Frequency control method and system based on measured power and online strategy

Abstract

The invention discloses a frequency control method and system based on measured power and an online strategy, and belongs to the technical field of power systems and automation thereof. The method is applied to low-frequency load shedding devices deployed on different stations, and comprises the following steps: measuring a bus frequency, and when the bus frequency is reduced to an action value, calculating an effective value f'of the bus frequency f in action delay time T; according to the value of f ', searching power P needing to be cut off in a frequency power mapping table; identifying the line property according to the power of each load line in the station, performing controlled quantity distribution on the power P needing to be cut off based on the line property and the priority of each load line, generating a load line cut-off instruction, and cutting off the corresponding load line by an action outlet; and according to the power of all the load lines before and after the removal action, calculating the actual removal load capacity of the removal action. According to the invention, real-time coordination of the load control quantity is realized when the low-frequency load shedding device acts, and the frequency stability of a power system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power systems and their automation, and particularly relates to a frequency emergency control method and system based on measured power and online strategies. Background Art

[0002] The under-frequency load shedding device is an automatic device used in the power system. By collecting the electrical quantities of the substation busbar, calculating the busbar frequency and the rate of change of frequency, when the power system has a power deficit resulting in a frequency drop, it cuts off some secondary loads to restore the balance of the active power in the system and prevent frequency collapse. Generally, according to the frequency action value and the action delay, the pre-arranged secondary loads are divided into several rounds and cut off in sequence.

[0003] With the wide access of new energy-consuming devices such as distributed power sources, microgrids, energy storage, and electric vehicles, the power supply and demand pattern shows diverse characteristics, and the load characteristics show obvious differences and complementarities. The proportion of the original traditional load lines with the dual characteristics of "source and load" is increasing continuously. The traditional method of the under-frequency load shedding device shows inadaptability. When the device operates, it is difficult to distinguish the load line, the power line or the out-of-service line in real time, and it may cut off small power lines. In the blind cut state, it is easy to cause over-cutting or under-cutting, seriously affecting the stability of the system frequency and voltage. Summary of the Invention

[0004] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, as well as in the abstract and title of the present invention, to avoid obscuring the purpose of this part, the abstract, and the title. However, such simplifications or omissions shall not be used to limit the scope of the present invention.

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a frequency control method and system based on measured power and online strategies, which realizes the real-time coordination of the load control amount when the under-frequency load shedding device operates, solves the over-cutting or under-cutting problems caused by the blind cut of the traditional under-frequency load shedding device, and improves the frequency stability of the power system.

[0006] In order to achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, a frequency control method based on measured power and online strategies is applied to the under-frequency load shedding devices deployed at different sites. The method includes:

[0008] Measuring the busbar frequency. When the busbar frequency drops to the action value, calculating the effective value f′ of the busbar frequency f within the action delay time T;

[0009] According to the effective value of frequency f′, look up the power P to be cut in the frequency-power mapping table, which is issued by the dispatching master station and contains the power to be cut corresponding to different frequencies under the current operation mode;

[0010] Identify the line nature according to the power of each load line in the station. Based on the line nature and the priority of each load line, allocate the control amount for the power P to be cut, generate a load line cut instruction, and execute the cut action on the corresponding load line based on the load line cut instruction;

[0011] Calculate the actual cut load amount of this cut action according to the power of all load lines before and after the cut action.

[0012] Further, the calculation formula for the effective value f′ of the bus frequency f within the action delay time T is as follows:

[0013]

[0014] where T is the action delay time, t1 is the moment when the bus frequency f drops to the action value, and t2 = t1 + T.

[0015] Further, looking up the power P to be cut in the frequency-power mapping table according to the effective value of frequency f′ includes:

[0016] If the effective value of frequency f′ is in the frequency-power mapping table, directly obtain the power P corresponding to the effective value of frequency f′ through the frequency-power mapping table;

[0017] If the effective value of frequency f′ is not in the frequency-power mapping table, obtain three candidate frequencies within a specified range near the effective value of frequency f′ in the frequency-power mapping table. Obtain the candidate power values corresponding to the candidate frequencies in the frequency-power mapping table, and process the candidate power values corresponding to the three candidate frequencies through the quadratic interpolation method to obtain the value of the power P to be cut.

[0018] Further, identifying the line nature according to the power of each load line in the station includes:

[0019] If the power value of the cable in the station is positive, the cable is a load line; if the power value of the cable in the station is negative, the cable is a power supply line; if the power value of the cable in the station is zero, the cable is an out-of-service line.

[0020] Further, allocating the control amount for the power P to be cut based on the line nature and the priority of each load line, generating a load line cut instruction, and executing the cut action on the corresponding load line based on the load line cut instruction includes:

[0021] Sort all load lines from low to high according to the priority setting value of each load line to form a sorting table. Multiple load lines with the same priority are sorted according to their serial numbers. The sorting table does not include load lines with a priority setting value of 0.

[0022] Calculate the sum of the load-shedding capacities P of the 1st to the i-th load lines in the sorting table. i总 , and the calculation formula is: P i总 = P1 + P2 + …… + P i , where P i is the load-shedding capacity of the i-th load line, and the value range of i is from 1 to N, where N is the number of load lines in the sorting table;

[0023] Allocate the lines according to the power P to be shed. If P N总 < P, it indicates that all load lines in the sorting table need to be shed, and generate load line shedding instructions for all load lines in the sorting table; if P N总 >= P, then use the minimum over-shedding method to find i, that is, which load line in the sorting table needs to be shed up to. The searching method is: P i总 >= P and P i-1总 < P, where P i-1总 is the sum of the load-shedding capacities of the 1st to the i - 1-th load lines in the sorting table, which indicates that the 1st to the i-th load lines in the sorting table all need to be shed, and generate load line shedding instructions for the 1st to the i-th load lines in the sorting table;

[0024] Execute the shedding action on the corresponding load lines according to the generated load line shedding instructions.

[0025] In a second aspect, a low-frequency load shedding device includes:

[0026] A frequency monitoring module for measuring the bus frequency. When the bus frequency drops to the action value, calculate the effective value f′ of the bus frequency f within the action delay time T.

[0027] A control quantity determination module for finding the power P to be shed in the frequency-power mapping table according to the frequency effective value f′. The frequency-power mapping table is sent by the dispatching master station and contains the power to be shed corresponding to different frequencies under the current operation mode.

[0028] A control quantity allocation and shedding module for identifying the line nature according to the power of each load line in the station, allocating the control quantity for the power P to be shed based on the line nature and the priority of each load line, generating load line shedding instructions, and executing the shedding action on the corresponding load lines based on the load line shedding instructions;

[0029] The actual cut-off amount calculation module is used to calculate the actual cut-off load amount of this cut-off action according to the power of all load lines before and after the cut-off action.

[0030] Furthermore, the calculation formula for the effective value f′ of the bus frequency f within the action delay time T is as follows:

[0031]

[0032] Where T is the action delay time, t1 is the moment when the bus frequency f drops to the action value, and t2 = t1 + T.

[0033] Furthermore, according to the effective frequency value f′, look up the power P to be cut off in the frequency-power mapping table, including:

[0034] If the effective frequency value f′ is in the frequency-power mapping table, directly obtain the power P corresponding to the effective frequency value f′ through the frequency-power mapping table;

[0035] If the effective frequency value f′ is not in the frequency-power mapping table, obtain three candidate frequencies within a specified range near the effective frequency value f′ in the frequency-power mapping table, obtain the candidate power values to be cut off corresponding to the candidate frequencies in the frequency-power mapping table, and process the candidate power values to be cut off corresponding to the three candidate frequencies through quadratic interpolation to obtain the value of the power P to be cut off.

[0036] Furthermore, identify the line nature according to the power of each load line in the station, including:

[0037] If the power value of the cable in the station is positive, the cable is a load line; if the power value of the cable in the station is negative, the cable is a power supply line; if the power value of the cable in the station is zero, the cable is an out-of-service line.

[0038] Furthermore, based on the line nature and the priority of each load line, allocate the control amount for the power P to be cut off, generate a load line cut-off instruction, and perform a cut-off action on the corresponding load line based on the load line cut-off instruction, including:

[0039] Sort all load lines from low to high according to the priority setting value of each load line to form a sorting table. Multiple load lines with the same priority are sorted according to the serial number. The sorting table does not include load lines with a priority setting value of 0;

[0040] Calculate the sum P of the cuttable load amounts of the first load line to the i-th load line in the sorting table i总 , and the calculation formula is: P i总 = P1 + P2 + …… + P i , where P iis the load shedding capacity of the i-th load line, where the value range of i is from 1 to N, and N is the number of load lines in the sorting table;

[0041] Perform line allocation according to the power P to be shed. If P N总 < P, it means that all load lines in the sorting table need to be shed, and generate load line shedding instructions for all load lines in the sorting table; if P N总 >= P, then use the minimum over-shedding method to find i, that is, which load line in the sorting table needs to be shed to. The searching method is: P i总 >= P and P i-1总 < P, P i-1总 is the sum of the load shedding capacities of the first load line to the (i - 1)-th load line in the sorting table, which means that the first load line to the i-th load line in the sorting table all need to be shed, and generate load line shedding instructions for the first load line to the i-th load line in the sorting table;

[0042] According to the generated load line shedding instructions, perform shedding actions on the corresponding load lines.

[0043] In a third aspect, a frequency control system based on measured power and online strategy includes a plurality of under-frequency load shedding devices deployed at different sites and a dispatching master station deployed at a dispatching center;

[0044] The under-frequency load shedding device is configured to execute the frequency control method based on measured power and online strategy described in the first aspect, or adopt the under-frequency load shedding device as described in the second aspect;

[0045] The dispatching master station is configured to calculate the power that needs to be shed at different frequencies during low frequency in the current operation mode, form a frequency-power mapping table and send it to the under-frequency load shedding device.

[0046] Compared with the prior art, the present invention has the following beneficial effects: The under-frequency load shedding device obtains the load line power in real time, automatically identifies the line properties, calculates the under-frequency control amount based on the power system frequency, and allocates the control amount considering the line active nature, whether it is out of service, etc., so that when the under-frequency load shedding device operates, the real-time coordination of the load control amount is realized, and the load line can be accurately shed while retaining the active line. The present invention effectively solves the over-shedding or under-shedding problems caused by blind shedding of traditional under-frequency load shedding devices and improves the frequency stability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic diagram of the under-frequency load shedding architecture of the system-level online strategy in the embodiment of the present invention.

[0048] Figure 2 is a flowchart of the frequency control method based on measured power and online strategy in the embodiment of the present invention.

[0049] Figure 3 Schematic diagram of the low-frequency control quantity calculation method in the embodiment of the present invention.

[0050] Figure 4 Schematic diagram of the quadratic difference method for obtaining the power P to be cut according to the effective frequency f′ in the embodiment of the present invention. Specific implementation manners

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings.

[0052] A low-frequency load shedding architecture with a system-level online strategy is proposed in the embodiment of the present invention, as Figure 1 shown. Multiple low-frequency load shedding devices are deployed at different sites, and they communicate with the dispatching master station deployed in the dispatching center through a communication network.

[0053] Functions of the low-frequency load shedding device: It has the low-frequency control function, measures the bus frequency, obtains the power information of the in-station load lines, and uploads it to the dispatching master station. When the system low-frequency is identified, the corresponding load line is cut off. In the following text, the bus frequency is also simply referred to as frequency.

[0054] Functions of the dispatching master station: Obtain the operation mode and frequency of the system in real time; receive the power of each load line uploaded by the low-frequency load shedding device; calculate the power P that needs to be cut at different frequencies under low-frequency in the current operation mode, form a frequency-power mapping table Tab, and send it to the low-frequency load shedding device. Exemplarily, the dispatching master station can obtain the operation mode and frequency of the system through various methods such as SCADA and WAMS.

[0055] The dispatching master station calculates the power values to be cut at different frequencies, that is, the frequency-power mapping table Tab, through simulation, that is, by establishing a mathematical model and numerical calculation methods to simulate the steady-state, transient, and dynamic processes of the power system, as shown in Table 1 below, under the constraint conditions of ensuring the stability of the power system. The simulation process can be realized through the existing technology and will not be elaborated here.

[0056] Table 1 Frequency-power mapping table

[0057] Frequency Power to be cut off f1 P1 f2 P2 …… …… fn Pn

[0058] According to an embodiment of the present invention, the low-frequency load shedding device automatically identifies the line nature based on the power of the load line. First, the power of all in-station cables can be obtained in the following two ways: 1) The low-frequency load shedding device is connected to the secondary sides of the PT / CT of all cables to collect voltage, power and other information in real time and calculate the power; 2) The low-frequency load shedding device accesses the in-station monitoring system through Ethernet to obtain the power of all cables, and the communication protocol can be MMS or IEC60870-5-103 protocol. Although this method is not as real-time as direct sampling, the original low-frequency load shedding device and the overall secondary circuit remain unchanged, and the on-site transformation and upgrade are less difficult. At the same time, the time window for collecting load data can be controlled within seconds.

[0059] Then, the low-frequency load shedding device automatically identifies the line nature according to the power value: if the power value is positive, the cable is a load line; if the power value is negative, the cable is a power supply line; if the power value is zero, the cable is an out-of-service line.

[0060] The core function of the low-frequency load shedding device is to cut off the corresponding load line when the system low frequency is identified, so as to maintain the system frequency stability. The present invention proposes a frequency control method based on measured power and online strategy, referring to Figure 2 , the method includes the following steps:

[0061] Step S1, measure the bus frequency. When the bus frequency drops to the action value, calculate the effective value f′ of the frequency f within the action delay time T.

[0062] The low-frequency load shedding device measures the bus frequency. When the frequency f drops to the action value f1, record the time at this time as t1. Within the action delay T time, the frequency will continue to change, as Figure 3 shown. According to an embodiment of the present invention, the low-frequency load shedding device considers the frequency change to determine the power to be cut off (i.e., the control quantity). First, calculate the effective value f′ of the frequency within the time t1 and t2, and the calculation formula is as follows:

[0063]

[0064] where t2 = t1 + T.

[0065] Step S2, according to the frequency effective value f′, look up the power P to be cut off in the frequency-power mapping table. The frequency-power mapping table is issued by the dispatching master station and contains the power to be cut off corresponding to different frequencies under low frequency in the current operation mode.

[0066] Specifically, the method for obtaining the power to be cut off (abbreviated as the power to be cut) P is as follows:

[0067] If the effective frequency value f′ is in the frequency-power mapping table Tab, the power P to be shed corresponding to the effective frequency value f′ can be directly obtained through the frequency-power mapping table.

[0068] If the effective frequency value f′ is not in the frequency-power mapping table Tab, then through the quadratic interpolation method, the value of the power P to be shed is obtained according to f′, and the calculation formula is as follows:

[0069]

[0070] Where f0, f1, and f2 are the three frequencies closest to the effective frequency value f′, and P0, P1, and P2 are the power values to be shed corresponding to f0, f1, and f2 in the frequency-power mapping table Tab, respectively. As Figure 4 shown, if the effective frequency value f′ is not in the frequency-power mapping table Tab, three candidate frequencies f0, f1, and f2 within a specified range near the effective frequency value f′ can be selected in the frequency-power mapping table Tab. Exemplarily, f0 < f′ < f1 < f2, or f0 < f1 < f′ < f2.

[0071] Step S3: Control quantity allocation is performed on the power P to be shed according to the line nature and priority of each load line in the station to generate a load line shedding instruction, and a shedding action is performed on the corresponding load line based on the load line shedding instruction.

[0072] When the power system has a power deficit resulting in a frequency drop, when the frequency f drops to the action value f1, timing starts. During the action delay T time, if the bus frequency is always less than the action value f1, load lines start to be shed, and the power of the load lines to be shed is the power P to be shed in this round calculated above. The control quantity allocation method is as follows.

[0073] S3-1: All load lines are sorted according to the priority setting value of each load line to form a sorting table, with the load lines with lower priority ranked in the front and those with higher priority ranked in the back. For multiple load lines with the same priority, they are sorted according to the serial number, with the load line with a lower serial number ranked in the front and the one with a higher serial number ranked in the back.

[0074] According to the importance of the load lines, the priority setting values of each load line are set in the under-frequency load shedding device. The priority setting values of all load lines can be different or partially the same. Load lines with the same priority setting value are in the same priority level. The load line with a smaller priority setting value is shed first, but the load line with a priority setting value of 0 cannot be shed and is not in the above sorting table; the power supply line with a negative power and the out-of-service line with a power of zero cannot be shed and are not in the above sorting table.

[0075] S3-2: Calculate P i总 , and the calculation formula is P i总 =P1 + P2 + …… + Pi , P i总 is the sum of the load shedding capacities from the first load line to the i-th load line in the sorting table, and P i is the load shedding capacity of the i-th load line. The value range of i is from 1 to N, where N is the number of load lines in the sorting table.

[0076] S3-3: Allocate load shedding measures according to the required load shedding capacity P. If the available cutting power P N总 >= P of all load lines in the sorting table, use the minimum over-cut method to find i, that is, which load line in the sorting table needs to be cut off. The method of finding is: P i总 >= P and P i-1总 < P, and P i-1 is always the sum of the load shedding capacities from the first load line to the (i - 1)-th load line in the sorting table. All load lines from the first to the i-th load line in the sorting table need to be cut off to complete the allocation of the control amount and generate a load line cut-off instruction; if P N总 < P, then all load lines in the sorting table need to be cut off to complete the allocation of the control amount and generate a load line cut-off instruction.

[0077] S3-4: According to the load line cut-off instruction generated in step S3-3, the under-frequency load shedding device operates to cut off the corresponding load line at the outlet.

[0078] Step S4: Calculate the actual load shedding amount of this cut-off operation based on the power of all load lines before and after the cut-off action.

[0079] The load shedding capacity cut by each under-frequency load shedding device is calculated according to the following formula:

[0080] P 实切 = P1 – P2

[0081] where P 实切 is the actual load shedding capacity of the under-frequency load shedding device, P1 is the power of all load lines before the cut-off action, and P2 is the power of all load lines after the cut-off action.

[0082] The under-frequency load shedding device calculates the actual load shedding capacity and uploads it to the dispatching master station. The dispatching master station can then calculate how much load has been cut off in this area during this under-frequency event, which is convenient for power grid dispatching personnel to analyze data. The actual under-frequency load shedding capacity in the area is the sum of the actual load shedding capacities of all under-frequency load shedding devices.

[0083] Based on the same technical concept as the method embodiment, the present invention also provides an under-frequency load shedding device, including:

[0084] A frequency monitoring module for measuring the bus frequency. When the bus frequency drops to the action value, calculate the effective value f' of the bus frequency f within the action delay time T;

[0085] A control quantity determination module, configured to look up the power P to be shed in a frequency-power mapping table according to the effective frequency value f′, where the frequency-power mapping table is issued by a dispatching master station and includes the power to be shed corresponding to different frequencies under the current operating mode;

[0086] A control quantity allocation and shedding module, configured to identify the line nature according to the power of each load line in the station, allocate the power P to be shed based on the line nature and the priority of each load line to generate a load line shedding instruction, and perform a shedding action on the corresponding load line based on the load line shedding instruction;

[0087] An actual shedding quantity calculation module, configured to calculate the actual load quantity shed in this shedding action according to the power of all load lines before and after the shedding action.

[0088] Among them, the calculation formula for the effective value f′ of the bus frequency f calculated by the frequency monitoring module within the action delay time T is as follows:

[0089]

[0090] Among them, T is the action delay time, t1 is the moment when the bus frequency f drops to the action value, and t2 = t1 + T.

[0091] The control quantity determination module looks up the power P to be shed in the frequency-power mapping table according to the effective frequency value f′, including:

[0092] If the effective frequency value f′ is in the frequency-power mapping table, the power P to be shed corresponding to the effective frequency value f′ is directly obtained through the frequency-power mapping table;

[0093] If the effective frequency value f′ is not in the frequency-power mapping table, three candidate frequencies within a specified range near the effective frequency value f′ are obtained in the frequency-power mapping table, the candidate power values to be shed corresponding to the candidate frequencies are obtained in the frequency-power mapping table, and the candidate power values to be shed corresponding to the three candidate frequencies are processed by a quadratic interpolation method to obtain the value of the power P to be shed.

[0094] The control quantity allocation and shedding module identifies the line nature according to the power of each load line in the station, including:

[0095] If the power value of the cable in the station is positive, the cable is a load line; if the power value of the cable in the station is negative, the cable is a power supply line; if the power value of the cable in the station is zero, the cable is an out-of-service line.

[0096] The control quantity allocation and removal module allocates the power P to be removed based on the line nature and the priorities of each load line, generates a load line removal instruction, and performs a removal action on the corresponding load line according to the load line removal instruction, including:

[0097] Sort all load lines from low to high according to the priority setting value of each load line to form a sorting table. Multiple load lines with the same priority are sorted according to the serial number. The sorting table does not include load lines with a priority setting value of 0;

[0098] Calculate the sum P of the load shedding amounts of the 1st to the i-th load lines in the sorting table i总 , and the calculation formula is P i总 =P1+P2+……+P i , where P i is the load shedding amount of the i-th load line, and the value range of i is from 1 to N, and N is the number of load lines in the sorting table;

[0099] Perform line allocation according to the power P to be removed. If P N总 <P, it means that all load lines in the sorting table need to be removed, and generate a load line removal instruction for all load lines in the sorting table; if P N总 >=P, the minimum over-cut method is used to find i, that is, which load line in the sorting table needs to be removed to. The search method is: P i总 >=P and P i-1总 <P, P i-1总 is the sum of the load shedding amounts of the 1st to the i-1th load lines in the sorting table, which means that the 1st to the i-th load lines in the sorting table need to be removed, and generate a load line removal instruction for the 1st to the i-th load lines in the sorting table;

[0100] Perform a removal action on the corresponding load line according to the generated load line removal instruction.

Claims

1. A frequency control method based on measured power and online strategy, which is applied to under-frequency load shedding devices deployed at different sites, is characterized in that, The method includes: Measuring the bus frequency. When the bus frequency drops to the action value, calculating the effective value f' of the bus frequency f within the action delay time T; According to the effective frequency value f', looking up the power P to be cut off in the frequency-power mapping table, which is issued by the dispatching master station and contains the power to be cut off corresponding to different frequencies under the current operation mode; Identifying the line nature based on the power of each load line in the station. Based on the line nature and the priority of each load line, distributing the control quantity for the power P to be cut off, generating a load line cut-off instruction, and performing a cut-off action on the corresponding load line based on the load line cut-off instruction; Calculating the actual cut-off load quantity of this cut-off action according to the power of all load lines before and after the cut-off action.

2. The method according to claim 1, wherein The calculation formula for the effective value f' of the bus frequency f within the action delay time T is as follows: Where T is the action delay time, t1 is the moment when the bus frequency f drops to the action value, and t2 = t1 + T.

3. The method according to claim 1, wherein Looking up the power P to be cut off in the frequency-power mapping table according to the effective frequency value f' includes: If the effective frequency value f' is in the frequency-power mapping table, directly obtaining the power P to be cut off corresponding to the effective frequency value f' through the frequency-power mapping table; If the effective frequency value f' is not in the frequency-power mapping table, obtaining three candidate frequencies within a specified range near the effective frequency value f' in the frequency-power mapping table, obtaining the candidate power values to be cut off corresponding to the candidate frequencies in the frequency-power mapping table, and processing the candidate power values to be cut off corresponding to the three candidate frequencies through quadratic interpolation to obtain the value of the power P to be cut off.

4. The method according to claim 1, wherein Identifying the line nature based on the power of each load line in the station includes: If the power value of the cable in the station is positive, the cable is a load line; if the power value of the cable in the station is negative, the cable is a power supply line; if the power value of the cable in the station is zero, the cable is an out-of-service line.

5. The method according to claim 1, characterized in that Distributing the control quantity for the power P to be cut off based on the line nature and the priority of each load line, generating a load line cut-off instruction, and performing a cut-off action on the corresponding load line based on the load line cut-off instruction includes: Sorting all load lines from low to high according to the priority setting value of each load line to form a sorting table. Multiple load lines with the same priority are sorted according to the serial number. The sorting table does not include load lines with a priority setting value of 0; Calculate the sum P of the load shedding amounts from the first load line to the i-th load line in the sorting table i总 , and the calculation formula is: P i总 = P1 + P2 + …… + P i , where P i is the load shedding amount of the i-th load line, and the value range of i is from 1 to N, and N is the number of load lines in the sorting table; Perform line allocation according to the power P to be cut. If P N总 < P, it indicates that all load lines in the sorting table need to be cut, and generate load line cut instructions for all load lines in the sorting table; if P N总 >= P, the minimum over-cut method is used to find i, that is, which load line in the sorting table needs to be cut to. The method of finding is: P i总 >= P and P i-1总 < P, where P i-1总 is the sum of the cuttable load amounts of the first load line to the (i - 1)-th load line in the sorting table, it indicates that the first load line to the i-th load line in the sorting table all need to be cut, and generate load line cut instructions for the first load line to the i-th load line in the sorting table; Performing a cut-off action on the corresponding load line according to the generated load line cut-off instruction.

6. A low-frequency load shedding device, characterized in that, Includes: A frequency monitoring module for measuring the bus frequency. When the bus frequency drops to the action value, calculating the effective value f' of the bus frequency f within the action delay time T; A control quantity determination module for looking up the power P to be cut off in the frequency-power mapping table according to the effective frequency value f'. The frequency-power mapping table is issued by the dispatching master station and contains the power to be cut off corresponding to different frequencies under the current operation mode; The control quantity allocation and removal module is used to identify the line nature according to the power of each load line in the station, allocate the control quantity for the power P to be removed based on the line nature and the priority of each load line, generate a load line removal instruction, and execute the removal action on the corresponding load line based on the load line removal instruction; The actual removal quantity calculation module is used to calculate the actual removed load quantity of this removal action according to the power of all load lines before and after the removal action.

7. The low-frequency load shedding device according to claim 6, characterized in that, The calculation formula for the effective value f′ of the bus frequency f within the action delay time T is as follows: where T is the action delay time, t1 is the moment when the bus frequency f drops to the action value, and t2 = t1 + T.

8. The low-frequency load shedding device according to claim 6, characterized in that, According to the frequency effective value f′, look up the power P to be removed in the frequency-power mapping table, including: If the frequency effective value f′ is in the frequency-power mapping table, directly obtain the power P to be removed corresponding to the frequency effective value f′ through the frequency-power mapping table; If the frequency effective value f′ is not in the frequency-power mapping table, obtain three candidate frequencies within a specified range near the frequency effective value f′ in the frequency-power mapping table, obtain the candidate power values to be removed corresponding to the candidate frequencies in the frequency-power mapping table, and process the candidate power values to be removed corresponding to the three candidate frequencies through the quadratic interpolation method to obtain the value of the power P to be removed.

9. The low-frequency load shedding device according to claim 6, wherein identifying the line nature according to the power of each load line in the station includes: If the power value of the cable in the station is positive, the cable is a load line; If the power value of the cable in the station is negative, the cable is a power supply line; If the power value of the cable in the station is zero, the cable is an out-of-service line.

10. The low-frequency load shedding device according to claim 6, wherein allocating the control quantity for the power P to be removed based on the line nature and the priority of each load line, generating a load line removal instruction, and executing the removal action on the corresponding load line based on the load line removal instruction includes: Sort all load lines from low to high according to the priority setting value of each load line to form a sorting table. Multiple load lines with the same priority are sorted according to the serial number. The sorting table does not include load lines with a priority setting value of 0; Calculate the sum P of the load shedding amounts from the first load line to the i-th load line in the sorting table i总 , and the calculation formula is: P i总 = P1 + P2 + …… + P i , where P i is the load shedding amount of the i-th load line, and the value range of i is from 1 to N, where N is the number of load lines in the sorting table; Perform line allocation according to the power P to be cut. If P N总 < P, it indicates that all load lines in the sorting table need to be cut, and generate load line cut instructions for all load lines in the sorting table; if P N总 >= P, the minimum over-cut method is used to find i, that is, which load line in the sorting table needs to be cut to. The method of finding is: P i总 >= P and P i-1总 < P, where P i-1总 is the sum of the cuttable load amounts of the 1st to the (i - 1)th load lines in the sorting table, it indicates that the 1st to the ith load lines in the sorting table need to be cut, and generate load line cut instructions for the 1st to the ith load lines in the sorting table; Execute the removal action on the corresponding load line according to the generated load line removal instruction.

11. A frequency control system based on measured power and online strategy, characterized in that, It includes multiple low-frequency load shedding devices deployed at different sites and a dispatching master station deployed at the dispatching center; The low-frequency load shedding device is configured to execute the frequency control method based on measured power and online strategy as described in any one of claims 1-5, or adopt the low-frequency load shedding device as described in any one of claims 6-10; The dispatching master station is configured to calculate the power to be removed at different frequencies during low frequency in the current operation mode, form a frequency-power mapping table and send it to the low-frequency load shedding device.

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