A network configuration converter transient energy compensation control method and system adaptive to fault ride through and recovery

Abstract

The application discloses a network construction converter transient energy compensation control method and system suitable for fault ride through and recovery, relates to the field of network construction converter transient energy compensation, and comprises the following steps: based on the converter output current amplitude, mode switching is carried out, and power angle state data at the mode switching time is acquired; in the voltage control mode, instability margin evaluation, active power dynamic adjustment and damping adaptive compensation are carried out based on a transient energy function; in the current amplitude limiting control mode, dynamic gain adjustment is carried out based on a power angle deviation; saturated phase angle values are calculated to dynamically compensate active power under fault conditions; and when mode switching conditions are reached, smooth switching of the voltage control mode and smooth lifting of the active power to a steady-state value before the fault are carried out based on a quadratic slope function. Through active transient energy compensation, the method can effectively cope with transient out-of-step risks under large disturbances, and can improve the safe and stable operation capability of a new energy power system.

Description

Technical Field

[0001] This invention relates to the technical field of transient energy replenishment for grid converters, and in particular to a transient energy compensation control method and system for grid converters that adapts to fault ride-through and recovery. Background Technology

[0002] Currently, with the large-scale grid connection of new energy sources causing a continuous decrease in the inertia and damping of the power system, the system's ability to resist disturbances, such as frequency and voltage instability, has been reduced. Grid-type converters, which have the ability to actively support the grid frequency and voltage and can simulate the external characteristics of synchronous generators, have become a key means to ensure the stability of the new power system.

[0003] However, the transient synchronization stability defects of grid-connected converters also constrain the stability of power systems, especially under large disturbance conditions such as sudden voltage drops and short-circuit faults. The transient synchronization stability problem of grid-connected converters becomes increasingly prominent. On the one hand, during grid system faults, the output power of the converter is forced to be current-limited, and the severe imbalance between acceleration torque and braking torque causes the power angle to show an accelerating deviation trend. At the same time, the power angle swings rapidly during the transient process, and the entire power system experiences a severe transient energy imbalance. During acceleration, the system accumulates too much kinetic energy, but the braking torque is insufficient during braking, making it difficult for the power angle to recover in time, ultimately leading to transient loss of synchronization or even grid disconnection of the power system. On the other hand, in order to ensure equipment safety and suppress transient overcurrent, the converter needs to switch between voltage control mode and current limiting control mode. The nonlinear abrupt change between mode switching further aggravates the transient energy imbalance of the converter, compresses the effective braking range of the power system, and makes the transient performance of the system more complex and difficult to control. Summary of the Invention

[0004] To address the lack of proactive transient energy evolution analysis and compensation during the entire fault ride-through process under large disturbances in existing technologies, which is insufficient to effectively address the risk of transient loss of synchronization, this application provides a transient energy compensation control method and system for grid converters that adapts to fault ride-through and recovery. This method can effectively address the risk of transient loss of synchronization under large disturbances through proactive transient energy compensation, thereby improving the safe and stable operation capability of new energy power systems.

[0005] Firstly, the above-mentioned inventive objective of this application is achieved through the following technical solution: A transient energy compensation control method for a grid converter adapted to fault ride-through and recovery, the method comprising: Obtain the effective output current of the grid-type converter, perform fault ride-through judgment based on the effective output current and switch the control mode of the grid-type converter, and obtain the power angle state data at the time of mode switching. When switching to voltage control mode, the current transient energy is calculated based on the power angle state data to perform instability margin assessment. Based on the instability margin assessment results, the active power is dynamically adjusted and the power angle change rate is calculated to perform damping adaptive compensation. When switching to the current limiting control mode, the power angle deviation of the power angle state data is calculated for dynamic gain adjustment, and the saturation phase angle value is calculated based on the adjustment result to dynamically compensate the active power under fault conditions. When the preset mode switching conditions are met, the current limiting control mode is smoothly switched back to the voltage control mode, and the active power after fault compensation is smoothly adjusted to the steady-state value before the fault according to the preset fault recovery strategy.

[0006] In a preferred embodiment, this application can be further configured as follows: obtaining the effective output current of the grid-connected converter, performing fault ride-through judgment based on the effective output current and switching the control mode of the grid-connected converter, and obtaining the power angle state data at the time of mode switching, specifically includes: The effective output current of the grid-type converter is obtained and its split-axis transformation is performed to obtain the split-axis component of the effective output current. The output current amplitude is calculated based on the split-axis component of the effective output current. When the output current amplitude exceeds the preset current limit threshold, it is determined that a large disturbance has occurred in the power grid, and the grid-type converter is simultaneously subjected to fault ride-through determination. During fault crossing, the control mode of the grid-type converter is switched to switch the control conditions during the fault, and the power angle and angular velocity deviation at the time of mode switching are obtained to obtain the power angle state data.

[0007] In a preferred embodiment, this application can be further configured as follows: when switching to voltage control mode, the current transient energy is calculated based on the power angle state data to perform an instability margin assessment; the active power is dynamically adjusted based on the instability margin assessment result, and the power angle change rate is calculated for damping adaptive compensation. Specifically, this includes: When the output current amplitude does not exceed the preset current limit threshold, it is determined to be a normal operating condition. The grid-type converter is then switched to voltage control mode, and the current transient energy is calculated based on the power angle state data. The calculation expression for the current transient energy is as follows: (1) in, This represents the current transient energy value. , These represent the current work angle and the work angle at the stable equilibrium point, respectively. Indicates angular velocity deviation. Represents the virtual inertia coefficient. Indicates the current angle of attack. and the work angle at the stable equilibrium point The integration interval The actual output electromagnetic power, This represents the reference value for active power. At the unstable equilibrium point of the grid-type converter, a critical energy value is obtained. Based on the current transient energy and the critical energy value, an instability margin is calculated. An instability margin assessment is then performed in conjunction with a preset instability threshold. The calculation expression for the instability margin is as follows: (2) in, Indicates instability margin, This represents the critical energy value at the unbalanced stable point. Indicates the current angle of attack. and angular velocity deviation The calculated current transient energy value; Based on the instability margin assessment results, when the instability margin is lower than a preset instability threshold, the active power reference value of the grid-type converter is dynamically lowered. The expression for the dynamic lowering of the active power reference value is as follows: (3) in, This indicates the dynamic downward adjustment of the active power reference value. This represents the dynamic downward adjustment ratio of the active power reference value. Indicates the preset instability voltage threshold; During the adjustment of the active power reference value, the corresponding rate of change of the power angle is calculated. Based on the rate of change of the power angle, the damping coefficient compensation value is calculated for adaptive damping compensation. The expression for the adaptive damping compensation is as follows: (4) in, This represents the damping coefficient after compensation by the grid converter. Indicates the foundation damping coefficient. Represents the adaptive gain coefficient. This represents the rate of change of the work angle.

[0008] In a preferred embodiment, this application can be further configured as follows: when switching to voltage control mode, calculating the current transient energy based on the power angle state data to perform an instability margin assessment, dynamically adjusting the active power based on the instability margin assessment result, and calculating the power angle change rate to perform damping adaptive compensation, further includes: The active power control equation of the converter in the voltage control mode is as follows: (5) in, , These represent the virtual rotational speed and the rated angular frequency, respectively. This represents the reference value for active power. Indicates the actual output electromagnetic power. This is the damping coefficient after compensation.

[0009] In a preferred embodiment, this application can be further configured such that: the step of dynamically lowering the active power reference value of the grid-type converter when the instability margin is lower than a preset instability threshold, based on the instability margin assessment result, further includes: The reduction rate is calculated based on the reduction amount of the active power reference value and the instability margin, and the active power reference value is dynamically reduced according to the calculated reduction rate.

[0010] In a preferred embodiment, this application can be further configured as follows: when switching to the current limiting control mode, the power angle deviation of the power angle state data is calculated for dynamic gain adjustment, and the saturation phase angle value is calculated based on the adjustment result to dynamically compensate the active power under fault conditions, specifically including: In the current limiting control mode, the power angle deviation of the power angle state data is calculated, and the power angle deviation is dynamically adjusted according to the grid voltage drop depth to obtain the phase angle dynamic compensation amount. The basic saturation current limiting phase angle of the grid-type converter is dynamically compensated by the phase angle dynamic compensation amount to obtain the saturation current phase angle. The power angle swing state under fault conditions is obtained, and the effective output current is adjusted based on the power angle swing state and the phase angle of the saturated current to perform dynamic compensation of active power.

[0011] In a preferred embodiment, this application can be further configured as follows: obtaining the power angle oscillation state under fault conditions, and adjusting the effective output current based on the power angle oscillation state and the saturated current phase angle branch axis to perform dynamic active power compensation, specifically includes: The power angle swing state under fault conditions is obtained. When the power angle swing state exceeds the preset power angle swing threshold, the effective output current is adjusted according to the phase angle of the saturated current under the control mode switching threshold constraint during fault crossing. The active power of the grid converter is dynamically compensated based on the current adjustment result.

[0012] In a preferred embodiment, this application can be further configured as follows: when the preset mode switchback condition is met, the current limiting control mode is smoothly switched back to the voltage control mode, and the active power after fault compensation is smoothly adjusted to the pre-fault steady-state value according to the preset fault recovery strategy, specifically including: When the effective output current meets the fault recovery conditions, the current limiting control mode is smoothly switched to the voltage control mode according to the set slope, and it is determined whether the power grid operation state has entered the steady-state recovery stage after the fault is cleared. When entering the steady-state recovery phase, the active power after fault compensation is adjusted to the steady-state value before the fault according to the preset slope.

[0013] In a preferred embodiment, this application can be further configured as follows: when the effective output current meets the fault recovery conditions, the current limiting control mode is smoothly switched to the voltage control mode according to a set slope, and it is determined whether the power grid operation state has entered the steady-state recovery stage after fault clearing, specifically including: When the current amplitude of the effective output current is lower than the preset cut-back threshold and the power angle deviation reaches the preset convergence condition, the effective output current is determined to meet the fault recovery condition, wherein the preset cut-back threshold is lower than the control mode switching threshold during fault ride-through.

[0014] Secondly, the above-mentioned inventive objective of this application is achieved through the following technical solutions: A transient energy compensation control system for a grid converter adapted to fault ride-through and recovery, the system comprising: The data acquisition and mode switching judgment module is used to acquire the effective output current of the grid-type converter, perform fault ride-through judgment based on the effective output current and switch the control mode of the grid-type converter, and acquire the power angle status data at the time of mode switching. The transient energy assessment and damping control module is used to calculate the current transient energy based on the power angle state data to assess the instability margin when switching to voltage control mode, dynamically adjust the active power based on the instability margin assessment result, and calculate the power angle change rate to perform damping adaptive compensation. The phase angle compensation and power adjustment module is used to calculate the power angle deviation of the power angle state data and perform dynamic gain adjustment when switching to the current limiting control mode, and calculate the saturated phase angle value based on the adjustment result to dynamically compensate the active power under fault conditions. The mode switchback control and fault recovery module is used to smoothly switch the current limiting control mode back to the voltage control mode when the preset mode switchback conditions are met, and to smoothly adjust the active power after fault compensation to the steady-state value before the fault according to the preset fault recovery strategy.

[0015] In summary, this application includes at least one of the following beneficial technical effects: 1. This application collects the electrical quantities of the converter in real time and uses the comparison result of the current amplitude and the limiting threshold as the mode switching criterion. Under large disturbances, it switches to the current limiting control mode to achieve fault ride-through, and under normal operating conditions, it switches to the voltage control mode. During mode switching, the instability margin is evaluated by the transient energy function, and then the active power reference value is dynamically corrected to achieve transient energy compensation. In the voltage control mode, an adaptive damping injection strategy is adopted, and the damping coefficient is dynamically adjusted according to the power angle change rate. In the current limiting control mode, a saturated current phase angle dynamic compensation strategy is adopted, and the saturated current vector phase angle is adjusted in real time according to the power angle deviation. The active and reactive current components are dynamically allocated to provide additional braking torque and absorb excess transient energy. Through the dual compensation strategy of adaptive damping injection and saturated current phase angle dynamic compensation, it can effectively cope with the phenomenon of large power angle deviation, significantly expand the transient stability domain of the converter, realize transient synchronous stability control under large disturbances, and improve the safety and reliability of the new power system. 2. After detecting the clearing of a power grid fault and the restoration of voltage, this application adopts a fault recovery and reconfiguration strategy to smooth the active power reference value with a second slope to restore the adjusted active power to the steady state before the fault. The smooth back-cut mechanism ensures the continuity of the state during the mode switching process, avoids secondary disturbances, and improves the robustness and engineering applicability of the control system. 3. This application incorporates the fault ride-through process into the transient energy compensation control framework. It assesses the instability margin online through the transient energy function and dynamically corrects the power reference to achieve energy compensation. This can actively suppress power angle deviation during faults and effectively expand the transient stability domain. It adopts a dual strategy of adaptive damping injection and dynamic compensation of saturated current phase angle to provide sufficient damping in voltage control mode and current limiting mode, respectively, and synergistically ensures the transient synchronization stability of the entire process. This effectively expands the transient stability domain of the grid-type converter under large disturbances and improves the safe and stable operation capability of the new power system. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. The elements or parts in the drawings are not necessarily drawn to scale.

[0017] Figure 1 This is a schematic diagram of the framework of the transient energy compensation control method for the grid converter adapted for fault ride-through and recovery in this embodiment.

[0018] Figure 2 This is a schematic diagram of the transient mode switching mechanism of the network converter in this embodiment during fault ride-through.

[0019] Figure 3This is a schematic diagram of the transient energy and critical stability boundary in this embodiment.

[0020] Figure 4 This is a schematic diagram of the adaptive damping control module in this embodiment.

[0021] Figure 5 This is a schematic diagram of the current limiting saturation current phase angle dynamic compensation module in this embodiment.

[0022] Figure 6 This is a logic framework diagram of the active power secondary ramp control after the grid voltage is restored in this embodiment.

[0023] Figure 7 This is a block diagram of the transient energy compensation control system for the grid converter adapted for fault ride-through and recovery in this embodiment. Detailed Implementation

[0024] 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, not all, of the embodiments of the present invention. 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.

[0025] It should be understood that, when used in this specification, the terms “comprising” and “including” indicate the presence of the described 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 collections thereof.

[0026] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” are intended to include the plural forms.

[0027] It should also be further understood that the term "and / or" as used in this specification refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0028] In one embodiment, such as Figure 1 As shown, this application discloses a transient energy compensation control method for grid converters adapted to fault ride-through and recovery, which specifically includes the following steps: S1: Obtain the effective output current of the grid-type converter, perform fault ride-through judgment based on the effective output current, switch the control mode of the grid-type converter, and obtain the power angle status data at the time of mode switching.

[0029] Specifically, the control mode switching diagram of the grid-type converter during fault ride-through in this embodiment is shown in the figure below. Figure 2 As shown, step S1 includes: S11: Obtain the effective output current of the grid-type converter and perform a split-axis transformation to obtain the split-axis component of the effective output current. Calculate the output current amplitude based on the split-axis component of the effective output current.

[0030] Specifically, the grid-connected converter in this embodiment adopts a three-phase two-level voltage source converter topology, connected to the grid through an LCL filter, with the DC side supported by energy storage devices or new energy sources. The output current, terminal voltage, DC-side voltage, and grid voltage of the grid-connected converter are collected in real time. A coordinate transformation is performed on the effective output current to obtain the dq-axis components and calculate the output current amplitude. The expression for calculating the output current amplitude is shown below: (6) in, Indicates the output current amplitude. , These represent the d-axis and q-axis components of the effective output current, respectively.

[0031] S12: When the output current amplitude exceeds the preset current limit threshold, it is determined that a large disturbance has occurred in the power grid, and the fault ride-through determination is performed on the grid-type converter simultaneously.

[0032] Specifically, a current limiting threshold is set based on the change in current amplitude before and after a large disturbance in the power grid. When the output current amplitude exceeds the current limiting threshold, it is determined that a large disturbance has occurred in the power grid, and at the same time, it is determined that the grid-type converter has experienced a fault ride-through phenomenon.

[0033] S13: Switch the control mode of the grid-type converter at the moment of fault crossing to switch the control conditions during the fault, obtain the power angle and angular velocity deviation at the moment of mode switching, and obtain the power angle state data.

[0034] Specifically, at the moment of fault ride-through, the control mode of the grid-type converter is switched to the current limiting control mode, and the power angle and angular velocity deviation at the moment of mode switching are obtained to obtain the power angle state data.

[0035] S2: When switching to voltage control mode, the current transient energy is calculated based on the power angle state data to perform instability margin assessment. Based on the instability margin assessment results, the active power is dynamically adjusted and the power angle change rate is calculated to perform damping adaptive compensation.

[0036] Specifically, step S2 includes: S21: When the output current amplitude does not exceed the preset current limit threshold, it is determined to be a normal operating condition. The grid-type converter is switched to voltage control mode, and the current transient energy is calculated based on the power angle state data. The calculation expression for the current transient energy is as follows: (1) in, This represents the current transient energy value. , These represent the current work angle and the work angle at the stable equilibrium point, respectively. This indicates the angular velocity deviation. The current power angle and angular velocity deviation are obtained from the power angle state data. Represents the virtual inertia coefficient. Indicates the current angle of attack. and the work angle at the stable equilibrium point The integration interval The actual output electromagnetic power, This indicates the reference value for active power.

[0037] In this embodiment, the virtual inertia coefficient J is adaptively adjusted online according to the system's inertia support requirements. The adjustment range is 0.5 to 2 times the rated inertia. Specifically, the virtual inertia coefficient J is adjusted online based on the system frequency deviation and frequency change rate. When the frequency deviation is large or exceeds a preset threshold, J is increased to provide stronger inertia support; when the system tends to a steady state, J is restored to the rated value to avoid excessive inertia leading to increased system oscillation. Obtained by integrating the virtual rotational speed: , Indicates virtual rotational speed. Indicates the rated angular frequency.

[0038] S22: Obtain the critical energy value at the unstable equilibrium point of the grid-type converter, calculate the instability margin based on the current transient energy and the critical energy value, and evaluate the instability margin in combination with the preset instability threshold. The calculation expression for the instability margin is as follows: (2) in, Indicates instability margin, This represents the critical energy value at the unstable equilibrium point. In this embodiment, the potential energy value at the unstable equilibrium point is used as the critical energy value. Indicates the current angle of attack. and angular velocity deviation The calculated current transient energy value.

[0039] The schematic diagram of the critical stability boundary based on transient energy and temporary energy values ​​in this embodiment is shown below. Figure 3As shown in the figure, Mode I represents voltage control mode and Mode II represents current limiting control mode.

[0040] S23: Based on the instability margin assessment results, when the instability margin is lower than the preset instability threshold, the active power reference value of the grid-type converter is dynamically lowered. The expression for the dynamic lowering of the active power reference value is as follows: (3) in, This indicates the dynamic downward adjustment of the active power reference value. This represents the dynamic downward adjustment ratio of the active power reference value. This indicates the preset instability voltage threshold.

[0041] In this embodiment, the reduction rate is calculated based on the reduction amount of the active power reference value and the instability margin. The active power reference value is then dynamically reduced according to the calculated reduction rate. Specifically, the ratio between the reduction amount and the negative value of the instability margin is used as the reduction slope. The reduction rate is then smoothly adjusted according to the reduction slope to control the active power to be dynamically reduced and avoid sudden power changes.

[0042] S24: During the adjustment of the active power reference value, calculate the corresponding rate of change of the power angle, and perform adaptive damping compensation based on the rate of change of the power angle. The expression for adaptive damping compensation is as follows: (4) in, This represents the damping coefficient after compensation by the grid converter. Indicates the foundation damping coefficient. Represents the adaptive gain coefficient. This represents the rate of change of the power angle. When the rate of change of the power angle is large, the dynamic damping coefficient automatically increases to provide stronger damping. When the system approaches stability, the dynamic damping coefficient returns to the basic damping coefficient to avoid introducing unnecessary losses. The principle block diagram of the adaptive damping control module in this embodiment is shown below. Figure 4 As shown.

[0043] In this embodiment, the active power control of the converter is driven by the active power control equation based on the principle of virtual synchronous machine. The active power control equation of the converter in voltage control mode is as follows: (5) in, , These represent the virtual rotational speed and the rated angular frequency, respectively. This represents the reference value for active power. Indicates the actual output electromagnetic power. This is the damping coefficient after compensation.

[0044] S3: When switching to the current limiting control mode, the power angle deviation of the calculated power angle state data is dynamically adjusted for gain, and the saturation phase angle value is calculated based on the adjustment result to dynamically compensate the active power under fault conditions.

[0045] Specifically, the principle block diagram of the current limiting saturation current phase angle dynamic compensation module in this embodiment is as follows: Figure 5 As shown, step S3 includes: S31: In the current limiting control mode, calculate the power angle deviation of the power angle state data, and dynamically adjust the power angle deviation according to the grid voltage drop depth to obtain the phase angle dynamic compensation amount.

[0046] Specifically, in current limiting control mode, the virtual power angle of the converter and the steady-state reference power angle before the fault are collected and the difference is calculated to obtain the power angle deviation. The power angle deviation is input into a dynamic gain PI regulator to calculate the dynamic phase angle compensation. The proportional gain and integral gain of the dynamic gain PI regulator are adaptively adjusted according to the grid voltage sag depth, thereby outputting the dynamic phase angle compensation that conforms to the grid voltage sag depth constraint. The expression for calculating the grid voltage sag depth in this embodiment is: , Indicates the grid voltage. This indicates the rated voltage of the power grid.

[0047] S32: The basic saturation current limiting phase angle of the grid-type converter is dynamically compensated by the phase angle dynamic compensation amount to obtain the saturation current phase angle.

[0048] Specifically, the basic saturation current limiting phase angle of the grid-type converter is obtained, and the basic saturation current limiting phase angle is added to the phase angle dynamic compensation amount to obtain the final saturation current phase angle. Based on the saturation current phase angle, the corresponding phase angle value is adjusted at the phase angle control terminal of the converter in the current limiting control mode.

[0049] S33: Obtain the power angle swing state under fault conditions, and perform dynamic compensation of active power by adjusting the effective output current based on the power angle swing state and the phase angle of the saturated current.

[0050] Specifically, the power angle swing state under fault conditions is obtained. When the power angle swing state exceeds the preset power angle swing threshold, the effective output current is adjusted according to the phase angle of the saturated current under the control mode switching threshold constraint during fault crossing. The active power of the grid-type converter is dynamically compensated based on the current adjustment result.

[0051] In this embodiment, the real-time power angle swing state under fault conditions, i.e., large disturbances, is obtained. When the power angle swings upward, it indicates the real-time power angle... hour, This indicates the preset power angle swing threshold. The PI regulator adjusts the effective output current by adjusting the phase angle of the adjusted saturation current, such as adaptively increasing the active current component injected into the grid. The effective output current split-axis adjustment expression in this embodiment is as follows: (7) in, , These represent the active current components along the d-axis and q-axis, respectively. This indicates the maximum current amplitude during fault ride-through. This represents the phase angle of the saturation current.

[0052] By injecting the active current component along the d-axis, the output electromagnetic power can be increased without changing the total current amplitude, achieving dynamic compensation of active power. The active power that dynamically increases with the oscillation of the power angle is equivalent to injecting an additional damping torque into the virtual rotor's motion equation. This torque can effectively absorb the excess kinetic energy of the virtual rotor and force the power angle to... By backtracking and absorbing excess transient energy, the power angle is suppressed from further shift, significantly improving the transient synchronization stability of the converter under hard-limiting conditions.

[0053] S4: When the preset mode switching conditions are met, the current limiting control mode will be smoothly switched back to the voltage control mode, and the active power after fault compensation will be smoothly adjusted to the steady-state value before the fault according to the preset fault recovery strategy.

[0054] Specifically, the block diagram of the active power secondary slope control after grid voltage recovery in this embodiment is as follows: Figure 6 As shown, Figure 6 In This indicates the reference value of active power after dynamic downcompensation during the fault period. Step S4 includes: S41: When the effective output current meets the fault recovery conditions, the current limiting control mode is smoothly switched to the voltage control mode according to the set slope, and it is determined whether the grid operation status has entered the steady-state recovery stage after the fault is cleared.

[0055] Specifically, when the amplitude of the effective output current is lower than the preset cut-off threshold and the power angle deviation reaches the preset convergence condition, the effective output current is determined to meet the fault recovery condition. The preset cut-off threshold is lower than the control mode switching threshold during fault ride-through.

[0056] This embodiment incorporates hysteresis control logic, including a switching threshold and a back-off threshold. The back-off threshold is lower than the switching threshold, creating a dead zone between them to prevent control oscillations caused by frequent mode switching. In this embodiment, when the effective output current amplitude of the converter is lower than the back-off threshold and the power angle deviation reaches a preset convergence condition (e.g., the power angle change rate is lower than a preset acceleration threshold), the effective output current of the converter is determined to meet the fault recovery condition. Control mode back-off is initiated, and the current limiting control mode is smoothly switched to the voltage control mode under constant slope constraints. At the back-off initiation moment, the initial value of the integrator in the active power control loop of the voltage control mode is set to the final power value of the current limiting control mode, and the initial value of the adaptive damping coefficient is set to the base value to ensure the continuity of control quantities before and after mode switching. Furthermore, after switching to the voltage control mode, the grid voltage is collected in real time. When the grid voltage recovers to a stable normal range and the duration exceeds the preset anti-interference delay, the system is determined to have entered the steady-state recovery phase after fault clearance.

[0057] S42: When entering the steady-state recovery phase, adjust the active power after fault compensation to the steady-state value before the fault according to the preset slope.

[0058] Specifically, since the active power reference value was dynamically lowered during the transient period, if the reference value were instantly restored to the steady-state dispatch command value after switching to voltage control mode, a huge step excitation would be introduced into the active power control loop. For a virtual synchronous machine with second-order synchronous dynamic characteristics, this step could easily cause severe low-frequency power oscillations or even secondary grid disconnection. Therefore, when the system enters the steady-state recovery phase, the active power reference value at the end of the transient period is gradually raised to the steady-state command value before the fault according to a preset constant slope. The ramp recovery method effectively smooths the sudden change in the input command, limits the acceleration torque impact on the virtual rotor motion equation, and allows the output active power to smoothly return to steady state without significant overshoot, achieving seamless transition and synchronous stability throughout the entire system process.

[0059] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0060] In one embodiment, a transient energy compensation control system for grid converters adapted to fault ride-through and recovery is provided. This system corresponds one-to-one with the transient energy compensation control method for grid converters adapted to fault ride-through and recovery described in the above embodiments. Figure 7As shown, the transient energy compensation control system for the grid converter adapted for fault ride-through and recovery includes a data acquisition and mode switching judgment module, a transient energy assessment and damping control module, a phase angle compensation and power adjustment module, and a mode return control and fault recovery module. Detailed descriptions of each functional module are as follows: The data acquisition and mode switching judgment module is used to obtain the effective output current of the grid-type converter, perform fault ride-through judgment based on the effective output current, switch the control mode of the grid-type converter, and obtain the power angle status data at the time of mode switching.

[0061] The transient energy assessment and damping control module is used to calculate the current transient energy based on the power angle state data to assess the instability margin when switching to voltage control mode. Based on the instability margin assessment results, the active power is dynamically adjusted and the rate of change of the power angle is calculated for adaptive damping compensation.

[0062] The phase angle compensation and power adjustment module is used to dynamically adjust the gain by calculating the power angle deviation of the power angle state data when switching to the current limiting control mode, and to calculate the saturation phase angle value based on the adjustment result to dynamically compensate the active power under fault conditions.

[0063] The mode switching control and fault recovery module is used to smoothly switch the current limiting control mode back to the voltage control mode when the preset mode switching conditions are met, and to smoothly adjust the active power after fault compensation to the steady-state value before the fault according to the preset fault recovery strategy.

[0064] Specific limitations regarding the transient energy compensation control system for grid-connected converters adapted for fault ride-through and recovery can be found in the limitations of the transient energy compensation control method for grid-connected converters adapted for fault ride-through and recovery described above, and will not be repeated here. Each module in the aforementioned transient energy compensation control system for grid-connected converters adapted for fault ride-through and recovery can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in hardware or independent of the processor in a computer device, or stored in software in the memory of a computer device, so that the processor can call and execute the corresponding operations of each module.

[0065] Those skilled in the art will recognize that the units of the various examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application of the technical solution and the constraints involved. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the invention.

[0066] In the embodiments provided by the present invention, it should be understood that the division of units is only a logical functional division. In actual implementation, there may be other division methods, such as multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored.

[0067] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0068] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several 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 methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A transient energy compensation control method for a grid converter adapted to fault ride-through and recovery, characterized in that, The method includes: Obtain the effective output current of the grid-type converter, perform fault ride-through judgment based on the effective output current and switch the control mode of the grid-type converter, and obtain the power angle state data at the time of mode switching. When switching to voltage control mode, the current transient energy is calculated based on the power angle state data to perform instability margin assessment. Based on the instability margin assessment results, the active power is dynamically adjusted and the power angle change rate is calculated to perform damping adaptive compensation. When switching to the current limiting control mode, the power angle deviation of the power angle state data is calculated for dynamic gain adjustment, and the saturation phase angle value is calculated based on the adjustment result to dynamically compensate the active power under fault conditions. When the preset mode switching conditions are met, the current limiting control mode is smoothly switched back to the voltage control mode, and the active power after fault compensation is smoothly adjusted to the steady-state value before the fault according to the preset fault recovery strategy.

2. The transient energy compensation control method for grid converters with adaptive fault ride-through and recovery according to claim 1, characterized in that, The process of acquiring the effective output current of the grid-type converter, performing fault ride-through judgment based on the effective output current, switching the control mode of the grid-type converter, and acquiring the power angle state data at the time of mode switching specifically includes: The effective output current of the grid-type converter is obtained and its split-axis transformation is performed to obtain the split-axis component of the effective output current. The output current amplitude is calculated based on the split-axis component of the effective output current. When the output current amplitude exceeds the preset current limit threshold, it is determined that a large disturbance has occurred in the power grid, and the grid-type converter is simultaneously subjected to fault ride-through determination. During fault crossing, the control mode of the grid-type converter is switched to switch the control conditions during the fault, and the power angle and angular velocity deviation at the time of mode switching are obtained to obtain the power angle state data.

3. The transient energy compensation control method for grid converters with adaptive fault ride-through and recovery according to claim 2, characterized in that, When switching to voltage control mode, the current transient energy is calculated based on the power angle state data to perform an instability margin assessment. Based on the instability margin assessment result, the active power is dynamically adjusted and the power angle change rate is calculated for damping adaptive compensation. Specifically, this includes: When the output current amplitude does not exceed the preset current limit threshold, it is determined to be a normal operating condition. The grid-type converter is then switched to voltage control mode, and the current transient energy is calculated based on the power angle state data. The calculation expression for the current transient energy is as follows: (1) in, This represents the current transient energy value. , These represent the current work angle and the work angle at the stable equilibrium point, respectively. Indicates angular velocity deviation. Represents the virtual inertia coefficient. Indicates the current angle of attack. and the work angle at the stable equilibrium point within the integration interval The actual output electromagnetic power, This represents the reference value for active power. At the unstable equilibrium point of the grid-type converter, a critical energy value is obtained. Based on the current transient energy and the critical energy value, an instability margin is calculated. An instability margin assessment is then performed in conjunction with a preset instability threshold. The calculation expression for the instability margin is as follows: (2) in, Indicates instability margin, This represents the critical energy value at the unbalanced stable point. Indicates the current angle of attack. and angular velocity deviation The calculated current transient energy value; Based on the instability margin assessment results, when the instability margin is lower than a preset instability threshold, the active power reference value of the grid-type converter is dynamically lowered. The expression for the dynamic lowering of the active power reference value is as follows: (3) in, This indicates the dynamic downward adjustment of the active power reference value. This represents the dynamic downward adjustment ratio of the active power reference value. Indicates the preset instability voltage threshold; During the adjustment of the active power reference value, the corresponding rate of change of the power angle is calculated. Based on the rate of change of the power angle, the damping coefficient compensation value is calculated for adaptive damping compensation. The expression for the adaptive damping compensation is as follows: (4) in, This represents the damping coefficient after compensation by the grid converter. Indicates the foundation damping coefficient. Represents the adaptive gain coefficient. This represents the rate of change of the work angle.

4. The transient energy compensation control method for grid converters with adaptive fault ride-through and recovery according to claim 3, characterized in that, When switching to voltage control mode, the method of calculating the current transient energy based on the power angle state data to perform instability margin assessment, dynamically adjusting the active power based on the instability margin assessment result, and calculating the power angle change rate for damping adaptive compensation, further includes: The active power control equation of the converter in the voltage control mode is as follows: (5) in, , These represent the virtual rotational speed and the rated angular frequency, respectively. This represents the reference value for active power. Indicates the actual output electromagnetic power. This is the damping coefficient after compensation.

5. The transient energy compensation control method for grid converters with adaptive fault ride-through and recovery according to claim 3, characterized in that, The step of dynamically lowering the active power reference value of the grid converter when the instability margin is lower than a preset instability threshold, based on the instability margin assessment result, further includes: The reduction rate is calculated based on the reduction amount of the active power reference value and the instability margin, and the active power reference value is dynamically reduced according to the calculated reduction rate.

6. The transient energy compensation control method for grid converters with adaptive fault ride-through and recovery according to claim 1, characterized in that, When switching to the current limiting control mode, the power angle deviation of the power angle state data is calculated for dynamic gain adjustment. Based on the adjustment result, the saturation phase angle value is calculated to dynamically compensate the active power under fault conditions. Specifically, this includes: In the current limiting control mode, the power angle deviation of the power angle state data is calculated, and the power angle deviation is dynamically adjusted according to the grid voltage drop depth to obtain the phase angle dynamic compensation amount. The basic saturation current limiting phase angle of the grid-type converter is dynamically compensated by the phase angle dynamic compensation amount to obtain the saturation current phase angle. The power angle swing state under fault conditions is obtained, and the effective output current is adjusted based on the power angle swing state and the phase angle of the saturated current to perform dynamic compensation of active power.

7. The transient energy compensation control method for grid converters with adaptive fault ride-through and recovery according to claim 6, characterized in that, The process of acquiring the power angle oscillation state under fault conditions and adjusting the effective output current based on the power angle oscillation state and the saturation current phase angle branch axis to perform dynamic active power compensation specifically includes: The power angle swing state under fault conditions is obtained. When the power angle swing state exceeds the preset power angle swing threshold, the effective output current is adjusted according to the phase angle of the saturated current under the control mode switching threshold constraint during fault crossing. The active power of the grid converter is dynamically compensated based on the current adjustment result.

8. The transient energy compensation control method for grid converters with adaptive fault ride-through and recovery according to claim 1, characterized in that, When the preset mode switching condition is met, the current limiting control mode is smoothly switched back to the voltage control mode, and the active power after fault compensation is smoothly adjusted to the pre-fault steady-state value according to the preset fault recovery strategy. Specifically, this includes: When the effective output current meets the fault recovery conditions, the current limiting control mode is smoothly switched to the voltage control mode according to the set slope, and it is determined whether the power grid operation state has entered the steady-state recovery stage after the fault is cleared. When entering the steady-state recovery phase, the active power after fault compensation is adjusted to the steady-state value before the fault according to the preset slope.

9. The transient energy compensation control method for grid converters with adaptive fault ride-through and recovery according to claim 8, characterized in that, When the effective output current meets the fault recovery conditions, the current limiting control mode is smoothly switched to the voltage control mode according to a set slope, and it is determined whether the power grid operation has entered the steady-state recovery stage after fault clearing. Specifically, this includes: When the current amplitude of the effective output current is lower than the preset cut-back threshold and the power angle deviation reaches the preset convergence condition, the effective output current is determined to meet the fault recovery condition, wherein the preset cut-back threshold is lower than the control mode switching threshold during fault ride-through.

10. A transient energy compensation control system for a grid converter adapted to fault ride-through and recovery, characterized in that, The system includes: The data acquisition and mode switching judgment module is used to acquire the effective output current of the grid-type converter, perform fault ride-through judgment based on the effective output current and switch the control mode of the grid-type converter, and acquire the power angle status data at the time of mode switching. The transient energy assessment and damping control module is used to calculate the current transient energy based on the power angle state data to assess the instability margin when switching to voltage control mode, dynamically adjust the active power based on the instability margin assessment result, and calculate the power angle change rate to perform damping adaptive compensation. The phase angle compensation and power adjustment module is used to calculate the power angle deviation of the power angle state data and perform dynamic gain adjustment when switching to the current limiting control mode, and calculate the saturated phase angle value based on the adjustment result to dynamically compensate the active power under fault conditions. The mode switchback control and fault recovery module is used to smoothly switch the current limiting control mode back to the voltage control mode when the preset mode switchback conditions are met, and to smoothly adjust the active power after fault compensation to the steady-state value before the fault according to the preset fault recovery strategy.

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