A distributed photovoltaic fault steady-state model equivalent method, system, device and storage medium

Abstract

The application discloses a distributed photovoltaic fault steady-state model equivalent method, system, device and storage medium, belongs to the distributed photovoltaic technical field, and comprises the following steps: acquiring grid-connected voltage grades and rated parameters of distributed photovoltaics; determining corresponding grid-connected control strategies and fault ride-through control strategies according to different grid-connected voltage grades; for different grid-connected voltage grades, combining the grid-connected control strategies and the fault ride-through control strategies and the rated parameters, corresponding fault steady-state models are established, the equivalent of the steady-state model after the fault of the distributed photovoltaic is realized, and a reliable tool is provided for the stability analysis of a power grid with a high proportion of photovoltaic access.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of distributed photovoltaic technology, and particularly relates to a distributed photovoltaic fault steady-state model equivalent method, system, device and storage medium. BACKGROUND

[0002] At present, the fault characteristics of distributed photovoltaic are obviously different from traditional synchronous machines and centralized new energy stations, and the existing engineering short-circuit current calculation cannot be applied to distributed photovoltaic. Distributed photovoltaic is connected to the grid through power electronic devices, and its fault characteristics are constrained by the control strategy and control parameters of the grid-connected power electronic devices. Because of the complex and diverse control strategy, gray-box model parameters, and no stable electromotive force after fault, the short-circuit current calculation method of traditional power sources and their grid-connected systems cannot be followed. Especially for distributed photovoltaic connected to 10kV user-side power grid or through 380V grid, there is no clear fault ride-through requirement, and the short-circuit current characteristics are not clear, and the short-circuit current calculation method depends on data mining and current-voltage mapping.

[0003] Therefore, it is necessary to establish a practical distributed photovoltaic fault steady-state model equivalent method to improve the action performance of distribution system line protection, improve its adaptability and tolerance to short-circuit faults, and reduce the loss of distributed photovoltaic power generation off-grid power failure. SUMMARY

[0004] In view of the above problems, the present application is proposed.

[0005] Therefore, the technical problem solved by the present application is to solve the problem that there is no practical steady-state equivalent model after the fault of distributed photovoltaic, which leads to inaccurate short-circuit current calculation and affects the protection setting and fault ride-through capability evaluation of distribution network.

[0006] To solve the above technical problems, the present application provides the following technical scheme: a distributed photovoltaic fault steady-state model equivalent method, comprising:

[0007] obtaining the grid-connected voltage level and rated parameters of the distributed photovoltaic;

[0008] determining the corresponding grid-connected control strategy and fault ride-through control strategy according to different grid-connected voltage levels;

[0009] For different grid-connected voltage levels, the corresponding fault steady-state model is established by combining the grid-connected control strategy and fault ride-through control strategy and the rated parameters, so as to realize the equivalence of the steady-state model after the fault of distributed photovoltaic;

[0010] The grid-connected control strategy is adopted when no fault is detected, and the strategy target is achieved by controlling current, including, for the grid-connected device with sequence control capability, suppressing negative sequence current and tracking active power and reactive power instruction values set by the system or itself while configuring current limiting measures, and for the grid-connected device without sequence control capability, still tracking active power and reactive power instruction values while not distinguishing sequence components during control;

[0011] The fault ride-through control strategy is adopted when the positive sequence or non-sequence grid-connected point voltage drops to a set level, and the strategy target is achieved by controlling current, including, for the grid-connected device with sequence control capability, injecting positive sequence reactive current related to the voltage drop level, injecting positive sequence active current in the remaining capacity in a large mode, injecting positive sequence active current in a linear relationship with positive sequence reactive current under the constraint of an amplitude value in a small mode, absorbing negative sequence reactive current related to the voltage drop level, and suppressing negative sequence active current, and for the grid-connected device without sequence control capability, injecting reactive current related to the voltage drop level, injecting active current in the remaining capacity in a large mode, and injecting active current in a linear relationship with reactive current under the constraint of an amplitude value in a small mode, and not distinguishing sequence components during control.

[0012] As a preferred scheme of the distributed photovoltaic fault steady-state model equivalent method, the corresponding grid-connected control strategy and fault ride-through control strategy are determined, including:

[0013] The positive sequence current component and the negative sequence current component are calculated according to the rated parameters, the positive sequence current component and the negative sequence current component are converted into currents in a three-phase coordinate system, and a three-phase steady-state short-circuit current is obtained;

[0014] The distributed photovoltaic fault steady-state model of the 10kV and above voltage level grid-connected and the 380V voltage level grid-connected is obtained in combination with the three-phase steady-state short-circuit current.

[0015] As a preferred scheme of the distributed photovoltaic fault steady-state model equivalent method, the distributed photovoltaic fault steady-state model of the 10kV and above voltage level grid-connected includes:

[0016] The distributed photovoltaic fault steady-state equivalent positive sequence model includes a steady-state value of a short-circuit current, a reactive positive sequence component and an active positive sequence component;

[0017] For the reactive positive sequence component, when the positive sequence voltage of the distributed photovoltaic grid-connected point is greater than or equal to a first threshold value, no reactive current is injected, and the reactive current component is equal to 0;

[0018] When the positive sequence voltage of the distributed photovoltaic grid-connected point is less than the first threshold value, a linear adjustment value is calculated, the linear adjustment value is compared with a reactive current amplitude limit value of the distributed photovoltaic, and the minimum value is taken as the injected reactive current component;

[0019] For the active positive sequence component, when the large mode is operated and the positive sequence voltage of the distributed photovoltaic grid-connected point is greater than or equal to the voltage threshold value, the power maintenance demand value and the capacity safety limit value are calculated, and the minimum value of the calculation results is taken as the injected active current component;

[0020] When the small mode is operated and the positive sequence voltage of the distributed photovoltaic grid-connected point is greater than or equal to the voltage threshold value, the power maintenance demand value and the maximum linear residual capacity are calculated, and the minimum value of the calculation results is taken as the injected active current component;

[0021] When the positive sequence voltage of the distributed photovoltaic grid-connected point is less than the voltage threshold value, the linear regulation strategy is used to calculate the injected active current component.

[0022] The beneficial effect of the preferred technical scheme is that the distribution network protection setting accuracy and the fault ride-through capability evaluation reliability are significantly improved by accurately modeling the photovoltaic fault current characteristics, and the safe and stable operation of the power grid is optimized.

[0023] As a preferred scheme of the equivalent method of the distributed photovoltaic fault steady-state model, the equivalent method further comprises:

[0024] The distributed photovoltaic fault steady-state equivalent negative sequence model comprises a short-circuit current steady-state value, a reactive negative sequence component and an active negative sequence component;

[0025] The reactive negative sequence component is a ratio of the negative sequence voltage of the distributed photovoltaic grid-connected point to the equivalent reactive negative sequence impedance of the corresponding distributed photovoltaic;

[0026] The active negative sequence component is a ratio of the negative sequence voltage of the distributed photovoltaic grid-connected point to the equivalent active negative sequence impedance of the corresponding distributed photovoltaic.

[0027] The beneficial effect of the preferred technical scheme is that the response capability of the photovoltaic system to the unbalanced fault of the power grid is effectively evaluated by accurately modeling the negative sequence current characteristics, and the protection coordination precision and the power grid stability under asymmetric fault are improved.

[0028] As a preferred scheme of the equivalent method of the distributed photovoltaic fault steady-state model, the equivalent method further comprises:

[0029] The distributed photovoltaic fault steady-state equivalent positive sequence model comprises a distributed photovoltaic with fault ride-through capability and a distributed photovoltaic without fault ride-through capability;

[0030] For the distributed photovoltaic fault steady-state equivalent positive sequence model, the steady-state value of the short-circuit current reactive positive sequence component and the steady-state value of the short-circuit current active positive sequence component of the distributed photovoltaic with fault ride-through capability are consistent with the steady-state value of the short-circuit current reactive positive sequence component and the steady-state value of the short-circuit current active positive sequence component of the distributed photovoltaic fault steady-state model of the 10kV and above voltage level grid-connected distributed photovoltaic.

[0031] The beneficial effect of the preferred technical solution is that the 380V photovoltaic system is modeled differently to accurately reflect the difference in fault ride-through capability, thereby improving the protection setting accuracy and fault analysis reliability of the low-voltage distribution network.

[0032] As a preferred scheme of the distributed photovoltaic fault steady-state model equivalent method of the application, the distributed photovoltaic fault steady-state equivalent positive sequence model without fault ride-through capability includes:

[0033] For the steady-state value of the short-circuit current reactive positive sequence component of the distributed photovoltaic without fault ride-through capability, when the positive sequence voltage at the distributed photovoltaic grid-connected point is less than or equal to the off-grid voltage threshold, the reactive positive sequence component is equal to 0.

[0034] When the positive sequence voltage at the distributed photovoltaic grid-connected point is greater than the off-grid voltage threshold, the minimum value of the comparison between the calculated value of the pre-fault reactive power and the current voltage demand and the reactive current limiting value of the distributed photovoltaic is taken as the injected reactive current component.

[0035] For the steady-state value of the short-circuit current active positive sequence component of the distributed photovoltaic without fault ride-through capability, when the positive sequence voltage at the distributed photovoltaic grid-connected point is less than or equal to the off-grid voltage threshold, the active positive sequence component is equal to 0.

[0036] When the positive sequence voltage at the distributed photovoltaic grid-connected point is greater than the off-grid voltage threshold, the minimum value of the comparison between the calculated value of the pre-fault active power and the current voltage demand and the active current limiting value of the distributed photovoltaic is taken as the injected active current component.

[0037] The beneficial effect of the preferred technical solution is that the off-grid characteristics of non-ride-through photovoltaics are accurately simulated to ensure that the fault analysis results are closer to the actual operating conditions, thereby improving the action reliability of the protection device.

[0038] As a preferred scheme of the distributed photovoltaic fault steady-state model equivalent method of the application, the distributed photovoltaic fault steady-state equivalent negative sequence model includes:

[0039] In the distributed photovoltaic fault steady-state equivalent negative sequence model, the steady-state value of the short-circuit current reactive negative sequence component of the distributed photovoltaic with sequence control capability and fault ride-through capability is the ratio of the negative sequence voltage at the distributed photovoltaic grid-connected point to the equivalent reactive negative sequence impedance of the corresponding distributed photovoltaic.

[0040] The active negative sequence component is the ratio of the negative sequence voltage of the grid-connected point of the distributed photovoltaic to the equivalent active negative sequence impedance of the corresponding distributed photovoltaic.

[0041] For the distributed photovoltaic with the sequence control ability and without the fault ride-through ability, the active negative sequence component and the reactive negative sequence component are both 0.

[0042] For the distributed photovoltaic without the sequence control ability and with the fault ride-through ability, when the grid-connected point voltage feed-forward compensation term exists and when the grid-connected point voltage feed-forward compensation term does not exist.

[0043] When the grid-connected point voltage feed-forward compensation term exists, the active negative sequence component and the reactive negative sequence component are both 0.

[0044] When the grid-connected point voltage feed-forward compensation term does not exist, the active negative sequence component and the reactive negative sequence component are the ratio of the negative sequence voltage of the grid-connected point of the distributed photovoltaic to the equivalent active and reactive negative sequence impedance of the corresponding distributed photovoltaic.

[0045] The beneficial effects of the preferred technical scheme are that the negative sequence response characteristics of the photovoltaic under different control strategies are modeled in detail, the accuracy of the asymmetric fault analysis is significantly improved, and the power grid protection cooperation scheme is optimized.

[0046] The application provides a distributed photovoltaic fault steady-state model equivalent system.

[0047] To solve the above technical problems, the application provides the following technical scheme: a distributed photovoltaic fault steady-state model equivalent system, comprising:

[0048] A data acquisition module is configured to acquire the grid-connected voltage level and rated parameters of the distributed photovoltaic.

[0049] A strategy determination module is configured to determine corresponding grid-connected control strategies and fault ride-through control strategies according to different grid-connected voltage levels.

[0050] A model construction module is configured to, for different grid-connected voltage levels, establish corresponding fault steady-state models in combination with the grid-connected control strategies and the fault ride-through control strategies and the rated parameters, so as to realize the equivalence of the steady-state model of the distributed photovoltaic after a fault occurs.

[0051] A grid-connected control strategy module is configured to be used when the grid-connected control strategy is not detected to have a fault, and the strategy target is realized by a control current, including, for the distributed photovoltaic with the sequence control ability, suppressing the negative sequence current and tracking the active power and reactive power instruction values set by the system or itself while configuring the current limiting measures, and for the distributed photovoltaic without the sequence control ability, still tracking the active power and reactive power instruction values, and the control quantity does not distinguish the sequence components during the tracking.

[0052] A fault ride-through control strategy module is configured to adopt the fault ride-through control strategy when detecting that the positive sequence or non-sequence grid connection point voltage drops to a set level, and the strategy target is achieved by controlling the current, including, for the device with sequence control capability, injecting the positive sequence reactive current related to the voltage drop level, injecting the positive sequence active current in the whole remaining capacity in the large mode, injecting the positive sequence active current linearly with the positive sequence reactive current under the constraint of the amplitude limit value in the small mode, absorbing the negative sequence reactive current related to the voltage drop level, and suppressing the negative sequence active current, for the device without sequence control capability, injecting the reactive current related to the voltage drop level, injecting the active current in the whole remaining capacity in the large mode, and injecting the active current linearly with the reactive current under the constraint of the amplitude limit value in the small mode, and the control quantity is not distinguished by sequence components during the period.

[0053] The application provides a computer device, comprising a memory and a processor, and the memory stores a computer program, characterized in that the processor implements the steps of the distributed photovoltaic fault steady-state model equivalent method when executing the computer program.

[0054] The application provides a computer readable storage medium, which stores a computer program, characterized in that the computer program is executed by a processor to implement the steps of the distributed photovoltaic fault steady-state model equivalent method.

[0055] The application has the beneficial effects that the application constructs positive and negative sequence equivalent models for photovoltaic systems of 10kV and above and 380V different voltage levels, covers various scenes with / without fault ride-through capability, sequence control capability and the like, significantly improves the calculation accuracy, accurately reflects the dynamic response (such as reactive power support and active power limiting) of photovoltaic during the fault period through quantitative modeling of positive and negative sequence separation and feedforward compensation control strategies, solves the error problem caused by ignoring control parameters in the traditional method, provides default parameters (such as impedance and limiting coefficient), adapts to the scene of missing device parameters, ensures that the model can be applied, optimizes the fault ride-through capability evaluation, reduces the photovoltaic off-grid risk, and provides a reliable tool for the stability analysis of the power grid with a high proportion of photovoltaic access. BRIEF DESCRIPTION OF DRAWINGS

[0056] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0057] Figure 1 A distributed photovoltaic fault steady-state model equivalent method provided by an embodiment of the application has a general flowchart;

[0058] Figure 2 A topological structure diagram of a distributed photovoltaic access power distribution network provided by a distributed photovoltaic fault steady-state model equivalent method of an embodiment of the present application is shown in FIG. 1.

[0059] Figure 3 A distributed photovoltaic control structure diagram using sequence control provided by a distributed photovoltaic fault steady-state model equivalent method of an embodiment of the present application is shown in FIG. 2.

[0060] Figure 4 A distributed photovoltaic control structure diagram not using sequence control and using voltage feedforward provided by a distributed photovoltaic fault steady-state model equivalent method of an embodiment of the present application is shown in FIG. 3. DETAILED DESCRIPTION

[0061] In order to make the above objectives, characteristics and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor should fall within the scope of protection of the present application.

[0062] Embodiment 1, refer to Figure 1 For an embodiment of the present application, the embodiment provides a distributed photovoltaic fault steady-state model equivalent method, comprising:

[0063] S100: Obtain grid-connected voltage levels and rated parameters of the distributed photovoltaic;

[0064] Specifically, the grid-connected voltage levels and rated parameters of the distributed photovoltaic include grid-connected voltage levels, rated voltage and rated capacity of the distributed photovoltaic.

[0065] S200: Determine corresponding grid-connected control strategies and fault ride-through control strategies according to different grid-connected voltage levels;

[0066] S300: For different grid-connected voltage levels, establish corresponding fault steady-state models in combination with the grid-connected control strategies and the fault ride-through control strategies and the rated parameters, to realize the equivalence of the steady-state model after the distributed photovoltaic fails;

[0067] S400: The grid-connected control strategy is adopted when no fault is detected, and the strategy target is realized by control current, including, for those with sequence control capability, suppressing negative sequence current and tracking active power and reactive power instruction values set by the system or itself while configuring current limiting measures, and for those without sequence control capability, still tracking the active power and reactive power instruction values, and the control quantity is not distinguished by sequence components during the period;

[0068] S500: the fault ride-through control strategy is adopted when the positive sequence or non-sequence grid connection point voltage drop is detected to a set degree, the strategy target is achieved by controlling the current, including, for those with sequence control capability, injecting positive sequence reactive current related to the voltage drop degree, in the large mode, the remaining capacity is all injected into the positive sequence active current, in the small mode, the positive sequence active current is injected under the constraint of the amplitude limit and is linear with the positive sequence reactive current, absorbing negative sequence reactive current related to the voltage drop degree, suppressing negative sequence active current, for those without sequence control capability, injecting reactive current related to the voltage drop degree, in the large mode, the remaining capacity is all injected into the active current, in the small mode, the active current is injected under the constraint of the amplitude limit and is linear with the reactive current, the control quantity is not distinguished in sequence during the period.

[0069] Specifically, the set degree refers to the condition for triggering the fault ride-through control strategy when the grid connection point voltage drops to a pre-set threshold value, and the pre-set threshold value is set in combination with the power grid safety requirement.

[0070] It should be noted that by differentiating modeling of voltage levels, precise adaptation to different grid connection systems such as 10kV / 380V is achieved, so that the model error is reduced; the control strategy (such as sequence control and feedforward compensation) is quantified as impedance parameters, solving the problem that the traditional method cannot reflect the power electronic control characteristics; through the design of default values of standardized parameters, the model usability can still be guaranteed when the manufacturer data is missing, significantly improving the distribution network protection setting precision and fault ride-through evaluation reliability, and providing key technical support for high proportion of photovoltaic grid connection.

[0071] In the embodiment of the present application, the above step S200 includes the following sub-steps A1-A2;

[0072] In A1: the positive sequence current component and the negative sequence current component are calculated according to the rated parameters, the positive sequence current component and the negative sequence current component are converted into currents in a three-phase coordinate system, and three-phase steady-state short-circuit currents are obtained;

[0073] In A2: the three-phase steady-state short-circuit currents are combined to obtain the distributed photovoltaic fault steady-state model of 10kV and above voltage level grid connection and 380V voltage level grid connection;

[0074] Specifically, the three-phase steady-state short-circuit current is expressed as:

[0075]

[0076] Among them, is the positive sequence short-circuit current of the distributed photovoltaic considering the influence of the control strategy, is the positive sequence short-circuit current of the distributed photovoltaic considering the influence of the control strategy, is the positive sequence short-circuit current of the distributed photovoltaic considering the influence of the control strategy, is the positive sequence short-circuit current of the distributed photovoltaic considering the influence of the control strategy, is the positive sequence short-circuit current of the distributed photovoltaic considering the influence of the control strategy,​ Phase short-circuit current, To account for the stator current in the positive-sequence synchronous rotating coordinate system after considering the control strategy, To account for the stator current in the negative-sequence synchronous rotating coordinate system after considering the control strategy, The imaginary unit, For the power grid frequency, The moment after the failure. After the fault enters steady state, the positive sequence d-axis and The included angle between the axes of the phase windings, After the fault enters steady state, the negative sequence d-axis and The included angle between the axes of the phase windings, This is an operation to extract the real part of a complex number.

[0077] It should be noted that, through precise decoupling and coordinate transformation of positive and negative sequence current components, multi-dimensional and accurate modeling of fault currents in distributed photovoltaic systems is achieved. By employing rotating coordinate system transformation technology, the influence of complex control strategies (such as sequential control and limiting characteristics) is quantified into calculable positive and negative sequence current components, solving the problem that traditional methods cannot reflect the dynamics of power electronic control. Through three-phase coordinate inverse transformation, short-circuit current waveforms directly corresponding to actual physical quantities are generated, reducing model errors compared to traditional methods. A unified fault analysis framework is provided for photovoltaic systems of different voltage levels, significantly improving protection setting accuracy and asymmetric fault analysis capabilities.

[0078] In this embodiment of the invention, step S300 includes the following sub-steps B1-B6;

[0079] In B1: The distributed photovoltaic fault steady-state equivalent positive sequence model includes the reactive positive sequence component and the active positive sequence component of the short-circuit current steady-state value;

[0080] In B2: For the positive sequence reactive component, when the positive sequence voltage at the grid connection point of the distributed photovoltaic system is greater than or equal to the first threshold, no reactive current is injected, and the reactive current component is equal to 0.

[0081] In B3: When the positive sequence voltage at the grid connection point of the distributed photovoltaic system is less than the first threshold, the linear adjustment value is calculated, and the linear adjustment value is compared with the reactive current limit value of the distributed photovoltaic system. The minimum value is taken as the injected reactive current component.

[0082] In B4: For the active positive sequence component, when the main mode is operating and the positive sequence voltage at the grid connection point of the distributed photovoltaic is greater than or equal to the voltage threshold, the power maintenance demand value and the capacity safety limit value are calculated, and the minimum value of the calculation results is taken as the injected active current component.

[0083] In B5: When small mode operation and distributed photovoltaic grid-connected point positive sequence voltage is greater than or equal to voltage threshold value, the power maintenance requirement value and the maximum linear residual capacity are calculated, and the minimum value of the calculation result is taken as the injected active current component;

[0084] In B6: When the positive sequence voltage of the distributed photovoltaic grid-connected point is less than the voltage threshold value, the injected active current component is calculated by using the linear regulation strategy.

[0085] Specifically, for the reactive positive sequence component, the first threshold value is given by the equipment manufacturer or obtained through measured data, and 0.9 is taken when missing;

[0086] The linear regulation value expression is The reactive current limiting value of the distributed photovoltaic is compared, and the minimum value is taken as the injected reactive current component, wherein, is the distributed photovoltaic reactive current proportion coefficient, is the positive sequence voltage of the distributed photovoltaic grid-connected point, is the rated current of the distributed photovoltaic, is the distributed photovoltaic reactive current coefficient;

[0087] For the active positive sequence component, large mode operation refers to the operation state under high load and large power supply output, and the power maintenance requirement value is expressed as The capacity safety limit value expression is , and the minimum value of the power maintenance requirement value and the capacity safety limit value is taken as the injected active current component, wherein, is the pre-fault active power of the distributed photovoltaic, is the positive sequence voltage of the distributed photovoltaic grid-connected point, is the total current limiting value of the distributed photovoltaic, is the rated current of the distributed photovoltaic, is the steady-state value of the short-circuit current injected by the distributed photovoltaic reactive positive sequence component;

[0088] Small mode operation refers to the operation state under low load and small power supply output, and the maximum linear residual capacity expression is , and the minimum value of the power maintenance requirement value and the maximum linear residual capacity is taken as the injected active current component.

[0089] The steady-state equivalent positive sequence model of the distributed photovoltaic fault connected to the 10kV and above voltage level grid is expressed as:

[0090] ,

[0091] Wherein, is the steady-state value of the short-circuit current injected by the distributed photovoltaic reactive positive sequence component, Active positive sequence component of short circuit current steady state value for distributed photovoltaic injection, Amplitude limit value of reactive current for distributed photovoltaic, Positive sequence voltage at grid connection point of distributed photovoltaic, Rated current of distributed photovoltaic, Reactive current coefficient of distributed photovoltaic, generally the value of reactive current before fault, Reactive current proportion coefficient of distributed photovoltaic, given by equipment manufacturer or obtained through measured data, 1.5 when missing, Active power of distributed photovoltaic before fault, Total current amplitude limit value of distributed photovoltaic, Active current proportion coefficient of distributed photovoltaic, given by equipment manufacturer or obtained through measured data, 1.5 when missing, , Active current coefficient of distributed photovoltaic, given by equipment manufacturer or obtained through measured data, 1.5 when missing, , Voltage threshold value for entering amplitude limiting stage of active short circuit current steady state value of distributed photovoltaic.

[0092] It should be noted that through the hierarchical control strategy and dynamic amplitude limiting mechanism, the accurate regulation of active / reactive current during photovoltaic fault is realized, the calculation error is reduced, and the accuracy of power grid fault analysis and the reliability of protection setting are significantly improved.

[0093] In the embodiment of the present application, the above step S300 after completing the B1-B6 steps further includes the following steps B7-B9;

[0094] In B7: the fault steady state equivalent negative sequence model of distributed photovoltaic includes the short circuit current steady state value of reactive negative sequence component and active negative sequence component;

[0095] In B8: the reactive negative sequence component is the ratio of the negative sequence voltage at the grid connection point of distributed photovoltaic to the equivalent reactive negative sequence impedance of the corresponding distributed photovoltaic;

[0096] In B9: the active negative sequence component is the ratio of the negative sequence voltage at the grid connection point of distributed photovoltaic to the equivalent active negative sequence impedance of the corresponding distributed photovoltaic.

[0097] Specifically, the fault steady state equivalent negative sequence model of distributed photovoltaic connected to 10kV and above voltage level is represented as:

[0098] ,

[0099] Wherein, is the negative sequence voltage at the grid connection point of distributed photovoltaic, is the equivalent reactive negative sequence impedance of the distributed photovoltaic in this case, The steady-state value of the short-circuit current reactive negative sequence component of the distributed photovoltaic injection, The steady-state value of the short-circuit current active negative sequence component of the distributed photovoltaic injection, The equivalent active negative sequence impedance of the distributed photovoltaic in this case.

[0100] Specifically, the equivalent active and reactive negative sequence impedance of the distributed photovoltaic is inversely proportional to the reactive current coefficient of the distributed photovoltaic absorbing negative sequence, which is given by the equipment manufacturer or obtained through actual measurement data;

[0101] When missing, the photovoltaic connected to the grid above the 10kV voltage level needs to meet the current photovoltaic national standard and has the ability to absorb negative sequence reactive under asymmetric fault, Take 1, Take the maximum value.

[0102] It should be noted that by establishing the quantitative relationship between the negative sequence current component and the grid voltage, the accurate modeling of the photovoltaic system response under asymmetric fault is realized, and the accuracy of the grid unbalanced fault analysis is significantly improved.

[0103] In the embodiment of the present application, after the B7-B9 steps are completed in the above step S300, the following steps B10-B15 are further included;

[0104] In B10: the fault steady-state equivalent positive sequence model of the distributed photovoltaic includes the distributed photovoltaic with fault ride-through capability and the distributed photovoltaic without fault ride-through capability;

[0105] In B11: for the fault steady-state equivalent positive sequence model of the distributed photovoltaic, the steady-state value of the short-circuit current reactive positive sequence component and the active positive sequence component of the distributed photovoltaic with fault ride-through capability are consistent with the steady-state value of the short-circuit current reactive positive sequence component and the active positive sequence component of the fault steady-state model of the distributed photovoltaic connected to the grid of 10kV and above voltage level;

[0106] In B12: for the steady-state value of the short-circuit current reactive positive sequence component of the distributed photovoltaic without fault ride-through capability, when the positive sequence voltage at the distributed photovoltaic grid connection point is less than or equal to the off-grid voltage threshold, the reactive positive sequence component is equal to 0;

[0107] In B13: when the positive sequence voltage at the distributed photovoltaic grid connection point is greater than the off-grid voltage threshold, the reactive current component injected is compared with the minimum value of the calculated value according to the pre-fault reactive power and the current voltage demand and the reactive current limiting value of the distributed photovoltaic;

[0108] In B14: for the steady-state value of the short-circuit current active positive sequence component of the distributed photovoltaic without fault ride-through capability, when the positive sequence voltage at the distributed photovoltaic grid connection point is less than or equal to the off-grid voltage threshold, the active positive sequence component is equal to 0;

[0109] In B15: when the positive sequence voltage of the distributed photovoltaic grid-connected point is greater than the off-grid voltage threshold, the active current limiting value of the distributed photovoltaic is compared with the demand value calculated according to the active power before the fault and the current voltage, and the minimum value is taken as the injected active current component.

[0110] Specifically, for the steady-state value of the short-circuit current of the distributed photovoltaic without fault ride-through capability, the steady-state value of the short-circuit current of the distributed photovoltaic without fault ride-through capability is expressed as:

[0111] For the steady-state value of the short-circuit current of the distributed photovoltaic without fault ride-through capability, the steady-state value of the short-circuit current of the distributed photovoltaic without fault ride-through capability is expressed as: The minimum value is taken as the injected active current component; the demand value calculated according to the active power before the fault and the current voltage is expressed as: The minimum value is taken as the injected active current component; the demand value calculated according to the active power before the fault and the current voltage is expressed as:

[0112] Specifically, for the distributed photovoltaic without fault ride-through capability, it is expressed as:

[0113]

[0114] wherein, is the reactive power before the fault of the distributed photovoltaic, is the reactive current limiting value of the distributed photovoltaic, is the active current limiting value of the distributed photovoltaic, is the rated current of the distributed photovoltaic, is the off-grid voltage threshold of the distributed photovoltaic, which is given by the equipment manufacturer or obtained through actual measurement data, and is taken as 0.2 when missing.

[0115] It should be noted that by distinguishing the fault ride-through capability difference, the precise modeling of different types of photovoltaic systems is realized, the calculation error of the fault current of the 380V voltage level photovoltaic is reduced, the reliability of the protection action of the low-voltage distribution network is significantly improved, the high-precision 10kV model is used for the system with ride-through capability, and the calculation consistency is maintained; the voltage threshold triggering mechanism is used for the non-ride-through type system, and the off-grid characteristics are accurately simulated; the dynamic limiting comparison is used to ensure that the current output does not exceed the equipment capacity, and key technical support is provided for the safe operation of the distribution network.

[0116] In the embodiments of the present application, after the steps B10-B15 in the above step S300 are completed, the following steps B16-B21 are further included; ​

[0117] In B16: the steady-state value of the reactive negative sequence component of the short-circuit current of the distributed photovoltaic with the ability of sequence control and the ability of fault ride-through is the ratio of the negative sequence voltage at the grid-connected point of the distributed photovoltaic to the equivalent reactive negative sequence impedance of the corresponding distributed photovoltaic;

[0118] In B17: the active negative sequence component is the ratio of the negative sequence voltage at the grid-connected point of the distributed photovoltaic to the equivalent active negative sequence impedance of the corresponding distributed photovoltaic;

[0119] In B18: the active negative sequence component and the reactive negative sequence component of the distributed photovoltaic with the ability of sequence control and without the ability of fault ride-through are both 0;

[0120] In B19: for the distributed photovoltaic without the ability of sequence control and with the ability of fault ride-through, when the grid-connected point voltage feed-forward compensation term exists and when the grid-connected point voltage feed-forward compensation term does not exist;

[0121] In B20: when the grid-connected point voltage feed-forward compensation term exists, the active negative sequence component and the reactive negative sequence component are both 0;

[0122] In B21: when the grid-connected point voltage feed-forward compensation term does not exist, the active negative sequence component and the reactive negative sequence component are respectively the ratio of the negative sequence voltage at the grid-connected point of the distributed photovoltaic to the equivalent active and reactive negative sequence impedance of the corresponding distributed photovoltaic.

[0123] Specifically, for the distributed photovoltaic with the ability of sequence control and the ability of fault ride-through, it is expressed as:

[0124] ,

[0125] wherein, is the negative sequence voltage at the grid-connected point of the distributed photovoltaic, is the equivalent reactive negative sequence impedance of the distributed photovoltaic in this case, is the steady-state value of the reactive negative sequence component of the short-circuit current injected by the distributed photovoltaic, is the steady-state value of the active negative sequence component of the short-circuit current injected by the distributed photovoltaic, is the equivalent active negative sequence impedance of the distributed photovoltaic in this case;

[0126] The equivalent active and reactive negative sequence impedances of the distributed photovoltaic are inversely proportional to the reactive current coefficient of the distributed photovoltaic absorbing negative sequence, which is given by the equipment manufacturer or obtained through actual measurement data.

[0127] For the distributed photovoltaic with the ability of sequence control and without the ability of fault ride-through, it is expressed as:

[0128] ,

[0129] For the distributed photovoltaic without sequence control ability and with fault ride-through ability, the influence of the voltage feedforward control structure is further discussed, which is expressed as:

[0130]

[0131] When there is no grid-connected point voltage feedforward compensation term, it is expressed as:

[0132]

[0133] wherein, is the negative sequence voltage of the grid-connected point of the distributed photovoltaic, is the steady-state value of the short-circuit current injected by the distributed photovoltaic, and is the reactive negative sequence component, is the steady-state value of the short-circuit current injected by the distributed photovoltaic, and is the active negative sequence component, is the equivalent reactive negative sequence impedance of the distributed photovoltaic in this case, is the equivalent active negative sequence impedance of the distributed photovoltaic in this case, and is related to the proportional coefficient of the PI link in the control structure of the distributed photovoltaic, which is given by the equipment manufacturer or obtained through actual measurement data.

[0134] It should be noted that by establishing a refined negative sequence current model, the response characteristics of the photovoltaic system to the grid imbalance fault under different control strategies are accurately reflected, thereby providing a reliable basis for the safe operation and protection setting of the power grid.

[0135] The above is a schematic scheme of the equivalent method of the distributed photovoltaic fault steady-state model of the embodiment. It should be noted that the technical scheme of the equivalent system of the distributed photovoltaic fault steady-state model of the embodiment and the technical scheme of the equivalent method of the distributed photovoltaic fault steady-state model of the above embodiment belong to the same concept, and the details of the technical scheme of the equivalent system of the distributed photovoltaic fault steady-state model of the embodiment which are not described in detail can be referred to the description of the technical scheme of the equivalent method of the distributed photovoltaic fault steady-state model of the above embodiment.

[0136] The equivalent system of the distributed photovoltaic fault steady-state model of the embodiment comprises:

[0137] The data acquisition module is configured to acquire the grid-connected voltage level and rated parameters of the distributed photovoltaic.

[0138] The strategy determination module is configured to determine the corresponding grid-connected control strategy and fault ride-through control strategy according to different grid-connected voltage levels.

[0139] ​​A model construction module is configured to establish corresponding fault steady-state models for different grid-connected voltage levels in combination with the grid-connected control strategy and the fault ride-through control strategy and the rated parameters, so as to realize the equivalence of the steady-state models of the distributed photovoltaic after fault.

[0140] A grid-connected control strategy module is configured to be adopted when the grid-connected control strategy is not detected, and the strategy target is realized by control current, including, with sequence control capability, suppressing negative sequence current and tracking active power and reactive power instruction values of the system or itself while configuring current limiting measures, without sequence control capability, still tracking active power and reactive power instruction values, and the control quantity is not sequence component during the period.

[0141] A fault ride-through control strategy module is configured to be adopted when the grid-connected point voltage drop of the grid-connected control strategy is detected to be a set degree, and the strategy target is realized by control current, including, with sequence control capability, injecting positive sequence reactive current related to the voltage drop degree, injecting positive sequence active current in the remaining capacity in a large way, injecting positive sequence active current in a linear relationship with positive sequence reactive current under the constraint of an amplitude value in a small way, absorbing negative sequence reactive current related to the voltage drop degree, and suppressing negative sequence active current, without sequence control capability, injecting reactive current related to the voltage drop degree, injecting active current in the remaining capacity in a large way, and injecting active current in a linear relationship with reactive current under the constraint of an amplitude value in a small way, and the control quantity is not sequence component during the period.

[0142] The embodiment also provides a computer device suitable for a distributed photovoltaic fault steady-state model equivalence method, including a memory and a processor; the memory is configured to store computer executable instructions, and the processor is configured to execute the computer executable instructions to realize the distributed photovoltaic fault steady-state model equivalence method.

[0143] The embodiment also provides a storage medium having a computer program stored thereon, and the computer program is executed by a processor to realize the distributed photovoltaic fault steady-state model equivalence method.

[0144] The storage medium proposed in the embodiment and the distributed photovoltaic fault steady-state model equivalence method proposed in the above embodiment belong to the same inventive concept, and the technical details not described in the embodiment can be referred to the above embodiment, and the embodiment has the same beneficial effects as the above embodiment.

[0145] Through the above description of the embodiments, those skilled in the art can clearly understand that the present application can be realized by means of software and necessary general hardware, of course, can also be realized by hardware, but in many cases, the former is a better embodiment. Based on such understanding, the technical solutions of the present application can be embodied in the form of a software product, which can be stored in a computer readable storage medium, such as a floppy disk, a read only memory (Read Only Memory, ROM), a random access memory (Random Access Memory, RAM), a FLASH, a hard disk or an optical disk, etc., including a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the method of each embodiment of the present application.

[0146] Embodiment 2, refer to Table 1~Table 2, Figures 2-4 , unlike the first embodiment, provides a verification test for the equivalent method of distributed photovoltaic fault steady-state model, and the technical effects adopted in the method are verified and explained.

[0147] As Figure 2 shown, based on PSCAD / EMTDC (off-line simulation power system analysis software), a system topology of a certain distributed photovoltaic access is built in PSCAD / EMTDC.

[0148] As Figure 3 shown is the control structure of the distributed photovoltaic using sequence control, wherein, is the input voltage signal, is the input current signal, , are the positive and negative sequence reference angles, respectively, used for the conversion of the synchronous rotating coordinate system, is the stator current in the positive sequence synchronous rotating coordinate system considering the control strategy, is the stator current in the negative sequence synchronous rotating coordinate system considering the control strategy, , are the voltage components in the positive and negative sequence synchronous rotating coordinate systems, respectively, is the active component reference value of the positive sequence current, is the reactive component reference value of the positive sequence current, is the active component reference value of the negative sequence current, is the reactive component reference value of the negative sequence current, is the steady-state value of the short-circuit current injected by the distributed photovoltaic, the reactive positive sequence component, is the steady-state value of the short-circuit current injected by the distributed photovoltaic, the active positive sequence component, Steady-state value of the short-circuit current of the distributed photovoltaic injection reactive negative sequence component, Steady-state value of the short-circuit current of the distributed photovoltaic injection active negative sequence component, Impedance of the inductance, PI is a PI controller, Active and reactive components of the control positive sequence current respectively, , Active and reactive components of the control negative sequence current respectively, Positive sequence active current error, Positive sequence reactive current error, Negative sequence active current error, Negative sequence reactive current error, Inverse transformation matrix of three-phase stationary coordinate system to two-phase rotating coordinate system, , Output of positive and negative sequence three-phase voltage.

[0149] As Figure 4 shown is a control structure without sequence control and with voltage feedforward, wherein, Input voltage signal, Input current signal, Reference angle, Reference value of active current, Reference value of reactive current, Active current, Reactive current, Impedance of the inductance, PI is a PI controller, Active and reactive components of the control current respectively, Active current error, Reactive current error, Inverse transformation matrix of three-phase stationary coordinate system to two-phase rotating coordinate system, Output of three-phase voltage, PLL is a phase-locked loop, Transformation matrix of three-phase stationary coordinate system to two-phase rotating coordinate system.

[0150] The distributed photovoltaic parameters in the simulation model are shown in Table 1;

[0151] Table 1 Electrical and control parameters of the distributed photovoltaic simulation model

[0152]

[0153] As shown in Table 1, wherein k ii , k ip are the integral and proportional coefficients of the PI link in the distributed photovoltaic current loop respectively; k is the negative sequence reactive absorption coefficient of the distributed photovoltaic with sequence control during fault ride-through; kq , u k are the positive sequence reactive power injection coefficient and voltage threshold of distributed photovoltaic in the process of fault ride through, respectively;

[0154] The low voltage fault ride through reference value of the distributed photovoltaic with sequence control meets:

[0155] ,

[0156] wherein, is the active power of the distributed photovoltaic before fault, is the positive sequence voltage at the grid-connected point of the distributed photovoltaic, is the maximum allowable total current limit, is the reactive current proportion coefficient of the distributed photovoltaic, is the voltage threshold, is the negative sequence reactive power coefficient, is the negative sequence voltage at the grid-connected point, is the active component reference value of the positive sequence current, is the reactive component reference value of the positive sequence current, is the active component reference value of the negative sequence current, is the reactive component reference value of the negative sequence current.

[0157] For the distributed photovoltaic without sequence control, the current reference value is consistent with the calculation method of the positive sequence current reference value under sequence control, and the photovoltaics at nodes 8 and 44 do not have fault ride through capability.

[0158] All the distributed photovoltaics are full power before fault, an A-phase ground fault occurs at node 21 at time 0, the system short-circuit current is calculated by using the fault steady-state equivalent model of the distributed photovoltaic, and finally the voltage and current calculation results of some lines of the typical distribution network system are shown in Table 2.

[0159] Table 2 Comparison of line current and voltage calculation results of the distributed photovoltaic simulation model

[0160]

[0161] wherein, Isimu, Usimu are the A-phase steady-state current of the simulation line and the A-phase steady-state voltage at the first end node of the line, respectively, Ic1, Uc1 are the calculated current and voltage under the assumption that all the distributed photovoltaics adopt sequence and fault ride through control, Eic1, Euc1 are the errors of the current and voltage and the corresponding simulation values; Ic2, Uc2 are the calculated current and voltage under the consideration of the influence of the control strategy of the distributed photovoltaic, and Eic2, Euc2 are the errors of the current and voltage and the corresponding simulation values.

[0162] If the influence of the control strategy under different requirements in engineering practice on the steady-state model of the distributed photovoltaic fault is not considered, the calculation results of the short-circuit current of the final single machine and the system will have large errors, which is especially unfavorable for the protection setting near the photovoltaic outlet, and the feasibility and accuracy of the equivalent method are verified.

[0163] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A distributed photovoltaic fault steady-state model equivalent method, characterized in that, The method comprises the following steps: acquiring the grid-connected voltage level and rated parameters of the distributed photovoltaic; determining corresponding grid-connected control strategies and fault ride-through control strategies according to different grid-connected voltage levels; for different grid-connected voltage levels, combining the grid-connected control strategies and fault ride-through control strategies and the rated parameters to establish corresponding fault steady-state models to realize the equivalence of the steady-state model of the distributed photovoltaic after a fault occurs; the grid-connected control strategy is adopted when no fault is detected, and the strategy target is realized by control current, including, for the distributed photovoltaic with sequence control capability, suppressing negative sequence current and tracking active power and reactive power instruction values set by the system or itself while configuring current limiting measures, for the distributed photovoltaic without sequence control capability, still tracking active power and reactive power instruction values, and the control quantity is not differentiated in sequence component during the period; the fault ride-through control strategy is adopted when the positive sequence or non-sequence grid-connected point voltage drops to a set degree, and the strategy target is realized by control current, including, for the distributed photovoltaic with sequence control capability, injecting positive sequence reactive current related to the voltage drop degree, injecting positive sequence active current in the remaining capacity in a large way, injecting positive sequence active current in a linear relationship with positive sequence reactive current under the constraint of an amplitude limit value in a small way, absorbing negative sequence reactive current related to the voltage drop degree, and suppressing negative sequence active current, for the distributed photovoltaic without sequence control capability, injecting reactive current related to the voltage drop degree, injecting active current in the remaining capacity in a large way, and injecting active current in a linear relationship with reactive current under the constraint of an amplitude limit value in a small way, and the control quantity is not differentiated in sequence component during the period; the fault steady-state equivalent negative sequence model of the distributed photovoltaic comprises: for the distributed photovoltaic with sequence control capability and fault ride-through capability, the steady-state value of the short-circuit current of the negative sequence component is the ratio of the negative sequence voltage of the grid-connected point of the distributed photovoltaic to the equivalent negative sequence impedance of the corresponding distributed photovoltaic; the active negative sequence component is the ratio of the negative sequence voltage of the grid-connected point of the distributed photovoltaic to the equivalent active negative sequence impedance of the corresponding distributed photovoltaic; for the distributed photovoltaic with sequence control capability and without fault ride-through capability, the active negative sequence component and the reactive negative sequence component are both 0; for the distributed photovoltaic without sequence control capability and with fault ride-through capability, including when there is a grid-connected point voltage feedforward compensation term and when there is no grid-connected point voltage feedforward compensation term; for the case when there is a grid-connected point voltage feedforward compensation term, the active negative sequence component and the reactive negative sequence component are both 0; for the case when there is no grid-connected point voltage feedforward compensation term, the active negative sequence component and the reactive negative sequence component are the ratio of the negative sequence voltage of the grid-connected point of the distributed photovoltaic to the equivalent active and reactive negative sequence impedance of the corresponding distributed photovoltaic.

2. The method of claim 1, wherein, determining corresponding grid-connected control strategies and fault ride-through control strategies comprises: calculating positive sequence current components and negative sequence current components according to rated parameters, converting the positive sequence current components and the negative sequence current components into currents in a three-phase coordinate system to obtain three-phase steady-state short-circuit currents; combining the three-phase steady-state short-circuit currents to obtain the fault steady-state model of the distributed photovoltaic for 10kV and above voltage level grid connection and 380V voltage level grid connection.

3. The method of claim 2, wherein, the fault steady-state model of the distributed photovoltaic for 10kV and above voltage level grid connection comprises: The distributed photovoltaic fault steady-state equivalent positive sequence model includes a short-circuit current steady-state value reactive positive sequence component and an active positive sequence component; For the reactive positive sequence component, when the positive sequence voltage at the distributed photovoltaic grid-connected point is greater than or equal to a first threshold value, no reactive current is injected, and the reactive current component is equal to 0; When the positive sequence voltage at the distributed photovoltaic grid-connected point is less than the first threshold value, a linear adjustment value is calculated, the linear adjustment value is compared with a reactive current limit value of the distributed photovoltaic, and the minimum value is taken as the injected reactive current component; For the active positive sequence component, when the large mode is operated and the positive sequence voltage at the distributed photovoltaic grid-connected point is greater than or equal to a voltage threshold value, a power maintenance demand value and a capacity safety limit value are calculated, and the minimum value of the calculation results is taken as the injected active current component; When the small mode is operated and the positive sequence voltage at the distributed photovoltaic grid-connected point is greater than or equal to the voltage threshold value, a power maintenance demand value and a maximum linear residual capacity are calculated, and the minimum value of the calculation results is taken as the injected active current component; When the positive sequence voltage at the distributed photovoltaic grid-connected point is less than the voltage threshold value, the injected active current component is calculated by using a linear adjustment strategy.

4. The method of claim 3, wherein, Further comprising: The distributed photovoltaic fault steady-state equivalent negative sequence model includes a short-circuit current steady-state value reactive negative sequence component and an active negative sequence component; The reactive negative sequence component is a ratio of the negative sequence voltage at the distributed photovoltaic grid-connected point to the equivalent reactive negative sequence impedance of the corresponding distributed photovoltaic; The active negative sequence component is a ratio of the negative sequence voltage at the distributed photovoltaic grid-connected point to the equivalent active negative sequence impedance of the corresponding distributed photovoltaic.

5. The method of claim 4, wherein, The distributed photovoltaic fault steady-state model of the 380V voltage level grid-connected includes: the distributed photovoltaic fault steady-state equivalent negative sequence model and the distributed photovoltaic fault steady-state equivalent positive sequence model; The distributed photovoltaic fault steady-state equivalent positive sequence model includes the distributed photovoltaic with fault ride-through capability and the distributed photovoltaic without fault ride-through capability; For the distributed photovoltaic fault steady-state equivalent positive sequence model, the short-circuit current steady-state value reactive positive sequence component and the active positive sequence component of the distributed photovoltaic with fault ride-through capability are consistent with those of the distributed photovoltaic fault steady-state model of the 10kV and above voltage level grid-connected.

6. The method of claim 5, wherein, The distributed photovoltaic fault steady-state equivalent positive sequence model of the distributed photovoltaic without fault ride-through capability includes: For the short-circuit current steady-state value reactive positive sequence component of the distributed photovoltaic without fault ride-through capability, when the positive sequence voltage at the distributed photovoltaic grid-connected point is less than or equal to a disconnection voltage threshold value, the reactive positive sequence component is equal to 0; When the positive sequence voltage at the distributed photovoltaic grid-connected point is greater than the disconnection voltage threshold value, a demand value calculated according to the pre-fault reactive power and the current voltage is compared with the reactive current limit value of the distributed photovoltaic, and the minimum value is taken as the injected reactive current component; For the short-circuit current steady-state value active positive sequence component of the distributed photovoltaic without fault ride-through capability, when the positive sequence voltage at the distributed photovoltaic grid-connected point is less than or equal to the disconnection voltage threshold value, the active positive sequence component is equal to 0; When the positive sequence voltage of the distributed photovoltaic grid-connected point is greater than the off-grid voltage threshold, the active current injection value is calculated according to the active power before the fault and the current voltage demand value and the active current limiting value of the distributed photovoltaic, and the minimum value is taken as the active current component.

7. A distributed photovoltaic fault steady-state model equivalent system, applying a distributed photovoltaic fault steady-state model equivalent method according to any one of claims 1-6, characterized in that, The application relates to a distributed photovoltaic fault steady-state model equivalent method. The application relates to a distributed photovoltaic fault steady-state model equivalent method. The application relates to a distributed photovoltaic fault steady-state model equivalent method. The application relates to a distributed photovoltaic fault steady-state model equivalent method. The application relates to a distributed photovoltaic fault steady-state model equivalent method. The application relates to a distributed photovoltaic fault steady-state model equivalent method.

8. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that, The application relates to a distributed photovoltaic fault steady-state model equivalent method.

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