Converter fault ride-through reactive power support method with adjustable positive sequence and negative sequence reactive power priority

Abstract

The invention provides a positive sequence and negative sequence reactive power priority adjustable converter fault ride-through reactive power support method, which comprises the following steps: S1, when an asymmetric voltage fault of a power grid is detected, entering a fault ride-through control mode, and obtaining an active current reference value and a reactive current reference value before the fault; s2, obtaining a reactive priority strategy pre-configured by a user, and reading a preset reactive current maximum amplitude limiting value and a current maximum amplitude limiting value of the converter; wherein the reactive priority strategy comprises a positive sequence priority mode, a negative sequence priority mode or an equal-proportion derating mode; by introducing a configurable reactive priority strategy, the converter can flexibly adapt to different requirements of different grid-connected standards or application scenes on positive-sequence and negative-sequence reactive support capabilities, and the flexibility and applicability of reactive support are remarkably improved while the technical specifications of fault ride-through are met.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically, to a converter fault-through reactive power support method with adjustable positive and negative sequence reactive power priority. Background Technology

[0002] In recent years, with the accelerated global energy structure transition to clean and low-carbon technologies, the installed capacity of new energy power generation, represented by photovoltaic and wind power, has continued to grow rapidly, and energy storage systems have also been gradually connected to the grid on a large scale. As a key interface device connecting new energy sources and the power grid, the deployment scale of power electronic converters on the source side is constantly expanding, and their grid connection performance has an increasingly significant impact on the safe and stable operation of the power system. To enhance the support capacity of new energy power plants for the power grid, relevant grid connection technical standards at home and abroad (such as the Chinese national standard GB / T 19964 "Technical Regulations for Photovoltaic Power Plants Connected to the Power System" and the energy industry standard NB / T32004 "Technical Specifications for Photovoltaic Power Generation Grid-Connected Inverters") have been updated one after another, clearly requiring that new energy converters not only have low voltage ride-through (LVRT) capability when the grid experiences asymmetrical faults (such as single-phase or two-phase short circuits), but also provide negative sequence reactive current support to assist the grid in suppressing voltage imbalance and accelerating fault recovery.

[0003] However, the introduction of negative-sequence reactive current makes the vector composition of the converter's output current more complex. Under asymmetrical fault conditions, the converter needs to simultaneously output positive-sequence active current, positive-sequence reactive current, and negative-sequence reactive current. Due to the limitations of semiconductor device thermal stress and drive capability, the total output current amplitude of the converter has a physical upper limit. When the combined current of the three exceeds this limit, the current components must be coordinated and distributed to ensure that the converter maximizes its support for the power grid without exceeding the limits.

[0004] Currently, the mainstream current allocation strategy in the industry is the "proportional derating" scheme, which means that when the total reactive current (the sum of positive and negative sequence currents) exceeds the limit, the positive and negative sequence reactive currents are reduced synchronously in the same proportion. This method is simple to implement and has good symmetry, but it faces challenges in practical engineering applications: on the one hand, different countries, regions, and even specific power plant acceptance agencies interpret the current allocation logic differently within the standard framework; on the other hand, some application scenarios (such as simulation modeling certification and specific grid operator specifications) explicitly require priority to be given to positive sequence reactive current output, as it has a more direct effect on restoring grid voltage amplitude, while negative sequence reactive current is mainly used to suppress voltage imbalance. Therefore, a single proportional derating strategy is no longer sufficient to meet the current diverse and refined grid connection compliance requirements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a converter fault-through reactive power support method that can adjust the reactive power priority of positive and negative sequence reactive currents and limit the active current reference value, so as to meet the needs of various applications.

[0006] This invention provides a converter fault ride-through reactive power support method with adjustable positive and negative sequence reactive power priority, the method comprising the following steps: S1, when an asymmetrical voltage fault is detected in the power grid, enters the fault ride-through control mode and obtains the active current reference value before the fault. and reactive current reference value ; S2, obtain the user-preconfigured reactive power priority strategy, and read the preset maximum reactive current limit value and the maximum current limit value of the converter; wherein, the reactive power priority strategy includes positive sequence priority mode, negative sequence priority mode or proportional derating mode. S3, based on the positive sequence voltage of the power grid and negative sequence voltage Based on the reactive current support characteristics specified in the grid connection specifications, an initial positive sequence reactive current reference value is generated. and negative sequence reactive current reference value Wherein, the positive sequence reactive current reference value The negative sequence reactive current reference value is obtained by superimposing the positive sequence reactive current increment with the reactive current reference value before the fault. Equal to negative-order reactive power increment; S4, regarding the positive sequence reactive current reference value and negative sequence reactive current reference value Independent amplitude limiting processing is performed on each of them to ensure that the positive sequence reactive current reference value is... and negative sequence reactive current reference value All are limited to the maximum negative reactive current limit. With positive maximum reactive current limit value The closed interval formed Within, the reference values ​​of the positive sequence reactive current after limiting are calculated respectively. The absolute value and negative sequence reactive current reference value The absolute value; S5, the positive sequence reactive current reference value The absolute value and negative sequence reactive current reference value Adding the absolute values ​​together yields the given modulus of the reactive current. ; S6, when the reactive current is given a magnitude Greater than the maximum limit value of reactive current At that time, based on the reactive power priority strategy, the positive sequence reactive current reference value is... and negative sequence reactive current reference value The corresponding positive sequence reactive current derating factors are applied respectively. and negative sequence reactive current derating factor Make proportional adjustments to obtain the reference value of the positive sequence reactive current after dereasing. With negative sequence reactive current reference value Otherwise, maintain the current positive sequence power current reference value. With negative sequence reactive current reference value The process remains unchanged, and proceeds to step S8; S7, based on the derated positive sequence reactive current reference value and negative sequence reactive current reference value Recalculate the positive sequence reactive current reference value. and negative sequence reactive current reference value The sum of the absolute values ​​of the positive sequence reactive current reference value is used to calculate the positive sequence reactive current reference value. and negative sequence reactive current reference value The sum of the absolute values ​​is used as the updated reactive current given magnitude. ; S8. Based on the maximum current limit of the converter and the current reactive current reference value, calculate the maximum allowable amplitude of the active current, and adjust the original active current reference value according to the maximum allowable amplitude. Dynamic limiting is performed to obtain the final active current reference value; S9, the reference value of the limited active current. Reference value of positive sequence reactive current after dereasing and the reference value of negative sequence reactive current after derating As the final current control command output, it is used to drive the converter to provide active and reactive power support to the grid in accordance with the selected reactive power priority strategy during fault ride-through.

[0007] In the converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority described in this invention, the reactive current support characteristic in step S3 includes the positive-sequence reactive current support coefficient. and negative sequence reactive current support coefficient ; The positive sequence reactive current reference value The positive-sequence reactive power increment is obtained by superimposing the pre-fault reactive current reference value, where the positive-sequence reactive power increment is... ; The negative sequence reactive current reference value Equal to the negative-sequence reactive power increment, wherein the negative-sequence reactive power increment is ; in, For positive sequence reactive power calculation voltage, It is a negative sequence voltage. This is the rated current of the converter.

[0008] In the converter fault-crossing reactive power support method with adjustable positive and negative sequence reactive power priority described in this invention; in step S3, the positive sequence reactive power calculation voltage... Establish a threshold for low-voltage ride-through. With positive sequence voltage The difference, i.e. It is a positive sequence voltage during high voltage ride-through. High voltage ride-through confirmation threshold The difference, i.e. .

[0009] In the converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority described in this invention; in step S4, if the positive-sequence reactive current reference value... Greater than the preset maximum reactive current limit Then the positive sequence reactive current reference value Set as If the positive sequence reactive current reference value is less than the preset negative reactive current maximum limit value... Then the positive sequence reactive current reference value will be... Set as If the negative sequence reactive current reference value Greater than the preset maximum reactive current limit Then the negative sequence reactive current reference value Set as If the negative sequence reactive current reference value Less than the maximum limit value of negative reactive current Then the negative sequence reactive current reference value Set as .

[0010] In the converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority described in this invention; in step S5, the reference value of the positive-sequence reactive current after limiting is... The absolute value of the positive sequence reactive current reference value is used. The absolute value is used as the given magnitude of the positive sequence reactive current. The reference value of negative sequence reactive current after limiting The absolute value of the negative sequence reactive current reference value is used. The absolute value is used as the given magnitude of the negative sequence reactive current. ; The positive sequence reactive current is given a magnitude value. With respect to the given magnitude of the negative sequence reactive current Adding them together, we obtain the given modulus of reactive current. .

[0011] In the converter fault-crossing reactive power support method with adjustable positive and negative sequence reactive power priority described in this invention; in step S6, if the reactive current has a given modulus value Greater than the preset maximum reactive current limit If the condition is met, the differentiated derating process is executed; otherwise, the positive sequence reactive current reference value is maintained. and the negative sequence reactive current reference value The process remains unchanged, and proceeds to step S8.

[0012] In the converter fault-crossing reactive power support method with adjustable positive and negative sequence reactive power priority described in this invention; in step S6, under the positive sequence priority mode, the differentiated derating processing includes: If the positive sequence reactive current is given a magnitude Greater than or equal to the maximum limit value of the reactive current Then the negative sequence reactive current derating factor will be... Set it to zero; and set the positive sequence reactive current derating factor to zero. Set to the maximum limit value of reactive current The absolute value of the positive sequence reactive current given magnitude The ratio; Otherwise, the positive sequence reactive current derating factor is... Set to 1.0; and calculate the first temporary value. The first temporary value The maximum limit value of the reactive current The absolute value of the positive sequence reactive current given magnitude difference; For the first temporary value Perform lower limit protection to make the first temporary value Not less than the preset minimum positive value; Based on the first temporary value after lower limit protection As an upper limit, a given magnitude is applied to the sequence reactive current. Amplitude limiting is applied to obtain a second temporary value. ; wherein the second temporary value Equal to the given magnitude of the negative sequence reactive current Compared with the first temporary value after lower limit protection The minimum value in; If the negative sequence reactive current has a given magnitude If the value is greater than zero, then the derating factor of the negative sequence reactive current will be... Set to the second temporary value With respect to the given magnitude of the negative sequence reactive current The ratio; otherwise, the negative sequence reactive current is given a modulus value. Set to 1.0; Based on the positive sequence reactive current derating factor and the negative sequence reactive current derating factor The original positive sequence reactive current reference values ​​were respectively... and negative sequence reactive current reference value After adjusting the ratio, the reference value of the positive sequence reactive current after dereasing is obtained. and the reference value of negative sequence reactive current after derating ; The preset minimum positive value is an engineering safety threshold to prevent abnormal calculation of the derating factor or output jitter, and its value ranges from 0.001 to 0.01 times the rated current of the converter.

[0013] In the converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority described in this invention; in step S6, under the proportional derating mode, the differentiated derating processing includes: If the reactive current is given a magnitude Greater than the maximum limit value of reactive current Then calculate the positive sequence reactive current derating factor. The positive sequence reactive current derating factor The maximum limit value of the reactive current With the given modulus of the reactive current The ratio; Degradation factor for negative sequence reactive current Set to the derating factor of the positive sequence reactive current equal; Otherwise, maintain the positive sequence reactive current reference value. and negative sequence reactive current reference value constant; Based on the positive sequence reactive current derating factor and the negative sequence reactive current derating factor The original positive sequence reactive current reference values ​​were respectively... and negative sequence reactive current reference value After adjusting the ratio, the reference value of the positive sequence reactive current after dereasing is obtained. and the reference value of negative sequence reactive current after derating .

[0014] In the converter fault-crossing reactive power support method with adjustable positive and negative sequence reactive power priority described in this invention; in step S6, under the negative sequence priority mode, the differentiated derating processing includes: If the negative sequence reactive current has a given magnitude Greater than or equal to the maximum limit value of the reactive current Then the positive sequence reactive current derating factor will be... Set it to zero; and set the negative sequence reactive current derating factor to zero. Set to the maximum limit value of reactive current The absolute value of the negative sequence reactive current and the given magnitude of the reactive current The ratio; Otherwise, the negative sequence reactive current derating factor will be... Set to 1.0; and calculate the first temporary value. The first temporary value The maximum limit value of the reactive current The absolute value of the negative sequence reactive current and the given magnitude of the reactive current difference; For the first temporary value Perform lower limit protection so that the first temporary value Not less than a preset minimum positive value, wherein the preset minimum positive value is an engineering safety threshold to prevent abnormal calculation of the derating factor or output jitter, and its value range is 0.001 to 0.01 times the rated current of the converter; Based on the first temporary value after lower limit protection As an upper limit, a given magnitude is applied to the positive sequence reactive current. Amplitude limiting is applied to obtain a second temporary value. Wherein the second temporary value Equal to the given modulus of the positive sequence reactive current The first temporary value after lower limit protection The minimum value in; If the positive sequence reactive current is given a magnitude If the value is greater than zero, then the positive sequence reactive current derating factor will be increased. Set to the second temporary value With respect to the given modulus of the positive sequence reactive current The ratio; otherwise, the positive sequence reactive current derating factor. Set to 1.0; Based on the positive sequence reactive current derating factor and the negative sequence reactive current derating factor The original positive sequence reactive current reference values ​​were respectively... and negative sequence reactive current reference value After adjusting the ratio, the reference value of the positive sequence reactive current after dereasing is obtained. and the reference value of negative sequence reactive current after derating .

[0015] In the converter fault-crossing reactive power support method with adjustable positive and negative sequence reactive power priority described in this invention; in step S8, the active current reference value is... Dynamic limiting includes: Calculate an intermediate value that is equal to the maximum current limit of the converter. The square of the given reactive current magnitude The difference of squares; If the intermediate value is greater than zero, then take the square root of the intermediate value to obtain the maximum allowable amplitude of the active current. Otherwise, the maximum allowable amplitude of the active current will be... Set to zero; Based on the maximum permissible amplitude of the active current Reference value of active current before the fault Amplitude limiting is applied to obtain the final active current reference value. .

[0016] The present invention provides a converter fault ride-through reactive power support method with adjustable positive and negative sequence reactive power priority. By introducing a user-pre-configured reactive power priority strategy into the fault ride-through control and constructing a corresponding differentiated derating mechanism for positive and negative sequence reactive current reference values, the present invention effectively solves the technical problem of rigid reactive power support capacity allocation and difficulty in adapting to diverse grid connection requirements when existing converters cope with asymmetrical grid faults.

[0017] Specifically, this application first generates initial positive-sequence reactive current reference values ​​and negative-sequence reactive current reference values ​​based on the positive-sequence and negative-sequence voltages of the power grid, and then independently limits their amplitudes. Subsequently, the absolute values ​​of the limited positive-sequence and negative-sequence reactive current reference values ​​are added together to obtain the reactive current given modulus. When this combined reactive current given modulus exceeds the preset maximum reactive current limit, the traditional proportional reduction method is no longer used. Instead, differentiated derating is applied to the positive-sequence and negative-sequence reactive current reference values ​​based on the selected reactive power priority strategy. After derating, the updated combined reactive current given modulus is recalculated, and based on this value and the converter's maximum current limit, the maximum allowable amplitude of the active current is calculated. This results in dynamic limiting of the original active current reference value to obtain the final active current reference value.

[0018] Through the above complete control process, the converter can flexibly adapt to the differentiated requirements of different grid connection standards or operating scenarios for positive and negative sequence reactive power support capabilities, under the premise of strictly meeting the total current safety limit and reactive power support specifications, which significantly improves the controllability, adaptability and engineering practicality of reactive power support during fault ride-through. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the workflow of an embodiment of the converter fault-crossing reactive power support method with adjustable positive and negative sequence reactive power priority according to the present invention. Figure 2 This is a flowchart illustrating an embodiment of the converter fault-crossing reactive power support method with adjustable positive and negative sequence reactive power priority according to the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] like Figure 1-2 As shown, Figure 1 This is a flowchart illustrating an embodiment of a converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to the present invention. The method provides a converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority, the method comprising the following steps: In step S1, when an asymmetrical voltage fault is detected in the power grid, the fault ride-through control mode is entered, and the active current reference value before the fault is obtained. and reactive current reference value ; In step S2, the user-preconfigured reactive power priority strategy is obtained, and the preset maximum reactive current limit value and the maximum current limit value of the converter are read; wherein, the reactive power priority strategy includes positive priority mode, negative priority mode or proportional derating mode. In step S3, based on the positive sequence voltage of the power grid and negative sequence voltage Based on the reactive current support characteristics specified in the grid connection specifications, an initial positive sequence reactive current reference value is generated. and negative sequence reactive current reference value Wherein, the positive sequence reactive current reference value The negative sequence reactive current reference value is obtained by superimposing the positive sequence reactive current increment with the reactive current reference value before the fault. Equal to negative-order reactive power increment; In step S4, the positive sequence reactive current reference value is... and negative sequence reactive current reference value Independent amplitude limiting processing is performed on each of them to ensure that the positive sequence reactive current reference value is... and negative sequence reactive current reference value All are limited to the maximum negative reactive current limit. With positive maximum reactive current limit value The closed interval formed Within, the reference values ​​of the positive sequence reactive current after limiting are calculated respectively. The absolute value and negative sequence reactive current reference value The absolute value; In step S5, the positive sequence reactive current reference value is... The absolute value and negative sequence reactive current reference value Adding the absolute values ​​together yields the given modulus of the reactive current. ; In step S6, when the reactive current is given a magnitude... Greater than the maximum limit value of reactive current At that time, based on the reactive power priority strategy, the positive sequence reactive current reference value is... and negative sequence reactive current reference value The corresponding positive sequence reactive current derating factors are applied respectively. and negative sequence reactive current derating factor Make proportional adjustments to obtain the reference value of the positive sequence reactive current after dereasing. With negative sequence reactive current reference value Otherwise, maintain the current positive sequence power current reference value. With negative sequence reactive current reference value The process remains unchanged, and proceeds to step S8; In step S7, based on the derating positive sequence reactive current reference value... and negative sequence reactive current reference value Recalculate the positive sequence reactive current reference value. and negative sequence reactive current reference value The sum of the absolute values ​​of the positive sequence reactive current reference value is used to calculate the positive sequence reactive current reference value. and negative sequence reactive current reference value The sum of the absolute values ​​is used as the updated reactive current given magnitude. ; In step S8, based on the maximum current limit of the converter and the current reactive current reference value, the maximum allowable amplitude of the active current is calculated, and the original active current reference value is adjusted according to the maximum allowable amplitude. Dynamic limiting is performed to obtain the final active current reference value; In step S9, the reference value of the limited active current is... Reference value of positive sequence reactive current after dereasing and the reference value of negative sequence reactive current after derating As the final current control command output, it is used to drive the converter to provide active and reactive power support to the grid in accordance with the selected reactive power priority strategy during fault ride-through.

[0023] In one embodiment, the reactive current support characteristic in step S3 includes a positive-sequence reactive current support coefficient. and negative sequence reactive current support coefficient ; The positive sequence reactive current reference value The positive-sequence reactive power increment is obtained by superimposing the pre-fault reactive current reference value, where the positive-sequence reactive power increment is... ; The negative sequence reactive current reference value Equal to the negative-sequence reactive power increment, wherein the negative-sequence reactive power increment is ; in, For positive sequence reactive power calculation voltage, It is a negative sequence voltage. This is the rated current of the converter.

[0024] In one embodiment, the positive-sequence reactive power calculation voltage in step S3 Establish a threshold for low-voltage ride-through. With positive sequence voltage The difference, i.e. It is a positive sequence voltage during high voltage ride-through. High voltage ride-through confirmation threshold The difference, i.e. .

[0025] In one embodiment, in step S4, if the positive sequence reactive current reference value Greater than the preset maximum reactive current limit Then the positive sequence reactive current reference value Set as If the positive sequence reactive current reference value is less than the preset negative reactive current maximum limit value... Then the positive sequence reactive current reference value will be... Set as If the negative sequence reactive current reference value Greater than the preset maximum reactive current limit Then the negative sequence reactive current reference value Set as If the negative sequence reactive current reference value Less than the maximum limit value of negative reactive current Then the negative sequence reactive current reference value Set as .

[0026] In one embodiment, in step S5, the positive sequence reactive current reference value is limited. The absolute value of the positive sequence reactive current reference value is used. The absolute value is used as the given magnitude of the positive sequence reactive current. The reference value of negative sequence reactive current after limiting The absolute value of the negative sequence reactive current reference value is used. The absolute value is used as the given magnitude of the negative sequence reactive current. ; The positive sequence reactive current is given a magnitude value. With respect to the given magnitude of the negative sequence reactive current Adding them together, we obtain the given modulus of reactive current. .

[0027] In one embodiment, in step S6, if the reactive current has a given modulus... Greater than the preset maximum reactive current limit If the condition is met, the differentiated derating process is executed; otherwise, the positive sequence reactive current reference value is maintained. and the negative sequence reactive current reference value The process remains unchanged, and proceeds to step S8.

[0028] In one embodiment, in step S6, under the positive priority mode, the differentiated de-rating process includes: If the positive sequence reactive current is given a magnitude Greater than or equal to the maximum limit value of the reactive current Then the negative sequence reactive current derating factor will be... Set it to zero; and set the positive sequence reactive current derating factor to zero. Set to the maximum limit value of reactive current The absolute value of the positive sequence reactive current given magnitude The ratio; Otherwise, the positive sequence reactive current derating factor is... Set to 1.0; and calculate the first temporary value. The first temporary value The maximum limit value of the reactive current The absolute value of the positive sequence reactive current given magnitude difference; For the first temporary value Perform lower limit protection to make the first temporary value Not less than the preset minimum positive value; Based on the first temporary value after lower limit protection As an upper limit, a given magnitude is applied to the sequence reactive current. Amplitude limiting is applied to obtain a second temporary value. Wherein the second temporary value Equal to the given magnitude of the negative sequence reactive current Compared with the first temporary value after lower limit protection The minimum value in; If the negative sequence reactive current has a given magnitude If the value is greater than zero, then the derating factor of the negative sequence reactive current will be... Set to the second temporary value With respect to the given magnitude of the negative sequence reactive current The ratio; otherwise, the negative sequence reactive current is given a modulus value. Set to 1.0; Based on the positive sequence reactive current derating factor and the negative sequence reactive current derating factor The original positive sequence reactive current reference values ​​were respectively... and negative sequence reactive current reference value After adjusting the ratio, the reference value of the positive sequence reactive current after dereasing is obtained. and the reference value of negative sequence reactive current after derating ; The preset minimum positive value is an engineering safety threshold to prevent abnormal calculation of the derating factor or output jitter, and its value ranges from 0.001 to 0.01 times the rated current of the converter.

[0029] In one embodiment, in step S6 under the proportional derating mode, the differentiated derating process includes: If the reactive current is given a magnitude Greater than the maximum limit value of reactive current Then calculate the positive sequence reactive current derating factor. The positive sequence reactive current derating factor The maximum limit value of the reactive current With the given modulus of the reactive current The ratio; Degradation factor for negative sequence reactive current Set to the derating factor of the positive sequence reactive current equal; Otherwise, maintain the positive sequence reactive current reference value. and negative sequence reactive current reference value constant; Based on the positive sequence reactive current derating factor and the negative sequence reactive current derating factor The original positive sequence reactive current reference values ​​were respectively... and negative sequence reactive current reference value After adjusting the ratio, the reference value of the positive sequence reactive current after dereasing is obtained. and the reference value of negative sequence reactive current after derating .

[0030] In one embodiment, in step S6 under the negative priority mode, the differentiated de-rating process includes: If the negative sequence reactive current has a given magnitude Greater than or equal to the maximum limit value of the reactive current Then the positive sequence reactive current derating factor will be... Set it to zero; and set the negative sequence reactive current derating factor to zero. Set to the maximum limit value of reactive current The absolute value of the negative sequence reactive current and the given magnitude of the reactive current The ratio; Otherwise, the negative sequence reactive current derating factor will be... Set to 1.0; and calculate the first temporary value. The first temporary value The maximum limit value of the reactive current The absolute value of the negative sequence reactive current and the given magnitude of the reactive current difference; For the first temporary value Perform lower limit protection so that the first temporary value Not less than a preset minimum positive value, wherein the preset minimum positive value is an engineering safety threshold to prevent abnormal calculation of the derating factor or output jitter, and its value range is 0.001 to 0.01 times the rated current of the converter; Based on the first temporary value after lower limit protection As an upper limit, a given magnitude is applied to the positive sequence reactive current. Amplitude limiting is applied to obtain a second temporary value. Wherein the second temporary value Equal to the given modulus of the positive sequence reactive current The first temporary value after lower limit protection The minimum value in; If the positive sequence reactive current is given a magnitude If the value is greater than zero, then the positive sequence reactive current derating factor will be increased. Set to the second temporary value With respect to the given modulus of the positive sequence reactive current The ratio; otherwise, the positive sequence reactive current derating factor. Set to 1.0; Based on the positive sequence reactive current derating factor and the negative sequence reactive current derating factor The original positive sequence reactive current reference values ​​were respectively... and negative sequence reactive current reference value After adjusting the ratio, the reference value of the positive sequence reactive current after dereasing is obtained. and the reference value of negative sequence reactive current after derating .

[0031] In one embodiment, the active current reference value is set in step S8. Dynamic limiting includes: Calculate an intermediate value that is equal to the maximum current limit of the converter. The square of the given reactive current magnitude The difference of squares; If the intermediate value is greater than zero, then take the square root of the intermediate value to obtain the maximum allowable amplitude of the active current. Otherwise, the maximum allowable amplitude of the active current will be... Set to zero; Based on the maximum permissible amplitude of the active current Reference value of active current before the fault Amplitude limiting is applied to obtain the final active current reference value. .

[0032] In one embodiment, the reactive current reference value before the fault in step S1 It is zero under normal operating conditions.

[0033] Specific explanation of the meanings of the symbols used in this application: Low voltage ride-through confirmation threshold; High voltage ride-through confirmation threshold; Calculate the voltage for positive sequence reactive power; Reference value for positive sequence reactive current; : Negative sequence reactive current reference value; Positive sequence reactive current support coefficient; Negative sequence reactive current support coefficient; Positive sequence voltage; Negative sequence voltage; : Rated current of the converter; Reference value for positive sequence reactive current; : Negative sequence reactive current reference value; Active current reference value; : Reactive current reference value; : The preset maximum current limit value of the converter; : Maximum limit value of reactive current; : Positive sequence reactive current given magnitude; Negative sequence reactive current given magnitude; : Reactive current given modulus; : Derating factor for positive sequence reactive current; Negative sequence reactive current derating factor; : Maximum permissible amplitude of active current; Input variable Var, limit its amplitude to a maximum of Max and a minimum of Min, and finally return Var.

[0034] Specifically, this application uses a photovoltaic grid-connected converter as an example, but this application is also applicable to grid-connected power electronic equipment with fault ride-through capability, such as wind power converters and electrochemical energy storage converters.

[0035] When an asymmetrical voltage fault occurs in the power grid (such as a single-phase ground fault, a two-phase short circuit, etc.), the converter control system detects the positive sequence voltage. With negative sequence voltage A significant imbalance occurs. The system is determined to have entered an asymmetrical undervoltage ride-through or overvoltage ride-through state. At this point, the system immediately enters fault ride-through control mode and latches the active current reference value from the moment before the fault. and reactive current reference value Due to positive sequence voltage Below the low voltage ride-through confirmation threshold (Based on standards, typically 0.9 pu), the system confirms entry into asymmetric low-voltage ride-through control mode. At this moment, the system immediately latches and acquires the operating status at the moment before the fault, and at this time, latches the active current reference value at the moment before the fault. and reactive current reference value (All power current reference values) and reactive current reference value All have been per-unit rated, converter rated current ).

[0036] Based on the real-time collected positive sequence voltage and negative sequence voltage Based on the reactive current support characteristics specified in grid connection standards (such as GB / T 34120-2023), the positive sequence reactive power increment is calculated. and negative order reactive power increment ;in, and These are the positive sequence reactive current support coefficient and the negative sequence reactive current support coefficient, respectively. Calculate voltage for positive sequence reactive power: In this embodiment, the positive sequence voltage is acquired in real time. Negative sequence voltage Below the low voltage ride-through confirmation threshold The system has confirmed that it has entered an asymmetric low-voltage ride-through state.

[0037] The system reads the reactive power priority strategy pre-configured by the user through the human-machine interface or communication interface. This strategy can be: positive sequence priority mode, negative sequence priority mode, or proportional derating mode. Simultaneously, the system reads two preset limiting parameters: the maximum reactive current limit value. and the maximum current limit of the converter. ,in The rated current of the converter (per unit) Furthermore, the positive sequence reactive current support factor should be set according to the grid connection standard followed (such as GB / T 34120-2023). Negative sequence reactive current support coefficient ; Positive sequence voltage was collected Negative sequence voltage In conjunction with the aforementioned positive sequence reactive current support coefficient Negative sequence reactive current support coefficient Generate initial positive sequence reactive current reference values. With negative sequence reactive current reference value First, calculate the positive sequence voltage. For low voltage ride-through, This embodiment takes Therefore ; Next, calculate the positive-sequence reactive power increment. Calculate the negative-sequence reactive power increment ,in, ; ; Finally, the initial positive-sequence reactive current reference value is generated. With negative sequence reactive current reference value : ; ; To prevent individual current components from becoming too large, the initial generation of the above-mentioned components is... and Perform independent amplitude limiting separately (e.g., using a Sat limiter, with a limiting range of [...]). [1.5, 1.5]. Since both 1.0736 and 0.7098 are within this range, the value after limiting remains unchanged. ; ; Calculate the given magnitude of the composite reactive current That is, the reference value of positive sequence reactive current after two limiting steps. The absolute value and negative sequence reactive current reference value The sum of absolute values: ; .

[0038] .

[0039] After completing the given modulus of the synthesized reactive current After calculation, if it is determined that FRT_IqRefMag > FRT_IqAbsRefMax (for example, FRT_IqRefMag = 1.7834, while the preset maximum reactive current limit FRT_IqAbsRefMax = 1.1), then the differentiated derating process is initiated. This process is executed in three scenarios based on the reactive current priority strategy selected by the user, as follows: First scenario: Upward-sequence reactive power priority mode When the reactive power support strategy is configured as "positive sequence reactive power priority", the system first checks whether the positive sequence reactive current reference value FRT_IqPosRefMag is less than FRT_IqAbsRefMax. In this example, FRT_IqPosRefMag = 1.0736 < 1.1, which meets the condition. Therefore, the positive sequence reactive current reference value remains unchanged, and its corresponding derating factor IqRefScalDownCoeff is set to 1.0.

[0040] Then, the first temporary value is calculated: Temp1=FRT_IqAbsRefMax FRT_IqPosRefMag=1.1 1.0736 = 0.0264; By applying a lower bound protection to Temp1, i.e., restricting it to the interval [0.001, FRT_IqAbsRefMax] using a saturation function, we obtain: Temp1=Sat(0.0264,1.1,0.001)=0.0264; Using the protected Temp1 as the upper limit, the negative sequence reactive current given modulus FRT_IqNegRefMag=0.7098 is then limited to obtain the second temporary value: Temp2=Sat(FRT_IqNegRefMag,Temp1,0)=Sat(0.7098,0.0264,0)=0.0264; Finally, the derating factor for the negative sequence reactive current reference value is calculated as follows: IqNegRefScalDownCoeff=Temp2 / FRT_IqNegRefMag=0.0264 / 0.7098≈0.0372; The second scenario: proportional derating mode for positive and negative sequence reactive currents. When the policy is configured as "proportional reduction" and FRT_IqRefMag > FRT_IqAbsRefMax, calculate the uniform reduction factor: IqRefScalDownCoeff=FRT_IqAbsRefMax / FRT_IqRefMag=1.1 / 1.7834≈0.6168; This coefficient is applied to both positive-sequence and negative-sequence reactive current reference values, that is: IqNegRefScalDownCoeff=IqRefScalDownCoeff=0.6168; The third scenario: Negative-order reactive power priority mode When the strategy is configured as "negative sequence reactive power priority", the given modulus value of negative sequence reactive current is checked and found to be FRT_IqNegRefMag=0.7098<1.1, which meets the condition. Therefore, the reference value of negative sequence reactive current remains unchanged, and its derating factor IqNegRefScalDownCoeff=1.0.

[0041] Calculate the first temporary value: Temp1=FRT_IqAbsRefMax FRT_IqNegRefMag=1.1 0.7098 = 0.3902; After lower limit protection: Temp1 = Sat(0.3902, 1.1, 0.001) = 0.3902; then, the positive sequence reactive current given modulus FRT_IqPosRefMag = 1.073 is limited: Temp2 = Sat(1.0736, 0.3902, 0) = 0.3902; finally, the derating factor of the positive sequence reactive current reference value is: IqRefScalDownCoeff = Temp2 / FRT_IqPosRefMag = 0.3902 / 1.0736 ≈ 0.3635.

[0042] Through differentiated derating processing under the above three strategies, the system can flexibly allocate the output capacity of positive and negative sequence reactive current according to the operating requirements when the total reactive demand exceeds the limit, ensuring that the converter meets the grid connection specifications and achieves the optimal grid support effect during fault ride-through.

[0043] Specifically; Case 1: Ascending order priority mode like If the positive-order reactive power is completely preserved, then the negative-order reactive power is restricted to not exceeding the difference between the two:

[0044] ;final, ;

[0045] .

[0046] Case 2: Negative order priority mode like Then, negative-order reactive power is completely preserved, while positive-order reactive power is restricted to not exceeding the difference between the two: ,final ; .

[0047] Scenario 3: Proportional Reduction Model Positive sequence reactive current derating factor With negative sequence reactive current derating factor When the values ​​are the same, this value is the ratio of the limit value to the demand: .

[0048] final, ; .

[0049] After derating using any of the above modes, the new composite reactive current given modulus is 1.1, which meets the reactive current limiting requirements.

[0050] Based on the reference value of reactive current after dereasing (Its composite modulus is 1.1) and the maximum limit of the total current of the converter (1.2), for the active current reference value Dynamic limiting is implemented to ensure that the total output current does not exceed the limit.

[0051] Calculate the maximum allowable amplitude of the active current: Calculate the intermediate value in Due to the intermediate value Taking the square root of the median value yields: ; The original active current reference value Limit to [ Within the range of 0.4796, the final active current reference value is obtained: .

[0052] It should be noted that since the combined reactive power after the dereasing of the three modes—positive priority mode, negative priority mode, and equal proportional dereasing mode—is 1.1, the active power limiting results are the same.

[0053] The system will ultimately determine the active current reference value. Positive sequence reactive current reference value and negative sequence reactive current reference value These commands serve as instructions for the current control loop. The control results, after being tracked by the regulator, are then pulse-width modulated to drive the power devices of the converter, enabling them to inject precisely controllable positive-sequence and negative-sequence reactive currents into the grid during fault ride-through, in accordance with the selected reactive power priority strategy.

[0054] This application can flexibly implement three different reactive power support strategies—positive sequence priority, negative sequence priority, or proportional derating—under the same fault scenario, based on user configuration. This effectively solves the problem that existing technologies only support a single derating strategy (such as proportional derating) and cannot meet diverse certification and application requirements, successfully achieving the technical objective of adjustable priority for positive and negative sequence reactive power support capabilities during converter fault ride-through.

[0055] In this embodiment, all limiting and calculations are completed in real time in a digital controller (such as a DSP or FPGA), ensuring precise control and meeting the accuracy requirements of grid connection standards.

[0056] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0057] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods according to the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal device (which may be a mobile phone, computer, server, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0058] Therefore, the above description is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A converter fault-through reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority, characterized in that, The method includes the following steps: S1, when an asymmetrical voltage fault is detected in the power grid, enters the fault ride-through control mode and obtains the active current reference value before the fault. and reactive current reference value ; S2, obtain the user-preconfigured reactive power priority strategy, and read the preset maximum reactive current limit value and the maximum current limit value of the converter; wherein, the reactive power priority strategy includes positive sequence priority mode, negative sequence priority mode or proportional derating mode. S3, based on the positive sequence voltage of the power grid and negative sequence voltage Based on the reactive current support characteristics specified in the grid connection specifications, an initial positive sequence reactive current reference value is generated. and negative sequence reactive current reference value Wherein, the positive sequence reactive current reference value The negative sequence reactive current reference value is obtained by superimposing the positive sequence reactive current increment with the reactive current reference value before the fault. Equal to negative-order reactive power increment; S4, regarding the positive sequence reactive current reference value and negative sequence reactive current reference value Independent amplitude limiting processing is performed on each of them to ensure that the positive sequence reactive current reference value is... and negative sequence reactive current reference value All are limited to the maximum negative reactive current limit. With positive maximum reactive current limit value The closed interval formed Within, the reference values ​​of the positive sequence reactive current after limiting are calculated respectively. The absolute value and negative sequence reactive current reference value The absolute value; S5, the positive sequence reactive current reference value The absolute value and negative sequence reactive current reference value Adding the absolute values ​​together yields the given modulus of the reactive current. ; S6, when the reactive current is given a magnitude Greater than the maximum limit value of reactive current At that time, based on the reactive power priority strategy, the positive sequence reactive current reference value is... and negative sequence reactive current reference value The corresponding positive sequence reactive current derating factors are applied respectively. and negative sequence reactive current derating factor Make proportional adjustments to obtain the reference value of the positive sequence reactive current after dereasing. With negative sequence reactive current reference value Otherwise, maintain the current positive sequence power current reference value. With negative sequence reactive current reference value The process remains unchanged, and proceeds to step S8; S7, based on the derated positive sequence reactive current reference value and negative sequence reactive current reference value Recalculate the positive sequence reactive current reference value. and negative sequence reactive current reference value The sum of the absolute values ​​of the positive sequence reactive current reference value is used to calculate the positive sequence reactive current reference value. and negative sequence reactive current reference value The sum of the absolute values ​​is used as the updated reactive current given magnitude. ; S8. Based on the maximum current limit of the converter and the current reactive current reference value, calculate the maximum allowable amplitude of the active current, and adjust the original active current reference value according to the maximum allowable amplitude. Dynamic limiting is performed to obtain the final active current reference value; S9, the reference value of the limited active current. Reference value of positive sequence reactive current after dereasing and the reference value of negative sequence reactive current after derating As the final current control command output, it is used to drive the converter to provide active and reactive power support to the grid in accordance with the selected reactive power priority strategy during fault ride-through.

2. The converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to claim 1, characterized in that, The reactive current support characteristic in step S3 includes the positive sequence reactive current support coefficient. and negative sequence reactive current support coefficient ; The positive sequence reactive current reference value The positive-sequence reactive power increment is obtained by superimposing the pre-fault reactive current reference value, where the positive-sequence reactive power increment is... ; The negative sequence reactive current reference value Equal to the negative-sequence reactive power increment, wherein the negative-sequence reactive power increment is ; in, For positive sequence reactive power calculation voltage, It is a negative sequence voltage. This is the rated current of the converter.

3. The converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to claim 3, characterized in that, The positive sequence reactive power calculation voltage in step S3 Establish a threshold for low-voltage ride-through. With positive sequence voltage The difference, i.e. It is a positive sequence voltage during high voltage ride-through. High voltage ride-through confirmation threshold The difference, i.e. .

4. The converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to claim 1, characterized in that, In step S4, if the positive sequence reactive current reference value Greater than the preset maximum reactive current limit Then the positive sequence reactive current reference value Set as ; If the positive sequence reactive current reference value is less than the preset negative reactive current maximum limit value Then the positive sequence reactive current reference value will be... Set as ; If the negative sequence reactive current reference value Greater than the preset maximum reactive current limit Then the negative sequence reactive current reference value Set as ; If the negative sequence reactive current reference value Less than the maximum limit value of negative reactive current Then the negative sequence reactive current reference value Set as .

5. The converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to claim 1, characterized in that, In step S5, the positive sequence reactive current reference value after limiting is... The absolute value of the positive sequence reactive current reference value is used. The absolute value is used as the given magnitude of the positive sequence reactive current. The reference value of negative sequence reactive current after limiting The absolute value of the negative sequence reactive current reference value is used. The absolute value is used as the given magnitude of the negative sequence reactive current. ; The positive sequence reactive current is given a magnitude value. With respect to the given magnitude of the negative sequence reactive current Adding them together, we obtain the given modulus of reactive current. .

6. The converter fault-through reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to claim 5, characterized in that, In step S6, if the reactive current is given a magnitude... Greater than the preset maximum reactive current limit If so, the differentiated deduction process will be executed; Otherwise, maintain the aforementioned positive sequence reactive current reference value. and the negative sequence reactive current reference value The process remains unchanged, and proceeds to step S8.

7. The converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to claim 6, characterized in that, In step S6, under the positive priority mode, the differentiated debit processing includes: If the positive sequence reactive current is given a magnitude Greater than or equal to the maximum limit value of the reactive current Then the negative sequence reactive current derating factor will be... Set it to zero; and set the positive sequence reactive current derating factor to zero. Set to the maximum limit value of reactive current The absolute value of the positive sequence reactive current given magnitude The ratio; Otherwise, the positive sequence reactive current derating factor is... Set to 1.0; and calculate the first temporary value. The first temporary value The maximum limit value of the reactive current The absolute value of the positive sequence reactive current given magnitude difference; For the first temporary value Perform lower limit protection to make the first temporary value Not less than the preset minimum positive value; Based on the first temporary value after lower limit protection As an upper limit, a given magnitude is applied to the sequence reactive current. Amplitude limiting is applied to obtain a second temporary value. ; wherein the second temporary value Equal to the given magnitude of the negative sequence reactive current Compared with the first temporary value after lower limit protection The minimum value in; If the negative sequence reactive current has a given magnitude If the value is greater than zero, then the derating factor of the negative sequence reactive current will be... Set to the second temporary value With respect to the given magnitude of the negative sequence reactive current The ratio; otherwise, the negative sequence reactive current is given a modulus value. Set to 1.0; Based on the positive sequence reactive current derating factor and the negative sequence reactive current derating factor The original positive sequence reactive current reference values ​​were respectively... and negative sequence reactive current reference value After adjusting the ratio, the reference value of the positive sequence reactive current after dereasing is obtained. and the reference value of negative sequence reactive current after derating ; The preset minimum positive value is an engineering safety threshold to prevent abnormal calculation of the derating factor or output jitter, and its value ranges from 0.001 to 0.01 times the rated current of the converter.

8. The converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to claim 7, characterized in that, In step S6, under the proportional derating mode, the differentiated derating process includes: If the reactive current is given a magnitude Greater than the maximum limit value of reactive current Then calculate the positive sequence reactive current derating factor. The positive sequence reactive current derating factor The maximum limit value of the reactive current With the given modulus of the reactive current The ratio; Degradation factor for negative sequence reactive current Set to the derating factor of the positive sequence reactive current equal; Otherwise, maintain the positive sequence reactive current reference value. and negative sequence reactive current reference value constant; Based on the positive sequence reactive current derating factor and the negative sequence reactive current derating factor The original positive sequence reactive current reference values ​​were respectively... and negative sequence reactive current reference value After adjusting the ratio, the reference value of the positive sequence reactive current after dereasing is obtained. and the reference value of negative sequence reactive current after derating .

9. The converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to claim 7, characterized in that, In step S6, under the negative priority mode, the differentiated debit processing includes: If the negative sequence reactive current has a given magnitude Greater than or equal to the maximum limit value of the reactive current Then the positive sequence reactive current derating factor will be... Set it to zero; and set the negative sequence reactive current derating factor to zero. Set to the maximum limit value of reactive current The absolute value of the negative sequence reactive current and the given magnitude of the reactive current The ratio; Otherwise, the negative sequence reactive current derating factor will be... Set to 1.0; and calculate the first temporary value. The first temporary value The maximum limit value of the reactive current The absolute value of the negative sequence reactive current and the given magnitude of the reactive current difference; For the first temporary value Perform lower limit protection so that the first temporary value Not less than a preset minimum positive value, wherein the preset minimum positive value is an engineering safety threshold to prevent abnormal calculation of the derating factor or output jitter, and its value range is 0.001 to 0.01 times the rated current of the converter; Based on the first temporary value after lower limit protection As an upper limit, a given magnitude is applied to the positive sequence reactive current. Amplitude limiting is applied to obtain a second temporary value. The second temporary value Equal to the given modulus of the positive sequence reactive current The first temporary value after lower limit protection The minimum value in; If the positive sequence reactive current is given a magnitude If the value is greater than zero, then the positive sequence reactive current derating factor will be increased. Set to the second temporary value With respect to the given modulus of the positive sequence reactive current The ratio; otherwise, the positive sequence reactive current derating factor. Set to 1.0; Based on the positive sequence reactive current derating factor and the negative sequence reactive current derating factor The original positive sequence reactive current reference values ​​were respectively... and negative sequence reactive current reference value After adjusting the ratio, the reference value of the positive sequence reactive current after dereasing is obtained. and the reference value of negative sequence reactive current after derating .

10. The converter fault-crossing reactive power support method with adjustable positive-sequence and negative-sequence reactive power priority according to claim 1, characterized in that, In step S8, the active current reference value is... Dynamic limiting includes: Calculate an intermediate value that is equal to the maximum current limit of the converter. The square of the given reactive current magnitude The difference of squares; If the intermediate value is greater than zero, then take the square root of the intermediate value to obtain the maximum allowable amplitude of the active current. Otherwise, the maximum allowable amplitude of the active current will be... Set to zero; Based on the maximum permissible amplitude of the active current Reference value of active current before the fault Amplitude limiting is applied to obtain the final active current reference value. .

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