Self-adaptive control method and system for high and low voltage fault ride-through of network-forming converter

Abstract

The invention discloses a self-adaptive control method and system for high and low voltage fault ride-through of a network-constructed converter, and relates to the field of network-constructed converters. The existing network-forming converter is difficult to consider voltage source characteristic maintenance and current safety amplitude limiting in a fault ride-through period. The method comprises the following steps: acquiring voltage amplitudes of a grid-connected point and an infinite bus before and after a fault, and calculating a ratio of products of the voltage amplitudes to judge a fault state; based on the ratio, the active power before the fault, the power grid impedance and the power angle variation, adaptively calculating an active power reference value; in response to the fault state, a reactive power reference value is calculated with the aim of ensuring that the current does not exceed the safety limit value; and finally, inputting the power reference value to an inherent active-frequency and reactive-voltage droop control ring of the converter to complete fault ride-through. According to the technical scheme, the external characteristics of the voltage source of the grid-forming converter can be kept during the fault period, internal coordination of power support and equipment safety is achieved, and the adaptability and stability of the system under different fault working conditions are improved.

Description

Technical Field

[0001] This invention relates to the field of grid-connected converters, and more particularly to an adaptive control method and system for high and low voltage fault ride-through in grid-connected converters. Background Technology

[0002] Large-scale grid connection of renewable energy generation is a key link in achieving the clean and low-carbon transformation of the new power system. As a core interface device, the converter's control strategy has a significant impact on grid stability. High-voltage and low-voltage fault ride-through capability is crucial for ensuring uninterrupted grid operation and supporting system voltage recovery during faults. Grid-connected converters, due to their autonomous voltage and frequency regulation capabilities and ability to simulate synchronous external characteristics, are gradually becoming the technical choice for scenarios with high proportions of renewable energy integration. However, their operation during faults differs fundamentally from that of grid-connected converters, making direct application of current command tracking ride-through control methods unsuitable.

[0003] Currently, existing methods for addressing voltage ride-through issues in grid-connected converters during grid faults largely rely on predefined switching logic or fixed parameter strategies, making them ill-suited to varying grid conditions and different fault types. In actual operation, especially in weak grids or situations with high fault impedance, traditional control methods are prone to causing active and reactive power oscillations, continuous voltage fluctuations at the grid connection point, and even protective disconnection of the converter, threatening system transient stability. Furthermore, because grid-connected control needs to consider both voltage source characteristics and current physical limiting, the coordination mechanism between power reference command generation and dynamic current limiting during faults has not yet been systematically analyzed and designed.

[0004] Existing research mostly focuses on post-fault stability criteria and power flow feasibility analysis. It has failed to establish a clear dynamic mapping relationship between PQ command and fault voltage and grid impedance, and also lacks a quantitative description of the response characteristics of internal control parameters under limiting conditions. Ultimately, this results in insufficient adaptability and robustness of grid-type converters under real fault conditions. Summary of the Invention

[0005] The technical problem to be solved and the technical task proposed by this invention is to improve and refine existing technical solutions, and to provide an adaptive control method and system for high and low voltage fault ride-through of grid-type converters. This aims to solve the problem that existing grid-type converters struggle to simultaneously maintain voltage source characteristics and limit current safety during fault ride-through. To this end, this invention adopts the following technical solution.

[0006] An adaptive control method for high and low voltage fault ride-through in a grid-type converter includes the following steps: 1) Obtain the voltage amplitude at the grid connection point and the voltage amplitude of the infinite bus before and after the fault occurred; 2) Calculate the ratio of the product of voltage amplitudes after the fault to the product of voltage amplitudes before the fault; 3) Determine the fault ride-through status based on the ratio: when the ratio is less than the low voltage threshold, it is determined that the fault has entered the low voltage ride-through status; when the ratio is greater than the high voltage threshold, it is determined that the fault has entered the high voltage ride-through status. 4) Calculate the reference value of active power based on the ratio, the active power before the fault, the grid impedance, and the change in power angle; 5) In response to the fault ride-through state determined in step 3), calculate the reactive power reference value based on the voltage amplitude after the fault, the grid impedance and the maximum allowable current of the converter. 6) The calculated active power reference value and reactive power reference value are input to the active-frequency droop control loop and reactive-voltage droop control loop of the grid-type converter, respectively, to control the converter output and achieve adaptive fault ride-through while maintaining the external characteristics of the voltage source.

[0007] This technical solution utilizes real-time monitoring of voltage amplitudes before and after a fault, calculating the ratio of their products as the basis for judgment and control. This ratio is a dynamic parameter that can accurately quantify the depth of a grid fault. Based on this parameter, a power reference command is generated, enabling the control method to automatically adapt to high and low voltage faults of varying severity, rather than relying on fixed predefined switching points. This significantly improves adaptability and robustness under different fault scenarios. This solution processes active and reactive power reference values ​​through two parallel calculation paths. The calculation of the active power reference considers the physical relationship of system power transmission (power angle change), aiming to maintain transient stability. The calculation of the reactive power reference explicitly aims to ensure that the output current does not exceed the maximum allowable current. This organically combines the two objectives of "power support" and "equipment safety" at the control source, rather than passively limiting the current after it exceeds the limit. This allows for smoother and more proactive avoidance of current surges and prevents protective disconnection. This technical solution is built upon the classic grid-based control (droop control) framework, eliminating the need for complex virtual impedance or additional control mode switching logic. Its adaptive mechanism is mainly achieved by modifying the input reference value of the droop control loop, requiring minimal changes to the existing grid-connected converter control platform, resulting in high reliability and reducing the complexity and cost of algorithm development and engineering implementation. This technical solution, through dynamic voltage ratio parameters, achieves adaptive coordination between power control and current limiting without altering the original grid-connected control structure. This ensures equipment safety while maximizing the grid-connected converter's role in supporting grid stability.

[0008] As a preferred technical means: in step 3), the low voltage threshold is 0.9; the high voltage threshold is 1.1.

[0009] This technical solution provides clear and quantifiable judgment criteria for identifying high and low voltage faults in grid-connected converters. It can accurately distinguish between normal voltage fluctuations in the power grid and actual high / low voltage faults, avoiding false or missed control triggers caused by ambiguous judgments. At the same time, the fixed threshold makes the fault triggering logic clear and unified, eliminating the need to dynamically adjust parameters based on power grid strength, fault impedance, and other operating conditions. This allows for rapid fault response to shorten control delays and reduce the possibility of active and reactive power oscillations, current over-limits, and converter protective disconnection during faults. It also provides accurate fault type basis for subsequent targeted calculation of active and reactive power reference values. Furthermore, the engineering implementation only requires simple numerical comparison logic, reducing the development difficulty of the control program and the costs of later debugging and maintenance. This effectively improves the problems of poor adaptability and insufficient robustness in fault judgment of grid-connected converters in existing technologies.

[0010] As a preferred technical means: In step 4), the active power reference value is calculated in the following way: the active power before the fault is scaled according to the ratio, and an adjustment term proportional to the product of the power angle change and the voltage amplitude after the fault is added.

[0011] This technical solution first scales the active power before the fault by voltage ratio, allowing the active power reference value to initially adapt to the voltage change after the fault, thus avoiding an imbalance between active power output and grid carrying capacity caused by sudden voltage fluctuations. Simultaneously, an additional adjustment term specifically compensates for the impact of power angle changes before and after the fault on system power balance—power angle changes are directly related to the synchronization characteristics and transient stability of grid-connected converters. This adjustment term allows the active power reference value to dynamically respond to power angle fluctuations, rather than using a fixed scaling ratio, significantly improving the accuracy and dynamic adaptability of active power control. Furthermore, this calculation logic does not require changing the voltage source characteristics that the grid-connected converter needs to maintain. While ensuring the core operating characteristics of the converter, it can limit the fault current amplitude through fine-tuning of the active power reference value, reducing the risk of active power oscillation during the fault period. This lays a stable active power output foundation for subsequent high / low voltage adaptive ride-through. Moreover, the calculation process only relies on voltage and power angle parameters that can be directly collected or derived before and after the fault, making it convenient for engineering implementation and highly robust.

[0012] As a preferred technical means: in step 5), the reactive power reference value is calculated in the following way: Based on the converter's maximum allowable current, the grid voltage after the fault, and the grid impedance, the reference value of the grid connection point voltage required to maintain the current not exceeding the maximum allowable current is derived in reverse. The reactive power reference value is generated based on the grid connection point voltage reference value.

[0013] This technical solution, based on the premise of "maintaining the current not exceeding the maximum allowable value," fundamentally avoids the current over-limit problem caused by reactive power output loss during faults, effectively reducing the risk of grid-connected converters tripping due to overcurrent triggering protection. It also aligns with the core requirement of grid-connected converters to maintain the external characteristics of the voltage source. The reverse derivation process fully integrates the grid voltage and grid impedance after the fault, ensuring that the obtained grid connection point voltage reference value accurately adapts to the current fault condition, rather than using fixed parameters. This significantly improves the adaptability of reactive power control to various grid fault scenarios. Based on... The reactive power reference value is generated from the voltage reference value under fault conditions, which can ensure that the reactive power output can respond to the voltage regulation requirements of the grid connection point in a targeted manner, further ensuring the stability of the grid connection point voltage during the fault period and reducing voltage fluctuations and reactive power oscillations. Moreover, the maximum allowable current of the converter, the voltage after the fault, and the grid impedance on which the entire calculation process depends are all parameters that can be directly collected or obtained in advance in the project, without the need for complex additional detection equipment. It is simple to implement and has strong robustness, effectively making up for the shortcomings of existing technologies in reactive power control and current limiting of grid-type converters and insufficient grid condition adaptability.

[0014] As a preferred technical means, in the step of reverse derivation of the grid connection point voltage reference value, a quadratic equation in one variable is solved for the low voltage ride-through state and the high voltage ride-through state respectively: the summation solution of the equation is taken for the low voltage ride-through state, and the difference solution of the equation is taken for the high voltage ride-through state, which are used as the grid connection point voltage reference value.

[0015] This technical solution addresses the distinctly different voltage regulation needs under two fault conditions: low-voltage ride-through requires a reasonable voltage reference value to assist in raising the grid connection point voltage to support grid recovery, while high-voltage ride-through requires an appropriate voltage reference value to suppress excessively high grid connection point voltage to avoid equipment overload. The selection of different solutions ensures that the voltage reference value matches the fault type, avoiding the problem of insufficient adaptability to high and low voltage faults caused by using a single solution. Furthermore, the solution to the quadratic equation is derived analytically based on the converter's maximum allowable current, the grid voltage after the fault, and the grid impedance, rather than relying on empirical parameters. This mathematically ensures that the selected solution strictly satisfies the condition that "the current does not exceed the maximum allowable current." The core constraint of "value" avoids the overcurrent risk caused by unreasonable voltage reference values ​​during faults from the root, ensuring that grid-connected converters do not trigger protective disconnection. In addition, this state-by-state analytical solution method has clear mathematical logic, without the need for complex dynamic parameter adjustments or fuzzy judgments. It can make the grid connection point voltage reference value fit the current fault condition, effectively maintain the voltage source external characteristics of the grid-connected converter, reduce grid connection point voltage fluctuations and reactive power oscillations, and reduce the complexity of control logic in engineering implementation. It is easy to develop and debug and has strong robustness, making up for the shortcomings of existing technologies in voltage reference value generation that lack scenario specificity and are difficult to balance current safety and voltage stability.

[0016] As a preferred technical means, the maximum allowable current of the converter is 1.5 times the rated current of the converter.

[0017] This technical solution balances the fault regulation requirements of grid-connected converters with the safety boundaries of the equipment. The 1.5 times rated current provides sufficient current regulation margin for the converter during high / low voltage faults, ensuring that it can output reactive power adapted to the fault conditions (such as outputting reactive power to support the grid connection point voltage during low voltage ride-through and regulating reactive power to suppress excessive voltage rise during high voltage ride-through), avoiding insufficient power regulation capability due to excessive current limiting, which would affect the fault ride-through effect; at the same time, it does not exceed the short-time overload tolerance range of the converter's conventional design, which can effectively prevent the current from exceeding the limit during the fault period, causing insulation damage to the converter or protective disconnection, and ensuring the safe operation of the equipment. Meanwhile, the 1.5 times rated current serves as a fixed and explicit constraint, providing a stable and reliable calculation basis for the reverse derivation of the grid connection point voltage reference value. This avoids deviations in the voltage reference value derivation caused by dynamic fluctuations in the current limiting parameter, thereby ensuring the accuracy of the subsequent reactive power reference value generation. Furthermore, this value conforms to the common design standards for short-term overload of converters in industry engineering practice, eliminating the need for additional modifications to the converter hardware. This reduces the implementation cost and complexity of the technical solution, and enhances the feasibility and robustness of engineering applications.

[0018] Another technical solution of the present invention is: an adaptive control system for high and low voltage fault ride-through of a grid-type converter, the system comprising: Voltage acquisition module: used to acquire the voltage amplitude at the grid connection point and the voltage amplitude at the infinite bus before and after a fault occurs in the grid-connected converter; Ratio calculation module: connected to the voltage acquisition module, used to calculate the ratio of the product of voltage amplitudes after the fault to the product of voltage amplitudes before the fault; Fault determination module: connected to the calculation module, used to determine the fault ride-through state based on the ratio. When the ratio is less than the low voltage threshold, the system is determined to have entered the low voltage ride-through state; when the ratio is greater than the high voltage threshold, the system is determined to have entered the high voltage ride-through state. Active power reference value calculation module: connected to the voltage acquisition module and the ratio calculation module, used to calculate the active power reference value based on the ratio, active power before the fault, grid impedance and power angle change; Reactive power reference value calculation module: Connects the voltage acquisition module and the fault judgment module, and is used to calculate the reactive power reference value based on the voltage amplitude after the fault, the grid impedance and the maximum allowable current of the converter in response to the judged fault state. Active power-frequency droop control loop and reactive power-voltage droop control loop: receive active power and reactive power reference values ​​respectively, and coordinate to control the output of the grid-type converter to maintain the external characteristics of the voltage source and achieve adaptive fault ride-through.

[0019] This technical solution, through the coordinated operation of various functional modules, constructs a complete control system that closely matches the external characteristics of the voltage source of a grid-connected converter and adapts to various fault conditions: the voltage acquisition module obtains the voltage amplitudes of the grid connection point and the infinite bus before and after a fault, providing reliable basic data support for subsequent fault judgment and parameter calculation; the fault judgment module determines the fault state based on the "ratio of the product of the voltage amplitudes before and after the fault," which, compared to judging a single voltage parameter, more comprehensively reflects the overall voltage change characteristics of the power grid, avoids misjudgment of faults due to local voltage fluctuations, and provides accurate direction for subsequent targeted control; the active and reactive power reference value calculation modules dynamically generate reference values ​​by combining fault characteristic parameters (ratio, power angle change, grid impedance, and maximum allowable current of the converter), rather than relying on fixed parameters, thus enabling... The reference values ​​closely match the voltage and impedance characteristics of the current fault, ensuring the accuracy of power regulation. The active-frequency and reactive-voltage droop control loops closely adhere to the core requirement of maintaining the external characteristics of the voltage source in grid-connected converters. By coordinating the control of active and reactive power outputs, it avoids the damage to the voltage source characteristics caused by the current inner loop command of the grid-connected converter, and effectively suppresses active and reactive power oscillations and voltage fluctuations during faults. At the same time, the entire system has a clear division of labor among modules and a clear data transmission logic. The voltage, impedance, and other parameters it relies on are all quantities that can be directly acquired or pre-stored in the project, without the need for additional complex detection equipment. This makes the project implementation convenient and can prevent the converter from being disconnected from the grid due to overcurrent from the control logic, significantly improving the stability and reliability of grid-connected converters during high / low voltage fault ride-through.

[0020] As a preferred technical means: the fault judgment module includes a state judgment unit, in which a low voltage threshold of 0.9 and a high voltage threshold of 1.1 are pre-stored; the state judgment unit compares the calculated ratio with 0.9 and 1.1 respectively, and outputs the judgment result of low voltage ride-through state or high voltage ride-through state.

[0021] This technical solution establishes a clear quantitative standard for identifying high and low voltage faults in grid-connected converters. It can accurately distinguish between normal voltage fluctuations in the power grid and actual faults, effectively avoiding control mis-triggers (interference with the external voltage source characteristics of the converter under non-fault conditions) or missed triggers (failure to respond to faults in a timely manner, leading to current over-limits and increased voltage fluctuations) caused by ambiguous judgments. Fixed thresholds make the fault judgment logic clear and unified, eliminating the need to dynamically adjust parameters based on power grid strength, fault impedance, and other operating conditions. This allows for rapid fault type identification, shortens control response delays, and reduces the risk of active and reactive power oscillations and converter protective disconnection during faults. At the same time, the accurate output of low-voltage / high-voltage state results provides a clear fault type basis for subsequent reactive power reference value calculation modules (such as using the "sum solution" of a quadratic equation in low-voltage cases and the "difference solution" in high-voltage cases to derive voltage reference values). This ensures that subsequent control strategies are highly compatible with fault requirements, and only requires simple numerical comparison logic to achieve, reducing the difficulty of control program development and the cost of later debugging and maintenance, and improving the engineering practicality and robustness of the technical solution.

[0022] As a preferred technical means, the active power reference value calculation module includes: Power scaling unit: used to scale the active power before the fault according to the ratio output by the fault judgment module; Adjustment Item Generation Unit: Used to generate adjustment items that are proportional to the product of the power angle change and the voltage amplitude after the fault, based on the voltage amplitude after the fault, grid impedance, and power angle change. The active power reference value calculation module obtains the active power reference value by superimposing the output of the power scaling unit and the output of the adjustment item generation unit.

[0023] The power scaling unit in this technical solution scales the pre-fault active power according to the ratio output by the fault judgment module. This allows the active power reference value to initially adapt to the post-fault grid voltage change, preventing an imbalance between active power output and the grid's current carrying capacity due to sudden voltage fluctuations, thus laying the foundation for stable power output during fault periods. The adjustment term generation unit generates an adjustment term proportional to the product of the post-fault voltage amplitude, grid impedance, and power angle change. This term can specifically compensate for the impact of power angle fluctuations before and after the fault on the system's power balance—the power angle is directly related to the synchronization characteristics and transient stability of the grid-type converter. This adjustment term enables the active power reference value to dynamically respond to power angle changes, rather than relying solely on... By relying on a fixed scaling ratio, the accuracy of active power control and the dynamic adaptability to fault conditions are significantly improved. The calculation method of superimposing the results of the two methods not only preserves the basic adaptability of power under voltage changes, but also supplements the dynamic compensation for power angle fluctuations. Under the premise of not destroying the external characteristics of the voltage source of the grid-type converter (unlike the current inner loop command adjustment of the grid-connected converter), it can effectively limit the fault current amplitude and reduce the risk of active power oscillation. Moreover, the parameters such as active power before the fault, ratio, and voltage after the fault on which the entire module depends are all quantities that can be directly collected or derived in engineering. The calculation logic is clear, and no complex algorithms are required, which reduces the difficulty of development and debugging and improves the engineering practicality and robustness of the technical solution.

[0024] As a preferred technical means, the reactive power reference value calculation module includes: Voltage reference value derivation unit: used to derive the grid connection point voltage reference value required to "maintain the current not exceeding the maximum allowable current" based on the maximum allowable current of the converter, the grid voltage after the fault, and the grid impedance; the voltage reference value derivation unit includes an equation solving subunit, which is used to construct and solve quadratic equations for low voltage ride-through state and high voltage ride-through state respectively, and take the sum solution of the equation in low voltage ride-through state and the difference solution of the equation in high voltage ride-through state as the grid connection point voltage reference value; Reactive power reference value generation unit: connected to the voltage reference value derivation unit, used to generate reactive power reference values ​​based on the grid connection point voltage reference value; The reactive power reference value calculation module outputs a reactive power reference value through the collaborative calculation of the voltage reference value derivation unit and the reactive power reference value generation unit.

[0025] The voltage reference value derivation unit of this technical solution focuses on "maintaining the current below the converter's maximum allowable current." It derives the grid connection point voltage reference value by inversely calculating the grid voltage and impedance after a fault, fundamentally mitigating the overcurrent risk caused by uncontrolled reactive power output during a fault and ensuring that the grid-connected converter does not trigger protective disconnection. Its equation-solving subunit constructs quadratic equations for low-voltage ride-through and high-voltage ride-through states, obtaining different solutions to match the drastically different voltage regulation requirements under these two fault conditions—in low-voltage ride-through, the adapted solution assists in raising the grid connection point voltage to support grid recovery; in high-voltage ride-through, the adapted solution suppresses excessive voltage to avoid equipment overload. This avoids the problem of insufficient adaptability of a single solution to different fault scenarios. The reactive power reference value generation unit generates reactive power reference values ​​based on the grid connection point voltage reference values ​​that fit the fault conditions. This ensures that the reactive power output responds to the voltage regulation requirements in a targeted manner, effectively reducing grid connection point voltage fluctuations and reactive power oscillations during faults. At the same time, it meets the core requirement of grid-type converters to maintain the external characteristics of the voltage source. Furthermore, the maximum allowable current of the converter, the voltage after the fault, and the grid impedance on which the entire module depends are all parameters that can be directly collected or pre-stored in the project. The calculation logic is based on clear mathematical derivation and does not require complex dynamic adjustments, which reduces the difficulty of development and debugging and improves the engineering practicality and robustness of the technical solution.

[0026] Beneficial effects: 1. Strong adaptability: The fault depth is dynamically determined by the ratio of the voltage product before and after the fault, and a power reference value is generated adaptively based on this, rather than relying on a fixed threshold or logic switching. It can effectively adapt to different grid strengths and fault types.

[0027] 2. Maintaining grid-connected characteristics: The entire control process is completed within the original droop control framework of the grid-connected converter, without the need for a lockout control loop or the introduction of virtual impedance. This fully maintains the external voltage source characteristics of the converter, resulting in stronger support for the power grid.

[0028] 3. Balancing safety and stability: The calculation of the active power reference value takes into account changes in the power angle, which is beneficial for transient stability; the calculation of the reactive power reference value aims at current limiting, avoiding overcurrent risks at the source. The two work together to ensure equipment safety while providing grid support. Attached Figure Description

[0029] Figure 1 This is a flowchart of the present invention.

[0030] Figure 2 This is a simulation waveform of the converter output current in the LVRT mode of this invention.

[0031] Figure 3 This is a simulation waveform diagram of the grid connection point voltage under the LVRT mode of the present invention.

[0032] Figure 4 This is a simulation waveform diagram of the converter output power in the LVRT mode of this invention.

[0033] Figure 5 This is a simulation waveform of the output current of the HVRT mode converter of the present invention.

[0034] Figure 6 This is a simulation waveform diagram of the grid connection point voltage in the HVRT mode of the present invention.

[0035] Figure 7 This is a simulation waveform diagram of the output power of the HVRT mode converter of the present invention.

[0036] Figure 8 This is a schematic diagram of the converter-grid interconnection system. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. It should be noted beforehand that the parameter symbols used in the following embodiments have the following meanings: V , U : Voltage amplitude at the grid connection point and voltage amplitude at the infinite bus before the fault.

[0038] , : Voltage amplitude at the grid connection point and voltage amplitude at the infinite bus after the fault.

[0039] Fault diagnosis coefficient .

[0040] , Active power before the fault, and reference value of active power.

[0041] : Reactive power reference value.

[0042] : Grid impedance from the connection point to the infinite busbar.

[0043] , Power angle (phase difference between grid connection point voltage and infinite bus voltage), power angle change.

[0044] : Rated current of the converter.

[0045] Example 1: like Figure 1 As shown, the present invention includes the following steps: S1: Obtain the voltage amplitude at the grid connection point before and after the fault. , Voltage amplitude of the infinite bus , ; S2: Calculate the ratio of the product of voltage amplitudes after the fault to the product of voltage amplitudes before the fault. ; S3: The ratio Compare with a preset threshold; if <0.9, it is determined to be a low voltage ride-through (LVRT) state; if If the value is greater than 1.1, it is considered a High Voltage Ride-Through (HVRT) state; if 0.9 ≤ If the value is ≤1.1, it is in normal operating condition; S4: Based on the ratio Active power before the fault Grid impedance and the change in work angle Calculate the reference value of active power. , ; S5: In response to the fault ride-through state determined in step S3, based on the voltage amplitude after the fault. , grid impedance ω L g And the maximum allowable current of the converter, calculate the reference value of reactive power. ; S6: Calculate the active power reference value. and reactive power reference value These inputs are respectively fed into the active-frequency droop control loop and the reactive-voltage droop control loop of the grid-type converter to control the converter output, thereby achieving adaptive fault ride-through while maintaining the external characteristics of the voltage source.

[0046] The following provides further explanation of certain aspects relating to this invention: The model of this invention adopts a droop control model, in which both the synchronization loop and the reactive power voltage loop are droop control structures, and the input of the synchronization control loop is active power. P The reactive voltage loop input is reactive power. Q and grid connection point voltage amplitude U t Its specific structure is as follows: Figure 8 As shown.

[0047] The control equations for active and reactive power droop are: (1) (2) in: and These are the active and reactive power droop control coefficients, which are fixed constants. and These are active and reactive power control commands, respectively. During high / low voltage fault ride-through, calculations must be performed based on the fault voltage amplitude to achieve adaptive control during high / low voltage ride-through. V and These are the reference values ​​for the grid connection point voltage amplitude and the control command; the latter also needs to be recalculated during a fault. The adaptive control method below essentially calculates these values ​​under fault conditions. , and . ω It is the output angular frequency of the converter. ω 0 is the rated angular frequency.

[0048] I. Calculation of Active Power Reference Values ​​During High / Low Voltage Ride Before the fault, let the grid connection point voltage be V, the infinite bus voltage be U, and the power angle be... After the fault, record the voltage at the grid connection point as follows: The infinite bus voltage is The angle of attack is . The grid impedance is from the connection point to the infinite busbar.

[0049] The active power P before the fault was: (3) Active power after fault for: (4) If the power angles before and after the fault are similar, then a first-order Taylor expansion of equation (4) yields: (5) in, (6) The ratio of voltage amplitude before and after the fault can be used in practice by... The magnitude of the value determines whether the system has entered a high-penetration or low-penetration phase. For example, when <0.9 indicates the vehicle has entered a low-voltage ride-through state. >1.1 Determine if the system has entered a high-voltage ride-through state.

[0050] The active power control command value after a high / low voltage fault is modified to: (7) The above instruction values ​​are based on the assumption that Calculated under conditions close to 0, when the change in power angle before and after a fault is close to 0, the amplitude of the fault current in the system will also be limited accordingly, which helps to avoid problems such as transient power angle instability caused after entering the limiting stage.

[0051] II. Calculation of Reactive Power Reference Values ​​During High / Low Voltage Ride-Through First consider the low-voltage scenario, and calculate the corresponding grid connection point voltage reference value when limiting the current. and no merit And substitute it into formula (2).

[0052] The relationship between the current amplitude and the fault voltage after a fault is known to be: (8) When wearing low, substitute , I n For the rated current, and with Indicates the voltage after the fault. k This is the proportionality coefficient; during normal operation, substitute it into... .

[0053] Substitute fault current, voltage and Next, solve equation (8) for... The quadratic equation in one variable can be obtained as follows: for (9) in, (10) Considering the high penetration situation, let ,get (11) Note that equations (9) and (11) are two solutions to a quadratic equation. The lower solution is added together, and the higher solution is subtracted.

[0054] Using equations (9) and (11) as Substituting into (2) will yield the result. V and Q require actual measured values.

[0055] III. To verify the effectiveness of this method, a system was built in MATLAB / Simulink. Figure 8 The system shown was simulated, and the parameters are shown in Table 1.

[0056] Table 1 Simulation Data

[0057] LVRT (Low Voltage Ride-Through) simulation verification was performed: the grid-side voltage (infinite bus voltage) was set to 0.6U for 4~8s (at this time...). =0.6), and the rest of the time is the normal value U. The converter output current is obtained respectively. I Grid connection point voltage UThere is also the active power output of the converter. P reactive power Q Changes such as Figure 2 , Figure 3 , Figure 4 As shown.

[0058] In LVRT simulation verification (4-8s fault period), k f =0.6), the d-axis component of the converter output current drops from the normal 1 p.u. to approximately 0.8 p.u., and the q-axis component changes from 0 to -1.5 p.u. (corresponding to a current limit of 1.5 p.u.). This stems from the adaptive control method of this invention, which adjusts the active and reactive power reference values ​​( , To ensure current safety; the d-axis component of the grid connection point voltage drops from 1 p.u. to 0.85 p.u. (the q-axis remains at 0), active power P From 1 p.u. to 0.6 p.u., reactive power Q The change from 0 to 1.1 pu is consistent with the calculation results of formulas (2), (7), (9), and (11). The q-axis current is limited by -1.5 pu to trigger the current. Q Increasing the reactive power to 1.1 pu to provide reactive power support to improve voltage (d-axis recovery from 0.6U at fault to 0.85 pu) verifies the robustness of the adaptive method under fault voltage and impedance dynamic mapping. This method successfully coordinates power regulation and current limiting, improving system stability.

[0059] Perform HVRT (High Voltage Ride-Through) simulation verification: Using the experimental parameters in Table 1, build the following simulation system in SINULINK software: Figure 8 The diagram shows the converter-grid interconnection system topology. The grid-side voltage (infinite bus voltage) is set to 1.2U for 4-8 seconds (at this time...). =1.2), and the rest of the time is the normal value U. The converter output current is then calculated. I Grid connection point voltage U There is also the active power output of the converter. P reactive power Q Changes such as Figure 5 , Figure 6 , Figure 7 As shown.

[0060] In HVRT simulation verification (4-8s fault period), =1.2), the q-axis component of the converter output current changes from 0 to 0.9pu (less than the current limit of 1.5). The d-axis component of the grid connection point voltage increases from 1 p.u. to 1.05 p.u. (the q-axis remains at 0), and the reactive power... Q The values ​​increased from 0 to 0.8 pu, and these changes were consistent with the calculation results of formulas (2), (7), (9), and (11). This verified the robustness of the adaptive method under fault voltage and impedance dynamic mapping. This method successfully coordinated power adjustment and current limiting, improving system stability.

[0061] Example 2: Another technical solution of the present invention is: an adaptive control system for high and low voltage fault ride-through of a grid-type converter, the system comprising: Voltage acquisition module: used to acquire the voltage amplitude at the grid connection point and the voltage amplitude at the infinite bus before and after a fault occurs in the grid-connected converter; Ratio calculation module: connected to the voltage acquisition module, used to calculate the ratio of the product of voltage amplitudes after the fault to the product of voltage amplitudes before the fault; Fault determination module: connected to the calculation module, used to determine the fault ride-through state based on the ratio. When the ratio is less than the low voltage threshold, the system is determined to have entered the low voltage ride-through state; when the ratio is greater than the high voltage threshold, the system is determined to have entered the high voltage ride-through state. Active power reference value calculation module: connected to the voltage acquisition module and the ratio calculation module, used to calculate the active power reference value based on the ratio, active power before the fault, grid impedance and power angle change; Reactive power reference value calculation module: Connects the voltage acquisition module and the fault judgment module, and is used to calculate the reactive power reference value based on the voltage amplitude after the fault, the grid impedance and the maximum allowable current of the converter in response to the judged fault state. Active power-frequency droop control loop and reactive power-voltage droop control loop: receive active power and reactive power reference values ​​respectively, and coordinate to control the output of the grid-type converter to maintain the external characteristics of the voltage source and achieve adaptive fault ride-through.

[0062] This embodiment accurately determines the fault state by calculating the dynamic ratio of the product of the grid voltage amplitude before and after the fault in real time, and adaptively generates active and reactive power reference values ​​based on this ratio, system power, and grid impedance. This scheme directly injects the optimized power command into the inherent active-frequency and reactive-voltage droop control loop of the grid-type converter, rather than introducing additional control mode switching or virtual impedance links. This maintains the external voltage source characteristics of the converter throughout the fault ride-through process, ensuring equipment current safety and achieving active power support for the grid, effectively improving the system's adaptability and stability under different fault conditions.

[0063] It is understood that the detailed functional implementation of each of the above modules can be found in the description of the aforementioned method embodiments, and will not be elaborated further here.

[0064] The adaptive control method and system for high and low voltage fault ride-through of grid-type converters shown above are specific embodiments of the present invention, demonstrating the substantial features and progress of the present invention. Equivalent modifications can be made to it according to actual usage needs, under the guidance of the present invention, and all such modifications are within the scope of protection of this solution.

Claims

1. A method for adaptive control of high and low voltage fault ride-through in a grid-type converter, characterized in that, Includes the following steps: 1) Obtain the voltage amplitude at the grid connection point and the voltage amplitude of the infinite bus before and after the fault occurred; 2) Calculate the ratio of the product of voltage amplitudes after the fault to the product of voltage amplitudes before the fault; 3) Determine the fault ride-through status based on the ratio: when the ratio is less than the low voltage threshold, it is determined that the fault has entered the low voltage ride-through status; when the ratio is greater than the high voltage threshold, it is determined that the fault has entered the high voltage ride-through status. 4) Calculate the reference value of active power based on the ratio, the active power before the fault, the grid impedance, and the change in power angle; 5) In response to the fault ride-through state determined in step 3), calculate the reactive power reference value based on the voltage amplitude after the fault, the grid impedance and the maximum allowable current of the converter. 6) The calculated active power reference value and reactive power reference value are input to the active-frequency droop control loop and reactive-voltage droop control loop of the grid-type converter, respectively, to control the converter output and achieve adaptive fault ride-through while maintaining the external characteristics of the voltage source.

2. The adaptive control method for high and low voltage fault ride-through of a grid-type converter according to claim 1, characterized in that: In step 3), the low voltage threshold is 0.9; the high voltage threshold is 1.

1.

3. The adaptive control method for high and low voltage fault ride-through of a grid-type converter according to claim 1, characterized in that: In step 4), the active power reference value is calculated by scaling the active power before the fault according to the ratio, and adding an adjustment term that is proportional to the product of the power angle change and the voltage amplitude after the fault.

4. The adaptive control method for high and low voltage fault ride-through of a grid-type converter according to claim 1, characterized in that: In step 5), the reactive power reference value is calculated in the following way: Based on the converter's maximum allowable current, the grid voltage after the fault, and the grid impedance, the reference value of the grid connection point voltage required to maintain the current not exceeding the maximum allowable current is derived in reverse. The reactive power reference value is generated based on the grid connection point voltage reference value.

5. The adaptive control method for high and low voltage fault ride-through of a grid-type converter according to claim 4, characterized in that: In the step of reverse derivation of the grid connection point voltage reference value, a quadratic equation is solved for both the low voltage ride-through state and the high voltage ride-through state: the summation solution of the equation is taken for the low voltage ride-through state, and the difference solution of the equation is taken for the high voltage ride-through state, which are used as the grid connection point voltage reference value.

6. The adaptive control method for high and low voltage fault ride-through of a grid-type converter according to claim 4, characterized in that: The maximum allowable current of the converter is 1.5 times the rated current of the converter.

7. A high and low voltage fault ride-through adaptive control system for a grid-type converter, characterized in that: The system is used to execute the adaptive control method for high and low voltage fault ride-through of a grid-type converter according to any one of claims 1-6, the system comprising: Voltage acquisition module: used to acquire the voltage amplitude at the grid connection point and the voltage amplitude at the infinite bus before and after a fault occurs in the grid-connected converter; Ratio calculation module: connected to the voltage acquisition module, used to calculate the ratio of the product of voltage amplitudes after the fault to the product of voltage amplitudes before the fault; Fault determination module: connected to the calculation module, used to determine the fault ride-through state based on the ratio. When the ratio is less than the low voltage threshold, the system is determined to have entered the low voltage ride-through state; when the ratio is greater than the high voltage threshold, the system is determined to have entered the high voltage ride-through state. Active power reference value calculation module: connected to the voltage acquisition module and the ratio calculation module, used to calculate the active power reference value based on the ratio, active power before the fault, grid impedance and power angle change; Reactive power reference value calculation module: Connects the voltage acquisition module and the fault judgment module, and is used to calculate the reactive power reference value based on the voltage amplitude after the fault, the grid impedance and the maximum allowable current of the converter in response to the judged fault state. Active power-frequency droop control loop and reactive power-voltage droop control loop: receive active power and reactive power reference values ​​respectively, and coordinate to control the output of the grid-type converter to maintain the external characteristics of the voltage source and achieve adaptive fault ride-through.

8. The adaptive control system for high and low voltage fault ride-through of a grid-type converter according to claim 7, characterized in that: The fault judgment module includes a status judgment unit, in which a low voltage threshold of 0.9 and a high voltage threshold of 1.1 are pre-stored. The status judgment unit compares the calculated ratio with 0.9 and 1.1 respectively, and outputs the judgment result of low voltage ride-through state or high voltage ride-through state.

9. The adaptive control system for high and low voltage fault ride-through of a grid-type converter according to claim 8, characterized in that: The active power reference value calculation module includes: Power scaling unit: used to scale the active power before the fault according to the ratio output by the fault judgment module; Adjustment Item Generation Unit: Used to generate adjustment items that are proportional to the product of the power angle change and the voltage amplitude after the fault, based on the voltage amplitude after the fault, grid impedance, and power angle change. The active power reference value calculation module obtains the active power reference value by superimposing the output of the power scaling unit and the output of the adjustment item generation unit.

10. The adaptive control system for high and low voltage fault ride-through of a grid-type converter according to claim 9, characterized in that: The reactive power reference value calculation module includes: Voltage reference value derivation unit: used to derive the grid connection point voltage reference value required to "maintain the current not exceeding the maximum allowable current" based on the maximum allowable current of the converter, the grid voltage after the fault, and the grid impedance; the voltage reference value derivation unit includes an equation solving subunit, which is used to construct and solve quadratic equations for low voltage ride-through state and high voltage ride-through state respectively, and take the sum solution of the equation in low voltage ride-through state and the difference solution of the equation in high voltage ride-through state as the grid connection point voltage reference value; Reactive power reference value generation unit: connected to the voltage reference value derivation unit, used to generate reactive power reference values ​​based on the grid connection point voltage reference value; The reactive power reference value calculation module outputs a reactive power reference value through the collaborative calculation of the voltage reference value derivation unit and the reactive power reference value generation unit.

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