the power grid is stable due to cascading faults, Udp LVRTIt is the per-unit value of the positive sequence vector when the low voltage of the power grid is stable due to cascading faults.

[0074] Among them, the larger the mutation amplitude, the longer the blocking time. Generally, the blocking time is less than 4 power grid cycles to facilitate the recovery of the system transient process; at the same time, the convenience and operability in practical applications are considered.

[0075] It should be noted that low-high fault crossing is divided into transient and steady-state processes. When entering the voltage transient state, when the current impact exceeds the threshold, the grid-side converter pulse is blocked first to suppress the overcurrent fault and ensure that no fault shutdown occurs; after blocking the pulse, the bus voltage reference value is dynamically adjusted according to the grid voltage rise or drop amplitude to adapt to the grid voltage fault process and ensure that no overmodulation fault occurs; during transient and steady-state periods, when the converter is a doubly fed converter, the grid side of the doubly fed converter adopts an active current priority control strategy, and when the converter is a full-power converter, the grid side of the full-power converter adopts a reactive current priority control strategy; during the steady-state period of the grid, control is performed based on the current controller using reference and error filter decoupling to improve the current response speed.

[0076] Among them, the grid side of the doubly fed converter adopts an active current priority control strategy: the maximum current of the converter is limited by capacity, and the sum of the squares of the active current and reactive current should not be greater than the square of the total current. In order to stabilize the DC bus voltage of the converter, the grid-side converter gives priority to meeting the demand for active current, and then obtains the maximum reactive current value through the square difference, and uses this value as the limit value of the reactive current reference value.

[0077] The grid side of the full-power converter adopts a reactive current priority control strategy: the maximum current of the converter is limited by capacity, and the square sum of the active current and reactive current should not be greater than the square of the total current. In order to reduce the voltage amplitude of the grid at the converter end, the grid-side converter gives priority to meeting the reactive current demand, and then obtains the maximum active current value through the square difference, and uses this value as the limit value of the active current reference value.

[0078] The current controller using reference and error filter decoupling controls the current of the grid as follows:

[0079] After the conventional current controller obtains the current signal, it first separates the positive and negative sequences, and then inputs the separated sequence components into the PI regulator. Since a lag will be generated during the positive and negative sequence separation process, the response speed of the current controller is reduced.

[0080] like Figure 2 The current control algorithm based on the decoupling of the reference and error filter signals is shown in FIG. The current is transformed into the current in the positive sequence coordinate system after rotation, which is recorded as the positive sequence coordinate system current The current is transformed into the current in the negative sequence coordinate system after rotation, which is recorded as the negative sequence coordinate system current Active current reference for positive sequence current controller and reactive current reference Respectively with the positive sequence coordinate system current Make a difference and get the active current error signal and reactive current error signal Enter the PI regulator. Active current reference The low-pass filtered active current error signal Make and get the d-axis positive and negative sequence decoupling terms The product of the inductive reactance ωL is used as the reactive decoupling feedforward term, and the reactive current reference The error signal after the low pass filter Make a difference to get the q-axis positive and negative sequence decoupling term The product multiplied by the inductive reactance ωL is used as the active decoupling feedforward term; and After double reverse rotation The positive sequence component in the negative sequence coordinate system is obtained, which is different from the current in the negative sequence coordinate system Take the difference to get the negative sequence current Active current reference for negative sequence current controller and reactive current reference Set to 0, the negative sequence current controller structure is the same as the positive sequence current controller described in the above steps. Positive sequence current controller output After coordinate transformation get Negative sequence current controller output After coordinate transformation get After taking the sum, we get v αβ Enter the SVPWM debugging algorithm to drive the power unit to operate.

[0081] Furthermore, the controlling of the DC load unloading Chopper device based on the grid-side Chopper control strategy includes:

[0082] When the DC bus voltage connected to the grid-side converter is greater than the preset upper threshold of the Chopper device action voltage, the Chopper circuit is controlled to be enabled, and the load shedding enable duty cycle is set to 1;

[0083] When the DC bus voltage connected to the grid-side converter is lower than the preset lower limit threshold of the Chopper device action voltage, the Chopper circuit is controlled to be cut out and the load shedding input duty cycle is set to 0.

[0084] It should be noted that the grid-side Chopper control strategy is specifically as follows:

[0085] Immediately raise the upper and lower thresholds of the Chopper device's action voltage to the parameter values ​​corresponding to the low-high voltage interlocking fault; when the DC bus voltage is greater than the upper threshold, the Chopper device is put into discharge, and when it is less than the lower threshold, the Chopper device is cut out and does not discharge; through the Chopper device releasing the energy injected into the DC bus from the grid-side converter and the machine-side converter during the dynamic process of voltage mutation, the fluctuation of the DC bus voltage is controlled within a certain safety range, providing support for the stable operation of the machine-side converter;

[0086] At the same time, a DC unloading control strategy is proposed. Since there is a current shock in the transient process of voltage increase and recovery, which may cause bus overvoltage, unloading suppression is usually adopted. When the DC bus voltage is greater than the set threshold, unloading is started, and when the DC bus voltage is less than the set threshold, unloading is cut out. A hysteresis loop is set between the two thresholds. The lower threshold setting has a faster response speed, but in the process of grid voltage increase, the uncontrolled rectifier current will flow from the grid to the bus and then be consumed by the unloading resistor, resulting in loss of power generation. A higher threshold setting can avoid the input of unloading during the process of grid voltage increase, but it sacrifices the response speed. Combined with the DC bus voltage reference value in one of the control methods, the unloading action is driven by pulse width modulation, and the duty cycle value D is the deviation ΔU from the actual value and reference value of the DC bus voltage. dc The duty cycle value D is set as follows:

[0087]

[0088] In the formula, ΔU dcMin To completely cut out the DC bus voltage deviation value for load unloading, ΔU dcMax It is the DC bus voltage deviation value when the load is fully unloaded.

[0089] When the DC bus voltage is greater than the input threshold, the load shedding input duty cycle D=1 is set, and when the DC bus voltage is less than the cut-out threshold, the load shedding input duty cycle D=0 is set. In this way, in the transient state of grid voltage increase, since the DC bus voltage reference value threshold is relatively low, the load shedding can be quickly put into operation to suppress overvoltage, and in the steady state of grid voltage increase, unnecessary active power consumption by load shedding can be avoided.

[0090] Furthermore, the controlling the machine-side converter based on the single closed-loop current control strategy includes:

[0091] The given active current given value is subtracted from the active current of the fed-back rotor current to obtain the active current difference value, and the given reactive current given value is subtracted from the reactive current of the fed-back rotor current to obtain the reactive current difference value;

[0092] The active current difference and the reactive current difference are input into a PI controller to obtain an active voltage value and a reactive voltage value of the rotor, and the machine-side converter is controlled based on the active voltage value and the reactive voltage value.

[0093] It should be noted that the generator-side converter adopts a single closed-loop current control strategy such as Figure 3 As shown in the figure, the active current set value is directly calculated based on the active power command value of the wind turbine main control system to ensure the active output of the unit; the reactive current set value is directly given according to the high voltage ride-through standard of the wind turbine. This greatly improves the dynamic response performance of the system, further suppresses the instability of the rotor current transient process, and supports the recovery of the grid voltage.

[0094] When using vector control technology, the three-phase voltage and current components are converted into the excitation (reactive) component and torque (active) component of the analog DC motor through coordinate transformation, and then these two components are independently controlled to achieve the decoupling of active power and reactive power. The main control torque signal and reactive signal are given by calculating the motor parameters to obtain the active current given and reactive current given The feedback rotor current i rq and i rd Make a difference, enter the PI controller, and get the corresponding voltage u rq and u rd , added to the feedforward voltage and driven by the coordinate transformation to operate the IGBT.

[0095] For a doubly-fed converter, the machine side is the core of controlling active power and reactive power, so its grid voltage fault suppression scheme mainly relies on the machine side. The premise of machine side control is bus stability, and the premise of bus stability is to prevent overmodulation of the grid side, so the machine-grid side converter must work together. The machine-side converter operates in reactive power priority mode, generates inductive reactive power, and suppresses the increase of grid voltage; the remaining capacity maintains sufficient torque output to suppress generator overspeed.

[0096] In the transient process of voltage increase and recovery, due to the attenuated DC component in the stator flux and the negative sequence component of the stator flux generated by voltage imbalance, the rotor is cut at high speed, causing the rotor voltage to oscillate and increase, which in turn causes overcurrent. The pulse blocking solution is adopted; if the current is about to exceed the tolerance range of the converter, pulse blocking supplemented by Crowbar release is considered.

[0097] It should be noted that the full-power converter does not involve the grid voltage and the original control strategy is continued to be used.

[0098] In an embodiment of the present disclosure, the method further includes:

[0099] When the detection channel pulse blocking timing time is equal to T, the pulse of the grid-side converter is unlocked, and the DC bus voltage setting value is increased according to the grid voltage value after the voltage surge.

[0100] It should be noted that when the detection pulse blocking timing time is up, the grid-side pulse is unlocked, and the DC bus voltage setting value is raised according to the grid voltage value after the voltage surge, and the grid-side control strategy is executed.

[0101] In an embodiment of the present disclosure, the method further includes:

[0102] During the low-high voltage cascading fault ride-through period, the grid voltage is detected at the same time to determine whether the grid voltage positive sequence vector per unit value Udp is less than 1.06pu; if Udp is less than 1.06pu, it means that the low-high voltage cascading fault ride-through is over, the dual closed-loop control strategy of the machine-side converter is restored, the upper and lower limit thresholds of the Chopper device are restored, and the DC bus voltage setting value is restored.

[0103] The detailed process of the coordinated control method for converter low-high voltage cascading fault ride-through proposed in this embodiment can be as follows: Figure 4 As shown, no further description is given here.

[0104] The coordinated control method for converter low- and high-voltage cascading fault riding proposed in the present application detects the grid voltage in real time, quickly and accurately obtains the grid voltage positive sequence vector scalar value by decoupling the dual synchronous reference coordinate system phase-locked loop, and combines the low-through end mark signal to quickly determine the occurrence of low- and high-voltage cascading faults; when a low- and high-voltage cascading fault occurs in the grid, the coordinated control of the grid-side converter, the Chopper device, and the machine-side converter is synchronously performed to effectively improve the reliability of the converter of the doubly fed wind turbine generator set to operate without disconnecting the wind turbine when a low- and high-voltage cascading fault occurs in the grid, and ensure that the converter continues to output active power during the fault riding period; according to the amplitude of the sudden change of the low and high voltages of the grid, the pulse blocking time is determined, and the system's ability to ride through low and high voltage cascading faults is simply and efficiently improved.

[0105] In summary, the coordinated control method for converter low-high voltage cascading fault ride-through proposed in this embodiment can ensure the continuous active output of the converter during fault ride-through and the safe and stable operation of the power grid.

[0106] Embodiment 2

[0107] Figure 5 A structural diagram of a coordinated control system for low-high voltage cascading fault ride-through of a converter provided according to an embodiment of the present application, such as Figure 5 As shown, the system comprises:

[0108] An acquisition module 100 is used to acquire the real-time voltage of the wind turbine connected to the power grid and a signal of whether the wind turbine enters a low-high voltage cascading fault ride-through mode;

[0109] A determination module 200, configured to determine a per-unit value of a positive sequence vector of the real-time voltage based on the real-time voltage of the power grid;

[0110] The control module 300 is used to control the grid-side converter, the DC load shedding Chopper device and the machine-side converter based on a preset control strategy to achieve coordinated control of the low-high voltage interlocking fault ride-through of the wind turbine converter when the positive-sequence vector per-unit value of the real-time voltage is greater than a preset positive-sequence vector threshold and the low-high voltage interlocking fault ride-through mode signal is a signal for entering the low-high voltage interlocking fault ride-through mode.

[0111] Among them, the preset control strategies include: low-high voltage interlocking control strategy, grid-side Chopper control strategy, and single closed-loop current control strategy;

[0112] The preset positive sequence vector threshold is 1.1 pu.

[0113] In this embodiment, the control module 300 is further used for:

[0114] Controlling the grid-side converter based on the low-high voltage interlocking control strategy;

[0115] Controlling the DC load unloading Chopper device based on the grid-side Chopper control strategy;

[0116] The machine-side converter is controlled based on the single closed-loop current control strategy.

[0117] Furthermore, the control module 300 is also used for:

[0118] When the power grid is in a transient process, the pulse of the grid-side converter is blocked for a period of T, and then the DC bus voltage reference value is dynamically adjusted according to the real-time voltage of the power grid;

[0119] When the power grid is in a steady state, the current of the power grid is controlled by using a current controller with reference and error filter decoupling.

[0120] The calculation formula of the blocking time is as follows:

[0121]

[0122] Where T is the blocking time, ΔU = Udp HVRT -Udp LVRT , Udp HVRTis the per-unit value of the positive sequence vector when the high voltage of the power grid is stable due to cascading faults, Udp LVRT It is the per-unit value of the positive sequence vector when the low voltage of the power grid is stable due to cascading faults.

[0123] Furthermore, the control module 300 is also used for:

[0124] When the power grid is in a transient state or a steady state, an active current priority control strategy is adopted to control the grid side of the double-fed converter, or a reactive current priority control strategy is adopted to control the grid side of the full-power converter.

[0125] Furthermore, the control module 300 is also used for:

[0126] When the DC bus voltage connected to the grid-side converter is greater than the preset upper threshold of the Chopper device action voltage, the Chopper circuit is controlled to be enabled, and the load shedding enable duty cycle is set to 1;

[0127] When the DC bus voltage connected to the grid-side converter is lower than the preset lower limit threshold of the Chopper device action voltage, the Chopper circuit is controlled to be cut out and the load shedding input duty cycle is set to 0.

[0128] Furthermore, the control module 300 is also used for:

[0129] The given active current given value is subtracted from the active current of the fed-back rotor current to obtain the active current difference value, and the given reactive current given value is subtracted from the reactive current of the fed-back rotor current to obtain the reactive current difference value;

[0130] The active current difference and the reactive current difference are input into a PI controller to obtain an active voltage value and a reactive voltage value of the rotor, and the machine-side converter is controlled based on the active voltage value and the reactive voltage value.

[0131] In the embodiment of the present disclosure, the control module 300 is also used for:

[0132] When the detection channel pulse blocking timing time is equal to T, the pulse of the grid-side converter is unlocked, and the DC bus voltage setting value is increased according to the grid voltage value after the voltage surge.

[0133] In summary, the coordinated control system for converter low-high voltage cascading fault ride-through proposed in this embodiment can ensure the continuous active output of the converter during fault ride-through and the safe and stable operation of the power grid.

[0134] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0135] Any process or method description in the flowchart or otherwise described herein may be understood to represent a module, fragment or portion of a code including one or more executable instructions for implementing the steps of a custom logic function or process, and the scope of the preferred embodiments of the present application includes additional implementations, in which the functions may not be performed in the order shown or discussed, including performing the functions in a substantially simultaneous manner or in a reverse order according to the functions involved, which should be understood by those skilled in the art to which the embodiments of the present application belong. Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Those of ordinary skill in the art may make changes, modifications, substitutions and modifications to the above embodiments within the scope of the present application.

Claims

1. A coordinated control method for low- and high-voltage cascading fault ride-through of a converter, characterized in that: The method comprises: Obtain the real-time voltage of the wind turbine connected to the grid and whether it has entered the low-high voltage cascading fault ride-through mode signal; Determining a per-unit value of a positive sequence vector of the real-time voltage based on the real-time voltage of the power grid; When the positive sequence vector per unit value of the real-time voltage is greater than the preset positive sequence vector threshold and the low-high voltage interlocking fault ride-through mode signal is collected to enter the low-high voltage interlocking fault ride-through mode signal, the grid-side converter, the DC load unloading Chopper device and the machine-side converter are controlled based on the preset control strategy to achieve coordinated control of the low-high voltage interlocking fault ride-through of the wind turbine converter; Among them, the preset control strategies include: low and high voltage interlocking control strategy, grid-side Chopper control strategy, and single closed-loop current control strategy.

2. The method according to claim 1, characterized in that The preset positive sequence vector threshold is 1.1 pu.

3. The method according to claim 2, characterized in that The controlling of the grid-side converter, the DC load shedding Chopper device and the machine-side converter based on the preset control strategy includes: Controlling the grid-side converter based on the low-high voltage interlocking control strategy; Controlling the DC load unloading Chopper device based on the grid-side Chopper control strategy; The machine-side converter is controlled based on the single closed-loop current control strategy.

4. The method according to claim 3, characterized in that The controlling of the grid-side converter based on the low-high voltage interlocking control strategy includes: When the power grid is in a transient process, the pulse of the grid-side converter is blocked for a period of T, and then the DC bus voltage reference value is dynamically adjusted according to the real-time voltage of the power grid; When the power grid is in a steady state, the current of the power grid is controlled by using a current controller with reference and error filter decoupling.

5. The method according to claim 4, characterized in that The controlling of the grid-side converter based on the low-high voltage interlocking control strategy also includes: When the power grid is in a transient state or a steady state, an active current priority control strategy is adopted to control the grid side of the double-fed converter, or a reactive current priority control strategy is adopted to control the grid side of the full-power converter.

6. The method according to claim 5, characterized in that The controlling of the DC load unloading Chopper device based on the grid-side Chopper control strategy includes: When the DC bus voltage connected to the grid-side converter is greater than the preset upper threshold of the Chopper device action voltage, the Chopper circuit is controlled to be enabled, and the load shedding enable duty cycle is set to 1; When the DC bus voltage connected to the grid-side converter is lower than the preset lower limit threshold of the Chopper device action voltage, the Chopper circuit is controlled to be cut out and the load shedding input duty cycle is set to 0.

7. The method according to claim 6, characterized in that The controlling the machine-side converter based on the single closed-loop current control strategy includes: The given active current given value is subtracted from the active current of the fed-back rotor current to obtain the active current difference value, and the given reactive current given value is subtracted from the reactive current of the fed-back rotor current to obtain the reactive current difference value; Inputting the active current difference and the reactive current difference into a PI controller to obtain an active voltage value and a reactive voltage value of the rotor, and controlling the machine-side converter based on the active voltage value and the reactive voltage value; The calculation formula of the blocking time is as follows: Where T is the blocking time, ΔU = Udp HVRT -Udp LVRT , Udp HVRT is the per-unit value of the positive sequence vector when the high voltage of the power grid is stable due to cascading faults, Udp LVRT It is the per-unit value of the positive sequence vector when the low voltage of the power grid is stable due to cascading faults.

8. The method according to claim 7, characterized in that The method further comprises: When the detection channel pulse blocking timing time is equal to T, the pulse of the grid-side converter is unlocked, and the DC bus voltage setting value is increased according to the grid voltage value after the voltage surge.

9. A coordinated control system for converter low-high voltage cascading fault ride-through, characterized in that: The system comprises: An acquisition module is used to obtain the real-time voltage of the wind turbine connected to the grid and whether it has entered the low-high voltage cascading fault ride-through mode signal; A determination module, configured to determine a per-unit value of a positive sequence vector of the real-time voltage based on the real-time voltage of the power grid; A control module, for controlling the grid-side converter, the DC load shedding Chopper device and the machine-side converter based on a preset control strategy to achieve coordinated control of the low-high voltage interlocking fault ride-through of the wind turbine converter when the positive-sequence vector per-unit value of the real-time voltage is greater than a preset positive-sequence vector threshold and a low-high voltage interlocking fault ride-through mode signal is collected to enter a low-high voltage interlocking fault ride-through mode signal; Among them, the preset control strategies include: low and high voltage interlocking control strategy, grid-side Chopper control strategy, and single closed-loop current control strategy.

10. The system according to claim 9, characterized in that The preset positive sequence vector threshold is 1.1 pu.

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