A source-network-load-storage integrated local power grid low-frequency fault self-healing coordination control method

Abstract

This invention belongs to the technical field of self-healing coordinated control for low-frequency faults in power grids. Specifically, it relates to a method for self-healing coordinated control of low-frequency faults in a local power grid integrating source, grid, load, and energy storage. This method includes: firstly, real-time acquisition of the power grid system frequency, frequency change rate, tie-line power, and energy storage state of charge; after identifying low-frequency faults, generating a predicted frequency trajectory; determining the frequency safety margin index and classifying fault levels based on tie-line power; allocating power regulation amounts hierarchically according to response speed priority; executing frequency recovery; synchronously and dynamically adjusting the reverse power protection blocking duration and tie-line power exchange boundary; determining whether preset exit conditions are met; if not, correcting the regulation amounts; and finally, exiting control step-by-step in reverse sequence to achieve self-healing recovery of low-frequency faults in the local power grid. This invention improves the accuracy of frequency recovery and the power supply stability of the local power grid by performing self-healing coordinated control of low-frequency faults.

Description

Technical Field

[0001] This invention belongs to the technical field of self-healing coordinated control of low-frequency faults in power grids. Specifically, it relates to a method for self-healing coordinated control of low-frequency faults in a local power grid integrating source, grid, load and storage. Background Technology

[0002] With the large-scale integration of new energy power plants and the increasing proportion of large industrial users in local power grids, the frequency drop rate after a power grid system fault is accelerating. In order to reduce the risk of equipment tripping, grid disconnection, or even local power outages caused by this, it is necessary to use a low-frequency fault self-healing coordination control method to achieve coordinated control of multiple resources, while ensuring the safety of frequency recovery and the reliability of power supply.

[0003] Existing methods typically trigger control based on a fixed frequency threshold or a frequency change rate threshold, and then adjust the control accordingly. This results in the control strength not matching the actual risk of the fault, leading to undercontrol or overcontrol.

[0004] In addition, most existing technologies adjust through energy storage and flexible loads without hierarchical coordination, which can easily cause unnecessary power outages for users or premature depletion of energy storage, affecting the continuity of frequency recovery and the reliability of power supply. Summary of the Invention

[0005] In view of this, in order to solve the above problems, a coordinated control method for low-frequency fault self-healing in a local power grid integrating source, grid, load and storage is proposed.

[0006] The objective of this invention can be achieved through the following technical solution: This invention provides a coordinated control method for low-frequency fault self-healing in a local power grid integrating source, grid, load and storage. The method includes: real-time acquisition of power grid system frequency, frequency change rate, tie line power and energy storage charge status to form an operating status dataset.

[0007] When a low-frequency fault is identified, a predicted frequency trajectory is generated based on the operating status dataset. At the same time, the regulation margin parameters of the power grid system are calculated. Combining the predicted frequency trajectory with tie-line power, the frequency safety margin index is determined to classify the fault level.

[0008] Based on the fault level, determine the control object and the corresponding power adjustment amount, and adjust it to restore the system frequency.

[0009] During frequency recovery, the reverse power protection blocking duration and tie-line power exchange boundary are dynamically adjusted based on the current frequency, tie-line power, and frequency safety margin indicators, and the frequency trajectory is regenerated.

[0010] Based on the regenerated frequency trajectory, it is determined whether the preset exit conditions are met. If not, the power adjustment amounts are corrected in combination with the current predicted trajectory. Otherwise, the control is exited step by step in the preset reverse order to achieve self-healing recovery of low-frequency faults in the local power grid.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention divides the fault level by real-time frequency prediction trajectory and frequency safety margin index, and performs layered coordinated control of energy storage, flexible load and graded load reduction, so that the control intensity is in line with the actual scenario, reduces the occurrence of over-cut or under-cut, improves the stability of power supply, and improves the accuracy of frequency recovery.

[0012] (2) By dynamically adjusting the reverse power protection blocking time and tie line power exchange boundary, the present invention takes into account frequency safety, equipment thermal stability constraints and protection maloperation risk during the frequency recovery process, prevents protection maloperation, and reduces the risk of protection device maloperation caused by power fluctuation, thereby improving the continuity and stability of the local power grid self-healing process.

[0013] (3) By correcting each power regulation amount based on the predicted trajectory and exiting the control step by step in reverse order, the present invention reduces the possibility of secondary frequency drop caused by simultaneous or disordered exit and improves the low-frequency fault self-healing capability of the integrated source-grid-load-storage local power grid. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the overall implementation process of the present invention;

[0016] Figure 2 This is a schematic diagram illustrating the process for determining the frequency safety margin index of the present invention.

[0017] Figure 3 This is a schematic diagram illustrating the fault level classification process of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention is primarily based on the scenario of low-frequency fault frequency recovery after a tie-line trip in an integrated local power grid of an industrial park. Specific implementation examples are analyzed within this scenario. For details, please refer to [link / reference needed]. Figure 1 As shown, the present invention provides a coordinated control method for low-frequency fault self-healing in a local power grid integrating source, grid, load and storage. The method includes: S1, real-time acquisition of power grid system frequency, frequency change rate, tie line power and energy storage charge status to form an operating status dataset.

[0020] It should be added that the frequency change rate mentioned above is the rate of change of the power grid frequency over time. After the frequency waveform of the power grid is collected in real time by a frequency relay installed at the power grid bus, the ratio of the frequency difference between two adjacent time points to the corresponding time interval is calculated as the frequency change rate.

[0021] It should be noted that the above-mentioned energy storage state of charge is expressed as the ratio of the energy currently stored in the electrochemical energy storage (such as lithium-ion battery energy storage) to its rated capacity.

[0022] S2. When a low-frequency fault is identified, a predicted frequency trajectory is generated based on the operating status dataset. At the same time, the regulation margin parameters of the power grid system are calculated. Combining the predicted frequency trajectory with the tie-line power, the frequency safety margin index is determined to classify the fault level.

[0023] It should be added that when the frequency of the power grid system is less than the preset frequency threshold, and the absolute value of the frequency change rate is greater than the preset change rate threshold (the preset change rate threshold is a positive number), it is judged as a low-frequency fault.

[0024] The preset frequency threshold is set according to the power grid benchmark operation procedure. Preferably, the preset frequency threshold is 49.5 Hz.

[0025] The process of obtaining the preset rate of change threshold is as follows: statistically analyze all frequency change rates under the operating conditions of the local power grid without faults from historical data, sort them in ascending order, and extract the 95th percentile as the preset rate of change threshold.

[0026] Specifically, the frequency trajectory prediction process includes: taking the current moment as the starting point, the current measured frequency as the initial value, and the current measured frequency change rate as the slope of the first straight line.

[0027] The equivalent inertia constant of the system is read from the energy management system of the local power grid. Combined with the current change in tie line power and the rated frequency of the system, the maximum frequency change rate is calculated, and the negative value of the maximum frequency change rate is used as the slope of the second straight line.

[0028] It should be added that the above maximum frequency change rate The calculation formula is as follows: .

[0029] In the formula, This represents the change in tie-line power, measured in megawatts. It is the difference between the instantaneous value of the tie-line transmitted power after the disturbance and the steady-state value of the tie-line transmitted power before the disturbance. The rated frequency of the power grid system, measured in Hertz. The system's equivalent inertia constant is expressed in seconds. This refers to the total installed capacity of the local power grid, expressed in megavolt-amperes (MVA). The frequency change rate is measured in real time, in Hertz per second. For the absolute value function, As per-unit values, the change in tie-line power can be converted into a dimensionless relative value. It indicates the degree of energy imbalance in the system per unit time. It represents the total rotational kinetic energy of the power grid system.

[0030] If the absolute value of the current measured frequency change rate is less than the maximum frequency change rate, then the intersection of the first and second straight lines is taken as the predicted minimum frequency, and its occurrence time is determined.

[0031] Otherwise, the x-coordinate of the intersection point of the line corresponding to the maximum frequency change rate and the horizontal line where the current frequency value is located is used as the predicted time of occurrence of the minimum frequency.

[0032] Starting from the predicted minimum frequency, the frequency recovery speed is calculated based on the preset system adjustment power coefficient and the current frequency. This speed is used as the slope of the third straight line. The time required for the predicted frequency to recover to the preset safety threshold is recorded as the predicted frequency recovery time.

[0033] It should be noted that the above frequency recovery speed The calculation formula is as follows: .

[0034] In the formula, The preset system regulation power coefficient represents the regulation power that the power grid system can provide per unit frequency deviation, expressed in megawatts per hertz. For the current frequency, To preset a safety threshold, This indicates the degree to which the frequency of the power grid system deviates from the safe operating point. This represents the total regulating power that the power grid system can provide at the current frequency deviation.

[0035] The preset system regulation power coefficient is the amount of power regulation that the power grid system can call upon within a unit frequency deviation. The specific acquisition process is as follows: First, the droop rate parameters, rated capacity, available upward regulation capacity, available downward regulation capacity, AGC regulation dead zone, and total system load of each online generator unit are read in real time from the local power grid's energy management system (EMS). Then, the ratio of the rated capacity of each online generator unit to its corresponding droop rate is calculated, and the sum of all ratios is used as the primary frequency regulation coefficient. Next, the ratio of the sum of the available upward regulation capacity and the available downward regulation capacity to twice the AGC regulation dead zone is calculated as the secondary frequency regulation coefficient. Then, the product of the load frequency characteristic coefficient and the total system load is calculated, and the ratio of this product to the standardization factor is used as the load frequency regulation efficiency coefficient. Finally, the sum of the primary frequency regulation coefficient, the secondary frequency regulation coefficient, and the load frequency regulation efficiency coefficient is calculated as the preset system regulation power coefficient.

[0036] The load frequency characteristic coefficient represents the percentage change in load when the frequency changes by 0.1 Hz. It is set in the range of 1.0% to 3.0% per 0.1 Hz according to the characteristics of the system load composition. 0.1 is a standardization factor used to convert the frequency change reference from 0.1 Hz to 1 Hz.

[0037] The preset safety threshold is set according to the power grid operation industry standard, and preferably, the value is 49 Hz.

[0038] Starting from the current frequency, taking the predicted minimum frequency and its occurrence time as the inflection point, and ending at the preset frequency safety threshold, a predicted frequency trajectory is generated.

[0039] Specifically, the process of obtaining the adjustment margin parameter includes: calculating the difference between the current energy storage state of charge and the preset minimum allowable state of charge, and calculating the product of the difference and the rated energy of the energy storage as the current remaining releasable energy of the energy storage.

[0040] Calculate the duration from the current moment to the time corresponding to the predicted minimum frequency, multiply the duration by the upper limit of the energy storage discharge power to obtain the maximum sustainable discharge energy of the energy storage, and take the minimum value between the current remaining releaseable energy of the energy storage and the maximum sustainable discharge energy of the energy storage as the energy release margin of the energy storage.

[0041] It should be noted that in this embodiment, all calculations involving the product of power and time use hours as the unit of time to ensure consistency with the rated energy unit of energy storage. If the original time data is in seconds, it needs to be divided by 3600 for conversion.

[0042] The difference between the current operating power of the flexible load and the preset minimum operating power of the flexible load is calculated as the current adjustable capacity of the flexible load. The preset minimum operating power is pre-set by the dispatching department according to load management requirements; preferably, it can be 20% of the rated power of the flexible load equipment.

[0043] The minimum value between the current adjustable capacity of the flexible load and the upper limit of the adjustable power of the flexible load is taken as the adjustable capacity margin of the flexible load.

[0044] It should be added that the aforementioned upper limit of adjustable power for flexible loads is the minimum of the product of the rated power of the flexible load equipment and the safety factor, plus the preset maximum adjustable power. The rated power of the flexible load equipment is read from its nameplate, and the preset maximum adjustable power is set by the dispatching system according to the equipment's safe operation requirements. The safety factor is set according to the type of flexible load equipment. For example, for electric heating load equipment, the safety factor ranges from 0.8 to 0.95, and for energy storage load equipment, the safety factor ranges from 0.9 to 1.

[0045] The thermal stability limit of the tie line is read from the energy management system of the local power grid. The difference between the thermal stability limit of the tie line and the absolute value of the current transmission power of the tie line is calculated as the thermal stability margin of the tie line. It should be noted that when the difference is negative, the thermal stability margin of the tie line is 0.

[0046] The energy release margin of energy storage, the adjustable capacity margin of flexible load, and the thermal stability margin of tie line are respectively processed into dimensionless values ​​to obtain the energy storage support margin, flexible load margin, and thermal stability margin, which together constitute the adjustment margin parameters.

[0047] It should be added that the dimensionless processing methods for the energy release margin of energy storage, the adjustable capacity margin of flexible load, and the thermal stability margin of tie line are as follows: the energy release margin of energy storage is compared with the rated energy of energy storage, the adjustable capacity margin of flexible load is compared with the total rated power of flexible load, and the thermal stability margin of tie line is compared with the thermal stability limit of tie line.

[0048] Since the energy release margin of energy storage reflects the energy potential of the energy storage system to continuously discharge during the fault period, the adjustable capacity margin of flexible load quantifies the instantaneous power support that the load can provide without affecting the user's power consumption, and the residual margin of tie line thermal stability limits the safe boundary of the power transmitted by the tie line during power regulation, the current regulation potential of the power grid can be evaluated from the three dimensions of energy storage, flexible load, and tie line. This can prevent the energy storage system from experiencing a secondary frequency drop due to energy depletion, provide a quantitative basis for hierarchical coordinated control, and prevent reverse power protection from malfunctioning or equipment thermal stability from being damaged due to regulation actions.

[0049] Specifically, please refer to Figure 2 As shown, the process of determining the frequency safety margin index includes: extracting the predicted frequency minimum point and the predicted frequency recovery time from the predicted frequency trajectory, and performing minimum-maximum linear normalization processing respectively to obtain the frequency minimum point margin and the recovery time margin.

[0050] The maximum and minimum values ​​required to normalize the predicted minimum frequency point are the rated frequency and the preset frequency threshold, respectively. The minimum value required to normalize the predicted frequency recovery time is 0. The method for obtaining the maximum value required to normalize the predicted frequency recovery time is as follows: statistically analyze all recovery times in historical data, calculate the average value of the recovery times, and use the average value as the required maximum value.

[0051] The frequency safety margin index is composed of the minimum frequency margin, recovery time margin, energy storage support margin, flexible load margin, and thermal stability margin.

[0052] Specifically, please refer to Figure 3 As shown, the fault level classification process includes: if at least two of the frequency safety margin indicators are less than the corresponding preset first threshold and greater than or equal to the corresponding preset second threshold, or if any indicator is less than the preset second threshold, then it is determined to be a severe fault.

[0053] When any frequency safety indicator falls below the preset second threshold, the system is already in a state of frequency instability and has an irreversible risk. Therefore, it must be judged as a severe fault. When the frequency safety indicator has not yet exceeded the second threshold but two or more indicators are simultaneously below the first threshold, it indicates that the system's multi-adjustment capability is insufficient and it is difficult to cope with subsequent disturbances. It should also be judged as a severe fault.

[0054] If only one indicator is less than the corresponding preset first threshold and greater than or equal to the corresponding preset second threshold, and all other indicators are greater than or equal to the corresponding preset first threshold, then it is judged as a moderate fault.

[0055] This indicates that a certain type of regulation capability has declined, but other regulation methods and frequency safety indicators are normal. The overall risk of the power grid system is controllable. There is no situation of coordinated deterioration due to multiple margins being insufficient at the same time. The system still has a certain frequency response redundancy. Irreversible risks have not yet materialized and can be compensated for by a single measure. The risk is repairable and needs attention but does not require emergency handling. Therefore, it is judged as a moderate fault.

[0056] If all indicators are greater than or equal to the corresponding preset first threshold, the fault is determined to be minor. The preset first threshold is greater than the corresponding preset second threshold.

[0057] At this time, all adjustment measures and frequency safety indicators are normal, but the power grid system is in a low-frequency fault, so it is judged as a minor fault.

[0058] It should be added that the preset first and second thresholds corresponding to the frequency minimum point margin and recovery time margin are set according to the power system safety criteria of the system. The preset first and second thresholds for energy storage support margin are set according to the parameter characteristics of the energy storage system. The preset first and second thresholds for flexible load margin are set according to the safety requirements of the load equipment. The preset first and second thresholds for tie line thermal stability margin are set according to the relay protection setting regulations. For example, taking an industrial park power grid as an example, the preset first threshold for the frequency minimum point margin is 0.7, and the preset second threshold is 0.3; the preset first threshold for the recovery time margin is 0.75, and the preset second threshold is 0.4; the preset first threshold for the energy storage support margin is 0.7, and the preset second threshold is 0.3; the preset first threshold for the flexible load margin is 0.6, and the preset second threshold is 0.2; and the preset first threshold for the thermal stability margin is 0.8, and the preset second threshold is 0.4.

[0059] S3. Based on the fault level, determine the control object and the corresponding power adjustment amount, and adjust it to restore the system frequency.

[0060] Specifically, the process of determining the power regulation amount includes: when the fault level is a minor fault, based on the predicted minimum frequency point, regulation margin parameter and tie line power, calculating and executing the power value to be released, controlling the electrochemical energy storage device to switch from the current state to the discharge mode, and discharging according to the calculated power value.

[0061] It should be added that the calculation method for the power value to be released is as follows: First, calculate the difference between the preset safety threshold and the predicted minimum frequency to obtain the frequency deviation. Then, the product of the preset system adjustment power coefficient and the frequency deviation is used as the predicted power deficit. Finally, the smaller value between the predicted power deficit and the upper limit of the energy storage discharge power is taken as the power value to be released by the electrochemical energy storage device.

[0062] When the fault level is medium, the power value released by the energy storage system is calculated and executed in the same way as in the case of a minor fault. Based on the remaining power deficit after energy storage support and the adjustable capacity margin of the flexible load, the load power value that needs to be adjusted is calculated and executed. Instructions are sent to the flexible load control system to reduce the operating power of the load and control the flexible load to perform corresponding load adjustments.

[0063] The calculation method for the load power value that needs to be adjusted is as follows: First, calculate the difference between the predicted power deficit and the power value that needs to be released by the electrochemical energy storage device, which is taken as the remaining power deficit after energy storage support. Then, select the minimum value from the remaining power deficit and the adjustable capacity margin of the flexible load as the load power value that needs to be adjusted.

[0064] When the fault level is severe, the power value released by the energy storage system and the load power value are calculated and executed in the same way as in the case of a medium fault.

[0065] Based on the current remaining power deficit and the preset power cut-off threshold, the load power value to be cut off is calculated and executed. The loads are cut off sequentially according to the preset load priority, until the cumulative load power value cut off is greater than or equal to the required load power value. The preset load priority is a comprehensive ranking principle based on the magnitude of economic loss from load interruption, followed by power size.

[0066] The calculation process for the load power to be cut off is as follows: First, calculate the difference between the remaining power deficit after energy storage support and the load power to be adjusted, which is taken as the current remaining power deficit. Then, calculate the load power to be cut off. , ,in, The preset cut-off power threshold represents the minimum power value for a single cut-off, ranging from 10 to 20 megawatts. This represents the current power deficit. This is the floor function.

[0067] Because energy storage offers the fastest response time and the lowest control cost, it is prioritized for use under any fault level. When the energy margin available for release from energy storage is insufficient or frequency recovery time is limited, flexible loads are introduced to provide backup. Flexible loads have a response time on the order of seconds, a smooth adjustment process, and do not interrupt power supply as long as the power output does not fall below the preset minimum operating power, making controllable. However, when both energy storage and flexible loads have reached their adjustment limits and a power deficit still exists, it is necessary to forcibly balance power through load shedding to prevent the frequency from falling below the safety threshold, which could lead to grid disconnection or large-scale blackouts. By implementing tiered control based on response speed priority and increasing control cost, a balance between frequency recovery effectiveness and power supply reliability can be achieved.

[0068] S4. During the frequency recovery process, the reverse power protection blocking duration and tie-line power exchange boundary are dynamically adjusted according to the current frequency, tie-line power and frequency safety margin index, and the frequency trajectory is regenerated.

[0069] Specifically, the adjustment process of the reverse power protection blocking duration includes: calculating the frequency difference based on a preset safety threshold and the current frequency. , In the formula, To maximize the function, the difference in thermal stability margin is calculated based on the preset thermal stability margin threshold and the remaining thermal stability margin. , In the formula, To preset the thermal stability margin threshold, This refers to the thermal stability margin. The preset thermal stability margin threshold is set based on industry experience in power grid systems; preferably, the preset thermal stability margin threshold is 5 MW.

[0070] When both the frequency difference and the thermal stability margin difference are 0, the blocking time is gradually reduced according to a preset blocking time attenuation ratio until the reverse power protection blocking time is less than or equal to the initial blocking time. The preset blocking time attenuation ratio is pre-set based on industry experience in power grid systems; preferably, it is set to 0.9. For example, if the initial blocking time is set to 3 seconds and the reverse power protection blocking time is set to 10 seconds, the blocking time is reduced to 9 seconds initially, 8.1 seconds later, 7.29 seconds later, and so on, until the reduced reverse power protection blocking time is less than or equal to the initial blocking time of 3 seconds.

[0071] Otherwise, the frequency difference and thermal stability margin difference are respectively subjected to minimum-maximum linear normalization, and the normalized values ​​are linearly weighted and summed to obtain the extension coefficient. The extension coefficient is multiplied by the preset maximum extension time threshold to calculate the extension time of the blocking duration. The sum of the extension time and the initial blocking duration is calculated as the reverse power protection blocking duration.

[0072] It should be added that the minimum value of the frequency difference and the thermal stability margin difference after minimum-maximum linear normalization is 0, the maximum value of the frequency difference after minimum-maximum linear normalization is the difference between the preset safety threshold and the preset minimum frequency threshold, and the maximum value of the thermal stability margin difference after minimum-maximum linear normalization is the preset thermal stability margin threshold. The preset minimum frequency threshold is preset by the grid operation technicians; for example, the preset minimum frequency threshold is set to 47 Hz.

[0073] It should be added that the frequency difference reflects the frequency security of the power grid, while the thermal stability margin difference reflects the thermal stability security of the transmission equipment. Since frequency security is a first-level security requirement in the power system, while equipment thermal stability is a second-level security requirement, the weight of the frequency difference is greater than the weight of the thermal stability margin difference. Preferably, the weight of the frequency difference is 0.6 and the weight of the thermal stability margin difference is 0.4.

[0074] The preset maximum extension time threshold is set based on industry experience values ​​of power grid systems. Preferably, the preset extension threshold is 3 seconds.

[0075] Specifically, the adjustment process of the tie-line power exchange boundary includes: when the current frequency is lower than a preset safety threshold, calculating the difference between the rated frequency of the power grid system and the current frequency as the frequency deviation value; multiplying the preset system regulation power coefficient by the frequency deviation value as the regulation power; taking the minimum value between the regulation power and the tie-line thermal stability margin as the increase in the tie-line power receiving limit; calculating the sum of the preset tie-line power receiving limit benchmark value and the increase as the new tie-line power receiving limit; and adjusting the lower limit of the tie-line power transmission capacity to the preset minimum external power transmission capacity limit. The preset tie-line power receiving limit benchmark value can be pre-set according to the power grid dispatching regulations. Preferably, the preset tie-line power receiving limit benchmark value is 80% of the tie-line thermal stability limit.

[0076] It should be added that the above-mentioned preset minimum external power limit is set according to the power grid operation procedure. As a preferred embodiment of the present invention, the preset minimum external power limit threshold is -10 megawatts.

[0077] When the current frequency is greater than or equal to a preset safety threshold, the power receiving limit of the tie line is gradually reduced according to a preset tie line power attenuation ratio until the tie line power receiving limit is less than the preset tie line power receiving limit threshold. Simultaneously, the lower limit of the tie line power supply is gradually increased according to the same tie line power attenuation ratio until the lower limit of the tie line power supply is greater than or equal to the preset lower limit threshold of the tie line power supply. Note that since the lower limit of the tie line power supply is negative, multiplying the lower limit by the tie line power attenuation ratio will result in an increase; therefore, the lower limit of the tie line power supply is increased gradually.

[0078] It should be noted that the preset tie-line power attenuation ratio is preset according to the power control system. For example, the preset tie-line power attenuation ratio is 0.9.

[0079] The preset threshold value for the power limit of the tie line is the same as the value of the thermal stability limit of the tie line.

[0080] It should be added that the aforementioned preset lower limit threshold for the power transmission of the tie line is a negative number of the threshold for the power reception of the tie line.

[0081] S5. Based on the regenerated frequency trajectory, determine whether the preset exit conditions are met. If not, adjust each power regulation amount according to the current predicted trajectory. Otherwise, exit the control step by step according to the preset reverse order to realize the self-healing recovery of low-frequency faults in the local power grid.

[0082] Before setting the exit conditions, the predicted trajectory is first reconstructed based on the current real-time frequency and the rate of frequency change according to the generation process of the predicted frequency trajectory, and the minimum predicted frequency of the reconstructed predicted trajectory is obtained.

[0083] At the same time, by combining the regenerated frequency trajectory, the current real-time frequency and the frequency change rate, the frequency safety margin index after recovery is re-evaluated and obtained in accordance with the above-mentioned method for determining the frequency safety margin index.

[0084] Finally, the frequency safety margin indicators in the restored frequency safety margin are weighted and summed to obtain the restored frequency safety margin.

[0085] First, in power systems, system safety takes precedence over equipment safety, and frequency safety takes precedence over economic efficiency. The frequency minimum point margin and recovery time margin directly reflect frequency safety and have irreversible risks, therefore they have the highest weight. The frequency minimum point margin is closely related to system safety, so its weight is higher than that of the recovery time margin. The energy storage support margin and flexible load margin reflect the system's regulation capability. Energy storage support has a millisecond-level response speed and does not affect users, while flexible load control has a second-level response speed but affects user power supply. Therefore, the weight of the energy storage support margin is greater than that of the flexible load margin. Equipment safety indicators include thermal stability margin, which involves equipment protection and has repairability, so it has the lowest weight. As a preferred embodiment of the present invention, the weights of the frequency minimum point margin, recovery time margin, energy storage support margin, flexible load margin, and thermal stability margin are 0.35, 0.3, 0.2, 0.1, and 0.05, respectively.

[0086] Specifically, the preset exit condition is: the minimum predicted frequency in the reconstructed predicted trajectory is greater than or equal to a preset safety threshold and the frequency safety margin index after recovery meets the preset safety margin requirement, wherein the preset safety margin requirement is that the frequency safety margin after recovery is greater than or equal to the preset safety margin threshold.

[0087] It should be added that the process of obtaining the above-mentioned preset safety margin threshold is as follows: statistically analyze the historical operating data of the power grid system, calculate the historical frequency safety margin in the same way as the frequency safety margin calculation method, arrange them in descending order, and extract the 95th percentile as the preset safety margin threshold.

[0088] Specifically, the self-healing recovery process includes: when the preset exit condition is met, the power adjustment amount of each controlled object is gradually reduced in a preset reverse order with a preset power adjustment amount attenuation ratio until the power adjustment amount of all controlled objects is zero.

[0089] It should be noted that following the preset reverse order means following the order opposite to the input order, that is, first exiting load shedding control, then exiting flexible load control, and finally exiting energy storage support control. The preset power regulation attenuation ratio is preset according to the power grid system. For example, the preset power regulation attenuation ratio is 0.9.

[0090] Conversely, the product of the frequency deviation value and the preset system adjustment power coefficient is calculated and recorded as the power adjustment amount.

[0091] Simultaneously, the difference between the preset safety margin threshold and the restored frequency safety margin is calculated, and the ratio of this difference to the preset safety margin threshold is used as the adjustment coefficient for the margin deviation.

[0092] Multiply the adjustment coefficient by the power adjustment amount to obtain the total increase in the power adjustment amount of all controlled objects.

[0093] Based on the current available adjustment margin of each control object (the current available adjustment margin of energy storage control objects is the energy release margin of energy storage, and the current available adjustment margin of flexible load control objects is the adjustable capacity margin of flexible load), the proportion of the adjustment margin of each control object to the total adjustment margin is calculated as the allocation weight. The total adjustment margin is the sum of the energy release margin of energy storage and the adjustable capacity margin of flexible load.

[0094] The total increase is allocated to each control object according to the allocation weight, and the current power adjustment of each control object is added to the allocated increase to obtain the corrected power adjustment of each control object.

[0095] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined by the present invention, and all such modifications and additions should fall within the protection scope of the present invention.

Claims

1. A coordinated control method for self-healing low-frequency faults in a local power grid integrating source, grid, load, and storage, characterized in that, The method includes: Real-time data collection of power grid system frequency, frequency change rate, tie line power, and energy storage state of charge constitutes an operational status dataset. When a low-frequency fault is identified, a predicted frequency trajectory is generated based on the operating status dataset. At the same time, the regulation margin parameters of the power grid system are calculated. The frequency safety margin index is determined by combining the predicted frequency trajectory with the tie-line power to classify the fault level. Based on the fault level, determine the control object and the corresponding power adjustment amount, and adjust it to restore the system frequency; During frequency recovery, the reverse power protection blocking duration and tie-line power exchange boundary are dynamically adjusted based on the current frequency, tie-line power, and frequency safety margin indicators, and the frequency trajectory is regenerated. Based on the regenerated frequency trajectory, it is determined whether the preset exit conditions are met. If not, the power adjustment amounts are corrected in combination with the current predicted trajectory. Otherwise, the control is exited step by step in the preset reverse order to achieve self-healing recovery of low-frequency faults in the local power grid.

2. The integrated source-grid-load-storage local power grid low-frequency fault self-healing coordinated control method as described in claim 1, characterized in that: The process of generating the predicted frequency trajectory includes: Starting from the current moment, with the current measured frequency as the initial value, and with the rate of change of the current measured frequency as the slope of the first straight line; The equivalent inertia constant of the system is read from the energy management system of the local power grid. Combined with the current change in tie line power and the rated frequency of the system, the maximum frequency change rate is calculated, and the negative value of the maximum frequency change rate is used as the slope of the second straight line. If the absolute value of the current measured rate of change of frequency is less than the maximum rate of change of frequency, then the intersection of the first and second straight lines is taken as the predicted minimum frequency, and its occurrence time is determined. Otherwise, the x-coordinate of the intersection of the line corresponding to the maximum frequency change rate and the horizontal line where the current frequency value is located is used as the predicted time of occurrence of the minimum frequency. Starting from the predicted minimum frequency, the frequency recovery speed is calculated based on the preset system unit adjustment power and the current frequency, and used as the slope of the third straight line. The time required for the predicted frequency to recover to the preset safety threshold is recorded as the predicted frequency recovery time. Starting from the current frequency, taking the predicted minimum frequency and its occurrence time as the inflection point, and ending at the preset frequency safety threshold, a predicted frequency trajectory is generated.

3. The integrated source-grid-load-storage local power grid low-frequency fault self-healing coordinated control method as described in claim 1, characterized in that: The process of obtaining the adjustment margin parameter includes: Calculate the difference between the current state of charge of the energy storage and the preset minimum allowable state of charge, and calculate the product of the difference and the rated energy of the energy storage as the current remaining releasable energy of the energy storage; Calculate the duration from the current moment to the time corresponding to the predicted minimum frequency, multiply the duration by the upper limit of the energy storage discharge power to obtain the maximum sustainable discharge energy of the energy storage, and take the minimum value between the current remaining releaseable energy of the energy storage and the maximum sustainable discharge energy of the energy storage as the energy releaseable energy margin of the energy storage. Calculate the difference between the current operating power of the flexible load and the preset minimum operating power of the flexible load, and use it as the current adjustable capacity of the flexible load; Take the minimum value between the current adjustable capacity of the flexible load and the upper limit of the adjustable power of the flexible load as the adjustable capacity margin of the flexible load; Read the thermal stability limit of the tie line from the energy management system of the local power grid, and calculate the difference between the thermal stability limit of the tie line and the absolute value of the current transmission power of the tie line as the thermal stability margin of the tie line. The energy release margin of energy storage, the adjustable capacity margin of flexible load, and the thermal stability margin of tie line are respectively processed into dimensionless values ​​to obtain the energy storage support margin, flexible load margin, and thermal stability margin, which together constitute the adjustment margin parameters.

4. The integrated source-grid-load-storage local power grid low-frequency fault self-healing coordinated control method as described in claim 3, characterized in that: The process of determining the frequency safety margin index includes: The predicted frequency minimum point and the predicted frequency recovery time are extracted from the predicted frequency trajectory, and then min-max linear normalization is performed to obtain the frequency minimum point margin and the recovery time margin. The frequency safety margin index is composed of the minimum frequency margin, recovery time margin, energy storage support margin, flexible load margin, and thermal stability margin.

5. The integrated source-grid-load-storage local power grid low-frequency fault self-healing coordinated control method as described in claim 4, characterized in that: The process of classifying the fault levels includes: If at least two of the frequency safety margin indicators are less than the corresponding preset first threshold and greater than or equal to the corresponding preset second threshold, or if any indicator is less than the preset second threshold, then it is determined to be a severe fault. If only one indicator is less than the corresponding preset first threshold and greater than or equal to the corresponding preset second threshold, and all other indicators are greater than or equal to the corresponding preset first threshold, then it is judged as a moderate fault. If all indicators are greater than or equal to the corresponding preset first threshold, it is judged as a minor fault.

6. The integrated source-grid-load-storage local power grid low-frequency fault self-healing coordinated control method as described in claim 1, characterized in that: The process of determining the power regulation amount includes: When the fault level is a minor fault, the power value that needs to be released is calculated and executed based on the predicted frequency minimum point, adjustment margin parameters and tie line power. When the fault level is a medium fault, the power value released by the energy storage system is calculated and executed in the same way as in a light fault. Based on the current remaining power deficit and the adjustable capacity margin of the flexible load, the load power value that needs to be adjusted is calculated and executed. When the fault level is severe, the power value released by the energy storage system and the load power value are calculated and executed in the same way as in the case of a moderate fault. Based on the current remaining power deficit and the preset power cut-off threshold, the load power value that needs to be cut off is calculated and executed. The loads are cut off in order of preset load priority until the cumulative load power value cut off is greater than or equal to the load power value that needs to be cut off.

7. The integrated source-grid-load-storage local power grid low-frequency fault self-healing coordinated control method as described in claim 1, characterized in that: The process for adjusting the reverse power protection lockout duration includes: The frequency difference is calculated based on the preset safety threshold and the current frequency. At the same time, the thermal stability margin difference is calculated based on the preset thermal stability margin threshold and the thermal stability remaining margin. When the frequency difference and the thermal stability margin difference are both 0, the blocking time is gradually reduced according to the preset blocking time attenuation ratio until the reverse power protection blocking time is less than or equal to the initial blocking time. Otherwise, the frequency difference and thermal stability margin difference are respectively subjected to minimum-maximum linear normalization, and the normalized values ​​are linearly weighted and summed to obtain the extension coefficient. The extension coefficient is multiplied by the preset maximum extension time threshold to calculate the extension time of the blocking duration. The sum of the extension time and the initial blocking duration is calculated as the reverse power protection blocking duration.

8. The integrated source-grid-load-storage local power grid low-frequency fault self-healing coordinated control method as described in claim 1, characterized in that: The adjustment process for the tie-line power exchange boundary includes: When the current frequency is lower than the preset safety threshold, the difference between the rated frequency of the power grid system and the current frequency is calculated as the frequency deviation value, and the product of the preset system regulation power coefficient and the frequency deviation value is used as the regulation power. The minimum value between the regulating power and the residual margin of the tie line thermal stability is taken as the increase in the tie line power receiving limit. The sum of the preset tie line power receiving limit benchmark value and the increase is calculated as the new tie line power receiving limit. The lower limit of the tie line power transmission power is adjusted to the preset minimum external power transmission limit. When the current frequency is greater than or equal to the preset safety threshold, the power limit of the tie line is gradually reduced according to the preset tie line power attenuation ratio until the power limit of the tie line is less than the preset tie line power limit threshold. At the same time, the lower limit of the tie line power supply is gradually increased according to the same tie line power attenuation ratio until the lower limit of the tie line power supply is greater than or equal to the preset lower limit threshold of the tie line power supply.

9. The integrated source-grid-load-storage local power grid low-frequency fault self-healing coordinated control method as described in claim 4, characterized in that: The preset exit condition is: the minimum predicted frequency in the reconstructed predicted trajectory is greater than or equal to the preset safety threshold, and the frequency safety margin index after recovery meets the preset safety margin requirements.

10. The integrated source-grid-load-storage local power grid low-frequency fault self-healing coordinated control method as described in claim 1, characterized in that: The self-healing process includes: When the preset exit condition is met, the power adjustment amount of each controlled object is gradually reduced in a preset reverse order with a preset power adjustment amount attenuation ratio until the power adjustment amount of all controlled objects is zero. Conversely, the product of the frequency deviation value and the preset system unit adjustment power coefficient is calculated and recorded as the power adjustment amount. At the same time, the difference between the preset safety margin threshold and the restored frequency safety margin is calculated, and the ratio of the difference to the preset safety margin threshold is calculated as the adjustment coefficient of the margin deviation. Multiply the adjustment coefficient by the power adjustment amount to calculate the total increase in the power adjustment amount of all controlled objects. Based on the current available adjustment margin of each control object, calculate the proportion of the adjustment margin of each control object to the total adjustment margin, and use it as the allocation weight; The total increase is allocated to each control object according to the allocation weight, and the current power adjustment of each control object is added to the allocated increase to obtain the corrected power adjustment of each control object.

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