A voltage sag amplitude calculation method considering transient response characteristics of optical storage resources

Abstract

The application provides a voltage sag amplitude calculation method considering transient response characteristics of optical storage resources, and relates to the technical field of power electronics. The method comprises the following steps: based on system load and power generation of a power system, the available voltage regulation capacity of energy storage is calculated; based on voltage recording data of a photovoltaic grid-connected point, a parameter identification model is constructed and solved to obtain equivalent control parameters of photovoltaic transient current, and further calculation is performed to obtain photovoltaic transient output current; the photovoltaic off-grid time is calculated according to a photovoltaic low-voltage ride-through curve, and a voltage sag evolution time sequence is constructed; the voltage sag amplitude is calculated in combination with the voltage sag evolution time sequence, the available voltage regulation capacity and the photovoltaic transient output current. The method can realize the characterization of the transient response characteristics of optical storage during voltage sag, and the quantitative calculation of the voltage support margin of optical storage resources during voltage sag; can be well adapted to a new type of power system, and is helpful to improve the calculation accuracy and precision of the voltage sag amplitude characteristics.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a method for calculating voltage sag amplitude that takes into account the transient response characteristics of photovoltaic and energy storage resources. Background Technology

[0002] Voltage sags cause tripping of equipment such as AC contactors, variable speed drives, and computers, resulting in significant economic losses for industrial users. With the development of new power systems, the scale of photovoltaic (PV) and energy storage resources in the power grid is increasing year by year. Electrochemical energy storage has a fast transient response speed, capable of millisecond-level responses to power disturbances, and can buffer the impact of supply voltage and frequency fluctuations on sensitive loads. During voltage sags, energy storage resources in the system can support node voltages to mitigate the sag. The impact of PV integration on voltage sags is reflected in two aspects: firstly, the response of PV low-voltage ride-through control strategies can support the voltage sag amplitude; secondly, PV grid disconnection during voltage sag events may lead to further voltage deterioration. Traditional methods for calculating voltage sag amplitude do not adequately consider the transient response characteristics of PV and energy storage resources, which may lead to large calculation errors in voltage sag amplitude.

[0003] The existing technology has the following main problems:

[0004] 1) Existing technologies lack methods for characterizing the transient response characteristics of photovoltaic and energy storage resources, and the voltage support capabilities of photovoltaic and energy storage under voltage sags are unclear.

[0005] 2) Existing methods for calculating voltage sag amplitude do not adequately consider the transient response process of photovoltaic and energy storage systems. Traditional calculation methods are poorly applicable to new power systems and lack sufficient accuracy and precision. Summary of the Invention

[0006] To address the aforementioned technical problems in the prior art, this invention provides a method for calculating voltage sag amplitude that takes into account the transient response characteristics of photovoltaic and energy storage resources.

[0007] Specifically, the technical solution includes:

[0008] Calculate the available voltage regulation capacity of energy storage based on the system load and power generation of the power system;

[0009] Based on the voltage waveform data of the photovoltaic grid connection point, a parameter identification model is constructed and solved to obtain the equivalent control parameters of the photovoltaic transient current; based on the equivalent control parameters of the photovoltaic transient current, the photovoltaic transient output current is calculated.

[0010] The photovoltaic grid disconnection time was calculated based on the photovoltaic low-voltage ride-through curve, and the voltage sag evolution time series was constructed.

[0011] The voltage sag amplitude characteristics are calculated by combining the voltage sag evolution time series, available voltage regulation capacity, and photovoltaic transient output current.

[0012] Preferably, the available voltage regulation capacity of energy storage is calculated based on the system load and power generation of the power system, specifically including:

[0013] Calculate the active power P of energy storage ESSi ,

[0014]

[0015] In the formula, P V P represents the power value of the load filler line. net,i Let P be the net load power at time i. F t1 is the peak load shaving line power value, t2 is the start time of energy storage charging, t3 is the start time of energy storage discharging, and t4 is the end time of energy storage discharging.

[0016] Calculate the remaining energy S stored at time i. i ,

[0017]

[0018] In the formula, η c For the charging efficiency of energy storage, η d For the discharge efficiency of energy storage, S n This refers to the rated capacity of the energy storage.

[0019] Calculate the available voltage regulation capacity of the stored energy at the i-th time during the voltage sag, including the adjustable active power P′. ESS，i and adjustable reactive power Q′ ESS,i ,

[0020]

[0021] In the formula, t p t is the duration of the voltage sag. ESS For energy storage response delay, t p -t ESS P represents the energy storage voltage support time. ESS,max For the maximum discharge power of energy storage, P n Q represents the active power deficit at the node during voltage sags. n This refers to the reactive power deficit at the node during a voltage sag.

[0022] Preferably, based on the voltage recording data of the photovoltaic grid connection point, a parameter identification model is constructed and solved to obtain the equivalent control parameters of the photovoltaic transient current; based on the equivalent control parameters of the photovoltaic transient current, the photovoltaic transient output current is calculated, specifically including:

[0023] Construct a photovoltaic transient control parameter identification model.

[0024]

[0025] In the formula, f is the optimization objective function, and U PV,dm and U PV,qm These are the d-axis and q-axis voltage components after the three-phase monitoring voltage transformation at the photovoltaic grid-connected node, respectively. PV,de and U PV,qe These are the estimated d-axis voltage component and q-axis voltage component values ​​at the grid connection point of the photovoltaic power station, respectively. PV U represents the voltage amplitude at the photovoltaic grid-connected node. min and U max These are the lower and upper limits of the grid-connected voltage for photovoltaic systems, respectively. d and I q These are the d-axis and q-axis currents of the photovoltaic grid-connected node, respectively. max P is the output current limit for photovoltaic grid-connected nodes. PV and Q PV S represents the active power and reactive power output of the photovoltaic grid-connected node, respectively. PV For the capacity of photovoltaic power stations, and These are the minimum and maximum values ​​of reactive power output from the photovoltaic grid-connected node, respectively.

[0026] in,

[0027]

[0028] In the formula, θ is the rotation angle of the dq coordinate system relative to the three-phase coordinate system, and U PV,a U PV,b and U PV,c These are the photovoltaic grid connection point voltages U PV The voltage components of phase a, phase b, and phase c;

[0029]

[0030] In the formula, U PV,pred and U PV,preq These are the d-axis voltage component monitoring values ​​and q-axis voltage component monitoring values ​​before the transient response of the photovoltaic grid-connected node, respectively. g L is the equivalent resistance of the photovoltaic power station. g ω is the equivalent inductance of the photovoltaic power station, and w is the angular frequency of the power system.

[0031] By inputting voltage waveform data into the parameter identification model and solving it, the equivalent control parameters K1 and K2 of photovoltaic transient current are obtained.

[0032] Calculate the transient output current of the photovoltaic system, including the d-axis current I of the photovoltaic grid-connected node. d and q-axis current I q ,

[0033]

[0034] In the formula, I dr and I qr These are the d-axis reference current and q-axis reference current of the photovoltaic grid-connected node, respectively. n This is the rated current of the photovoltaic grid-connected node.

[0035] Preferably, the photovoltaic grid disconnection time is calculated based on the photovoltaic low-voltage ride-through curve, and a voltage sag evolution time series is constructed, specifically including:

[0036] Calculate the photovoltaic grid disconnection time t trip ,

[0037]

[0038] In the formula, U PV U represents the voltage amplitude at the photovoltaic grid-connected node. X and U M These represent the maximum and minimum values ​​of the ordinate of the low-voltage ride-through curve, T. max and T min These represent the maximum and minimum x-coordinate values ​​of the low-voltage crossing inclined section curve, respectively.

[0039] Construct a voltage sag evolution time series T that includes multiple stages.

[0040] T = rank(t) PV ,t ESS ,t trip ,t p );

[0041] In the formula, rank(·) represents the ascending order operator, and t PV For the photovoltaic low voltage ride-through duration, t ESS For energy storage response time, t p This represents the duration of the voltage sag.

[0042] Preferably, the voltage sag amplitude characteristics are calculated by combining the voltage sag evolution time series, available voltage regulation capacity, and photovoltaic transient output current, specifically including:

[0043] Before the photovoltaic-storage response, the voltage sag magnitude matrix U of the power system is calculated using a voltage divider model. sag ;

[0044] During energy storage response, calculate the photovoltaic injection transient current I′ at time i. ESS，i ,

[0045]

[0046] In the formula, QESS,i Z represents the energy storage reactive power at time i. ESS The transient equivalent impedance for energy storage;

[0047] During photovoltaic low-voltage ride-through, calculate the transient current fault component I′ at time i. PV，i ,

[0048]

[0049] In the formula, I d.i and I q.i These are the d-axis and q-axis currents of the photovoltaic grid-connected node at the i-th time, respectively, where j represents the imaginary part, and P... PV,i and Q PV,i Let be the active power and reactive power output of the photovoltaic grid-connected node at the i-th time, respectively, and be the transient equivalent impedance of the photovoltaic grid-connected node;

[0050] When the photovoltaic grid is disconnected, calculate the photovoltaic injection current deviation value I at time i. PV,i ,

[0051]

[0052] Calculate the voltage sag amplitude U for multiple voltage sag evolution time stages. sag,k ,

[0053] U sag,k =U sag,k-1 +I k ·Z S,k ;

[0054] In the formula, U sag,k Usag,k-1 and I are the voltage sag values ​​in the k-th and (k-1)-th stages, respectively. k Z is the transient injection current in the k-th stage. S,k This is the system impedance matrix for the k-th stage;

[0055] in,

[0056]

[0057] In the formula, t represents time.

[0058] In summary, the technical solution provided by this invention, through available capacity calculation and photovoltaic transient control parameter identification, enables the characterization of the transient response characteristics of photovoltaic-storage systems during voltage sags, as well as the quantitative calculation of the voltage support margin of photovoltaic-storage resources during voltage sags. By constructing a voltage sag amplitude evolution time series and a multi-stage voltage sag amplitude calculation model, the multi-stage voltage sag amplitude characteristics considering the transient response of photovoltaic-storage systems can be calculated. This approach is well-suited to new power systems and helps improve the accuracy and precision of voltage sag amplitude characteristic calculations. Attached Figure Description

[0059] Figure 1 This is a flowchart of the method for calculating the voltage sag amplitude in this invention.

[0060] Figure 2 This is the photovoltaic low-voltage ride-through curve in this invention. Detailed Implementation

[0061] The technical solution provided by the present invention will be further described in detail below with reference to the accompanying drawings.

[0062] Voltage sag calculation is fundamental to voltage sag frequency assessment and risk characterization. To improve the applicability and accuracy of voltage sag calculation methods for new power systems, this invention proposes a voltage sag calculation method that takes into account the transient response characteristics of photovoltaic and energy storage resources.

[0063] like Figure 1 As shown, the basic flowchart consists of four steps:

[0064] Step S1: Using system load and power generation data as input, construct a calculation model for transient voltage regulation margin of energy storage and calculate the available voltage regulation capacity of energy storage.

[0065] Assume the system load power dataset and generation dataset are P. L and P G Then the net load dataset P net for:

[0066] P net =P L -P G ;

[0067] Under the variable power control strategy, the energy storage power can be calculated using the following formula:

[0068]

[0069] Among them, P ESS,i Let P be the energy storage power at time i. V P represents the power value of the load filler line. net,i Let P be the net load power at time i. F Let t1 be the peak load power value, t2 be the start time of energy storage charging, t3 be the start time of energy storage discharging, and t4 be the end time of energy storage discharging. When i∈[t1,t2], the energy storage power absorbed during charging is t1, and when i∈[t1,t2], the energy storage power released during discharging is t4.

[0070] The remaining energy storage capacity S at time i. i Calculate using the following formula:

[0071]

[0072] Where, η c For the charging efficiency of energy storage, η d For the discharge efficiency of energy storage, S n This refers to the rated capacity of the energy storage.

[0073] During a voltage sag, the adjustable capacity of the energy storage at the i-th time moment is calculated using the following formula;

[0074]

[0075] Among them, t p t is the duration of the voltage sag. ESS For energy storage response delay, t p -t ESS P represents the energy storage voltage support time. ESS,max For the maximum discharge power of energy storage, P n Q represents the active power deficit at the node during voltage sags. n This refers to the reactive power deficit at the node during a voltage sag.

[0076] Step S2: Using the voltage recording data of the photovoltaic access point monitoring device as input, construct a parameter identification model and solve for the equivalent control parameters of the photovoltaic transient current.

[0077] The photovoltaic transient control parameter identification model is shown below:

[0078]

[0079] In the formula, f is the optimization objective function, and U PV,dm and U PV,qm These are the d-axis and q-axis voltage components after the three-phase monitoring voltage transformation at the photovoltaic grid-connected node, respectively. PV,de and U PV,qe These are the estimated d-axis voltage component and q-axis voltage component values ​​for the photovoltaic grid-connected point, respectively. PV U represents the voltage amplitude at the photovoltaic grid-connected node. min and U max These are the lower and upper limits of the grid-connected voltage for photovoltaic systems, respectively. d and I q These are the d-axis and q-axis currents of the photovoltaic grid-connected node, respectively. max P is the output current limit for photovoltaic grid-connected nodes. PV and Q PV S represents the active power and reactive power output of the photovoltaic grid-connected node, respectively. PV For the capacity of photovoltaic power stations, and These are the minimum and maximum values ​​of the reactive power output of the photovoltaic grid-connected node, respectively.

[0080] U is obtained by transforming the three-phase voltage monitoring value PV,dm and U PV,qm The formula is as follows:

[0081]

[0082] In the formula, θ is the rotation angle of the dq coordinate system relative to the three-phase coordinate system, and U PV,a U PV,b and U PV,c These are the photovoltaic grid connection point voltages U PV The voltage components of phase a, phase b, and phase c are the fault recording monitoring values.

[0083] Estimated values ​​of d-axis and q-axis voltage components U at the photovoltaic grid connection point PV,de and U PV,qe The calculation process is as follows:

[0084]

[0085] In the formula, U PV,pred and U PV,preq These are the d-axis voltage component monitoring values ​​and q-axis voltage component monitoring values ​​before the transient response of the photovoltaic grid-connected node, respectively. g L is the equivalent resistance of the photovoltaic power station. g ω is the equivalent inductance of the photovoltaic power station, and w is the angular frequency of the power system.

[0086] According to the photovoltaic low-voltage ride-through control strategy, the d-axis component I of the photovoltaic transient output current is... d q-axis component I q As shown below:

[0087]

[0088] In the formula, I dr and I qr These are the d-axis reference current and q-axis reference current of the photovoltaic grid-connected node, respectively. PV I is the voltage at the photovoltaic grid connection point. n The rated current of the photovoltaic power station is given. The equivalent control parameters K1 and K2 of the photovoltaic transient current are parameters to be identified.

[0089] The parameter identification model takes the monitoring data as input and minimizes the voltage estimate and the monitoring value as the optimization objective. Solving the parameter identification model yields the equivalent control parameters K1 and K2 of the photovoltaic transient current, and the photovoltaic transient output current can be further calculated.

[0090] Step S3: As Figure 2As shown, the photovoltaic grid disconnection time is calculated based on the photovoltaic low voltage ride-through curve (obtained according to the national standard low voltage ride-through requirements), and the voltage sag evolution time series is constructed.

[0091] Photovoltaic grid disconnection time t trip The calculation formula is as follows:

[0092]

[0093] In the formula, U PV U represents the voltage amplitude at the photovoltaic grid-connected node. X and U M These represent the maximum and minimum ordinate values ​​of the low-voltage ride-through curve as required by national standards, T. max and T min These represent the maximum and minimum x-coordinate values ​​of the low-voltage crossing inclined section curve, respectively.

[0094] The voltage sag evolution time series T is shown below:

[0095] T = rank(t) PV ,t ESS ,t trip ,t p );

[0096] Here, `rank(·)` is the ascending order operator, which arranges the times within the parentheses in ascending order to form a time series. PV For the photovoltaic low voltage ride-through duration, t ESS For energy storage response time, t p This represents the duration of the voltage sag.

[0097] Step S4: After obtaining the multi-stage evolution time series of voltage sag, combine the available energy storage capacity and photovoltaic transient output current obtained from S1 and S2 to calculate the multi-stage voltage sag amplitude characteristics.

[0098] Before the photovoltaic-storage response, the voltage sag magnitude matrix U of the power system is calculated using a traditional voltage divider model. sag That is, the voltage sag amplitude matrix of the first stage.

[0099] Energy storage t ESS Time response, injecting transient current I′ ESS，i Calculated by the following formula:

[0100]

[0101] Among them, Q ESSi Z represents the energy storage reactive power at time i. ESS It is the transient equivalent impedance for energy storage.

[0102] During photovoltaic (PV) low-voltage ride-through, the PV low-voltage ride-through control strategy response has a transient current fault component of I′. PV,i :

[0103]

[0104] In the formula, I d.i and I q.i These are the d-axis and q-axis currents of the photovoltaic grid-connected node at the i-th time, respectively, where j represents the imaginary part, and P... PV,i and Q PV,i Let be the active power and reactive power output of the photovoltaic grid-connected node at time i, respectively, and let be the transient equivalent impedance of the photovoltaic grid-connected node.

[0105] When a photovoltaic system is disconnected from the grid, no current is injected into the grid connection point. At this time, the photovoltaic injection current deviation value I” PV,i Represented as:

[0106]

[0107] It can be seen that t trip ≥t PV At that time, the photovoltaic low-voltage ride-through time precedes the grid disconnection time, and the photovoltaic grid disconnection loss transient current fault component, t trip <t PV At that time, the grid disconnection time precedes the response of the photovoltaic low voltage ride-through control strategy, and the photovoltaic grid disconnection results in the loss of the injected current under normal operating conditions.

[0108] For multiple voltage sag evolution time series, the formula for calculating the voltage sag amplitude is expressed as follows:

[0109] U sag,k =U sag,k-1 +I k ·Z S,k ;

[0110] Among them, U sag,k and U sag,k-1 I represents the voltage sag in the k-th and (k-1)-th stages, respectively. k Z is the transient injection current in the k-th stage. S,k Let I be the system impedance matrix for the k-th stage. k The rules for determining the value are as follows:

[0111]

[0112] Where t is a time variable, when t takes any element in the voltage sag evolution time series T, the voltage sag amplitude evolves, and the corresponding I needs to be updated and calculated. k .

[0113] It is important to note that steps S1, S2, and S3 are independent of each other, and executing any one of these steps alone does not affect the other two. Therefore, steps S1, S2, and S3 can be executed in any order.

[0114] In summary, the technical solution provided by this invention, through available capacity calculation and photovoltaic transient control parameter identification, enables the characterization of the transient response characteristics of photovoltaic-storage systems during voltage sags, as well as the quantitative calculation of the voltage support margin of photovoltaic-storage resources during voltage sags. By constructing a voltage sag amplitude evolution time series and a multi-stage voltage sag amplitude calculation model, the multi-stage voltage sag amplitude characteristics considering the transient response of photovoltaic-storage systems can be calculated. This approach is well-suited to new power systems and helps improve the accuracy and precision of voltage sag amplitude characteristic calculations.

Claims

1. A method for calculating voltage sag magnitude considering transient response characteristics of photovoltaic storage resources, characterized in that, The method comprises the following steps: Based on the system load and power generation of the power system, the available voltage regulation capacity of the energy storage is calculated; Based on the voltage recording data of the photovoltaic grid-connected point, a parameter identification model is constructed and solved to obtain the equivalent control parameters of the photovoltaic transient current; based on the equivalent control parameters of the photovoltaic transient current, the photovoltaic transient output current is calculated; According to the photovoltaic low-voltage ride-through curve, the photovoltaic off-grid time is calculated, and the voltage sag evolution time sequence is constructed; combined with the voltage sag evolution time sequence, the available voltage regulation capacity and the photovoltaic transient output current, the voltage sag amplitude characteristics are calculated, which specifically include: Before the light storage response, the voltage sag amplitude matrix U of the power system is calculated by using a voltage divider model sag ; At the energy storage response time, the i-th time photovoltaic injection transient current I' is calculated ESSi , P' = P - P ESS,i P = P ESS,i Q' = Q - Q ESS,i Q = Q ESS,i Z = Z ESS Z = Z At the photovoltaic low voltage ride through, the transient current fault component I' of the i-th moment is calculated PVi , In the formula, I d.i and I q.i are the d-axis current and the q-axis current of the photovoltaic grid-connected node at the i th moment, P PV,i and Q PV,i are the active power and the reactive power output by the photovoltaic grid-connected node at the i th moment, and Z PV is the transient equivalent impedance of the photovoltaic grid-connected node. at the ith time instant, when the photovoltaic is off-grid, the injection current deviation value I PV,i , In the formula, t trip is the photovoltaic off-grid time, P PV,i and Q PV,i are the active power and reactive power output by the photovoltaic grid-connected node at the i th moment, Z PV is the transient equivalent impedance of the photovoltaic grid-connected node, t PV is the photovoltaic low-voltage ride-through duration; Calculating the voltage dip magnitude U for a plurality of voltage dip evolution time sequence phases sag,k , U sag,k = U sag,k-1 + I k · Z S,k ; wherein U sag,k and U sag,k-1 are the voltage sag magnitude of the kth and k-1th phase, respectively, I k is the transient injection current of the kth phase, and Z S,k is the system impedance matrix of the kth phase. Wherein, The formula (1) is used to calculate the voltage sag amplitude characteristics.

2. The method for calculating voltage sag magnitude considering transient response characteristics of optical storage resources according to claim 1, wherein, The available voltage regulation capacity of the energy storage is calculated based on the system load and power generation of the power system, which specifically includes: Computing the energy storage active power P ESSi , In the formula, P V is the load valley filling line power value, P net,i is the net load power at the i th moment, P F is the load peak shaving line power value, t1 is the storage charging starting moment, t2 is the storage charging ending moment, t3 is the storage discharging starting moment, and t4 is the storage discharging ending moment. calculating the remaining power amount S of the energy storage at the i-th time point i , wherein η c is the charging efficiency of the energy storage, η d is the discharging efficiency of the energy storage, S n is the rated capacity of the energy storage; The available voltage regulation capacity of the energy storage at the i-th time between voltage sags includes adjustable active power P' ESS,i and adjustable reactive power Q' ESS,i , where t p is the voltage sag duration, t ESS is the energy storage response time delay, t p -t ESS denotes the energy storage voltage support time, P ESS,max is the maximum discharging power of the energy storage, P n is the active power deficiency of the node during the voltage sag, Q n is the reactive power deficiency of the node during the voltage sag.

3. The method of claim 1, wherein the voltage sag magnitude is calculated considering the transient response characteristics of the optical storage resource. The equivalent control parameters of the photovoltaic transient current are obtained by constructing a parameter identification model based on the voltage recording data of the photovoltaic grid-connected point and solving the model; based on the equivalent control parameters of the photovoltaic transient current, the photovoltaic transient output current is calculated, which specifically includes: The photovoltaic transient control parameter identification model is constructed, where f is the optimization objective function, U PV,dm and U PV,qm are the d-axis and q-axis voltage components of the transformed three-phase monitoring voltage at the photovoltaic grid-connected node, respectively, U PV,de and U PV,qe are the estimated d-axis and q-axis voltage components at the photovoltaic grid-connected node, respectively, U PV is the voltage amplitude at the photovoltaic grid-connected node, U min and U max are the lower and upper limits of the voltage at the photovoltaic grid-connected node, respectively, I d and I q are the d-axis and q-axis currents at the photovoltaic grid-connected node, respectively, I max is the current limit at the photovoltaic grid-connected node, P PV and Q PV are the active and reactive power outputs at the photovoltaic grid-connected node, respectively, S PV is the capacity of the photovoltaic power station, and are the minimum and maximum values of the reactive power output at the photovoltaic grid-connected node, respectively; Wherein, where θ is a rotation angle of the dq coordinate system with respect to the three-phase coordinate system, U PV,a , U PV,b , and U PV,c are a-phase, b-phase, and c-phase voltage components of a photovoltaic grid-connected point voltage U PV , respectively In the formula, U PV,pred and U PV,preq are the monitored d-axis voltage component and the monitored q-axis voltage component respectively before the transient response of the photovoltaic grid-connected node, R g is the equivalent resistance of the photovoltaic power station, L g is the equivalent inductance of the photovoltaic power station, and w is the angular frequency of the power system. The voltage recording data is input into the parameter identification model and solved to obtain the equivalent control parameters K1 and K2 of the photovoltaic transient current; Computing a photovoltaic transient output current, including a d-axis current I d and a q-axis current I q of a photovoltaic grid-connected node where I dr and I qr are the d-axis and q-axis reference currents of the photovoltaic grid-connected node, respectively, and I n is the rated current of the photovoltaic grid-connected node.

4. The method of claim 1, wherein the voltage sag magnitude is calculated considering the transient response characteristics of the optical storage resource. The photovoltaic off-grid time is calculated according to the photovoltaic low-voltage ride-through curve, and the voltage sag evolution time sequence is constructed, which specifically includes: Calculating photovoltaic off-grid time t trip , In the formula, U PV is the voltage amplitude of the photovoltaic grid-connected node, U X and U M are the maximum and minimum values of the ordinate of the low-voltage ride-through curve, T max and T min are the maximum and minimum values of the abscissa of the low-voltage ride-through inclined segment curve, respectively. The voltage sag evolution time sequence T including multiple stages is constructed, T = rank(t PV ,t ESS ,t trip ,t p ); where rank( ) denotes the ascending rank operator, t PV is the photovoltaic low voltage ride through duration, t ESS is the energy storage response time, t p is the voltage sag duration.

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