A control method and system for fault ride-through

Abstract

The application provides a control method and system for fault ride-through, which collects three-phase instantaneous voltage values and current values of a grid-connected point, calculates a unit value of an effective value of a fundamental positive sequence component, judges a current state of a power generation unit and calculates a low-voltage ride-through control output value; a reactive current reference value of a first selector is adjusted to switch a gear position, so that a first final reactive current reference value is obtained; an active current reference value of a second selector is adjusted to switch a gear position, so that a first final active current reference value is obtained; an inverter output instantaneous power is calculated, a third selector is adjusted to switch a gear position, and Boost operation is controlled; and according to the first final reactive current reference value and the first final active current reference value, a reactive current value of the inverter is controlled to a first target value. The application solves the problem of poor grid operation stability caused by a large increase of a direct-current voltage of the inverter due to an imbalance of active power between an alternating-current side and a direct-current side of the inverter during low-voltage ride-through.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power grid control, and in particular to a fault ride-through control method and system. Background Technology

[0002] The rapid development of new energy sources has brought enormous challenges to the stability of power system operation. In my country, some regions with a high proportion of new energy sources have already experienced problems such as insufficient synchronous power sources, weak power grids, and susceptibility to transient instability, which in turn limits the capacity for new energy absorption and transmission. Among these challenges, voltage stability is one of the most prominent. To ensure the continuous operation of new energy sources during grid voltage short-circuit faults, the ability to ride through low voltage and provide active and reactive power support during faults is a necessary condition for the large-scale integration of new energy power generation systems into the grid.

[0003] Two-stage photovoltaic (PV) power generation systems are currently one of the mainstream structures for PV power generation. Due to the presence of a DC / DC converter in the middle, the coordinated operation of the DC / DC inverter and DC / AC converter during faults is crucial for the stable operation of the inverter. However, current technologies for controlling PV power grids struggle to maintain a balance between the active power on the inverter's DC side and the active power on the AC side, resulting in an unsafe DC voltage level in the system. Furthermore, during fault recovery, excessive fluctuations in active and reactive power lead to poor stability of the power grid system. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a fault ride-through control method and system. The aim is to solve the problem of poor grid stability caused by a significant increase in inverter DC voltage due to the imbalance of active power on the AC and DC sides of the inverter during low-voltage ride-through. The invention proposes a fault ride-through control method and system, including:

[0005] Collect the instantaneous three-phase voltage and current values ​​at the grid connection point, calculate the per-unit value of the fundamental positive sequence component RMS value based on the three-phase instantaneous voltage values, determine the current state of the power generation unit based on the per-unit value of the fundamental positive sequence component RMS value, and calculate the low voltage ride-through control output value.

[0006] Based on the low voltage ride-through control output value, the reactive current reference value of the first selector is adjusted to switch the gear, and the first final reactive current reference value is obtained.

[0007] Based on the active power output value, the active power current reference value of the second selector is adjusted to switch the gear, and the first final active power current reference value is obtained. The active power output value is calculated based on the low voltage ride-through control output value.

[0008] Based on the instantaneous three-phase voltage and current values ​​at the grid connection point, the instantaneous output power of the inverter is calculated, and the average active power is calculated from the instantaneous output power of the inverter.

[0009] Based on the average active power, the duty cycle of the first Boost of the third selector is adjusted to switch gears and control the Boost operation.

[0010] Based on the first final reactive current reference value and the first final active current reference value, the reactive current value of the inverter is controlled to the first target value.

[0011] This invention, through the aforementioned steps, limits the inverter's reactive current to a target value during low-voltage ride-through, thereby controlling the active current to a safe level and preventing excessive AC active voltage. Simultaneously, by reducing Boost converter regulation and instead calculating active power and directly looking up the Boost duty cycle from a table, it ensures a balance between Boost output active power and inverter output active power, effectively resolving the DC-side voltage imbalance problem. Finally, through the interaction between the DC and AC sides, it solves the problem of a significant increase in inverter DC voltage caused by the imbalance of active power on the AC and DC sides. By addressing the issue of a significant increase in inverter DC voltage due to the imbalance of active power on the AC and DC sides, the stability of the power grid operation is improved.

[0012] Furthermore, based on the low-voltage ride-through control output value, the reactive current reference value of the first selector is adjusted to switch gears to obtain a first final reactive current reference value; based on the active power output value, the active power current reference value of the second selector is adjusted to switch gears to obtain a first final active power current reference value. The active power output value is calculated based on the low-voltage ride-through control output value, specifically as follows:

[0013] The reactive current reference value of the first selector is switched from the reactive voltage outer loop output value to the low voltage ride-through control output. The reactive current reference value is then passed through a limiting circuit to obtain the first final reactive current reference value.

[0014] The active current reference value of the second selector is switched from the DC voltage outer loop output value to the active output value. The active current reference value is passed through a limiting circuit to obtain the first final active current reference value. The active output value is calculated based on the inverter's maximum output current capability combined with the low voltage ride-through control output value.

[0015] Furthermore, the process involves collecting the instantaneous three-phase voltage and current values ​​at the grid connection point, calculating the per-unit value of the fundamental positive sequence effective value based on the three-phase instantaneous voltage values, determining the current state of the power generation unit based on the per-unit value of the fundamental positive sequence effective value, and calculating the low-voltage ride-through control output value. Specifically:

[0016] Collect the instantaneous three-phase voltage and current values ​​at the grid connection point, and calculate the per-unit value of the effective value of the fundamental positive sequence component at the current moment;

[0017] If the per-unit value of the effective value of the fundamental positive sequence component is less than or equal to the preset fault threshold, it is determined that the power generation unit has entered a low voltage ride-through.

[0018] Once the power generation unit is determined to have entered low voltage ride-through, the low voltage ride-through control output value is calculated based on the per-unit value of the fundamental positive sequence component RMS value and the RMS value of the rated current of the photovoltaic power station.

[0019] If the per-unit value of the fundamental positive sequence component is greater than the preset fault threshold, it is determined that the power generation unit will not enter low voltage ride-through. The instantaneous three-phase voltage and current values ​​of the grid connection point are obtained at the next moment. The per-unit value of the fundamental positive sequence component is calculated at the next moment, and the state of the power generation unit at the next moment is judged.

[0020] Furthermore, based on the instantaneous three-phase voltage and current values ​​at the grid connection point, the instantaneous output power of the inverter is calculated, and the average active power is calculated using the instantaneous output power of the inverter. Based on the average active power, the duty cycle of the first Boost of the third selector is adjusted to switch gears and control the Boost operation, specifically as follows:

[0021] The inverter output instantaneous power is obtained by multiplying and summing the three-phase instantaneous voltage and current values ​​at the grid connection point. The inverter output instantaneous power is then passed through a first-order low-pass filter to obtain the average active power.

[0022] Based on the average active power, the duty cycle of the second Boost is obtained by directly looking up the table. The duty cycle of the first Boost of the third selector is switched from the output of the maximum power tracking control loop to the output of the second Boost duty cycle, and the Boost is controlled to work through the trigger loop.

[0023] Furthermore, the step of controlling the inverter's reactive current value to the first target value based on the first final reactive current reference value and the first final active current reference value specifically involves:

[0024] Based on the first final reactive current reference value and the first final active current reference value, the current inner loop of the corresponding inverter controller is input. Through the modulation triggering loop, the reactive current value of the inverter is controlled to the target value. The first target value is used to control the active power on the inverter side to be equal to the active power on the Boost side.

[0025] Furthermore, the fault ride-through control method proposed in this invention further includes: determining the current state of the power generation unit as fault recovery based on the per-unit value of the effective value of the fundamental positive sequence component; and controlling the reactive voltage control outer loop and the DC voltage control outer loop to be instantaneously cleared based on the falling edge detection.

[0026] The reactive current reference value of the first selector is adjusted back to obtain the second final reactive current reference value.

[0027] Adjust the active current reference value of the second selector to return to the previous value, and obtain the second final active current reference value;

[0028] Adjusting the first Boost duty cycle of the third selector to return to the normal MPTT working mode;

[0029] Based on the second reactive current reference value and the second active current reference value, the current inner loop of the corresponding inverter control module controller is input, and the reactive current value of the inverter is controlled to the second target value through the modulation triggering circuit.

[0030] Furthermore, the step of determining the current state of the power generation unit as a fault and confirming recovery based on the per-unit value of the fundamental positive sequence component's effective value, and instantaneously clearing the reactive voltage control outer loop and the DC voltage control outer loop to zero based on falling edge detection, specifically involves:

[0031] The per-unit value of the effective value of the fundamental positive sequence component is determined to be greater than the preset fault threshold value, and the fault recovery is determined. Through falling edge detection, the reactive voltage control outer loop and the DC voltage control outer loop are instantly cleared to zero, and the output values ​​of the reactive voltage outer loop and the DC voltage outer loop are instantly 0.

[0032] Furthermore, the step of adjusting the reactive current reference value of the first selector to obtain a second final reactive current reference value, and adjusting the active current reference value of the second selector to obtain a second final active current reference value, further includes:

[0033] The reactive current reference value of the first selector is switched from the low voltage ride-through control output value to the reactive voltage outer loop output value. The reactive current reference value is then passed through a limiting circuit to obtain the second final reactive current reference value.

[0034] The active current reference value of the second selector is switched from the active output value to the DC voltage outer loop output value. The active current reference value is then passed through a limiting circuit to obtain the second final active current reference value.

[0035] Furthermore, the step of adjusting the duty cycle of the first Boost of the third selector to return to a lower setting, controlling the Boost to enter the normal MPTT operating mode, also includes:

[0036] The duty cycle of the first Boost of the third selector is switched from the duty cycle of the second Boost to the output of the maximum power point tracking control circuit, and then the Boost is controlled to enter the normal MPTT working mode through the trigger circuit.

[0037] This invention also proposes a fault ride-through control system, comprising: a fault judgment module, a first selector module, a second selector module, a third selector module, and an inverter control module. The fault judgment module includes a fault occurrence confirmation module and a fault recovery confirmation module. The first selector module includes a first selector shifting module and a first selector return module. The second selector module includes a second selector shifting module and a second selector return module. The third selector module includes a third selector shifting module and a third selector return module. The inverter control module includes a first inverter control module and a second inverter control module.

[0038] The fault occurrence confirmation module is used to collect the instantaneous three-phase voltage and current values ​​at the grid connection point, calculate the per-unit value of the fundamental positive sequence component effective value based on the three-phase instantaneous voltage values, determine the current state of the power generation unit based on the per-unit value of the fundamental positive sequence component effective value, and calculate the low voltage ride-through control output value.

[0039] The first selector shifting module is used to switch gears by adjusting the reactive current reference value of the first selector according to the low voltage ride-through control output value, so as to obtain the first final reactive current reference value.

[0040] The second selector shifting module is used to switch gears by adjusting the active current reference value of the second selector according to the active output value, so as to obtain the first final active current reference value. The active output value is calculated based on the low voltage ride-through control output value.

[0041] The third selector shifting module is used to calculate the instantaneous output power of the inverter based on the instantaneous three-phase voltage and current values ​​at the grid connection point, and to calculate the average active power based on the instantaneous output power of the inverter; based on the average active power, the first Boost duty cycle of the third selector is adjusted to switch gears and control the Boost to work;

[0042] The first inverter control module is used to control the reactive current value of the inverter to a first target value based on the first final reactive current reference value and the first final active current reference value.

[0043] The fault recovery confirmation module is used to determine the current state of the power generation unit as fault recovery based on the per-unit value of the effective value of the fundamental positive sequence component, and to control the reactive voltage control outer loop and the DC voltage control outer loop to be instantly cleared based on the falling edge detection.

[0044] The first selector reset module is used to adjust the reactive current reference value of the first selector to reset, so as to obtain the second final reactive current reference value.

[0045] The second selector rollback module is used to adjust the active current reference value of the second selector to roll back, so as to obtain the second final active current reference value.

[0046] The third selector backoff module is used to adjust the first Boost duty cycle of the third selector backoff, and control the Boost to enter the normal MPTT working mode.

[0047] The second inverter control module is used to input the inverter's inner current loop according to the second reactive current reference value and the second active current reference value, and control the inverter's reactive current value to the second target value through the modulation triggering circuit.

[0048] The fault ride-through control system proposed in this invention, through the control of the inverter and the adjustment of the selector's range, enables the system to balance the active power on the AC side and the active power on the DC side during low-voltage ride-through. At the same time, during fault recovery, the system can avoid excessive active and reactive power disturbances, thereby improving the operational stability of the power grid system.

[0049] Furthermore, the first selector shifting module is used to switch gears based on the low-voltage ride-through control output value, adjusting the reactive current reference value of the first selector to obtain a first final reactive current reference value; the second selector shifting module is used to switch gears based on the active power output value, adjusting the active power current reference value of the second selector to obtain a first final active power current reference value, wherein the active power output value is calculated based on the low-voltage ride-through control output value, specifically:

[0050] The reactive current reference value of the first selector is switched from the reactive voltage outer loop output value to the low voltage ride-through control output. The reactive current reference value is then passed through a limiting circuit to obtain the first final reactive current reference value.

[0051] The active current reference value of the second selector is switched from the DC voltage outer loop output value to the active output value. The active current reference value is passed through a limiting circuit to obtain the first final active current reference value. The active output value is calculated based on the inverter's maximum output current capability combined with the low voltage ride-through control output value.

[0052] Furthermore, the fault occurrence confirmation module is used to collect the three-phase instantaneous voltage and current values ​​at the grid connection point, calculate the per-unit value of the fundamental positive sequence component RMS value based on the three-phase instantaneous voltage values, determine the current state of the power generation unit based on the per-unit value of the fundamental positive sequence component RMS value, and calculate the low voltage ride-through control output value, and also includes:

[0053] Data acquisition unit, fault diagnosis unit, and cyclic operation unit;

[0054] The data acquisition unit is used to acquire the instantaneous three-phase voltage and current values ​​at the grid connection point and calculate the per-unit value of the effective value of the fundamental positive sequence component at the current moment.

[0055] The fault judgment unit is used to determine that the per-unit value of the effective value of the fundamental positive sequence component is less than or equal to the preset fault threshold value, and to determine that the power generation unit has entered a low voltage ride-through.

[0056] Once the power generation unit is determined to have entered low voltage ride-through, the low voltage ride-through control output value is calculated based on the per-unit value of the fundamental positive sequence component RMS value and the RMS value of the rated current of the photovoltaic power station.

[0057] The cyclic working unit is used to determine that the power generation unit will not enter a low voltage ride-through when the per-unit value of the effective value of the fundamental positive sequence component is greater than the preset fault threshold value. It then obtains the instantaneous three-phase voltage and current values ​​at the grid connection point at the next moment, calculates the per-unit value of the effective value of the fundamental positive sequence component at the next moment, and judges the state of the power generation unit at the next moment.

[0058] Furthermore, the third selector shifting module is used to calculate the instantaneous output power of the inverter based on the instantaneous three-phase voltage and current values ​​at the grid connection point, and to calculate the average active power using the instantaneous output power of the inverter; based on the average active power, the first Boost duty cycle of the third selector is adjusted to switch gears, controlling the Boost operation, specifically:

[0059] The inverter output instantaneous power is obtained by multiplying and summing the three-phase instantaneous voltage and current values ​​at the grid connection point. The inverter output instantaneous power is then passed through a first-order low-pass filter to obtain the average active power.

[0060] Based on the average active power, the duty cycle of the second Boost is obtained by directly looking up the table. The duty cycle of the first Boost of the third selector is switched from the output of the maximum power tracking control loop to the output of the second Boost duty cycle, and the Boost is controlled to work through the trigger loop.

[0061] Furthermore, the first inverter control module is used to control the reactive current value of the inverter to a first target value based on the first final reactive current reference value and the first final active current reference value, specifically:

[0062] Based on the first final reactive current reference value and the first final active current reference value, the current inner loop of the corresponding inverter controller is input. Through the modulation triggering loop, the reactive current value of the inverter is controlled to the first target value, wherein the first target value is used to control the active power on the inverter side to be equal to the active power on the Boost side.

[0063] Furthermore, the first selector rollback module is used to adjust the reactive current reference value of the first selector to roll back, thereby obtaining a second final reactive current reference value; the second selector rollback module is used to adjust the active current reference value of the second selector to roll back, thereby obtaining a second final active current reference value, specifically as follows:

[0064] The reactive current reference value of the first selector is switched from the low voltage ride-through control output value to the reactive voltage outer loop output value. The reactive current reference value is then passed through a limiting circuit to obtain the second final reactive current reference value.

[0065] The active current reference value of the second selector is switched from the active output value to the DC voltage outer loop output value. The active current reference value is then passed through a limiting circuit to obtain the second final active current reference value.

[0066] Furthermore, the fault recovery confirmation module is used to determine the current state of the power generation unit as fault-recovered based on the per-unit value of the fundamental positive sequence component's effective value. Based on falling edge detection, it controls the reactive voltage control outer loop and the DC voltage control outer loop to be instantaneously reset to zero. Specifically:

[0067] The per-unit value of the effective value of the fundamental positive sequence component is determined to be greater than the preset fault threshold value, and the fault recovery is determined. Through falling edge detection, the reactive voltage control outer loop and the DC voltage control outer loop are instantly cleared to zero, and the output values ​​of the reactive voltage outer loop and the DC voltage outer loop are instantly 0.

[0068] Furthermore, the third selector backoff module is used to adjust the first Boost duty cycle of the third selector backoff, controlling the Boost to enter the normal MPTT working mode, specifically as follows:

[0069] The duty cycle of the first Boost of the third selector is switched from the duty cycle of the second Boost to the output of the maximum power point tracking control circuit, and then the Boost is controlled to enter the normal MPTT working mode through the trigger circuit.

[0070] Furthermore, the second inverter control module is used to input the current inner loop of the corresponding inverter control module controller according to the second reactive current reference value and the second active current reference value, and through the modulation triggering circuit, the reactive current value of the inverter control module is adjusted to the second target value, specifically:

[0071] The second final reactive current reference value and the second final active current reference value are input into the current inner loop of the corresponding inverter controller. Through the modulation triggering loop, the reactive current value of the inverter is controlled to the second target value, wherein the second target value is used to control the active power on the inverter side to be equal to the active power on the Boost side. Attached Figure Description

[0072] Figure 1 This is a flowchart of the steps of a fault-crossing control method provided in a certain embodiment of the present invention.

[0073] Figure 2 This is a flowchart of the fault recovery and rollback steps of a fault crossing control method provided in a certain embodiment of the present invention.

[0074] Figure 3 This is a block diagram of a fault-crossing control system provided in a certain embodiment of the present invention.

[0075] Figure 4 This is a block diagram of a fault judgment module of a fault-crossing control system provided in a certain embodiment of the present invention.

[0076] Figure 5 This is a block diagram of a fault occurrence confirmation module for a fault-crossing control system provided in a certain embodiment of the present invention.

[0077] Figure 6 This is a block diagram of the first selector module of a fault-crossing control system provided in a certain embodiment of the present invention.

[0078] Figure 7 This is a flowchart of the first selector operation of a fault-crossing control system provided in a certain embodiment of the present invention.

[0079] Figure 8 This is a block diagram of the second selector module of a fault-crossing control system provided in a certain embodiment of the present invention.

[0080] Figure 9 This is a flowchart of the second selector operation of a fault-crossing control system provided in a certain embodiment of the present invention.

[0081] Figure 10 This is a block diagram of the third selector module of a fault-crossing control system provided in a certain embodiment of the present invention.

[0082] Figure 11 This is a flowchart of the third selector operation of a fault-crossing control system provided in a certain embodiment of the present invention.

[0083] Figure 12 This is a block diagram of an inverter control module of a fault ride-through control system provided in a certain embodiment of the present invention.

[0084] Figure 13 This is a flowchart of the inverter control process of a fault ride-through control system provided in a certain embodiment of the present invention. Detailed Implementation

[0085] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0086] See Figure 1 , Figure 1 This is a flowchart illustrating the steps of a fault-crossing control method. (Example) Figure 1 As shown in the figure, this embodiment of the invention proposes a fault ride-through control method, including steps 101 to 106, the specific steps of which are as follows:

[0087] Step 101: Collect the instantaneous three-phase voltage and current values ​​at the grid connection point, calculate the per-unit value of the fundamental positive sequence component effective value based on the three-phase instantaneous voltage values, determine the current state of the power generation unit based on the per-unit value of the fundamental positive sequence component effective value, and calculate the low voltage ride-through control output value.

[0088] As an example of this embodiment, the present invention collects the three-phase instantaneous voltage value U at the grid connection point. a U b U c and current value i a i b i c Calculate the per-unit value Vest of the effective value of the fundamental positive sequence component at the current moment. If the per-unit value Vest of the effective value of the fundamental positive sequence component is less than or equal to the preset fault threshold (set to 0.9 in this embodiment), it is determined that the power generation unit has entered the low voltage ride-through stage, and the low voltage ride-through flag CTR = 1 is set.

[0089] The generator unit is determined to have entered a low-voltage ride-through state based on the per-unit value of the fundamental positive sequence component RMS value Vest and the RMS value of the rated current of the photovoltaic power station I. N Calculate the low voltage ride-through control output value I. qref2 Specifically:

[0090]

[0091] If the per-unit value Vest of the fundamental positive sequence component is greater than the preset fault threshold, it is determined that the power generation unit will not enter a low-voltage ride-through, and the instantaneous three-phase voltage value U′ of the grid connection point is obtained at the next moment. a 、U′ b 、U′ c and current value i′ a 、i′ b 、i′ c Calculate the per-unit value Vest′ of the effective value of the fundamental positive sequence component at the next moment, and determine the state of the power generation unit at the next moment.

[0092] Step 102: Based on the low voltage ride-through control output value, adjust the reactive current reference value of the first selector to switch gears and obtain the first final reactive current reference value.

[0093] As an example of this embodiment, the reactive current reference value I of the first selector is adjusted. qref1 The reactive voltage outer loop output value I qref0 Switch to the low voltage ride-through control output I qref2 The reactive current reference value I qref1 The first final reactive current reference value I is obtained through the limiting process. q re f The initial output value of the limiting circuit is I. qmax and-I qmax .

[0094] Step 103: Based on the active power output value, adjust the active power current reference value of the second selector to switch gears and obtain the first final active power current reference value. The active power output value is calculated based on the low voltage ride-through control output value.

[0095] As an example of this embodiment, the active current reference value I of the second selector is adjusted. dref1 Output value I from the outer loop of DC voltage dref0 Switch to active output value I dref2 The active current reference value I dref1 The first final active current reference value I is obtained through the limiting process. dref The active power output value I dref2Based on the inverter's maximum output current capability I m Combined with low voltage ride-through control output value I qref2 The calculation yields the following results:

[0096]

[0097] The initial output value of the limiting circuit is I. dmax and-I dmax ;

[0098] Step 104: Calculate the instantaneous output power of the inverter based on the instantaneous three-phase voltage and current values ​​at the grid connection point, and calculate the average active power using the instantaneous output power of the inverter.

[0099] As an example of this embodiment, based on the instantaneous three-phase voltage value U at the grid connection point a U b U c and current value i a i b i c The instantaneous output power P of the inverter is obtained by multiplying and summing the products. The instantaneous output power P of the inverter is then passed through a first-order low-pass filter to obtain the average active power P0, specifically:

[0100] P = U a ×i a +U b ×i b +U c ×i c

[0101]

[0102] Step 105: Based on the average active power, adjust the duty cycle of the first Boost of the third selector to switch gears and control the Boost to work;

[0103] As an example of this embodiment, the second Boost duty cycle D2 is obtained directly by looking up the table based on the average active power P0. The first Boost duty cycle D1 of the third selector is switched from the output D0 of the maximum power tracking control loop to the output D2 of the second Boost duty cycle, and the Boost is controlled to work through the triggering loop.

[0104] Step 106: Based on the first final reactive current reference value and the first final active current reference value, control the reactive current value of the inverter to the first target value.

[0105] As an example of this embodiment, based on the first final reactive current reference value I qrefand the first final active current reference value I dref Input the current inner loop of the corresponding inverter controller, and through the modulation triggering circuit, control the reactive current value of the inverter to a first target value, wherein the first target value is used to control the active power on the inverter side to be equal to the active power on the Boost side.

[0106] This invention, through the aforementioned steps, limits the inverter's reactive current to a target value during low-voltage ride-through, thereby controlling the active current to a safe level and preventing excessive AC active voltage. Simultaneously, by reducing Boost converter regulation and instead calculating active power and directly looking up the Boost duty cycle from a table, it ensures a balance between Boost output active power and inverter output active power, effectively resolving the DC-side voltage imbalance problem. Finally, through the interaction between the DC and AC sides, it solves the problem of a significant increase in inverter DC voltage caused by the imbalance of active power on the AC and DC sides. By addressing the issue of a significant increase in inverter DC voltage due to the imbalance of active power on the AC and DC sides, the stability of the power grid operation is improved.

[0107] Example 2

[0108] See Figure 2 , Figure 2 This is a flowchart illustrating the rollback steps after fault recovery in a fault-crossing control method. (Example) Figure 2 As shown, after the fault is recovered, the system reverts to the selector rollback process, including steps 201 to 205. The specific steps are as follows:

[0109] Step 201: Determine the current state of the power generation unit as fault recovery based on the per-unit value of the effective value of the fundamental positive sequence component. Based on the falling edge detection, control the reactive voltage control outer loop and the DC voltage control outer loop to be instantly cleared to zero.

[0110] As an example of this embodiment, when the per-unit value Vest of the fundamental positive sequence component is determined to be greater than a preset fault threshold, fault recovery is confirmed, and the low-pass flag CTR is changed from 1 to 0. Through falling edge detection, the reactive voltage control outer loop and the DC voltage control outer loop are instantaneously reset to zero, and the reactive voltage outer loop outputs I. qref0 and DC voltage outer loop output value I dref0 It is 0 at an instant.

[0111] Step 202: Adjust the reactive current reference value of the first selector to return to the previous value, and obtain the second final reactive current reference value;

[0112] As an example of this embodiment, the reactive current reference value I of the first selector is adjusted. qref1 Output value I controlled by low voltage ride-through qref2Switch to reactive voltage outer loop output value I qref0 The reactive current reference value I qref1 The second final reactive current reference value I is obtained through the limiting process. qrefs The limiting element changes from 0 to I at a certain rate. qmax It then remained unchanged.

[0113] Step 203: Adjust the active current reference value of the second selector to return to the previous value, and obtain the second final active current reference value;

[0114] As an example of this embodiment, the active current reference value I of the second selector is adjusted. dref1 From the active power output value I dref2 Switch to DC voltage outer loop output value I dref0 The active current reference value I dref1 The second final active current reference value I is obtained through the limiting process. drefs The limiting element changes from 0 to I at a certain rate. dmax It then remained unchanged.

[0115] Step 204: Adjust the first Boost duty cycle of the third selector to return to normal, and control the Boost to enter the normal MPTT working mode.

[0116] As an example of this embodiment, the first Boost duty cycle D1 of the third selector is switched from the second Boost duty cycle D2 to the maximum power point tracking control output D0, and the Boost is controlled to enter the normal MPTT working mode through the triggering circuit.

[0117] Step 205: Input the second final reactive current reference value and the second final active current reference value into the current inner loop of the corresponding inverter control module controller, and control the reactive current value of the inverter to the second target value through the modulation triggering circuit.

[0118] As an example of this embodiment, based on the second final reactive current reference value I qrefs Second final active current reference value I drefs Input the current inner loop of the corresponding inverter controller, and through the modulation triggering circuit, control the reactive current value of the inverter to the second target value, wherein the second target value is used to reduce the disturbance during the switching process of active power and reactive power of the inverter during fault recovery.

[0119] Example 3

[0120] See Figure 3 , Figure 3 This is a block diagram of a fault-ride control system. (Example) Figure 3 As shown, this embodiment provides a fault ride-through control system, including modules 301 to 305. The specific modules and their functions are as follows: fault judgment module 301, first selector module 302, second selector module 303, third selector module 304, and inverter control module 305.

[0121] Among them, see Figure 4 , Figure 4 This is a block diagram of the fault diagnosis module of the fault ride-through control system. Figure 4 As shown, the fault judgment module 301 includes: a fault occurrence confirmation module 401 and a fault recovery confirmation module 402;

[0122] See Figure 6 , Figure 6 This is a block diagram of the first selector module in a fault-crossing control system. Figure 6 As shown, the first selector module 302 includes: a first selector shifting module 601 and a first selector return module 602;

[0123] See Figure 8 , Figure 8 This is a block diagram of the second selector module in a fault-crossing control system. Figure 8 As shown, the second selector module 303 includes: a second selector shifting module 801 and a second selector return module 802;

[0124] See Figure 10 , Figure 10 This is a block diagram of the second selector module in a fault-crossing control system. Figure 10 As shown, the third selector module 304 includes: a third selector shifting module 1001 and a third selector rewinding module 1002;

[0125] See Figure 12 , Figure 12 This is a block diagram of the second selector module in a fault-crossing control system. Figure 12 As shown, the inverter control module 305 includes: a first inverter control module 1201 and a second inverter control module 1202;

[0126] The fault occurrence confirmation module 401 is used to collect the instantaneous three-phase voltage and current values ​​at the grid connection point, calculate the per-unit value of the fundamental positive sequence component effective value based on the three-phase instantaneous voltage values, determine the current state of the power generation unit based on the per-unit value of the fundamental positive sequence component effective value, and calculate the low voltage ride-through control output value.

[0127] As an example of this embodiment, the fault occurrence confirmation module 401 further includes: a data acquisition unit 501, a fault judgment unit 502, and a cyclic working unit 503;

[0128] The data acquisition unit 501 is used to acquire the instantaneous three-phase voltage value U at the grid connection point. a U b U c and current value i a i b i c Calculate the per-unit value Vest of the effective value of the fundamental positive sequence component at the current moment;

[0129] The fault judgment unit 502 is used to determine that the per-unit value Vest of the effective value of the fundamental positive sequence component is less than or equal to the preset fault threshold value (set to 0.9 in this embodiment), determine that the power generation unit has entered low voltage ride-through, and set the low voltage ride-through flag CTR=1.

[0130] The generator unit is determined to have entered a low-voltage ride-through state based on the per-unit value of the fundamental positive sequence component RMS value Vest and the RMS value of the rated current of the photovoltaic power station I. N Calculate the low voltage ride-through control output value I. qref2 ;

[0131] The cyclic working unit 503 is used to obtain the three-phase instantaneous voltage value U′ of the grid connection point at the next moment when the per-unit value Vest of the effective value of the fundamental positive sequence component is greater than the preset fault threshold value, and the generator unit is determined not to enter the low voltage ride-through. a 、U′ b 、U′ c and current value i′ a 、i′ b 、i′ c Calculate the per-unit value Vest′ of the effective value of the fundamental positive sequence component at the next moment, and determine the state of the power generation unit at the next moment.

[0132] The first selector shifting module 601 is used to switch gears by adjusting the reactive current reference value of the first selector according to the low voltage ride-through control output value, so as to obtain the first final reactive current reference value.

[0133] As an example of this embodiment, the reactive current reference value I of the first selector is adjusted. qref1 The reactive voltage outer loop output value I qref0 Switch to the low voltage ride-through control output I qref2 The reactive current reference value I qref1 The first final reactive current reference value I is obtained through the limiting process. qrefThe initial output value of the limiting circuit is I. qmax and-I qmax .

[0134] As another example of this embodiment, see Figure 7 , Figure 7 This is a flowchart illustrating the workflow of the first selector in a fault-crossing control system. Figure 7 As shown, the first selector's workflow consists of the workflow of the fault judgment module 301 and the workflow of the first selector module 302. The fault judgment module 301 performs fault judgment, determines the value of the low-pass flag CTR, controls the first selector module 302 to perform a shift or return operation, and outputs the first final reactive current reference value I through a limiting circuit. qref Or the second final reactive current reference value I qrefs .

[0135] The second selector shifting module 801 is used to switch gears by adjusting the active current reference value of the second selector according to the active output value, so as to obtain the first final active current reference value. The active output value is calculated based on the low voltage ride-through control output value.

[0136] As an example of this embodiment, the active current reference value I of the second selector is adjusted. dref1 Output value I from the outer loop of DC voltage dref0 Switch to active output value I dref2 The active current reference value I dref1 The first final active current reference value I is obtained through the limiting process. dref The active power output value I dref2 Based on the inverter's maximum output current capability I m Combined with low voltage ride-through control output value I qref2 The calculation shows that the initial output value of the limiting circuit is I. dmax and--I dmax .

[0137] As another example of this embodiment, see Figure 9 , Figure 9 This is a flowchart illustrating the workflow of the second selector in a fault-crossing control system. Figure 9 As shown, the second selector's workflow consists of the workflow of the fault judgment module 301, the workflow of the first selector module 302, and the workflow of the second selector module 303. The fault judgment module 301 determines the value of the low-voltage ride-through flag CTR, and the first selector module 302 determines the low-voltage ride-through control output I. qref2The second selector module 303 is controlled to perform shifting or reverting operations, and the first final active current reference value I is output through a limiting circuit. dref Or the second final active current reference value I drefs .

[0138] The third selector shifting module 1001 is used to calculate the instantaneous output power of the inverter based on the instantaneous three-phase voltage and current values ​​at the grid connection point, and to calculate the average active power based on the instantaneous output power of the inverter; based on the average active power, the first Boost duty cycle of the third selector is adjusted to switch gears and control the Boost to work.

[0139] As an example of this embodiment, see Figure 11 , Figure 11 This is a flowchart illustrating the workflow of the third selector in a fault-crossing control system. Figure 11 As shown, based on the instantaneous three-phase voltage value U at the grid connection point a U b U c and current value i a i b i c The inverter output instantaneous power P is obtained by multiplying the two components. The inverter output instantaneous power P is then passed through a first-order low-pass filter to obtain the average active power P0. Based on the average active power P0, the second Boost duty cycle D2 is obtained by directly looking up a table. The first Boost duty cycle D1 of the third selector is switched from the maximum power point tracking control output D0 to the second Boost duty cycle output D2, and the Boost is controlled to work through a triggering circuit.

[0140] The first inverter control module 1201 is used to control the reactive current value of the inverter to a first target value according to the first final reactive current reference value and the first final active current reference value.

[0141] As an example of this embodiment, based on the first final reactive current reference value I qref and the first final active current reference value I dref Input the current inner loop of the corresponding inverter controller, and through the modulation triggering circuit, control the reactive current value of the inverter to a first target value, wherein the first target value is used to control the active power on the inverter side to be equal to the active power on the Boost side.

[0142] The fault recovery confirmation module 402 is used to determine the current state of the power generation unit as fault recovery based on the per-unit value of the effective value of the fundamental positive sequence component, and to control the reactive voltage control outer loop and the DC voltage control outer loop to be instantly cleared based on the falling edge detection.

[0143] As an example of this embodiment, when the per-unit value Vest of the fundamental positive sequence component is determined to be greater than a preset fault threshold, fault recovery is confirmed, and the low-pass flag CTR is changed from 1 to 0. Through falling edge detection, the reactive voltage control outer loop and the DC voltage control outer loop are instantaneously reset to zero, and the reactive voltage outer loop outputs I. qref0 and DC voltage outer loop output value I dref0 It is 0 at an instant.

[0144] The first selector back-off module 602 is used to adjust the reactive current reference value of the first selector for back-off to obtain the second final reactive current reference value.

[0145] As an example of this embodiment, the reactive current reference value I of the first selector is adjusted. qref1 Output value I controlled by low voltage ride-through qref2 Switch to reactive voltage outer loop output value I qref0 The reactive current reference value I qref1 The second final reactive current reference value I is obtained through the limiting process. qrefs The limiting element changes from 0 to I at a certain rate. qmax It then remained unchanged.

[0146] The second selector backtracking module 802 is used to adjust the active current reference value of the second selector for backtracking to obtain the second final active current reference value.

[0147] As an example of this embodiment, the active current reference value I of the second selector is adjusted. dref1 From the active power output value I dref2 Switch to DC voltage outer loop output value I dref0 The active current reference value I dref1 The second final active current reference value I is obtained through the limiting process. drefs The limiting element changes from 0 to I at a certain rate. dmax It then remained unchanged.

[0148] The third selector backoff module 1002 is used to adjust the first Boost duty cycle of the third selector backoff, and control the Boost to enter the normal MPTT working mode.

[0149] As an example of this embodiment, the first Boost duty cycle D1 of the third selector is switched from the second Boost duty cycle D2 to the maximum power point tracking control output D0, and the Boost is controlled to enter the normal MPTT working mode through the triggering circuit.

[0150] The second inverter control module 1202 is used to input the inverter's inner current loop according to the second reactive current reference value and the second active current reference value, and control the inverter's reactive current value to the second target value through the modulation triggering circuit.

[0151] As an example of this embodiment, based on the second final reactive current reference value I qrefs Second final active current reference value I drefs Input the current inner loop of the corresponding inverter controller, and through the modulation triggering circuit, control the reactive current value of the inverter to the second target value, wherein the second target value is used to reduce the disturbance during the switching process of active power and reactive power of the inverter during fault recovery.

[0152] As another example of this embodiment, see Figure 13 , Figure 13 This is a flowchart illustrating the inverter control process of a fault-ride control system. Figure 13 As shown, the inverter control workflow includes the workflow of the first inverter control module 1201 and the workflow of the second inverter control module 1202. The active current reference value and reactive current reference value are input into the current inner loop of the corresponding inverter controller according to the calculated active current reference value and reactive current reference value. Through the modulation triggering link, the reactive current value of the inverter is controlled to the target value.

[0153] The fault ride-through control system proposed in this invention, through the control of the inverter and the adjustment of the selector's range, enables the system to balance the active power on the AC side and the active power on the DC side during low-voltage ride-through. At the same time, during fault recovery, the system can avoid excessive active and reactive power disturbances, thereby improving the operational stability of the power grid system.

[0154] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0155] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0156] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0157] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fault ride-through control method, characterized in that, include: Collect the instantaneous three-phase voltage and current values ​​at the grid connection point, calculate the per-unit value of the fundamental positive sequence component RMS value based on the three-phase instantaneous voltage values, determine the current state of the power generation unit based on the per-unit value of the fundamental positive sequence component RMS value, and calculate the low voltage ride-through control output value. Based on the low voltage ride-through control output value, the reactive current reference value of the first selector is adjusted to switch the gear, and the first final reactive current reference value is obtained. Based on the active power output value, the active power current reference value of the second selector is adjusted to switch the gear, and the first final active power current reference value is obtained. The active power output value is calculated based on the low voltage ride-through control output value. Based on the instantaneous three-phase voltage and current values ​​at the grid connection point, the instantaneous output power of the inverter is calculated, and the average active power is calculated from the instantaneous output power of the inverter. Based on the average active power, the duty cycle of the first Boost of the third selector is adjusted to switch gears and control the Boost operation. Based on the first final reactive current reference value and the first final active current reference value, the reactive current value of the inverter is controlled to the first target value. Specifically, the first final reactive current reference value and the first final active current reference value are input into the current inner loop of the corresponding inverter controller. Through the modulation triggering loop, the reactive current value of the inverter is controlled to the first target value. The first target value is used to control the active power on the inverter side to be equal to the active power on the Boost side.

2. The fault ride-through control method as described in claim 1, characterized in that, The first final reactive current reference value is obtained by adjusting the reactive current reference value of the first selector according to the low voltage ride-through control output value. Based on the active power output value, the active current reference value of the second selector is adjusted to switch gears, resulting in the first final active current reference value. The active power output value is calculated based on the low voltage ride-through control output value, specifically: The reactive current reference value of the first selector is switched from the reactive voltage outer loop output value to the low voltage ride-through control output. The reactive current reference value is then passed through a limiting circuit to obtain the first final reactive current reference value. The active current reference value of the second selector is switched from the DC voltage outer loop output value to the active output value. The active current reference value is passed through a limiting circuit to obtain the first final active current reference value. The active output value is calculated based on the inverter's maximum output current capability combined with the low voltage ride-through control output value.

3. The fault ride-through control method as described in claim 1, characterized in that, The system collects the instantaneous three-phase voltage and current values ​​at the grid connection point. Based on the instantaneous three-phase voltage values, it calculates the per-unit value of the fundamental positive-sequence effective value. Based on the per-unit value of the fundamental positive-sequence effective value, it determines the current state of the power generation unit and calculates the low-voltage ride-through control output value. Specifically: Collect the instantaneous three-phase voltage and current values ​​at the grid connection point, and calculate the per-unit value of the effective value of the fundamental positive sequence component at the current moment; If the per-unit value of the effective value of the fundamental positive sequence component is less than or equal to the preset fault threshold, it is determined that the power generation unit has entered a low voltage ride-through. Once the power generation unit is determined to have entered low voltage ride-through, the low voltage ride-through control output value is calculated based on the per-unit value of the fundamental positive sequence component RMS value and the RMS value of the rated current of the photovoltaic power station. If the per-unit value of the fundamental positive sequence component is greater than the preset fault threshold, it is determined that the power generation unit will not enter low voltage ride-through. The instantaneous three-phase voltage and current values ​​of the grid connection point are obtained at the next moment. The per-unit value of the fundamental positive sequence component is calculated at the next moment, and the state of the power generation unit at the next moment is judged.

4. The fault ride-through control method as described in claim 1, characterized in that, The instantaneous output power of the inverter is calculated based on the instantaneous three-phase voltage and current values ​​at the grid connection point. The average active power is then calculated from the instantaneous output power. Based on the average active power, the duty cycle of the first Boost of the third selector is adjusted to switch gears and control the Boost operation. Specifically: The inverter output instantaneous power is obtained by multiplying and summing the three-phase instantaneous voltage and current values ​​at the grid connection point. The inverter output instantaneous power is then passed through a first-order low-pass filter to obtain the average active power. Based on the average active power, the duty cycle of the second Boost is obtained by directly looking up the table. The duty cycle of the first Boost of the third selector is switched from the output of the maximum power tracking control loop to the output of the second Boost duty cycle, and the Boost is controlled to work through the trigger loop.

5. The fault ride-through control method as described in claim 1, characterized in that, Also includes: Based on the per-unit value of the effective value of the fundamental positive sequence component, the current state of the power generation unit is determined to be faulty and recovery is confirmed. Based on the falling edge detection, the reactive voltage control outer loop and the DC voltage control outer loop are instantly cleared to zero. The reactive current reference value of the first selector is adjusted back to obtain the second final reactive current reference value. Adjust the active current reference value of the second selector to return to the previous value, and obtain the second final active current reference value; Adjusting the first Boost duty cycle of the third selector to return to the normal MPTT working mode; Based on the second final reactive current reference value and the second final active current reference value, the current inner loop of the corresponding inverter control module controller is input, and the reactive current value of the inverter is controlled to the second target value through the modulation triggering circuit.

6. The fault ride-through control method as described in claim 5, characterized in that, The process of determining the current state of the power generation unit as a fault and confirming recovery based on the per-unit value of the fundamental positive sequence component's effective value, and instantaneously clearing the reactive voltage control outer loop and DC voltage control outer loop based on falling edge detection, specifically involves: The per-unit value of the effective value of the fundamental positive sequence component is determined to be greater than the preset fault threshold value, and the fault recovery is determined. Through falling edge detection, the reactive voltage control outer loop and the DC voltage control outer loop are instantly cleared to zero, and the output values ​​of the reactive voltage outer loop and the DC voltage outer loop are instantly 0.

7. The fault ride-through control method as described in claim 5, characterized in that, The process involves adjusting the reactive current reference value of the first selector to obtain a second final reactive current reference value; and adjusting the active current reference value of the second selector to obtain a second final active current reference value, specifically as follows: The reactive current reference value of the first selector is switched from the low voltage ride-through control output value to the reactive voltage outer loop output value. The reactive current reference value is then passed through a limiting circuit to obtain the second final reactive current reference value. The active current reference value of the second selector is switched from the active output value to the DC voltage outer loop output value. The active current reference value is then passed through a limiting circuit to obtain the second final active current reference value.

8. The fault ride-through control method as described in claim 5, characterized in that, The step of adjusting the duty cycle of the first Boost of the third selector to return to a lower setting, thereby controlling the Boost to enter the normal MPTT operating mode, specifically involves: The duty cycle of the first Boost of the third selector is switched from the duty cycle of the second Boost to the output of the maximum power point tracking control circuit, and then the Boost is controlled to enter the normal MPTT working mode through the trigger circuit.

9. A fault-ride control system, characterized in that, include: The system includes a fault diagnosis module, a first selector module, a second selector module, a third selector module, and an inverter control module. The fault diagnosis module comprises a fault occurrence confirmation module and a fault recovery confirmation module. The first selector module comprises a first selector shifting module and a first selector return module. The second selector module comprises a second selector shifting module and a second selector return module. The third selector module comprises a third selector shifting module and a third selector return module. The inverter control module comprises a first inverter control module and a second inverter control module. The fault occurrence confirmation module is used to collect the instantaneous three-phase voltage and current values ​​at the grid connection point, calculate the per-unit value of the fundamental positive sequence component effective value based on the three-phase instantaneous voltage values, determine the current state of the power generation unit based on the per-unit value of the fundamental positive sequence component effective value, and calculate the low voltage ride-through control output value. The first selector shifting module is used to switch gears by adjusting the reactive current reference value of the first selector according to the low voltage ride-through control output value, so as to obtain the first final reactive current reference value. The second selector shifting module is used to switch gears by adjusting the active current reference value of the second selector according to the active output value, so as to obtain the first final active current reference value. The active output value is calculated based on the low voltage ride-through control output value. The third selector shifting module is used to calculate the instantaneous output power of the inverter based on the instantaneous three-phase voltage and current values ​​at the grid connection point, and to calculate the average active power based on the instantaneous output power of the inverter; based on the average active power, the first Boost duty cycle of the third selector is adjusted to switch gears and control the Boost to work; The first inverter control module is used to control the reactive current value of the inverter to a first target value according to the first final reactive current reference value and the first final active current reference value. Specifically, it inputs the current inner loop of the corresponding inverter controller according to the first final reactive current reference value and the first final active current reference value, and controls the reactive current value of the inverter to a first target value through the modulation triggering loop. The first target value is used to control the active power on the inverter side to be equal to the active power on the Boost side. The fault recovery confirmation module is used to determine the current state of the power generation unit as fault recovery based on the per-unit value of the effective value of the fundamental positive sequence component, and to control the reactive voltage control outer loop and the DC voltage control outer loop to be instantly cleared based on the falling edge detection. The first selector reset module is used to adjust the reactive current reference value of the first selector to reset, so as to obtain the second final reactive current reference value. The second selector rollback module is used to adjust the active current reference value of the second selector to roll back, so as to obtain the second final active current reference value. The third selector backoff module is used to adjust the first Boost duty cycle of the third selector backoff, and control the Boost to enter the normal MPTT working mode. The second inverter control module is used to input the second final reactive current reference value and the second final active current reference value into the inverter's current inner loop, and control the inverter's reactive current value to the second target value through the modulation triggering circuit.

10. The fault ride-through control system as described in claim 9, characterized in that, The first selector shifting module is used to switch gears by adjusting the reactive current reference value of the first selector according to the low voltage ride-through control output value, so as to obtain the first final reactive current reference value. The second selector shifting module is used to switch gears based on the active power output value and the active power current reference value of the second selector to obtain a first final active power current reference value. The active power output value is calculated based on the low-voltage ride-through control output value, specifically: The reactive current reference value of the first selector is switched from the reactive voltage outer loop output value to the low voltage ride-through control output. The reactive current reference value is then passed through a limiting circuit to obtain the first final reactive current reference value. The active current reference value of the second selector is switched from the DC voltage outer loop output value to the active output value. The active current reference value is passed through a limiting circuit to obtain the first final active current reference value. The active output value is calculated based on the inverter's maximum output current capability combined with the low voltage ride-through control output value.

11. The fault-ride control system as described in claim 9, characterized in that, The fault occurrence confirmation module is used to collect the instantaneous three-phase voltage and current values ​​at the grid connection point, calculate the per-unit value of the fundamental positive sequence component RMS based on the three-phase instantaneous voltage values, determine the current state of the power generation unit based on the per-unit value of the fundamental positive sequence component RMS, and calculate the low-voltage ride-through control output value. It also includes: Data acquisition unit, fault diagnosis unit, and cyclic operation unit; The data acquisition unit is used to acquire the instantaneous three-phase voltage and current values ​​at the grid connection point and calculate the per-unit value of the effective value of the fundamental positive sequence component at the current moment. The fault judgment unit is used to determine that the per-unit value of the effective value of the fundamental positive sequence component is less than or equal to the preset fault threshold value, and to determine that the power generation unit has entered a low voltage ride-through. Once the power generation unit is determined to have entered low voltage ride-through, the low voltage ride-through control output value is calculated based on the per-unit value of the fundamental positive sequence component RMS value and the RMS value of the rated current of the photovoltaic power station. The cyclic working unit is used to determine that the power generation unit will not enter a low voltage ride-through when the per-unit value of the effective value of the fundamental positive sequence component is greater than the preset fault threshold value. It then obtains the instantaneous three-phase voltage and current values ​​at the grid connection point at the next moment, calculates the per-unit value of the effective value of the fundamental positive sequence component at the next moment, and judges the state of the power generation unit at the next moment.

12. The fault-ride control system as described in claim 9, characterized in that, The third selector shifting module is used to calculate the instantaneous output power of the inverter based on the instantaneous three-phase voltage and current values ​​at the grid connection point, and to calculate the average active power using the instantaneous output power of the inverter; based on the average active power, the first Boost duty cycle of the third selector is adjusted to switch gears and control the Boost operation, specifically: The inverter output instantaneous power is obtained by multiplying and summing the three-phase instantaneous voltage and current values ​​at the grid connection point. The inverter output instantaneous power is then passed through a first-order low-pass filter to obtain the average active power. Based on the average active power, the duty cycle of the second Boost is obtained by directly looking up the table. The duty cycle of the first Boost of the third selector is switched from the output of the maximum power tracking control loop to the output of the second Boost duty cycle, and the Boost is controlled to work through the trigger loop.

13. The fault-ride control system as described in claim 9, characterized in that, The first selector rollback module is used to adjust the reactive current reference value of the first selector to roll back, thereby obtaining a second final reactive current reference value; the second selector rollback module is used to adjust the active current reference value of the second selector to roll back, thereby obtaining a second final active current reference value, specifically as follows: The reactive current reference value of the first selector is switched from the low voltage ride-through control output value to the reactive voltage outer loop output value. The reactive current reference value is then passed through a limiting circuit to obtain the second final reactive current reference value. The active current reference value of the second selector is switched from the active output value to the DC voltage outer loop output value. The active current reference value is then passed through a limiting circuit to obtain the second final active current reference value.

14. The fault-ride control system as described in claim 9, characterized in that, The fault recovery confirmation module is used to determine the current state of the power generation unit as fault-confirmed recovery based on the per-unit value of the fundamental positive sequence component's effective value. Based on falling edge detection, it controls the reactive voltage control outer loop and the DC voltage control outer loop to be instantaneously reset to zero. Specifically: The per-unit value of the effective value of the fundamental positive sequence component is determined to be greater than the preset fault threshold value, and the fault recovery is determined. Through falling edge detection, the reactive voltage control outer loop and the DC voltage control outer loop are instantly cleared to zero, and the output values ​​of the reactive voltage outer loop and the DC voltage outer loop are instantly 0.

15. The fault-ride control system as described in claim 9, characterized in that, The third selector backoff module is used to adjust the first Boost duty cycle of the third selector backoff, controlling the Boost to enter the normal MPTT working mode, specifically: The duty cycle of the first Boost of the third selector is switched from the duty cycle of the second Boost to the output of the maximum power point tracking control circuit, and then the Boost is controlled to enter the normal MPTT working mode through the trigger circuit.

16. The fault-ride control system as described in claim 9, characterized in that, The second inverter control module is used to input the second final reactive current reference value and the second final active current reference value into the current inner loop of the corresponding inverter control module controller. Through the modulation triggering circuit, the reactive current value of the inverter control module is adjusted to the second target value, specifically: The second final reactive current reference value and the second final active current reference value are input into the current inner loop of the corresponding inverter controller. Through the modulation triggering circuit, the reactive current value of the inverter is controlled to the second target value. The second target value is used to reduce the disturbance during the switching process of active and reactive power of the inverter during fault recovery.

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