Network construction type converter fault ride-through control method, device and system, and storage medium

Abstract

The embodiment of the invention provides a fault ride-through control method, device and system for a network construction type converter, and a storage medium, and relates to the technical field of intelligent power grid control. The method comprises the following steps: establishing a basic control system mathematical model of the network-forming converter; virtual impedance control is introduced into the mathematical model of the basic control system, and an extended control system mathematical model containing virtual impedance is formed; determining an adaptive adjustment range of a virtual impedance control parameter based on an extended control system mathematical model and an operation constraint during a fault period; and executing online adaptive adjustment on the virtual impedance control parameters according to the adaptive adjustment range so as to realize current limitation and voltage support during a power grid fault period. By adopting the method, the network construction type converter can continuously provide the network construction function during the fault period and after the fault is cleared, and the problems of difficult recovery, loss of the network construction function and insufficient voltage active support capability caused by forced switching to the network following mode are avoided.

Description

Technical Field

[0001] This application relates to the field of smart grid control technology, specifically to a fault ride-through control method and device for grid-type converters, a fault ride-through control system, and a storage medium. Background Technology

[0002] Currently, with the integration of a high proportion of renewable energy sources, such as photovoltaics and wind power, into the grid, modern power systems are characterized by a high proportion of renewable energy and a high proportion of power electronic converters. Against this backdrop, grid-based control technology, capable of simulating the external characteristics of synchronous generators and providing active inertia and damping support for the grid, has become an important means of improving grid stability. However, grid-based converters themselves have limited overcurrent capacity. When a grid fault causes a voltage drop, they are highly susceptible to triggering protection mechanisms or damaging equipment due to excessive output current, posing a serious challenge to their fault ride-through capability.

[0003] The relevant technology employs a ring current limiter control to monitor the output current of the grid-connected converter in real time. Once the current exceeds a set safety threshold, the control logic immediately forces the converter to switch from a voltage source grid-connected control mode to a current source grid-connected control mode. In this mode, the converter's output current is directly limited to the maximum allowable value, effectively preventing power devices from being damaged by overcurrent. This method offers rapid response and provides a direct and reliable effect in current limiting during fault periods.

[0004] In the process of implementing the embodiments of this application, at least the following problems were found in the related technology:

[0005] Once the fault is cleared and the grid voltage is restored, the converter, because its outer control loop has entered a saturation state, often cannot automatically or smoothly switch back to its original grid-connected control mode, causing it to remain in grid-connected mode for an extended period. This not only causes it to lose its grid-connected function of providing inertia and voltage support to the grid, but may also lead to a series of stability problems such as chaotic system control modes and slow recovery processes. Summary of the Invention

[0006] This application provides a fault ride-through control method and device for a grid-type converter, a fault ride-through control system, and a storage medium.

[0007] A first aspect of this application provides a fault ride-through control method for a grid-type converter, comprising:

[0008] Establish a mathematical model for the basic control system of a grid-type converter;

[0009] Virtual impedance control is introduced into the mathematical model of the basic control system to form an extended control system mathematical model that includes virtual impedance.

[0010] Based on the mathematical model of the extended control system and the operating constraints during the fault period, the adaptive adjustment range of the virtual impedance control parameters is determined.

[0011] Based on the adaptive adjustment range, online adaptive adjustment of the virtual impedance control parameters is performed to achieve current limiting and voltage support during grid faults.

[0012] In an optional embodiment of this application, a mathematical model of the basic control system of the grid-type converter is established, including:

[0013] Establish a control structure model for a grid-type converter under virtual synchronous control mode; wherein, the control structure model includes a virtual synchronous control loop, a virtual impedance control loop, a current limiting loop, an outer voltage loop control loop, and / or an inner current loop control loop.

[0014] Based on the control structure model, a power output characteristic model of the grid-type converter is established.

[0015] In an optional embodiment of this application, virtual impedance control is introduced into the mathematical model of the basic control system to form an extended control system mathematical model that includes virtual impedance, including:

[0016] In the voltage outer loop reference value based on the mathematical model of the basic control system, a voltage compensation amount determined by the virtual impedance value and the output current of the grid-type converter is superimposed.

[0017] Based on the voltage outer loop reference value with superimposed voltage compensation and the grid-side circuit relationship of the grid-type converter, the grid-side circuit equation after introducing virtual impedance control is established.

[0018] Based on the grid-side circuit equations after the introduction of virtual impedance control, mathematical models of the grid-connected voltage, output active power, and output reactive power of the grid-type converter after the introduction of virtual impedance control are established.

[0019] In an optional embodiment of this application, the virtual impedance value in the virtual impedance control parameters includes:

[0020] The virtual resistance portion is dynamically calculated based on the output current of the grid-type converter; and / or,

[0021] The virtual reactance is associated with the virtual resistance portion through an adjustable scaling factor.

[0022] In an optional embodiment of this application, the operational constraints during a failure include:

[0023] The total output current of the grid-connected converter does not exceed the maximum allowable current amplitude constraint; and / or,

[0024] Grid-type converters require reactive current injection into the grid that is linearly proportional to the voltage drop depth.

[0025] In an optional embodiment of this application, the adaptive adjustment range of the virtual impedance control parameters is determined based on the extended control system mathematical model and the operational constraints during a fault, including:

[0026] Calculate the target reactive current value based on the reactive current injection requirements;

[0027] By combining the current amplitude constraint, the overall constraint condition for the output current is formed;

[0028] Based on the extended control system mathematical model, the target reactive current value, and the overall constraints, the numerical range of the proportional coefficient in the virtual impedance control parameters is solved.

[0029] In an optional embodiment of this application, online adaptive adjustment of the virtual impedance control parameters is performed according to the adaptive adjustment range, including:

[0030] Continuously monitor the grid connection point voltage of the grid-connected converter;

[0031] When the grid connection point voltage is lower than the preset fault identification threshold, the fault ride-through control mode is triggered.

[0032] In fault-crossing control mode, subsequent adaptive adjustment steps are executed.

[0033] In one optional embodiment of this application, the fault identification threshold is a configurable value preset according to power grid operation standards or system requirements.

[0034] In an optional embodiment of this application, in fault ride-through control mode, subsequent adaptive adjustment steps are performed, including:

[0035] Monitor the output current of the grid-type converter;

[0036] Virtual impedance control is enabled when the output current exceeds its rated current.

[0037] Based on the current system state and the adaptive adjustment range, the virtual impedance control parameters are calculated and updated.

[0038] In an optional embodiment of this application, the virtual impedance control parameters are calculated and updated based on the current system state and the adaptive adjustment range, including:

[0039] Within the defined numerical range of the adaptive adjustment range, the specific value of the proportional coefficient is dynamically selected according to the preset optimization target.

[0040] In an optional embodiment of this application, the preset optimization objectives include:

[0041] While ensuring that the output current of the grid-connected converter does not exceed the limit, priority should be given to maximizing its reactive current support to the power grid.

[0042] In an optional embodiment of this application, in fault ride-through control mode, the subsequent adaptive adjustment steps further include:

[0043] The updated virtual impedance control parameters are used to generate voltage compensation, which is then applied to the control system of the grid-type converter.

[0044] In an optional embodiment of this application, performing online adaptive adjustment of the virtual impedance control parameters according to the adaptive adjustment range further includes:

[0045] When the grid connection point voltage is detected to recover to above the fault identification threshold and the output current is lower than its rated current, the fault ride-through control mode is exited and virtual impedance control is stopped.

[0046] A second aspect of the present application provides a grid-type converter fault ride-through control device, including a processor and a memory storing program instructions. The processor is configured to execute the grid-type converter fault ride-through control method as described in the first aspect of the present application when running the program instructions.

[0047] A third aspect of this application provides a fault ride-through control system, comprising:

[0048] The fault-crossing control system itself; and,

[0049] The grid-type converter fault ride-through control device, as described in the second aspect of this application, is installed on the fault ride-through control system body.

[0050] A fourth aspect of the embodiments of this application provides a computer-readable storage medium storing program instructions, which, when executed, cause a computer to perform the grid-type converter fault ride-through control method as described in the first aspect of the embodiments of this application.

[0051] The fault ride-through control method and apparatus, fault ride-through control system, and storage medium for grid-type converters provided in the embodiments of this application have the following beneficial effects:

[0052] This application's embodiments establish a mathematical model of the basic control system and introduce virtual impedance control to form an extended model. This allows the system to actively suppress fault current by superimposing a voltage compensation amount determined by the virtual impedance and output current in the voltage outer loop. This ensures that the grid-connected converter does not need to switch control modes throughout the fault process and always maintains operation in grid-connected control mode. Furthermore, based on this extended model and the operational constraints during the fault, the adaptive adjustment range of the virtual impedance control parameters is predetermined, setting a safe boundary that meets grid connection requirements for real-time parameter adjustment. Finally, online adaptive adjustment performed within this range can dynamically optimize control parameters based on the real-time system status, thereby prioritizing maximizing reactive current injection into the grid while strictly ensuring that the output current does not exceed the limit. Using the above method, the grid-connected converter can continuously provide grid-connected functionality during and after a fault, avoiding recovery difficulties, loss of grid-connected functionality, and insufficient active voltage support caused by forced switching to grid-connected mode. Attached Figure Description

[0053] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0054] Figure 1 This is a schematic diagram of a fault ride-through control method for a grid-type converter provided in an embodiment of this application;

[0055] Figure 2 This is a typical control strategy diagram of a grid-type converter provided in an embodiment of this application;

[0056] Figure 3 This is a schematic diagram of a grid-type converter fault ride-through control device provided in an embodiment of this application.

[0057] Figure label:

[0058] 800: Fault ride-through control device for grid-type converters; 801: Processor; 802: Memory; 803: Communication interface; 804: Bus. Detailed Implementation

[0059] To make the technical solutions and advantages of the embodiments of this application clearer, the exemplary embodiments of this application will be described in further detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not an exhaustive list of all embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0060] Figure 1This is a schematic diagram of the fault ride-through control method for a grid-type converter provided in the embodiments of this application. Any of the following methods can be executed in the fault ride-through control system, or in a server or terminal device that is communicatively connected to the fault ride-through control system.

[0061] Combination Figure 1 As shown in the figure, this application provides a fault ride-through control method for a grid-type converter, including:

[0062] S01, Establish the basic control system mathematical model of the grid-type converter.

[0063] S02 introduces virtual impedance control into the mathematical model of the basic control system to form an extended control system mathematical model that includes virtual impedance.

[0064] S03. Based on the extended control system mathematical model and the operating constraints during the fault period, determine the adaptive adjustment range of the virtual impedance control parameters.

[0065] S04, based on the adaptive adjustment range, performs online adaptive adjustment of the virtual impedance control parameters to achieve current limiting and voltage support during grid faults.

[0066] The fault ride-through control method for grid-connected converters provided in this application establishes a mathematical model of the basic control system and introduces virtual impedance control to form an extended model. This allows the system to actively suppress fault current by superimposing a voltage compensation amount determined by the virtual impedance and output current in the outer voltage loop. This ensures that the grid-connected converter does not need to switch control modes throughout the fault process and always maintains operation in grid-connected control mode. Furthermore, based on this extended model and the operational constraints during the fault, the adaptive adjustment range of the virtual impedance control parameters is predetermined, setting a safe boundary for real-time parameter adjustment that meets grid connection requirements. Finally, online adaptive adjustment within this range can dynamically optimize control parameters based on the real-time system status, thereby prioritizing maximizing reactive current injection into the grid while strictly ensuring that the output current does not exceed the limit. This method enables the grid-connected converter to continuously provide grid-connected functionality during and after a fault, avoiding recovery difficulties, loss of grid-connected functionality, and insufficient active voltage support caused by forced switching to grid-connected mode.

[0067] In an optional embodiment of this application, establishing a basic control system mathematical model for a grid-type converter includes: establishing a control structure model of the grid-type converter under virtual synchronous control mode; wherein the control structure model includes a virtual synchronous control loop, a virtual impedance control loop, a current limiting loop, a voltage outer loop control loop, and / or a current inner loop control loop; and based on the control structure model, establishing a power output characteristic model of the grid-type converter.

[0068] In this way, the virtual synchronization control loop provides the grid-connected converter with phase synchronization with the power grid, ensuring its basic grid-connected operation. The virtual impedance control loop can dynamically adjust the voltage outer loop reference value using current parameters, initially reducing the possibility of current exceeding limits. The current limiting loop provides protection when the current approaches or may exceed the safe range. The voltage outer loop and current inner loop provide stable trigger signals to the switching transistors through dual-loop control, ensuring the basic stability of the converter output. Based on this control structure model with clearly defined functions and coordinated cooperation, a power output characteristic model can be established. This model can accurately capture the operating rules of the grid-connected converter under virtual synchronization control mode, clearly reflect the impact of each control loop on power output, and thus help the grid-connected converter maintain a stable power output state during normal operation.

[0069] In an optional embodiment of this application, virtual impedance control is introduced into the mathematical model of the basic control system to form an extended control system mathematical model that includes virtual impedance. This includes: superimposing a voltage compensation amount determined by the virtual impedance value and the output current of the grid-connected converter into the voltage outer loop reference value based on the mathematical model of the basic control system; establishing the grid-side circuit equations after introducing virtual impedance control based on the voltage outer loop reference value with superimposed voltage compensation amount and the grid-side circuit relationship of the grid-connected converter; and establishing a mathematical model of the grid-connected point voltage, output active power, and output reactive power of the grid-connected converter after introducing virtual impedance control based on the grid-side circuit equations.

[0070] In this way, a voltage compensation amount, determined by both the virtual impedance value and the output current of the grid-connected converter, is superimposed on the voltage outer-loop reference value of the basic control system's mathematical model. Since this voltage compensation amount can dynamically adjust with changes in the grid-connected converter's output current, the voltage outer-loop reference value more closely matches the converter's real-time operating state, preventing deviations in the voltage outer-loop control from actual requirements due to current fluctuations. Based on the relationship between the voltage outer-loop reference value after superimposing the compensation amount and the grid-side circuit of the grid-connected converter, the grid-side circuit equations after introducing virtual impedance control are established. This integrates the voltage adjustment effect of virtual impedance control into the description of the grid-side electrical characteristics, more accurately reflecting the current-voltage interaction relationship on the grid side of the converter after introducing virtual impedance, and reducing the deviation between the model and actual operating conditions. Furthermore, based on these grid-side circuit equations, mathematical models of the grid-connected point voltage, output active power, and output reactive power of the grid-connected converter after introducing virtual impedance control are established. This allows the calculation of key operating parameters to fully reflect the impact of virtual impedance control, thereby more accurately capturing the converter's output characteristics after introducing virtual impedance control.

[0071] In an optional embodiment of this application, the virtual impedance value in the virtual impedance control parameters includes: a virtual resistance portion dynamically calculated based on the output current of the grid-type converter; and / or a virtual reactance portion associated with the virtual resistance portion by an adjustable proportional coefficient.

[0072] In this way, the virtual resistance component of the virtual impedance control parameters is dynamically calculated based on the output current of the grid-connected converter. This allows the virtual resistance value to adjust accordingly when the output current changes. As a component of the virtual impedance, the dynamic change of the virtual resistance directly affects the voltage compensation amount, which is jointly determined by the virtual impedance value and the output current. This makes the voltage compensation amount more closely match the real-time current state, helping to accurately adjust the outer voltage reference value in a timely manner when current fluctuations occur, thereby assisting in suppressing excessive current growth and reducing the risk of current exceeding limits. The virtual reactance component is linked to the virtual resistance component through an adjustable proportional coefficient. This adjustable coefficient allows the virtual reactance value to be flexibly set according to the actual operating requirements of the grid-connected converter. For example, adjusting the proportional coefficient based on the normal operating state or slight fluctuations of the power grid can change the size of the virtual reactance, enabling the overall virtual impedance to better adapt to the control requirements of different scenarios and improving the flexibility of virtual impedance control.

[0073] In an optional embodiment of this application, the operational constraints during a fault include: a current amplitude constraint that the total output current of the grid-connected converter does not exceed the maximum allowable value; and / or a reactive current injection requirement that the grid-connected converter injects reactive current into the grid in a manner that is linearly proportional to the voltage drop depth.

[0074] Thus, the current amplitude constraint during fault periods requires that the total output current of the grid-connected converter not exceed the maximum allowable value. Grid-connected converters have limited overcurrent capacity, and voltage dips during grid faults can easily lead to abnormal increases in their output current. This constraint defines a clear safety boundary for the converter's output current, preventing current exceeding the maximum allowable value from causing device damage or triggering unnecessary protection shutdowns, thereby maintaining the converter's basic operational capability during fault periods. The reactive current injection requirement stipulates that grid-connected converters must inject reactive current into the grid in a manner linearly proportional to the voltage dip depth. Voltage dips during faults affect grid stability; reactive current injection matching the voltage dip depth can specifically support the grid voltage, complying with grid connection requirements and helping to mitigate the degree of grid voltage dips. These two operational constraints clarify the operational principles during fault periods from two dimensions: converter current safety and grid voltage support. This ensures both the reliable operation of the grid-connected converter and provides support for grid stability during fault periods.

[0075] In an optional embodiment of this application, the adaptive adjustment range of the virtual impedance control parameters is determined based on the extended control system mathematical model and the operating constraints during the fault period, including: calculating the target reactive current value according to the reactive current injection requirements; forming the total constraint condition of the output current by combining the current amplitude constraint; and solving the numerical range of the proportional coefficient in the virtual impedance control parameters based on the extended control system mathematical model, the target reactive current value and the total constraint condition.

[0076] In this way, by calculating the target reactive current value based on the reactive current injection requirements, the voltage support requirements of the grid connection standard are transformed into specific control objectives. Combined with current amplitude constraints, a total constraint condition for the output current is formed, unifying equipment safety limits and system support requirements into complete boundary conditions. Furthermore, based on the established mathematical model of the extended control system including virtual impedance, the target reactive current value, and the total constraint condition, the numerical range of the proportional coefficient in the virtual impedance control parameters is solved. This predetermines a feasible parameter range that satisfies both the current limitation requirements during faults and the reactive current injection requirements for subsequent online adaptive adjustment. This allows the adjustment of virtual impedance to systematically and effectively support the grid voltage while ensuring the safety of the grid-connected converter.

[0077] In an optional embodiment of this application, online adaptive adjustment of the virtual impedance control parameters is performed according to the adaptive adjustment range, including: continuously monitoring the grid connection point voltage of the grid-connected converter; triggering the fault ride-through control mode when the grid connection point voltage is lower than a preset fault identification threshold; and performing subsequent adaptive adjustment steps in the fault ride-through control mode.

[0078] In this way, by continuously monitoring the grid connection point voltage of the grid-connected converter, the system can perceive the grid status in real time. When the grid connection point voltage is lower than the preset fault identification threshold, the comparison and judgment mechanism can reliably identify the grid voltage drop event, thereby triggering the fault ride-through control mode in a timely manner. This ensures that the subsequent online adaptive adjustment steps based on the extended control system mathematical model and the pre-determined virtual impedance control parameter adaptive adjustment range can be accurately activated when the fault actually occurs, so that the entire control strategy can enter the actual execution state from the theoretical preparation state, providing the necessary mode switching and start-up conditions for achieving current limiting and voltage support during the fault period.

[0079] In one optional embodiment of this application, the fault identification threshold is a configurable value preset according to power grid operation standards or system requirements. Preferably, the preset fault identification threshold is 0.9 per unit.

[0080] In this way, by defining the fault identification threshold as a configurable value preset according to the power grid operation standards or system requirements, the triggering condition can be flexibly adapted to different grid connection specifications and actual power grid operation environments, thereby improving the adaptability and accuracy of the fault ride-through control mode triggering mechanism.

[0081] In an optional embodiment of this application, in fault ride-through control mode, subsequent adaptive adjustment steps are performed, including: monitoring the output current of the grid-type converter; enabling virtual impedance control when the output current exceeds its rated current; and calculating and updating the virtual impedance control parameters based on the current system state and the adaptive adjustment range.

[0082] In this way, by monitoring the output current of the grid-connected converter, the system can detect whether it faces overcurrent risk in real time. When the output current exceeds its rated current, the virtual impedance control judgment mechanism is activated, ensuring that this current limiting method is activated only when necessary, thereby avoiding malfunctions and unnecessary interventions in the control loop. Furthermore, based on the current system state and the pre-determined adaptive adjustment range, the virtual impedance control parameters are calculated and updated, allowing the virtual impedance value to be dynamically and accurately adjusted within the parameter boundaries that ensure safety, according to the actual fault severity and system operating point. This effectively suppresses fault current and creates conditions for maintaining the grid-connected converter's grid-connected function in the process.

[0083] In an optional embodiment of this application, the virtual impedance control parameters are calculated and updated based on the current system state and the adaptive adjustment range, including: within the numerical range determined by the adaptive adjustment range, dynamically selecting the specific value of the proportional coefficient according to the preset optimization target.

[0084] In this way, by constraining the selection of the proportional coefficient in the virtual impedance control parameters within a defined numerical range of the adaptive adjustment range, it is ensured that the parameter adjustment always remains within a safe and feasible region that simultaneously satisfies current limiting and reactive power injection requirements. Based on this, the specific value of the proportional coefficient is dynamically selected within this range according to a preset optimization objective (such as prioritizing maximizing reactive power support, which may be mentioned later). This allows the control system to proactively and purposefully seek the optimal control parameters based on real-time operating status, while ensuring equipment safety and grid connection compliance. This elevates virtual impedance control from a passive current-limiting measure to an intelligent adjustment mechanism capable of proactively optimizing support performance during fault periods, enhancing the refinement and effectiveness of the entire adaptive control strategy.

[0085] In an optional embodiment of this application, the preset optimization objective includes: prioritizing maximizing the reactive current support of the grid converter to the grid while ensuring that the output current of the grid-connected converter does not exceed the limit.

[0086] Thus, the preset optimization objective prioritizes ensuring that the output current of the grid-connected converter does not exceed its limit. Since the grid-connected converter has limited overcurrent capacity, exceeding the current limit during a fault could damage components or trigger protection shutdown, preventing it from continuing to participate in grid operation. Therefore, this premise sets a basic boundary for the safe operation of the converter during faults, preventing the neglect of current safety due to excessive pursuit of other control objectives and maintaining the converter's basic operational capability. Simultaneously, under this premise, maximizing reactive current support to the grid is prioritized. Considering the voltage dips that are prone to occur during faults, reactive current injection can support the grid voltage, meeting grid connection requirements. Prioritizing this objective allows the grid-connected converter to allocate more control resources to mitigating grid voltage dips while ensuring its own safety, avoiding insufficient attention to reactive current support that could affect grid stability during faults. The above optimization target setting provides clear guidance for the subsequent dynamic selection of the specific value of the proportional coefficient within the adaptive adjustment range. This ensures that the selection of the proportional coefficient will not deviate from the core control requirements during faults, thus guaranteeing the reliable operation of the grid-connected converter itself and providing more effective voltage support to the power grid. It also helps to balance the relationship between converter safety and power grid stability, thereby improving the overall operating performance of the system during faults.

[0087] In an optional embodiment of this application, in the fault ride-through control mode, the subsequent adaptive adjustment steps further include: generating a voltage compensation amount using the updated virtual impedance control parameters and applying it to the control system of the grid-type converter.

[0088] In this way, by converting the virtual impedance control parameters calculated and updated based on the current system state and adaptive adjustment range into specific voltage compensation quantities, and applying these compensation quantities to the control system of the grid-connected converter, a closed-loop feedback of the actual control effect of the previous theoretical calculations and online decisions is achieved to the controlled object. This allows the virtual impedance value dynamically selected according to the preset optimization target to be reflected as a specific adjustment amount of the voltage outer loop reference value, thereby directly adjusting the output voltage command of the grid-connected converter. Ultimately, this enables the entire adaptive control strategy to move from the parameter calculation stage to the actual execution stage, ensuring that the limiting effect on fault current and the reactive power support effect on the power grid can be realized through the real-time action of the control system.

[0089] In an optional embodiment of this application, the online adaptive adjustment of the virtual impedance control parameters according to the adaptive adjustment range further includes: when the grid connection point voltage is detected to recover to above the fault identification threshold and the output current is lower than its rated current, exiting the fault ride-through control mode and stopping the virtual impedance control.

[0090] In this way, if the grid connection voltage recovers to above the fault identification threshold, it can be determined that the grid fault has most likely been cleared and the voltage has returned to the normal operating range. If the output current is lower than its rated current, it can be confirmed that the current of the grid-connected converter is within the safe and normal range, and there is no need to suppress the current or support the voltage through virtual impedance control. Combining these two conditions as the basis for exiting the fault ride-through control mode and stopping virtual impedance control can avoid misoperation caused by judging based on a single condition. For example, exiting only when the voltage has recovered but the current is still above the rated value may cause the current to become abnormal again. Exiting only when the current is low but the voltage has not recovered is difficult to deal with faults that have not been completely cleared, thus ensuring the accuracy of the exit timing. After exiting the fault ride-through control mode and stopping virtual impedance control, the grid-connected converter can return to the normal operating mode, avoiding the continued effect of special controls during the fault period (such as the adjustment of the voltage outer loop reference value by virtual impedance) on normal operating conditions, preventing interference with the converter's normal grid-connected functions (such as normal power output and voltage regulation), helping the converter to smoothly transition to normal operating conditions, and maintaining the overall stability of the system.

[0091] In practical applications, a fault ride-through control method for a grid-type converter can be specifically implemented based on, for example: Figure 1 The typical control strategy diagram for the grid-type converter is shown.

[0092] To establish the basic control system mathematical model of the grid-type converter, the control structure model of the grid-type converter under virtual synchronization control mode is first established. This control structure model includes the virtual synchronization control element. Figure 1 Virtual synchronization control loop and virtual impedance control loop ( Figure 1 Virtual impedance control and current limiting circuit ( Figure 1 Medium current limit), voltage outer loop control ( Figure 1 Medium voltage outer loop) and current inner loop control loop ( Figure 1 The system consists of two loops: an inner loop for voltage control and an inner loop for current control. The virtual synchronization control loop's main function is to control the active power output of the grid-connected converter to provide the grid-connected converter with a dq-axis phase synchronized with the grid. The virtual impedance control loop's main function is to dynamically adjust the reference value of the outer voltage loop through current parameters, thereby preventing the grid-connected converter from exceeding its current limit. The current limiting loop's main function is to prevent the grid-connected converter from exceeding its current limit. If the current exceeds the limit, this control loop will force the grid-connected converter to switch to a grid-following control mode based on the external characteristics of the current source. The main functions of the outer voltage loop control loop and the inner current loop control loop are to provide trigger signals for the grid-connected converter's switching transistors through dual-loop control.

[0093] Based on the above control structure model, a mathematical model of the basic control system of the grid-type converter is established. Specifically, this includes establishing a control structure model of the grid-type converter under virtual synchronization control mode. This control structure model includes virtual synchronization control, virtual impedance control, current limiting, outer voltage loop control, and inner current loop control. Based on this control structure model, a power output characteristic model of the grid-type converter is established. For example, the active power output P... VSG With reactive power output Q VSG The model can be represented as:

[0094]

[0095] In the above formula, V pcc For the grid connection point voltage of the grid-connected converter, V g R is the infinite bus voltage. g X g Here, θ represents the equivalent resistance and reactance between the grid-connected converter and the grid connection point, respectively, and δ is the power angle of the grid-connected converter, defined as δ = θ. VSG -θ g .

[0096] Virtual impedance control is introduced into the mathematical model of the basic control system, forming an extended control system mathematical model that includes virtual impedance. Specifically, this involves superimposing a voltage compensation amount, determined jointly by the virtual impedance value and the output current of the grid-connected converter, onto the voltage outer-loop reference value based on the basic control system mathematical model. The mathematical description of virtual impedance control is as follows:

[0097] V drefv =V dref -R v I d +X v I q

[0098] V qrefv =V qref -R v I q -X v I d

[0099] In the above formula, V drefv V qrefv To introduce the outer loop reference value of the dq-axis voltage after virtual impedance control, V dref V qref I is the outer loop reference value of the dq axis voltage during normal operation. d I q R represents the dq-axis component of the output current of the grid-connected converter. v X v These are the resistance and reactance values ​​of the virtual impedance, respectively.

[0100] The virtual impedance value itself can be determined according to the following formula:

[0101]

[0102] In the above formula, k is a virtual resistance control parameter related to current, σ is a proportional control parameter between virtual reactance and virtual resistance, and I max I is the maximum current allowed to pass through a grid-type converter. n Its rated current.

[0103] Based on the voltage outer loop reference value superimposed with this voltage compensation, and the grid-side circuit relationship of the grid-type converter, the grid-side circuit equation after introducing virtual impedance control is established. The equation is:

[0104]

[0105] In the above formula, V gd V gq The dq-axis component is the infinite bus voltage.

[0106] Furthermore, based on the grid-side circuit equations and instantaneous power theory after introducing virtual impedance control, the output active power P of the grid-type converter after introducing virtual impedance control is established. VSG With output reactive power Q VSG Mathematical model:

[0107]

[0108] Furthermore, the grid connection point voltage V of the grid-connected converter can be derived. pcc Mathematical model:

[0109]

[0110] Based on the extended control system mathematical model and operational constraints during fault periods, the adaptive adjustment range of the virtual impedance control parameters is determined. The operational constraints during fault periods include the current amplitude constraint that the sum of the output currents of the grid-connected converter does not exceed the maximum allowable value. And the reactive current injection requirement for grid-connected converters to inject reactive current into the grid that meets national standards. This reactive current injection requirement can be described as follows:

[0111]

[0112] In the above formula, V f V is the grid voltage during the fault. n I is the rated voltage of the power grid. qf This represents the target value of reactive current to be injected during a fault.

[0113] The process of determining the adaptive adjustment range includes: deriving the reactive current I based on the relationships in the mathematical model of the extended control system. q The expression between the virtual impedance control parameter σ and the virtual impedance control parameter σ is as follows:

[0114]

[0115] Combined with current amplitude constraints Reactive current injection requirements I q ≥I qf Solve for the dynamic range of the virtual impedance control parameter σ, σ∈[σ min ,σ max ]. Wherein, σ min and σ max The calculation formula is:

[0116]

[0117] In the above formula, all parameters are those that can be directly detected or calculated in the control system.

[0118] Based on the adaptive adjustment range, online adaptive adjustment of virtual impedance control parameters is performed to achieve current limiting and voltage support during grid faults. Specifically, this includes continuously monitoring the grid connection point voltage of the grid-connected converter; when the grid connection point voltage is lower than a preset fault identification threshold (e.g., 0.9 per unit), the fault ride-through control mode is triggered. In fault ride-through control mode, the output current of the grid-connected converter is monitored; when the output current exceeds its rated current, virtual impedance control is activated; based on the current system state and the aforementioned determined adaptive adjustment range, within the interval [σ... min ,σ max The specific value of the proportional coefficient σ is dynamically selected based on the preset optimization objective (e.g., prioritizing maximizing reactive current support while ensuring the current does not exceed the limit). The updated virtual impedance control parameters are used to generate voltage compensation, which is then applied to the control system of the grid-connected converter. When the grid connection point voltage recovers to above the fault identification threshold and the output current is lower than its rated current, the fault ride-through control mode is exited, and virtual impedance control is stopped.

[0119] Combination Figure 3As shown, this application embodiment provides a grid-type converter fault ride-through control device 800, including a processor 801 and a memory 802. Optionally, the device may further include a communication interface 803 and a bus 804. The processor 801, communication interface 803, and memory 802 can communicate with each other via the bus 804. The communication interface 803 can be used for information transmission. The processor 801 can call logical instructions in the memory 802 to execute the grid-type converter fault ride-through control method of the above embodiment.

[0120] Furthermore, the logic instructions in the aforementioned memory 802 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium.

[0121] The memory 802, as a computer-readable storage medium, can be used to store software programs and computer-executable programs, such as the program instructions / modules corresponding to the methods in the embodiments of this application. The processor 801 executes functional applications and data processing by running the program instructions / modules stored in the memory 802, thereby realizing the grid-type converter fault ride-through control method in the above embodiments.

[0122] The memory 802 may include a program storage area and a data storage area. The program storage area may store the operating system and application programs required for at least one function; the data storage area may store data created based on the use of the terminal device. Furthermore, the memory 802 may include high-speed random access memory and may also include non-volatile memory.

[0123] This application provides a fault ride-through control system, including a fault ride-through control system body and the aforementioned grid-type converter fault ride-through control device 800. The grid-type converter fault ride-through control device 800 is installed on the fault ride-through control system body. The installation relationship described herein is not limited to placement within the fault ride-through control system, but also includes installation connections with other components of the fault ride-through control system, including but not limited to physical connections, electrical connections, or signal transmission connections. Those skilled in the art will understand that the grid-type converter fault ride-through control device 800 can be adapted to feasible fault ride-through control system bodies, thereby realizing other feasible embodiments.

[0124] This application provides a computer-readable storage medium storing computer-executable instructions configured to execute the above-described grid-type converter fault ride-through control method.

[0125] The technical solutions of this application embodiment can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes one or more instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in this application embodiment. The aforementioned storage medium can be a non-transitory storage medium, including: USB flash drive, portable hard drive, read-only memory (ROM), random access memory (RAM), magnetic disk, or optical disk, and other media capable of storing program code.

[0126] The technical solutions of this application embodiment can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes one or more instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in this application embodiment. The aforementioned storage medium can be a non-transitory storage medium, including: USB flash drive, portable hard drive, read-only memory (ROM), random access memory (RAM), magnetic disk, or optical disk, and other media capable of storing program code.

[0127] The foregoing description and accompanying drawings fully illustrate embodiments of this application to enable those skilled in the art to practice them. Other embodiments may include structural, logical, electrical, procedural, and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. Moreover, the terminology used in this application is for describing embodiments only and is not intended to limit the claims. As used in the description of embodiments and claims, the singular forms “a,” “an,” and “the” are intended to equally include the plural forms unless the context clearly indicates otherwise. Similarly, the term “and / or,” as used herein, means including one or more of the associated listed items and all possible combinations thereof. Additionally, when used in this application, the term "comprise" and its variations "comprises" and / or "comprising" refer to the presence of stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof. Without further limitations, an element defined by the phrase "comprising a..." does not exclude the presence of other identical elements in the process, method, or apparatus that includes said element. In this document, each embodiment may focus on the differences from other embodiments, and similar or identical parts between embodiments can be referred to mutually. For methods, products, etc., of the embodiments claimed, if they correspond to the method section of the embodiments claimed, then the relevant parts can be referred to the description of the method section.

[0128] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments claimed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the embodiments of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0129] The methods and products (including but not limited to devices and equipment) disclosed in the embodiments herein can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of units may be merely a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed may be through some interfaces, and the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to implement this embodiment according to actual needs. In addition, the functional units in the embodiments of this application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0130] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than that shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. In the descriptions corresponding to the flowcharts and block diagrams in the accompanying drawings, the operations or steps corresponding to different blocks may also occur in a different order than disclosed in the description; sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. Each block in a block diagram and / or flowchart, and combinations of blocks in a block diagram and / or flowchart, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

Claims

1. A fault ride-through control method for a grid-type converter, characterized in that, include: Establish a mathematical model for the basic control system of a grid-type converter; Virtual impedance control is introduced into the mathematical model of the basic control system to form an extended control system mathematical model that includes virtual impedance. Based on the mathematical model of the extended control system and the operating constraints during the fault period, the adaptive adjustment range of the virtual impedance control parameters is determined. Based on the adaptive adjustment range, online adaptive adjustment of the virtual impedance control parameters is performed to achieve current limiting and voltage support during grid faults.

2. The method according to claim 1, characterized in that, Establish the mathematical model of the basic control system of the grid-type converter, including: Establish a control structure model for a grid-type converter under virtual synchronous control mode; wherein, the control structure model includes a virtual synchronous control loop, a virtual impedance control loop, a current limiting loop, an outer voltage loop control loop, and / or an inner current loop control loop. Based on the control structure model, a power output characteristic model of the grid-type converter is established.

3. The method according to claim 1, characterized in that, Virtual impedance control is introduced into the mathematical model of the basic control system to form an extended control system mathematical model that includes virtual impedance, including: In the voltage outer loop reference value based on the mathematical model of the basic control system, a voltage compensation amount determined by the virtual impedance value and the output current of the grid-type converter is superimposed. Based on the voltage outer loop reference value with superimposed voltage compensation and the grid-side circuit relationship of the grid-type converter, the grid-side circuit equation after introducing virtual impedance control is established. Based on the grid-side circuit equations after the introduction of virtual impedance control, mathematical models of the grid-connected voltage, output active power, and output reactive power of the grid-type converter after the introduction of virtual impedance control are established.

4. The method according to claim 1, characterized in that, The virtual impedance values ​​in the virtual impedance control parameters include: The virtual resistance portion is dynamically calculated based on the output current of the grid-type converter; and / or, The virtual reactance is associated with the virtual resistance portion through an adjustable scaling factor.

5. The method according to claim 1, characterized in that, Operational constraints during a failure include: The total output current of the grid-connected converter does not exceed the maximum allowable current amplitude constraint; and / or, Grid-type converters require reactive current injection into the grid that is linearly proportional to the voltage drop depth.

6. The method according to any one of claims 1 to 5, characterized in that, Based on the extended control system mathematical model and the operational constraints during faults, the adaptive adjustment range of the virtual impedance control parameters is determined, including: Calculate the target reactive current value based on the reactive current injection requirements; By combining the current amplitude constraint, the overall constraint condition for the output current is formed; Based on the extended control system mathematical model, the target reactive current value, and the overall constraints, the numerical range of the proportional coefficient in the virtual impedance control parameters is solved.

7. The method according to any one of claims 1 to 5, characterized in that, Based on the adaptive adjustment range, online adaptive adjustment of the virtual impedance control parameters is performed, including: Continuously monitor the grid connection point voltage of the grid-connected converter; When the grid connection point voltage is lower than the preset fault identification threshold, the fault ride-through control mode is triggered. In fault-crossing control mode, subsequent adaptive adjustment steps are executed.

8. The method according to claim 7, characterized in that, The fault identification threshold is a configurable value preset according to power grid operation standards or system requirements.

9. The method according to claim 7, characterized in that, In fault ride-through control mode, subsequent adaptive adjustment steps are executed, including: Monitor the output current of the grid-type converter; Virtual impedance control is enabled when the output current exceeds its rated current. Based on the current system state and the adaptive adjustment range, the virtual impedance control parameters are calculated and updated.

10. The method according to claim 9, characterized in that, Based on the current system state and the adaptive adjustment range, calculate and update the virtual impedance control parameters, including: Within the defined numerical range of the adaptive adjustment range, the specific value of the proportional coefficient is dynamically selected according to the preset optimization target.

11. The method according to claim 10, characterized in that, The preset optimization objectives include: While ensuring that the output current of the grid-connected converter does not exceed the limit, priority should be given to maximizing its reactive current support to the power grid.

12. The method according to claim 7, characterized in that, In fault ride-through control mode, the subsequent adaptive adjustment steps also include: The updated virtual impedance control parameters are used to generate voltage compensation, which is then applied to the control system of the grid-type converter.

13. The method according to claim 7, characterized in that, Based on the adaptive adjustment range, online adaptive adjustment of the virtual impedance control parameters is performed, which also includes: When the grid connection point voltage is detected to recover to above the fault identification threshold and the output current is lower than its rated current, the fault ride-through control mode is exited and virtual impedance control is stopped.

14. A fault ride-through control device for a grid-type converter, comprising a processor and a memory storing program instructions, characterized in that, The processor is configured to execute the grid-type converter fault ride-through control method as described in any one of claims 1 to 13 when running the program instructions.

15. A fault-ride control system, characterized in that, include: The fault-crossing control system itself; and, The grid-type converter fault ride-through control device as described in claim 14 is installed on the fault ride-through control system body.

16. A computer-readable storage medium storing program instructions, characterized in that, When the program instructions are executed, they cause the computer to perform the fault ride-through control method for grid-type converters as described in any one of claims 1 to 13.

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